removal of various pollutants from water and wastewater by

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Removal of various pollutants from water andwastewater by modified chitosan adsorbents

Jianlong Wang & Shuting Zhuang

To cite this article: Jianlong Wang & Shuting Zhuang (2017) Removal of various pollutants fromwater and wastewater by modified chitosan adsorbents, Critical Reviews in Environmental Scienceand Technology, 47:23, 2331-2386, DOI: 10.1080/10643389.2017.1421845

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Removal of various pollutants from water and wastewaterby modified chitosan adsorbents

Jianlong Wang a,b and Shuting Zhuanga

aCollaborative Innovation Center for Advanced Nuclear Energy Technology, INET, Tsinghua University,Beijing, P. R. China; bBeijing Key Laboratory of Radioactive Waste Treatment, INET, Tsinghua University,Beijing, P. R. China

ABSTRACTChitosan-based adsorbents have attracted increasing attention inwater and wastewater treatment in recent years due to itsabundance and low price, as well as rich amino and hydroxylgroups. However, there are some drawbacks hindering itspractical use, such as low mechanical strength, low solubility inacidic mediums, low adsorption capacity, and lack of selectivity.Therefore, a variety of modification methods, including physicaland chemical modifications, have been investigated to improvethe physicochemical properties of chitosan. This review providesa summary of (a) the intrinsic nature of chitosan associatedwith its structure and physicochemical properties; (b) thepreparation strategies for modified chitosan together with itscharacterization; (c) the application of chitosan-based adsorbentsfor the removal of both organic pollutants (e.g., dyes, PPCPs,PFOS, and humus) and inorganic pollutants (e.g., heavy metalions, nitrate, phosphate, borate, and fluoride). Recent advancesin the fabrication and application of chitosan-based adsorbentsinvolving the intrinsic nature of pollutants are highlighted in thisreview, as well as the effects of process variables (e.g., pH,contact time, ionic strength, competitive ions, temperature),modeling (kinetics and isotherm), adsorption mechanisms, andregeneration.

KEYWORDSBiosorption; chitosan; heavymetals; modification;pollutants

1. Introduction

Water is the most important and essential resource on the earth. However, waterquality of our water resources is deteriorating continuously due to industrialization,domestic, and agricultural activities. Thousands of organic (pesticides, fertilizers,hydrocarbons, phenols, plasticizers, biphenyls, detergents, oils, greases, pharmaceuti-cals, etc.), inorganic (heavymetals, nitrate, sulfate, phosphate, fluoride etc.), and biolog-ical pollutants (virus, bacteria, fungi, algae, amoebas, and planktons etc.) have been

CONTACT Prof. Jianlong Wang [email protected] Collaborative Innovation Center for AdvancedNuclear Energy Technology, INET, Energy Science Building, Tsinghua University, Beijing 100084, P. R. China.

Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/best.© 2018 Taylor & Francis Group, LLC

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found as water contaminants. Different methods have been developed and applied forwater and wastewater treatment.

Adsorption is considered as an important method for disposing of many kindsof pollutants in aqueous solutions due to its ease of operation and the availabilityof a wide range of adsorbents. There are various kinds of adsorbents includingorganic adsorbents, such as activated carbon (Amerkhanova et al., 2017) and bio-sorbent (Wang and Chen, 2006, 2009), and inorganic adsorbents, such as silica gel(Jones and Ross, 1967), vermiculite (Stawinski et al., 2017), and montmorillonite(Barrer and MacLeod, 1954). With the rapid development of industry and strictersupervision, the need to find a better adsorbent is increasingly vital. Generally, anideal adsorbent possesses the following advantages: high adsorption capacity andselectivity, good mechanical stability, resource abundance, low cost, environmentalfriendly, and easy regeneration.

As mentioned in other reviews and articles, several important reasons make chi-tosan-based material a good adsorbent (Abu-Saied et al., 2017; Bailey et al., 1999),for example,(1) Chitosan is an abundant, cheap resource, which makes it economically

viable;(2) With abundant amino and hydroxyl groups, chitosan has a good adsorption

capacity for many pollutions;(3) Chitosan can be easily modified through physical or chemical methods for

more versatile applications;(4) As a biodegradable polymer, chitosan is non-toxic and environmental

friendly.There have been several reviews of chitosan as an adsorbent (Salehi et al., 2016b;

Vakili et al., 2014; Wang et al., 2016, Zhang et al., 2016a). Our research group hasalso written an important review on chitosan and its application in the removal ofheavy metal ions and radionuclides in 2014 (Wang and Chen, 2014). Consideringthe fast progress of chitosan-based research, as well as the emergence of new pollu-tants, it is vital to provide a summary of all the recent progress in chitosan-basedadsorbents for a range of applications. In this review, we summarize chitosan-based adsorbents in regards to their synthetization and applications. Chitosan-based adsorbents are noted as biosorbents because chitosan is obtained frombiomaterials.

This review presents three aspects of chitosan-based adsorbents: (a) Thestructure and physiochemical properties of chitosan; (b) preparation of desir-able chitosan-based biosorbents via physical or chemical modification methodsand its physicochemical structure change; (c) versatile application of chitosan-based adsorbents with various mechanisms and how this influences relevantfactors.

The purpose of this review paper is to provide comprehensive understanding ofchitosan-based adsorbents and inspire ideas for the development of better adsorb-ents that could be applied in industrial settings.

2332 J. WANG AND S. ZHUANG

2. Structure and physicochemical properties of chitosan

Chitosan is a linear polysaccharides with b-1,4 linked 2 amino-2-deoxy-D-glucose.It’s also regarded as N-deacetylated form of chitin, which is the second most abun-dant natural organic resource on Earth, as shown in Fig. 1. There are three mainreactive groups of chitosan that can be used for chemical modification. They areC2-NH2, C3-OH, and C6-OH, as shown in Fig. 1. Though it can be found in asmall variety of mushrooms, chitosan is mainly obtained as a product of chitinthrough an alkaline deacetylation method performed industrially, due to the lowcost and ample resources (Rafique et al., 2016). Chitosan and its derivatives havebeen widely used in many fields including pharmacy, biotechnology, cosmetics,food, agriculture, environmental remediation; however, it has not yet been fullyutilized on an industrial scale (Rinaudo, 2006).

Commercial chitosan is offered with varying degrees of deacetylation (DD), rep-resenting the ratio of 2-acetamido-2-deoxy-D-glucopyranose to 2-amino-2-deoxy-D-glucopyranose structural units. DD depends on the raw material source and thepreparation procedure and can be calculated by different methods, such as NMRand infra-red spectroscopy analysis (Brugnerotto et al., 2001; Rinaudo et al., 1992).Because it can greatly influence chitosan/chitin’s solubility and solution properties,DD is a vital parameter for the identification of chitosan and chitin. The descrip-tion of chitosan on the deacetylation degree of chitin typically ranges from 50–70%. Usually, with DD more than 50%, this polymer can be dissolved in diluteacidic solutions (Rinaudo, 2006).

Figure 2 shows the chitosan structure composed of glucosamine and N-acetyl-glucosamine units. The presence of N-acetylglucosamine and glucosamine units inchitosan structure contributes to its versatility and its heterogeneity in the polymer.Figure 2 also shows the possible reactive sites in chitosan. Usually, amino groups of

Figure 1. Chemical structure of chitin and chitosan.

CRITICAL REVIEWS IN ENVIRONMENTAL SCIENCE AND TECHNOLOGY 2333

chitosan is much more active than hydroxyl groups following the order of C2-NH2

> C6-OH > C3-OH.The deacetylation of chitin leads to it becoming chitosan, which differs in crys-

talline structure and crystallinity. Due to the hydrogen bonds, the crystal structureof chitin possesses a low solubility. With a lower crystalline degree, chitosan is stilla semi-crystalline polymer in its solid phase making it insoluble in water at near-neutral pH and in most common organic solvents and organic alcohols. However,chitosan can be water dissolvable in some diluted organic acids and mineral acid.With free amino groups at the C2 position protonated in these dilute aqueousacids, chitosan becomes fully soluble when pH <5 (Crini and Badot, 2008).

Both the type and concentration of the acid can influence its solubility. Chitosan isinsoluble in water and organic solvents, but not in inorganic acids (nitric acids andhydrochloric acids), organic acids (propionic, succinic, formic, acetic, toluene, acrylic,oxalic, and ascorbic acids), oxy-acid (maleic, gluconic, malic, tartaric, lactic, and citricacids), and acidic amino acids (such as glutamic acid) by forming corresponding acidsalts with the amino groups in chitosan molecules (Wang and Chen, 2014). Chitosan isrelatively stable in dilute sulfuric acid and phosphoric acid solutions.

The solubility of chitosan can also be influenced by the polymer weight and thepresence of other ions in the solution (Rinaudo et al., 1993). With different molec-ular weights and DD, commercial chitosan is offered in the forms of flakes or pow-ders. As a partial or total deacetylated product from chitin, chitosan can beobtained with an ideal polymer weight. Using its solubility in different solvents,chitosan salt particles or flakes can be dissolved in dilute acids and then immersedor injected into alkaline solutions to prepare chitosan gels in different forms suchas particles, beads, flakes, and membranes that can be easily utilized. In the pres-ence of other salt ions, the electrostatic interaction could be screened, which couldincrease its solubility.

Figure 2. Difference between chitin and chitosan in chemical structure (Pillai et al., 2009).


Though the presence of hydrophilic functional groups including amino andhydroxyl groups cannot change chitosan’s hydrophobic nature, it helps to makechitosan apt for adsorption and modification. With abundant amino groups, chito-san is the only pseudo-natural cationic polymer. Its pKa varies from 6.5 to 6.7 inliterature depending on the ionic strength, DD, and the charge neutralization ofamine groups (Guibal, 2005). This unique property expands chitosan’s potentialapplication including the ability to adsorb different pollutants. For example, aminegroups are strongly reactive with metal ions due to the nitrogen atoms with freeelectron doublets. What’s more, the protonation of these amine groups of chitosanmay lead to its electrostatic attraction of anionic compounds (such as metal anions,anionic dyes, F¡). Kurita et al. (1979) noted that the adsorption capacity of chito-san depends on its affinity to water, crystallinity, deacetylation percentage, andamino group content.

Chitosan has also been developed as a drug carrier, tissue repair material, etc.due to its bio-comparable and antibacterial nature. Additionally, the versatileapplication forms of chitosan make it easy to separate. The discarded chitosan canalso be biodegraded via microorganisms. As a biomaterial obtained from nature,chitosan has a good affinity towards organisms and is regarded as an environmen-tally compatible material.

The above properties of chitosan and advantages make it a promising biomate-rial in adsorption.

3. Modification of chitosan

The modification of chitosan is necessary as there are still some drawbacks hinder-ing its practical use, such as a low mechanical strength, low solubility in acidicmediums, low adsorption capacity, and lack of selectivity. The modification ofadsorbents via physical and chemical method will change its physiochemical prop-erty and further affect its adsorption behavior to meet the requirements of specificapplications.

The identification of adsorption mechanism could provide important informationfor the modification process. After modification, the adsorption mechanism betweenthe adsorbates and adsorbents varies from physical to chemical force. However, it’swidely accepted that amino groups play an important role in the process of adsorp-tion. Having more available and useful functional groups is good for the adsorbatesbeing selectively adsorbed by the adsorption sites, which could enhance its adsorp-tion capacity and selectivity (Yu et al., 2016b; Zhang et al., 2017).

Chitosan-based adsorbents could be modified by physical and chemical methodsto expand their application. The physical structure of chitosan with a bigger surfacearea, more porosity, and smaller size can accelerate the process of adsorption short-ening the time required for adsorption equilibrium (Zhang et al., 2016a). To obtainan ideal structure for special utilization, different forms of chitosan, like beads (Laz-aridis and Keenan, 2010), film (Salehi et al., 2016a), powder (Chang et al., 2006), and


nanofiber (Habiba et al., 2017) were obtained through various physical modifica-tions. The conversion of chitosan into different kinds of gels could reduce its crystal-linity and increase intraparticle diffusion. Besides, chitosan-based composites haveattracted much attention as the composites can not only overcome the shortcomingsof chitosan but also offer more benefits, such as physical strength and magnetism(Golie and Upadhyayula, 2017; Liu, et al., 2015). On the other hand, the chemicalstructure of adsorbents dominates adsorption capacity. With reactive functionalgroups including hydroxyl and amino groups, chitosan can be chemically modifiedeasily. Crosslinking and grafting are widely used in the chemical modification of chi-tosan. To overcome the chemical resistance and the weak physical strength of chito-san, crosslinking is used to reinforce the chemical stability of chitosan, although thiscompromises the consumption of active functional groups, mainly amino andhydroxyl groups. To obtain adsorbents with better adsorption capacity and selectiv-ity, different functional groups, including amino groups, sulfur groups, carboxylgroups, alky groups, and other special structures like b-cyclodextrininto are graftedonto the backbone of chitosan (Yu et al., 2016b).

3.1. Physical modification

Physical modification includes blending and conversion of chitosan’s forms. Usu-ally, polymer chains of chitosan are expanded through physical modification,which is good for the access to internal sorption sites and decreases the crystallinestate (Babel and Kurniawan, 2003). Besides this, blending with other materials isanother good method of synthesizing composites with the desired structure. It canenrich chitosan with better physical strength, adsorption performance, pH, tem-perature sensitivity, magnetism, etc.

3.1.1. Different forms of chitosanThe commercial chitosan offered is in the form of powder or flakes with a low sur-face area and no porosity. It may result in serious column clogging and drop in thenecessary high pressure during column operation, which will generate high opera-tion costs. Besides this, the drawbacks of commercial chitosan include low hydro-philicity and high crystallinity, hindering its application. The conversion ofchitosan into beads, films, nanofiber, particles, sponges etc. has been widelyreported (Crini and Badot, 2008; Thakur and Voicu, 2016).

Usually, the conversion method is chosen based on chitosan’s solubility in dif-ferent solvents. Chitosan gel beads can be obtained via injecting the acid-dissolvedchitosan (2–4 wt%) into alkali solution. The diameter of the beads can be con-trolled by the syringe needle and injection rate (Zhang et al., 2011). Owing to thehigh viscosity of chitosan solution, when the pinhead become smaller, more pres-sure is needed which is not economical for industrial application. Without alkalisolution, Zhang et al. (2017) reported chitosan microspheres with a diameter ofless than 10 mm via a spray drying method. Membranes or film can be obtained by


casting chitosan solution with alkali solution onto a flat surface (Mi et al., 2001).Alkali solution can also be replaced by sodium tripolyphosphate (TPP) solutionaccording to the research of Chiou and Li (2003). In practical use, chitosan mem-brane can be cut into smaller particles for a more versatile application.

Chitosan sponges with 3-dimensional (3D) structures can be synthesizedthrough freeze-drying (Vincent et al., 2015). It has been reported that the freezingtemperature affects the formation of 3D network structure. The lower temperaturewas favorable for synthetization of single oriented porous structures with goodmechanical properties (Su et al., 2016). However, it could consume large quantitiesof energy, which is not economical.

Compared with other application forms of chitosan, chitosan nanofibers withcustomizable pore sizes and reasonably high specific surface areas have attractedmuch attention (Habiba et al., 2017; Huang et al., 2015; Li et al., 2013b; Min et al.,2015). Min et al. (2015) synthesized pure chitosan electrospun nanofiber mem-branes with an average diameter of 129 nm in order to remove As(V) frombatches. Despite the beneficial properties, fiber adsorbent is limited in widespreadapplications due to its weak physical strength and low reusability. Li et al. (2013b)prepared modified nanofibers chitosan through crosslinking with glutaraldehyde.The results showed that both its solubility and thermal stability had improved.Habiba et al. (2017) reported the production of chitosan/(polyvinyl alcohol)/zeolitecomposite nanofibers via blending and electrospinning methods. It showed goodstability in solutions with different pH and could be reused in up to five runs.

Besides its intrinsic properties, the physical structure of chitosan-based adsorbentsis strongly influenced by the forming conditions, including the dissolved stage (theconcentration of chitosan and solvent), casting stage (the nature and concentrationof casting solution), crosslinking stage (the nature of the crosslinker, the crosslinkingextent, hetero- or homogeneous crosslinking), and its post-processing method (blastdrying, freeze-drying, grinding, or in more moisture filled processes).

Chitosan in different forms affects adsorption behavior. Chitosan-based adsorb-ents with higher specific surface areas could improve access to internal sorption sitesand expose more functional groups to the outside. Chiou and Li (2003) noted thatsmaller beads could reach equilibrium earlier while the adsorption capacity remainedalmost unchanged. Kyzas et al. (2012) concluded that the adsorption kinetics weregreatly affected by chitosan’s swelling, and the liquid forms could reach adsorptionequilibrium faster than the dry ones. In his research, a model was applied to quanti-tate the interaction between adsorption and swelling. It also indicates that adsorptionkinetics of chitosan-based gels with varying levels of moisture cannot be compareddirectly. Demey et al. (2014) observed that both the adsorption capacity at equilib-rium and kinetic profile was influenced by the drying methods.

3.1.2. BlendingChitosan composites consisting of two or more materials combine the strength, struc-ture, and chemical properties of those different materials, together with the specific


characteristics of chitosan. Various kinds of chitosan-based composites have beenreported. Ngah et al. (2011) have a good review of different kinds of chitosan compo-sites and its application in the removal of dye and heavy metal ions. As listed inTable 1, a great number of substances have been used for the formation of chitosan-based composites, including porous materials (such as active carbon and graphene),magnetic materials (such as Fe3O4 and g-Fe2O3), polymers (such as alginate, cellulose,PVA, and PVC), biomass (such as Saccharomyces cerevisiae), and clay (such as perliteand montmorillonite) (Ngah et al., 2011; Rafique et al., 2016; Wang et al., 2016).

Incorporating different kinds of materials could bring unpredictable benefits inthe composites. Yang et al. (2010) indicated that the incorporation of 1 wt% GOcould enhance the tensile strength by about 112% and its elongation was greatlyimproved. The incorporation of highly porous active carbon into chitosan can bedispersed well via electrostatic repulsion and hydrogen bonding (Liu et al., 2015). Toexpose more active sites, Boddu et al. (2003) coated chitosan with ceramic alumina.Results showed that its maximum adsorption capability of Cr(VI), obtained fromthe Langmuir model, was 153.85 mg/g, a great improvement. Chang and Juang(2004) reported that the addition of activated clay into chitosan could improve itsmechanical strength, specific gravity, and adsorption capacity compared with chito-san alone. Chitosan-derivative/polyethersulfone hybrid particles with semi-inter-penetrating network structures for versatile adsorption have been investigated byWang et al. (2015). The results showed that compared with the chitosan particles,chitosan-based hybrid particles exhibited better acid–alkali resistance and mechani-cal properties.

Various magnetic materials have been used to fabricate magnetic chitosan. Severalkinds of magnetic materials have been widely used, including iron oxides (such asFe3O4 and g-Fe2O3) and spinel ferrites (such as MnFe2O4, CoFe2O4, and CuFe2O4)(Chang et al., 2006; Garza-Navarro et al., 2010). The traditional separation methodslike filtration and sedimentation may block the filters or lose some adsorbent. After

Table 1. Types of chitosan composites.

Blending materials Examples References

Porous materials Active carbon, graphene, graphene oxide,pumice

Aliramaji et al., 2017; Liu et al., 2015; Yanget al., 2010

Magnetic materials Iron oxides: Fe3O4, g-Fe2O3, Fe3O4@Al2O3,Fe3O4@SiO2

Badry et al., 2017; Chen and Wang, 2016;Tanhaei et al., 2015

Spinel ferrites: MnFe2O4, CoFe2O4 CuFe2O4

Polymer Natural polymer: cellulose, alginate, silkfibroin, cotton fiber, etc.

Aliramaji et al., 2017; Guo et al., 2017;Mukhopadhyay et al., 2015; Spera et al.,2017

Synthesized polymer: polyvinyl chloride(PVC), polyvinyl alcohol (PVA), etc.

Zhu et al., 2014

Clay Perlite, montmorillonite, zeolite,clinoptilolite or Sepiolite-chitosancomposites, alumina

Boddu et al., 2003; Chang and Juang, 2004

Biomass Saccharomyces cerevisiae, Lemna gibba L. Chen and Wang, 2010; Turker and Baran,2017

Others TiO2, zero-valent iron, molybdate, cerium Bai et al., 2016; Dhanya and Aparna, 2016;Kaushik et al., 2009; Su et al., 2016


adsorption, magnetic materials can be separated from the solution via the applica-tion of an external magnetic field (Wang et al., 2013). Tanhaei et al. synthesized acore-shell composite containing chitosan and Fe3O4@Al2O3, in nano (Tanhaei et al.,2015) and micro sizes (Tanhaei et al., 2016). This core-shell structure coating mag-netic particles with alumina as a shell could maintain its magnetics, improve chemi-cal stability, and prevent oxidation especially in acidic conditions. Fe3O4@SiO2 weresynthesized by Yi et al. (2016) for the same purpose. Paulino et al. (2011) investi-gated chitosan-based hydrogels with and without magnetite for the removal of Cd(II), Pb(II), and Cu(II) ions from aqueous solutions. Results showed that magnetitein chitosan will compete for active sites with metal ions resulting in a decrease inadsorption capacity. Besides, it would increase crosslinking points in the polymerhydrogel network resulting in a decrease in the water diffusion rate.

Su et al. (2016) proposed nanoscale zero-valent iron/chitosan composite foams(ICCFs) for the removal of inorganic arsenic. This unique composite possessed manybenefits including good mechanical stability and oriented porous structure with highadsorption capacity. This structure combined the adsorption capacity of chitosan andthe oxidation capacity of zero-valent iron, successfully avoiding the Fe3C releasing intothe solution producing secondary pollution, instead of being adsorbed by the chitosan.

Our research group has synthesized various kinds of novel chitosan compositebiosorbents, especially magnetic chitosan. These composites consist of porous mate-rials (such as chitosan/Fe3O4/GO), polymers (such as magnetic PVA/chitosan (Zhuet al., 2014)), or biomass (such as Saccharomyces cerevisiae (Chen and Wang, 2010;Yin et al., 2017)), were obtained in different forms (such as beads and nanoparticles),and were used for the removal of heavy metal ions and radioclides. The formation ofmagnetic chitosan gel via one step co-precipitation in basic solution is very simple asonly the extra chemicals, Fe3C and Fe2C (molar ratio 2:1), are needed. They presenthigher magnetic recovery and good adsorption capacity during application.

3.2. Chemical modification

With abundant amino and hydroxyl groups, chitosan can be chemically modifiedthrough different kinds of reactions, such as etherification (Ge and Luo, 2005; Vis-wanathan et al., 2009), acylation (Guo et al., 2016; Repo et al., 2013), esterification,oxidation, xanthation (Chen and Wang, 2012a; Zhu et al. 2012), Schiff base reac-tion (Elwakeel et al., 2017; Tanhaei et al., 2015), and alkylation (C�ardenas et al.,2001; Qin et al., 2003). Various chitosan derivatives could be obtained via chemicalmodification and they show good adsorption capacity together with good mechan-ical resistance and chemical stability.

3.2.1. CrosslinkingChitosan is limited from being widely used due to its weak mechanical resistanceand low chemical stability in acidic solutions. To overcome these, various kinds ofcrosslinked chitosan were obtained via crosslinkers (Li and Bai, 2006). Crosslinked


chitosan can also be obtained via radiation; however, the related articles are scarce.Our research group has a good summary of radiation-induced synthesis of hydro-gels including chitosan (Chen and Wang, 2009).(1) CrosslinkerLogically, a chemical agent that can react with at least two functional groups of chito-

san could be used as a crosslinker. Thatmeans chemical agents with at least two reactivefunctional groups per molecule (e.g., aldehydes, anhydrides, and epoxide) (Vakili et al.,2014) or some special mono-functional agents (e.g., epichlorohydrin) (Wang andChen, 2014) could be used in crosslinking. The commonly used crosslinkers referred inthe research include glutaraldehyde (GLA) (Chen and Wang, 2016; Nagireddi et al.,2017), epichlorohydrin (ECH) (Chen et al., 2008; Li et al., 2016a), ethylene glycol digly-cidyl ether (EGDE) (Kamari et al., 2009b; Ngah et al., 2002), etc.

Figure 3 shows the chemical structure of these commonly used crosslinked chi-tosan. These crosslinkers serve as a bridge linking different polymer chains or thesame chain reducing segment mobility, forming a 3D network, improving chemi-cal resistance and the mechanical strength of adsorption.

The nature of crosslinkers and the extent of their reactions has a great influenceon the physicochemical structure of adsorbents and further improved its adsorp-tion performance.

For adsorption performance, picking up a crosslinker is very important becauseit determines which functional groups of chitosan are consumed, formed, andintroduced. Amino groups of chitosan are more active than hydroxyl groups notonly in the adsorption process but also in crosslinking reactions. Crosslinkers suchas GLA and EGDE are more likely to react with amino groups than hydroxyl

Figure 3. Schematic representation of the crosslinked chitosan (a) Chitosan-GLA (b) Chitosan-ECH(c) Chitosan-EGDE.


groups of chitosan, as shown in Fig. 3. However, there are other kinds of cross-linkers such as ECH that mainly target the hydroxyl groups rather than aminogroups. Chitosan modified by different crosslinkers are compared in dye and heavymetal removal by many researchers. Ngah et al. (2002) noted that the maximumadsorption capacity of Cu(II) on different crosslinked chitosan obtained from theLangmuir model followed the order: chitosan (80.71 mg/g) > chitosan-ECH(62.47 mg/g) > chitosan-GLA (59.67 mg/g) > chitosan-EGDE (45.94 mg/g). Simi-lar results were obtained by Chiou and Li (2003) for the removal of anionic dye,Reactive Red 189. Compared with other crosslinked ones, chitosan modified withECH showed higher adsorption capacity owing to the lower diminishment ofamino groups, which are the major adsorption sites for many pollutants.

Besides, crosslinkers can offer more functional groups to the adsorbents. Shimizuet al. (2006) utilized 1,3,5-Triacryloylhexahydro-1,3,5-triazine (TAT) as a new cross-linker to synthesize crosslinked chitosan for the removal of acid dyes and metal ionsfrom solution. The introduction of hexahydrotriazine rings of TAT into crosslinkedchitosan enhanced its adsorption of anionic dyes. And the new material exhibitedselectivity for metal ions in the order of Cu2C >> Ni2C > Cd2C, Pb2C, Ca2C. Ourresearch group has synthesized crosslinked chitosan using EDTA anhydride as a cross-linker and chelating agent (Zhuang et al., 2017). The results showed that the adsorp-tion capacity for cobalt ions increased from 2.00 to 7.97 mg/g. Shimizu et al. (2006)reported a novel crosslinker, higher fatty diacid diglycidyl, with a particularly long car-bon chain. The longer the crosslinker is, the more flexible the chain could be. Radwanet al. (2010) reported crown ether crosslinked chitosan via a di-Schiff type reaction.The unique structure of crown ether provided modified chitosan with high particularadsorption selectivity for Hg2C in the presence of Pb2C at various pH conditions.

Generally, the adsorption capacity of chitosan-based adsorbents depends on theextent of crosslinking. The higher the degree of crosslinking is, the lower theadsorption capacity can be (Shimizu et al., 2006). It is explained by many research-ers that the active groups, especially amino and hydroxyl of chitosan, are con-sumed during crosslinking. Kamari et al. (2009b) synthesized chitosan beads withand without the crosslinker EGDE separately for acid dye (Acid Red 37 and AcidBlue 25) sorption. The results showed that adsorption capacities of crosslinked chi-tosan for both acid dyes were comparatively lower than those of chitosan beads,owing to the consumption of adsorption sites -NH3 by crosslinkers. Besides, thehigher degree of crosslinking may result in a narrow and complicated networkstructure which is hard for the penetration of pollution (Crini and Badot, 2008).Especially when concerning the crosslinking under heterogeneous condition, theexposure outside gets crosslinked firstly delaying or preventing the crosslinker orpolluter from further reactions. However, crosslinking is necessary for it enricheschitosan with better physical resistance, chemical stability, and higher adsorptioncapacity in some cases due to the introduction of the new functional groups of thecrosslinker. So the optimal crosslinking degree should balance the adsorptioncapacity and its other characteristics.


These commonly used crosslinkers are considered to be toxic which may bringabout negative effects on the environment. From the perspective of environmentalprotection, some researchers think highly of much safer crosslinkers such as geni-pin and Tripolyphosphate (TPP). However, the reports of genipin and TPP are farless than that of ECH, GLA, or EGDE as the crosslinkers for chitosan. Yang et al.(2011) studied the optimal crosslinking condition of the chitosan beads co-cross-linked with TPP/genipin for the selective adsorption of phytic acid from soybeanwhey solution. It was proved that the crosslinking degree depended on pH valueand decreased when the pH values increased. CB7 (co-crosslinked in pH 7 solu-tion) showed the best mechanical strength, together with a good selective adsorp-tion capacity for phytic acid. Chiou and Li (2003) noted that TPP as a crosslinkerfor chitosan could save the time needed for aging and obtain a more rigid structuredue to the ionic attractions between positively charged amino group of chitosanand negatively charged P3O10

5¡ of TPP in acid solutions.(2) Molecularly imprinted chitosan (MIC)To overcome the decreasing adsorption capacity during the crosslinking process,

molecularly imprinted chitosan (MIC) has been developed. It was obtained by usingtargeted pollution as a template, crosslinking, and then removing the template mole-cules (Varma et al., 2004; Xu et al., 2015). During the crosslinking, some active func-tional groups are occupied by the template molecules ensuring they do not diminish.At the same time, crosslinkers in polymeric networks ensured the functional groupsof chitosan are oriented in specific directions and locations around template mole-cules to preserve the structure of the adsorption sites (Xu et al., 2015). After elution,the MIC possesses selective adsorption sites for the targeted molecule.

To enhance adsorption selectivity, many pollutants have been tested as tem-plates. Au(III) ion-imprinted thiol-modified chitosan was synthesized by Monierand Abdel-Latif (2017) using ECH as the crosslinker. This polymer showed higheradsorption capacity (370 mg/g) than that of non-imprinted one (195 mg/g).Nishad et al. (2012) synthesized Co(II) imprinted chitosan and studied the selec-tive adsorption of Co(II) in the presence of Fe(II) at various solution conditions,which was the major non-radioactive ion present in excess during decontamina-tion. Although the raw chitosan showed better selectivity to Fe(II) over Co(II), theimprinted chitosan showed selective sorption toward Co(II) over Fe(II); Zhu et al.(2017) proposed MIC with Cu(II) as the ionic template and compared its adsorp-tion selectivity towards many metal ions with similar ionic radii (Cu(II), Co(II),Mn(II)), similar affinity (Cu(II), Zn(II)), same charge (Cu(II), Pb(II), Ca(II)), ordifferent charges (Cu(II), Na(I), Al(III)). Results showed that MIC showed higheradsorption capacity for most metal ions than the non-imprinted one due to theprotection of amino groups. Besides, MIC showed better adsorption selectivity fol-lowing the order: Cu2C > Zn2C > Mn2C > Co2C > Ca2C > Pb2C > Al3C > NaC.It was demonstrated that the selectivity of MIC was related to the ionic radius ofthe template ion and the affinity. Cr(II) (Tang et al., 2017) and Zn(II) (Kazemiet al., 2017) imprinted chitosan also presented better adsorption selectivity toward


the ion template than the raw one. Chang et al. (2010) synthesized MIC usingdibenzothiophene as the template and studied the influence of crosslinking and itsadsorption for gasoline. With the imprinting effect reaching 2.45, the maximumrebinding capacity of MIP was 22.69 mg/g. Yu et al. (2008) studied chitosan modi-fied by perfluorooctane sulfonate (PFOS) as a template and ECH as a crosslinkerfor the selective removal of PFOS from aqueous solution. Compared with the non-imprinted polymer (qm D 258 mmol/g), the optimized MIC presented higheradsorption capacity for PFOS (qm D 560 mmol/g).

3.2.2. GraftingSmall molecules or polymers with desirable functional groups or structures can becovalently bonded into chitosan via graft copolymerization, etherification, acyla-tion, etc. Chemical grafting of chitosan with specific ligands, such as carboxylicgroups, amine groups, alkyl groups, sulfur compounds, and special structures likecrown ether, cyclodextrin can alter its physicochemical structure and improve itsadsorption performance (including adsorption capacity and selectivity, sensitivityto conditions, and adsorption kinetics) (Radwan et al., 2010).(1) Grafting copolymerizationGrafting copolymerization is a very important method of enriching chitosan with

more functional groups. It can be initiated by free radicals, radiation, enzymes, etc.(Ge and Luo, 2005; Jayakumar et al., 2005; P�erez-Calixto et al., 2016). The mono-mers used for the polymerization are required to carry reactive groups capable ofcarrying out radical polymerization, which comprises of an unsaturated structurebetween carbon and carbon atoms or carbon and heteroatoms. Different kinds ofvinyl monomers including acrylic acid, acrylamide, vinylpyridine, 2-hydroxyethylmethacrylate have been used in literature for chitosan grafting as shown in Table 2.

The efficiency of grafting is found to depend on the grafting methods and its pro-cedure parameters. Free radicals including S2O8

2¡ and ceric ion have been widelyreported for a long time. Yazdani-Pedram et al. (2000) noted that the efficiency ofgrafting was found to depend on monomer, initiator, and ferrous ion concentrations,as well as reaction time and temperature. Radiation-induced graft polymerization isa convenient and powerful technique to introduce desirable properties in polymers.No extra catalysts or additives are needed to initiate the reaction; it can be easilystarted and stopped. The reaction extent could be easily controlled by the dose ofirradiation. P�erez-Calixto et al. (2016) synthesized grafted chitosan via four routesand compared the effects of direct and indirect irradiation. Results showed that one-step irradiation showed the best grafting yield (30%) than that of pre-irradiation (2–3%). Benamer et al. (2011) fabriated acrylic acid grafted chitosan by gamma irradia-tion and explored its adsorption performace. Results showed that the grafting yieldincreased with the increasing dose. The grafted chitosan possessed a lower degree ofswelling with a higher adsorption capacity for Cd2C and Pb2C than raw chitosan.

Yu et al. (2016a) synthesized multifunctional adsorbents containing –COOH,–NH2, -SO3H, -OH groups via a glow discharge electrolysis plasma technique for


Table2.

Typesof

monom

ersingraftin

gcopolymerization.

Monom

ers

Structure

Methods

References

N-vinylcaprolactam

g-irradiation

P� erez-Calixto

etal.,2016

N,N-dimethylacrylam

ide

g-irradiation

P� erez-Calixto

etal.,2016

(2-m

ethacryloyloxyethyl)trimethylammoniumchlorid

eg-irradiation

Wangetal.,2007

poly(ethyleneglycol)m

ethylethermethacrylate(PEG

MA)

g-irradiation

Kong

kaoroptham

etal.,2015

2-hydroxyethylmethacrylate

g-irradiation

Casimiro

etal.,2005

UVradiation

ElbarbaryandGhobashy,2017


Acrylic

acid

g-irradiation

Benameret

al.,2011

Free

radicals(S2O

82¡)

Linetal.,2017

Free

radicals(S2O

82¡)

Yazdani-Pedrametal.,2000

Maleicacid

Free

radicals(S2O

82¡)

GeandHua,2016

Acrylamide

Free

radicals

LiandBai,2006

4-vinylpyridine

Free

radicals(cericion)

Caneretal.,1998

Methylmethacrylate

Microwave

Sing

hetal.,2006

n-bu

tylacrylate

Microwave

Santhana

Krishn

aKu

maretal.2014


the removal of Pb2C. The maximum adsorptive capacity of Pb2C was 673.3 mg/gdue to the coordination between N atom and Pb2C, and the ion-exchange betweenNaC and Pb2C.(2) Substitution of N/O groupsAdditionally, chitosan derivatives can also be obtained via various chemical

modifications. The functionalization of chitosan frequently consists of the graftingof amino, quaternary ammonium, carboxyl, and thiol groups, as well as other spe-cial structures. This contributes to an increased density of reactive groups, insert-ing additional functions with higher selectivity or higher affinity and to a largerpH-range of applications.

There are many reviews and articles on the synthetization of various chitosanderivatives. Jayakumar et al. (2010) had a good summary of the synthetic chemicalmodification methods of obtaining carboxymethyl derivatives of chitosan. Theintroduction of derivatives of chitosan containing N, P, or S as heteroatom hasbeen presented by Varma et al. (2004) and Pestov and Bratskaya (2016). Though,during the process, the intrinsic potential adsorption sites of chitosan are con-sumed, its adsorption capacity is seldom compromised because more chelatingproperties are introduced into the chitosan backbone.

The grafting order influences structures, especially in core-shell structures, andother adsorption behaviors. Chitosan grafted by other materials can offer more func-tional groups to the adsorbents, while chitosan grafting into other materials showedhigher adsorption capacity due to the fully exposure adsorption sites. Yang et al.(2016) synthesized adsorbents via grafting chitosan into magnetic bentonite by aplasma-induced method. The adsorption sites of chitosan were exposed outside mostlyand the maximum adsorption capacity for CsC was greatly improved to 1.21 mmol/g.

It is well known that chitosan is rich in amino groups. Grafting carboxyl groupsinto chitosan could turn it into amphoteric polymer and expand its potential appli-cation. Carboxyl group modified chitosan has proved to be beneficial for the removalof many pollutants. Guo et al. (2005) reported crosslinked chitosan with carboxylgroups introduced by maleic anhydride. Rocha et al. (2016) reported crosslinked chi-tosan with the grafting of caffeic acid, which contained carboxyl groups for theremoval of Hg(II). The results showed that the sorption efficiency was greatlyimproved from 2.2 mg/g (crosslinked chitosan) to 4.0 mg/g (grafted chitosan).Geand Hua (2016) obtained a higher adsorption capacity (qm D 1044 mg/g at pH D 6)for the removal of Hg(II) on the synthesized carboxyl functional chitosan via graft-ing maleic acid. The removal of fluoride ions into carboxylated crosslinked chitosanwas investigated by Viswanathan et al. (2009). The maximum adsorption capacitywas proved to be 11.11 mg/g owing to the H bonding between–COOH and F¡.

Some chelating agents, such as EDTA and DTPA, which contain carboxyl groupshave attracted much attention in the modification of chitosan, as shown in Table 3.

EDTA and DTPA have been widely used as hexadentate ligands and chelatingagents for metal ions, but they are too soluble to be recovered after use. To avoid mate-rial loss, these chelating agents are immobilized into chitosan backbone. With the help


of these chelating agents, adsorption capacity and selectivity can be vastly improved.EDTA- and DTPA-functionalized chitosan can be synthesized through the reactionbetween anhydride of EDTA or DTPA and amino groups of chitosan (Ge and Huang,2010; Repo et al., 2010, 2011, 2013). Ge et al. (2012) prepared EDTA-modified cross-linked chitosan through the reaction between ECH-O-crosslinked chitosan and EDTAdianhydride under microwave irradiation. It can also be obtained via a dehydration–condensation reaction between amino groups of chitosan and the carboxyl groups inthe chelating agent with the help of EDC (Ayati et al., 2017). Ayati et al. (2017) notedthat having the EDTAmodified chitosan in novel nano- and microsizes increased theiradsorption capacities of Pb(II) about 31.5 and 38 times, respectively. Shimizu et al.(2004) concluded that EDTA residues left by the crosslinked chitosan significantlyenhanced the adsorption power for metal ions in the order: Cu2C >> Ni2C > Pb2C >

Cd2C > Ca2C. At the same time, with the modification of chelating agents, theiradsorption capacities are more than just higher than raw chitosan, but even higherthan both that of rice husk (7.1–30.0 mg/g for Cu2C; 33.1–45.6 mg/g for Cr6C;8.58 mg/g for Cd2C) (Malik et al., 2016) and activated carbon (3.88–46.3 mg/g forCu2C; 9.1 mg/g for Ni2C; 40.3–64.1 mg/g for Pb2C) (Hadi et al., 2015).

Grafting more cationic groups, such as amino and quaternary ammonium, intochitosan has been used for different purposes. It has proved to be useful for theremoval of anionic pollutions. Li et al. (2016b) prepared chitosan adsorbents modi-fied by a quaternary ammonium salt for the removal of methyl orange and Cr(VI).Results showed that the additional strong cationic groups enriched modified chito-san with better adsorption capacity for both Cr(VI) and methyl orange than thatof pure chitosan. Besides, the adsorption was greatly affected by pH, indicatingthat electrostatic attractions played a major role in the adsorption process. Thepresence of an amino group in chitosan is considered to be responsible for theadsorption of metal ions. To obtain chitosan-based adsorbents with more aminogroups, Wang et al. (2011) fabricated ethylenediamine-modified magnetic chitosan

Table 3. Maximum adsorption capacity of various pollutants by EDTA- or DTPA-modified chitosan.

Adsorbents Pollutants qm (mg/g) Reference

EDTA-modified chitosan Co2C 63.0 Repo et al., 2010Ni2C 71.0

DTPA-modified chitosan Co2C 49.1 Repo et al., 2010Ni2C 53.1

EDTA-modified chitosan/SiO2/Fe3O4 adsorbent (EDCMS) Cu2C 48.99 Ren et al., 2013Cd2C 64.52Pb2C 128.26

EDTA-modified cross-linked chitosan Pb2C 265.22 Ge and Huang, 2010Cu2C 135.35Cd2C 145.01Ni2C 78.64Co2C 75.43

Chitosan derivative (C2) Cu2C 44.35 Rezende de Almeidaet al., 2016

Co2C 66.30Ni2C 42.55Cr6C 99.32

Modified chitosan beads Co2C 7.97 Zhuang et al., 2017


for the removal of uranyl ions from aqueous solutions. Its adsorption capacity wassuperior over some reported adsorbents for uranium.

Chitosan modified with thiol groups (-SH) displays a good adsorption affinitytowards heavy metals. The removal of Hg(II) from aqueous solutions on thiol-graftedchitosan introduced by cysteine was investigated by Merrifield et al. (2004). The maxi-mum adsorption capacity of Hg(II) was obtained as approximately 8.0 mmol/g at pH7. Our research group introduced thiol group into chitosan using xanthate (Zhu et al.,2012). The competitive adsorption of Pb(II), Cu(II), and Zn(II) was investigated.Results showed that the metal sorption followed the order: Pb(II) (79.9 mg/g) > Cu(II) (34.5 mg/g) > Zn(II) (20.8 mg/g). Crini and Badot (2008) proposed grafting ofsulfonate groups into chitosan in order to increase the adsorption capacity of the basicdye “basic blue 3.” In this experiment, adsorbent showed an interesting sorption capac-ity toward cationic dye (166.5 mg/g) due to the presence of sulfonate groups.

Chitosan derivatives containing b-cyclodextrin or crown ethers in their sidechains became interesting due to their selective formation of complexes with certainkinds of pollutants (Alsbaiee et al., 2016; Yagi, et al., 1980). Sashiwa and Aiba (2004)have a good summary of chitosan modified by b-cyclodextrin or crown ethers. Thehydrophobic cavity of b-cyclodextrin could encapsulate pollutants to form well-defined host–guest complexes. The research group of Luo C.N has done much workon the application of b-cyclodextrin modified chitosan for the removal of pollutants.It was proved that b-cyclodextrin–chitosan was favored for the removal of hydroqui-nol (1.23 mmol/g) (Fan et al., 2012), methylene blue (MB) (50.12 mg/g) (Fan et al.,2013), Cr(VI) (Li et al., 2013a), over reported sorbents. Crown ethers have good anddifferent complex selectivities for many metal ions. It’s reported that the adsorptionof CsC into crown ethers immobilized should be owed to the Cs–p interaction of thebenzene ring with a stable complex mechanism.

Recently, grafting indicators into adsorbents has gained much attention. Metalion indicators such as basic orange 2 and rhodamine have been grafted into algi-nate as probes for radioisotopes (Co2C and Sr2C) (Jo et al., 2015) and toxic metals(Hg2C and Cr3C) (Saha et al., 2012), respectively. Our research group has success-fully grafted 4-(5-chloro-2-pyridylazo)-1,3-phenylenediamine (5-Cl-PADAB), aselective indicator for Co2C, into chitosan (Zhuang et al., 2017) and alginate(Zhuang and Wang, 2017) via different routes.

Figure 4 shows the formation of these two kinds of beads and their digital pho-tos before and after adsorption of Co2C. These modified beads could indicate thepresence of cobalt ions with a remarkable color change from white to pink, whichcan be observed by the naked eye. With dual functions of detection and theremoval of metal ions, these polymer beads are an increasingly hopeful prospect.

4. Characterization of chitosan-based materials

The characterization of materials can provide important information about thestructure and properties of the adsorbents and the interaction mechanism


between adsorbents and adsorbates. It is a fundamental process in the applica-tion of chitosan-based adsorbents, without which no scientific understandingof the materials can be obtained. With the rapid development of technology,more and more powerful characterization tools have arisen including all formsof chemical, microscopic, and macroscopic analysis. Table 4 shows differentcharacterization tools utilized in the reports of chitosan-based adsorbents,including scanning electron microscope (SEM), Fourier transform infrared(FTIR), energy dispersive X-ray spectroscopy (EDX), nuclear magnetic reso-nance spectroscopy (NMR), elemental analysis (EA), Brunauer–Emmett–Telleranalyzer (BET), X-ray photoelectron spectroscopy (XPS), magnetic testing, andmechanical testing.

Usually, the synthesized chitosan-based adsorbent is characterized in thearticles before and after application. Different kinds of characterization tools canprovide different information. For chemical analysis, FTIR and IR can offerdetails regarding the chemical structure, especially the functional groups; NMRcan provide the structure and chemical environment of molecules using the mag-netic properties of certain atomic nuclei; XRD can be used to analyze the crystalstructure; EA is a qualitative method determining what elements are present inthe samples and their quantities. For microscopic analysis, SEM-EDX can be uti-lized to get the details of chitosan’s surface topography and semi-quantitativeEA; TEM can further identify the inside structure via transmitted electrons. Asfor magnetic materials, it is necessary to carry out magnetic testing using a vibra-tion sample magnetometer (VSM).

Various kinds of characterization methods have been used to provide impor-tant clues for the understanding of adsorption mechanisms. The adsorption ofPb2C into crosslinked carboxymethyl-chitosan (crosslinked CMC) resin wasdetected by FTIR and XPS by Sun et al. (2006). It was revealed that the adsorp-tion of crosslinked CMC template and CMC for Pb(II) was a chelation processwhere the carboxymethyl group, amino group, and the secondary hydroxyl groupof chitosan participated. In the Zhu et al. (2012) research, it was proved to bethiol and amino groups of modified chitosan that participated in the Co(II)adsorption process according to FTIR and XPS analysis. Yu et al. (2016a) utilizedXPS to study the adsorption mechanism of Pb2C ions into chitosan-basedadsorbents. The XPS results of the adsorbent before and after adsorption of Pb2C

indicated that the adsorption should be attributed to the coordination between Natom and Pb2C, and ion-exchange between NaC and Pb2C. To identify whichfunctional groups are responsible for Sr2C binding, Chen and Wang (2012b)compared the FTIR spectroscopy of magnetic chitosan beads before and aftersorption of Sr2C. It revealed that –NH2 was mainly involved in the adsorptionprocess. According to the IR results, Rangel-Mendez et al. (2009) proposed anadsorption mechanism, where electrostatic interactions and covalent bonds wereresponsible for the adsorption of metal ions on chitosan.


5. Adsorption kinetics and isotherms

The application of chitosan-based biosorbents for pollution removal has been welldocumented (Bhatnagar and Sillanpaa, 2009). There are numerous materials includingbooks, reviews, articles, patents focusing on the utilization of chitosan-based biosorb-ents in wastewater treatment, such as organic pollutants (dye, pharmaceutical and per-sonal care products (PPCPs), PFOS, etc.) and inorganic pollutants (heavy metal ions,radioclide, nitration, fluoridation, etc.). Among them, the removal of dyes and metalions using chitosan-based adsorbents accounts formost of the research.

In literature, adsorption behaviors involving the solution conditions (like pH,ionic strength, competitive molecular, or ions) and the process variables (like con-tact time, initial concentration of pollutants, the dose of adsorbents, temperature,stirring rate), as well as the regeneration of adsorbents, have been widely discussed.Based on the adsorption data, adsorption kinetics and equilibrium studies with

Figure 4. Schematic formation and digital photos of (a) 5-Cl-PADAB-grafted alginate (b) 5-Cl-PADAB and EDTA modified chitosan.


different models are shown in Tables 5 and 6, respectively. However, the applica-tion of chitosan on an industrial scale is still rare.

6. Removal of organic pollutants

6.1. Dye removal

The development of various industries, including the dyeing industry involving tex-tiles, food, paper, printing, leather, and plastic industries, has caused the productionof more and more colored substances being ejected into the environment. The harm-ful nature of the dyes associated with their high visibility, resistance, and toxicimpact has aroused public concerned. Even low concentration of dyes in water canprevent the penetration of light and oxygen, which not only makes it highly visiblecausing aesthetical issues, but also reduces photosynthetic activities in aquatic envi-ronments, endangering the aqueous organisms and ecology. Besides, it can arousetoxic effects on humans, such as skin irritation, tumors, and allergies, via direct orindirect ways. With stable aromatic structures, dyes are non-biodegradable and sta-ble under different conditions (Wang and Xu, 2012). According to their charge dif-ference, dyes can be classified into three categories: anionic dyes (like reactive, direct,and acid dyes), cationic dyes (like basic dyes), and non-ionic dyes (like dispersedyes). Scheme 1 shows the chemical structure of the commonly used dyes.

For years, numerous studies have showed that chitosan-based biosorbents havehigh affinity towards many classes of dyes, as listed in Table 7 (Chiou et al., 2004;Crini and Badot, 2008; Liu et al., 2013; Vakili et al., 2014). Vakili et al. (2014)

Table 4. Characterization tools for chitosan-based adsorbents (Hadi et al., 2015; Wang and Chen,2014).

Category Methods

Chemical analysis Infrared spectroscopy (IR)Fourier transform infrared spectroscopy (FTIR)Attenuated total reflectance micro-Fourier transform infrared (ATR-FTIR)Nuclear magnetic resonance spectroscopy (NMR)One-pulse magic angle spinning and cross-polarization nuclear magnetic resonance

spectroscopy (13C-CPMAS-NMR)X-ray diffraction (XRD)X-ray photoelectron spectroscopy (XPS)X-ray fluorescence spectroscopy (XRF)Elemental analysis (EA)

Microscopic analysis Optical microscopeBrunauer–Emmett–Teller analyzer (BET)Scanning electron microscope with energy dispersive X-ray spectroscopy (SEM C EDX)Transmission electron microscope (TEM)Zetasizer

Macroscopic analysis Thermo-gravimetric analysis (TGA)Digital imagingMagnetic testingMechanical testingTensile testingCompressive testingToughness testingHardness testing


summarized various chitosan-based biosorbents for the removal of dye from aque-ous solutions, including unmodified chitosan and modified chitosan (crosslinkedchitosan, grafting chitosan, and surface impregnated chitosan). Crini and Badot(2008) had a good review of the chitosan-based adsorbents for the removal of dyefrom aqueous solutions involving the influence of the process variables, modeling,and mechanisms. Additionally, compared with activated carbon (summarized byHadi et al., 2015), chitosan-based adsorbents show a better adsorption capacitytoward different dyes, especially for MB (30–935 mg/g according to Table 7; 22.4–24.5 mg/g according to Table 3 of Hadi et al., 2015).

Among various dyes, anionic dyes are the most widely studied. It was found thatchemisorption was the main adsorption mechanism where amino groups were themain reactive groups (Chiou and Li, 2003). As shown in Scheme 1, the uniquemolecular structure of chitosan enables amino groups on its main chain to be pro-tonated under acidic conditions. With a negative charge, anionic dye can beadsorbed into chitosan (positively charged) through electrostatic attraction (Chiouand Li, 2002; Chiou et al., 2004). That explains why the adsorption capacity ofanionic dyes into chitosan increases with the decreasing of pH. Based on this the-ory, Chatterjee et al. (2011b) grafted polyethyleneimine (PEI) into chitosan inorder to increase its adsorption sites for anionic dyes. The results showed that theadsorption capacity increased with the increasing amount of PEI. The maximumadsorption capacity of the modified chitosan (709.27 mg/g) was more than threetimes that of raw chitosan (201.90 mg/g). Zhang et al. (2016b) synthesized modi-fied chitosan via grafting co-polymerization on the surface of the chitosan/Fe3O4

Table 5. Adsorption kinetic models.

Kinetic models Dynamic expression Integral form Model parameters

Pseudo-first-order dqdt D k1.qeq ¡ q/ log.qe1 ¡ qt/ D logqe1 ¡ k1

2:303 t qe1, k1qt D qe1 ¡ qe1e ¡ k1t

Pseudo-second-order dqdt D k2.qeq ¡ q/2 t

qtD 1

k2q2e2C t

qe2qe2, k2

qt D q2e2k2 t1 C qe2k2 t

Elovich dptdt D aexp.¡bqt/ qt D 1

b ln.ab/ C 1b lnt abt> > 1 a, b

Weber–Morris intraparticle diffusion model

— qt D kit0:5 C C ki, C

Table 6. Adsorption isotherm models.

Adsorption isotherms Expressions Model parameters

Langmuir qe D qmKLCe

1 C KLCeqm, KL

Freundlich qe D KFC1ne n, KF

Tempkin qe DBln.ACe/B D RTb A, b

Dubinin–Radushkevich qe D qsexp.¡BDRe2/e D RTln½1 C 1Ce� qs, -BDR

Redlich–Peterson qe D KRPCe

1 C aCbe

KRP, a, b

Slips qe D KLFCbLFe

1 C aLFCbLFe

KLF, aLF, bLF


composite particles. The unique core-brush topology provided larger specific areaand higher adsorption due to the electrostatic attraction between the graftingbrushes (positively charged) and the anionic contaminant’s species (negativelycharged).

At the same time, there are only a limited number of published studies focusingon the utilization of chitosan-based adsorbents for the removal of cationic dyes.It’s well known that chitosan shows a low affinity toward cation dyes except aftermodification. Both chitosan and cationic dyes are protonated under acidic condi-tions and the electrostatic repulsion between them prevents the adsorption, asshown in Scheme 2.

Besides, hydrogen atoms compete with cationic dyes for the adsorption sites atacid condition. To overcome this problem, different kinds of chitosan derivativesand composites have been tested. To enhance the removal of cationic dye (basicblue 3) on chitosan, Crini et al. (2008a) synthesized chitosan grafting with sulfo-nate groups. Compared with raw ones, modified chitosan showed no drastic

Scheme 1. Chemical structures of the commonly used dyes.


Table 7. Removal of different dyes from aqueous solutions by chitosan-based adsorbents.

Dye Type AdsorbentAdsorption

capacity (mg/g) Reference

Acid black 1 Anionic Chitosan bead (crosslinked, GLA) 18–76 Guibal et al., 2003Acid blue 25 Anionic Chitosan 127.06–178.56 Kamari et al., 2009a

Crosslinked chitosanAcid blue 9 Anionic Chitosan 35–256 Dotto and Pinto, 2011a,

2011b; Sarkar et al.,2012

Acid green 25 Anionic Chitosan 179–645.5 Guibal et al., 2003;Wong et al., 2004a,2004c

Acid orange 10 Anionic Chitosan 696.65–922.9 Wong et al., 2004a,2004c

Acid orange 12 Anionic Chitosan 931.85–1954 Chiou et al., 2004; Wonget al., 2004b

Chitosan bead (crosslinked, TPP)Acid orange 7 Anionic Grafted chitosan 1215.61–1940 Chiou et al., 2004; Zhou

et al., 2011Chitosan bead (crosslinked, TPP)EMCN

Acid red 14 Anionic Chitosan bead (crosslinked, TPP) 1940 Chiou et al., 2004Acid red 18 Anionic Chitosan beads 194.6–693.2 Dotto et al., 2013; Wong

et al., 2004a, 2004cChitosan film

Acid red 37 Anionic Chitosan-EGDE 59.52–357.14 Kamari et al., 2009a,2009b

Crosslinked chitosanAcid red 73 Anionic Chitosan 695.6–728.2 Cheung et al., 2007;

Wong et al., 2004a,2004c

Acid violet 5 Anionic Crosslinked chitosan 140–194 Guibal et al., 2003Acid yellow 25 Anionic Crosslinked chitosan 124–179 Guibal et al., 2003Congo red Anionic Chitosan 93–223.25 Chatterjee et al., 2007;

Wang et al., 2015PES/CS-derivative

Direct blue 71 Anionic Chitosan 14–101 Guibal et al., 2003Crosslinked chitosan

Direct blue 95 Anionic Chitosan 41.84 Ignat et al., 2012Direct red 23 Anionic Chitosan 155 Mahmoodi et al., 2011Direct red 81 Anionic Chitosan bead (crosslinked, TPP) 2383 Chiou et al., 2004Direct Scarlet B Anionic Chitosan 37.18 Annadurai, 2000Eosin Y Anionic Chitosan 79–170.65 Chatterjee et al., 2005;

Huang et al., 2011FD&C blue 2 Anionic Chitosan hollow fibers 154.8–3032 Mirmohseni et al., 2012FD&C red 40 Anionic Chitosan hollow fibers 3316 Mirmohseni et al., 2012FD&C yellow 5 Anionic Chitosan hollow fibers 1078 Mirmohseni et al., 2012FD&C yellow 6 Anionic Chitosan hollow fibers 788 Mirmohseni et al., 2012Food blue 2 Anionic Chitosan hollow fibers 112.4–155.1 Mirmohseni et al., 2012Food red 17 Anionic Chitosan-based hybrid

hydrogels92.9–133.9 Goncalves et al., 2017

Food red 2 Anionic Chitosan hollow fibers 1552 Mirmohseni et al., 2012Food yellow 3 Anionic Chitosan 352.6 Dotto and Pinto, 2011a,

2011bMethyl orange Anionic Crosslinked chitosan 130 Morais et al., 2007Mordant blue 29 Anionic Chitosan 37–114 Guibal et al., 2003

Crosslinked chitosanMordant brown 33 Anionic Chitosan 91–130 Guibal et al., 2003

Crosslinked chitosanMordant orange 10 Anionic Chitosan 103–157 Guibal et al., 2003

Crosslinked chitosan

(Continued on next page )


difference in the specific surface area value while its adsorption capacity wasgreatly improved (166.5 mg/g) due to the sulfonate groups. It was proved thatadsorption was exothermic and spontaneous in nature following the pseudo-sec-ond order kinetic model and Langmuir equilibrium model. Crini et al. (2008b)proposed N-benzyl mono- and disulfonate derivatives of chitosan to improve theadsorption selectivity of the cationic dye “basic blue 9.” It was proved that disulfo-nate derivatives of chitosan exhibited higher sorption capacities (121.9 mg/g)towards cationic dyes than that of monosulfonic ones. Adsorption of MB and neu-tral red (NR) onto pyromellitic dianhydride (PMDA) grafted chitosan micro-spheres was studied by Xing et al. (2009). Grafting of PMDA was carried out toincrease the content of carboxyl groups. The adsorption followed the pseudo-sec-ond-order and Langmuir models. Results showed that the maximum adsorptivecapacities obtained from the Langmuir model were 935 and 909mg/g for MB andNR, respectively, higher than those of the unmodified chitosan. Similar carboxyl

Table 7. (Continued )

Dye Type AdsorbentAdsorption

capacity (mg/g) Reference

Orange-G Anionic Chitosan 95–435 Konaganti et al., 2010Grafted chitosan

Reactive black 5 Anionic Chitosan 238–2014 Guibal et al., 2005; Kimet al., 2012; Lazaridisand Keenan, 2010

Crosslinked chitosanReactive black 8 Anionic Modified chitosan 387–487 Filipkowska, 2006Reactive blue 19 Anionic CC/OPA 43.4–423.5 Hasan et al., 2008Reactive blue 2 Anionic Chitosan bead (crosslinked, TPP) 131.4–2498 Chiou et al., 2004Reactive blue 222 Anionic Swollen chitosan beads 199–1009 Wu et al., 2001Reactive red 11 Anionic Chitosan 450–480 Filipkowska, 2006

Modified chitosanReactive red 141 Anionic Chitosan 68–156 Sakkayawong et al.,

2005Reactive red 189 Anionic Chitosan bead (crosslinked) 950–1936 Chiou and Li, 2002, 2003Reactive red 2 Anionic Chitosan bead (crosslinked, TPP) 2422 Chiou et al., 2004Reactive red 222 Anionic Chitosan 299–1653 Juang et al., 1997; Wu

et al., 2001Swollen chitosan bead

Reactive red 3 Anionic Chitosan 151.5 Ignat et al., 2012Reactive violet Anionic Chitosan 398 Kyzas et al., 2011Reactive yellow 145 Anionic Chitosan 119–885 Juang et al., 1997; Wu

et al., 2001Swollen chitosan bead

Reactive yellow 2 Anionic Chitosan bead (crosslinked, TPP) 2436 Chiou et al., 2004Reactive yellow 86 Anionic Chitosan bead (crosslinked, TPP) 1911 Chiou et al., 2004Remazole black 13 Anionic Chitosan 91.47–130.0 Annadurai et al., 2008Basic blue 3 Cationic Ch 254–1022 Crini et al., 2008a; Kyzas

et al., 2012Ch-g-Sulf

Basic blue 9 Cationic Chitosan derivatives 121.9 Crini et al., 2008bBasic yellow 37 Cationic Chitosan 363–598 Kyzas et al., 2011Methylene blue Cationic GLA-CTS 99.01–935 Chatterjee et al., 2011a;

Xing et al., 2009PMDA-GLA-CTS

Metyl green Cationic Chitosan 74.83–93.55 Bekci et al., 2008Neutral red Cationic PMDA-GLA-CTS 909 Xing et al., 2009


groups-modified chitosan have been reported by Mello et al. (2006) via succinicanhydride. Besides, chitosan hydrogel beads consisting of chitosan and anionicsurfactant gelation, sodium dodecyl sulphate (SDS), have been reported by Chat-terjee et al. (2011a) in order to improve the adsorption of MB. Results showed thatthe adsorption capacity increased with the increasing pH value and presentedhigher maximum adsorption capacity (226.24 mg/g) than that of chitosan(99.01 mg/g).

In practical use, the regeneration of the adsorbent is very important for financialreasons. However, compared with adsorption results, there is only a small amountof supplementary batch desorption statistics attached in a complete dye adsorptionstudy. Only some experiments focus on the selection of an appropriate eluent andits optimal conditions for desorption. Some acid solutions, basic solutions, andorganic solutions have been tested in the desorption process as well.

Generally, desorption of non-covalent adsorption can be obtained in acid solu-tions. In that case, crosslinked chitosan shows better chemical stability in acid solu-tions than that of raw chitosan. Oladipo et al. (2015) investigated the adsorption ofanionic dyes onto chitosan-based hydrogel. The results showed that the values ofDG (¡17.012 to ¡22.473 kJ/mol) of adsorption were within the ranges of expectedphysisorption mechanisms. HCl solution (0.1 M) was proposed as a desorbing agentand the repeated utilization of hydrogel proved to be feasible for up to six cycles. Sul-furic acid has also been reported as a desorbing agent by Trung et al. (2003). In thisexperiment, decrystallized chitosan were regenerated by a sulfuric acid solution(2 M) and was reusable more than 10 times. In addition, Crini et al. (2008b) sug-gested organic solvents be used for the regeneration of chitosan-based adsorbents.

Multiple basic solutions have been widely used as desorbing agents, especiallyfor chitosan that has adsorbed anionic dyes. In basic solutions, the electrostaticinteraction between chitosan and anionic dyes becomes weak due to the deproto-nation of chitosan. Because of this, the adsorbed dyes can be released from the

Scheme 2. Mechanism of anionic and cation dyes adsorption by chitosan under acidic condition.


adsorption sites of chitosan. Chiou and Li (2003) reported that chemical cross-linked chitosan beads can be regenerated by NaOH solution (pH D 10) at 30�Cwith a removal rate of about 63%. Goncalves et al. (2017) compared two kinds ofeluents (NaOH and NaCl) with different concentrations in desorption of dyesfrom the chitosan-based hydrogel. NaOH (0.01 mol/L) proved to be the best eluentamong those tested. Hydrogel after five cycles of reuse still maintained at 70% of itsoriginal adsorption capacity. However, higher concentrations of NaOH solutionmay result in hydrogel disintegration.

Kyzas et al. (2014) did important work on this desorption phenomenon anddeveloped a phenomenological model which was capable of describing the data forall the initial dye concentrations. The model was extended to repeated batch adsorp-tion/desorption cycles. Results showed that the decrease in adsorption efficiency dur-ing the cycles can be owed to the requirement for total adsorbate mass conservationduring each step, rather than thermodynamic irreversibility of the process. Theinherent irreversibility cannot be identified by the adsorption/desorption cycle only,but requires advanced diagnostic tools (such as spectroscopic techniques) to showany changes in the structure and functional groups of the adsorbent.

6.2. Removal of emerging pollutants

Emerging pollutants, including PPCPs and PFOS have attracted global concerns inrecent years due to their global distribution, notable bioaccumulation, and poten-tial endangerment to human beings and other animals. Various technologies havebeen studied for the degradation of emerging pollutants (Wang and Chu, 2016;Wang and Wang, 2016; Wang and Bai, 2017). The application of chitosan-basedadsorbents for the removal of these emerging pollutants has been reported bysome researchers.

The adsorption of PFOS by crosslinked chitosan beads was examined by Zhanget al. (2011). As shown in Scheme 3, different concentrations of PFOS result in dif-ferent adsorption mechanisms. Electrostatic and hydrophobic interactions domi-nated the adsorption at low concentrations, while hemi-micelles and micelles mayform in the porous structure of chitosan at high concentrations. The adsorptiondata fitted well with double-exponential kinetic model and the Freundlich equilib-rium model. Introparticle diffusion was the rate-limiting step in the adsorption.

The removal of PFOS by chitosan-based molecularly imprinted adsorbents wasreported by Yu et al. (2008). The adsorption process was pH-dependent indicatingthat electrostatic interaction played an important role in adsorption. Comparedwith non-imprinted ones (qm D 258 mmol/g), the optimized polymer presented ahigher adsorption capacity of 560 mmol/g for PFOS. The synthesized adsorbenthad high sorption capacity and good selectivity for PFOS in the presence of otheranionic adsorbates (except phenol) due to the unique molecular imprinted struc-ture. Without any loss of adsorption capacity for PFOS, regeneration could beachieved by using a NaOH/acetone mixture at least five times.


The application of magnetic MIC for carbamazepine (CBZ) removal from realwater was demonstrated by Zhang et al. (2013). The obtained CBZ imprinted mag-netic polymers exhibited higher specific recognition and selectivity to CBZ in thepresence of interference. The adsorption data followed the Freundlich isothermequilibrium model and the pseudo-second-order kinetic model. Higher tempera-ture had a positive effect on adsorption capacity, indicating the endothermicnature of the adsorption process.

The adsorption of pharmaceuticals (diclofenac sodium (DCF) and tetracyclinehydrochloride (TC)) on chitosan-based magnetic composite particles (CD-MCP)with core-brush topology was reported by Zhang et al. (2016b). The adsorption ofDCF and TC onto CD-MCP proved to be 103 mg/g and 35 mg/g, respectively. Thehigh removal rate of anionic pharmaceuticals on CS-MCP was attributed to core-brush topology and charge attraction.

The application of magnetic chitosan nanoparticles grafted with b-cyclodextrinas adsorbents for the removal of hydroquinol from aqueous solution was reportedby Fan et al. (2012). Modified chitosan showed high adsorption capacity for hydro-quinol (1.75 mmol/g, 303 K) due to its unique characteristics including a very largesurface area and high surface reactivity. Results showed that the adsorption processwas exothermic and spontaneous (DH D ¡28.45 kJ/mol, DS D ¡83.38 J/(mol¡1

K¡1)), following the Freundlich model. Improvement in adsorption capacity andthe magnetic properties make it suitable for water and wastewater treatment.

6.3. Humus removal

With large content and wide distribution in natural water bodies, humus hasattracted much attention. According to the solubility in acid and alkali solutions, itcan be divided into humic acid (HA), fulvic acid (FA), and humin. Among them,

Scheme 3. Diagram for the adsorption of PFOS at (a) low and (b) high concentration by porous chi-tosan beads. (Zhang et al., 2011).


HA and FA are the most water-soluble. It was found that in the process of disin-fecting water, HA can react with the disinfectant generating a series of halidesincluding trichloromethane (THM). Therefore, to improve the quality of drinkingwater, removal of water humus is a priority

There are some reports on application of chitosan for the removal of HA andFA. Dong et al. (2014) synthesized magnetic chitosan nanoparticles via one-stepco-precipitation. It was proved that pH and ionic strength greatly influenced theadsorption of HA from aqueous solutions. Electrostatic attraction and hydrogenbonding may mainly account for adsorption mechanism, as shown in Scheme 3.Ngah and Musa (1998) noted that the qm obtained from the Langmuir model forthe removal of HA by chitosan and chitin were 28.88 and 27.30 mg/g, respectively.The adsorption was quite pH-dependent and decreased as the pH increased. Sunet al. (2008) studied the HA removal by chitosan. The results showed that theadsorption capacity increased when the pH decreased and the ionic strength con-centration increased. The presence of other cations and anions had positive effectson the removal of HA in the order of CO3

2¡ > NO3¡ > Cl¡ and KC > Mg2C >

Ca2C. Wang et al. (2008) studied the adsorption mechanism of HA into chitosanvia FTIR and XPS. It was concluded that amino groups of chitosan in a protonatedstate played the key role in the adsorption process via forming the surface complexwith FA, as shown in Scheme 4.

7. Removal of heavy metals and nuclides

Metal ions are important water pollutants which are generated by different indus-trial activities, such as mining, smelting, electrolysis, and electroplating. They canhave toxic effects on humans via the food pyramid. For example, one of the mostfamous environmental hazards is associated with cadmium poisoning in Japan.Biosorption is an effective method of removing heavy metal ions from water andwastewater (Wang and Chen, 2006, 2009). Chitosan-based adsorbents shows goodadsorption capacities for the majority of heavy metal cations (e.g., Pb(II), Cu(II),Cd(II), Hg(II)), precious metal ions (e.g., Pd(II), Pt(IV)), heavy metal oxyanions(e.g., Cr(VI), As(III), As(V)), and radioclides (e.g., Co(II), Sr(II), Cs(I)), togetherwith other metal ions as listed in Table 8.

The earlier research conducted by Masri et al. (1974) showed that chitosan-basedadsorbents possess extremely high adsorption capacities, greater than 1 mmol metal/g for most metals (except for Cr). The adsorption mechanism between chitosan andmetal ions has not yet been fully understood, but it is believed to be associated withsingle or mixed mechanisms (e.g., metal chelation, electrostatic interactions, and ionpair formations). This depends on the conditions of the solution (pH, ion strength,etc.), metal ions, and the chitosan-based adsorbents (Guibal, 2005).

Various modified chitosan has been prepared and used in the removal ofmetal ions, as listed in Table 8. Their selective orders for different metal ionshave been presented in Table 9. Optimal conditions, especially pH and


temperature, adsorption kinetics, isotherms, and thermodynamics of adsorb-ents for various heavy metals, have been investigated in this experiment. Theadsorption of metal ions on chitosan-based adsorbents is usually highly pH-dependent. pH affects the charge status of chitosan, variation, and the stabilityof metal speciation in solutions. This further impacts the interactions betweenadsorbents and metal ions. Usually, the experiments are conducted in a certainpH range, avoiding the solubility of chitosan in acidic solutions and the pre-cipitation of mental ions in alkali solutions. However, thermodynamics is notspecifically researched in all experiments. The pseudo second-order mode fitsquite well with the data in most cases, indicating that the rate-limiting stepmay be owed to chemisorption. However, this may be contradictory to theconclusion obtained from other analysis methods, such as EDS and thermody-namics. More advanced kinetic models should be used in data fitting in thefuture. Additionally, the optimal conditions obtained from different experi-ments vary from each other making comparison difficult. In most cases themaximum adsorption capacities (qm) obtained from the Langmuir model areused for comparison, showing the advantages of the synthesized adsorbentover others. It should be noted that the maximum adsorption capacityobtained from the Langmuir model still relies on various conditions, such astemperature. Considering the difficulty in synthesizing and comparing, qmobtained from the Langmuir model provides some valuable information forfuture comparisons. Over the past few decades, many studies have focused onthe investigation of higher adsorption capacity of modified chitosan and thecompetition between different pollutants on chitosan-based adsorbents.

Compared with other sorbents, chitosan-based adsorbents showed a competi-tive adsorption capacity for heavy metal ions. It has been reported by Renu et al.(2017) that Cd2C removal using activated carbon, carbon nanotubes, rice husk,surfactant modified waste, and modified wheat bran as an adsorbent range from2.7 to 140.8 mg/g, 0.5 to 638.56 mg/g, 8.7 to 13.1 mg/g, 29.96 to 76.3 mg/g, and5.28 to 133 mg/g, respectively. As shown in Table 8, the adsorption capacity of chi-tosan-based adsorbents for Cd2C ranges from 6.07 to 358.3 mg/g, which hasproved to be promising for future applications.

Scheme 4. Adsorption mechanism of HA and FA onto chitosan.


Table8.

Adsorptio

nof

vario

usmetalions

bychito

san-basedadsorbents.

Adsorbents

Sorbates

Form

sq m

(mg/g)

pHT(�C)

Kinetics

Isotherm

sDH(kJ/mol)

DS(JK¡

1mol¡1)

References

Heavy

metalcatio

nsCTS-g-PA

A/GESemi-IPN

Hydrogels

Pb(II)

Granu

lar

781.25

5.0

30PSO

L—

—Huang

etal.,2012

CS/P(AMPS-co-AA

)Pb(II)

particles

673.3

4.8

25PSO

——

—Yu

etal.,2016a

Lead-ionimprintedcrosslinked

electro-spun

chito

san

Pb(II)

Nanofibrousmats

577

6—

PSO

——

—Lietal.,2013b

CS/PEG

/PAA

Pb(II)

Particles

431.7

4.8

25PSO

——

—Yu

etal.,2016b

CCTM

Pb(II)

Powder

246.3

530

PSO

L¡2

9.67

¡65.36

Geet

al.,2012

CS-M

A-DETA

Pb(II)

Microspheres

239.2

525

PSO

L—

—Zhanget

al.,2017

CS-co-MMB-co-PAA

Pb(II)

Particles

151.82

5.5

25—

Redlich–Peterson

——

Paulinoetal.,2011

Xanthate-m

odified

magnetic

chito

san

Pb(II)

Particle

76.9

5.0

25—

L—

—Zhuet

al.,2012

Crosslinkedchito

san

Pb(II)

Particles

34.13

7RT

PSO

L—

—Ch

enetal.,2008

CS/P(AMPS-co-AA

)Cu

(II)

Particles

235

4.8

25PSO

——

—Yu

etal.,2016b

CS-co-MMB-co-PAA

Cu(II)

Particles

163.03

5.5

25—

Redlich–Peterson

——

Paulinoetal.,2011

CCTM

Cu(II)

Powder

132.5

530

PSO

L¡9

.995

5.951

Geet

al.,2012

m-ECC

SBCu

(II)

Pieces

123.1

650

PSO

L15.699

0.0814

Gutha

etal.,2017

CSmicrocapsules

Cu(II)

Particles

100.4

5.6

25—

F262,807.7

925.619

SarginandArslan,2016

Chito

san

Cu(II)

Particles

80.71

6.0

RT—

L—

—Ngahetal.,2002

Chito

san/PN

N(50/50)

Cu(II)

Film

794

25—

——

—Huang

etal.,2015

Activated

carbon/chitosan

Cu(II)

Particles

74.35

5–6

20PSO

L&F

——

Liuet

al.,2015

Thiourea-m

odified

magnetic

chito

san

Cu(II)

Microbeads

66.7

528

PSO

L—

—Zhou

etal.,2009b

Chito

san-ECH

Cu(II)

Particles

62.47

6.0

RT—

L—

—Ngahetal.,2002

Chito

san-GLA

Cu(II)

Particles

59.67

6.0

RT—

L—

—Ngahetal.,2002

Chito

san-cellulose

Cu(II)

Beads

53.2

622–23

—L

——

LiandBai,2005

Chito

san-EG

DE

Cu(II)

Particles

45.94

6RT

—L

——

Ngahetal.,2002

Crosslinkedchito

san

Cu(II)

Particles

35.46

7RT

PSO

L—

—Ch

enetal.,2008

Xanthate-m

odified

magnetic

chito

san

Cu(II)

Particle

34.5

5.0

25—

L—

—Zhuet

al.,2012

SI-PES/CSTr

Cu(II)

Particles

15.12

NT

25PSO

L&IR

——

Wangetal.,2015

CS/P(AMPS-co-AA

)Cd

(II)

Particles

358.3

4.8

25PSO

——

—Yu

etal.,2016a

CS/PEG

/PAA

Cd(II)

Particles

265

4.8

25PSO

——

Yuet

al.,2016b

CS-M

A-DETA

Cd(II)

Microspheres

201.6

525

PSO

L—

—Zhanget

al.,2017

CS-co-MMB-co-PAA

Cd(II)

Particles

132.76

5.5

25—

Redlich–Peterson

——

Paulinoetal.,2011

Activated

Eskomflyash/chito

san

Cd(II)

Particles

87.72

825

PSO

L—

—Pand

eyandTiwari,2015

(Continuedon

nextpage)


Table8.

(Continued)

Adsorbents

Sorbates

Form

sq m

(mg/g)

pHT(�C)

Kinetics

Isotherm

sDH(kJ/mol)

DS(JK¡

1mol¡1)

References

Immobilizedchito

san

Cd(II)

Film

50.58

7.0

25PFO

L—

—Copello

etal.,2008

Chito

san

Cd(II)

—6.07

725

—F

——

Rang

el-M

endezet

al.,2009

Thiol-g

rafted

chito

san

Hg(II)

Beads

1604

725

——

——

Merrifi

eldetal.,2004

Thiourea-m

odified

magnetic

chito

san

Hg(II)

Microbeads

625.2

528

PSO

L—

—Zhou

etal.,2009b

CG-M

CSHg(II)

Nanoparticles

285.71

—30

PSO

L—

—Wangetal.,2013

ChgCc

afHg(II)

Film

18.8

6.8

—PFO

Sips

——

Rochaet

al.,2016

Chg

Hg(II)

Film

16.4

6.8

—PFO

Sips

——

Rochaet

al.,2016

Precious

metalions

Glutaraldehydecrosslinkedchito

san

Pd(II)

Particles

166.67

825

IPD

L¡3

2.06

¡103.34

Nagiredd

ietal.,2017

EMCN

Pd(II)

Particle

138

225

—L

——

Zhou

etal.,2010

Thiourea-m

odified

chito

san

Microspheres

Pd(II)

Particle

112.40

2PSO

L¡5

4.77

¡89.19

Zhou

etal.,2009a

Chito

san

Pd(II)

Particle

62.5

2RT

PSO

L¡5

3.320

¡102.2

Sharififard

etal.,2013

Activated

carbon

coated

with

chito

san

Pd(II)

Particle

43.48

2RT

PSO

L—

—Sharififard

etal.,2013

Crosslinkedcarboxymethylchitosan

Pd(II)

—1.05

4RT

—L

——

Wasikiewiczetal.,2007

Thiourea-m

odified

chito

san

Pt(IV)

Particle

129.00

2PSO

L¡5

5.25

¡92.99

Zhou

etal.,2009a

EMCN

Pt(IV)

Particle

171

225

—L

——

Zhou

etal.,2010

Chito

san

Pt(IV)

Particle

66.6

2RT

PSO

F&L

¡29.838

¡31

Sharififard

etal.,2013

Activated

carbon

coated

with

chito

san

Pt(IV)

Particle

52.63

2RT

PSO

L—

—Sharififard

etal.,2013

Crosslinkedcarboxylmethylchitosan

Pt(IV)

—1.16

4T

—L

——

Wasikiewiczetal.,2007

Heavy

metaloxyanions

CS-CTA-M

CMCr(VI)

Powder

171

225

PSO

L¡1

1.72

57.71

Lietal.,2016b

SCSCS

Cr(VI)

Film

216

425

PFO

L—

—Copello

etal.,2008

Chito

san/ceramicalum

ina

Cr(VI)

Particles

153.85

425

—L

——

Bodd

uetal.,2003

SCS

Cr(VI)

Film

55.12

425

PFO

L—

—Copello

etal.,2008

AlCs

Cr(VI)

Particles

8.62

4PSO&IPM

D–R

13.93

30Rajiv

Gandh

ietal.,2010

ICCFs

As(III)

Sponge

114.9

625

PSO

L—

—Su

etal.,2016

ICCFs

As(V)

Sponge

86.87

625

PSO

L—

—Su

etal.,2016


Radioclides

CS/P(AMPS-co-AA

)Co(II)

Particles

176.7

4.8

25PSO

——

—Yu

etal.,2016a

Magnetic

chito

san

Co(II)

Nanoparticles

27.42

5.5

25—

L¡1

2.04

—Ch

anget

al.,2006

Xanthate-m

odified

magnetic

chito

san

Co(II)

Particles

18.5

530

PSO

L—

—Ch

enandWang,2012a

PVA/chito

sanbeads

Co(II)

Beads

14.39

630

PSO

L—

—Zhuet

al.,2014

Magnetic

chito

san

Co(II)

Particles

2.98

530

PSO

L—

—Ch

enandWang,2012a

Carboxym

ethylatedchito

san

Sr(II)

—99

425

—L

——

Wangetal.,2009

Magnetic

chito

san

Sr(II)

Beads

11.58

8.2

30IPD

L—

—Ch

enandWang,2012b

CS-g-M

BCs(I)

Particles

160.81

6.5

——

L—

—Yang

etal.,2016

Others

CS/P(AMPS-co-AA

)Ni(II)

Particles

171.7

4.8

25PSO

——

—Yu

etal.,2016a

Thiourea-m

odified

magnetic

chito

san

Ni(II)

Microbeads

15.3

528

PSO

L—

—Zhou

etal.,2009b

Xanthate-m

odified

magnetic

chito

san

Zn(II)

Particle

20.8

5.0

25—

L—

—Zhuet

al.,2012

Crosslinkedchito

sans

Zn(II)

Particles

10.21

7RT

PSO

L—

—Ch

enetal.,2008


The value of pH has different effects on the adsorption of metal cations andmetal oxyanions into chitosan-based adsorbents. For most metal cations, theadsorption capacity of chitosan-based adsorbents increases with an increase in pH,but may drop off at a particularly high pH (Sargin and Arslan, 2016; Yu et al.,2016b). It was observed that the lower pH was not favorable for the adsorptiondue to the electrostatic repulsion between heavy metal cations and the protonatedchitosan, as well as the completion adsorption between HC and metal cations intochitosan (Ge et al., 2012). At near-neutral pH, uptake may occur through chelationon ¡NH2 or ¡OH groups (as the Lewis bases donate electron pairs) and metal iongroups with empty orbital functions (as the Lewis acids accept electron pairs) (Gui-bal et al., 2005). For the disposal of metal oxyanions such as Cr and As, the varia-tion of its speciation depends on the pH of the solution and its intrinsic nature, asshown in Fig. 5 (a) and (b). In most cases, these metal oxyanions are negativelycharged. The acid–base properties of the amine groups account for the obvious fea-tures of electrostatic attraction, and the protonation of amine groups results insorption of metal anions by ion exchange (Rajiv Gandhi, 2010; Wang et al., 2016).

To improve the adsorption capacity and selectivity, modified chitosan viaphysical methods or chemical methods have been studied. Chitosan gels inthe forms of beads, sponge, membranes, fibers, hollow fibers, etc. have allbeen studied for the removal of metal ions. The conversion of chitosan intodifferent forms cannot change the total number of functional groups, whilethe number of accessible free amine groups may change which alters itsadsorption capacity (Guibal et al., 2005). Copello et al. (2008), synthesizedlayer-by-layer silicate–chitosan composites for the removal of Cd(II), Cr(III)and Cr(VI) from aqueous solutions. Using the Langmuir model, the maximumadsorption capacity of Cd(II) (optimal pH D 7) and Cr(VI) (optimal pH D 4)on modified chitosan was 1.87 and 5.03 mmol/L, respectively. With a highadsorption capacity, as shown in Table 3, EDTA- and DTPA-modified chito-san has widely been reported to remove metal ions due to its complexation.Min et al. (2015) synthesized chitosan-based electrospun nanofiber membraneswith a large specific surface area (13.0 m2/g). The fast dynamic adsorptionequilibrium (within 0.5 hr) and the high adsorption capacity of As(V)(30.8 mg/g) made the modified chitosan feasible for application.

For practical use, adsorbents with a high selectivity could not only enhance theadsorption efficiency but also reduce costs. In real wastewater, the competitive

Table 9. Selective order of metal ions by chitosan-based adsorbents.

Adsorbents Selectivity order References

CS-MA-DETA microspheres Pb2C > Cd2C Zhang et al., 2017CS/PEG/PAA Pb2C > Cd2C Yu et al., 2016bCS/P(AMPS-co-AA) Pb2C > Cu2C > Cd2C > Co2C � Ni2C. Yu et al., 2016aChitosan Cu2C > Cd2C > Pb2C Rangel-Mendez et al., 2009CTS-PAAm Hg2C > Pb2C Li and Bai, 2006Xanthate-modified magnetic chitosan Pb2C > Cu2C > Zn2C Zhu et al., 2012


adsorption of adsorbents is complicated, involving not only different metal ionsbut also natural organic matters, other ions, etc. The polymer shows a selectivity oraffinity towards different metal ions. Table 5 lists the conclusions of these differentarticles. Although some theories, such as the hard and soft acids and bases (HSAB)concept, have been utilized to explain this phenomenon, the mystery of the mecha-nism is not yet fully understood. This is a big drawback for improving the adsorp-tion properties of these materials.

Many researchers used the HSAB concept to explain the selective adsorptionorder of different metal ions. According to that concept, Lewis bases are com-pounds with available pairs of electrons and Lewis acids have vacant orbitals.The unshared pairs of electrons in Lewis bases could form covalent bonds withthe vacant orbitals of Lewis acids. Zhang et al. (2017) and Yu et al. (2016b)ordered some chitosan-based adsorbents’ performances with metal ions: Pb(II)> Cd(II). Pb(II) ions are soft ions, and Cd(II) ions are intermediate ions. Theamino group, hydroxyl group, and grafted carboxyl group adsorption sites ofadsorbents are all considered to be hard bases. According to the rule of theHSAB concept that hard acids prefer to bond to hard bases and soft acids pre-fer to bond to soft bases, Pb(II) is more stable than Cd(II) when adsorbed intochitosan. Zhu et al. (2012) discovered the competitive adsorption of xanthate-modified magnetic chitosan beads to be in the order of Pb2C > Cu2C > Zn2C,as per the HSAB theory. However, HSAB theory can’t be used to explain thereport from Rangel-Mendez et al. (2009) that chitosan selectivity for theremoval of heavy metals decreased in the following order: Cu2C > Cd2C >

Figure 5. Species fractions of (a) chromium (b) arsenic and (c) borate at different pH values.


Pb2C. Li and Bai (2006) synthesized modified chitosan with amino groupssubstituted by amine groups. The results showed that modified chitosan pre-sented higher adsorption selectivity towards Hg(II) than Pb(II) due to the spe-cial property of amide groups and the typical structure of mercury.

Adsorption/desorption is vital for the regeneration of adsorbents and the recov-ery of metal ions, especially precious metals. Acid solutions (e.g., HCl and HNO3),alkali solutions (e.g., NaOH), inorganic salts (e.g., NaCl, KCl, and NH4Cl), organicchelating agents (e.g., EDTA), etc. can all be used as eluents (Huang et al., 2015;Rangel-Mendez et al., 2009; Shaker, 2015). Among them, acids and EDTA haveproved to possess the highest desorption capacity. However, the acid required forthis is in a high concentration that will corrode the equipment during desorption.Besides, with low solubility, EDTA cannot fully recover the adsorbent, especiallyfor neutralized hydrogel adsorbents. Therefore, finding a new eluent is essential.

8. Removal of other inorganic pollutants

8.1. Nitrate and phosphate

Nitrate and phosphate are two major nutrients for plant growth. However, higherconcentrations of nitrate and phosphate discharged by excessive usage of fertilizersin agriculture and untreated disposal of municipal and industrial waste have causedmany problems, including water eutrophication and methemoglobinemia. Theremoval of nitrate and phosphate by chitosan-based adsorbents is scarce in literaturedue to their high solubility and very weak adsorption affinity toward adsorbents.

Electrostatic attraction plays an important role in the adsorption of nitrate andphosphate into chitosan and this can be regenerated by alkali solution, as shown inScheme 5. Golie and Upadhyayula (2017) studied the adsorption capacity of nitrateinto chitosan with different degrees of crosslinking. It was observed that a crosslinkerhad a positive effect on the stability of chitosan under acidic conditions but had anegative effect on the adsorption capacity due to consumption of amino groups.

Quaternary ammonium chloride group modified sorbents proved to be usefulfor the removal of nitrate and phosphate from aqueous solutions. To enhance theadsorption capacity, chitosan grafted quaternized resin was studied by Banu andMeenakshi (2017) with the removal efficiency of nitrate and phosphate being 78and 90%, respectively (0.1 g adsorbent and 100 mg/L initial concentration). Com-pared with phosphate, nitrate showed low affinity toward modified chitosan due toits lower ionic potential. The adsorption process was found to be exothermic andspontaneous. The adsorption mechanism behind it was mainly due to electrostaticattraction between quaternized sites (positively charged) and anions (negativelycharged). This was followed by ion exchange via replacing chloride ions from thematrix, as well as hydrogen bonding between the primary amine groups of chito-san and anionic ions. N, N, N-triethyl ammonium functionalized crosslinked chi-tosan beads were studied by Sowmya and Meenakshi (2013) and Appunni et al.(2016) for the removal of nitrate and phosphate in aqueous solutions, and nitrate


from brackish water, respectively. The adsorbents can be used within wide pHranges (3–9) without the influence of common anions like Cl¡, HCO3

¡, andSO4

2¡. After 10 cycles of regeneration by NaCl (0.025 M), 97.5% of its adsorptioncapacity can still be maintained (Sowmya and Meenakshi, 2013). The high, quickremoval efficiency of nitrate into modified chitosan can be attributed to the pres-ence of NC(C2H5)3 groups. There was no difference in adsorption capacity betweenthe beads forms and powder forms of chitosan (2.26 meq/g) indicating that themechanism behind nitrate removal was ion exchange (Appunni et al., 2016). Theadsorption followed the pseudo-second-order and exhibited more favor for nitrateions than sulphate and chloride ions.

Golie and Upadhyayula (2016) reported on a continuous column study for theremoval of nitrate using chitosan/alumina composite as adsorbents, and studied theadsorption performance under different process variables including bed depth, flowrate, and influent nitrate concentration. Results showed that the nitrate removal effi-ciency increased with an increase in bed height, whilst a lower flow rate and influentnitrate concentration were good for a higher adsorption capacity.

Metal ion loaded chitosan has been used for the removal of nutritional elements.Cu(II)-saturated chitosan has been reported by Zavareh et al. (2017) and Dai et al.(2011). Dai et al. (2011) made used of the discarded adsorbents (Cu2C-saturatedchitosan) for the removal of phosphate from aqueous solutions directly. It wasproved that the chitosan-Cu was stable for the removal of phosphate at a pH above4 and favored H2PO4

¡. The adsorption followed the first-order kinetic model andLangmuir equilibrium model indicating that the adsorption behavior was mainlythat of chemical monolayer adsorption, as the phosphate facile binded with Cu(II).Based on this work, Zavareh et al. (2017) synthesized Cu (II) binded chitosan/Fe3O4 nanocomposite with a porous surface. In this composite, cupric ions tendedtowards phosphate anions more than common anions, to form very stable, insolu-ble copper (II) phosphate. The magnetic materials enriched the composites with

Scheme 5. The representation of the interaction between nitrate, phosphate, and functional groupsof chitosan (¡NH3

C).


the ability to magnetically recycle without compromising its adsorption capacity.According to the Langmuir model, its calculated adsorption capacity (qm D39.7 mg P/Chitosan-Cu-Fe3O4 g) was much higher than even that reported by Daiet al. (2011) (qm D 30.12 mg P/Chitosan-Cu g).

8.2. Borate

Boron (B) is a vital micronutrient for plants and small amounts of B can even bebeneficial for humans. However, high concentrations of B are harmful and evenlethal to humans. It can cause disorders in the central nervous system and damagethe reproductive system of humans. Therefore, the removal of B from aqueous sol-utions is vital. Table 10 lists the removal of B ions by chitosan-based adsorbents.

With pKa D 9.2, the form of the B in aqueous solutions depends on pH, asshown in Fig. 5(c). The adsorption of B by chitosan beads was examined by Bursaliet al. (2011). The conditions of its maximum adsorption capacity were obtained atpH D 8, temperature D 308 K, C0(B) D 4 mg/L, chitosan beads D 0.15 g and ionicstrength D 0.1 M (NaCl). The adsorption process was pH-dependent. The optimalpH proved to be 8 § 0.5. At a lower pH range (4.5–7.5) with amino group chito-san, B(OH)3 is the dominant form of B in the solution, and there is slight interac-tion occurring between the chitosan and the B(OH)3. However, beyond a pH valueof 8.5, the competition between OH¡ and B(OH)4

¡ for the –NH2 and -OH¡

adsorption sites in chitosan resulted in a decrease in adsorption capacity. The ionicstrength presented positive effects for the removal of B due to the field of electro-static interactions.

The applicability of incorporating different metal oxides (TiO2, Cr2O3 andFe3O4 and Fe(OH)3) into chitosan as adsorbents for the removal of B from waterwas studied by Kluczka et al. (2017). The adsorption capacity of B on these adsorb-ents follows the order of Fe(OH)3-chitosan > Fe3O4-chitosan > TiO2–chitosan >

Cr2O3-chitosan. Their adsorption behavior all fitted well with the pseudo second-order and Freundlich models and proved to be a nonspontaneous and exothermicprocess. The desorption of loaded composites was obtained by increasing the pHto 12. Nickel (II) hydroxide was incorporated into chitosan by Demey et al. (2014)due to its outstanding adsorption capacity for B compared with other metalhydroxides (Turek et al., 2007). The adsorption capacity was 61.4 mg/g at 298 Kand pH of 8–9. The presence of NaCl did not have a significant influence on theadsorption of B.

The adsorption of B into chitosan beads modified by a crosslinker (EGDE) andiminobis-(propylene glycol) was investigated by Gazi and Shahmohammadi(2012). The adsorption of B on polymer beads was determined to be 2.20 §0.05 mmol/g in non-buffered conditions. As shown in Scheme 6, a new adsorptionmechanism was tested, where four hydroxyl groups connected to a nitrogen froman amino group worked as one component binding site for the entrapment of oneboric acid molecule. Desorption of B from the loaded chitosan beads was achieved


Table10.A

dsorptionof

borateby

chito

san-basedadsorbents.

Adsorbents

Form

sq m

(mg/g)

pHT(�C)

Kinetics

Isotherm

sDH(kJ/mol)

DS(JK¡

1mol¡1)

References

Chito

san/Ni(O

H) 2-based

sorbent

Beads

61.4

8–9

25PSO

L—

—Dem

eyetal.,2014

Magnetic

porous

chito

san-

basedmicrobeads

Microbeads

66.85

8RT

PSO

L—

—Oladipo

andGazi,2016

Chito

sanbeads

Beads

—8

35PSO

F—

—Bu

rsalietal.,2011

CCTS–IBPG

Beads

23.78

8RT

PSO

——

—Gaziand

Shahmoham

madi,2012

TiO2–CTS

Beads

4.3

425

PSO

F¡7

.31

¡30

Kluczkaet

al.,2017

Cr2O

3–CTS

Beads

3.5

425

PSO

F¡1

.44

¡10

Fe3O

4–CTS

Beads

4.4

425

PSO

F¡3

.32

¡20

Fe(OH) 3–C

TSBeads

7.8

425

PSO

F¡5

.44

¡40

Chito

san-basedmulti-hydroxyl

magnetic

microbeads

Microbeads

128.5

7RT

PSO

R–P

¡45.156

¡33.88

Oladipo

andGazi,2016


using a HCl-containing solution (4 M). Selectivity and adsorption tests indicatedthat modified chitosan presented higher selectivity towards B in the presence of Ca(II), Mg(II), and Fe(III) ions. Oladipo and Gazi (2016) synthesized glycidol modi-fied magnetic chitosan and applied it as an adsorbent for the removal of B. Thegrafting of hydroxyl groups offered modified chitosan with a higher adsorptioncapacity of up to 128.50 mg/g. The magnetic properties provided the benefit of afaster separation, within 45 s. A novel adsorbent consisting of chitosan and duck-weed (Lemna gibba L.) was prepared by Turker and Baran (2017) to remove Bfrom drinking water. The maximum adsorption capacity was 3.18 mg/g at optimalpH D 7.

8.3. Fluoride

Fluoride, an essential micronutrient, plays a double role in organisms. Fluoride is neces-sary for the prevention of tooth decay and the formation of bone, especially for children,so long as the concentration ranges from 0.5 to 1.5mg/L (according to theWHOguide-lines). However, excessive intake of fluoride may lead to skeletal, non-skeletal, and den-tal forms of fluorosis. In some countries, such as India and China, the naturalgeochemistry of certain regions with higher land fluoride concentrations maymake thelocal water unsuitable for instant consumption. Nowadays, fluoride contamination inthe water, especially groundwater, has aroused worldwide concern.

Different kinds of electropositive multivalent metals, including Mg (II), Al(III),Fe(III), Ti(IV), Si(II), La (III), and Zr(IV), have been incorporated into chitosan toenhance its adsorption capacity for F¡ (Miretzky and Cirelli, 2011). These electro-positive multivalent metals present a strong affinity towards F-, which is regardedas a hard base. Viswanathan and Meenakshi (2010) prepared an alumina/chitosan(AlCs) composite with different forms and studied its equilibrium parameters,

Scheme 6. Sorption and desorption of modified beads. (Gazi and Shahmohammadi, 2012).


kinetics, and thermodynamics. In a desired form, AlCs showed a higher adsorptioncapacity (3809 mg/kg) than chitosan (52 mg/kg) and alumina (1566 mg/kg). Sad-hana Rayalu’s research group incorporated titanium, alumina, and binary metaloxides into chitosan via co-precipitation in a basic solution both with and withoutcalcination (Jagtap et al., 2009, 2011; Thakre et al., 2010). Its maximum adsorptioncapacities were 7.21, 8.264, and 2.22 mg/g, respectively. The adsorption processproved to be highly pH-dependent. Both the fluoride adsorption on Ti-Al binarymetal and Al blending chitosan composites is exothermic and a spontaneous pro-cess, while it is spontaneous and endothermic for the removal process of fluorideon titanium macrospheres. It is believed that metal chelating or ligand exchangedominates the adsorption process (Jagtap et al., 2009, 2011).

9. Concluding remarks and perspectives

For years, intensive developments and studies have been done on chitosan asadsorbents due to its abundant supply, low cost, high adsorption capacity, andease of modification, as well as being environmental friendly and easy to regener-ate. However, the application of chitosan-based adsorbents is still limited to labora-tories, far away from industrial application. To improve its adsorptionperformance, physical and chemical methods have been applied to modify chitosanto have a higher chemical stability, better mechanical strength, and higher adsorp-tion capacity and selectivity, as well as other benefits including magnetism and theability to indicate the presence of metal ions.

Chitosan-based adsorbents show outstanding adsorption for many pollutantsincluding organic materials such as dyes, PPCPs, PFOS, humus, metal ions, nitrate,as well as inorganic materials such as metal ions, nitrate, phosphate, B, and fluo-ride. During this process, its optimal conditions were studied and the adsorptioncapacities were obtained and compared.

The further understanding of adsorption mechanisms via various characteriza-tion methods could provide important clues for future modification and regenera-tion strategies. Chitosan-based adsorbents have proved to be potential alternativesfor water and wastewater treatment worldwide.

Acknowledgments

The research was supported by the National Natural Science Foundation of China (51578307),the National Key Research and Development Program (2016YFC1402507), the Program forChangjiang Scholars and Innovative Research Team in University (IRT-13026), the NationalS&T Major Project (2013ZX06002001) and Tsinghua Fudaoyuan Research Fund.

Funding

National Natural Science Foundation of China, 51578307


ORCID

Jianlong Wang http://orcid.org/0000-0001-9572-851X

References

Abu-Saied, M. A., Wycisk, R., Abbassy, M. M., El-Naim, G. A., El-Demerdash, F., Youssef, M.E., Bassuony, H., and Pintauro, P. N. (2017). Sulfated chitosan/PVA absorbent membranefor removal of copper and nickel ions from aqueous solutions—Fabrication and sorptionstudies. Carbohydrate Polymers 165, 149–158. doi:10.1016/j.carbpol.2016.12.039.

Aliramaji, S., Zamanian, A., and Mozafari, M. (2017). Super-paramagnetic responsive silkfibroin/chitosan/magnetite scaffolds with tunable pore structures for bone tissue engineeringapplications. Materials Science & Engineering C-Materials for Biological Applications 70,736–744. doi:10.1016/j.msec.2016.09.039.

Alsbaiee, A., Smith, B. J., Xiao, L., Ling, Y., Helbling, D. E., and Dichtel, W. R. (2016). Rapidremoval of organic micropollutants from water by a porous beta-cyclodextrin polymer.Nature 529(7585), 190–194. doi:10.1038/nature16185.

Amerkhanova, S., Shlyapov, R., and Uali, A. (2017). The active carbons modified by industrialwastes in process of sorption concentration of toxic organic compounds and heavy metalsions. Colloids and Surfaces A: Physicochemical and Engineering Aspects 532(5), 36–40.doi:10.1016/j.colsurfa.2017.07.015.

Annadurai, G. (2000). Design of optimum response surface experiments for adsorption of directdye on chitosan. Bioprocess Engineering 23(5), 451–455. doi:10.1007/s004499900164.

Annadurai, G., Ling, L. Y., and Lee, J. F. (2008). Adsorption of reactive dye from an aqueoussolution by chitosan: Isotherm, kinetic and thermodynamic analysis. Journal of HazardousMaterials 152(1), 337–346. doi:10.1016/j.jhazmat.2007.07.002.

Appunni, S., Rajesh, M. P., and Prabhakar, S. (2016). Nitrate decontamination through func-tionalized chitosan in brackish water. Carbohydrate Polymers 147, 525–532. doi:10.1016/j.carbpol.2016.03.075.

Ayati, A., Tanhaei, B., and Sillanp€a€a, M. (2017). Lead(II)-ion removal by ethylenediaminetetra-acetic acid ligand functionalized magnetic chitosan-aluminum oxide-iron oxide nanoadsorb-ents and microadsorbents: Equilibrium, kinetics, and thermodynamics. Journal of AppliedPolymer Science 134(4), 44360. doi:10.1002/app.44360.

Babel, S., and Kurniawan, T. A. (2003). Low-cost adsorbents for heavy metals uptake from con-taminated water: A review. Journal of Hazardous Materials 97(1–3), 219–243. doi:10.1016/S0304-3894(02)00263-7.

Badry, M. D., Wahba, M. A., Khaled, R., Ali, M. M., and Farghali, A. A. (2017). Synthesis, char-acterization, and in vitro anticancer evaluation of iron oxide/chitosan nanocomposites. Inor-ganic and Nano-Metal Chemistry 47(3), 405–411. doi:10.1080/15533174.2016.1186064.

Bai, Z. Y., Zhou, C. L., Gao, N., Pang, H. J., and Ma, H. Y. (2016). A chitosan-Pt nanopar-ticles/carbon nanotubes-doped phosphomolybdate nanocomposite as a platform for thesensitive detection of nitrite in tap water. Rsc Advances 6(2), 937–946. doi:10.1039/C5RA19383D.

Bailey, S. E., Olin, T. J., Bricka, R. M., and Adrian, D. D. (1999). A review of potentially low-costsorbents for heavy metals. Water Research 33(11), 2469–2479. doi:10.1016/S0043-1354(98)00475-8.

Banu, H. T., and Meenakshi, S. (2017). One pot synthesis of chitosan grafted quaternized resinfor the removal of nitrate and phosphate from aqueous solution. International Journal ofBiological Macromolecules 104(Pt B), 1517–1527. doi:10.1016/j.ijbiomac.2017.03.043.


http://orcid.org/0000-0001-9572-851X

https://doi.org/10.1016/j.carbpol.2016.12.039

https://doi.org/10.1016/j.msec.2016.09.039

https://doi.org/10.1038/nature16185

https://doi.org/10.1016/j.colsurfa.2017.07.015

https://doi.org/10.1007/s004499900164

https://doi.org/10.1016/j.jhazmat.2007.07.002



https://doi.org/10.1002/app.44360

https://doi.org/10.1016/S0304-3894(02)00263-7

https://doi.org/10.1016/S0304-3894(02)00263-7

https://doi.org/10.1080/15533174.2016.1186064

https://doi.org/10.1039/C5RA19383D

https://doi.org/10.1039/C5RA19383D

https://doi.org/10.1016/S0043-1354(98)00475-8

https://doi.org/10.1016/S0043-1354(98)00475-8

https://doi.org/10.1016/j.ijbiomac.2017.03.043

Barrer, R. M., and MacLeod, D. M. (1954). Intercalation and sorption by montmorillonite trans-actions of the Faraday Society, 50, 980–989.

Bekci, Z., Ozveri, C., Seki, Y., and Yurdakoc, K. (2008). Sorption of malachite green on chitosanbead. Journal of Hazardous Materials 154(1–3), 254–261. doi:10.1016/j.jhazmat.2007.10.021.

Benamer, S., Mahlous, M., Tahtat, D., Nacer-Khodja, A., Arabi, M., Lounici, H., and Mameri, N.(2011). Radiation synthesis of chitosan beads grafted with acrylic acid for metal ions sorp-tion. Radiation Physics and Chemistry 80(12), 1391–1397. doi:10.1016/j.radphyschem.2011.06.013.

Bhatnagar, A., and Sillanpaa, M. (2009). Applications of chitin- and chitosan-derivatives for thedetoxification of water and wastewater – A short review. Advances in Colloid and InterfaceScience 152(1–2), 26–38. doi:10.1016/j.cis.2009.09.003.

Boddu, V. M., Abburi, K., Talbott, J. L., and Smith, E. D. (2003). Removal of hexavalent chro-mium from wastewater using a new composite chitosan biosorbent. Environmental Science& Technology 37(19), 4449–4456. doi:10.1021/es021013a.

Brugnerotto, J., Lizardi, J., Goycoolea, F. M., Arguelles-Monal, W., Desbrieres, J., and Rinaudo,M. (2001). An infrared investigation in relation with chitin and chitosan characterization.Polymer 42(8), 3569–3580. doi:10.1016/S0032-3861(00)00713-8.

Bursali, E. A., Seki, Y., Seyhan, S., Delener, M., and Yurdakoc, M. (2011). Synthesis of chitosanbeads as boron sorbents. Journal of Applied Polymer Science 122(1), 657–665. doi:10.1002/app.33331.

Caner, H., Hasipoglu, H., Yilmaz, O. and Yilmaz, E. (1998). Graft copolymerization of 4-vinyl-pyridine onto chitosan-I. by ceric ion initiation. European Polymer Journal 34(3–4), 493–497.

C�ardenas, G., Orlando, P., and Edelio, T. (2001). Synthesis and applications of chitosan mercap-tanes as heavy metal retention agent. International Journal of Biological Macromolecules 28(2), 167–174. doi:10.1016/S0141-8130(00)00156-2.

Casimiro, M. H., Botelho, M. L., Leal, J. P. and Gil, M. H. (2005). Study on chemical, UV andgamma radiation-induced grafting of 2-hydroxyethyl methacrylate onto chitosan. RadiationPhysics and Chemistry 72(6), 731–735.

Chang, M. Y., and Juang, R. S. (2004). Adsorption of tannic acid, humic acid, and dyes fromwater using the composite of chitosan and activated clay. Journal of Colloid and Interface Sci-ence 278(1), 18–25. doi:10.1016/j.jcis.2004.05.029.

Chang, Y. C., Chang, S. W., and Chen, D. H. (2006). Magnetic chitosan nanoparticles: Studieson chitosan binding and adsorption of Co(II) ions. Reactive and Functional Polymers 66(3),335–341. doi:10.1016/j.reactfunctpolym.2005.08.006.

Chang, Y. H., Zhang, L., Ying, H. J., Li, Z. J., Lv, H., and Ouyang, P. K. (2010). Desulfurization ofgasoline using molecularly imprinted chitosan as selective adsorbents. Applied Biochemistryand Biotechnology 160(2), 593–603. doi:10.1007/s12010-008-8441-7.

Chatterjee, S., Chatterjee, S., Chatterjee, B. P., Das, A. R., and Guha, A. K. (2005). Adsorption ofa model anionic dye, eosin Y, from aqueous solution by chitosan hydrobeads. Journal of Col-loid and Interface Science 288(1), 30–35. doi:10.1016/j.jcis.2005.02.055.

Chatterjee, S., Chatterjee, S., Chatterjee, B. P., and Guha, A. K. (2007). Adsorptive removal ofcongo red, a carcinogenic textile dye by chitosan hydrobeads: Binding mechanism, equilib-rium and kinetics. Colloids and Surfaces A: Physicochemical and Engineering Aspects 299(1–3), 146–152. doi:10.1016/j.colsurfa.2006.11.036.

Chatterjee, S., Chatterjee, T., Lim, S. R., and Woo, S. H. (2011a). Adsorption of a cationic dye,methylene blue, on to chitosan hydrogel beads generated by anionic surfactant gelation.Environmental Technology 32(13), 1503–1514. doi:10.1080/09593330.2010.543157.



https://doi.org/10.1016/j.radphyschem.2011.06.013


https://doi.org/10.1016/j.cis.2009.09.003

https://doi.org/10.1021/es021013a

https://doi.org/10.1016/S0032-3861(00)00713-8



https://doi.org/10.1016/S0141-8130(00)00156-2

https://doi.org/10.1016/j.jcis.2004.05.029

https://doi.org/10.1016/j.reactfunctpolym.2005.08.006

https://doi.org/10.1007/s12010-008-8441-7



https://doi.org/10.1080/09593330.2010.543157

Chatterjee, S., Chatterjee, T., and Woo, S. H. (2011b). Influence of the polyethyleneimine graft-ing on the adsorption capacity of chitosan beads for Reactive Black 5 from aqueous solutions.Chemical Engineering Journal 166(1), 168–175. doi:10.1016/j.cej.2010.10.047.

Chen, A. H., Liu, S. C., Chen, C. Y., and Chen, C. Y. (2008). Comparative adsorption of Cu(II),Zn(II), and Pb(II) ions in aqueous solution on the crosslinked chitosan with epichlorohy-drin. Journal of Hazardous Materials 154(1–3), 184–191. doi:10.1016/j.jhazmat.2007.10.009.

Chen, C., and Wang, J. L. (2010). Removal of heavy metal ions by waste biomass of Saccharomy-ces Cerevisiae. Journal of Environmental Engineering 136(1), 95–102. doi:10.1061/(ASCE)EE.1943-7870.0000128.

Chen, Y. W., and Wang, J. L. (2009). The radiation-induced synthesis of hydrogels and theirapplication for removal of heavy metal ions from aqueous solution. Progress in Chemistry (inChinese) 21(10), 2250–2256.

Chen, Y. W., and Wang, J. L. (2012a). The characteristics and mechanism of Co(II) removalfrom aqueous solution by a novel xanthate-modified magnetic chitosan. Nuclear Engineeringand Design 242, 452–457. doi:10.1016/j.nucengdes.2011.11.004.

Chen, Y. W., and Wang, J. L. (2012b). Removal of radionuclide Sr2C ions from aqueous solutionusing synthesized magnetic chitosan beads. Nuclear Engineering and Design 242, 445–451.doi:10.1016/j.nucengdes.2011.10.059.

Chen, Y. W., and Wang, J. L. (2016). Removal of cesium from radioactive wastewater usingmagnetic chitosan beads cross-linked with glutaraldehyde. Nuclear Science and Techniques27(2), 1–6. doi:10.1007/s41365-016-0033-6.

Cheung, W. H., Szeto, Y. S., and McKay, G. (2007). Intraparticle diffusion processes during aciddye adsorption onto chitosan. Bioresource Technology 98(15), 2897–2904. doi:10.1016/j.biortech.2006.09.045.

Chiou, M. S., Ho, P. Y., and Li, H. Y. (2004). Adsorption of anionic dyes in acid solutions usingchemically cross-linked chitosan beads. Dyes and Pigments 60(1), 69–84. doi:10.1016/S0143-7208(03)00140-2.

Chiou, M. S., and Li, H. Y. (2002). Equilibrium and kinetic modeling of adsorption of reactivedye on cross-linked chitosan beads. Journal of Hazardous Materials 93(2), 233–248.doi:10.1016/S0304-3894(02)00030-4.

Chiou, M. S., and Li, H. Y. (2003). Adsorption behavior of reactive dye in aqueous solution onchemical cross-linked chitosan beads. Chemosphere 50(8), 1095–1105. doi:10.1016/S0045-6535(02)00636-7.

Copello, G. J., Varela, F., Vivot, R. M., and Diaz, L. E. (2008). Immobilized chitosan as biosorb-ent for the removal of Cd(II), Cr(III) and Cr(VI) from aqueous solutions. Bioresource Tech-nology 99(14), 6538–6544. doi:10.1016/j.biortech.2007.11.055.

Crini, G., and Badot, P. M. (2008). Application of chitosan, a natural aminopolysaccharide, fordye removal from aqueous solutions by adsorption processes using batch studies: A reviewof recent literature. Progress in Polymer Science 33(4), 399–447. doi:10.1016/j.progpolymsci.2007.11.001.

Crini, G., Gimbert, F., Robert, C., Martel, B., Adam, O., Morin-Crini, N., De Giorgi, F., andBadot, P. M. (2008a). The removal of Basic Blue 3 from aqueous solutions by chitosan-basedadsorbent: Batch studies. Journal of Hazardous Materials 153(1–2), 96–106. doi:10.1016/j.jhazmat.2007.08.025.

Crini, G., Martel, B., and Torri, G. (2008b). Adsorption of C.I. Basic Blue 9 on chitosan-basedmaterials. International Journal of Environment and Pollution 34(1–4), 451–465.doi:10.1504/IJEP.2008.020809.

Dai, J., Yang, H., Yan, H., Shangguan, Y. G., Zheng, Q., and Cheng, R. S. (2011). Phosphateadsorption from aqueous solutions by disused adsorbents: Chitosan hydrogel beads after the


https://doi.org/10.1016/j.cej.2010.10.047


https://doi.org/10.1061/(ASCE)EE.1943-7870.0000128

https://doi.org/10.1061/(ASCE)EE.1943-7870.0000128

https://doi.org/10.1016/j.nucengdes.2011.11.004

https://doi.org/10.1016/j.nucengdes.2011.10.059

https://doi.org/10.1007/s41365-016-0033-6

https://doi.org/10.1016/j.biortech.2006.09.045


https://doi.org/10.1016/S0143-7208(03)00140-2

https://doi.org/10.1016/S0143-7208(03)00140-2

https://doi.org/10.1016/S0304-3894(02)00030-4

https://doi.org/10.1016/S0045-6535(02)00636-7

https://doi.org/10.1016/S0045-6535(02)00636-7


https://doi.org/10.1016/j.progpolymsci.2007.11.001




https://doi.org/10.1504/IJEP.2008.020809

removal of copper(II). Chemical Engineering Journal 166(3), 970–977. doi:10.1016/j.cej.2010.11.085.

Demey, H., Vincent, T., Ruiz, M., Sastre, A. M., and Guibal, E. (2014). Development of a newchitosan/Ni(OH)2-based sorbent for boron removal. Chemical Engineering Journal 244,576–586. doi:10.1016/j.cej.2014.01.052.

Dhanya, A., and Aparna, K. (2016). Synthesis and evaluation of TiO2/Chitosan based hydrogelfor the adsorptional photocatalytic degradation of azo and anthraquinone dye under UVlight irradiation. Procedia Technology 24, 611–618.

Dong, C. L., Chen, W., Liu, C., Liu, Y., and Liu, H. C. (2014). Synthesis of magnetic chitosannanoparticle and its adsorption property for humic acid from aqueous solution. Colloids andSurfaces a-Physicochemical and Engineering Aspects 446, 179–189.

Dotto, G. L., Moura, J. M., Cadaval, T. R. S., and Pinto, L. A. A. (2013). Application of chitosanfilms for the removal of food dyes from aqueous solutions by adsorption. Chemical Engineer-ing Journal 214, 8–16. doi:10.1016/j.cej.2012.10.027.

Dotto, G. L., and Pinto, L. A. (2011a). Adsorption of food dyes acid blue 9 and food yellow 3onto chitosan: Stirring rate effect in kinetics and mechanism. Journal of Hazardous Materials187(1–3), 164–170. doi:10.1016/j.jhazmat.2011.01.016.

Dotto, G. L., and Pinto, L. A. A. (2011b). Adsorption of food dyes onto chitosan: Optimizationprocess and kinetic. Carbohydrate Polymers 84(1), 231–238. doi:10.1016/j.carbpol.2010.11.028.

Elbarbary, A. M., and Ghobashy, M. M. (2017). Phosphorylation of chitosan/HEMA interpene-trating polymer network prepared by g-radiation for metal ions removal from aqueous solu-tions. Carbohydrate Polymers 162, 16–27.

Elwakeel, K. Z., El-Bindary, A. A., Ismail, A., and Morshidy, A. M. (2017). Magnetic chitosangrafted with polymerized thiourea for remazol brilliant blue R recovery: Effects of uptakeconditions. Journal of Dispersion Science and Technology 38(7), 943–952. doi:10.1080/01932691.2016.1216436.

Fan, L., Li, M., Lv, Z., Sun, M., Luo, C. N., Lu, F. G., and Qiu, H. M. (2012). Fabrication of mag-netic chitosan nanoparticles grafted with beta-cyclodextrin as effective adsorbents towardhydroquinol. Colloids and Surfaces B: Biointerfaces 95, 42–49. doi:10.1016/j.colsurfb.2012.02.007.

Fan, L. L., Luo, C. N., Sun, M., Qiu, H. M., and Li, X. J. (2013). Synthesis of magnetic beta-cyclo-dextrin-chitosan/graphene oxide as nanoadsorbent and its application in dye adsorption andremoval. Colloids and Surfaces B-Biointerfaces 103, 601–607. doi:10.1016/j.colsurfb.2012.11.023.

Filipkowska, U. (2006). Adsorption and desorption of reactive dyes onto chitin and chitosanflakes and beads. Adsorption Science and Technology 24(9), 781–795. doi:10.1260/026361706781388932.

Garza-Navarro, M. A., Torres-Castro, A., Garc�ıa-Guti�errez, D. I., Ortiz-Rivera, L., Wang, Y. C.,and Gonz�alez-Gonz�alez, V. A. (2010). Synthesis of spinel-metal-oxide/biopolymer hybridnanostructured materials. The Journal of Physical Chemistry C 114(41), 17574–17579.doi:10.1021/jp106811w.

Gazi, M., and Shahmohammadi, S. (2012). Removal of trace boron from aqueous solution usingiminobis-(propylene glycol) modified chitosan beads. Reactive and Functional Polymers 72(10), 680–686. doi:10.1016/j.reactfunctpolym.2012.06.016.

Ge, H. C., Chen, H., and Huang, S. Y. (2012). Microwave preparation and properties of O-cross-linked maleic acyl chitosan adsorbent for Pb2C and Cu2C. Journal of Applied Polymer Science125(4), 2716–2723. doi:10.1002/app.36588.









https://doi.org/10.1080/01932691.2016.1216436

https://doi.org/10.1080/01932691.2016.1216436

https://doi.org/10.1016/j.colsurfb.2012.02.007




https://doi.org/10.1260/026361706781388932

https://doi.org/10.1260/026361706781388932

https://doi.org/10.1021/jp106811w



Ge, H. C., and Hua, T. T. (2016). Synthesis and characterization of poly(maleic acid)-graftedcrosslinked chitosan nanomaterial with high uptake and selectivity for Hg(II) sorption. Car-bohydrate Polymers 153, 246–252. doi:10.1016/j.carbpol.2016.07.110.

Ge, H. C., and Huang, S. Y. (2010). Microwave preparation and adsorption properties of EDTA-modified cross-linked chitosan. Journal of Applied Polymer Science 115(1), 514–519.doi:10.1002/app.30843.

Ge, H. C., and Luo, D. K. (2005). Preparation of carboxymethyl chitosan in aqueous solutionunder microwave irradiation. Carbohydrate Research 340(7), 1351–1356. doi:10.1016/j.carres.2005.02.025.

Golie, W. M., and Upadhyayula, S. (2016). Continuous fixed-bed column study for the removalof nitrate from water using chitosan/alumina composite. Journal of Water Process Engineer-ing 12, 58–65. doi:10.1016/j.jwpe.2016.06.007.

Golie, W. M., and Upadhyayula, S. (2017). An investigation on biosorption of nitrate fromwater by chitosan based organic-inorganic hybrid biocomposites. International Journal ofBiological Macromolecules 97, 489–502. doi:10.1016/j.ijbiomac.2017.01.066.

Goncalves, J. O., Santos, J. P., Rios, E. C., Crispim, M. M., Dotto, G. L., and Pinto, L. A. A.(2017). Development of chitosan based hybrid hydrogels for dyes removal from aqueousbinary system. Journal of Molecular Liquids 225, 265–270. doi:10.1016/j.molliq.2016.11.067.

Guibal, E. (2005). Heterogeneous catalysis on chitosan-based materials: A review. Progress inPolymer Science 30(1), 71–109. doi:10.1016/j.progpolymsci.2004.12.001.

Guibal, E., McCarrick, P., and Tobin, J. M. (2003). Comparison of the sorption of anionic dyeson activated carbon and chitosan derivatives from dilute solutions. Separation Science andTechnology 38(12–13), 3049–3073. doi:10.1081/SS-120022586.

Guibal, E., Touraud, E., and Roussy, J. (2005). Chitosan interactions with metal ions and dyes:Dissolved-state vs. solid-state application. World Journal of Microbiology and Biotechnology21(6), 913–920. doi:10.1007/s11274-004-6559-5.

Guo, H. F., Lam, N. Y. K., Yang, C. X., and Li, L. (2017). Simulating three-dimensional dynam-ics of flexible fibers in a ring spinning triangle: Chitosan and cotton fibers. Textile ResearchJournal 87(11), 1403–1410. doi:10.1177/0040517516654106.

Guo, P., Anderson, J. D., Bozell, J. J., and Zivanovic, S. (2016). The effect of solvent compositionon grafting gallic acid onto chitosan via carbodiimide. Carbohydrate Polymers 140, 171–180.doi:10.1016/j.carbpol.2015.12.015.

Guo, T. Y., Xia, Y. Q., Hao, G. J., Zhang, B. H., Fu, G. Q., Yuan, Z., He, B. L., and Kennedy, J. F.(2005). Chemically modified chitosan beads as matrices for adsorptive separation of proteinsby molecularly imprinted polymer. Carbohydrate Polymers 62(3), 214–221. doi:10.1016/j.carbpol.2005.03.012.

Gutha, Y., Zhang, Y., Zhang, W. and Jiao, X. (2017). Magnetic-epichlorohydrin crosslinked chi-tosan schiff's base (m-ECCSB) as a novel adsorbent for the removal of Cu(II) ions fromaqueous environment. International Journal of Biological Macromolecules 97, 85–98.

Habiba, U., Afifi, A. M., Salleh, A., and Ang, B. C. (2017). Chitosan/(polyvinyl alcohol)/zeoliteelectrospun composite nanofibrous membrane for adsorption of Cr6C, Fe3C and Ni2C. Jour-nal of Hazardous Materials 322(Pt A), 182–194. doi:10.1016/j.jhazmat.2016.06.028.

Hadi, P., Xu, M., Ning, C., Sze Ki Lin, C., and McKay, G. (2015). A critical review on prepara-tion, characterization and utilization of sludge-derived activated carbons for wastewatertreatment. Chemical Engineering Journal 260, 895–906. doi:10.1016/j.cej.2014.08.088.

Hasan, M., Ahmad, A. L., and Hameed, B. H. (2008). Adsorption of reactive dye onto cross-linked chitosan/oil palm ash composite beads. Chemical Engineering Journal 136(2–3), 164–172. doi:10.1016/j.cej.2007.03.038.




https://doi.org/10.1016/j.carres.2005.02.025

https://doi.org/10.1016/j.carres.2005.02.025

https://doi.org/10.1016/j.jwpe.2016.06.007


https://doi.org/10.1016/j.molliq.2016.11.067


https://doi.org/10.1081/SS-120022586

https://doi.org/10.1007/s11274-004-6559-5

https://doi.org/10.1177/0040517516654106







Huang, C. H., Hsieh, T. H., and Chiu, W. Y. (2015). Evaluation of thermally crosslinkable chito-san-based nanofibrous mats for the removal of metal ions. Carbohydrate Polymers 116, 249–254. doi:10.1016/j.carbpol.2014.07.029.

Huang, D. J., Wang, W. B., Kang, Y. R. and Wang, A. Q. (2012). Efficient adsorption and recov-ery of Pb(II) from aqueous solution by a granular pH-sensitive chitosan-based semi-IPNhydrogel. Journal of Macromolecular Science A 49(11), 971–979.

Huang, X. Y., Bin, J. P., Bu, H. T., Jiang, G. B., and Zeng, M. H. (2011). Removal of anionic dyeeosin Y from aqueous solution using ethylenediamine modified chitosan. Carbohydrate Poly-mers 84(4), 1350–1356. doi:10.1016/j.carbpol.2011.01.033.

Ignat, M. E., Dulman, V., and Onofrei, T. (2012). Reactive red 3 and direct brown 95 dyesadsorption onto chitosan. Cellulose Chemistry and Technology 46(5–6), 357–367.

Jagtap, S., Thakre, D., Wanjari, S., Kamble, S., Labhsetwar, N., and Rayalu, S. (2009). New modi-fied chitosan-based adsorbent for defluoridation of water. Journal of Colloid and InterfaceScience 332(2), 280–290. doi:10.1016/j.jcis.2008.11.080.

Jagtap, S., Yenkie, M. K. N., Labhsetwar, N., and Rayalu, S. (2011). Defluoridation of drinkingwater using chitosan based mesoporous alumina. Microporous and Mesoporous Materials142(2–3), 454–463. doi:10.1016/j.micromeso.2010.12.028.

Jayakumar, R., Prabaharan, M., Nair, S. V., Tokura, S., Tamura, H., and Selvamurugan, N.(2010). Novel carboxymethyl derivatives of chitin and chitosan materials and their biomedi-cal applications. Progress in Materials Science 55(7), 675–709. doi:10.1016/j.pmatsci.2010.03.001.

Jayakumar, R., Prabaharan, M., Reis, R. L., and Mano, J. F. (2005). Graft copolymerized chitosan– present status and applications. Carbohydrate Polymers 62(2), 142–158. doi:10.1016/j.carbpol.2005.07.017.

Jo, A., Jang, G., Namgung, H., Kim, C., Kim, D., Kim, Y., Kim, J., and Lee, T. S. (2015). Simulta-neous detection and removal of radioisotopes with modified alginate beads containing anazo-based probe using RGB coordinates. Journal of Hazardous Materials 300, 227–234.doi:10.1016/j.jhazmat.2015.06.051.

Jones, W. J., and Ross, R. A. (1967). The sorption of sulphur dioxide on silica gel. Journal of theChemical Society A: Inorganic, Physical, Theoretical 1021–1026. doi:10.1039/j19670001021.

Juang, R. S., Tseng, R. L., Wu, F. C., and Lee, S. H. (1997). Adsorption behavior of reactive dyesfrom aqueous solutions on chitosan. Journal of Chemical Technology and Biotechnology 70(4), 391–399. doi:10.1002/(SICI)1097-4660(199712)70:4%3c391::AID-JCTB792%3e3.0.CO;2-V.

Kamari, A., Ngah, W. S. W., Chong, M. Y., and Cheah, M. L. (2009a). Sorption of acid dyes ontoGLA and H2SO4 cross-linked chitosan beads. Desalination 249(3), 1180–1189. doi:10.1016/j.desal.2009.04.010.

Kamari, A., Wan Saime, W. N., and Lai Ken, L. (2009b). Chitosan and chemically modified chi-tosan beads for acid dyes sorption. Journal of Environmental Sciences 21(3), 296–302.doi:10.1016/S1001-0742(08)62267-6.

Kaushik, A., Solanki, P. R., Pandey, M. K., Ahmad, S., and Malhotra, B. D. (2009). Ceriumoxide-chitosan based nanobiocomposite for food borne mycotoxin detection. Applied PhysicsLetters 95(17), 173707. doi:10.1063/1.3249586.

Kazemi, E., Dadfarnia, S., Shabani, A. M. H., and Ranjbar, M. (2017). Synthesis, characteriza-tion, and application of a Zn (II)-imprinted polymer grafted on graphene oxide/magneticchitosan nanocomposite for selective extraction of zinc ions from different food samples.Food Chemistry 237, 921–928. doi:10.1016/j.foodchem.2017.06.053.

Kim, T. Y., Park, S. S., and Cho, S. Y. (2012). Adsorption characteristics of Reactive Black 5 ontochitosan beads cross-linked with epichlorohydrin. Journal of Industrial and EngineeringChemistry 18(4), 1458–1464. doi:10.1016/j.jiec.2012.02.006.





https://doi.org/10.1016/j.micromeso.2010.12.028

https://doi.org/10.1016/j.pmatsci.2010.03.001

https://doi.org/10.1016/j.pmatsci.2010.03.001




https://doi.org/10.1039/j19670001021

https://doi.org/10.1002/(SICI)1097-4660(199712)70:4%3c391::AID-JCTB792%3e3.0.CO;2-V




https://doi.org/10.1016/j.desal.2009.04.010


https://doi.org/10.1016/S1001-0742(08)62267-6

https://doi.org/10.1063/1.3249586

https://doi.org/10.1016/j.foodchem.2017.06.053

https://doi.org/10.1016/j.jiec.2012.02.006

Kluczka, J., Gnus, M., Dudek, G., and Turczyn, R. (2017). Removal of boron from aqueous solu-tion by composite chitosan beads. Separation Science and Technology 52(9), 1559–1571.

Konaganti, V. K., Kota, R., Patil, S., and Madras, G. (2010). Adsorption of anionic dyes on chito-san grafted poly(alkyl methacrylate)s. Chemical Engineering Journal 158(3), 393–401.doi:10.1016/j.cej.2010.01.003.

Kongkaoroptham, P., Piroonpan, T., Hemvichian, K., Suwanmala, P., Rattanasakulthong, W.and Pasanphan, W. (2015). Poly(ethylene glycol) methyl ether methacrylate-graft-chitosannanoparticles as a biobased nanofiller for a poly(lactic acid) blend: Radiation-induced graft-ing and performance studies. Journal of Applied Polymer Science 132(37), 425522.

Kurita, K., Sannan, T., and Iwakura, Y. (1979). Studies on chitin. VI. Binding of metal cations.Journal of Applied Polymer Science 23(2), 511–515. doi:10.1002/app.1979.070230221.

Kyzas, G. Z., Kostoglou, M., Vassiliou, A. A., and Lazaridis, N. K. (2011). Treatment of realeffluents from dyeing reactor: Experimental and modeling approach by adsorption onto chi-tosan. Chemical Engineering Journal 168(2), 577–585. doi:10.1016/j.cej.2011.01.026.

Kyzas, G. Z., Lazaridis, N. K., and Kostoglou, M. (2012). Modelling the effect of pre-swelling onadsorption dynamics of dyes by chitosan derivatives. Chemical Engineering Science 81, 220–230. doi:10.1016/j.ces.2012.07.007.

Kyzas, G. Z., Lazaridis, N. K., and Kostoglou, M. (2014). Adsorption/desorption of a dye by achitosan derivative: Experiments and phenomenological modeling. Chemical EngineeringJournal 248, 327–336. doi:10.1016/j.cej.2014.03.063.

Lazaridis, N. K., and Keenan, H. (2010). Chitosan beads as barriers to the transport of azo dye insoil column. Journal of Hazardous Materials 173(1–3), 144–150. doi:10.1016/j.jhazmat.2009.08.062.

Li, C. G., Cui, J. H., Wang, F., Peng, W. G., and He, Y. H. (2016a). Adsorption removal of Congored by epichlorohydrin-modified cross-linked chitosan adsorbent. Desalination and WaterTreatment 57(30), 14060–14066. doi:10.1080/19443994.2015.1060904.

Li, K., Li, P., Cai, J., Xiao, S. J., Yang, H., and Li, A. (2016b). Efficient adsorption of both methylorange and chromium from their aqueous mixtures using a quaternary ammonium saltmodified chitosan magnetic composite adsorbent. Chemosphere 154, 310–318. doi:10.1016/j.chemosphere.2016.03.100.

Li, L. L., Fan, L. L., Sun, M., Qiu, H. M., Li, X. J., Duan, H. M., and Luo, C. N. (2013a). Adsor-bent for chromium removal based on graphene oxide functionalized with magnetic cyclo-dextrin-chitosan. Colloids and Surfaces B: Biointerfaces 107, 76–83. doi:10.1016/j.colsurfb.2013.01.074.

Li, N., and Bai, R. (2005). Copper adsorption on chitosan-cellulose hydrogel beads: behaviorsand mechanisms. Separation and Purification Technology 42(3), 237–247.

Li, N., and Bai, R. (2006). Development of chitosan-based granular adsorbents for enhanced andselective adsorption performance cn in heavy metal removal. Water Science and Technology54(10), 103–113. doi:10.2166/wst.2006.736.

Li, Y., Qiu, T. B., and Xu, X. Y. (2013b). Preparation of lead-ion imprinted crosslinked electro-spun chitosan nanofiber mats and application in lead ions removal from aqueous solutions.European Polymer Journal 49(6), 1487–1494. doi:10.1016/j.eurpolymj.2013.04.002.

Lin, Y., Hong, Y., Song, Q., Zhang, Z., Gao, J. and Tao, T. (2017). Highly efficient removal ofcopper ions from water using poly(acrylic acid)-grafted chitosan adsorbent. Colloid andPolymer Science 295(4), 627–635.

Liu, B. J., Wang, D. F., Yu, G. L., and Meng, X. H. (2013). Adsorption of heavy metal ions, dyesand proteins by chitosan composites and derivatives – A review. Journal of Ocean Universityof China 12(3), 500–508. doi:10.1007/s11802-013-2113-0.



https://doi.org/10.1002/app.1979.070230221


https://doi.org/10.1016/j.ces.2012.07.007




https://doi.org/10.1080/19443994.2015.1060904

https://doi.org/10.1016/j.chemosphere.2016.03.100




https://doi.org/10.2166/wst.2006.736

https://doi.org/10.1016/j.eurpolymj.2013.04.002

https://doi.org/10.1007/s11802-013-2113-0

Liu, Q., Yang, B. C., Zhang, L. J., and Huang, R. H. (2015). Simultaneous adsorption of anilineand Cu2C from aqueous solution using activated carbon/chitosan composite. Desalinationand Water Treatment 55(2), 410–419. doi:10.1080/19443994.2014.923331.

Mahmoodi, N. M., Salehi, R., Arami, M., and Bahrami, H. (2011). Dye removal from coloredtextile wastewater using chitosan in binary systems. Desalination 267(1), 64–72. doi:10.1016/j.desal.2010.09.007.

Malik, D. S., Jain, C. K., and Yadav, A. K. (2016). Removal of heavy metals from emerging cellu-losic low-cost adsorbents: A review. Applied Water Science 7(5), 2113–2136. doi:10.1007/s13201-016-0401-8.

Masri, M. S., Reuter, F. W., and Friedman, M. (1974). Binding of metal cations by natural sub-stances. Journal of Applied Polymer Science 18(3), 675–681. doi:10.1002/app.1974.070180305.

Mello, K. G. P. C. D., Bernusso, L. D. C., and Polakiewicz, B. (2006). Synthesis and physico-chemical characterization of chemically modified chitosan by succinic anhydride. BrazilianArchives of Biology and Technology 49(4), 665–668. doi:10.1590/S1516-89132006000500017.

Merrifield, J. D., Davids, W. G., MacRae, J. D., and Amirbahman, A. (2004). Uptake of mercuryby thiol-grafted chitosan gel beads. Water Research 38(13), 3132–3138. doi:10.1016/j.watres.2004.04.008.

Mi, F. L., Shyu, S. S., Wu, Y. B., Lee, S. T., Shyong, J. Y., and Huang, R. N. (2001). Fabricationand characterization of a sponge-like asymmetric chitosan membrane as a wound dressing.Biomaterials 22(2), 165–173. doi:10.1016/S0142-9612(00)00167-8.

Min, L. L., Yuan, Z. H., Zhong, L. B., Liu, Q., Wu, R. X., and Zheng, Y. M. (2015). Preparation ofchitosan based electrospun nanofiber membrane and its adsorptive removal of arsenate fromaqueous solution. Chemical Engineering Journal 267, 132–141. doi:10.1016/j.cej.2014.12.024.

Miretzky, P., and Cirelli, A. F. (2011). Fluoride removal from water by chitosan derivatives andcomposites: A review. Journal of Fluorine Chemistry 132(4), 231–240. doi:10.1016/j.jfluchem.2011.02.001.

Mirmohseni, A., Seyed Dorraji, M. S., Figoli, A., and Tasselli, F. (2012). Chitosan hollow fibersas effective biosorbent toward dye: Preparation and modeling. Bioresource Technology 121,212–220. doi:10.1016/j.biortech.2012.06.067.

Monier, M., and Abdel-Latif, D. A. (2017). Fabrication of Au(III) ion-imprinted polymer basedon thiol-modified chitosan. International Journal of Biological Macromolecules 105(Pt 1),777–787. doi:10.1016/j.ijbiomac.2017.07.098.

Morais, W. A., Fernandes, A. L. P., Dantas, T. N. C., Pereira, M. R., and Fonseca, J. L. C. (2007).Sorption studies of a model anionic dye on crosslinked chitosan. Colloids and Surfaces A:Physicochemical and Engineering Aspects 310(1–3), 20–31. doi:10.1016/j.colsurfa.2007.05.055.

Mukhopadhyay, P., Chakraborty, S., Bhattacharya, S., Mishra, R., and Kundu, P. P. (2015). pH-sensitive chitosan/alginate core-shell nanoparticles for efficient and safe oral insulin delivery.International Journal of Biological Macromolecules 72, 640–648. doi:10.1016/j.ijbiomac.2014.08.040.

Nagireddi, S., Katiyar, V., and Uppaluri, R. (2017). Pd(II) adsorption characteristics of glutaral-dehyde cross-linked chitosan copolymer resin. International Journal of Biological Macromo-lecules 94, 72–84. doi:10.1016/j.ijbiomac.2016.09.088.

Ngah, W. S. W., Endud, C. S., and Mayanar, R. (2002). Removal of copper(II) ions from aque-ous solution onto chitosan and cross-linked chitosan beads. Reactive & Functional Polymers50(2), 181–190. doi:10.1016/S1381-5148(01)00113-4.

Ngah, W. S. W., and Musa, A. (1998). Adsorption of humic acid onto chitin and chitosan. Jour-nal of Applied Polymer Science 69(12), 2305–2310. doi:10.1002/(SICI)1097-4628(19980919)69:12%3c2305::AID-APP1%3e3.0.CO;2-C.


https://doi.org/10.1080/19443994.2014.923331



https://doi.org/10.1007/s13201-016-0401-8

https://doi.org/10.1007/s13201-016-0401-8

https://doi.org/10.1002/app.1974.070180305

https://doi.org/10.1590/S1516-89132006000500017

https://doi.org/10.1016/j.watres.2004.04.008


https://doi.org/10.1016/S0142-9612(00)00167-8


https://doi.org/10.1016/j.jfluchem.2011.02.001

https://doi.org/10.1016/j.jfluchem.2011.02.001








https://doi.org/10.1016/S1381-5148(01)00113-4

https://doi.org/10.1002/(SICI)1097-4628(19980919)69:12%3c2305::AID-APP1%3e3.0.CO;2-C




Ngah, W. S. W., Teong, L. C., and Hanafiah, M. A. K. M. (2011). Adsorption of dyes and heavymetal ions by chitosan composites: A review. Carbohydrate Polymers 83(4), 1446–1456.doi:10.1016/j.carbpol.2010.11.004.

Nishad, P. A., Bhaskarapillai, A., Velmurugan, S., and Narasimhan, S. V. (2012). Cobalt (II)imprinted chitosan for selective removal of cobalt during nuclear reactor decontamination.Carbohydrate Polymers 87(4), 2690–2696. doi:10.1016/j.carbpol.2011.11.061.

Oladipo, A. A., and Gazi, M. (2016). Hydroxyl-enhanced magnetic chitosan microbeads forboron adsorption: Parameter optimization and selectivity in saline water. Reactive & Func-tional Polymers 109, 23–32. doi:10.1016/j.reactfunctpolym.2016.09.005.

Oladipo, A. A., Gazi, M., and Yilmaz, E. (2015). Single and binary adsorption of azo and anthra-quinone dyes by chitosan-based hydrogel: Selectivity factor and Box-Behnken processdesign. Chemical Engineering Research and Design 104, 264–279. doi:10.1016/j.cherd.2015.08.018.

Pandey, S. and Tiwari, S. (2015). Facile approach to synthesize chitosan based composite-Char-acterization and cadmium(II) ion adsorption studies. Carbohydrate Polymers 134, 646–656.

Paulino, A. T., Belfiore, L. A., Kubota, L. T., Muniz, E. C., Almeida, V. C., and Tambourgi, E. B.(2011). Effect of magnetite on the adsorption behavior of Pb(II), Cd(II), and Cu(II) in chito-san-based hydrogels. Desalination 275(1–3), 187–196. doi:10.1016/j.desal.2011.02.056.

P�erez-Calixto, M. P., Ortega, A., Garcia-Uriostegui, L., and Burillo, G. (2016). Synthesis andcharacterization of N-vinylcaprolactam/N,N-dimethylacrylamide grafted onto chitosan net-works by gamma radiation. Radiation Physics and Chemistry 119, 228–235. doi:10.1016/j.radphyschem.2015.10.030.

Pestov, A., and Bratskaya, S. (2016). Chitosan and its derivatives as highly efficient polymerligands.Molecules 21(3), 330. doi:10.3390/molecules21030330.

Pillai, C. K. S., Paul, W. and Sharma, C. P. (2009). Chitin and chitosan polymers: Chemistry, sol-ubility and fiber formation. Progress in Polymer Science 34(7), 641–678.

Qin, C. Q., Du, Y. M., Zhang, Z. Q., Liu, Y., Xiao, L., and Shi, X. W. (2003). Adsorption of Chro-mium (VI) on a Novel Quaternized Chitosan Resin. Journal of Applied Polymer Science 90(2), 505–510 doi:10.1002/app.12687.

Radwan, A. A., Alanazi, F. K., and Alsarra, I. A. (2010). Microwave irradiation-assisted synthesisof a novel crown ether crosslinked chitosan as a chelating agent for heavy metal ions (MnC).Molecules 15(9), 6257–6268. doi:10.3390/molecules15096257.

Rafique, A., Mahmood Zia, K., Zuber, M., Tabasum, S., and Rehman, S. (2016). Chitosan func-tionalized poly(vinyl alcohol) for prospects biomedical and industrial applications: A review.International Journal of Biological Macromolecules 87, 141–154. doi:10.1016/j.ijbiomac.2016.02.035.

Rajiv Gandhi, M., Viswanathan, N., and Meenakshi, S. (2010). Preparation and application ofalumina/chitosan biocomposite. International Journal of Biological Macromolecules 47(2),146–154. doi:10.1016/j.ijbiomac.2010.05.008.

Rangel-Mendez, J. R., Monroy-Zepeda, R., Leyva-Ramos, E., Diaz-Flores, P. E., and Shirai, K.(2009). Chitosan selectivity for removing cadmium (II), copper (II), and lead (II) from aque-ous phase: PH and organic matter effect. Journal of Hazardous Materials 162(1), 503–511.doi:10.1016/j.jhazmat.2008.05.073.

Renu, Agarwal, M., and Singh, K. (2017). Heavy metal removal from wastewater using variousadsorbents: A review. Journal of Water Reuse and Desalination 7(4), 387–419. doi:10.2166/wrd.2016.104.

Ren, Y., Abbood, H. A., He, F. B., Peng, H. and Huang, K. X. (2013). Magnetic EDTA-modifiedchitosan/SiO2/Fe3O4 adsorbent: Preparation, characterization, and application in heavymetal adsorption. Chemical Engineering Journal 226, 300–311.





https://doi.org/10.1016/j.cherd.2015.08.018

https://doi.org/10.1016/j.cherd.2015.08.018




https://doi.org/10.3390/molecules21030330


https://doi.org/10.3390/molecules15096257





https://doi.org/10.2166/wrd.2016.104

https://doi.org/10.2166/wrd.2016.104

Repo, E., Koivula, R., Harjula, R., and Sillanpaa, M. (2013). Effect of EDTA and some otherinterfering species on the adsorption of Co(II) by EDTA-modified chitosan. Desalination321, 93–102. doi:10.1016/j.desal.2013.02.028.

Repo, E., Malinen, L., Koivula, R., Harjula, R., and Sillanpaa, M. (2011). Capture of Co(II) fromits aqueous EDTA-chelate by DTPA-modified silica gel and chitosan. Journal of HazardousMaterials 187(1–3), 122–132. doi:10.1016/j.jhazmat.2010.12.113.

Repo, E., Warchol, J. K., Kurniawan, T. A., and Sillanpaa, M. E. T. (2010). Adsorption of Co(II)and Ni(II) by EDTA- and/or DTPA-modified chitosan: Kinetic and equilibrium modeling.Chemical Engineering Journal 161(1–2), 73–82. doi:10.1016/j.cej.2010.04.030.

Rezende de Almeida, F. T., Silva Ferreira, B. C., da Silva Lage Moreira, A. L., de Freitas, R. P.,Gil, L. F. and Alves Gurgel, L. V. (2016). Application of a new bifunctionalized chitosanderivative with zwitterionic characteristics for the adsorption of Cu2C, Co2C, Ni2C, and oxy-anions of Cr6C from aqueous solutions: Kinetic and equilibrium aspects. Journal of Colloidand Interface Science 466, 297–309.

Rinaudo, M. (2006). Chitin and chitosan: Properties and applications. Progress in Polymer Sci-ence 31(7), 603–632. doi:10.1016/j.progpolymsci.2006.06.001.

Rinaudo, M., Le Dung, P., Gey, C., and Milas, M. (1992). Substituent distribution on O,N-car-boxymethylchitosans by 1H and 13C n.m.r. International Journal of Biological Macromole-cules 14(3), 122–128. doi:10.1016/S0141-8130(05)80001-7.

Rinaudo, M., Milas, M., and Le Dung, P. (1993). Characterization of chitosan. Influence of ionicstrength and degree of acetylation on chain expansion. International Journal of BiologicalMacromolecules 15(5), 281–285. doi:10.1016/0141-8130(93)90027-J.

Rocha, L. S., Almeida, A., Nunes, C., Henriques, B., Coimbra, M. A., Lopes, C. B., Silva, C. M.,Duarte, A. C., and Pereira, E. (2016). Simple and effective chitosan based films for theremoval of Hg from waters: Equilibrium, kinetic and ionic competition. Chemical Engineer-ing Journal 300, 217–229. doi:10.1016/j.cej.2016.04.054.

Saha, S., Chhatbar, M. U., Mahato, P., Praveen, L., Siddhanta, A. K., and Das, A. (2012). Rhoda-mine-alginate conjugate as self indicating gel beads for efficient detection and scavenging ofHg2C and Cr3C in aqueous media. Chemical Communications (Cambridge, England) 48(11),1659–1661. doi:10.1039/C1CC16554B.

Sakkayawong, N., Thiravetyan, P., and Nakbanpote, W. (2005). Adsorption mechanism of syn-thetic reactive dye wastewater by chitosan. Journal of Colloid and Interface Science 286(1),36–42. doi:10.1016/j.jcis.2005.01.020.

Salehi, E., Daraei, P., and Arabi Shamsabadi, A. (2016a). A review on chitosan-based adsorptivemembranes. Carbohydrate Polymers 152, 419–432. doi:10.1016/j.carbpol.2016.07.033.

Salehi, E., Daraei, P., and Shamsabadi, A. A. (2016b). A review on chitosan-based adsorptivemembranes. Carbohydrate Polymers 152, 419–432. doi:10.1016/j.carbpol.2016.07.033.

Santhana Krishna Kumar, A., Uday Kumar, C., Rajesh, V., and Rajesh, N. (2014). Microwaveassisted preparation of n-butylacrylate grafted chitosan and its application for Cr(VI)adsorption. International Journal of Biological Macromolecules 66, 135–143.

Sargin, I., and Arslan, G. (2016). Effect of glutaraldehyde cross-linking degree of chitosan/spo-ropollenin microcapsules on removal of copper(II) from aqueous solution. Desalination andWater Treatment 57(23), 10664–10676. doi:10.1080/19443994.2015.1038738.

Sarkar, K., Banerjee, S. L., and Kundu, P. P. (2012). Removal of anionic dye in acid solution byself crosslinked insoluble dendronized chitosan. Journal of Hydrology Current Research 3, 2–9.

Sashiwa, H., and Aiba, S. I. (2004). Chemically modified chitin and chitosan as biomaterials.Progress in Polymer Science 29(9), 887–908. doi:10.1016/j.progpolymsci.2004.04.001.






https://doi.org/10.1016/S0141-8130(05)80001-7

https://doi.org/10.1016/0141-8130(93)90027-J


https://doi.org/10.1039/C1CC16554B




https://doi.org/10.1080/19443994.2015.1038738


Shaker, M. A. (2015). Adsorption of Co(II), Ni(II) and Cu(II) ions onto chitosan-modified poly(methacrylate) nanoparticles: Dynamics, equilibrium and thermodynamics studies. Journalof the Taiwan Institute of Chemical Engineers 57, 111–122. doi:10.1016/j.jtice.2015.05.027.

Sharififard, H., Zokaee Ashtiani, F., and Soleimani, M. (2013). Adsorption of palladium andplatinum from aqueous solutions by chitosan and activated carbon coated with chitosan.Asia-Pacific Journal of Chemical Engineering 8(3), 74–85.

Shimizu, Y., Izumi, S., Saito, Y., and Yamaoka, H. (2004). Ethylenediamine tetraacetic acid mod-ification of crosslinked chitosan designed for a novel metal-ion adsorbent. Journal of AppliedPolymer Science 92(5), 2758–2764. doi:10.1002/app.20262.

Shimizu, Y., Saito, Y., and Nakamura, T. (2006). Crosslinking of chitosan with a trifunctionalcrosslinker and the adsorption of acid dyes and metal ions onto the resulting polymer.Adsorption Science and Technology 24(1), 29–39. doi:10.1260/026361706778062568.

Singh, V., Tripathi, D. N., Tiwari, A. and Sanghi, R. (2006). Microwave synthesized chitosan-graft-poly(methylmethacrylate): An efficient Zn2C ion binder. Carbohydrate Polymers 65(1),35–41.

Sowmya, A., and Meenakshi, S. (2013). An efficient and regenerable quaternary amine modifiedchitosan beads for the removal of nitrate and phosphate anions. Journal of EnvironmentalChemical Engineering 1(4), 906–915. doi:10.1016/j.jece.2013.07.031.

Spera, M. B. M., Taketa, T. B., and Beppu, M. M. (2017). Roughness dynamic in surface growth:Layer-by-layer thin films of carboxymethyl cellulose/chitosan for biomedical applications.Biointerphases 12(4), 401. doi:10.1116/1.4986057.

Stawinski, W., Wegrzyn, A., Danko, T., Freitas, O., Figueiredo, S., and Chmielarz, L. (2017).Acid-base treated vermiculite as high performance adsorbent: Insights into the mechanismof cationic dyes adsorption, regeneration, recyclability and stability studies. Chemosphere173, 107–115. doi:10.1016/j.chemosphere.2017.01.039.

Su, F. C., Zhou, H. J., Zhang, Y. X., and Wang, G. Z. (2016). Three-dimensional honeycomb-likestructured zero-valent iron/chitosan composite foams for effective removal of inorganic arse-nic in water. Journal of Colloid and Interface Science 478, 421–429. doi:10.1016/j.jcis.2016.06.035.

Sun, S. L., Wang, L., and Wang, A. Q. (2006). Adsorption properties of crosslinked carboxy-methyl-chitosan resin with Pb(II) as template ions. Journal of Hazardous Materials 136(3),930–937. doi:10.1016/j.jhazmat.2006.01.033.

Sun, X. F., Wang, S. G., Liu, X. W., Gong, W. X., Bao, N., and Ma, Y. (2008). The effects of pHand ionic strength on fulvic acid uptake by chitosan hydrogel beads. Colloids and Surfaces a-Physicochemical and Engineering Aspects 324(1–3), 28–34.

Tang, X. J., Gan, L., Duan, Y. X., Sun, Y. M., Zhang, Y. F., and Zhang, Z. D. (2017). A novelCd2C-imprinted chitosan-based composite membrane for Cd2C removal from aqueous solu-tion.Materials Letters 198, 121–123. doi:10.1016/j.matlet.2017.04.006.

Tanhaei, B., Ayati, A., Lahtinen, M., Mahmoodzadeh Vaziri, B., and Sillanp€a€a, M. (2016). Amagnetic mesoporous chitosan based core-shells biopolymer for anionic dye adsorption:Kinetic and isothermal study and application of ANN. Journal of Applied Polymer Science133(22), n/a–n/a. doi:10.1002/app.43466.

Tanhaei, B., Ayati, A., Lahtinen, M., and Sillanp€a€a, M. (2015). Preparation and characterizationof a novel chitosan/Al2O3/magnetite nanoparticles composite adsorbent for kinetic, thermo-dynamic and isotherm studies of Methyl Orange adsorption. Chemical Engineering Journal259, 1–10. doi:10.1016/j.cej.2014.07.109.

Thakre, D., Jagtap, S., Sakhare, N., Labhsetwar, N., Meshram, S., and Rayalu, S. (2010). Chitosanbased mesoporous Ti-Al binary metal oxide supported beads for defluoridation of water.Chemical Engineering Journal 158(2), 315–324. doi:10.1016/j.cej.2010.01.008.


https://doi.org/10.1016/j.jtice.2015.05.027


https://doi.org/10.1260/026361706778062568

https://doi.org/10.1016/j.jece.2013.07.031

https://doi.org/10.1116/1.4986057





https://doi.org/10.1016/j.matlet.2017.04.006




Thakur, V. K., and Voicu, S. I. (2016). Recent advances in cellulose and chitosan based mem-branes for water purification: A concise review. Carbohydrate Polymers 146, 148–165.doi:10.1016/j.carbpol.2016.03.030.

Trung, T. S., Ng, C. H., and Stevens, W. F. (2003). Characterization of decrystallized chitosanand its application in biosorption of textile dyes. Biotechnology Letters 25(14), 1185–1190.doi:10.1023/A:1024562900548.

Turek, M., Dydo, P., Trojanowska, J., and Campen, A. (2007). Adsorption/co-precipitation—reverse osmosis system for boron removal. Desalination 205(1–3), 192–199. doi:10.1016/j.desal.2006.02.056.

Turker, O. C., and Baran, T. (2017). A combination method based on chitosan adsorption andduckweed (Lemna gibba L.) phytoremediation for boron (B) removal from drinking water.International Journal of Phytoremediation. doi:10.1080/15226514.2017.1350137.

Vakili, M., Rafatullah, M., Salamatinia, B., Abdullah, A. Z., Ibrahim, M. H., Tan, K. B., Gholami,Z., and Amouzgar, P. (2014). Application of chitosan and its derivatives as adsorbents fordye removal from water and wastewater: A review. Carbohydrate Polymers 113, 115–130.doi:10.1016/j.carbpol.2014.07.007.

Varma, A. J., Deshpande, S. V., and Kennedy, J. F. (2004). Metal complexation by chitosan andits derivatives: A review. Carbohydrate Polymers 55(1), 77–93. doi:10.1016/j.carbpol.2003.08.005.

Vincent, C., Barre, Y., Vincent, T., Taulemesse, J. M., Robitzer, M., and Guibal, E. (2015). Chi-tin-Prussian blue sponges for Cs(I) recovery: From synthesis to application in the treatmentof accidental dumping of metal-bearing solutions. Journal of Hazardous Materials 287, 171–179. doi:10.1016/j.jhazmat.2015.01.041.

Viswanathan, N., and Meenakshi, S. (2010). Enriched fluoride sorption using alumina/chitosancomposite. Journal of Hazardous Materials 178(1–3), 226–232. doi:10.1016/j.jhazmat.2010.01.067.

Viswanathan, N., Sundaram, C. S., and Meenakshi, S. (2009). Sorption behaviour of fluoride oncarboxylated cross-linked chitosan beads. Colloids and Surfaces B-Biointerfaces 68(1), 48–54.doi:10.1016/j.colsurfb.2008.09.009.

Wang, J. L., and Bai, Z. Y. (2017). Fe-Based Catalysts for heterogeneous catalytic ozonation ofemerging contaminants in water and wastewater. Chemical Engineering Journal 312, 79–98.

Wang, J. L., and Chen, C. (2006). Biosorption of heavy metals by Saccharomyces cerevisiae: Areview, Biotechnology Advances, 24, 427–451.

Wang, J. L., and Chen, C. (2009). Biosorbents for heavy metals removal and their future. Bio-technology Advances 27, 195–226. doi:10.1016/j.biotechadv.2008.11.002.

Wang, J. L., and Chen, C. (2014). Chitosan-based biosorbents: Modification and application forbiosorption of heavy metals and radionuclides. Bioresource Technology 160, 129–141.doi:10.1016/j.biortech.2013.12.110.

Wang, J. L., and Chu, L. B. (2016). Irradiation treatment of pharmaceutical and personal careproducts (PPCPs) in water and wastewater: An overview.. Radiation Physics and Chemistry125, 56–64.

Wang, J. L., and Wang, S. Z. (2016). Removal of pharmaceuticals and personal care products(PPCPs) from wastewater: A review. Journal of Environmental Management 182, 620–640.

Wang, J. L., and Xu, L. J. (2012). Advanced oxidation processes for wastewater treatment: for-mation of hydroxyl radical and application. Critical Reviews in Environmental Science andTechnology 42(3), 251–325.

Wang, J. P., Chen, Y. Z., Ge, X. W. and Yu, H. Q. (2007). Gamma radiation-induced grafting ofa cationic monomer onto chitosan as a flocculant. Chemosphere 66(9), 1752–1757.



https://doi.org/10.1023/A:1024562900548



https://doi.org/10.1080/15226514.2017.1350137








https://doi.org/10.1016/j.biotechadv.2008.11.002


Wang, J. S., Peng, R. T., Yang, J. H., Liu, Y. C., and Hu, X. J. (2011). Preparation of ethylenedi-amine-modified magnetic chitosan complex for adsorption of uranyl ions. Carbohydrate Pol-ymers 84(3), 1169–1175. doi:10.1016/j.carbpol.2011.01.007.

Wang, R., Jiang, X., He, A., Xiang, T., and Zhao, C. S. (2015). An in situ crosslinking approachtowards chitosan-based semi-IPN hybrid particles for versatile adsorptions of toxins. RscAdvances 5(64), 51631–51641. doi:10.1039/C5RA04638F.

Wang, S. G., Sun, X. F., Liu, X. W., Gong, W. X., Gao, B. Y., and Bao, N. (2008). Chitosan hydro-gel beads for fulvic acid adsorption: Behaviors and mechanisms. Chemical Engineering Jour-nal 142(3), 239–247. doi:10.1016/j.cej.2007.11.025.

Wang, X. L., Liu, Y. K., and Zheng, J. T. (2016). Removal of As(III) and As(V) from water bychitosan and chitosan derivatives: A review. Environmental Science and Pollution ResearchInternational 23(14), 13789–13801. doi:10.1007/s11356-016-6602-8.

Wang, Y., Qi, Y. X., Li, Y. F., Wu, J. J., Ma, X. J., Yu, C., and Ji, L. (2013). Preparation and char-acterization of a novel nano-absorbent based on multi-cyanoguanidine modified magneticchitosan and its highly effective recovery for Hg(II) in aqueous phase. Journal of HazardousMaterials 260, 9–15. doi:10.1016/j.jhazmat.2013.05.001.

Wasikiewicz, J. M., Mitomo, H., Seko, N., Tamada, M. and Yoshii, F. (2007). Platinum and pal-ladium ions adsorption at the trace amounts by radiation crosslinked carboxymethylchitinand carboxymethylchitosan hydrogels. Journal of Applied Polymer Science 104(6), 4015–4023.

Wong, Y. C., Szeto, Y. S., Cheung, W. H., and McKay, G. (2004a). Adsorption of acid dyes onchitosan – equilibrium isotherm analyses. Process Biochemistry 39(6), 693–702. doi:10.1016/S0032-9592(03)00152-3.

Wong, Y. C., Szeto, Y. S., Cheung, W. H., and McKay, G. (2004b). Comparison of the sorptionof anionic dyes on activated carbon and chitosan derivatives from dilute solutions. Journal ofApplied Polymer Science 92, 3049–3073.

Wong, Y. C., Szeto, Y. S., Cheung, W. H., and Mckay, G. (2004c). Psudo-first-order kinetic stud-ies of the sorption of acid dyes onto chitosan. Journal of Applied Polymer Science 92(3),1633–1645. doi:10.1002/app.13714.

Wu, F. C., Tseng, R. L., and Juang, R. S. (2001). Enhanced abilities of highly swollen chitosanbeads for color removal and tyrosinase immobilization. Journal of Hazardous Materials 81(1–2), 167–177. doi:10.1016/S0304-3894(00)00340-X.

Xing, Y., Sun, X. M., and Li, B. H. (2009). Pyromellitic dianhydride-modified chitosan micro-spheres for enhancement of cationic dyes adsorption. Environmental Engineering Science 26(3), 551–558. doi:10.1089/ees.2007.0346.

Xu, L., Huang, Y. A., Zhu, Q. J., and Ye, C. (2015). Chitosan in molecularly-imprinted polymers:Current and future prospects. International Journal of Molecular Sciences 16(8), 18328–18347. doi:10.3390/ijms160818328.

Yagi, K., Ruiz, J. A., and Sanchez, M. C. (1980). Cation binding properties of polymethacryla-mide derivatives of crown ethers.Macromolecular Chemistry Rapid Communications 1, 263–268. doi:10.1002/marc.1980.030010415.

Yang, C. Y., Hsu, C. H., and Tsai, M. L. (2011). Effect of crosslinked condition on characteristicsof chitosan/tripolyphosphate/genipin beads and their application in the selective adsorptionof phytic acid from soybean whey. Carbohydrate Polymers 86(2), 659–665. doi:10.1016/j.carbpol.2011.05.004.

Yang, S. B., Okada, N., and Nagatsu, M. (2016). The highly effective removal of CsC by low tur-bidity chitosan-grafted magnetic bentonite. Journal of Hazardous Materials 301, 8–16.doi:10.1016/j.jhazmat.2015.08.033.



https://doi.org/10.1039/C5RA04638F


https://doi.org/10.1007/s11356-016-6602-8


https://doi.org/10.1016/S0032-9592(03)00152-3

https://doi.org/10.1016/S0032-9592(03)00152-3


https://doi.org/10.1016/S0304-3894(00)00340-X

https://doi.org/10.1089/ees.2007.0346

https://doi.org/10.3390/ijms160818328

https://doi.org/10.1002/marc.1980.030010415




Yang, X. M., Tu, Y. F., Li, L., Shang, S. M., and Tao, X. M. (2010). Well-dispersed chitosan/gra-phene oxide nanocomposites. ACS Applied Materials & Interfaces 2(6), 1707–1713.doi:10.1021/am100222m.

Yazdani-Pedram, M., Retuert, J., and Quijada, R. (2000). Hydrogels based on modified chitosan,1. Synthesis and swelling behavior of poly(acrylic acid) grafted chitosan. MacromolecularChemistry and Physics 201(9), 923–930. doi:10.1002/1521-3935(20000601)201:9%3c923::AID-MACP923%3e3.0.CO;2-W.

Yi, R., Ye, G., Wu, F. C., Lv, D. C., and Chen, J. (2016). Magnetic solid-phase extraction of stron-tium using core-shell structured magnetic microspheres impregnated with crown etherreceptors: A response surface optimization. Journal of Radioanalytical and Nuclear Chemis-try 308(2), 599–608. doi:10.1007/s10967-015-4468-8.

Yin, Y. N., Wang, J. L., Yang, X. Y., and Li, W. H. (2017). Removal of strontium ions by immo-bilized Saccharomyces Cerevisiae in magnetic chitosan microspheres. Nuclear Engineeringand Technology 49(1), 172–177. doi:10.1016/j.net.2016.09.002.

Yu, J., Zheng, J. D., Lu, Q. F., Yang, S. X., Wang, X., Zhang, X. M., and Yang, W. (2016a). Reus-ability and selective adsorption of Pb2C on chitosan/P(2-acryl amido-2-methyl-1-propane-sulfonic acid-co-acrylic acid) hydrogel. Iranian Polymer Journal 25(12), 1009–1019.doi:10.1007/s13726-016-0487-8.

Yu, J., Zheng, J. D., Lu, Q. F., Yang, S. X., Zhang, X. M., Wang, X., and Yang, W. (2016b). Selec-tive adsorption and reusability behavior for Pb2C and Cd2C on chitosan/poly(ethylene gly-col)/poly(acrylic acid) adsorbent prepared by glow-discharge electrolysis plasma. Colloidand Polymer Science 294(10), 1585–1598. doi:10.1007/s00396-016-3920-9.

Yu, Q., Deng, S. B., and Yu, G. (2008). Selective removal of perfluorooctane sulfonate fromaqueous solution using chitosan-based molecularly imprinted polymer adsorbents. WaterResearch 42(12), 3089–3097. doi:10.1016/j.watres.2008.02.024.

Zavareh, S., Behrouzi, Z., and Avanes, A. (2017). Cu(II) binded chitosan/Fe3O4 nanocomompo-site as a new biosorbent for efficient and selective removal of phosphate. International Jour-nal of Biological Macromolecules 101, 40–50. doi:10.1016/j.ijbiomac.2017.03.074.

Zhang, H. F., Dang, Q. F., Liu, C. S., Cha, D. S., Yu, Z. Z., Zhu, W. J., and Fan, B. (2017). Uptakeof Pb(II) and Cd(II) on chitosan microsphere surface successively grafted by methyl acrylateand diethylenetriamine. ACS Applied Materials & Interfaces 9(12), 11144–11155.

Zhang, L., Zeng, Y. X., and Cheng, Z. J. (2016a). Removal of heavy metal ions using chitosanand modified chitosan: A review. Journal of Molecular Liquids 214, 175–191. doi:10.1016/j.molliq.2015.12.013.

Zhang, Q. Y., Deng, S. B., Yu, G., and Huang, J. (2011). Removal of perfluorooctane sulfonatefrom aqueous solution by crosslinked chitosan beads: Sorption kinetics and uptake mecha-nism. Bioresource Technology 102(3), 2265–2271. doi:10.1016/j.biortech.2010.10.040.

Zhang, S. P., Dong, Y. Y., Yang, Z., Yang, W. B., Wu, J. Q., and Dong, C. (2016b). Adsorption ofpharmaceuticals on chitosan-based magnetic composite particles with core-brush topology.Chemical Engineering Journal 304, 325–334. doi:10.1016/j.cej.2016.06.087.

Zhang, Y. L., Zhang, J., Dai, C. M., Zhou, X. F., and Liu, S. G. (2013). Sorption of carbamazepinefrom water by magnetic molecularly imprinted polymers based on chitosan-Fe3O4. Carbohy-drate Polymers 97(2), 809–816. doi:10.1016/j.carbpol.2013.05.072.

Zhou, L. M., Jin, J. Y., Liu, Z. R., Liang, X. Z., and Shang, C. (2011). Adsorption of acid dyesfrom aqueous solutions by the ethylenediamine-modified magnetic chitosan nanoparticles.Journal of Hazardous Materials 185(2–3), 1045–1052. doi:10.1016/j.jhazmat.2010.10.012.

Zhou, L. M., Liu, J. H. and Liu, Z. R. (2009a). Adsorption of platinum(IV) and palladium(II)from aqueous solution by thiourea-modified chitosan microspheres. Journal of Hazardousmaterials 172(1), 439–446.


https://doi.org/10.1021/am100222m

https://doi.org/10.1002/1521-3935(20000601)201:9%3c923::AID-MACP923%3e3.0.CO;2-W




https://doi.org/10.1007/s10967-015-4468-8

https://doi.org/10.1016/j.net.2016.09.002

https://doi.org/10.1007/s13726-016-0487-8

https://doi.org/10.1007/s00396-016-3920-9









Zhou, L. M., Wang, Y. P., Liu, Z. R. and Huang, Q. W. (2009b). Characteristics of equilibrium,kinetics studies for adsorption of Hg(II), Cu(II), and Ni(II) ions by thiourea-modified mag-netic chitosan microspheres. Journal of Hazardous materials 161(2–3), 995–1002.

Zhou, L. M., Xu, J. P., Liang, X. Z. and Liu, Z. R. (2010). Adsorption of platinum(IV) and palla-dium(II) from aqueous solution by magnetic cross-linking chitosan nanoparticles modifiedwith ethylenediamine. Journal of Hazardous materials 182(1–3), 518–524.

Zhu, Y., Bai, Z. S., Luo, W. Q., Wang, B. J., and Zhai, L. L. (2017). A facile ion imprinted synthe-sis of selective biosorbent for Cu2C via microfluidic technology. Journal of Chemical Technol-ogy and Biotechnology 92(8), 2009–2022. doi:10.1002/jctb.5193.

Zhu, Y. H., Hu, J., and Wang, J. L. (2012). Competitive adsorption of Pb(II), Cu(II) and Zn(II)onto xanthate-modified magnetic chitosan. Journal of Hazardous Materials 221–222, 155–161. doi:10.1016/j.jhazmat.2012.04.026.

Zhu, Y. H., Hu, J., and Wang, J. L. (2014). Removal of Co2C from radioactive wastewater bypolyvinyl alcohol (PVA)/chitosan magnetic composite. Progress in Nuclear Energy 71, 172–178. doi:10.1016/j.pnucene.2013.12.005.

Zhuang, S. T., and Wang, J. L. (2017). Modified alginate beads as biosensor and biosorbent forsimultaneous detection and removal of cobalt ions from aqueous solution. EnvironmentalProgress & Sustainable Energy. doi:10.1002/ep.12666.

Zhuang, S. T., Yin, Y. N., and Wang, J. L. (2017). Simultaneous detection and removal of cobaltions from aqueous solution by modified chitosan beads. International Journal of Environ-mental Science and Technology. doi:10.1007/s13762-017-1388-x.


https://doi.org/10.1002/jctb.5193


https://doi.org/10.1016/j.pnucene.2013.12.005

https://doi.org/10.1002/ep.12666

https://doi.org/10.1007/s13762-017-1388-x

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