Photocatalytic and antimicrobial activity of NiWO4 nanoparticles stabilized by the plant extract

Materials Science in Semiconductor Processing 40 (2015) 123–129

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Photocatalytic and antimicrobial activity of NiWO4 nanoparticles stabilized by the plant extract R. Karthiga a, B. Kavitha a, M. Rajarajan a,n, A. Suganthi b a b

P.G. & Research Department of Chemistry, C.P.A. College, Bodinayakanur 625513, Tamilnadu, India P.G. & Research Department of Chemistry, Thiagarajar College, Madurai 625009, Tamilnadu, India

art ic l e i nf o

a b s t r a c t

Article history: Received 15 November 2014 Received in revised form 15 May 2015 Accepted 19 May 2015

In recent years, biosynthesis of nanoparticles using plant extract has attracted great attention owing to its cost effective, non-toxic, eco-friendly and as an alternative approach to physical and chemical methods. Nickel tungstate (NiWO4) nanoparticles were synthesised via the aqueous leaf extract of Azadirachta indica plant. The prepared nanoparticles were characterized using UV–visible diffuse reflectance spectroscopy (UV–vis-DRS), fourier transform infra-red spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM) techniques. SEM results showed that plant extract modified NiWO4 (PNT) was composed of tiny sphere in shape. XRD results revealed that the average crystallite size of PNT was smaller (12.12 nm) when compared to the bare NiWO4 (NT) prepared using precipitation method (31.11 nm). The photocatalytic activity of NiWO4 nanoparticles were investigated using methylene blue (MB) as a model organic pollutant under visible light irradiation. PNT showed high efficiency for the degradation of MB compared to NT. The effect of operation parameters such as initial dye concentration, pH and catalyst concentration has been investigated in detail. PNT was subjected to antimicrobial studies and significant results were obtained. & 2015 Elsevier Ltd. All rights reserved.

Keywords: PNT NT Azadirachta indica Photocatalysis Methylene blue Antimicrobial studies

1. Introduction Metal tungstates with formula MWO4 have attracted much attention due to their interesting size and shape dependant optical, magnetic and electronic properties [1–5]. Transition metal tungstates have many applications, such as in gas sensors, optical fibres, humidity sensors, pigments, catalytic and biological activity. Nickel tungstates (NiWO4) is one of the important inorganic materials that have high application potential in various fields such as catalysis, humidity sensor, photoanodes, laser hosts, Microwave application and optical fibres [6–8]. Also, it is considered to be a potential candidate as a visible light photocatalyst for organic contaminants decomposition. Recently, many studies have been reported on the preparation and characterization of nickel tungstate using various preparation methods such as Czochralski method [9], precipitation [10], hydrothermal [11], solid state [1], pulsed laser deposition [12]. However, these methods usually require special equipment, high temperature, templates or substrates, which encounter difficulties with prefabrication and posts removes of the templates or substrate and usually result in n

Corresponding author. fax: þ91 4546 280793. E-mail address: [email protected] (M. Rajarajan).

http://dx.doi.org/10.1016/j.mssp.2015.05.037 1369-8001/& 2015 Elsevier Ltd. All rights reserved.

impurities. The toxic chemicals, non polar solvents and synthetic additives or capping agents immersing from the chemical reaction are often potentially dangerous to the environment. Azadirachta indica neem is evergreen tree found in most tropical countries. The aqueous extract from bark, leaves, fruits and root have been used to control leprosy, intestinal helminthiasis and respiratory disorder in children and it is uses as an anthelmintic, antifeedant, antiseptic, diuretic, parasiticides, pediculicide and insecticide [13,14]. The leaf bearer’s variety of phyotochemicals like saponic, Tannin, Phlobatanin, Anthraquinone, Terpene and Alkaloid which act as a capping agent. The plant extracts acts as a green corrosion inhibitors and its shows high antimicrobial activity over 500 microorganisms. Guptha et al studied adsorptional removal of methylene blue by guar gum–cerium (IV) tungstate as a hybrid cationic exchanger [15]. Shankar et al synthesized Ag, Cu and Au nanoparticles using broth extracts of A. indica [16]. Zawawi et al synthesised metal tungstates by sucrose template method to study its structural and optical properties [17]. The synthesis of nano-sized NiWO4 crystals includes co-precipitation, polymeric precursor method, modified citrate complex technique, hydrothermal method, molten salt method and spray pyrolysis [18,19]. Hence developing of reliable biosynthetic, an environment friendly approach has added much importance because of its eco-

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2. Experimental

were recorded in air at room temperature in the wave length range of 200–800 nm using shimadzu UV – 2450 spectrophotometer. Surface structure was characterized by a fourier transform infra-red (FT-IR) spectrophotometer (JASCO – FT-IR 460 plus). The crystalline structure of the nanoparticles was studied by an X-ray diffractometer (XRD; XPERT PRO X-RAY) with Cu Kα radiation at 25 °C and the structural assignments were made with reference to the JCPDS powder diffraction files. The surface morphology was examined using scanning electron microscopy (SEM) (JSM 6701F-6701) in both secondary and backscattered electron modes and the elemental analysis was also detected. Transmission electron microscopy (TEM) mapping images were obtained using TEM-TECNAI G2 model. pH was monitored using a EUTECH instrument pH metre.

2.1. Materials

2.4. Photocatalytic activity evaluation

Analytical grade Nickel chloride and sodium tungstates were used as received from Merck. The cleaned young A. indica leaves were collected from the Theni District. For all experimental work double distilled water was used.

The photocatalytic activity of the prepared PNT nanoparticles was studied using MB as a model dye under visible light irradiation at pH 7. 300 mL aqueous solution of MB with certain amount of photocatalyst was taken in the cylindrical glass vessel, which was surrounded by a circulating water jacket to cool the lamp [23,24]. Air was kept bubbling continuously into the aliquot by an air pump in order to provide a constant source of dissolved oxygen. Prior to light irradiation, the suspension was stirred in the dark for 30 min to ensure the adsorption–desorption equilibrium between the methylene blue and the surface of the catalyst [25,26]. A 300 W Xe arc lamp with an ultraviolet (l4400 nm) cut off filter was used as the visible light irradiation source. During the course of light irradiation, 5 mL aliquot was withdrawn at a regular time interval of 30 min. Then the samples were centrifuged and filtered through a millipore filter to remove the photocatalyst. The filtrate was analysed by UV–vis spectrophotometer at λmax ¼660 nm and the photodegradation percentage were calculated by the expression given below:

friendly products, biocompatibility and economic viability in the long run and also to avoid adverse effects during their environment application. In this work, we adopted a precipitation route for the synthesis of NiWO4 pure phase with uniform particle size distribution and plant extract as capping agent. The photocatalytic activity of the prepared NiWO4 for the degradation of MB under visible light irradiation was investigated. The reaction parameters such as pH, catalyst dosage and initial dye concentration influencing the photodegradation were investigated in detail. NiWO4 nanoparticles were explored with respect to their prospective antibacterial application.

2.2. Methods 2.2.1. Preparation of plant extract The collected A. indica leaf were washed thrice with tap water and twice with distilled water to remove the adhering salts and other associated contaminants and they were cut into small pieces. 10 g of leaf was taken and boiled with 100 ml of double distilled water at 100 °C for half an hour. The boiled extract was filtered through whatman No.1 and was stored in refrigerator at 4 °C for further studies [20]. The prepared plant extracts were subjected to preliminary phytochemical screening for the presence of alkaloids, flavonoids, tannins, carbohydrates, glycosides, saponins, triterphenoids, proteins and amino acids were tested [21] (Table 1). 2.2.2. Preparation of NiWO4 nanoparticles NiWO4 nanoparticles were prepared by simple precipitation method. 0.05 M NiCl2 and 0.05 M of NaWO4  2H2O were dissolved separately in 50 ml distilled water in two glass beakers. NaWO4  2H2O was added to NiCl2 solution dropwise with constant stirring which led to the rapid formation of green colour precipitation. To this 5 ml of plant extract was added and it was stirred for 2 h to form a homogeneous precipitate. After filtering, the precipitate was washed with distilled water and dried at 80 °C for 5 h. The obtained PNT nanoparticle was calcinated at 500 °C for 1 h [22]. The same procedure is followed without plant extract for the preparation of NT. 2.3. Characterization The optical properties were investigated using a UV–vis-DRS Table 1 Qualitative phytochemical analysis of Azadirachta indica. S. No.

Phytoconsitituents

Reagents

Aqueous

1 2 3 4 5 6 7 8 9

Alkaloids Flavonoids Tannins Carbohydrates Glycosides Saponins Triterpenoids Proteins Amino Acids

Mayer's test Alkaline reagent test Braymer's test Molisch’s test Liebermann's test Salkowski test Liebermann Burchard test Ninhydrin test Ninhydrin test

Presence Presence Absence Presence Presence Absence Presence Presence Presence

Photodegradation (%) =

C0 − C × 100 C0

(2.1)

Where C0 is the concentration of MB before irradiation and C is the concentration of MB after a certain irradiation time. 2.5. Measurement of antimicrobial activity PNT nanoparticles in sterilized distilled water were tested for their antimicrobial activity by the agar diffusion method. Four microbial strains, Staphylococcus, Salomonella, Klebsiella and Aspergillus were used for this analysis. The sample PNT is dissolved in dimethyl sulfoxide (DMSO) and their concentrations are fixed at 200 mg/mL (minimum inhibitory concentration) and ketoconazole was used as a reference drug. A lawn of test organism was made on the agar plate using a sterile cotton swab and then the antimicrobial discs (Whatman No. 1. filter disc with samples at 200 mg/mL) were placed on the agar plate. All the plates were incubated at 37 °C for 24 h. The zone of inhibition was measured and expressed as millimetre (mm) in diameter [27].

3. Result and discussion 3.1. Ultraviolet–visible diffuse reflectance spectroscopy (UV–visDRS) The light absorption ability of NiWO4 samples was studied by UV–vis-DRS. Fig. 1 shows the UV–vis-DRS of NT and PNT. As seen the Fig. 1. the absorption edge of PNT was highly shifted to visible

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Fig. 2. FTIR spectra of NT and PNT.

Fig. 3. XRD patten of NT and PNT.

1.35 eV respectively. This result confirms that on surface modification of NiWO4 can significantly improve the absorption of light effectively. Hence, PNT absorbs more visible light than that of NT.

Fig. 1. (a) UV–vis- DRS of NT and PNT (b) Tauc plot of NT (c) Tauc plot of PNT.

region when compared to that of NT. Generally, the band gap of semiconductors is related to its range of absorption wavelength and the band gap decreases with increasing of absorption edge. The band gaps can be evaluated using Tauc approach [28].

α=

C (hv − Egbulk )2 hv

(3.1)

Where α is the absorption co-efficient, hν is the photon energy, Egbulk the optical band gap energy, h is the plank constant and c is the constant depending on the electron – hole mobility. A plot of (αhν)1/2 versus hν afforded band gap of both the samples. The band gap values of NT and PNT were found to be 2.25 eV and

3.1.1. FT-IR The FT-IR spectra of NT and PNT are shown in Fig. 2. It has been reported that the main absorption bands of NiWO4 appeared in the range of 450–1000 cm  1.The bands appeared at 878 and 824 cm  1 arise from vibration of the WO2 entity present in the W2O8 groups. The absorption band at 629 cm  1 was typical of a two oxygen bridge (W2O2) and corresponds to the asymmetric stretching of the same unit. Additionally the observed band at 450 cm  1 confirms the stretching vibration of the NiO6 polyhideral building validating the formation of NiWO4 structure [29]. The peaks at 1120 cm  1, 1630 cm  1, 2360 cm  1 and 3442 cm  1 represent the diverse function groups of the absorbed biomolecules on the surface of the NiWO4 particles. The peaks around 1120 cm  1 denote stretching vibration bands responsible for compounds like flavonoids and terpenoids. Peak at 1465 cm  1 corresponded to the C–N stretching mode of the aromatic amine group. The band at 1643 cm  1 can be assigned to the amide I band of the proteins and aromatic ring, 2360 cm  1 confirmed to be C–C and 3442 cm  1 was related to N–H stretching [30]. The variation in the position indicated presumably some metabolites such as tannins, flavonoids, alkaloids and cartenoids which are abundant

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Fig. 4. (a) SEM image of NT (b) SEM image of PNT.

Fig. 5. (a) EDX of NT (b) EDX of PNT.

Fig. 7. Effect of pH on the photodegradation of MB.

Fig. 6. TEM image of PNT.

in plant extract have interacted with NiWO4 surface making NiWO4 highly stable. 3.1.2. XRD XRD is used to investigate the changes of phase structure and crystallite size of the synthesized nanoparticles with and without

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Table 2 Antimicrobial activity of PNT ((c) control, (s) standard (R) resistance). Zone of inhibition (mm) Types of pathogens

Name of the micro- Control (c) organism (DMSO)

Standard (s) (ketoconazole)

PNT (1)

Gram þve bacteria Gram  ve bacteria Fungal

Staphylococcus(a)

R

18

12

Salmonella(b) Klebsiella(c) Aspergillus (d)

R R R

18 18 18

10 14 R

when compared with the nanoparticles without plant extract. The average crystallite size was calculated using the Debye's scherrer equation [31]:

D= Fig. 8. Effect of PNT dosage on the photodegradation of MB.

Fig. 9. Effect of initial MB concentration on its photodegradation.

Kλ β cos θ

(3.2)

Where, β is the full width at half height maximum of the most intense 2θ peak, K is the shape factor (0.89). θ, λ are the incident angle and wavelength of X-rays respectively. The average particle obtained for PNT nanoparticles is 12.12 nm while the size was found to increase to 31.11 nm for NT. 3.1.3. SEM, EDX and TEM SEM images of the synthesized NiWO4 are shown in the Fig. 4. After the addition of plant extract the surface modification takes place and NiWO4 crystals with certain faces continue to grow into a more stable structure which makes the product present a small spherical shaped structure with uniform diameter favouring good photocatalytic activity [32,33]. The EDX spectra of NT and PNT are presented in Fig. 5. The peaks corresponding to Ni, W and O are clearly observed at their normal energy and their corresponding keV values are shown in the inset table in the Fig. 5. The average atomic percentage ratio of Ni, W and O was seen to be 17.74:18.06:64.20. This confirms the presence of corresponding elements in their stochiometric percentage prepared by precipitation method. Fig. 6 shows typical TEM microphotographs of the synthesized PNT nanophotocatalyst. The results indicate the catalyst obtained is olive spherical particles. The particles are highly dispersed with average diameter of 12.25 nm. The results agree well with those obtained from XRD patterns. The micrographs shows that the PNT are well separated from each other, suggesting effective capping by water-soluble heterocyclics present in the A. indica extract. 3.2. Photodegradation of MB

Fig. 10. Kinetic plot of  ln (C/Co) versus irradation time for the photodegradation of MB.

addition of plant extract. Fig. 3. shows the XRD patten of NT and PNT. The main diffraction peaks of PNT with monoclinic phases at 19.3°, 23.9°, 24.95°, 30.9°, 36.5°, 41.6°, 54.6° and 65.6° (JCPDS150755) which corresponds to (1 0 0), (1 0 0), (1 1 0), (1 1 1), (0 0 2), (1 0 2), (2 0 2) and (1 3 2) crystallographic planes respectively and is indexed as the primitive lattice. It can be seen that NiWO4 nanoparticles embedded in plant extract XRD peaks were broad

3.2.1. Effect of pH on PNT catalytic activity The effect of pH on the photocatalysis is considered an important parameter, as most of the industrial waste streams are at different pH. The pH effect was studied in the pH range of 4–10 with an initial dye concentration of 10 mM and PNT dosage of 0.05 g/L. MB degradation profile over PNT as a function of irradiation time is presented in Fig. 7. The photodegradation of MB increases with the increase of pH from 4 to 7 and then decreases as the pH increases to 10. This is due to the modification of the electrical double layer of the solid electrolyte interface, which affects the adsorption–desorption processes and the photogeneration of electron–hole pairs in the surface of the catalyst particles [34]. MB degradation proceeds as a result of oxidation by free radicals generated under UV irradiation on the surface of semiconductor catalysts. A UV photon generates highly reactive electron–hole pairs, which can produce active radicals (OH● and O2●  ) on the particle surface [35]. Studying the intermediates formed

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Fig. 11. The zone of inhibition of PNT against (a) Staphylococcus, (b) Salmonella (c) Klebsiella (d) Aspergillus.

during photoelectrocatalytic degradation of MB also showed that the degradation started with the oxidation of N–CH3 bonds and S atoms [36]. At low pH, the surface of the catalyst is more positive and rejects MB cation reducing its adsorption. At high pH, recombination of electron–hole pairs is, possibly, more intensive because of high concentration of OH  anions.

degradation. At high dye concentration, the generation of reactive species on the photocatalyst surface is reduced because the active sites are completely covered by the dye molecules. Once the MB concentration is increased most of light is absorbed by the MB molecules and photons do not reach the surface of photocatalyst to activate it to generate hydroxyl radicals [39,40] Fig. 9.

3.2.2. Effect of PNT on catalyst concentration The effect of catalyst concentration was investigated to avoid excess use of catalyst and to find optimum concentration. The photocatalytic experiments were conducted by varying PNT concentration from 0.025 g/L to 0.075 g/L and the other parameters are kept constant (MB concentration 10 mM and pH 7). The results are presented in Fig. 8 .The photo degradation of MB is negligible in the absence of catalyst .The degradation of MB increases with increase in photocatalyst concentration from 0.025 g/L to 0.05 g/L and a further increase in catalyst concentration leads to decrease in photodegradation. This is because with an increase of catalyst concentration total active surface area increases. Consequently the generation of reactive species required for MB degradation also increased. At the same time the suspension becomes more turbid at high photocatalyst concentration, which hinders the penetration of light. Hence the photoactivated volume of the suspension decreases [37, 38].

3.2.4. Photodegradation of MB on PNT The kinetics of photodegradation of MB can be described by pseudo first order equation and it can be expressed as follows [41]:

3.2.3. Effect of PNT on initial concentration of MB Experiments were conducted to study the effect of dye concentration at constant loading of catalyst 0.05 g/L and pH ¼7. The dye concentration was varied from 10 mM to 30 mM. An increase in the dye concentration leads to decrease in the percentage of its

3.2.5. Antimicrobial activity The antimicrobial activity of the PNT nanoparticles was tested against the gram positive (Staphylococcus), gram negative (Salmonella and Klebsiella) and fungal species (Aspergillus). The results for the antimicrobial activity of PNT are shown in Table 2 and

− ln (C /Co ) = kt

(3.3)

where Co is the initial concentration of MB at t¼ 0 min, C is the concentration of MB at irradiation time ‘t’ and k is the rate constant. The plot of  ln (C/Co) versus irradiation time ‘t’ is depicted in the Fig. 10 for the photodegradtion of MB in the presence of NiWO4 nanoparticles with and without the plant extract. Pseudo first order rate constant are evaluated from the slopes of  ln (C/Co) versus time plot. The rate constant (k) was calculated from the slopes and it was found to be 1.2  10  2 s  1 and 9  10  3 s  1 for PNT and NT respectively. Higher catalytic activity of NiWO4 obtained with the plant extract, presumably, explained by low electron-hole recombination restricted by the adsorbed layer of the extract.

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it is observed that PNT showed excellent anti-bacterial activity against staphylococcus, Klebsiella and Salmonella but it is resistance against Aspergillus. The remarkable antimicrobial activity of PNT is due to the generation of surface oxygen species which leads to the killing of the pathogens [42] (Fig. 11).

4. Conclusions Nanoparticles of NiWO4 are successfully prepared via precipitation method using A. indica plant extract as a capping agent and it is characterized by SEM, XRD, FT-IR and UV–vis-DRS. The TEM and XRD results show that the nanoparticles have spherical like morphology with an average crystallite size of 12.12 nm. PNT is found to be a more efficient photocatalyst for the degradation of MB under visible light than NT. The enhanced photocatalytic activity of PNT is presumably due to the suppression of electron– hole recombination. The reaction conditions are optimized and maximum photodegradation is achieved at 180 min with a PNT dosage of 0.05 g/L and MB concentration of 10 mM. PNT showed a better activity against Gram(þve) and Gram (  ve) bacteria.

Acknowledgement The authors are thankful to the Management of C.P.A. College for providing necessary laboratory facilities.

References [1] C.W.E. van Eijk, Nucl. Instrum. Methods A 392 (1997) 285–290. [2] R. Sundaram, K.S. Nagaraja, Mater. Res. Bull. 39 (2004) 557–565. [3] H. Wang, F.D. Medina, Y.D. Zhou, Q.N. Zhang, Phys. Rev. B 45 (1992) 10356–10361. [4] J.M. Quintana-Melgoza, A. Gomez-Cortes, M. Avalos-Borja, React. Kinet. Catal. Lett. 76 (2002) 131–140. [5] B. Scheffer, P. Molhoek, J.A. Moulijn, Appl. Catal. 46 (1989) 11–19. [6] T. Rabizadeh, S.R. Allahkaram, Mater. Des. 31 (2010) 3174–3179. [7] J. Ho Ryu, J. Yoon, C.S. Lim, W. Oh, K.B. Shim, Ceram. Int. 31 (2005) 883–888. [8] R.C. Pullar, S. Farrah, N.Mc.N. Alford, J. Eur. Ceram. Soc. 27 (2007) 1059–1063. [9] D.L. Stern, R.K. Grasselli, J. Catal. 167 (1997) 570–572. [10] R. Sundaram, K.S. Nagaraja, Mater. Res. Bull. 39 (2004) 581–590. [11] P.S. Pandey, N.S. Bhave, R.B. Kharat, Electrochim. Acta 51 (2006) 4659–4664.

129

[12] M. Asif, J. Pharmacogn. Phytochem. 4 (2012) 78–83. [13] A. Umar, H.T. Abdulrahman, M. Kokori, Res. J. Sci. 8 (1–2) (2002) 25–30. [14] A.M. Majumdar, A.S. Upadhyay, A.M. Pradhan, Indian J. Pharm. Sci. 60 (1998) 363–367. [15] V.K. Gupta, D. Pathaniab, P. Singh, A. Kumar, B.S. Rathore, Carbohydr. Polym. 101 (2014) 684–691. [16] S.S. Shankar, A. Rai, A. Ahmad, M. Sastry, J. Colloid Interface Sci. 275 (2004) 496–502. [17] M. Zawawi, R. Yahya, A. Hassan, H.N.M. Ekramul Mahmud, M.N. Daud, Chem. Cent. J. 7 (2013) 80. [18] A.L.M. de Oliveira, J.M. Ferreira, M.R.S. Silva, G.S. Braga, L.E.B. Soledade, A.M. A. Maurera, Dyes Pigments 77 (2008) 210–216. [19] A. Sen, P.A. Pramanik, J. Eur. Ceram. Soc. 21 (2001) 745–753. [20] R. Karimiana, F. Pirib, J. Nanostruct. 3 (2013) 87–92. [21] J.B. Harborne, Phytochemical Methods, 2nd ed., Chapman and Hall Ltd., London (1973), p. 49–188. [22] S.M. Pourmortazavi, M.R. Nasrabadi, M.K. Shalamzari, M.M. Zahedi, S. S. Hajimirsadeghi, I. Omrani, Appl. Surf. Sci. 263 (2012) 745–752. [23] K. Vignesh, A. Suganthi, M. Rajarajan, R. Sakthivadivel, Appl. Surf. Sci. 258 (2012) 4592–4600. [24] K. Vignesh, A. Suganthi, M. Rajarajan, S.A. Sara, Powder Technol. 224 (2012) 331–337. [25] M.M. Mohamed, S.A. Ahmeda, K.S. Khairou, Appl. Catal. B: Environ. 150–151 (2014) 63–73. [26] J. Zhu, W. Li, J. Li, Y. Li, H. Hu, Y. Yang, Electrochim. Acta 112 (2013) 191–198. [27] M.G. Nair, M. Nirmala, K. Rekha, A. Anukaliani, Mater. Lett. 65 (2011) 1797–1800. [28] P. Sathishkumar, R. Sweena, J.J. Wu, S. Anandan, Chem. Eng. J. 171 (2011) 136–140. [29] M. Mancheva, R. Iordanova, Y. Dimitriev, J. Alloys Compd. 509 (2011) 15–20. [30] P.V. Kamat, D. Meisel, Curr. Opin. Colloid Interface Sci. 7 (2002) 282–287. [31] M. Nasir, S. Bagwasi, Y. Jiao, F. Chen, B. Tian, J. Zhang, Chem. Eng. J. 236 (2014) 388–397. [32] B. Subhash, B. Krishnakumar, V. Pandian, M. Swaminathan, M. Shanthi, Sep. Purif. Technol. 96 (2012) 204–213. [33] N. Riaz, F.K. Chong, B.K. Dutta, Z.B. Man, M.S. Khan, E. Nurlaela, Chem. Eng. J. 108 (2012) 185–186. [34] A. Franco, M.C. Neves, M.M.L.R. Carrott, M.H. Mendonca, M.I. Pereira, O. C. Monteiro, J. Hazard. Mater. 161 (2009) 545–550. [35] R.J. Tayade, T.S. Natarajan, H.C. Bajaj, Ind. Eng. Chem. Res. 48 (2009) 10262–10267. [36] J. Lin, R. Zong, M. Zhou, Y. Zhu, Appl. Catal. B: Environ. 89 (2009) 425–431. [37] A. Nageswara Rao, B. Sivasankar, V. Sadasivam, J. Mol. Catal. A: Chem. 306 (2009) 77–81. [38] P. Bansal, D. Sud, Desalination 267 (2011) 244–249. [39] P. SathishKumar, R. Sivakumar, S. Anandan, J. Madhavan, P. Maruthamuthu, M. Ashokkumar, Water Res. 42 (2008) 4878–4884. [40] R. Velmurugan, M. Swaminathan, Sol. Energy Mater. Sol. Cells 95 (2011) 942–950. [41] W. Zhao, Z. Bai, A. Ren, B. Guo, C. Wu, Appl. Surf. Sci. 256 (2010) 3493–3498. [42] E.I. Rabea, M.E. Badawy, C.V. Stevens, G. Smagghe, W. Steurbaut, Biomacromolecules. 4 (6) (2003) 1457–1465.