J O U R N A L O F E N V I R O N M E N T A L S C I E N C E S 2 6 ( 2 0 1 4 ) 2 3 6 2 – 2 3 6 8

Ava i l ab l e on l i ne a t www.sc i enced i r ec t . com

ScienceDirect

www. jou rna l s . e l sev i e r . com/ jou rna l -o f - env i r onmenta l - sc i ences

Photocatalytic degradation of endocrine disruptor Bisphenol-Ain the presence of prepared CexZn1 − xO nanocomposites underirradiation of sunlight

Kamaraj M.1,⁎, Ranjith K.S.2, Rajeshwari Sivaraj3,Rajendra Kumar R.T.2, Hasna Abdul Salam3

1. Department of Biotechnology, Dr.N.G.P. Arts and Science College, Coimbatore 641048, Tamil Nadu, India. E-mail: drkamarajm@gmail.com2. Advanced Materials and Devices Laboratory, Department of Physics, Bharathiar University, Coimbatore 641046, Tamil Nadu, India3. Department of Biotechnology, School of Life Sciences, Karpagam University, Coimbatore 641021, Tamil Nadu, India

A R T I C L E I N F O

⁎ Corresponding author. E-mail: drkamarajm@

http://dx.doi.org/10.1016/j.jes.2014.09.0221001-0742/© 2014 The Research Center for Ec

A B S T R A C T

Article history:Received 29 December 2013Revised 30 June 2014Accepted 2 July 2014Available online 29 September 2014

Photocatalytic degradation of Bisphenol A (BPA), a representative endocrine disruptorchemical, was carried out under irradiation of sunlight in the presence of CexZn1 − xOnanophotocatalyst. Cerium (Ce) ions were successfully incorporated into the bulk latticeof ZnO by simple co-precipitation process. The CexZn1 − xO composite nanostructuresexhibited higher photocatalytic efficiency than pure ZnO in the degradation of BPA undersunlight irradiation and nearly complete mineralization of BPA was achieved. Thedegradation rate was strongly dependent on factors such as the size and structure ofcatalyst, doping material concentration, BPA concentration, catalyst load, irradiation timeand pH levels. This work suggested that the CexZn1 − xO assisted photocatalytic degradationis a versatile, economic, environmentally benign and efficient method for BPA removal inthe aqueous environment.© 2014 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences.

Published by Elsevier B.V.

Keywords:Bisphenol A (BPA)ZnOCexZn1 − xOSunlightCo-precipitationCerium

Introduction

Widevarieties of toxic organic contaminants from industrial effluentsoften pose the impetus for fundamental and applied research intoenvironmental areas (Shrivastava, 2010). Bisphenol A (BPA), commonname for 2,2-bis(4-hydroxylphenyl)-propane, is widely used as a rawmaterial for the production of polycarbonates, epoxy resins andvarious consumer products such as water bottles, medical devices,beverages, compact disks, food can linings, thermal paper, safetyhelmets, plastic windows, car parts, adhesives, protective coatings,powder paints and electronic devices (Staples et al., 1998; Kang et al.,2003). It is an endocrine disruptor that is released to the environmentduringmanufacturing process or by leaching from the final consumerproducts (Kang et al., 2007).

gmail.com (M. Kamaraj)

o-Environmental Science

Various treatment techniques have been developed for BPAremoval by using physical (Zeng et al., 2006), chemical (Fukahori etal., 2003) and biological procedures (Scully et al., 2006). In compar-ison to other treatments, photocatalytic degradation incorporatedwith light irradiation is of great importance owing to the ability tomineralize BPA (Tao et al., 2011). In recent years, ZnO has attractedmuch attention in degradation of various pollutants due to its highphotosensitivity (Ohtomo et al., 1999). ZnO has wide band gap(3.37 eV), large excitation binding energy (60 MeV) and low thresh-old power for optical pumping and is thus considered a low costalternative photocatalyst to TiO2 for degradation of organic com-pounds in aqueous solution (Daneshvar et al., 2004; Chen, 2007).

Various methods are used to prepare ZnO nanoparticles,co-precipitation being one of them (Shen et al., 2008). It is a synthetic

.

s, Chinese Academy of Sciences. Published by Elsevier B.V.

2363J O U R N A L O F E N V I R O N M E N T A L S C I E N C E S 2 6 ( 2 0 1 4 ) 2 3 6 2 – 2 3 6 8

method where particle size can be controlled easily at low processtemperature (Chauhan et al., 2012). Excellent photo catalytic activityof ZnO for liquid pollutants has been reported (Li et al., 2010; Habibiand Askari, 2011), but little is known for degradation of volatileorganic compounds (Liaoet al., 2012). Generation and recombinationof photo induced electrons and holes are critical in photocatalysis.Thus, doping with other metals improves the photochemicalperformance of semiconductor materials (Lei et al., 2009).

In this study, cerium (Ce)was chosen as themetal dopant as Ce2+

ions create an impurity state below the conduction band (CB) edge ofsemiconductors (Bubendorff et al., 2006). CeO2 has a band gap ofabout 3 eV and may be an ideal material for visible light-emittingphosphors in display, high-power laser, and light-emitting diode(Lang et al., 2010; Jung et al., 2012). Sunlight is an abundantlyavailable natural energy source, which can be utilized for irradiation(Nagaraja et al., 2012). Although cerium-doped TiO2 or CeO2/TiO2

composites have been reported in literature (Lamrani et al., 2007;Jung et al., 2012), Ce-doped ZnO nanocomposites' synthesis byco-precipitation method employed in this study, is a potential newapproach for the development of an efficient photocatalyst for BPAdegradation under sunlight irradiation.

1. Materials and methods

1.1. Chemicals and materials

Cerium nitrate (Ce(NO3)3·6H2O), hexamine (C6H12N4), zincnitrate hexahydrate (Zn(NO3)2·6H2O) and solution ammonia 30%of analytical grade were purchased from HiMedia LaboratoriesPvt Ltd, India. All solutions were prepared with distilledwater (Nihon Millipore, Yonezawa, Japan). Bisphenol A(GC grade > 99%) was purchased from Sigma-Aldrich (India).

1.2. Catalysts preparation and characterization

Ce-doped ZnO nanostructures were prepared by a simpleco-precipitation method. In typical synthesis of ZnO nanostruc-tures, 125 mmol/L of Zn(NO3)4·6H2O was dissolved in doubledistilled water and stirred for 5 min. Equal mole of hexaminewas added drop wise in the prepared Zn(NO3)4·6H2O precursorand stirred vigorously for 5 min. For preparing CexZn1 − xOnanostructures, different ratios of cerium nitrate (X = 0.03, 0.06,0.09) were taken with the Zn(NO3)4·6H2O precursor anddissolved in double distilled water under continuousstirring for 5 min. For controlling Zn(OH)2 formation, pHwas maintained at 9 using aqueous ammonia solution andthe growth precursor was maintained at 95°C for 3 hr. Afterbeing cooled to room temperature naturally, the precipi-tate, i.e., CexZn1 − xO, was collected by centrifugation,washed with deionized water and ethanol several timesand dried at 150°C. Based on doping concentration (3%, 6% and9%), samples were named as ZnO·Ce1, ZnO·Ce2 and ZnO·Ce3respectively.

The crystalline structure, phase, purity and size ofthe particles were determined by X-ray diffraction (XRD)using X-ray diffractometer (D8 Advance, Bruker, Karlsruhe,Germany) (SEIFERT PTS 3003). Shape, size and microstruc-tures of the particles were examined using scanningelectron microscopy (ZEISS, Oberkochen, Germany) (SEM)(Model JSM 6390LV, JOEL, USA) and TEM images takenusing Transmission scanning electron microscopy (JEOL

JEM 2100, Peabody, USA). Optical properties were mea-sured by UV–Vis spectrophotometer (JASCO, Easton, USA)(model UV2450—Shimadzu, Japan) and Photoluminescence (PL)spectra recorded on a Photoluminescence spectrophotometer(Perkin-Elmer LS-55, Massachusetts, USA). Fourier transforminfrared (FTIR) spectra of the sample were analyzed using FTIRSpectrophoto meter (Avatar 370 spectrometer, Thermo NicoletCorporation, Madison, USA).

1.3. Evaluation of photocatalytic degradation of BPA

The photo catalytic degradation of BPA was carried out withfour different ratios of Ce-doped ZnO nanostructures. Photo-catalytic experiments were performed under sunlight atambient temperature. The effect of the initial concentrationof catalyst was evaluated by varying the catalyst concentra-tion (10, 20, 30 and 40 mg) and BPA concentration (10, 20and 30 mg/L). The effect of time varied between 1–8 hr. Theeffect of pH was investigated through pH adjustment byusing HCl/NaOH in BPA solution. A blank study was carriedout in the presence of sunlight without any catalyst. Aftertreatment, particles and BPA solution were separated andcentrifuged at 3000 r/min for 5 min. The concentration of BPAwas determined by measuring the absorption intensity at itsmaximum absorbance wavelength of 276 nm, by using aUV–Vis spectrophotometer. The particle reusability capacitywas analyzed by using thematerial for several photocatalyticexperiments. All experiments were done in triplicates andthe data were analyzed using Origin Pro 7.5 SRO software(Origin Lab Corporation, Northampton, USA).

2. Results and discussion

2.1. XRD analysis of catalysts

Different mole presentable variations of Ce-doped ZnO nano-structures were synthesized by the simple co-precipitationmethod. Based on this, particles were assigned as ZnO,ZnO·Ce1, ZnO·Ce2 and ZnO·Ce3, respectively. The powderX-ray diffraction patterns of the samples were obtained asshown in Fig. 1. The peaks were indexed and it showedhexagonal phase of zinc oxide when compared with thestandard diffraction peaks of JCPDS card No. 89-0511 (Shim etal., 2001). The peaks located at angles (2θ) of 31.9°, 34.6° and36.4° are attributed to (100), (002) and (101) planes of ZnO. Peakshift towards lower angle clearly indicated that the Ce atomshave successfully entered into the ZnO lattices. In a lowconcentration of impurity incorporation (Ce ions), Ce atomreplaced few sites in the ZnO crystal structures and the peakcorresponding to Ce was absent in XRD spectrum of ZnO·Ce1.Increasing the concentration of Ce(NO3)3·6H2O leads to theformation of more number of Ce ions in the ZnO crystalstructure. In higher concentrations of Ce doping, XRD spectrumconfirmed the formation of CeO2 along with the ZnO crystalstructures and also clearly confirmed the formation of ZnO–CeO2 nanocomposites. The grain size for the peak (100) wascalculated using the Debye–Scherrer formula (Anandan andMiyauchi, 2012) as 40.31, 10.35, 11.2 and 12.05 nm for ZnO,ZnO·Ce1, ZnO·Ce2 and ZnO·Ce3, respectively, which was a

20 30 40 50 60 70 80

30 40 50 60 70

30 40 50 60 70

30 40 50 60 70

2θ (degree)

ZnO

ZnO.Ce1

ZnO.Ce2

ZnO.Ce3

Ce

Ce (110

)

(102

)

(101

)(0

02)

(100

)*

*In

tens

ity (a

.u.)

Fig. 1 – XRD pattern of the CexZn1 − xO nanostructures.

2364 J O U R N A L O F E N V I R O N M E N T A L S C I E N C E S 2 6 ( 2 0 1 4 ) 2 3 6 2 – 2 3 6 8

result of drastic reduction in the crystalline size of the Ce dopedZnO samples. Hence, Ce incorporation leads to an expansion ofthe ZnO lattice. Fig. 2 shows the variation of the hexagonallattice parameters with Ce doping. The lattice parameters ‘c’and ‘a’ increase on Ce doping and become almost constant forall doped samples. The lattice constant for the hexagonalstructure is determined by Eq. (1):

1d2

¼ 43

h2 þ hk þ k2� �

a2

0@

1Aþ l2

c2ð1Þ

where, d is lattice spacing, a and c are dimensions of the crystal,and h, k, and l aremiller indices of a particular diffraction plane.

2.2. SEM and TEM analyses of catalysts

The SEM image of ZnO (Fig. 3a1) showed flower morphologyhaving a size around ca, 2 μm. On inducing Ce as dopant,the flower-like morphology started to detract, and with anincrease in the doping, the flower morphology completelydetracted to form cluster of nanoparticle bunches with thesize of 100 nm due to the formation of small CeO2 crystalliteswhich disturbed the formation of isotropic ZnO nanostructures.The formation of Ce ions on the ZnO crystal structure, finallyyielded CeZnO nanocomposite structures (Fig. 3a2, a3). TEM

ZnO ZnO.Ce1

0.512

0.514

0.516

0.518

0.520

LaLa

Latti

ce c

onst

ant a

(nm

)

Fig. 2 – Variation of the hexagonal lattice parameters (a and

images (Fig. 3b1, b4), showed size reduction and decayed flowermorphology as Ce doping material increased. The sizes of theparticles were reduced up to the range of 20 nm on increasingthe Ce impurity concentration on the ZnO sites. Changes insurface and electronic properties provide an opportunity tocontrol catalytic activity and selectivity (Bell, 2003). Influence ofCe2+ ions in the ZnO crystalmay be responsible for the observedmorphology and size reduction frommicrometer to nanometer.

2.3. UV and PL analyses of catalysts

The UV–Vis spectra (200–800 nm) of each Ce-induced ZnOnanostructures were recorded and the absorbance at selectedwavelengths registered (Fig. 4). Due to incorporation of Cein ZnO, there was a blue shift when compared with ZnO. Athigher doping concentration of Ce, peak reduced in sharpnessand became blunt due to the formation of CeO2/ZnO compos-ite nature. Absorption spectrum appeared in the visible rangedue to the formation of defect states in Ce ions doped ZnOnanostructures.

Photoluminescence (PL) spectra of ZnO and Ce-doped ZnOnanostructures were taken at the excitation wavelength of350 nm (Fig. 5). Generally, ZnO shows four PL emissions(Ghosh et al., 2009) and in this study also, four emission peakswere observed. Sharp peak located at around 395 nm corre-sponds to the ultraviolet region caused by the recombinationof free exciton (Djurišić and Leung, 2006). The broad visibleemission band around 410–500 nm from pure ZnO nanoparti-cles can be attributed to a transition of a photo-generatedelectron from the conduction band to a deeply trapped holes(Van Dijken et al., 2000). Peak located at 468 nm (blue emission)might be attributed to intrinsic defects such as oxygen and zincinterstitials in ZnO (Umar et al., 2006). Broad peak located at560 nmcorresponded to green emission caused by the radiativerecombination of a photo-generated hole with an electronoccupying the oxygen vacancy (Vanheusden et al., 1996). Thechange in peak shift of excitonic emission of CeZnO wasan evidence for Ce incorporated into the ZnO lattice. Oncomparing the PL spectrum of ZnO with CeO2/ZnO composite,free excitonic emission was sharply suppressed, while oxygendefect green emission band was sharply enhanced. Broadeningand change in the peak position of green emission can be

ZnO.Ce2 ZnO.Ce3

ttice constant 'a' (nm)ttice constant 'c' (nm)

0.317

0.318

0.319

0.320

0.321

0.322

0.323

0.324

0.325

0.326

Latti

ce c

onst

ant c

(nm

)

c) with Ce concentration for CexZn1 − xO nanostructures.

a1 a2

a3

b1 b2

b3 b4

a4

Fig. 3 – SEM images (a) and TEM images (b) of the CexZn1 − xO nanocatalysts (1) ZnO, (2) ZnO·Ce1, (3) ZnO·Ce2, and (4) ZnO·Ce3.

2365J O U R N A L O F E N V I R O N M E N T A L S C I E N C E S 2 6 ( 2 0 1 4 ) 2 3 6 2 – 2 3 6 8

attributed to Ce dopant introduced into the ZnO layer becausein nanocrystallites, the deformation potential influences shortrange interaction (Bae et al., 2011).

2.4. Photocatalytic degradation of BPA

Photocatalytic activity of synthesized Ce-induced ZnO nanostruc-tures was evaluated by measuring the degradation of BPA.Experimentswereperformedunder sunlightduringsummerseasonbetween 8 am and 4 pm during which fluctuation in the solarintensity is minimum (Nagaraja et al., 2012). The effect of initialparticle concentration and BPA concentrationwas studied (Table 1).Maximum degradation was measured as 50% ZnO, 98% ZnO·Ce1,84%ZnO·Ce2, and70%ZnO·Ce3 forBPA (10 ppm)at8 hr. In thesamecondition, only 3.4% degradation was observed in control samples.

The reduction in the rate was constant when the catalystconcentration was increased above 40 mg/50 mL, which maybe due to light scattering and reduction in light penetration

through solution. When the catalysts reached higher concen-tration, reaction was dominated by deactivation of activatedmolecules by collision with ground state molecules (Nagaveniet al., 2004; Toor et al., 2006). Number of studies has shownthat the photocatalytic activity initially increased with catalystloading and then decreased at high dosage because of lightscattering and screening effects (Chen, 2007; Ahmed et al.,2011). When concentration of BPA increased, the solutionbecomesmore intense and the path length of photons enteringthe solution decreases and only few photons reach the catalyticsurface (Toor et al., 2006). It has been reported that the removalefficiency decreased from 98% to 67% with further increase inBPA concentration to 0.44 mmol/L (Tsai et al., 2009). At highconcentration the available OHU− radicals are inadequate fordegradation of pollutants, so the degradation rate decreases asthe pollutant concentration increases (Bahnemann et al., 2007).

Ce-doped ZnO (ZnO·Ce1) nanocatalysts showed better deg-radation of BPA compared with ZnO under sunlight. During

Table 1 – Effect of catalyst load and BPA concentration inphotocatalytic degradation.

Catalyst BPA degradation (%)

Catalyst load(mg/50 mL)

BPA concentration

10 mg/L 20 mg/L 30 mg/L

Control – 3.4 2.1 1.3ZnO 10 7.8 6.11 5.6

20 18.89 11.24 9.630 49.31 37.93 28.2940 49.82 38.02 29.30

ZnO·Ce1 10 25 19..24 16.6620 51 34.12 27.4330 97.03 67.03 35.9440 97.79 67.88 36.17

ZnO·Ce2 10 19 13.32 10.7420 40.42 25.57 20.3630 74.98 40.63 33.3040 84.1 40.85 33.96

ZnO·Ce3 10 16 12.28 9.2320 35.52 22.40 18.4830 55.03 32.93 30.3640 69.8 33.01 31.66

400 450 500 550 600 650

Oxygen defects

Zn In

tere

stia

ls

ZnO.Ce3

ZnO.Ce2

ZnO

ZnO.Ce1

Wavelength (nm)

PL in

tens

ity

Fig. 5 – Photoluminescence (PL) spectra of CexZn1 − xOnanocatalysts.

300 400 500 600 700 800

ZnO. Ce2

ZnO. Ce1

ZnO. Ce3ZnO

Wavelength (nm)

Abs

orba

nce

(a.u

.)

Fig. 4 – UV–Vis absorption spectrum of CexZn1 − xOnanocatalysts.

2366 J O U R N A L O F E N V I R O N M E N T A L S C I E N C E S 2 6 ( 2 0 1 4 ) 2 3 6 2 – 2 3 6 8

photocatalysis, the adsorption of photon by zinc oxide leadsto the promotion of an electron from the valence band to theconduction band and produce electron–hole pair (Prevot et al.,1999). These holes and electrons migrate to the surface andpromote interfacial oxidation and reduction reactions withthe substrate adsorbed on the surface of the semiconductoroxide. The separatemechanisms of BPA degradation during thephotocatalytic degradation or ozonizationhave beenpreviouslyreported (Gultekin and Ince, 2007).

Photocatalytic degradation of BPA at different time intervalswas examined under sunlight and it increased from 1 hr to 8 hrin all the four catalysts (Fig. 6); it is probably due to electron–hole formation in the photochemical reaction, which ismainly dependent on the light intensity to initiate the rateof photocatalyst (Cassano and Alfano, 2000). The catalystabsorbs more photons and produces more electron–holepairs in the catalyst surface when absorbing more photos,which increases the hydroxyl radicals' concentration andconsequently increases the degradation rate (Ahmed et al.,2011). The effect of light intensity on the solar photocatalyticdegradation of BPA in water with TiO2 on sunny and cloudydays has been investigated (Kaneco et al., 2004). The UVsource is expensive and hazardous while other light sourceslike tungsten light and mercury light which requires electricityare not cost-effective options. Therefore, the present studyhighlighted cheap photo energy (sunlight) as a potential naturalenergy source for irradiation of catalyst.

Polluted water has wide range of pH values based on theirorigin, and pH plays a major role in the generation of hydroxylradicals. Thus, understanding the effect of pH in the BPAdegradation by Ce-induced ZnO catalysts was necessary. In thepresent study, degradation efficiencywas observed in the orderas follows: pH unadjusted (6.5) > pH 5 > pH 9 > pH 3 > pH 11for BPA (10 mg/L) with the catalyst (30 mg/50 mL) undersunlight (Fig. 7). Highest degradation was obtained in pH 6.5,which subsequently reduced in high alkaline condition for allfour catalysts. Similar pH influence on BPA degradation byCN–TiO2 under white LED irradiation has been previouslyobserved (Wang and Lim, 2010). Kaneco et al (2004) have reportedthat, TiO2 nanostructure exhibited better photodegradationefficiency in the alkalinemedium (pH = 10) due to the generationof dominant oxidizing species (hydroxyl free radical) in the

photocatalytic process. But in the current study, betterphotodegradation efficiency was obtained near the neutralpH of medium and consequently, pH 6.5 was selected foroptimal experimental conditions, to avoid the unnecessarychemical treatment including neutralization process.

The reusable catalyst activity was performed for 10 cyclesfor un-doped ZnO and CexZn1 − xO nanostructures. Reusablecapacity of the catalysts was similar up to 8 cycles, and thenit decreased from 5% to 15%. CexZn1 − xO nanostructuresshowed maximum reusable efficiency compared to un-dopedZnO. Adsorption of pollutant molecules on the surface of thenanostructures during the photocatalytic experiment maybe the reason for the decrease in degradation efficiency onincreasing the number of recycling times.

Photocatalytic ability of ZnO nanoparticlesmay be affected bysurface area of particles, high carrier generation and the presenceof dopant or foreign particle in the sample. Increase in thecharge separation efficiency enhances the formation of both freeradicals and active oxygen species (Kato et al., 2005). Most of the

0 1 2 3 4 5 6 7 80

10

20

30

40

50

60

70

80

90

100D

egra

datio

n ef

ficie

ncy

(%)

Time (hr)

ControlZnOZnO.Ce1ZnO.Ce2ZnO.Ce3

Fig. 6 – Effect of time in photocatalytic degradation of BPAusing CexZn1 − xO nanostructures under sunlight.

2367J O U R N A L O F E N V I R O N M E N T A L S C I E N C E S 2 6 ( 2 0 1 4 ) 2 3 6 2 – 2 3 6 8

semiconductors have poor activity when used alone, but thepresence of a metal on the semiconductor markedly increasestheir efficiency. The role of the loaded material is to trap andsubsequently transfer photo excited electron onto surface, thusdecreasing the recombination of hole–electron pairs (Mirkhaniet al., 2009). In the present study, order of degradation efficiencywas observed as ZnO·Ce1 > ZnO·Ce2 > ZnO·Ce3 > ZnO. Structur-al studies clearly indicate that ZnO·Ce2 and ZnO·Ce3 were inCeO2/ZnOcomposite naturewhich reduced the activity species incatalytic degradation. In all conditions used in the study, betterdegradation rates were observed in ZnO·Ce1 (Ce doped ZnO)when compared with ZnO alone, possibly because of Ce beingused as a loadingmaterial to enhance the high electricalmobilityto the surface anddoped ions canalso act as charge trapping sitesthat may reduce electron–hole recombination which enhancesthe degradation efficiency.

3. Conclusions

ZnO and three different concentrations of Ce-doped ZnOnanocompositeswere synthesized via co-precipitationmethod.Prepared catalysts were characterized by various techniques

2 3 4 5 6 7 8 9 10 11 120.00.51.01.52.02.53.0

102030405060708090

100

Deg

rada

tion

effic

ienc

y (%

)

pH of the BPA solution

ControlZnOZnO.Ce1ZnO.Ce2ZnO.Ce3

Fig. 7 – Effect of pH in photocatalytic degradation of BPAusing CexZn1 − xO nanostructures under sunlight.

like XRD, SEM, TEM, UV and PL analyses. Ce-doped ZnOcatalysts showed enhanced efficiency for photocatalyticdegradation of BPA in comparison with pure ZnO catalysts.The degradation rate was strongly affected by several majorfactors, such as BPA concentration, catalyst load, exposuretime andpHvalue. Furthermore, nearly complete removal of BPAcan be achieved with Ce-doped ZnO (ZnO·Ce1) nanocatalystsbecause of its higher electron mobility and surface carrierdefects than ZnO catalysts. It can be concluded that CexZn1 − xOnanocomposite is a highly active photo catalyst for the photodegradation of BPA inwater under irradiation of sunlight,whichmight have a potential application in waste water treatment.

Acknowledgments

We are thankful to Advanced Materials and Devices Laboratory,Department of Physics, Bharathiar University, Coimbatore, TamilNadu, India and Karpagam University, Coimbatore, Tamil Nadu,India, for providing the necessary lab facilities for this work.

R E F E R E N C E S

Ahmed, S., Rasul, M.G., Martens, W.N., Brown, R., Hashib, M.A.,2011. Advances in heterogeneous photocatalytic degradationof phenols and dyes in wastewater: a review. Water Air SoilPollut. 215 (1–4), 1–35.

Anandan, S., Miyauchi, M., 2012. Improved photocatalytic efficiencyof a WO3 system by an efficient visible-light induced holetransfer. Chem. Commun. 48 (36), 4323–4325.

Bae, J.S., Won, M.S., Yoon, J.H., Lee, B.S., Pak, E.S., Seo, H.J., et al.,2011. Preparation and characterization of Ce doped ZnOnanofibers by an electrospinning method. J. Anal. Sci. Technol.2 (1), 1–6.

Bahnemann, W., Muneer, M., Haque, M.M., 2007. Titaniumdioxide-mediated photocatalysed degradation of few selectedorganic pollutants in aqueous suspensions. Catal. Today 124(3–4), 133–148.

Bell, A.T., 2003. The impact of nanoscience on heterogeneouscatalysis. Science 299 (5613), 1688–1691.

Bubendorff, J.L., Ebothe, J., El Hichou, A., Dounia, R., Addou,M., 2006.Luminescent spectroscopy and imaging of textured sprayedEr-doped ZnO films in the near ultraviolet and visible regions. J.Appl. Phys. 100 (1) (014505-014505-7).

Cassano, A.E., Alfano, O.M., 2000. Reaction engineering ofsuspended solid heterogeneous photocatalytic reactors. Catal.Today 58 (2–3), 167–197.

Chauhan, C., Kumar, A., Chaudhary, R.P., 2012. Structures and opticalproperties of Zn1 − xNixOnanoparticles by coprecipitationmethod.Res. Chem. Intermed. 38 (7), 1483–1493.

Chen, C.C., 2007. Degradation pathways of ethyl violet byphotocatalytic reaction with ZnO dispersions. J. Mol. Catal.A Chem. 264 (1–2), 82–92.

Daneshvar, N., Salari, D., Khataee, A.R., 2004. Photocatalyticdegradation of azo dye acid red 14 in water on ZnO as analternative catalyst to TiO2. J. Photochem. Photobiol. A 162(2–3), 317–322.

Djurišić, A.B., Leung, Y.H., 2006. Optical properties of ZnOnanostructures. Small 2 (8–9), 944–961.

Fukahori, S., Ichiura, H., Kitaoka, T., Tanaka, H., 2003. Capturing ofbisphenol A photodecomposition intermediates by compositeTiO2–zeolite sheets. Appl. Catal. B Environ. 46 (3), 453–462.

2368 J O U R N A L O F E N V I R O N M E N T A L S C I E N C E S 2 6 ( 2 0 1 4 ) 2 3 6 2 – 2 3 6 8

Ghosh, A., Deshpande, N.G., Gudage, Y.G., Joshi, R.A., Sagade, A.A.,Phase, D.M., et al., 2009. Effect of annealing on structural andoptical properties of zinc oxide thin film deposited bysuccessive ionic layer adsorption and reaction technique. J.Alloys Compd. 469 (1), 56–60.

Gultekin, I., Ince, N.H., 2007. Synthetic endocrine disruptors in theenvironment and water remediation by advanced oxidationprocesses. J. Environ. Manag. 85 (4), 816–832.

Habibi, M.H., Askari, E., 2011. The effect of operational parameterson the photocatalytic degradation of C.I. Reactive Yellow 86textile dye using manganese zinc oxide nanocomposite thinfilms. J. Adv. Oxid. Technol. 14 (2), 190–195.

Jung, Y., Noh, B.Y., Lee, Y.S., Baek, S.H., Kim, J.H., Park, I.K., 2012.Visible emission from Ce-doped ZnO nanorods grown byhydrothermal method without a post thermal annealingprocess. Nanoscale Res. Lett. 7 (1), 43–48.

Kaneco, S., Rahman, M.A., Suzuki, T., Katsumata, H., Ohta, K., 2004.Optimization of solar photocatalytic degradation conditions ofbisphenol A in water using titanium dioxide. J. Photochem.Photobiol. A Chem. 163 (3), 419–424.

Kang, J.H., Asai, D., Katayama, Y., 2007. Bisphenol A in the aquaticenvironment and its endocrine-disruptive effects on aquaticorganisms. Crit. Rev. Toxicol. 37 (7), 607–625.

Kang, J.H., Kito, K., Kondo, F., 2003. Factors influencing themigration of bisphenol-A from cans. J. Food Prot. 66 (8),1444–1447.

Kato, S., Hirano, Y., Iwata, M., Sano, T., Takeuchi, K., Matsuzawz, S.,2005. Photocatalytic degradation of gaseous sulphur compoundsby silver-deposited titanium dioxide. Appl. Catal. B Environ. 57(2), 109–115.

Lamrani, M.A., Addou, M., Soofiani, Z., Sahraoui, B., Ebothé, J., ElHichou, A., et al., 2007. Cathodoluminescent and nonlinearoptical properties of undoped and erbiumdopednanostructuredZnO films deposited by spray pyrolysis. Opt. Commun. 277 (1),196–201.

Lang, J., Han, Q., Yang, J., Li, C., Li, X., Yang, L., et al., 2010.Fabrication and optical properties of Ce-doped ZnO nanorods.J. Appl. Phys. 107 (7) (074302-074302-4).

Lei, Y.Z., Zhao, G.H., Liu, M.C., Zhang, Z.N., Tong, X.L., Cao, T.C.,2009. Fabrication, characterization, and photoelectrocatalyticapplication of ZnO nanorods grafted on vertically aligned TiO2

nanotubes. J. Phys. Chem. C 113 (44), 19067–19076.Li, Y., Xie, Z.W., Hu, X.L., Shen, G.F., Zhou, X., Xiang, Y., et al., 2010.

Comparison of dye photodegradation and its coupling withlight-to-electricity conversion over TiO2 and ZnO. Langmuir 26(1), 591–597.

Liao, Y.C., Xie, C.S., Liu, Y., Chen, H., Li, H.Y., Wu, J., 2012.Comparison on photocatalytic degradation of gaseousformaldehyde by TiO2, ZnO and their composite. Ceram. Int. 38(6), 4437–4444.

Mirkhani, V., Tangestaninejad, S., Moghadam, M., Habibi, M.H.,Roastami-Vartooni, A., 2009. Photocatalytic degradation of azodyes catalyzed by Ag doped TiO2 photocatalyst. J. Iran. Chem.Soc. 6 (3), 578–587.

Nagaraja, R., Nagaraju, K., Girija, C.R., Nagabhushana, B.M., 2012.Photocatalytic degradation of Rhodamine B dye under UV/solarlight using ZnO nanopowder synthesized by solutioncombustion route. Powder Technol. 215–216, 91–97.

Nagaveni, K., Sivalingam, G., Hegde, M.S., Madras, G., 2004. Solarphotocatalytic degradation of dyes: high activity of combus-tion synthesized nano TiO2. Appl. Catal. B Environ. 48 (2),83–93.

Ohtomo, A., Kawasaki, M., Ohkubo, I., Koinuma, H., Yasuda, T.,Segawa, Y., 1999. Structural and optical properties ofZnO/Mg0.2Zn0.8O superlattices. Appl. Phys. Lett. 75 (7), 980–982.

Prevot, A.B., Vincenti, M., Bianciotto, A., Pramauro, E., 1999.Photocatalytic and photolytic transformation of chloramben inaqueous solutions. Appl. Catal. B Environ. 22 (2), 149–158.

Scully, C., Collins, G., O'Flaherty, V., 2006. Anaerobic biologicaltreatment of phenol at 9.5–15°C in an expanded granularsludge bed (EGSB)-based bioreactor. Water Res. 40 (20),3737–3744.

Shen, W.Z., Liu, Z.J., Wang, H., Liu, Y.H., Guo, Q.J., Zhang, Y.L.,2008. Photocatalytic degradation for methylene blue using zincoxide prepared by codeposition and sol–gel methods. J. Hazard.Mater. 152 (1), 172–175.

Shim, S.H., Duffy, T.S., Shen, G., 2001. Stability and structure ofMgSiO3 perovskite to 2300-kilometer depth in earth's mantle.Science 293 (5539), 2437–2440.

Shrivastava, V.S., 2010. Metallic and organic nanomaterials andtheir use in pollution control: a review. Arch. Appl. Sci. Res. 2(6), 82–92.

Staples, C.A., Dorn, P.B., Klecka, G.M., O'Block, S.T., Harris, L.R.,1998. A review of the environmental fate, effects, andexposures of bisphenol A. Chemosphere 36 (10), 2149–2173.

Tao, H., Hao, S.Q., Chang, F., Wang, L., Zhang, Y., Cai, X.H., et al.,2011. Photodegradation of bisphenol A by titana nanoparticlesin mesoporous MCM-41. Water Air Soil Pollut. 214 (1–4),491–498.

Toor, P., Verma, A., Jotshi, C.K., Bajpai, P.K., Singh, V., 2006.Photocatalytic degradation of Direct Yellow 12 dye usingUV/TiO2 in a shallow pond slurry reactor. Dyes Pigments 68(1), 53–60.

Tsai, W.T., Lee, M.K., Su, T.Y., Chang, Y.M., 2009. Photodegradationof bisphenol-A in a batch TiO2 suspension reactor. J. Hazard.Mater. 168 (1), 269–275.

Umar, A., Ra, H.W., Jeong, J.P., Suh, E.K., Hahn, Y.B., 2006.Synthesis of ZnO nanowires on Si substrate by thermalevaporation method without catalyst: structural and opticalproperties. Korean J. Chem. Eng. 23 (3), 499–504.

Van Dijken, A., Meulenkamp, E.A., Vanmaekelbergh, D., Andries, M.,2000. Influence of adsorbedoxygenon the emission properties ofnanocrystalline ZnO particles. J. Phys. Chem. B 104 (18),4355–4360.

Vanheusden, K., Warren,W.L., Seager, C.H., Tallant, D.R., Voigt, J.A.,Gnade, B.E., 1996. Mechanisms behind greenphotoluminescence in ZnO phosphor powders. J. Appl. Phys. 79(10), 7983–7990.

Wang, X., Lim, T.T., 2010. Solvothermal synthesis of C–N codopedTiO2 and photocatalytic evaluation for bisphenol A degradationusing a visible-light irradiated LED photoreactor. Appl. Catal. BEnviron. 100 (1–2), 355–364.

Zeng, G.M., Zhang, C., Huang, G.H., Yu, J., Wang, Q., Li, J.B., 2006.Adsorption behavior of bisphenol A on sediments inXiangjiang River, central-south China. Chemosphere 65 (9),1490–1499.