UV-A/solar light induced Fenton mineralization of Acid Red 1 using Fe modified bentonite composite

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1 Indian Journal of Chemistry Vol 53A, June 2014, pp UV-A/solar light induced Fenton mineralization of Acid Red 1 using Fe modified bentonite composite I Muthuvel, B Krishnakumar & M Swaminathan* Photocatalysis Laboratory, Department of Chemistry, Annamalai University, Annamalainagar , India chemres50@gmail.com Received 1 January 2014; revised and accepted 21 May 2014 A novel heterogeneous bentonite based Fenton (Fe-B) catalyst has been synthesized by solid state dispersion method and characterized by inductively coupled plasma atomic emission spectrometer, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy images, diffuse reflectance spectra and Brunauer-Emmett-Teller surface area measurements. The Fe-B catalyst has been applied for the degradation of Acid Red 1 dye using both UV and solar light. The effects of various parameters such as ph, H 2 O 2 dosage, Fe dosage on degradation performance were evaluated. The catalyst was found to be stable, reusable and efficient over a wide ph range of 2 7. Mineralization of dye was confirmed by COD measurements. Keywords: Catalysts, Photocatalysts, Solid state dispersion, Dye degradation, Photodegradation, Hetero-Fenton degradation, Acid Red 1, Bentonite clay, Wastewater treatment The textile industry generates large volume of effluents with appreciable quantities of toxic organic compounds, which are not easily amenable to chemical or biological treatment. 1 The non-biodegradability of textile wastewater is due to a high content of dyestuffs, surfactants and additives. Alternative solutions to the conventional treatment such as electrochemical treatment, ozonation, semiconductor photocatalysis and Fenton process have been reported. 2-4 Over the past two decades, AOPs have emerged as efficient technologies for the destruction of various kind of recalcitrant organic pollutants in wastewater. 5-8 The application of Fenton s reagent (Fe 2+ /Fe 3+ /H 2 O 2 ) has been one of the most common homogeneous processes proposed for the treatment of textile wastewaters. Fenton process is reported to be more economical than UV/TiO 2 and UV/H 2 O 2 processes. 9 The homogeneous Fenton process usually suffers by two major drawbacks: (i) the narrow ph range of operation, typically between ph 2 and 3, and, (ii) Fe ions form sludge after treatment and the recovery of these ions is difficult. In this aspect, the immobilization of Fenton s catalyst on a carrier matrix would enable its use over a wide ph range as well as easy recovery of the catalyst from the treated effluent. Several supporting materials such as Nafion membrane, 10 alginate gel beads, 11 montmorillonite K10, 12 fire clay, 13 laponite clay, 14 bentonite, 15 neutral alumina, 16 cation exchange resin, 17 collagen fiber, 18 goethite 19 and zeolites 20 have been used as matrix for immobilization. Low cost materials such as fly ash 21 and activated carbon 22 have also been used as matrix for immobilization of active iron species. By combining the efficiency of the homogeneous-fenton process with the advantages of heterogeneous catalysis, these materials show great promise for the treatment of highly recalcitrant organic pollutants. Hetero-Fenton catalysts fulfill several requirements, such as high activity in terms of pollutant removal, minimum leaching of Fe ions, stability over a wide range of ph and a high hydrogen peroxide conversion with minimum decomposition. For practical applications, these materials are also available at a reasonable cost. Azo dyes are the most important class of synthetic organic dyes used in the textile industry and are therefore common industrial pollutants. As Acid Red 1 is largely used in leather and textile dyeing, we have chosen this dye as a model pollutant for the degradation study. Herein, we report the preparation and characterization of a new hetero-fenton bentonite composite catalyst and its photocatalytic activity for the degradation of a reactive azo dye, Acid Red 1 (AR 1), under UV-A and natural sunlight irradiation.

2 MUTHUVEL et al.: UV-A/SOLAR LIGHT INDUCED MINERALIZATION OF ACID RED 1 BY Fe-BENTONITE 673 Materials and Methods Bentonite clay was obtained from Loba Chemicals India Ltd. The chemical composition (%w/w) of the clay (main elements) was SiO 2 : 60.38; Al 2 O 3 : 13.86; Fe 2 O 3 : 2.71; MgO: Cation exchange capacity of the clay was 86.3 meq/100 g. Acid Red 1 (C.I ), K 2 Cr 2 O 7, Ag 2 SO 4 (SD Fine Chem), and, H 2 O 2, Fe(NO 3 ) 3 7H 2 O, HgSO 4, FeSO 4 7H 2 O, H 2 SO 4 and NaOH (Qualigens) were of analytical grade. Doubly distilled water was used to prepare experimental solutions. The ph of the solutions before irradiation was adjusted using H 2 SO 4 or NaOH. Heber multilamp photoreactor (model HML- MP 88) was used for photoreaction. The irradiation was carried out using four parallel medium pressure mercury lamps of 8 W each in open air condition (Supplementary Data, Fig. S1). XRD pattern of the catalysts were obtained using a Philps PANalytical X Pert PRO diffractometer equipped with a source of Cu-K α radiation and NaI (TI) scintillation detector. The iron content of the catalyst was determined by ICP-AES analysis by ISA Jobin Yuon (model JY-24) spectrometer. FT-IR spectra were recorded by Nicolet Avatar-360 spectrometer. SEM-EDS images were recorded on a Jeol-JSM-5610 scanning electron microscope. BET surface area and total pore volume measurements were made on Micromeritics ASAP 2020 system. UV spectral analysis was done using UV-1650 PC Shimadzu UV-visible spectrophotometer. The ph of the solution was measured by using Hanna Phep (model H ) digital ph meter. A Perkin-Elmer Lambda 35 UV/vis spectrometer equipped with an integrated sphere was used to record the diffused reflectance spectra (DRS). The baseline correction was carried out using a calibrated reference sample of barium sulfate. The reflectance spectra of the samples were analyzed under ambient conditions in the wavelength range of nm. Preparation of Fe-B catalyst Preparation of Fe 3+ loaded bentonite (Fe-B) is shown in Scheme 1. Ferric nitrate solutions of different concentrations were prepared in 60/40- ethanol-water (v/v) medium. Bentonite (5 g) was mixed with appropriate concentration of ferric nitrate solution. The mixed suspension was stirred for 3 5 h at room temperature. The product was centrifuged and washed with water several times. Then it was dried at 120 C for one hour. The Fe-B catalyst was obtained as a fine powder. Photocatalytic activity studies In all the cases, 50 ml of the dye solution containing appropriate quantity of the Fe-B and H 2 O 2 suspensions were used. The suspension was stirred for 30 min in dark to attain adsorption equilibrium and then it was irradiated. The dye solution was continuously aerated by a low horsepower aquarium air pump to provide oxygen and for complete mixing of reaction medium. At specific time intervals, 2 3 ml of the sample was withdrawn and centrifuged to separate the catalyst. The centrifugate (1 ml) was diluted to 10 ml and its absorbance at 302 and 512 nm was measured. The absorbance at 512 nm is due to colour of the dye and was used to monitor the decolourization. The absorbance at 302 nm represents the aromatic content of AR 1 and the decrease of absorbance at 302 nm indicates the degradation of aromatic ring. 23 Mineralization of dye was confirmed by the formation of CaCO 3 when the evolved gas (carbon dioxide) during the reaction was passed into limewater. The stoichiometric oxidant concentration required for the total oxidation of AR 1 was determined according to the following reaction. 2 C 18 H 13 N 3 Na 2 O 8 S H 2 O 2 94 H 2 O + 36 CO N Na 2 O SO 2 Heterogeneous photocatalytic degradation of AR 1 on iron immobilized catalyst was reported to follow pseudo-first order kinetics. 23 At low initial dye concentration, the rate expression is given by d[c]/dt = k [C], where k is the pseudo-first order rate constant. The dye was adsorbed on the catalyst surface and adsorption-desorption equilibrium was reached in 30 min. After adsorption, the equilibrium concentration of the dye solution was determined Preparation of Fe-B catalyst Scheme 1

3 674 INDIAN J CHEM, SEC A, JUNE 2014 and taken as the initial dye concentration (C 0 ) for kinetic analysis. At C = C 0 at t = 0, ln (C 0 /C) = k t, where C 0 is the equilibrium concentration of dye and C is the concentration at time t. Pseudo-first order rate constant (k ) was determined from the plot of ln C 0 /C versus t. COD was determined as per the reported procedure. 24 Solar experiments Solar experiments were carried out in open space on hot sunny days between 11 am and 2 pm. Solar light intensity was measured for every 10 min and the average light intensity over the duration of each experiment was calculated. The sensor was always set at the position of maximum intensity. The intensity of solar light was measured using LT Lutron LX-10/A digital Lux meter, and found to be ±100 Lux. The intensity was almost constant during the experiments. Results and Discussion Photocatalytic activity The photocatalytic activities of the Fe-B catalysts with 13, 20, 26 and 31% (w/w) ferric nitrate loading were evaluated by the degradation of AR 1. Controlled experiments under different conditions with UV and solar light were carried out and the results are displayed in Fig. 1a and 1b, respectively. In the presence of H 2 O 2 and UV light, a small decrease in dye concentration occurs initially at the time of 20 min and then remains constant (Fig. 1a, curve 1). There is no appreciable decrease in the concentration of dye when it is treated with Fe 3+ /UV light. There is a decrease in dye concentration (13%) when the dye was treated with the catalyst in the absence of light, which is due to adsorption. The dye on irradiation with Fe-B catalysts of different ferric nitrate loading on bentonite shows that the degradation increases with increase in percentage of ferric nitrate up to 20% (Fig. 1a, curves 2 and 3) and then decreases (Fig. 1a, curves 4 and 5). Nearly 95% degradation in 90 min was achieved with 20% Fe-B in heterogeneous process. However in the heterogeneous process, the photoreduction of Fe 3+ to Fe 2+ and the reaction between Fe 2+ with H 2 O 2 take place at the surface of Fe-B, generating highly oxidative OH radicals. Meanwhile H 2 O 2 itself produces a few OH radicals with UV light. These OH radicals attack dye molecules leading to reaction intermediates which are finally mineralized into CO 2 and H 2 O. The release of OH radicals to the solution from Fe-B catalyst is gradual and the time required for 99% degradation is 90 min. In homogeneous process also the mineralization is almost complete in 90 min. However, the heterogeneous photo-fenton catalyst has the advantages of easy removal and reusability. The decrease in dye degradation above 20% Fe 3+ loading may be due to the reaction of excess Fe 3+ with H 2 O 2 producing less reactive hydroperoxy radicals. 25 Fe 3+ + H 2 O 2 hν Fe 2+ + HO 2 + H + In the presence of H 2 O 2 and solar light, a small decrease in dye concentration occurs at the time of 60 min and then it remains constant (Fig. 1b, curve 1). As observed in the UV process, the degradation Fig. 1 Photodegradation of AR 1 under (a) UV*, and, (b) solar light. {[AR 1] = M; catalyst suspended = 1 g L 1 ; H 2 O 2 = 10 mmol; airflow rate = 8.1 ml s 1 ; ph = 3±0.1; *I 0 = einstein L 1 s 1. 1, Dye/H 2 O 2 /UV or solar; 2, Dye/Fe-B (13%)/H 2 O 2 /UV or solar; 3, Dye/Fe-B (20%)/H 2 O 2 /UV or solar; 4, Dye/Fe-B (26%)/H 2 O 2 /UV or solar; 5, Dye/Fe-B (31%)/H 2 O 2 /UV or solar; 6, Dye/Fe 3+ /H 2 O 2 /UV or solar; 7, Dye/Fe-B (20%)/H 2 O 2 /dark}.

4 MUTHUVEL et al.: UV-A/SOLAR LIGHT INDUCED MINERALIZATION OF ACID RED 1 BY Fe-BENTONITE 675 increases with increase in percentage of ferric nitrate up to 20% (Fig. 1b, curves 2 and 3) and then decreases (Fig. 1b, curves 4 and 5). Heterophoto-Fenton process with 20% Fe-B catalyst was compared with the homogeneous-fenton process (Fig. 1b, curve 6). Degradation in both homogeneous and heterogeneous processes at 90 min are almost same. The catalyst Fe-B prepared using bentonite with 20% ferric nitrate loading was found to be efficient for both UV and solar processes. Hence, the 20% Fe-B catalyst has been characterized and further investigated for other operational parameters. Catalyst characterization Figure 2 depicts the XRD pattern of the commercial bentonite and 20% Fe-B. The main diffraction peaks at 2θ 34.9, 20.9 and 36.6 are attributed to the crystalline phase of α-fe 2 O 3 (hematite) and α-feooh (goethite), respectively. 26 Intensity of these peaks increased in 20% Fe-B. The peak at 26.6 reveals the quartz impurity present in both the samples. The iron was extracted from 500 mg of commercial bentonite and 20% Fe 3+ loaded-bentonite by triple acid method and analyzed by ICP-AES. The amount of Fe obtained from commercial bentonite and 20% Fe-B was found to be 155 and 701 ppm, respectively, i.e., 6.5 times higher in Fe-B than in bentonite. BET surface area and total pore volume were determined from adsorption isotherms. The pore volume and BET Fig. 2 XRD patterns of bentonite (1), and, 20% Fe-B (2). surface area of the bentonite and the Fe-B (20%) are given in Table 1. After immobilization, the surface area of bentonite increased from 45.5 to 94 m 2 g 1. Increase in surface area may be due to the inhibition of aggregation of bentonite particles by Fe 3+ ions. 27 FT-IR spectra of bentonite and Fe-B catalyst are quite similar (Supplementary Data, Fig. S2). The spectra showed O H stretching at 3620/3621 cm 1 and OH bending at 1636/1637 cm 1. A band around 798 cm 1 is due to the stretching vibration of Al IV tetrahedral. 28 Nevertheless, the small shift of Si O stretching to a higher value from 1030 cm 1 in bentonite to 1033 cm 1 in iron supported bentonite catalysts suggests that there is a coordination of Si O Fe bond. 29 The peak at 1384 cm 1 is due to the presence of stretching vibration of NO 3, which shows that these ions are required to compensate some redundant positively charged iron aggregates present outside the interlayer space of the Fe-B. 30 SEM images show the presence of tiny iron aggregates spread on the 20% Fe-B catalyst (Fig. 3b), while pure bentonite reveals the layer structure (Fig. 3a). It is found from EDS that the iron contents in bentonite and 20% Fe-B catalyst at a particular region are 17.6 and 22.2 wt%, respectively. Increase in percentage of iron in Fe-B confirms Fe(III) loading in the catalyst. Diffused reflectance spectra of commercial bentonite and 20% Fe-B were taken in the absorbance mode (Supplementary Data, Fig. S3). The UV-vis spectrum of Fe-B shows higher absorption than bentonite in the region of 300 to 750 nm, which may be due to the increase in concentration of Fe 3+ in Fe-B. Effects of optimum operational parameters The influence of ph on the degradation of AR 1 under UV-A and solar light is presented in Fig. 4a and 4b, respectively. The degradation curves of AR 1 are displayed as time-dependent normalized dye concentration in solution. At ph 3, about 99% degradation was observed under both UV-A and solar light, whereas at ph 7, 69% and 84% of degradations were obtained with UV-A and solar light respectively. At ph 3, in both UV and solar processes 99% dye was degraded at 60 min. The rate constants at ph 3 for Table 1 Surface area, average pore diameter and total pore volume of bentonite and Fe-B catalyst Sample BET surface area in N 2 adsorption (m 2 g 1 ) Average Total pore vol. pore dia. (Å) (cm 3 g 1 ) Bentonite % Fe-B

5 676 INDIAN J CHEM, SEC A, JUNE 2014 Fig. 3 SEM images of bentonite (a), and, 20% Fe-B (b). both UV and solar process are min 1. However, at ph 7, the UV process showed 69% and solar process 84% degradation at 60 min. The rate constants at ph 7 of the UV and solar processes are and min 1, respectively. The results reveal that even up to initial ph 7.0, the heterogeneous photo-fenton process could proceed effectively with Fe-B as catalyst. Hence, this catalyst is effective for a wide ph range of 2 7. This observation is important since it is well known that the major drawback of homogeneous photo-fenton process is the narrow ph range of 2 3. As the acidification is costlier than the energy and oxidant used in Fenton degradation, practical industrial application of homo photo-fenton process has been limited. This limitation is overcome by the present heterophoto-fenton process. The effect of H 2 O 2 dosage on the removal process was studied under the following experimental conditions: M dye concentration, ph 3 and 1.0 g L 1 catalyst. The increase in H 2 O 2 from 5 to Fig. 4 Effect of initial solution ph on AR 1 degradation under (a) UV*, and, (b) solar light. {[AR 1] = M; Fe-B (20%) = 1 g L 1 ; H 2 O 2 = 20 mmol; airflow rate = 8.1 ml s 1 ; *I 0 = einstein L 1 s 1 }. 20 mmol increases the dye degradation in both the processes. For UV process, the degradation rate constant increases from to min -1 and for solar process the increase is from to min 1. Increasing H 2 O 2 concentration above 20 mmol decreases the removal efficiency. This indicates that addition of H 2 O 2 increases the OH radical generation up to 20 mmol. At higher H 2 O 2 concentration, i.e., above 20 mmol, it acts as a hydroxyl radical quencher, consequently lowering the OH radical concentration. 31 Therefore, it can be concluded that optimum dosage of H 2 O 2 is 20 mmol (Eqs 1 and 2). The Fe 3+ :H 2 O 2 ratio is 1:15 throughout the reaction. H 2 O 2 + OH HO 2 + H 2 O (1) HO 2 + OH H 2 O + O 2 (2)

6 MUTHUVEL et al.: UV-A/SOLAR LIGHT INDUCED MINERALIZATION OF ACID RED 1 BY Fe-BENTONITE 677 Table 2 Concentration of Fe(II) leached (ppm) at varying ph for three consecutive runs with Acid Red 1. {[AR 1] = M; catalyst suspended = 1 g L 1 ; H 2 O 2 = 20 mmol; irradiation time = 90 min; airflow rate = 8.1 ml s 1 ; *I 0 = einstein L 1 s 1 } Run UV* Solar ph 3 ph 5 ph 7 ph 3 ph 5 ph 7 I II III The influence of varying initial dye concentrations on the removal process were investigated between M dye solutions for both UV and solar processes. Increase in dye concentration from to M -1 decreases the degradation rate constant from to min 1 for UV and from to min 1 for solar process. The increase in dye concentration increases the number of dye molecules and competition with the OH radical concentration, and hence, the removal rate decreases. In photo-fenton process, at higher dye concentration the penetration of photons entering into solution also decreases, thereby lowering the hydroxyl radical production. Hence, the percentage of degradation decreases with increase in dye concentration. The stability of the catalyst was tested in order to evaluate the catalytic activity of Fe-B during successive experiments and thus to find the feasibility of its reuse. The catalyst was used for three consecutive experiments with fresh dye solution under optimum conditions ( M dye concentration, ph 3.0, 20 mmol H 2 O 2 and 1.0 g L 1 catalyst) using UV and solar light. Between each experiment, the catalyst was removed by filtration and then washed with deionized water for several times and dried. The initial activity decreases from 97% to 82% for UV process and from 98% to 87% for solar process (40 min). The decrease in catalytic activity may be due to the leaching of small amounts of iron from catalyst surface. The Fe 3+ leaching from the catalyst was analyzed at different ph. Analysis revealed that the solution after mineralization contained Fe 2+ ion and not Fe 3+ ions. The leached Fe 3+ ions might have been converted to Fe 2+ photolytically with H 2 O (Eq. 3). Fe 3+ + H 2 O hν Fe 2+ + OH + H + (3) The amount of Fe 2+ ions in solution after complete degradation of three dyes at ph 3, 5 and 7 for three consecutive runs are given in Table 2. The amount of Fe 3+ on bentonite surface + hν H 2 O Fe 2+ on bentonite surface + OH (i) Fe 2+ on bentonite surface + H 2 O 2 hν Fe 3+ on bentonite surface + OH + OH (ii) Dye molecules + OH hν Reaction intermediates (iii) Reactions intermediates + OH CO 2 + H 2 O + mineral acids (iv) Scheme 2 ion leached decreases with the increase in runs and there is no significant leaching after 3 runs. In all the three runs, the leaching is maximum at ph 3 and minimum at ph 7. This reveals that the catalyst is more stable at ph 7. Therefore, it is feasible and economical to apply this hetero-fenton catalyst for industrial cost effective wastewater treatment at neutral ph of 7. Since the reduction of chemical oxygen demand (COD) reflects the extent of degradation or mineralization of an organic species, the percentage reduction in COD was also analyzed for the dye sample under optimal conditions to confirm its mineralization. In the UV process, 97% COD reduction was obtained whereas in the solar process, 99% COD reduction was observed in 90 min. The results reveal the complete mineralization of AR 1 dye in both UV and solar processes. Dye degradation mechanism Hetero-Fenton process is similar to homo-fenton process as the degradation takes place by the attack of OH radicals. Based on the earlier report 31 on the degradation of Orange II by Fe-immobilized laponite clay (Fe-Lap-RD), the following mechanism is proposed (Scheme 2). The reactions are initiated by the photo-reduction of Fe 3+ on the surface of Fe-B clay to Fe 2+ under irradiation of UV/solar light. Then, the Fe 2+ formed on the surface of the solid reacts with H 2 O 2 in solution, generating highly oxidative OH radicals, while it is oxidized to Fe 3+ (Fenton s reaction). Hydroxyl radicals attack the dye molecules giving rise to reaction intermediates, which are mineralized into CO 2, H 2 O and mineral acids. Conclusions A novel heterogeneous bentonite based Fenton (Fe-B) catalyst was synthesized by solid state dispersion method and characterized by ICP-AES, FT-IR, XRD, SEM images, DRS and BET surface

7 678 INDIAN J CHEM, SEC A, JUNE 2014 area measurements. ICP-AES confirms the loading of Fe on bentonite. Loading of Fe on bentonite shifts its absorption edge from 300 nm to the entire visible region. BET surface area of Fe-B is twice that of bentonite clay. Fe-B is found to be efficient in the degradation of AR 1 dye with both UV and solar light. The main advantage of this process is its efficiency over a wide ph range (2 7). The optimum ph and hydrogen peroxide loading in both processes are found to be 3 and 20 mmol, respectively. Though the dye degradation is 100% degradation at the optimum ph 3, the dye degradation is also significant at ph 7 (69% in UV process and 84% in solar process). This catalyst is found to be reusable. The applicability of the studied hetero-fenton catalyst in solar process over a wide ph range and its reusability makes it a energy efficient and eco-friendly process for the treatment of dye effluents. Supplementary Data Supplementary Data associated with this article, i.e., Figs S1 S3 are available in electronic form at Acknowledgement One of the authors (MS) is thankful to Council of Scientific and Industrial Research, New Delhi, India, for financial support through research grant No. 21(0799)/10/EMR-II. The authors thank Catalysis Laboratory, Indian Institute of Technology Madras, Chennai, India, for BET surface area measurements. References 1 Muhammad A, Shafeeq A, Butt M A, Rizvi H, Chughtai M A & Rehman S, Brazil J Chem Eng, 25 (2008) Shannon M A, Bohn P W, Elimelech M, Georgiadis J G, Marias B J & Mayes A M, Nature, 452 (2008) De Leon M A, Castiglioni J, Bussi J & Sergio M, Catal Today, (2008) Gomathi Devi L, Rajashekhar K E, Anantha Raju K S & Girish Kumar S, J Mol Catal A, 314 (2009) Parson S, Advanced Oxidation Process for Water and Wastewater Treatment, (Inland Waterways Association, London) Ledakowicz S, Solecka M & Zylla R, J Biotechnol, 89 (2001) Pera-Titus M, Garcia-Molina V, Banos M A, Gimenez J & Esplugas S, Appl Catal B, 47 (2004) Oppenlander T, Photochemical Purification of Water and Air, (Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) Muruganandham M, Selvam K & Swaminathan M, J Hazard Mater, 144 (2007) Rios-Enriquez M, Shahin N, Duran-de-Bazua C, Lang J, Oliveros E, Bossmann S H & Braun A M, Sol Energy, 77 (2004) Fernandez J, Bandara J, Lopez A, Buffat P & Kiwi J, Langmuir, 15 (1999) Muthuvel I, Krishnakumar B & Swaminathan M, Indian J Chem, 51A (2012) Muthuvel I, Krishnakumar B & Swaminathan M, J Environ Sci, 24 (2012) Iurascu B, Siminiceanu I, Vione D, Vicente M A & Gil A, Water Res, 43 (2009) Carriazo J G, Molina R & Moreno S, Appl Catal A, 334 (2008) Muthuvel I & Swaminathan M, Sol Energy Mater Solar Cells, 92 (2008) Zhao Y, Jiangyong H & Chen H, J Photochem Photobiol A, 212 (2010) Liu X, Tang R, He Q, Liao X & Shi B, J Hazard Mater, 174 (2009) Guimaraes I R, Oliveira L C A, Queiroz P F, Ramalho T C, Pereira M, Fabris J D & Ardisson J D, Appl Catal A, 347 (2008) Aleksic M, Kusic H, Koprivanac N, Leszczynska D & Bozic A L, Desalination, 257 (2010) Flores Y, Flores R & Gallegos A A, J Mol Catal A, 281 (2008) Dhaouadi A & Adhoum N, Appl Catal B, 97 (2010) Sobana N & Swaminathan M, Sep Purif Technol, 56 (2007) American Public Health Association (APHA), Standard Methods for the Examination of Water and Wastewater, 10 th Edn (American Public Health Association, American Water Works Association, and Water Pollution Control Federation, Washington, DC) Kwan C Y & Chu W, Water Res, 37 (2003) Li Y, Lu Y & Zhu X, J Hazard Mater, 132 (2006) Jothivel S, Velmurugan R, Selvam K, Krishnakumar B & Swaminathan M, Sep Purif Technol, 77 (2011) Binitha N N & Sugunan S, Micropor Mesopor Mater, 93 (2006) Trakarnpruk W & Dumrongpong P, J Mater Sci, 41 (2006) Yuan P, Annabi-Bergaya F, Tao Q, Fan M D, Liu Z W & Zhu J X, J Colloid Interf Sci, 324 (2008) Buxton G V, Greenstock C, Hellmann W P & Ross A B, J Phys Chem, 17 (1988) 513.