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Photocatalytic activity of ZnO and Sr2+ doped ZnO nanoparticles
Journal of Water Process Engineering 17 (2017) 264–270
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Journal of Water Process Engineering journal homepage: www.elsevier.com/locate/jwpe
Photocatalytic activity of ZnO and Sr2+ doped ZnO nanoparticles Nimisha N. Kumaran, K. Muraleedharan
⁎
MARK
Department of Chemistry, University of Calicut, Calicut, 673635, India
A R T I C L E I N F O
A B S T R A C T
Keywords: Sr2+ doped ZnO nanoparticles Co-precipitation Photo-catalytic activity
The photocatalytic activity of ZnO and Sr2+ doped ZnO nanoparticles was evaluated by photocatalyic oxidation of methyl orange and methylene blue. The results show that the photocatalytic activity of Sr2+ doped ZnO was much higher than that of pure ZnO. The sample with mole ratio of Sr/Zn 1:2 show the maximum activity. The effect of heat treatment on photocatalytic activity of the samples was studied in the temperature range 400–800° C and found that the sample calcined at 600° C shows the maximum activity. The dependence of calcination time on the photo-catalytic activity was studied and observed that the best heat treatment time is 7 h.
1. Introduction The major sources of pollution in water and air are chemicals released from industries. Textile industry is one of the major sources of the pollutants such as coloured organic reagents; the dyes. The presence of such pollutants in ground and surface water are harmful to human as well as aquatic life. Some of them are carcinogenic and mutagenic as well as genotoxic and therefore, a technology for cleaning the water is very important [1]. Use of semiconductor based material as photocatalyst in the detoxification of pollutants has several advantages over any other treatment methods. Major advantage is that it gives complete mineralization in to eco-friendly products without generation of waste [2,3]. Even though anatase TiO2 is the most studied photocatalyst, many researchers are in search of an alternative to TiO2. ZnO appears to be one of the promising photocatalysts which has a band gap almost similar to that of anatase TiO2. Currently zinc oxide is used as a potential photocatalyst due to its powerful oxidation capability, nontoxicity, chemical stability and low cost. High surface reactivity of zinc oxide results in the formation of large number of defect sites arising from oxygen nonstoichiometry which make zinc oxide a good photocatalyst than other metal oxides. Also zinc oxide can generate hydroxyl ions more efficiently than titania [4]. Modification of the surface of zinc oxide plays an important role in making the material useful for numerous applications. The modification should improve the performance of materials like photocatalytic activity, conductivity, etc [5]. The most widely used method for modification of the surface of zinc oxide is doping. Changing the stiochiometric amounts of metal ions within a metal oxide by doping with another metal cation can generate new and interesting properties. Considering the factor electronic structure which affects the doping
⁎
Corresponding author. E-mail address: [email protected] (K. Muraleedharan).
http://dx.doi.org/10.1016/j.jwpe.2017.04.014 Received 17 March 2016; Received in revised form 13 April 2017; Accepted 29 April 2017 2214-7144/ © 2017 Elsevier Ltd. All rights reserved.
effects and size of the nanoparticles, alkaline earth metal ions are the best choice for doping than transition metals. Because localized d-levels are absent in alkaline earth metals. These localized d-levels can decrease the photo threshold energy of semiconductors in the case of transition metal doping [6]. Co- precipitation is one of the methods used for the synthesis of nanopowders. The major advantages of this method are; reaction temperature is reduced due to homogeneous mixing of reactant precipitates and metal powders formed are highly reactive in low temperature sintering, which lead to the formation of smaller particles [7–11]. Further in co-precipitation process, the concentration of the solution, pH, temperature and stirring speed of the mixture has a control over the formation of the final product with required properties [12,13]. Extensive investigations have been carried out to study the change in structure, photocatalytic activity, anti microbial activity, etc., of the doped ZnO nanoparticles by co-precipitation method [14–25]. NitiYongvanich reported the synthesis of Sr-doped ZnO based nanopowders by chemical co-precipitation. The effect of Sr doping on the microstructure of ZnO based varistors was also reported [26]. RamnYousefi et al. studied the enhanced visible light photocatalytic activity of Sr-doped ZnO nanoparticles by studying the degradation of methylene blue [27]. Efficient treatment of grey water by solar photocatalysis using TiO2–chitosan film [28], Liquid-phase photocatalytic oxidation of a secondary diazo dye compound, Congo red (CR, C32H22N6Na2O6S2) and pharmaceutical phthalylsulfathiazole, in a cylindrical photochemical reactor on gold-loaded titania systems [29], Photo-catalytic degradation of methyl violet dye using zinc oxide nano particles [30] etc., have been extensively studied. In the present study, ZnO and Sr2+ doped ZnO nanoparticles were prepared by co-precipitation method and the photocatalytic activity of
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N.N. Kumaran, K. Muraleedharan
the samples was evaluated by photocatalyic oxidation of methyl orange (anionic dye) and methylene blue (cationic dye). 2. Experimental 2.1. Materials Zinc nitrate, strontium nitrate, ammonium carbonate, methyl orange and methylene blue are used as raw maretials for the synthesis and photocatalytic study of Sr2+ doped ZnO nanoparticles. All the chemicals used were of AnalaR grade reagents of Merck India. 2.2. Synthesis of ZnO and Sr2+ doped ZnO nanoparticles ZnO and Sr2+ doped ZnO nanoparticles were prepared by simple coprecipitation method. For doping the solutions of Zn(NO3)2 and Sr (NO3)2 in distilled water were mixed by vigorous stirring for 30 min, 1 M (NH4)2CO3 solution is then added to the mixture drop wise till the formation of colloidal solution. The colloidal solution formed was dried at 70 °C for 24 h in an air oven, kept at 60 °C and then calcined. Different compositions of Sr2+ doped ZnO nanoparticles were prepared in a similar way. The calcination temperature ranges from 400 to 800 °C. Calcination time was also changed from 4 to 8 h. Un-doped ZnO was also prepared in the same manner without using Sr(NO3)2 (Table 1).
Fig. 1. XRD patterns of ZnO (a), SZO-12-400 (b), SZO-12-600 (c) and SZO-12-800 (d).
Table 2 The average crystalline size of pure and doped ZnO.
2.3. Photocatalytic study The photocatalytic activity of ZnO and Sr2+ doped ZnO were investigated by the degradation of methyl orange (MO) and methylene blue (MB) solution under UV light. A concentration of 10−5 M (MO and MB) was used in all experiments. For a typical experiment, 50 mL of 10−5 M solution of the dye was taken in a 100 mL beaker, added 0.1 g of calcined ZnO, stirred for 10 min in the dark and then irradiated under UV light in a Luzchem LZC-4X reactor containing 16 lamps. Degradation was monitored by taking aliquots at different time intervals. It was then centrifuged for 30 min, after recovering the catalyst the clear solution was subjected to absorption spectra analysis. The same experimental procedure was adopted for each sample of Sr2+ doped ZnO. The rate constant of degradation, k was obtained from the firstorder plot according to Eq. (1): ln A0/A = kt
Sample
2θ (degree)
Distance between planes (Å)
Full width at half maximum (degree)
Particle Size (nm)
ZnO SZO-12-400 SZO-12-600 SZO-12-800
36.27 36.14 36.13 36.06
2.4744 2.483 2.4841 2.489
0.417 0.412 0.410 0.328
20.9 21.2 21.3 26.6
(1)
2.4. Characterization The X-ray diffraction (XRD) patterns of the samples were obtained in a scanning range of 20–75° by an X-ray diffractometer (Model: RIGAKU MINIFLEX 600) with Cu Kα radiation (λ = 0.15406 nm). The XRD was used to examine the nature of crystalline state of the samples. Optical properties of the samples were characterized at room temperature by using a UV–visible spectrometer; Model: JASCO V 570. The surface morphology of the samples was observed by using a scanning electron microscope (SEM); Model: Hitachi SU-6600 FESEM. The
Fig. 2. FT-IR spectra of ZnO (a), SZO14 (b), SZO12 (c), SZO11 (d), SZO21 (e) and SZO41 (f) calcined at 400° C for 3 h.
chemical structure of the different samples were characterized by KBr disc method with a Fourier transform infrared (FTIR) spectrometer (JASCO FT-IR-4100) and analyzed over the range 3500–500 cm−1.
3. Results and discussion Table 1 Preparation of different compositions of Sr2+ doped ZnO nanoparticles. Sample
Sr/Zn molar ratio
Mass of Sr (NO3)2 (g)
Mass of Zn (NO3)2 (g)
SZO-14 SZO-12 SZO-11 SZO-21 SZO-41
1:4 1:2 1:1 2:1 4:1
2.1163 2.1163 2.1163 4.2326 8.4652
11.8988 7.097 5.9494 2.9747 2.9747
The XRD patterns of the prepared samples are shown in Fig. 1. The XRD peaks are located at angles (2θ) of 31.81, 34.45, 36.27, 38.36, 40.20, 47.49, 56.65, 62.85, 67.95 and 69.13° corresponding to (100), (002), (102), (110), (110), (103), (112), (201), (004) and (202) planes of ZnO nanoparticles respectively. The standard diffraction peaks shows the hexagonal wurtzite structure of ZnO nanoparticles with P63mc space group. This is also confirmed by the JCPDS data (Card No. 361451). The Sr2+ doped ZnO sample (SZO-12), calcined at 400° C, shows 265
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peaks at angles (2θ) of 31.65, 34.24, 36.14, 47.43, 56.59, 62.75, 67.79 and 69.05° corresponding to (100), (002), (102), (103), (112), (201), (004) and (202) planes respectively. When the sample SZO-12 is calcined at 600° C the peaks are observed at angles (2θ) of 31.64, 34.29, 36.13, 47.45, 56.51, 62.75, 67.82 and 69.01° corresponding to (100), (002), (102), (103), (112), (201), (004) and (202) planes respectively. The peaks are located at angles (2θ) of 31.68, 34.25, 36.06, 47.44, 56.50, 62.75, 67.62 and 68.97° corresponding to (100), (002), (102), (103), (112), (201), (004) and (202) planes respectively for the sample SZO-12, calcined at 800° C. The doped ZnO samples shows additional peaks located at angles (2θ) of 24.95, 24.96 and 25.03° when calcined respectively at 400, 600 and 800° C which indicate the presence of SrCO3. The particle size of the samples is determined by the X-ray line broadening method using the Scherrer equation. The average crystalline size of the pure and doped ZnO samples is given in Table 2. The FT-IR spectroscopic analysis reveals the different bond vibrations present in the pure and Sr2+ doped ZnO nanoparticles; the recorded FT-IR spectra are shown in Fig. 2. The intense absorption bands in the range 600–400 cm−1 are diagnostic of ZnO. For pure ZnO the FT-IR spectrum consists of a strong absorption band at 444 cm−1. The peak in the range of 3650–3020 cm−1 corresponds to the vibrational mode of OeH. The absorption peaks are observed at 3435, 3434, 3449, 3418, and 3426 cm−1 for the pure ZnO, doped SZO-11, SZO-12, SZO-14, SZO-21 and SZO-41 respectively due to the OeH stretching of the absorbed water molecules. The absorption band at 1632 cm−1 is assigned to the OeH bending vibrations. The bands observed in the range 1800- 400 cm−1 are due to the vibration in CO32−. The weak absorption bands observed at 1770 cm−1 is corresponding to SrCO3. The broad absorption bands observed at 1455, 1458, 1472, 1457 and 1444 cm−1 for doped SZO-11, SZO-12, SZO-14, SZO-21 and SZO-41 respectively are due to the asymmetric vibrations in SrCO3. The diffuse reflectance spectroscopy was used to obtain the band gap energy value of pure and Sr2+doped ZnO nanoparticles. The spectra of all the samples, studied, were measured in the wavelength region 200–800 nm and the results are shown in Figs. 3 and 4 . The undoped ZnO samples shows a maximum absorption peak in the range 350–450 nm which is due to the transition of electrons from valence band to conduction band. Sr2+ doped ZnO sample shows slightly red shifted peaks in the range 400–500 nm due to the effect of doping. As a result the band gap energy of Sr2+ doped ZnO sample is decreases compared to undoped ZnO. It can be speculated that the metal ions were in the internal ZnO lattice and that the interaction of the doping ions with the ZnO destroys part of the original lattice, forming lattice defects and making the ZnO absorption edge mobile [31]. The red shift in the absorption wavelength range and the increase in the absorption intensity shows that the rate of formation of electron – hole pairs on the catalyst surface increass greatly, resulting in the catalyst exhibiting a
Fig. 3. The DRS spectra of ZnO and Sr2+dopd ZnO calcined at 400° C.
Fig. 4. The DRS spectra of ZnO (a) and SZO-12 calcined at 400 (b), 500 (c), 600 (d), 700 (e) and 800° C (f). Table 3 The band gap energies of pure and doped ZnO nanoparticles. Without Calicination
Calcined
Sample
Band gap energy (eV)
Sample
Band gap energy (eV)
ZnO SZO-11 SZO-12 SZO-14 SZO-21 SZO-41
3.1 3.08 2.97 2.98 2.99 3.01
SZO-12-400 SZO-12-500 SZO-12-600 SZO-12-700 SZO-12-800
2.99 3 3.02 3.04 3.11
Fig. 5. SEM images of ZnO (a) and Sr2+ doped ZnO nanoparticles (b) calcined at 600° C for 7 h.
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Fig. 6. Absorption spectra of the degradation of the dye, methyl orange, under UV light by ZnO (a) and SZO-12 (b) calcined at 400 °C for 3 h.
Fig. 7. (1) Photocatalytic efficiency and (2) Kinetic study of the degradation of methyl orange under UV light by ZnO (a), SZO-14 (b), SZO-12 (c), SZO-11 (d), SZO-21 (e) and SZO-41(f) calcined at 400° C for 3 h.
Fig. 8. Effect of calcination temperature on photocatalytic activity of doped samples on the degradation of methyl orange.
high surface energy [32]. Methylene blue (MB) and methyl orange (MO) dyes were used in the present study as a target of photo degradation. The photocatalytic activity of the samples was executed by the degradation of dyes in aqueous solution. Before irradiation with a lamp light, the samples were stirred in the dark for fifteen minutes. The results shows that the concentration of dye decreases slightly, which indicates that there is no degradation in the absence of irradiation. When the photocatalytic reaction was conducted in aqueous medium, the holes were effectively scavenged by the water and generated hydroxyl radical OH%, which are strong and unselected oxidant species in respect of totally oxidative degradation for organic substrates. The holes, free electrons, superoxide and hydroxyl radicals have been the species responsible for the
higher photocatalytic efficiency. The reason for the red shift in the absorption wavelength range for the Sr2+ doped ZnO was likely to the formation of defect energy level between the valence band and the conduction band in the ZnO band structure. This would have an important role in improving the catalytic activity of ZnO. The band gap energies of all the samples of pure and doped ZnO, studied, are given in Table 3. The morphology of ZnO and Sr2+ doped ZnO samples were analyzed using scanning electron microscopy. The SEM images of ZnO and doped ZnO samples calcined at 600° C for 7 h is shown in Fig. 5. The images indicate the aggregation of particles in both undoped ZnO and Sr2+ doped ZnO samples. The aggregation of nanoparticles may be due to the presence of large surface area to volume ratio and 267
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Fig. 9. Effect of calcination time on photocatalytic activity of doped samples on the degradation of methyl orange.
Fig. 10. Absorption spectra of the degradation of the dye, methylene blue, under UV light by ZnO (a) and SZO-12 (b) calcined at 400 °C for 3 h.
Fig. 11. (1) Photocatalytic efficiency and (2) Kinetic study of the degradation of methylene blue under UV light by the samples ZnO (a), SZO-14 (b), SZO-12 (c), SZO-11 (d), SZO-21 (e) and SZO-41(f) calcined at 400° C for 3 h.
Fig. 12. Effect of calcination temperature on photocatalytic activity of doped samples on the degradation of methyl orange.
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Fig. 13. Effect of calcination time on photocatalytic activity of doped samples on the degradation of methylene blue.
place within 25 min for the sample SZO-12, whereas undoped ZnO takes about 70 min to complete its degradation. The SZO-12 samples were calcined at 400, 500, 600, 700 and 800 °C for 3 h and the photocatalytic activity of these samples were studied and the results are shown in Fig. 8. The sample calcined at 600 °C shows maximum activity. The calcination time of the sample at 600 °C was varied from 4 to 8 h and the results are shown in Fig. 9. The sample obtained after calcination for 7 h was found to be highly active. Fig. 10 shows the absorption spectra of the degradation of methylene blue dye under UV light by samples ZnO (a) and SZO-12 (b) calcined at 400 °C for 3 h. Fig. 11(1) shows the photocatalytic efficiency of undoped and doped ZnO. The kinetic studies (Fig. 11 (2)) show that the maximum photocatalytic activity was obtained for the doped sample SZO-12. The maximum reaction rate of 0.129 min−1 corresponds to the sample SZO-12 while its undoped counterpart shows only a value of 0.054 min−1. The degradation takes place within 15 min for the sample SZO-12, whereas undoped ZnO takes about 80 min to complete its degradation. When studied the effect of calcination temperature (SZO-12 samples were calcined at 400, 500, 600, 700 and 800 °C for 3 h) on the photocatalytic activity of these samples (shown in Fig. 12) it has been found that the sample calcined at 600 °C shows maximum activity. The dependence of calcination time on the photocatalytic activity shows (Fig. 13) that the sample obtained after calcination for 7 h was found to be highly active. Rate constant for the degradation of the dye by different samples are given in Tables 4 and 5.
Table 4 Values of rate constant for methyl orange degradation by different samples. Sample
Rate constant (min−1)
Calcination Temperature (°C)
ZnO SZO-14 SZO-12 SZO-11 SZO-21 SZO-41
0.043 0.063 0.098 0.085 0.066 0.010
SZO-12 400 500 600 700 800
Rate constant (min−1)
0.096 0.097 0.118 0.033 0.016
Calcination time (h)
SZO-12-600 4 5 6 7 8
Rate constant (min−1)
0.048 0.068 0.072 0.129 0.064
degradation of the organic substrates [33,34]. The reaction process can be proposed as: ZnO + hν → h+ + e−
(2)
e− + O2 → O2−
(3)
h+ + OH− → OH%
(4)
O2− + 2H+ → 2OH%
(5)
OH% + dye → degradation products
(6)
The degradation of both dyes was evaluated using pure and doped ZnO samples. Among the doped samples, the sample having Sr/Zn ratio 1:2 (SZO-12) shows the maximum activity. Fig. 6 shows the absorption spectra of the degradation of methyl orange dye under UV light by the samples ZnO (a) and SZO-12 (b) calcined at 400 °C for 3 h. Fig. 7 (1) shows the photocatalytic efficiency of undoped and doped ZnO. The kinetic studies (Fig. 7 (2)) show that the maximum photocatalytic activity was obtained for the doped sample SZO-12. The maximum reaction rate 0.098 min−1 corresponds to the sample SZO-12 while its undoped counterpart has only 0.043 min−1. The degradation takes
5. Conclusion ZnO and Sr2+ doped ZnO nanoparticles were prepared by coprecipitation method. XRD results reveal that both ZnO and doped ZnO have wurtzite structure. The particle size was found to be 20.9 nm for ZnO and in the range 21–26 nm for the doped samples. The FT-IR spectra confirm the presence of ZnO and also the presence of SrCO3 in the doped samples. The Diffuse reflectance spectra shows that the Sr2+ doped ZnO have a significant shift to longer wavelength and that results
Table 5 Values of rate constant for methylene blue degradation by different samples. Sample
Rate constant (min−1)
Calcination Temperature (°C)
Rate constant (min−1)
Calcination time (h)
Rate constant (min−1)
ZnO SZO-14 SZO-12 SZO-11 SZO-21 SZO-41
0.054 0.118 0.129 0.066 0.068 0.027
SZO-12 400 500 600 700 800
0.129 0.133 0.185 0.150 0.117
SZO-12-600 4 5 6 7 8
0.125 0.140 0.177 0.290 0.162
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[16] M. Mukhtar, L. Munisa, R. Saleh, Co-precipitation synthesis and characterization of nanocrystalline zinc oxide particles doped with Cu2+ ions, Mater. Sci. Appl. 3 (2012) 543–551. [17] R. Amrousse, B. Ahmed, Synthesis and characterization of homogeneous ZnO and Mn–doped ZnO nanoparticles, Adv. Sci. Focus 1 (2013) 9–12. [18] K. Rekha, M. Nirmala, Manjula G. Nair, A. Anukaliani, Structural, optical, photocatalytic and antibacterial activity of zinc oxide and manganese doped zinc oxide nanoparticles, Physica B 405 (2010) 3180–3185. [19] K. Milenova, I. Stambolova, V. Blaskov, A. Eliyas, S. Vassilev, M. Shipochka, The effect of introducing copper dopant on the photocatalytic activity of ZnO nanoparticles, J. Chem. Technol. Metall. 48 (2013) 259–264. [20] T.H. Le, A.T. Bui, T.K. Le, The effect of Fe doping on the suppression of photocatalytic activity of ZnO nanopowder for the application in sunscreens, Powder Technol. 268 (2014) 173–176. [21] Q. Xiao, L. Ouyang, Photocatalytic photodegradation of xanthate over Zn1-xMnxO under visible light irradiation, J. Alloys Compd. 479 (2009) L4–L7. [22] X. Qiu, L. Li, J. Zheng, J. Liu, X. Sun, G. Li, Origin of the enhanced photocatalytic activities of semiconductors: a case study of ZnO doped with Mg2+, J. Phys. Chem. C 112 (2008) 12242–12248. [23] C. Tang, Study of photocatalytic degradation of methyl orange on different morphologies of ZnO catalysts, Mod. Res. Catal. 2 (2013) 19–24. [24] K. Yu, J. Shi, Z. Zhang, Y. Liang, W. Liu, Synthesis, characterization and photocatalysis of ZnO and Er-doped ZnO, J. Nanomater. (2013) 1–5. [25] E. Vinodkumar, R. Roshan, V. Kumar, Mg-doped ZnO nanoparticles for efficient sunlight-driven photocatalysis, ACS Appl. Mater. Interfaces 4 (2012) 2717–2725. [26] N. Yongvanich, Synthesis of strontium-doped ZnO-based nanopowders by chemical co-precipitation, Chiang Mai J. Sci. 40 (2013) 1046–1054. [27] R. Yousefi, F.J. Sheini, M. Cheraghizade, S.K. Gandomani, A. Saaedi, N.M. Huang, W.J. Basirun, M. Azarang, Enhanced visible-light photocatalytic activity of strontium-doped zinc oxide nanoparticles, Mater. Sci. Semicond. Process 32 (2015) 152–159. [28] I. Grčić, D. Vrsaljko, Z. Katančić, S. Papić, Purification of household greywater loaded with hair colorants by solar photocatalysis using TiO2-coated textile fibers coupled flocculation with chitosan, J. Water Proc. Eng. 5 (2015) 15–27. [29] D. Zhang, J. Wang, UV–visible light-activated Au@ pre-sulphated, monodisperse TiO2 aggregates for treatment of congo red and phthalylsulfathiazole, J. Water Proc. Eng. 7 (2015) 187–195. [30] K. Jeyasubramaniana, G.S. Hikku, R. Krishna Sharma, Photo-catalytic degradation of methyl violet dye using zinc oxide nano particles prepared by a novel precipitation method and its anti-bacterial activities, J. Water Proc. Eng. 8 (2015) 35–44. [31] Y. Ling, W. Jiang, X. Wu, X. Bai, Preparation and visible light photocatalytic properties of (Er, La, N)-codoped TiO2 nanotube array films, J. Nanosci. Nanotechnol. 9 (2009) 714–717. [32] J. Kaur, S. Bansal, S. Singhal, Photocatalytic degradation of methyl orange using ZnO nanopowders synthesized via thermal decomposition of oxalate precursor method, Physica B 416 (2013) 33–38. [33] T. Tan, Y. Li, Y. Liu, B. Wang, X. Song, E. Li, H. Wang, H. Yan, Two- step preparation of Ag/tetrapod-like ZnO with photocatalytic activity by thermal evaporation and sputtering, Mater. Chem. Phys 111 (2008) 305–308. [34] D. Zhang, X. Pu, H. Li, Y.M. Yu, J.J. Shim, P. Cai, S.I. Kim, H.J. Seo, Microwaveassisted combustion synthesis of Ag/ZnO nanocomposites and their photocatalytic activities under ultraviolet and visible-light irradiation, Mater. Res. Bull. 61 (2015) 321–325.
a reduction in band gap. The SEM images confirm that the particles were aggregated. The photocatalytic activity of the samples were evaluated by photocatalyic oxidation of the dyes, methyl orange and methylene blue and the results shows that the photocatalytic activity of Sr2+ doped ZnO was much higher than that of pure ZnO. The sample with mole ratio of Sr/Zn 1:2 calcined at 600° C for 7 h shows the maximum activity. It has been found that the cationic methylene blue gets degraded faster than anionic methyl orange which may be due to the accumulation of more negative charges on the surface of the catalyst. References [1] T. Robinson, G. McMullan, R. Marchant, P. Nigam, Remediation of dyes in textile effluent: a critical review on current treatment technologies with a proposed alternative, Bioresour. Technol. 77 (2001) 247–255. [2] S. Chakrabarti, B.K. Dutta, Photocatalytic degradation of model textile dyes in wastewater using ZnO as semiconductor catalyst, J. Hazard. Mater. 112 (2004) 269–278. [3] G.P. Fotou, S.E. Pratsinis, Photocatalysis of phenol and salicylic acid by aerosolmade titania powders, Chem. Eng. Commun. 151 (1996) 251–269. [4] K. Gouvea, F. Wypych, S.G. Moraes, N. Duran, N. Nagataand, P. Peralta-Zamora, Semiconductor-assisted photocatalytic degradation of reactive dyes in aqueous solution, Chemosphere 40 (2000) 433–440. [5] V. Uskoković, M. Drofenik, Synthesis of materials within reverse micelles, Surf. Rev. Lett. 12 (2005) 239–277. [6] X. Qiu, G. Li, X. Sun, L. Li1, X. Fu, Doping effects of Co2+ ions on ZnO nanorods and their photocatalytic properties, Nanotechnology 19 (2008) 215–703. [7] A.B. Gaikwad, S.C. Navale, V. Samuel, A.V. Murugan, V. Ravi, A co-precipitation technique to prepare BiNbO4, MgTiO3 and Mg4Ta2O9 powders, Mater. Res. Bull. 41 (2006) 347–353. [8] A.K. Radzimska, T. Jesionowski, Zinc oxide—from synthesis to application: a review, Mater. Lett. 7 (2014) 2833–2881. [9] K.S. Suslick, S.B. Choe, A.A. Cichowlas, M.M. Grinstaff, Synthesis of amorphous iron, Nature 353 (1991) 414–416. [10] J. Chen, Y. Wang, F. Guo, X. Wang, C. Zheng, Synthesis of nanoparticles with novel technology: high-gravity reactive precipitation, Ind. Eng. Chem. Res. 39 (2000) 948–954. [11] John Regalbuto, Catalyst Preparation: Science and Engineering, CRC press, Tailor & Francis group, 2007. [12] M.F. Zawrah, H. Hamaad, S. Meky, Synthesis and characterization of nano MgAl2O4 spinel by the co-precipitated method, Ceram. Int. 33 (2007) 969–978. [13] G. Xu, X. Zhang, W. He, H. Liu, H. Li, R.I. Boughton, Preparation of highly dispersed YAG nano-sized powder by co-precipitation method, Mater. Lett. 60 (2006) 962–965. [14] S. Chen, Y. Yang, M. Ji, W. Liu, Preparation, characterisation and activity evaluation of CaCO3/ZnO photocatalyst, J. Exp. Nanosci. 6 (2011) 324–336. [15] A.S. Haja Hameed, C. Karthikeyan, S. Sasikumar, V. Senthil Kumar, S. Kumaresan, G. Ravi, Impact of alkaline metal ions Mg2+, Ca2+ Sr2+ and Ba2+ on the structural, optical, thermal and antibacterial properties of ZnO nanoparticles prepared by the co-precipitation method, J. Mater. Chem. B 1 (2013) 5950–5962.
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Photocatalytic activity of ZnO and Sr2+ doped ZnO nanoparticles Nimisha N. Kumaran, K. Muraleedharan
⁎
MARK
Department of Chemistry, University of Calicut, Calicut, 673635, India
A R T I C L E I N F O
A B S T R A C T
Keywords: Sr2+ doped ZnO nanoparticles Co-precipitation Photo-catalytic activity
The photocatalytic activity of ZnO and Sr2+ doped ZnO nanoparticles was evaluated by photocatalyic oxidation of methyl orange and methylene blue. The results show that the photocatalytic activity of Sr2+ doped ZnO was much higher than that of pure ZnO. The sample with mole ratio of Sr/Zn 1:2 show the maximum activity. The effect of heat treatment on photocatalytic activity of the samples was studied in the temperature range 400–800° C and found that the sample calcined at 600° C shows the maximum activity. The dependence of calcination time on the photo-catalytic activity was studied and observed that the best heat treatment time is 7 h.
1. Introduction The major sources of pollution in water and air are chemicals released from industries. Textile industry is one of the major sources of the pollutants such as coloured organic reagents; the dyes. The presence of such pollutants in ground and surface water are harmful to human as well as aquatic life. Some of them are carcinogenic and mutagenic as well as genotoxic and therefore, a technology for cleaning the water is very important [1]. Use of semiconductor based material as photocatalyst in the detoxification of pollutants has several advantages over any other treatment methods. Major advantage is that it gives complete mineralization in to eco-friendly products without generation of waste [2,3]. Even though anatase TiO2 is the most studied photocatalyst, many researchers are in search of an alternative to TiO2. ZnO appears to be one of the promising photocatalysts which has a band gap almost similar to that of anatase TiO2. Currently zinc oxide is used as a potential photocatalyst due to its powerful oxidation capability, nontoxicity, chemical stability and low cost. High surface reactivity of zinc oxide results in the formation of large number of defect sites arising from oxygen nonstoichiometry which make zinc oxide a good photocatalyst than other metal oxides. Also zinc oxide can generate hydroxyl ions more efficiently than titania [4]. Modification of the surface of zinc oxide plays an important role in making the material useful for numerous applications. The modification should improve the performance of materials like photocatalytic activity, conductivity, etc [5]. The most widely used method for modification of the surface of zinc oxide is doping. Changing the stiochiometric amounts of metal ions within a metal oxide by doping with another metal cation can generate new and interesting properties. Considering the factor electronic structure which affects the doping
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Corresponding author. E-mail address: [email protected] (K. Muraleedharan).
http://dx.doi.org/10.1016/j.jwpe.2017.04.014 Received 17 March 2016; Received in revised form 13 April 2017; Accepted 29 April 2017 2214-7144/ © 2017 Elsevier Ltd. All rights reserved.
effects and size of the nanoparticles, alkaline earth metal ions are the best choice for doping than transition metals. Because localized d-levels are absent in alkaline earth metals. These localized d-levels can decrease the photo threshold energy of semiconductors in the case of transition metal doping [6]. Co- precipitation is one of the methods used for the synthesis of nanopowders. The major advantages of this method are; reaction temperature is reduced due to homogeneous mixing of reactant precipitates and metal powders formed are highly reactive in low temperature sintering, which lead to the formation of smaller particles [7–11]. Further in co-precipitation process, the concentration of the solution, pH, temperature and stirring speed of the mixture has a control over the formation of the final product with required properties [12,13]. Extensive investigations have been carried out to study the change in structure, photocatalytic activity, anti microbial activity, etc., of the doped ZnO nanoparticles by co-precipitation method [14–25]. NitiYongvanich reported the synthesis of Sr-doped ZnO based nanopowders by chemical co-precipitation. The effect of Sr doping on the microstructure of ZnO based varistors was also reported [26]. RamnYousefi et al. studied the enhanced visible light photocatalytic activity of Sr-doped ZnO nanoparticles by studying the degradation of methylene blue [27]. Efficient treatment of grey water by solar photocatalysis using TiO2–chitosan film [28], Liquid-phase photocatalytic oxidation of a secondary diazo dye compound, Congo red (CR, C32H22N6Na2O6S2) and pharmaceutical phthalylsulfathiazole, in a cylindrical photochemical reactor on gold-loaded titania systems [29], Photo-catalytic degradation of methyl violet dye using zinc oxide nano particles [30] etc., have been extensively studied. In the present study, ZnO and Sr2+ doped ZnO nanoparticles were prepared by co-precipitation method and the photocatalytic activity of
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the samples was evaluated by photocatalyic oxidation of methyl orange (anionic dye) and methylene blue (cationic dye). 2. Experimental 2.1. Materials Zinc nitrate, strontium nitrate, ammonium carbonate, methyl orange and methylene blue are used as raw maretials for the synthesis and photocatalytic study of Sr2+ doped ZnO nanoparticles. All the chemicals used were of AnalaR grade reagents of Merck India. 2.2. Synthesis of ZnO and Sr2+ doped ZnO nanoparticles ZnO and Sr2+ doped ZnO nanoparticles were prepared by simple coprecipitation method. For doping the solutions of Zn(NO3)2 and Sr (NO3)2 in distilled water were mixed by vigorous stirring for 30 min, 1 M (NH4)2CO3 solution is then added to the mixture drop wise till the formation of colloidal solution. The colloidal solution formed was dried at 70 °C for 24 h in an air oven, kept at 60 °C and then calcined. Different compositions of Sr2+ doped ZnO nanoparticles were prepared in a similar way. The calcination temperature ranges from 400 to 800 °C. Calcination time was also changed from 4 to 8 h. Un-doped ZnO was also prepared in the same manner without using Sr(NO3)2 (Table 1).
Fig. 1. XRD patterns of ZnO (a), SZO-12-400 (b), SZO-12-600 (c) and SZO-12-800 (d).
Table 2 The average crystalline size of pure and doped ZnO.
2.3. Photocatalytic study The photocatalytic activity of ZnO and Sr2+ doped ZnO were investigated by the degradation of methyl orange (MO) and methylene blue (MB) solution under UV light. A concentration of 10−5 M (MO and MB) was used in all experiments. For a typical experiment, 50 mL of 10−5 M solution of the dye was taken in a 100 mL beaker, added 0.1 g of calcined ZnO, stirred for 10 min in the dark and then irradiated under UV light in a Luzchem LZC-4X reactor containing 16 lamps. Degradation was monitored by taking aliquots at different time intervals. It was then centrifuged for 30 min, after recovering the catalyst the clear solution was subjected to absorption spectra analysis. The same experimental procedure was adopted for each sample of Sr2+ doped ZnO. The rate constant of degradation, k was obtained from the firstorder plot according to Eq. (1): ln A0/A = kt
Sample
2θ (degree)
Distance between planes (Å)
Full width at half maximum (degree)
Particle Size (nm)
ZnO SZO-12-400 SZO-12-600 SZO-12-800
36.27 36.14 36.13 36.06
2.4744 2.483 2.4841 2.489
0.417 0.412 0.410 0.328
20.9 21.2 21.3 26.6
(1)
2.4. Characterization The X-ray diffraction (XRD) patterns of the samples were obtained in a scanning range of 20–75° by an X-ray diffractometer (Model: RIGAKU MINIFLEX 600) with Cu Kα radiation (λ = 0.15406 nm). The XRD was used to examine the nature of crystalline state of the samples. Optical properties of the samples were characterized at room temperature by using a UV–visible spectrometer; Model: JASCO V 570. The surface morphology of the samples was observed by using a scanning electron microscope (SEM); Model: Hitachi SU-6600 FESEM. The
Fig. 2. FT-IR spectra of ZnO (a), SZO14 (b), SZO12 (c), SZO11 (d), SZO21 (e) and SZO41 (f) calcined at 400° C for 3 h.
chemical structure of the different samples were characterized by KBr disc method with a Fourier transform infrared (FTIR) spectrometer (JASCO FT-IR-4100) and analyzed over the range 3500–500 cm−1.
3. Results and discussion Table 1 Preparation of different compositions of Sr2+ doped ZnO nanoparticles. Sample
Sr/Zn molar ratio
Mass of Sr (NO3)2 (g)
Mass of Zn (NO3)2 (g)
SZO-14 SZO-12 SZO-11 SZO-21 SZO-41
1:4 1:2 1:1 2:1 4:1
2.1163 2.1163 2.1163 4.2326 8.4652
11.8988 7.097 5.9494 2.9747 2.9747
The XRD patterns of the prepared samples are shown in Fig. 1. The XRD peaks are located at angles (2θ) of 31.81, 34.45, 36.27, 38.36, 40.20, 47.49, 56.65, 62.85, 67.95 and 69.13° corresponding to (100), (002), (102), (110), (110), (103), (112), (201), (004) and (202) planes of ZnO nanoparticles respectively. The standard diffraction peaks shows the hexagonal wurtzite structure of ZnO nanoparticles with P63mc space group. This is also confirmed by the JCPDS data (Card No. 361451). The Sr2+ doped ZnO sample (SZO-12), calcined at 400° C, shows 265
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peaks at angles (2θ) of 31.65, 34.24, 36.14, 47.43, 56.59, 62.75, 67.79 and 69.05° corresponding to (100), (002), (102), (103), (112), (201), (004) and (202) planes respectively. When the sample SZO-12 is calcined at 600° C the peaks are observed at angles (2θ) of 31.64, 34.29, 36.13, 47.45, 56.51, 62.75, 67.82 and 69.01° corresponding to (100), (002), (102), (103), (112), (201), (004) and (202) planes respectively. The peaks are located at angles (2θ) of 31.68, 34.25, 36.06, 47.44, 56.50, 62.75, 67.62 and 68.97° corresponding to (100), (002), (102), (103), (112), (201), (004) and (202) planes respectively for the sample SZO-12, calcined at 800° C. The doped ZnO samples shows additional peaks located at angles (2θ) of 24.95, 24.96 and 25.03° when calcined respectively at 400, 600 and 800° C which indicate the presence of SrCO3. The particle size of the samples is determined by the X-ray line broadening method using the Scherrer equation. The average crystalline size of the pure and doped ZnO samples is given in Table 2. The FT-IR spectroscopic analysis reveals the different bond vibrations present in the pure and Sr2+ doped ZnO nanoparticles; the recorded FT-IR spectra are shown in Fig. 2. The intense absorption bands in the range 600–400 cm−1 are diagnostic of ZnO. For pure ZnO the FT-IR spectrum consists of a strong absorption band at 444 cm−1. The peak in the range of 3650–3020 cm−1 corresponds to the vibrational mode of OeH. The absorption peaks are observed at 3435, 3434, 3449, 3418, and 3426 cm−1 for the pure ZnO, doped SZO-11, SZO-12, SZO-14, SZO-21 and SZO-41 respectively due to the OeH stretching of the absorbed water molecules. The absorption band at 1632 cm−1 is assigned to the OeH bending vibrations. The bands observed in the range 1800- 400 cm−1 are due to the vibration in CO32−. The weak absorption bands observed at 1770 cm−1 is corresponding to SrCO3. The broad absorption bands observed at 1455, 1458, 1472, 1457 and 1444 cm−1 for doped SZO-11, SZO-12, SZO-14, SZO-21 and SZO-41 respectively are due to the asymmetric vibrations in SrCO3. The diffuse reflectance spectroscopy was used to obtain the band gap energy value of pure and Sr2+doped ZnO nanoparticles. The spectra of all the samples, studied, were measured in the wavelength region 200–800 nm and the results are shown in Figs. 3 and 4 . The undoped ZnO samples shows a maximum absorption peak in the range 350–450 nm which is due to the transition of electrons from valence band to conduction band. Sr2+ doped ZnO sample shows slightly red shifted peaks in the range 400–500 nm due to the effect of doping. As a result the band gap energy of Sr2+ doped ZnO sample is decreases compared to undoped ZnO. It can be speculated that the metal ions were in the internal ZnO lattice and that the interaction of the doping ions with the ZnO destroys part of the original lattice, forming lattice defects and making the ZnO absorption edge mobile [31]. The red shift in the absorption wavelength range and the increase in the absorption intensity shows that the rate of formation of electron – hole pairs on the catalyst surface increass greatly, resulting in the catalyst exhibiting a
Fig. 3. The DRS spectra of ZnO and Sr2+dopd ZnO calcined at 400° C.
Fig. 4. The DRS spectra of ZnO (a) and SZO-12 calcined at 400 (b), 500 (c), 600 (d), 700 (e) and 800° C (f). Table 3 The band gap energies of pure and doped ZnO nanoparticles. Without Calicination
Calcined
Sample
Band gap energy (eV)
Sample
Band gap energy (eV)
ZnO SZO-11 SZO-12 SZO-14 SZO-21 SZO-41
3.1 3.08 2.97 2.98 2.99 3.01
SZO-12-400 SZO-12-500 SZO-12-600 SZO-12-700 SZO-12-800
2.99 3 3.02 3.04 3.11
Fig. 5. SEM images of ZnO (a) and Sr2+ doped ZnO nanoparticles (b) calcined at 600° C for 7 h.
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Fig. 6. Absorption spectra of the degradation of the dye, methyl orange, under UV light by ZnO (a) and SZO-12 (b) calcined at 400 °C for 3 h.
Fig. 7. (1) Photocatalytic efficiency and (2) Kinetic study of the degradation of methyl orange under UV light by ZnO (a), SZO-14 (b), SZO-12 (c), SZO-11 (d), SZO-21 (e) and SZO-41(f) calcined at 400° C for 3 h.
Fig. 8. Effect of calcination temperature on photocatalytic activity of doped samples on the degradation of methyl orange.
high surface energy [32]. Methylene blue (MB) and methyl orange (MO) dyes were used in the present study as a target of photo degradation. The photocatalytic activity of the samples was executed by the degradation of dyes in aqueous solution. Before irradiation with a lamp light, the samples were stirred in the dark for fifteen minutes. The results shows that the concentration of dye decreases slightly, which indicates that there is no degradation in the absence of irradiation. When the photocatalytic reaction was conducted in aqueous medium, the holes were effectively scavenged by the water and generated hydroxyl radical OH%, which are strong and unselected oxidant species in respect of totally oxidative degradation for organic substrates. The holes, free electrons, superoxide and hydroxyl radicals have been the species responsible for the
higher photocatalytic efficiency. The reason for the red shift in the absorption wavelength range for the Sr2+ doped ZnO was likely to the formation of defect energy level between the valence band and the conduction band in the ZnO band structure. This would have an important role in improving the catalytic activity of ZnO. The band gap energies of all the samples of pure and doped ZnO, studied, are given in Table 3. The morphology of ZnO and Sr2+ doped ZnO samples were analyzed using scanning electron microscopy. The SEM images of ZnO and doped ZnO samples calcined at 600° C for 7 h is shown in Fig. 5. The images indicate the aggregation of particles in both undoped ZnO and Sr2+ doped ZnO samples. The aggregation of nanoparticles may be due to the presence of large surface area to volume ratio and 267
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Fig. 9. Effect of calcination time on photocatalytic activity of doped samples on the degradation of methyl orange.
Fig. 10. Absorption spectra of the degradation of the dye, methylene blue, under UV light by ZnO (a) and SZO-12 (b) calcined at 400 °C for 3 h.
Fig. 11. (1) Photocatalytic efficiency and (2) Kinetic study of the degradation of methylene blue under UV light by the samples ZnO (a), SZO-14 (b), SZO-12 (c), SZO-11 (d), SZO-21 (e) and SZO-41(f) calcined at 400° C for 3 h.
Fig. 12. Effect of calcination temperature on photocatalytic activity of doped samples on the degradation of methyl orange.
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Fig. 13. Effect of calcination time on photocatalytic activity of doped samples on the degradation of methylene blue.
place within 25 min for the sample SZO-12, whereas undoped ZnO takes about 70 min to complete its degradation. The SZO-12 samples were calcined at 400, 500, 600, 700 and 800 °C for 3 h and the photocatalytic activity of these samples were studied and the results are shown in Fig. 8. The sample calcined at 600 °C shows maximum activity. The calcination time of the sample at 600 °C was varied from 4 to 8 h and the results are shown in Fig. 9. The sample obtained after calcination for 7 h was found to be highly active. Fig. 10 shows the absorption spectra of the degradation of methylene blue dye under UV light by samples ZnO (a) and SZO-12 (b) calcined at 400 °C for 3 h. Fig. 11(1) shows the photocatalytic efficiency of undoped and doped ZnO. The kinetic studies (Fig. 11 (2)) show that the maximum photocatalytic activity was obtained for the doped sample SZO-12. The maximum reaction rate of 0.129 min−1 corresponds to the sample SZO-12 while its undoped counterpart shows only a value of 0.054 min−1. The degradation takes place within 15 min for the sample SZO-12, whereas undoped ZnO takes about 80 min to complete its degradation. When studied the effect of calcination temperature (SZO-12 samples were calcined at 400, 500, 600, 700 and 800 °C for 3 h) on the photocatalytic activity of these samples (shown in Fig. 12) it has been found that the sample calcined at 600 °C shows maximum activity. The dependence of calcination time on the photocatalytic activity shows (Fig. 13) that the sample obtained after calcination for 7 h was found to be highly active. Rate constant for the degradation of the dye by different samples are given in Tables 4 and 5.
Table 4 Values of rate constant for methyl orange degradation by different samples. Sample
Rate constant (min−1)
Calcination Temperature (°C)
ZnO SZO-14 SZO-12 SZO-11 SZO-21 SZO-41
0.043 0.063 0.098 0.085 0.066 0.010
SZO-12 400 500 600 700 800
Rate constant (min−1)
0.096 0.097 0.118 0.033 0.016
Calcination time (h)
SZO-12-600 4 5 6 7 8
Rate constant (min−1)
0.048 0.068 0.072 0.129 0.064
degradation of the organic substrates [33,34]. The reaction process can be proposed as: ZnO + hν → h+ + e−
(2)
e− + O2 → O2−
(3)
h+ + OH− → OH%
(4)
O2− + 2H+ → 2OH%
(5)
OH% + dye → degradation products
(6)
The degradation of both dyes was evaluated using pure and doped ZnO samples. Among the doped samples, the sample having Sr/Zn ratio 1:2 (SZO-12) shows the maximum activity. Fig. 6 shows the absorption spectra of the degradation of methyl orange dye under UV light by the samples ZnO (a) and SZO-12 (b) calcined at 400 °C for 3 h. Fig. 7 (1) shows the photocatalytic efficiency of undoped and doped ZnO. The kinetic studies (Fig. 7 (2)) show that the maximum photocatalytic activity was obtained for the doped sample SZO-12. The maximum reaction rate 0.098 min−1 corresponds to the sample SZO-12 while its undoped counterpart has only 0.043 min−1. The degradation takes
5. Conclusion ZnO and Sr2+ doped ZnO nanoparticles were prepared by coprecipitation method. XRD results reveal that both ZnO and doped ZnO have wurtzite structure. The particle size was found to be 20.9 nm for ZnO and in the range 21–26 nm for the doped samples. The FT-IR spectra confirm the presence of ZnO and also the presence of SrCO3 in the doped samples. The Diffuse reflectance spectra shows that the Sr2+ doped ZnO have a significant shift to longer wavelength and that results
Table 5 Values of rate constant for methylene blue degradation by different samples. Sample
Rate constant (min−1)
Calcination Temperature (°C)
Rate constant (min−1)
Calcination time (h)
Rate constant (min−1)
ZnO SZO-14 SZO-12 SZO-11 SZO-21 SZO-41
0.054 0.118 0.129 0.066 0.068 0.027
SZO-12 400 500 600 700 800
0.129 0.133 0.185 0.150 0.117
SZO-12-600 4 5 6 7 8
0.125 0.140 0.177 0.290 0.162
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[16] M. Mukhtar, L. Munisa, R. Saleh, Co-precipitation synthesis and characterization of nanocrystalline zinc oxide particles doped with Cu2+ ions, Mater. Sci. Appl. 3 (2012) 543–551. [17] R. Amrousse, B. Ahmed, Synthesis and characterization of homogeneous ZnO and Mn–doped ZnO nanoparticles, Adv. Sci. Focus 1 (2013) 9–12. [18] K. Rekha, M. Nirmala, Manjula G. Nair, A. Anukaliani, Structural, optical, photocatalytic and antibacterial activity of zinc oxide and manganese doped zinc oxide nanoparticles, Physica B 405 (2010) 3180–3185. [19] K. Milenova, I. Stambolova, V. Blaskov, A. Eliyas, S. Vassilev, M. Shipochka, The effect of introducing copper dopant on the photocatalytic activity of ZnO nanoparticles, J. Chem. Technol. Metall. 48 (2013) 259–264. [20] T.H. Le, A.T. Bui, T.K. Le, The effect of Fe doping on the suppression of photocatalytic activity of ZnO nanopowder for the application in sunscreens, Powder Technol. 268 (2014) 173–176. [21] Q. Xiao, L. Ouyang, Photocatalytic photodegradation of xanthate over Zn1-xMnxO under visible light irradiation, J. Alloys Compd. 479 (2009) L4–L7. [22] X. Qiu, L. Li, J. Zheng, J. Liu, X. Sun, G. Li, Origin of the enhanced photocatalytic activities of semiconductors: a case study of ZnO doped with Mg2+, J. Phys. Chem. C 112 (2008) 12242–12248. [23] C. Tang, Study of photocatalytic degradation of methyl orange on different morphologies of ZnO catalysts, Mod. Res. Catal. 2 (2013) 19–24. [24] K. Yu, J. Shi, Z. Zhang, Y. Liang, W. Liu, Synthesis, characterization and photocatalysis of ZnO and Er-doped ZnO, J. Nanomater. (2013) 1–5. [25] E. Vinodkumar, R. Roshan, V. Kumar, Mg-doped ZnO nanoparticles for efficient sunlight-driven photocatalysis, ACS Appl. Mater. Interfaces 4 (2012) 2717–2725. [26] N. Yongvanich, Synthesis of strontium-doped ZnO-based nanopowders by chemical co-precipitation, Chiang Mai J. Sci. 40 (2013) 1046–1054. [27] R. Yousefi, F.J. Sheini, M. Cheraghizade, S.K. Gandomani, A. Saaedi, N.M. Huang, W.J. Basirun, M. Azarang, Enhanced visible-light photocatalytic activity of strontium-doped zinc oxide nanoparticles, Mater. Sci. Semicond. Process 32 (2015) 152–159. [28] I. Grčić, D. Vrsaljko, Z. Katančić, S. Papić, Purification of household greywater loaded with hair colorants by solar photocatalysis using TiO2-coated textile fibers coupled flocculation with chitosan, J. Water Proc. Eng. 5 (2015) 15–27. [29] D. Zhang, J. Wang, UV–visible light-activated Au@ pre-sulphated, monodisperse TiO2 aggregates for treatment of congo red and phthalylsulfathiazole, J. Water Proc. Eng. 7 (2015) 187–195. [30] K. Jeyasubramaniana, G.S. Hikku, R. Krishna Sharma, Photo-catalytic degradation of methyl violet dye using zinc oxide nano particles prepared by a novel precipitation method and its anti-bacterial activities, J. Water Proc. Eng. 8 (2015) 35–44. [31] Y. Ling, W. Jiang, X. Wu, X. Bai, Preparation and visible light photocatalytic properties of (Er, La, N)-codoped TiO2 nanotube array films, J. Nanosci. Nanotechnol. 9 (2009) 714–717. [32] J. Kaur, S. Bansal, S. Singhal, Photocatalytic degradation of methyl orange using ZnO nanopowders synthesized via thermal decomposition of oxalate precursor method, Physica B 416 (2013) 33–38. [33] T. Tan, Y. Li, Y. Liu, B. Wang, X. Song, E. Li, H. Wang, H. Yan, Two- step preparation of Ag/tetrapod-like ZnO with photocatalytic activity by thermal evaporation and sputtering, Mater. Chem. Phys 111 (2008) 305–308. [34] D. Zhang, X. Pu, H. Li, Y.M. Yu, J.J. Shim, P. Cai, S.I. Kim, H.J. Seo, Microwaveassisted combustion synthesis of Ag/ZnO nanocomposites and their photocatalytic activities under ultraviolet and visible-light irradiation, Mater. Res. Bull. 61 (2015) 321–325.
a reduction in band gap. The SEM images confirm that the particles were aggregated. The photocatalytic activity of the samples were evaluated by photocatalyic oxidation of the dyes, methyl orange and methylene blue and the results shows that the photocatalytic activity of Sr2+ doped ZnO was much higher than that of pure ZnO. The sample with mole ratio of Sr/Zn 1:2 calcined at 600° C for 7 h shows the maximum activity. It has been found that the cationic methylene blue gets degraded faster than anionic methyl orange which may be due to the accumulation of more negative charges on the surface of the catalyst. References [1] T. Robinson, G. McMullan, R. Marchant, P. Nigam, Remediation of dyes in textile effluent: a critical review on current treatment technologies with a proposed alternative, Bioresour. Technol. 77 (2001) 247–255. [2] S. Chakrabarti, B.K. Dutta, Photocatalytic degradation of model textile dyes in wastewater using ZnO as semiconductor catalyst, J. Hazard. Mater. 112 (2004) 269–278. [3] G.P. Fotou, S.E. Pratsinis, Photocatalysis of phenol and salicylic acid by aerosolmade titania powders, Chem. Eng. Commun. 151 (1996) 251–269. [4] K. Gouvea, F. Wypych, S.G. Moraes, N. Duran, N. Nagataand, P. Peralta-Zamora, Semiconductor-assisted photocatalytic degradation of reactive dyes in aqueous solution, Chemosphere 40 (2000) 433–440. [5] V. Uskoković, M. Drofenik, Synthesis of materials within reverse micelles, Surf. Rev. Lett. 12 (2005) 239–277. [6] X. Qiu, G. Li, X. Sun, L. Li1, X. Fu, Doping effects of Co2+ ions on ZnO nanorods and their photocatalytic properties, Nanotechnology 19 (2008) 215–703. [7] A.B. Gaikwad, S.C. Navale, V. Samuel, A.V. Murugan, V. Ravi, A co-precipitation technique to prepare BiNbO4, MgTiO3 and Mg4Ta2O9 powders, Mater. Res. Bull. 41 (2006) 347–353. [8] A.K. Radzimska, T. Jesionowski, Zinc oxide—from synthesis to application: a review, Mater. Lett. 7 (2014) 2833–2881. [9] K.S. Suslick, S.B. Choe, A.A. Cichowlas, M.M. Grinstaff, Synthesis of amorphous iron, Nature 353 (1991) 414–416. [10] J. Chen, Y. Wang, F. Guo, X. Wang, C. Zheng, Synthesis of nanoparticles with novel technology: high-gravity reactive precipitation, Ind. Eng. Chem. Res. 39 (2000) 948–954. [11] John Regalbuto, Catalyst Preparation: Science and Engineering, CRC press, Tailor & Francis group, 2007. [12] M.F. Zawrah, H. Hamaad, S. Meky, Synthesis and characterization of nano MgAl2O4 spinel by the co-precipitated method, Ceram. Int. 33 (2007) 969–978. [13] G. Xu, X. Zhang, W. He, H. Liu, H. Li, R.I. Boughton, Preparation of highly dispersed YAG nano-sized powder by co-precipitation method, Mater. Lett. 60 (2006) 962–965. [14] S. Chen, Y. Yang, M. Ji, W. Liu, Preparation, characterisation and activity evaluation of CaCO3/ZnO photocatalyst, J. Exp. Nanosci. 6 (2011) 324–336. [15] A.S. Haja Hameed, C. Karthikeyan, S. Sasikumar, V. Senthil Kumar, S. Kumaresan, G. Ravi, Impact of alkaline metal ions Mg2+, Ca2+ Sr2+ and Ba2+ on the structural, optical, thermal and antibacterial properties of ZnO nanoparticles prepared by the co-precipitation method, J. Mater. Chem. B 1 (2013) 5950–5962.
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