Procedia Engineering 75 ( 2014 ) 56 – 60

1877-7058 © 2013 The Authors. Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the scientific committee of Symposium [Advanced Structural and Functional Materials for Protection] – ICMAT.doi: 10.1016/j.proeng.2013.11.011

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MRS Singapore - ICMAT Symposia Proceedings

ICMAT2013-International Conference on Materials for Advanced Technologies

A hybrid material for sustainable environmental protection Anjali Bajpaia*, Neha Tripathia

a Department of Chemistry, Government Model Science College, Jabalpur 482001, India

Abstract

The hybrid nanocomposite was prepared by in situ intercalative polymerization of acrylamide in a fine dispersion of the sugarcane bagasse, chitin and fuller’s earth by microwave irradiation. The product was very efficient as an adsorbent for metal ions and organic dye. It was mechanically stable in wet condition, resistant to fast microbial attack and released no leachates.

© 2013 The Authors. Published by Elsevier Ltd.

Selection and/or peer-review under responsibility of the scientific committee of Symposium

[Symposium W: Advanced Structural and Functional Materials for Protection] – ICMAT.

Keywords: hybrid nanocomposite; adsorbent; sugarcane bagasse; fuller’s earth; chitin

1. Introduction

The 20th century witnessed the great industrial revolution which has changed the lifestyle of people on mother earth. The task for the present generation is to continue with the progress as well as to develop processes for sustainable environmental protection. Human activities, viz., domestic, industrial and agricultural, introduce a variety of pollutants in the natural water bodies, which are hazardous to living beings. Hence, the environmental protection authorities have imposed stringent regulations for treatment of effluents before their disposal into the water sources. Naturally there is an urgent demand for economic materials and convenient processes. A multitude of processes employed are: coagulation, precipitation, extraction, evaporation, adsorption on activated carbon, ion- exchange, oxidation, incineration, electro-floatation, electrochemical treatment, biodegradation and membrane filtration [1]. Adsorption is the most popular and widely used method. Activated carbon is the most significant adsorbent because it has a high capacity for adsorption of organic matter, but its use is limited due its high cost. This has led to search for economic substitutes [2-4].

The extreme variability of industrial wastewater must be taken into account in the design of any adsorbent system [5]. Polysaccharides are especially attractive as adsorbents because they are economical, abundant and biodegradable renewable resources. However, each type of pollutant may need a particular polysaccharide. Each polysaccharide has its specific application as well as inherent advantages and disadvantages in wastewater treatment. The ability of cellulose to adsorb organic dyes, metal ions is quite established but it is very low in comparison to activated carbon or zeolite. Further, the adsorption properties of native cellulose vary according to its origin and preliminary treatment [6]. The second abundant biopolymer in nature after cellulose is chitin, which is the most abundant natural amino polysaccharide. Chitin (CH) is insoluble and intractable; hence it is generally deacetylated to chitosan for various applications [7]. However, the use of chitosan to form superabsorbent materials has been limited because of their usually poor mechanical properties when compared to other polymers. The addition of reinforcing fillers into the hydrogel matrix can enhance their mechanical properties and improve their handling [8]. Fuller’s earth (FE) is a fine-grained naturally occurring earth substance that has a substantial ability to adsorb impurities or coloring bodies [8]. Montmorillonite is the principal clay mineral in fuller’s earth, but other minerals such as kaolinite, attapulgite and palygorskite also occur and account for its variable chemical composition.

* Corresponding author. Tel.: +91 0761 2601496; fax: +91 0761 2621272 E-mail address: abs_112@rediffmail.com

© 2013 The Authors. Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the scientific committee of Symposium [Advanced Structural and Functional Materials for Protection] – ICMAT.

57 Anjali Bajpai and Neha Tripathi / Procedia Engineering 75 ( 2014 ) 56 – 60

A novel hybrid material was developed from economical, abundant renewable resources, viz. sugarcane bagasse (SCB), CH and FE. SCB, an agricultural waste and CH, a food industry waste have been reported to possess affinity for metal ions, dyes and other organic materials. Montmorillonite, the major component of FE owes great adsorption properties due to the presence of cations in interlayers. However, biomaterials suffer from the drawback of fast microbial degradation under wet environment and FE, the inorganic material swells and disperses in water, which renders separation cumbersome. Polyacrylamide is being popularly used as a polymeric flocculent but with the disadvantage of releasing oligomers in water, which is objectionable. It was envisaged that if a filter/adsorbent medium composed of an economic nanocomposite constituted from SCB, CH and FE could be developed, it would adsorb a variety of pollutants. A semi-interpenetrating network formed by polymerization of vinyl monomer would result in an organic-inorganic hybrid nanocomposite.

2. Materials and methodology

Locally available SCB was thoroughly rinsed with water to remove water soluble extractives, dried in an air oven at 60 °C for 72 h, finely ground, sieved and dispersed in 0.25 M aqueous sodium hydroxide solution and magnetically stirred for 48 h. CH flakes were dispersed in 20 % (V/V) acetic acid solution and magnetically stirred for 24 h. The resulting emulsions of SCB and CH were thoroughly mixed with finely powdered FE and acrylamide (AAm). Potassium persulphate (KPS) and N, N’-methylenebisacrylamide (MBA) were added and the mixture was again stirred magnetically, and then finally irradiated in a domestic Kenstar microwave oven. The product was thoroughly extracted with water to eliminate loosely bound material. The compact mass was then dried in an air oven. Swelling properties were studied using conventional gravimetric procedure [10]. Accurately weighed pieces of the sample (mass mo) were immersed in 200 mL of deionized water for 24 h in respective experiments. The swollen samples were taken out, dried in an air oven and weighed again (mass md). Percent erosion was calculated using the equation 1.

0

0

% 100dm mErosion

m (1)

Dye loading was accomplished by placing the 1 g samples of nanocomposite in 200 mL of various concentration of methyl orange aqueous solution at room temperature for overnight. The samples were removed from the bath and washed with deionized water to remove excess of dye adhered at the surface of sample and dried at room temperature. Concentration of the dye solutions were determined by a UV-visible spectrophotometer. For the study of metal ion adsorption Nanocomposite samples were dipped in 0.1 M acidified aqueous solutions of Cu2+ or Ni2+, Hg2+ at room temperature for 24 h then 1 mL of aliquot was pipetted out and diluted with deionized water till desired concentration. The concentrations of metal ions in respective solutions were measured with a Shimadzu 6300 atomic absorption spectrometer. Percent adsorption was determined by following equation.

% Adsorption = (C0 –C / C0) × 100 (2)

Where, C0 and C (g/L) are the concentrations of adsorbate in the solution before and after the adsorption, respectively.

3. Results and discussion

A multicomponent nanocomposite was prepared by intercalative polymerization of AAm in presence of sugarcane bagasse, chitin and fuller’s earth. In the present study methyl orange was used as a model organic dye; and nickel, copper, and mercury as representative metal ions for evaluation of efficiency of this material as an adsorbent. SCB is the fibrous residue obtained from sugarcane juice extraction and consists of cellulose (50 %), hemicelluloses (25 %) and lignin (25 %) as the principal constituents [11]. SCB fibres were treated with 0.25 M NaOH solution to dissolve hemicellulose and lignin, and the suspension obtained was used as such for preparing the nanocomposite. Shaikh et al. [12] reported utilization of the hemicellulose as internal plasticizer. Similarly lignin would provide additional binding to the various constituents of nanocomposite and would impart slight hydrophobicity needed for mechanical stability under water swollen condition. Inclusion of lignin in printing inks and paint vehicles, showed a drastic reduction in misting, without any accompanying detrimental effects to their other functional parameters [13]. A reinforcement effect was reported on incorporation of lignin into composites [14,15]. Chitin a (1, 4)–linked polymer of 2-acetamido-2-deoxy-D-glucopyranose (N-acetyl-D-glucosamine) was pre-treated with 20% acetic acid to disperse it homogeneously in the reaction mixture as far as possible. It has been shown that amorphous regions in cellulose, chitin and chitosan are susceptible to acid attack allowing the formation of nanofibrils [16-18]. These nanofibrils show excellent dispersion in water [19,20]. Further their good dispersion in the polymeric matrix nanofibrils is possible through interactions among the nanosized moieties that form a percolated network connected by hydrogen bonds [21,22]. In the present study dilute solution of a week acid (acetic acid) was employed so that a partial dispersion of material could occur and the remaining aggregates would act as the reinforcing fillers.

58 Anjali Bajpai and Neha Tripathi / Procedia Engineering 75 ( 2014 ) 56 – 60

Formation of nanocomposite was indicated from IR spectral, XRD and SEM studies. The XRD patterns of NCPAAm and its constituents were recorded in 2Ө range of 0˚ to 80˚ and are presented in figure 1. XRD pattern of raw SCB suggested its amorphous structure. In the diffractograph of SCB treated with NaOH, besides the broad band characteristic of cellulose near 20˚, several other sharp bands originated at angles 2 Ө higher than 20˚, which indicated that the components of SCB, viz., cellulose, hemicellulose and lignin separated on alkali treatment and exhibited independent diffraction patterns. It is well known that an increase in the number of peaks is suggestive of the decreases in the symmetry of crystal structure. XRD patterns of CH and CH treated with acetic acid were almost identical; only the peaks became slightly broader, which indicated that self assembly of chitin chains was affected to some extent. XRD pattern of NCPAAm indicated its amorphous nature. The prominent peaks of FE below 10º reduced to a shoulder and the intensity of signal at 26.55º also reduced. The calculation of d-spacing of the band near 27º showed an increase from 3.3543 Å to 3.3814 Å in NCPAAm. The decreased intensity and increased width indicated the presence of disordered or exfoliated regions. Thus it was inferred that the increase in interlayer distance of the clay was due to in situ intercalative polymerization of AAm into the interlayer spaces [23].

A very rough morphology of nanocomposite was apparent in the SEM images (Fig. 2). Aggregates of average m size appeared to be dispersed in the continuous matrix of clay and polyacrylamide. The terminals of stacks of SCB fibres and chitin flakes could be seen. Fig. 2B showed SCB fibres completely covered by clay and PAAm as a bright elongated area. The sample appeared to be porous to unaided eye but in SEM image at magnification of 4000 times no pores were visible.

3.1 Swelling characteristics of nanocomposites

The results of percent swelling are presented in figure 3. Higher swelling was observed at higher temperature as expected. The increasing order of swelling for NCPAAm at various pH was 7 > 4 > 9. NCPAAm exhibited very high

Figure 3. Effect of temperature, pH and various solutions on swelling properties of NCPAAm samples

Figure 1. XRD patterns of NCPAAm and its constituents

Figure 2. SEM of NCPAAm : Magnification 4000× (a) Surface morphology (b) Fractured surface morphology

59 Anjali Bajpai and Neha Tripathi / Procedia Engineering 75 ( 2014 ) 56 – 60

Table 1. Metal Ion Uptake Capacity of Nanocomposites

swelling in alkaline solution certainly amide groups hydrolyzed to carboxylic acid groups which are strongly hydrophilic consequently swelled to greater extent. Moderate swelling in NaCl solution and minimum in acidic solutions (slightly lower than that in water) was observed. Erosion followed the opposite order but was not much significant and was found to be 5.042, 5.878 and 8.730 percent in NaOH, NaCl and HCl solutions respectively. This weight loss was due to tiny fragments which could be retained on filter paper.

3.2 Adsorption studies

The MO loading capacity of NCPAAm and NCPAA are shown in Figure 4 at various initial concentrations of MO. Adsorption was quite rapid and significant percent of MO was absorbed within 5 h. The LSCOM images depicted the visible change in morphology of samples on imbibing the adsorbate. This was further substantiated on the perusal of the FTIR spectra and XRD pattern of MO loaded samples which demonstrated strong interaction of nanocomposite with the adsorbate.

Metal ion adsorption was studied and a good uptake capacity was observed (Table 1). The sample adsorbed metal ions from the aqueous solutions. The surface of samples became smooth visibly as well as in the LSCOM images NCPAAm and appeared to be covered by coloured crystalline material. It appeared as if the highly hydrated crystals of metal ions crystallised within the voids of the mega porous sample. The FTIR spectra of these crystalline materials showed strong absorption due to water of hydration. However, absorption bands due to organic moieties were also visible. It was inferred that fine particles (nanofibrils) of CH in the swollen nanocomposites flocculated the metal salts quite efficiently within the nanocomposite matrix. This was very well apparent in the SEM images in figure 5 for copper salt loaded samples. In the SEM image of nickel salt loaded sample (Fig. 5A) the aggregates/ flakes of chitin appeared to become smaller and denser, as if their outer surface merged with the main matrix after adsorption of metal ions. The XRD patterns of the metal loaded samples (Fig. 6) showed the crystalline peaks showing strong interaction with the adsorbent matrix.

S. No.

Metal ion

Metal Ion Uptake

Capacity %

1 Ni (II) 99.76

2 Cu (II) 99.32

3 Hg (II) 99.64

Fig.5. SEM Images of Metal ion loaded NCPAAm : Cu (II) (a) 2000× (b) 4000× ; Ni (II): 4000× (c) Surface (d) Fractured surface

Fig.6. XRD patterns of SEM Images of Metal ion loaded NCPAAm

Figure 4. MO loading capacity of NCPAAm at various initial concentrations of methyl orange

60 Anjali Bajpai and Neha Tripathi / Procedia Engineering 75 ( 2014 ) 56 – 60

4. Conclusion

The natural inorganic and biodegradable biomaterials were bound together in a polymeric matrix composed of polyacrylamide. Potassium per sulphate was employed as the radical initiator for polymerization of AAm under microwave irradiation. Potassium per sulphate was employed as the radical initiator for polymerization of AAm and the OH groups on SCB and CH would also participate in the radical reactions and polyacrylamide (PAAm) chains might be grafted on these biopolymers. A chemical crosslinker N, N’-methylene bisacrylamide (MBA) was employed to produce extensive crosslinks to effectively bind the different components of nanocomposites. The microfibrillated sugarcane bagasse (SCB) provided a reinforcement and FE, CH and polyacrylamide (PAAm) attributed towards the strong adsorption characteristics. The nanocomposites were found to be mechanically quite stable in wet conditions in water, acid, alkali and salt solutions; as well as in organic solvents. Though fungal growth developed on the individual biomaterials used in this preparation under wet condition within a week, the nanocomposites was resistant towards fast biodegradation. The nanocomposites exhibited strong adsorption tendency for organic dye and the metal ions.

Acknowledgement

Part of this work was performed at UGC-DAE Consortium for Scientific Research, Indore, India. Authors confer gratefulness to the Dr. A. Gupta, Center-Director, Indore Center, UGC-DAE Consortium for Scientific Research, Indore. Special thanks are due to Dr. M. Gupta, Dr. V. Ganesan, Dr. A.M. Awasthi, Dr. N.P. Lalla and Shri S. Poddar. We are also thankful to Mr. A. Gome, Ms. L. Behera , Dr. V. K. Ahire, Mr. S. Bharadwaj, Mr. S. S. Samatham, Mr. D. Tiwari, Mr. S.M. Amir from UGC-DAE Consortium for Scientific Research, Indore.

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