Research ArticleImpregnation of ZnO onto a Vegetal Activated Carbon fromAlgerian Olive Waste: A Sustainable Photocatalyst forDegradation of Ethyl Violet Dye

Ala Abdessemed ,1,2 Shivatharsiny Rasalingam ,3 Sanna Abdessemed,1

Kamel El Zin Djebbar,2 and Ranjit Koodali4

1Biotechnology Research Centre, BPE 73, Ali Mendjeli, Nouvelle Ville, 25000 Constantine, Algeria2Laboratory of Science and Technology of the Environment, University Mentouri Constantine, Chaabat Errassas, Constantine,25000, Algeria3Department of Chemistry, University of Jaffna, 40000, Sri Lanka4Department of Chemistry, University of South Dakota, Vermillion, SD 50679, USA

Correspondence should be addressed to Shivatharsiny Rasalingam; srtharsha12@gmail.com

Received 25 July 2018; Revised 3 November 2018; Accepted 21 November 2018; Published 25 February 2019

Academic Editor: Xuxu Wang

Copyright © 2019 Ala Abdessemed et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work isproperly cited.

This study is aimed at developing a simple and low-cost method to fabricate ZnO-loaded porous activated carbon (AC-ZnO)prepared from the Algerian olive-waste cakes and utilize it as a photocatalyst for the degradation of Ethyl Violet dye. Thesynthesized AC-ZnO material was characterized using powder X-ray diffraction, BET surface area measurements, Ramanmicroscopy, thermogravimetric analysis, UV-visible diffuse reflectance spectroscopy, and zeta potential measurements. Thedegradation efficiency was evaluated with Ethyl Violet (EV) dye in aqueous solution under UV irradiation supplied by aXenon arc lamp through a Pyrex glass filter (cutoff 280 nm), and the degraded products were identified by using electrosprayionization mass spectroscopy. Additional experiments were carried out under N2 flow and with isopropyl alcohol to examinethe role of superoxide and hydroxyl radicals, respectively. The amount of ●OH radical formed on irradiated AC-ZnO wastested with terephthalic acid which can act as a chemical trap for the ●OH radicals. The results from this study indicate thatthe AC-ZnO is a potential catalyst for the pollutant removal and the ●OH radicals are the key species for the degradation ofEV. Further, this study opens up an opportunity to produce cheaper activated carbon support from olive wastes forenvironmental remediation applications.

1. Introduction

Semiconductor photocatalysis has become very attractive dueto its potential contributions in the field of environmentalremediation. In particular, TiO2 has been widely utilized as aphotocatalyst for the removal of aqueous pollutants. Althoughmost of the photocatalytic studies use TiO2 as an effectivephotocatalyst, ZnO has also gained attention due to itsfavorable photocatalytic properties [1–4]. The design anddevelopment of highly efficient photocatalytic materials seemto be challenging. Several methods have been utilized to pre-pare photocatalysts, such as sol-gel, hydrothermal process,

precipitation, and impregnation [5–9]. Fabricating materialswith favorable physicochemical characteristic features arekey for the design of effective photocatalysts. In this regard,porous materials, which have favorable textural properties,such as high surface areas and large pore volumes and poresizes, have been used as support to disperse semiconductorphotocatalysts.Among them, activated carbonhas been foundto be a promising candidate because of its favorable texturalproperties [10, 11].However, commercially available activatedcarbons are still expensive in many countries, (especiallydeveloping ones) due to the need of processing the raw mate-rial (charcoal, coal, or carbon) by physical and/or chemical

HindawiInternational Journal of PhotoenergyVolume 2019, Article ID 4714107, 13 pageshttps://doi.org/10.1155/2019/4714107

methods. Thus, the high costs hamper their application in sev-eralfields [12]. This subsequently leads to a growing interest inthe research on the economical production of activated car-bons. In recent years, a number of studies have shown thatsome industrial and agricultural by-products that includewaste paper [13], waste tires [14], rice hull [15], corncob[16], apricot stone [17], date stone [18], and coconut husk[19] have the potential for being used as precursors to prepareactivated carbons for the removal of dyes from wastewater. Inthis regard, olive wastes are potential candidates for thepreparation of activated carbon, in comparison to theabove materials. In particular, the use of lignocellulosicolive-waste cakes has received less consideration for acti-vated carbon production [20, 21].

Algeria is one of the major producers of olive oil in theworld [22]. During the manufacturing process of the oliveoil, about 20% of oil is obtained; of the remaining percent-ages, 30% are waste solids and 50% is wastewater [23].Olive-waste cakes or olive pomace, corresponding to the res-idue from the oil extraction process, represents a yearly aver-age of 2 × 105 tons [24]. The use of this material as aprecursor for the preparation of activated carbon not onlycontributes towards the preparation of a catalyst or adsor-bent for aquatic pollutant removal but also results in theeffective removal and recycling of solid wastes to value-added products from olive oil production. Although thereare several studies that have reported the preparation of acti-vated carbon-supported materials for photocatalytic applica-tions, existing studies are lacking in one or more of thefollowing: (i) a low-cost preparation of activated carbon usingAlgerian olive-waste cakes, (ii) impregnation of photoactiveZnO on activated carbon, (iii) comprehensive physicochemi-cal characterization of the support and the photoactive mate-rial, (iv) utilization of these materials for the removal ofaquatic pollutants, especially, dye removal, (v) a thoroughanalysis of the photocatalytic by-products using electrosprayionization mass spectrometry (ESI-MS) analysis, and (vi) asystematic analysis providing a structure-activity relationship.

The present works explore the use of Algerian olive-wastecakes as potential feedstock for the preparation of activated

carbon (AC) as a support for impregnation of ZnO. Further,the degradation of a cationic dye, Ethyl Violet (EV), usingthis sustainable catalyst prepared by dispersing ZnO on theAC catalyst (AC-ZnO) under (UV) light irradiation is alsoelaborated herein. Ethyl Violet (EV) is a synthetic cationicdye that belongs to the triphenylmethane (TPM) groupwhich is highly soluble in water [25]. Among the various clas-ses of synthetic dyes used in textile, paper, leather, cosmetic,and food industries, TPM dyes are the largest and most ver-satile group of dyes that plays a major role [26, 27]. Thesedyes are recalcitrant molecules as they are resistant to degra-dation. These dyes have complex aromatic structures, char-acterized by a chromophoric center comprising of threephenyl groups surrounding a central carbon atom [28, 29].In particular, these TPM dyes are toxic, carcinogenic ormutagenic, and hazardous to health. Further, it has beenreported that TPM can induce tumor growth in some speciesof fish and induce hepatic tumor formation in rodents. Inaddition, it causes reproductive abnormalities in rabbits andfish [30].

The study revealed that the newly synthesized materialcan be used for aquatic pollutant removal. Above all, themethod used here for the preparation of AC is cost-effective,and thus, this study will create a path to utilize the Algerianolive waste in a creative and economic manner.

2. Materials and Methods

2.1. Materials.Without further purification, EthylViolet (EV)(Basic Violet 4) (Sigma-Aldrich) was employed as a modelorganic dye and deionized water (resistivity > 18Ω·cm) wasused to prepare the solution mixtures. Hexane (Sigma-Aldrich), sodium hydroxide (Acros), potassium nitrate(Acros), conc. nitric acid (HNO3) (ACS grade), terephthalicacid (TPA) (Acros, 98%), zinc nitrate hexahydrate (Zn(NO3)2.6H2O) (Sigma-Aldrich), and isopropyl alcohol(Fisher Scientific) were used as received. Optima grade waterwas used for the ESI-MS studies.

20 30 40 50 60 700

100

200

300

400

500

600

700

67.962.9

56.547.4

36.2

34.4

31.7

Inte

nsity

(a.u

)

2�휃 degree

Figure 1: Powder X-ray diffraction patterns of AC-ZnO.100 200 300 400 500 600 700

150

200

250

300

350

400

450

437

Inte

nsity

(a.u

.)

Raman shift (cm−1)

Figure 2: Raman spectra of the AC-ZnO material.

2 International Journal of Photoenergy

2.2. Synthesis of the AC-ZnO Material. The olive-waste cakeobtained from an oil factory located in Béjaia, Algeria, wasused as raw material for the production of activated carbonsupport. First, the olive wastes were washed several timeswith tap water and then with distilled water to remove impu-rities; finally, it was purified by hexane to remove residual oil.The solid obtained was dried in open air. The dried olive-waste cakes were then calcined at 400°C for 30min. in a muf-fle furnace, and the obtained charcoal was ground and sievedusing standard sieves, where the diameter of the particleschosen was between 400 and 250μm. The particles were thensubjected to pyrolysis on a stream of nitrogen (N2)(50 cm3/min.) at 800°C in a tubular furnace for 1 h.

Generally, preparation of activated carbon can be classi-fied under two types, namely, physical activation andchemical activation [31]. In particular, chemical activationuses activation agents that include KOH, ZnCl2, H3PO4,and H2SO4. Activation with KOH produces activated carbonwith desirable pore size distribution [32, 33]. In addition,activation with KOH provides high specific surface area(~3000m2/g) materials [34]. Although, there are no generalmechanism for chemical activation, the type and amount ofactivating agent, the process, and the reaction condition thatplays an important role in determining the structural proper-ties of the materials. Therefore, according to a literaturereview, we adopted the most common chemical activationmethod, activation with KOH, which provides enhanced tex-tural properties to the material, in particular, mesoporosity[35]. In addition, activation with KOH has a long-term his-tory, where the activation of coal, coke, and charcoal has beenperformed with KOH since 1970s [31, 36, 37]. It was alsoreported that the activation with KOH will also increase theadsorbing capacity of the activated carbons [38, 39].

The carbonized olive cakes were then impregnated in asolution of KOH (3N) with a mass ratio of 4 : 1 (i.e., 4 g ofKOH per 1 g of pretreated carbon). After 24 h of stirring,the impregnated solid was separated by simple filtration ofthe solution and the product obtained was dried at 175°Cand allowed to cool. After cooling, the activated carbon pro-duced was washed several times with hot distilled water to

remove the residual KOH until the pH of the depleted solu-tion stabilized to a neutral value (pH ≈ 7). The next stepwas physical activation, where the activated carbon washeated to 900°C for 3 h in a tubular furnace under a nitrogenstream (N2) (50 cm

3/min.). The preparation of the catalyst(AC-ZnO) was done by impregnating the activated carbonwith Zn(NO3)2.6 H2O (10% w/w) followed by heating in atubular furnace at 400°C for 6 h under a stream of nitrogen(50 cm3/min.). 10% loading was selected as optimum loadingfrom the preliminary adsorption studies, and a betterremoval efficiency was attained with the 10% loading ofZnO. Therefore, in this study, we utilized the 10% (w/w)loading of ZnO on AC as the photocatalyst. Scheme S1 inthe supplementary section summarizes the different stepsfor the preparation of the activated carbon and AC-ZnO.

2.3. Characterization. Powder X-ray diffraction (XRD) pat-terns were recorded at ambient conditions using the RigakuUltima IV instrument with Cu Kα radiation (λ = 1 5408Å),operated at an accelerating voltage of 40 kV, and an emissioncurrent of 44mA. The angle (2θ values) scanned range wasbetween 20 and 80° with a step size of 0.02°, and the scanspeed was 1°/min. The crystallite sizes were determined byapplying the Debye-Scherrer equation to the peaks at 2θ =31 7°, 34.4°, 36.2°, 47.4°, and 56.5°. The diffraction patternswere analyzed using PDXL software provided by Rigaku.Raman spectra were recorded using a HORIBA Jobin YvonLabRAM ARAMIS spectrophotometer with an internalHe-Ne (532 nm) excitation laser. The unfiltered beam of scat-tered laser radiation was focused on the sample using amicroscope objective (×50) for an acquisition time of 10 s.The radiation was then dispersed by an 1800 line/mm gratingonto the CCD detector. Physisorption properties of the cata-lyst material were investigated by using the QuantachromeNova 2200e surface area and pore size analyzer. The materialwas dried overnight at 70°C followed by extensive degassingat 200°C, and the N2 adsorption-desorption isotherms wereobtained at 77K. Surface areas were calculated using theBrunauer-Emmett-Teller (BET) equation within the relativepressure (P/P0) range of 0.05-0.30. The pore volume was

0.0 0.2 0.4 0.6 0.8 1.0

80

85

90

95

100

105

110

115

120

Relative pressure (P/P0)

Vol

ume (

cc/g

)

(a)

0 25 50 75 100 125

0.00

0.05

0.10

dv(lo

gd) (

cc/g

)

Pore diameter (Å)

(b)

Figure 3: (a) N2 physisorption isotherm and (b) BJH pore size distribution plot of the AC-ZnO material.

3International Journal of Photoenergy

obtained from the nitrogen amount adsorbed at the highestrelative pressure P/P0 ≈ 0 99. The pore size distributionwas determined by applying the Barrett-Joyner-Halenda(BJH) equation to the desorption isotherm. Fourier trans-form infrared spectroscopy (FT-IR) was used to provideinformation regarding the surface properties. The spectrawere recorded between 4000 and 350 cm-1 on a Bruker-ALPHA instrument with 24 scans at a resolution of 4 cm-1

by placing a small amount of the sample on the diamondcrystal. The diffuse reflectance spectra (DRS) were obtainedin the wavelength range between 190 and 700nm using aCarry 100 Bio UV-Vis spectrophotometer equipped with aHarrick DR praying mantis accessory. SEM images were cap-tured on an Oxford instrument. The surface charge of thesynthesized materials was recorded by autotitration using aZetasizer analyzer (Malvern Nano ZS-90) by adjusting thepH of AC-ZnO-electrolyte (KNO3 in DI water) suspension.Deionized water was used as the diluent. Test samples wereprepared with the molarity of 1mg/mL by dispersing knownamounts of the sample in aqueous 0.01M KNO3 solution.The pH was controlled by the autoaddition of 0.1M KOHand/or HNO3.

2.4. Photocatalysis Experiments. The photocatalysis experi-ments were performed by the following procedure. 25mg ofthe photocatalyst AC-ZnO was dispersed in 50mL of EthylViolet ((EV) with the initial concentration of 20 ppm andthe initial pH was recorded as~ 8-9) solution in a quartzcylindrical jacket reactor. It was noted that the pH influencesthe behavior of Ethyl Violet spectrum; there was a change inthe colour when the medium of the dye solution was acidic(pH < 4 5). In particular, the colour of the dye turned to yel-low at the pH of 1 and green and blue when the pH was at 1.5and 3, respectively. Further, there was a widening in the bandobserved with a red shift when the medium was acidic. Thecharacteristic peak for the dye solution was found at λmax of596nm, and it was found that the dye is stable when thepH was maintained as basic (pH of ~8-9). Therefore, thepH was maintained as 8-9 throughout the experiment.

Then the suspension was stirred in the dark at 300 rpmfor 30min. to establish the adsorption-desorption equilib-rium. Subsequently, UV light was supplied by a Xenon arclamp (Newport 1000W) through a Pyrex glass filter (cutoff280 nm), while the reaction temperature was maintained at25 ± 2°C by channeling water in between the walls of thereactor throughout the course of the experiment (120min.).The intensity of the irradiation was estimated to be~95mW·cm-2. 5mL of the reaction mixture was withdrawninitially at 10min. intervals followed by 30min. and 1h inter-vals (i.e., 10, 20, 30, 60, and 120min.). Then the collectedsamples were centrifuged at 3200 rpm for 15min., filteredthrough 0.45μm Millipore filter membrane, and the filtratewas then analyzed using UV-Vis spectroscopy.

Additional experiments were carried out under N2 flow(absence of oxygen) and with isopropyl alcohol (IPA) toexamine the roles of O2

●– and ●OH radicals, respectively.In order to detect the amount of ●OH radicals formed onthe surface of the irradiated catalyst (AC-ZnO), terephthalicacid (TPA) was used as a chemical trap. It is well known that●OH radicals rapidly react with TPA to produce highly fluo-rescent 2-hydroxyterephthalic acid (2-HTPA). In a typicalprocedure, 25mg of the photocatalyst was added to 50mLof 5 × 10-4 M TPA solution prepared using 2 × 10-3 MNaOH.Then the suspension was irradiated with UV light. 3mL ali-quots was drawn every 20min. For a duration of 120min.,filtered through a 0.45μm Millipore filter membrane, theclear solution was analyzed using Flouromax-4 (JY Horiba)fluorimeter. The fluorescence emission intensity of the2-hydroxyterephthalic acid was recorded at 425nm, afterexcitation at 315 nm. The intensity of the peak at 425nm isproportional to the amount of ●OH formed.

2.5. Analytical Techniques. The remnant concentration of thedye solution after the photocatalytic reaction was estimatedby UV-Vis spectrophotometric method. The absorbancewas recorded by following the peak at a wavelength of596 nm, which corresponds to the absorption maximum ofEthyl Violet (EV). Quantification of the dye concentration

200 300 400 500 600 700 800-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Inte

nsity

(a.u

.)

Wavelength (nm)

(a)

6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.00

1

2

3

[K⁎ E

](1/2

) (eV

)(1/2

)

E (eV)

(b)

Figure 4: (a) DRS absorption plot and (b) Tauc plot of the AC-ZnO material.

4 International Journal of Photoenergy

at different time intervals was completed by using a calibra-tion plot of EV drawn in the concentration range between 5and 20 ppm.

A Varian 500-MS Ion Trap Mass Spectrometer was usedfor the identification of the dye fragments formed during thephotocatalytic degradation. Ionization was completed by anelectrospray ionization (ESI) source in a positive mode toseparate the fragments on the basis of their mass to chargeratio. A 1 : 1 volume ratio of optima grade methanol anddye solution mixture was used to inject into the mass spec-trometer. The operating parameters used for MS study aresummarized in the supplementary section (Table S1).Finally, the remnant carbon content of the dye solutionafter degradation was evaluated by using a ShimadzuTOC-VCSH Total Organic Carbon (TOC) analyzer.

3. Results and Discussion

3.1. Powder XRD. Powder XRD patterns of the AC-ZnO pre-pared are shown in Figure 1. Well-defined peaks at the twotheta degrees of 31.7°, 34.4°, 36.2°, 47.4°, 56.5°, 62.9°, and67.9° corresponding to the diffraction planes of (100),(002), (101), (102), (110), (103), and (112), respectively, con-firm the Wurtzite hexagonal structure of ZnO particles(JCPDS file 36-1451) [40–42].

Broad peaks at around 23° and 43° indicate the presenceof the carbon support due to the (002) and (101) planes,respectively. These two peaks resemble with the XRD peaksobtained for the pure activated carbon support as illustratedin Figure S1 in the supplementary section. The crystallitesize and the lattice constants of ZnO are calculated to be209Å and a = 3 2513Å, and c = 5 215Å, respectively,consistent with previous reports [43, 44].

3.2. Raman Spectra. The Raman study further confirms thepresence of ZnO on the carbon support. The Raman spectraof AC-ZnO (Figure 2) exhibit a sharp peak at 437 cm-1 corre-sponding to the ZnO structure attributed to the high-frequency E2 vibrationmode of theWurtzite phase [45, 46].

3.3. N2 Sorption Analysis. The nitrogen isotherm of theAC-ZnO material prepared is depicted in Figure 3(a).According to the IUPAC classification, the isotherm pos-sesses a combination of type I and type II, indicating the pres-ence of both micropores and mesopores in the material [47].Figure 3(b) illustrates the pore size distribution of theAC-ZnOmaterial. The catalyst exhibits hierarchical set poreswith one set of pores predominantly centered near the 13Åregion and a broad set of pores in the 50 to 125Å region.The total pore volume was calculated to be 0.12 cm3/g. Thespecific surface area of the material was found to 392m2/g.It is interesting to note that the pore volume obtained wasfound to be lower than that of pure activated carbon (AC)0.22 cm3/g. This may be due to the formation of the ZnOnanoparticles encapsulated within the pores.

3.4. UV-Visible Diffuse Reflectance Spectroscopy (DRS). Theband gap of the AC-ZnO was determined from the Tauc plot(Figure 4(a)), which is a transformation of the absorptionspectra through the Kubelka-Munk function vs. the energy

plot (Figure 4(b)). The catalyst synthesized exhibits a signifi-cant absorption below 400nm, which is attributed to electrontransitions from the valence band to the conduction band ofZnO [48]. The band gap energy was calculated to be 3.75 eVby extrapolating the steep portion of the plot in Figure 4(b) tothe x-axis. The measured optical band gap value is close tothe band gap of intrinsic ZnO powder and is in good agree-ment with the literature reports [49–52].

3.5. Zeta Potential Measurements. The change in zeta poten-tial (ζ) as a function of pH is illustrated in Figure 5. The iso-electric point (IEP) of AC-ZnO was found to be at a pH ofaround 6.8. These results suggest that the surface of theAC-ZnOmaterial is negatively charged at pH values of above6.8, whereas the surface possesses a positive charge below thepH of 6.8.

3.6. Thermogravimetric Analysis (TGA). Thermal stability ofthe synthesized catalyst, AC-ZnO, was studied by usingTGA analysis. The catalyst was found to be stable, andaround 2% of weight loss was recorded up to the temperatureof 450°C (Figure 6), and it can be clearly seen that theimpregnation decreases the carbon content and thus causesthe decrease in the weight loss.

In addition, the total weight loss of this ZnO-loadedcatalyst was found to be less than that of pure activated

2 4 6 8 10 12 14

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

pH

Zeta

pot

entia

l (m

V)

Figure 5: Zeta potential as a function of pH for the AC-ZnOmaterial.

100 200 300 400 500 600 700 800

88

90

92

94

96

98

100

Temperature (°C)

% w

eigh

t los

s

Figure 6: TGA analysis of the AC-ZnO material.

5International Journal of Photoenergy

carbon (AC) as illustrated in Figure S2 (3.2%). This lowweight loss further indicates the stability of the catalystagainst temperature.

3.7. Scanning Electron Microscopic Analysis (SEM). SEMstudies confirm the loading of ZnO on the activated carbonsupport, and Figure 7 illustrates the SEM image of theZnO-loaded materials. It can be seen that the activated sam-ple is in an irregular pattern with fine pores. In addition, ZnOparticulates are deposited on the surface and in the pores of

the activated carbon. A closer observation indicates theflake-like ZnO structure on the surface of activated carbon.

3.8. Fourier Transform Infrared Spectroscopic Analysis(FT-IR). FT-IR studies of AC-ZnO (Figure S3) indicatedthat the band at around 3470 cm−1 is due to the O-Hstretching vibration mode of hydroxyl functional groups[39]. The stretching at a wave number of 2920 cm-1 is due tothe C-H stretching, while the band visible near 2360 cm−1

corresponds to the C–O stretching vibration of the carbonmonoxide or carbon dioxide derivatives. The stretchingvibration band at around 1700 cm−1 is assigned to thecarbonyl C=O group, and the band at 1600 cm-1 is attributedto the sp2 character of C=C. The peak at around 1500 cm-1 isassigned to aromatic skeletal vibration. The bands between900 and 1300 cm-1 can be attributed to the C-OH groups.

1 um

1 um

1 um

100 nm

30.00 um 6.4 mm SE210.00 KX8.00 kV

30.00 um 6.4 mm SE25.00 KX8.00 kV

30.00 um 6.4 mm SE210.00 KX3.00 kV

30.00 um 6.4 mm SE226.00 KX3.00 kV

Figure 7: SEM image of the AC-ZnO material.

−20 0 20 40 60 80 100 1200.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

EV (photolysis)EV/(AC-ZnO)/UV

Time (minutes)

(C/C

0)

Dark

Figure 8: Plot of C/C0 vs. time for direct photolysis (□) and thedegradation of EV (■) in the presence of AC-ZnO under UVillumination.

Pure AC-ZnO0

2

4

6

8

10

12

14

TOC

(ppm

)

Sample name

Figure 9: TOC of EV (C0 = 20 ppm) before and after 120min. ofdegradation using AC-ZnO under UV-illumination.

6 International Journal of Photoenergy

The peaks appearing between 450 and 630 cm-1 are assignedto the Zn-oxygen (Zn–O) stretching mode [53, 54].

3.9. Photocatalytic Degradation of Ethyl Violet (EV). The sus-pension made with 25mg of the catalyst, AC-ZnO, and50mL of 20 ppm dye solution was first stirred for 30min. inthe dark, to attain an adsorption-desorption equilibrium. Itwas found that the adsorption-desorption equilibrium isattained within 30min. The amount of Ethyl Violet adsorbedafter 120min. was calculated to be qequilibrium = 16 96 mg/g.Then the reactor was illuminated. Similar experiments weredone without the catalyst for comparison purposes. Only dis-colouration was observed with the dye solution when thephotolysis was performed without the catalyst, whereas thedegradation occurred (the degradation profile is illustratedin Figure S4) when the catalyst was used. Figure 8illustrates the relative concentration (C/C0) of the remnantdye solution against irradiation time.

It can be seen that a reasonable adsorption was attainedin the dark and the concentration reached zero (completedegradation) after 60min. of irradiation in the presence of acatalyst with the rate constant of kAC−ZnO = 0 063 min-1.The solution without a catalyst reached an equilibrium after120min. of irradiation, and the rate constant of the directphotolysis was found to 0.0058min-1. These observationsclearly indicate the effectiveness of the photocatalyst.

In a reported work, Chen studied the degradation ofEthyl Violet (EV) dye using a ZnO nanoparticle (0.5 g/L)under UV illumination (365 nm). The initial concentrationof the dye chosen for their study was 50mg/L, and it wasfound that 99.9% of EV was removed after 5 h irradiation[1]. In another study, Chen with his coworkers examinedthe degradation of EV dye using TiO2 suspension under vis-ible light irradiation.

Photocatalytic degradation of EV dye mediated by TiO2under anaerobic condition was reported by Lee and Chen,

where they mainly focused on the degraded products andthe cleavage mechanism.

In another study, Wang et al. used a TiO2 catalyst dopedwith an upconversion luminescence agent for the degrada-tion of EV (initial concentration of 10mg/L), and they foundthat the degradation rate of Ethyl Violet in the presence of adoped rutile TiO2 photocatalyst reached 87.08% under 4 h ofvisible light irradiation, and it was observed that the rate ofdegradation was found to be higher than that of the undopedTiO2 material (35.42%) [55]. In comparison to all thesereported works, it can be clearly stated that our material ismore effective, since it can completely degrade the dye in60min. of irradiation.

Band gap excitation of AC-ZnO results in the promotionof electrons from the valence band to the conduction bandedge. These electrons can readily react with oxygenmolecules

−20 0 20 40 60 80 100 1200.0

0.2

0.4

0.6

0.8

1.0

Degradation

Ads

orpt

ion

Air-AC-ZnOIPA-AC-ZnON2-AC-ZnO

C/C

0

Time (minutes)

(a)

0 20 40 60 80 100 120

−8

−6

−4

−2

0

Air-AC-ZnOIPA-AC-ZnON2-AC-ZnO

Time (minutes)

1n C/C

0

(b)

Figure 10: Plot of (a) C/C0 vs. time under UV illumination with scavenging agents and (b) ln C/C0 vs. time.

0 20 40 60 80 100 1200

1 × 106

2 × 106

3 × 106

4 × 106

5 × 106

6 × 106

Inte

nsity

(a.u

.)

Time (minutes)

Figure 11: •OH trapping experiment over AC-ZnO under UVillumination.

7International Journal of Photoenergy

to produce reactive oxygen species (ROS), such as O2●¯,

●OOH, and ●OH [56]. These ROS then attack the dye mole-cule and destroy its auxochromic groups leading to destruc-tion of the ring structure. Equation (1) describes thephotocatalytic degradation process involving EV.

AC − ZnO hυ e− c b + h+ v b ,

e− + O2 → O2•− ,

O2•− +H+ → • OOH,

•OOH+O2•− + H+ → O2 + H2O2 ,

O2•− +H2O2 → •OH +OH− + O2,EV + ROS → photo‐degraded products

1

Although discolouration was observed during the photo-catalysis process, it is not an indication of the completeremoval of the dye from the aqueous solution. However, ashift in the prominent absorption band at λmax of 596 nmindicates the cleavage of the auxochromic group of the EVdye molecule [57, 58]. The decrease in the organic contentsduring the degradation process was further confirmed byTOC studies. Figure 9 represents the total organic contentsafter photocatalytic degradation of EV in comparison to theTOC of original dye solution used in this study. It can be seenthat the total organic carbon content present in the EV solu-tion decreases during the degradation and a 63% decrease inconcentration of EV dye was attained after 120min. of degra-dation. These results indicate that although the remnantsolution became colourless after degradation, there are some

organic residues existing in the resultant solution, which maybe the by-products formed during degradation.

3.10. Photocatalysis in the Presence of Scavenging Agents. Inorder to understand the role of ROS and identify the mostprominent ROS species, photocatalytic experiments werecarried out in the presence of scavenging agents. The impactof the different scavenging agents on the dye removal effi-ciencies was investigated with the catalyst prepared. Toinvestigate the role of oxygen (O2), N2 flow was used to dega-sify the suspension throughout the study and isopropyl alco-hol (IPA) was used as the ●OH trapping agent in thedegradation process of EV dye to provide more insight aboutthe role of ●OH radical. The obtained results for the twoscavenging agents are represented in Figure 10(a), and thevalues obtained for the apparent rate constant, kapp (min-1),are 0.014 and 0.010.

From the results, we can conclude that the rate of thereaction is very low, when these scavenging agents are used.Thus, the presence of dissolved oxygen plays an importantrole in degrading the dye molecules by providing the reactiveoxygen species, such as superoxide radicals and hydroxylradicals. Also, the results showed that the degradations obeypseudo-first-order kinetics with the R2 values of 0.986 (underN2 flow) and 0.997 (with IPA) and the apparent rate constant(kapp) was calculated from the plot of ln C/C0 vs. time(Figure 10(b)).

3.11. Photoluminescence (PL) Spectroscopic Studies. It isknown that hydroxyl radicals play an important role in thedegradation of organic pollutants. To shed more light on this,●OH trapping experiments were carried out. These radicalscan react with terephthalic acid (TPA) and form fluorescent

m/z = 456 m/z = 428

+2•OH

-H2O and CH3CHO

+ 4•OH

-2H2O and 2CH3CHO

C

+N(CH2CH3)2(H3CH2C)2N

C

+NH(CH2CH3)

NH(CH2CH3)

N(CH2CH3)2N(CH2CH3)2

(H3CH2C)2N

(H3CH2C)2N

C

+NH(CH2CH3)

NH(CH2CH3)

(H3CH2C)2N

(H3CH2C)2Nm/z = 400

C

+NH2

+NH2

N(CH2CH3)2

m/z = 400

C

m/z = 372

+6•OH -3H2O and 3CH3CHO

Scheme 1: The primary degraded products of EV dye.

8 International Journal of Photoenergy

2-hydroxyterephthalic acid (2-HTPA), and the formation of2-HTPA is proportional to the amount of ●OH formed.Figure 11 illustrates a plot of fluorescence intensity for2-HTPA at different times for the catalyst used in this study.

It can be seen from Figure 11 that the maximum photo-luminescence (PL) intensity of 5 × 106 (a.u.) was recordedafter 40min. of irradiation. This means that the generationof the •OH radicals by this system reaches its maximum at40min., and then the rate of formation started to decrease.This phenomenon is reflected in the rate of degradation ofEV, where a fast degradation is attained until 40min. of timeand the rate of degradation is found to be slow after 40min.(Figure 10(a)) of the degradation time. It is noteworthy tomention that 2-HTPA which is formed during the processcan be further degraded by •OH. Since the trapping agentcan itself be degraded, the formation of •OH radical seemsto decrease after 40min.

3.12. ESI-MS Analysis. The intermediates formed during thedegradation of EV dye was evaluated from the ESI-MS anal-ysis, and the structures of molecular fragments detected by

mass spectrometry are summarized in Schemes 1–3. Themass spectrum of pure EV dye solution shows two majorpeaks at m/z = 456 and 428 under our experimental condi-tions. The disappearance of the parent peak (m/z = 456)was achieved after 120min. of degradation. In addition, adecrease in the intensity (counts) of this major peak withtime and formation of several other peaks at lowerm/z valuesfurther validate the degradation of the EV dye molecule inthe presence of the catalyst, AC-ZnO, (Figure S5). On thebasis of these results, a general mechanism of photocatalyticdegradation of EV dye is proposed. The mechanismconsists of several steps that include (i) N-de-ethylation, (ii)destruction of the conjugated structure, and (iii) oxidativedegradation. The primary cleavage of the EV dye results inthe formation of peaks with m/z = 428, 400, and 372, whichare mainly due to the addition of ●OH radical and thesubsequent removal of water and acetaldehyde molecules,respectively, as indicated in Scheme 1.

The cleavage of the ring structure from the original mol-ecule (m/z = 456) leads to the secondary degraded productswith the m/z values of 325, 297, 269, and 241. This may be

m/z = 325

C

O

N(CH2CH3)2(H3CH2C)2N

+ 2•OH

-H2O and CH3CHO

C

O

NH(CH2CH3)(H3CH2C)2N m/z = 297

+ 2•OH

-H2O and CH3CHO

C

O

NH2(H3CH2C)2N

C

O

NH(CH3CH3)(H3CH2C)HNm/z = 269

C

+N(CH2CH3)2

N(CH3CH3)2

(H3CH2C)2N

+ • OH, O2

-C10H15NO

m/z = 269

+ 2•OH

-H2O and CH3CHO

+ 2•OH-H2O and CH3CHO

C

O

NH2(H3CH2C)HN

m/z = 241

m/z = 456

Scheme 2: The secondary degraded products of EV dye.

9International Journal of Photoenergy

due to the addition of ●OH radicals and the removal of waterand acetaldehyde molecules as illustrated in Scheme 2. Fur-ther cleavage of these degraded molecules results in theformation of secondary products with m/z values of 341,313, and 285. The small fragmented products, i.e., tertiaryproducts, detected in this study at m/z values of 95 and 74are phenol and diethylamine, respectively, as illustrated inScheme 3.

4. Conclusions

A sustainable and versatile photocatalyst, AC-ZnO, wasprepared by a facile method using Algerian olive-wastecakes as raw material for activated carbon. Impregnationmethod was utilized to load ZnO on the activated carbonsupport. Degradation of the Ethyl Violet (EV) dye wasevaluated with the prepared catalyst AC-ZnO, and thekinetic study suggests that the rate of the degradationobeys pseudo-first-order kinetics. The intermediate prod-ucts formed during the photocatalytic degradation of EVwere identified by using ESI-MS analysis, and a degrada-tion mechanism was proposed. The total organic contents(TOC) were found to decrease after 120min. of degrada-tion. Further, the scavenging experiments indicate that dis-solved oxygen is important to achieve faster and effectivedegradation, since this dissolved oxygen leads to the for-mation of reactive oxygen species, such as superoxideand hydroxyl radicals. Overall, this study exemplifies theusage of the Algerian olive waste for the preparation of

activated carbon and, thus, provides opportunity to reducethese wastes, as well as reduce the cost for importing acti-vated carbon to countries like Algeria. Further, modifyingthis activated carbon material using active oxide materials,such as TiO2 and ZnO, will open up the opportunity tointroduce cheaper catalysts to the market for environmen-tal remediation applications.

Data Availability

The data sets obtained during the research and the analysisare already available in the article and the supplementarydocument. However, if there are any information/data thatare needed, these may be obtained from the correspondingauthor on a reasonable request.

Conflicts of Interest

The authors declare that there is no conflict of interestregarding the publication of this paper.

Acknowledgments

Authors would like to acknowledge the National ScienceFoundation (CHE-1337707) for the financial support inpurchasing the SEM instrument and Dr. Aravind Baride,who assisted with the SEM analysis.

m/z = 325

C

O

N(CH2CH3)2(H3CH2C)2N

Oxidative degradation C

O

N+(H3CH2C)2N

CH2CH3

CH2CH2OHm/z = 341

+ 2•OH

-H2O and CH3CHO

C

O

HN+(H3CH2C)2NCH2CH2OHm/z = 313 m/z = 313

CO

N+(H3CH2C)HN

CH2CH3

CH2CH2OH

+ 2•OH

-H2OHO and CH3CHO

+ 2•OH

-H2O and CH3CHO

C

O

N+H2NCH2CH3

CH2CH2OH

C

O

HN+(H3CH2C)HNCH2CH2OH

m/z = 285 m/z = 285

+NH2(CH2CH3)2

m/z = 74

OH

m/z = 95

Scheme 3: The tertiary degraded products of EV dye.

10 International Journal of Photoenergy

Supplementary Materials

Supplementary 1. Scheme S1: different steps involved in thepreparation of the catalyst, AC-ZnO. Table S1: optimalinstrumental conditions for ESI-MS studies. Figure S1: pow-der X-ray diffraction patterns of blank activated carbon (AC).Figure S2: TGA of blank activated carbon (AC). Figure S3:FT-IR spectrum of AC-ZnO. Figure S4: absorption spectraof EV dye (after filtration) at various time intervals duringUV light irradiation for 120min. using AC-ZnO. Figure S5:mass spectrum (MS) of the by-products generated duringthe degradation of Ethyl Violet by the system (AC-ZnO/UV)at different times.

Supplementary 2. Graphical Abstract: the first two pictures ofthe graphical abstract explain how the oil waste was collectedfrom the site and the activated charcoal preparation process.Then the scheme illustrates the ZnO-loaded activated car-bon; the next photograph taken during the degradation pro-cess indicates the irradiation source and the photoreactorsetup. The final photograph illustrates the dye solution with-drawn in different time intervals. Disappearance of the col-our indicates the degradation of the dye material.

References

[1] C.-C. Chen, “Degradation pathways of ethyl violet by photo-catalytic reaction with ZnO dispersions,” Journal of MolecularCatalysis A: Chemical, vol. 264, no. 1-2, pp. 82–92, 2007.

[2] S. Chakrabarti and B. Dutta, “Photocatalytic degradation ofmodel textile dyes in wastewater using ZnO as semiconductorcatalyst,” Journal of Hazardous Materials, vol. 112, no. 3,pp. 269–278, 2004.

[3] G. Kumar, R. Kumar, S. W. Hwang, and A. Umar, “Photocat-alytic degradation of direct red-23 dye with ZnO nanoparti-cles,” Journal of Nanoscience and Nanotechnology, vol. 14,no. 9, pp. 7161–7166, 2014.

[4] S. Khezrianjoo and H. D. Revanasiddappa, “Photocatalyticdegradation of acid yellow 36 using zinc oxide photocatalystin aqueous media,” Journal of Catalysts, vol. 2013, Article ID582058, 6 pages, 2013.

[5] J. Kaur, S. Bansal, and S. Singhal, “Photocatalytic degradationof methyl orange using ZnO nanopowders synthesized viathermal decomposition of oxalate precursor method,” PhysicaB: Condensed Matter, vol. 416, no. 1, pp. 33–38, 2013.

[6] S. Rasalingam, C. M. Wu, and R. T. Koodali, “Modulationof pore sizes of titanium dioxide photocatalysts by a faciletemplate free hydrothermal synthesis method: implicationsfor photocatalytic degradation of rhodamine B,” ACSApplied Materials & Interfaces, vol. 7, no. 7, pp. 4368–4380, 2015.

[7] R. Ullah and J. Dutta, “Photocatalytic degradation of organicdyes with manganese-doped ZnO nanoparticles,” Journal ofHazardous Materials, vol. 156, no. 1–3, pp. 194–200, 2008.

[8] M. Vinayagam, S. Ramachandran, V. Ramya, and A. Sivasamy,“Photocatalytic degradation of orange G dye using ZnO/bio-mass activated carbon nanocomposite,” Journal of Environ-mental Chemical Engineering, vol. 6, no. 3, pp. 3726–3734,2018.

[9] X. Bai, C. Sun, D. Liu et al., “Photocatalytic degradation ofdeoxynivalenol using graphene/ZnO hybrids in aqueous

suspension,” Applied Catalysis B: Environmental, vol. 204,no. 1, pp. 11–20, 2017.

[10] K. Byrappa, A. K. Subramani, S. Ananda et al., “Impregnationof ZnO onto activated carbon under hydrothermal conditionsand its photocatalytic properties,” Journal of Materials Science,vol. 41, no. 5, pp. 1355–1362, 2006.

[11] T. Tsumura, N. Kojitani, H. Umemura, M. Toyoda, andM. Inagaki, “Composites between photoactive anatase-typeTiO2 and adsorptive carbon,” Applied Surface Science,vol. 196, no. 1–4, pp. 429–436, 2002.

[12] R. Baccar, J. Bouzid, M. Feki, and A. Montiel, “Preparation ofactivated carbon from Tunisian olive-waste cakes and itsapplication for adsorption of heavy metal ions,” Journal ofHazardous Materials, vol. 162, no. 2-3, pp. 1522–1529, 2009.

[13] K. Okada, N. Yamamoto, Y. Kameshima, and A. Yasumori,“Porous properties of activated carbons from waste newspa-per prepared by chemical and physical activation,” Journalof Colloid and Interface Science, vol. 262, no. 1, pp. 179–193, 2003.

[14] G. San Miguel, G. D. Fowler, and C. J. Sollars, “A study of thecharacteristics of activated carbons produced by steam andcarbon dioxide activation of waste tyre rubber,” Carbon,vol. 41, no. 5, pp. 1009–1016, 2003.

[15] Y. Guo and D. A. Rockstraw, “Activated carbons preparedfrom rice hull by one-step phosphoric acid activation,”Micro-porous and Mesoporous Materials, vol. 100, no. 1–3, pp. 12–19,2007.

[16] R. L. Tseng, S. K. Tseng, and F. C. Wu, “Preparation of highsurface area carbons from corncob with KOH etching plusCO2 gasification for the adsorption of dyes and phenols fromwater,” Colloids and Surfaces A: Physicochemical and Engineer-ing Aspects, vol. 279, no. 1–3, pp. 69–78, 2006.

[17] B. Karagozoglu, M. Tasdemir, E. Demirbas, and M. Kobya,“The adsorption of basic dye (Astrazon Blue FGRL) fromaqueous solutions onto sepiolite, fly ash and apricot shell acti-vated carbon: kinetic and equilibrium studies,” Journal of Haz-ardous Materials, vol. 147, no. 1-2, pp. 297–306, 2007.

[18] C. Bouchelta, M. S. Medjram, O. Bertrand, and J. P. Bellat,“Preparation and characterization of activated carbon fromdate stones by physical activation with steam,” Journal of Ana-lytical and Applied Pyrolysis, vol. 82, no. 1, pp. 70–77, 2008.

[19] I. A. W. Tan, A. L. Ahmad, and B. H. Hameed, “Adsorption ofbasic dye on high-surface-area activated carbon prepared fromcoconut husk: equilibrium, kinetic and thermodynamic stud-ies,” Journal of Hazardous Materials, vol. 154, no. 1–3,pp. 337–346, 2008.

[20] G. Cimino, R. M. Cappello, C. Caristi, and G. Toscano, “Char-acterization of carbons from olive cake by sorption of waste-water pollutants,” Chemosphere, vol. 61, no. 7, pp. 947–955,2005.

[21] A. Baçaoui, A. Yaacoubi, A. Dahbi et al., “Optimization of con-ditions for the preparation of activated carbons fromolive-waste cakes,” Carbon, vol. 39, no. 3, pp. 425–432, 2001.

[22] L. Louadj and A. Giuffré, “Analytical characteristics of olive oilproduced with three different processes in Algeria,” La RivistaItaliana Delle Sostanze Grasse, vol. 87, no. 3, pp. 186–195,2010.

[23] C. Moreno-Castilla, F. Carrasco-Marın, M. V. López-Ramón,and M. A. Alvarez-Merino, “Chemical and physical activationof olive-mill waste water to produce activated carbons,” Car-bon, vol. 39, no. 9, pp. 1415–1420, 2001.

11International Journal of Photoenergy

[24] F. Sellami, R. Jarboui, S. Hachicha, K. Medhioub, andE. Ammar, “Co-composting of oil exhausted olive-cake, poul-try manure and industrial residues of agro-food activity for soilamendment,” Bioresource Technology, vol. 99, no. 5, pp. 1177–1188, 2008.

[25] R. Selvasembian and B. P, “Utilization of unconventional lig-nocellulosic waste biomass for the biosorption of toxic triphe-nylmethane dye malachite green from aqueous solution,”International Journal of Phytoremediation, vol. 20, no. 6,pp. 624–633, 2018.

[26] W. Azmi, R. K. Sani, and U. C. Banerjee, “Biodegradation oftriphenylmethane dyes,” Enzyme and Microbial Technology,vol. 22, no. 3, pp. 185–191, 1998.

[27] R. Ahmad and P. K. Mondal, “Application of acid treatedalmond peel for removal and recovery of brilliant green fromindustrial wastewater by column operation,” Separation Sci-ence and Technology, vol. 44, no. 7, pp. 1638–1655, 2009.

[28] U. Shedbalkar, R. Dhanve, and J. Jadhav, “Biodegradation oftriphenylmethane dye cotton blue by Penicillium ochro-chloron MTCC 517,” Journal of Hazardous Materials,vol. 157, no. 2-3, pp. 472–479, 2008.

[29] A. Jasińska, S. Różalska, P. Bernat, K. Paraszkiewicz, andJ. Długoński, “Malachite green decolorization by non-basidiomycete filamentous fungi of Penicillium pinophilumand Myrothecium roridum,” International Biodeterioration& Biodegradation, vol. 73, pp. 33–40, 2012.

[30] W. Au, S. Pathak, C. J. Collie, and T. C. Hsu, “Cytogenetic tox-icity of gentian violet and crystal violet on mammalian cellsin vitro,” Mutation Research/Genetic Toxicology, vol. 58,no. 2-3, pp. 269–276, 1978.

[31] S. H. Lee and C. S. Choi, “Chemical activation of high sulfurpetroleum cokes by alkali metal compounds,” Fuel ProcessingTechnology, vol. 64, no. 1–3, pp. 141–153, 2000.

[32] A. Ahmadpour and D. D. Do, “The preparation of active car-bons from coal by chemical and physical activation,” Carbon,vol. 34, no. 4, pp. 471–479, 1996.

[33] P. Ehrburger, A. Addoun, F. Addoun, and J. B. Donnet, “Car-bonization of coals in the presence of alkaline hydroxides andcarbonates: formation of activated carbons,” Fuel, vol. 65,no. 10, pp. 1447–1449, 1986.

[34] N. Rie, N. Yoko, O. Naoto, and I. Michio, “Modification ofpore structure in activated carbons by heat treatment withthermoplastic resins,” New Carbon Materials, vol. 21, no. 4,pp. 289–296, 2006.

[35] Z. Hu, H. Guo, M. P. Srinivasan, and N. Yaming, “A simplemethod for developing mesoporosity in activated carbon,”Separation and Purification Technology, vol. 31, no. 1,pp. 47–52, 2003.

[36] A. N. Wennerberg and T. M. O'GradyUS Patent 4,082,694.

[37] H. Marsh, D. S. Yan, T. M. O'Grady, and A.Wennerberg, “For-mation of active carbons from cokes using potassium hydrox-ide,” Carbon, vol. 22, no. 6, pp. 603–611, 1984.

[38] G. G. Stavropoulos and A. A. Zabaniotou, “Production andcharacterization of activated carbons from olive-seed wasteresidue,” Microporous and Mesoporous Materials, vol. 82,no. 1-2, pp. 79–85, 2005.

[39] H. P. S. A. Khalil, M. Jawaid, P. Firoozian, U. Rashid, A. Islam,and H. M. Akil, “Activated carbon from various agriculturalwastes by chemical activation with KOH: preparation andcharacterization,” Journal of Biobased Materials and Bioe-nergy, vol. 7, no. 6, pp. 708–714, 2013.

[40] J. Jayachandiran, A. Raja, M. Arivanandhan, R. Jayavel, andD. Nedumaran, “A facile synthesis of hybrid nanocompos-ites of reduced graphene oxide/ZnO and its surface modifi-cation characteristics for ozone sensing,” Journal ofMaterials Science: Materials in Electronics, vol. 29, no. 4,pp. 3074–3086, 2018.

[41] D. M. Cunha, N. M. Ito, A. M. Xavier, J. T. Arantes, and F. L.Souza, “Zinc oxide flower-like synthesized under hydrother-mal conditions,” Thin Solid Films, vol. 537, no. 1, pp. 97–101, 2013.

[42] N. Bel Hadj Tahar, R. Bel Hadj Tahar, A. Ben Salah, andA. Savall, “Effects of individual layer thickness on the micro-structure and optoelectronic properties of sol–gel-derived zincoxide thin films,” Journal of the American Ceramic Society,vol. 91, no. 3, pp. 846–851, 2008.

[43] R. E. Marotti, P. Giorgi, G. Machado, and E. A. Dalchiele,“Crystallite size dependence of band gap energy for electrode-posited ZnO grown at different temperatures,” Solar EnergyMaterials & Solar Cells, vol. 90, no. 15, pp. 2356–2361, 2006.

[44] P. Bindu and S. Thomas, “Estimation of lattice strain in ZnOnanoparticles: X-ray peak profile analysis,” Journal of Theoret-ical and Applied Physics, vol. 8, no. 4, pp. 123–134, 2014.

[45] Y. H. Yang, B. Wang, and G. W. Yang, “Mechanisms of self-catalyst growth of agave-like zinc oxide nanostructures onamorphous carbons,” Crystal Growth & Design, vol. 7, no. 7,pp. 1242–1245, 2007.

[46] W. Han, L. Ren, X. Qi et al., “Synthesis of CdS/ZnO/graphenecomposite with high-efficiency photoelectrochemical activitiesunder solar radiation,” Applied Surface Science, vol. 299,pp. 12–18, 2014.

[47] X. Wang, X. Liang, Y. Wang et al., “Adsorption of copper (II)onto activated carbons from sewage sludge by microwaveinduced phosphoric acid and zinc chloride activation,” Desali-nation, vol. 278, no. 1–3, pp. 231–237, 2011.

[48] D. P. Joseph and C. Venkateswaran, “Bandgap engineering inZnO by doping with 3d transition metal ions,” Journal ofAtomic, Molecular, and Optical Physics, vol. 2011, article270540, 7 pages, 2011.

[49] D. Raoufi and T. Raoufi, “The effect of heat treatment on thephysical properties of sol–gel derived ZnO thin films,” AppliedSurface Science, vol. 255, no. 11, pp. 5812–5817, 2009.

[50] H. Hartnagel, A. L. Dawar, A. K. Jain, and C. Jagadish, Semi-conducting Transparent Thin Films, Institute of Physics Pub-lishing, 1995.

[51] J. I. Pankove, Optical Progress in Semiconductors, Dover publi-cation, New York, 1975.

[52] S. Rasalingam, H. S. Kibombo, C. M. Wu, R. Peng,J. Baltrusaitis, and R. T. Koodali, “Competitive role of struc-tural properties of titania–silica mixed oxides and a mecha-nistic study of the photocatalytic degradation of phenol,”Applied Catalysis B: Environmental, vol. 148-149, pp. 394–405, 2014.

[53] Y. Li and X. Liu, “Activated carbon/ZnO composites preparedusing hydrochars as intermediate and their electrochemicalperformance in supercapacitor,” Materials Chemistry andPhysics, vol. 148, no. 1-2, pp. 380–386, 2014.

[54] M. Ghaedi, A. Ansari, M. H. Habibi, and A. R. Asghari,“Removal of malachite green from aqueous solution by zincoxide nanoparticle loaded on activated carbon: kinetics andisotherm study,” Journal of Industrial and Engineering Chem-istry, vol. 20, no. 1, pp. 17–28, 2014.

12 International Journal of Photoenergy

[55] J. Wang, G. Zhang, Z. Zhang et al., “Investigation on photocat-alytic degradation of ethyl violet dyestuff using visible light inthe presence of ordinary rutile TiO2 catalyst doped withupconversion luminescence agent,” Water Research, vol. 40,no. 11, pp. 2143–2150, 2006.

[56] T. Wu, G. Liu, J. Zhao, H. Hidaka, and N. Serpone, “Photoas-sisted degradation of dye pollutants. V. Self-photosensitizedoxidative transformation of rhodamine B under visible lightirradiation in aqueous TiO2 dispersions,” The Journal of Phys-ical Chemistry B, vol. 102, no. 30, pp. 5845–5851, 1998.

[57] C. C. Chen, C. S. Lu, and Y. C. Chung, “Photocatalytic degra-dation of ethyl violet in aqueous solution mediated by TiO2suspensions,” Journal of Photochemistry and Photobiology A:Chemistry, vol. 181, no. 1, pp. 120–125, 2006.

[58] F. D. Mai, W. L. W. Lee, J. L. Chang, S. C. Liu, C. W. Wu, andC. C. Chen, “Fabrication of porous TiO2 film on Ti foil byhydrothermal process and Its photocatalytic efficiency andmechanisms with ethyl violet dye,” Journal of HazardousMaterials, vol. 177, no. 1–3, pp. 864–875, 2010.

13International Journal of Photoenergy

TribologyAdvances in

Hindawiwww.hindawi.com Volume 2018

Hindawiwww.hindawi.com Volume 2018

International Journal ofInternational Journal ofPhotoenergy

Hindawiwww.hindawi.com Volume 2018

Journal of

Chemistry

Hindawiwww.hindawi.com Volume 2018

Advances inPhysical Chemistry

Hindawiwww.hindawi.com

Analytical Methods in Chemistry

Journal of

Volume 2018

Bioinorganic Chemistry and ApplicationsHindawiwww.hindawi.com Volume 2018

SpectroscopyInternational Journal of

Hindawiwww.hindawi.com Volume 2018

Hindawi Publishing Corporation http://www.hindawi.com Volume 2013Hindawiwww.hindawi.com

The Scientific World Journal

Volume 2018

Medicinal ChemistryInternational Journal of

Hindawiwww.hindawi.com Volume 2018

NanotechnologyHindawiwww.hindawi.com Volume 2018

Journal of

Applied ChemistryJournal of

Hindawiwww.hindawi.com Volume 2018

Hindawiwww.hindawi.com Volume 2018

Biochemistry Research International

Hindawiwww.hindawi.com Volume 2018

Enzyme Research

Hindawiwww.hindawi.com Volume 2018

Journal of

SpectroscopyAnalytical ChemistryInternational Journal of

Hindawiwww.hindawi.com Volume 2018

MaterialsJournal of

Hindawiwww.hindawi.com Volume 2018

Hindawiwww.hindawi.com Volume 2018

BioMed Research International Electrochemistry

International Journal of

Hindawiwww.hindawi.com Volume 2018

Na

nom

ate

ria

ls

Hindawiwww.hindawi.com Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwww.hindawi.com