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Microwave-assisted synthesis and characterization of BiOIO3 nanoplates for photocatalysis
Materials Letters 209 (2017) 264–267
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Microwave-assisted synthesis and characterization of BiOIO3 nanoplates for photocatalysis Panudda Patiphatpanya a,b, Anukorn Phuruangrat c,⇑, Somchai Thongtem d,e, Titipun Thongtem a,⇑ a
Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand The Graduate School, Chiang Mai University, Chiang Mai 50200, Thailand c Department of Materials Science and Technology, Faculty of Science, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand d Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand e Materials Science Research Center, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand b
a r t i c l e
i n f o
Article history: Received 19 June 2017 Received in revised form 3 August 2017 Accepted 4 August 2017 Available online 5 August 2017 Keywords: BiOIO3 XRD TEM Spectroscopy Photocatalysis
a b s t r a c t New polar BiOIO3 nanostructures were successfully synthesized by 90 and 180 W microwave for 20–100 min. X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–visible spectroscopy revealed the presence of pure orthorhombic BiOIO3 nanoplates with 2.5–2.9 eV energy gap. The photodegradation of rhodamine B (RhB) by BiOIO3 photocatalyst was tested under visible radiation for 60 min. In this research, BiOIO3 photocatalyst synthesized by 180 W microwave for 60 min has the highest activity of 96%. Ó 2017 Elsevier B.V. All rights reserved.
1. Introduction
2. Experiment
Bismuth-based photocatalytic materials such as Bi2WO6 [1,2], Bi2MoO6 [3], Bi2O2CO3 [4] and BiOIO3 [5,6] have been very excellent for photodegradation of organic pollutants under visible radiation. As newly discovered Bi-based nonlinear optical materials, bismuth oxy-iodate (BiOIO3) is an efficient photocatalyst for removal of liquid and gaseous pollutants [7] and has a remarkable catalytic activity for the degradation of dye molecules under visible light because of its heterolayered structure and internal polar field [8]. Furthermore, the nanocomposites of BiOIO3 coupled with reduced grapheme oxide (RGO) and BiOI have better visible light efficiency for removal of NO [9,10], including BiOI/BiOIO3 nanocomposites exhibit significant photoreactivity to decompose some organic dye under simulated solar light [11]. In this study, BiOIO3 was synthesized by a microwave-assisted method. The effect of microwave power and reaction time on phase, morphology and optical properties were investigated. The photocatalytic activities of the as-synthesized BiOIO3 products were investigated through the degradation of rhodamine B (RhB) solutions under visible radiation.
Typically, 0.002 mol bismuth nitrate pentahydrate (Bi(NO3)3 5H2O) was dissolved in 5 ml acetic acid, and 0.002 mol potassium iodate (KIO3) in 70 ml DI water. Each solution was mixed well by being stirred at room temperature. They were mixed together and the pH was balanced to 2. The mixture solutions were heated in a microwave oven (2.45 GHz) at 90 W for 20 min and 180 W for 20, 40, 60, 80 and 100 min. In the end, white precipitates were synthesized, washed with DI water and ethanol, and dried for further analyses. Photocatalytic activities of the as-synthesized products were tested through the degradation of RhB solutions under visible radiation of Xe lamp. Each 150 mg photocatalyst was suspended in 150 ml of 2 105 M RhB solutions which were stirred in the dark for 30 min. To initiate photocatalysis, the Xe lamp was turned on. The solutions were analyzed by UV–visible spectroscopy. Decolorization efficiency was calculated by the equation
⇑ Corresponding authors. E-mail addresses: [email protected] (A. Phuruangrat), ttpthongtem@ yahoo.com (T. Thongtem). http://dx.doi.org/10.1016/j.matlet.2017.08.019 0167-577X/Ó 2017 Elsevier B.V. All rights reserved.
Decolorization efficiency ð%Þ ¼
C0 Ct 100 C0
ð1Þ
where C0 is the initial concentration of RhB and Ct is the concentration of RhB when the photocatalysis was proceeding within the elapsed time (t).
P. Patiphatpanya et al. / Materials Letters 209 (2017) 264–267
265
3. Results and discussion
Fig. 1. XRD patterns of BiOIO3 synthesized by 90 W microwave for 20 min and 180 W microwave for 20, 40, 60, 80 and 100 min, comparing with the ICSD database.
Phase, crystallinity and purity of BiOIO3 synthesized by 90 W microwave for 20 min and 180 W microwave for 20, 40, 60, 80 and 100 min were characterized by XRD (Fig. 1). Obviously, the XRD pattern of BiOIO3 at 90 W for 20 min shows a broad peak, implying that the product has very low crystallinity. The XRD patterns of the as-synthesized BiOIO3 by 180 W microwave for 20, 40, 60, 80 and 100 min appear as narrow peaks, certified as the products with good and high crystallinity. The diffraction peaks were indexed to pure orthorhombic BiOIO3 phase with Pca21 space group (ICSD No. 262019) [12]. The diffraction intensity was increased when the prolonged reaction time was increased from 20 to 100 min, indicating that the crystallinity and particle size of BiOIO3 were increased as well. These results indicated that microwave power and reaction time played the role in improving the degree of crystallinity and promoting the growth of BiOIO3 products. The morphology and phase were investigated by TEM and SAED (Fig. 2). Their morphologies appear as nanoplates with average size ranging from 20 to 150 nm and thickness of <20 nm. The assynthesized products by 180 W microwave for 20 and 40 min were agglomerates of nanoplates. The prolonged irradiation time can lead to enlarge BiOIO3 nanoplates caused by the Ostwald ripening process. At 180 W microwave, the sizes of BiOIO3 nanoplates were enlarged from 20 to 150 nm with prolonging the reaction time from 20 to 100 min. The SAED pattern of the product synthesized by 180 W microwave for 60 min can be assigned as the (1 2 1), (0 4 0), (0 4 2) and (3 3 0) planes of orthorhombic BiOIO3 crystal system [12]. The optical properties of BiOIO3 products were characterized by UV–visible spectroscopy (Fig. 3). In this research, the as-synthesized BiOIO3 products show excellent absorption in the
Fig. 2. TEM images and SAED pattern of BiOIO3 synthesized by 180 W microwave for (a–f) 20, 40, 60, 80, 100 and 60 min, respectively.
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Fig. 3. (a) UV–visible absorption and (b) the (ahm)2 versus hm curves of BiOIO3 synthesized by 180 W microwave for 20–100 min.
Fig. 4. (a) Decolorization efficiencies and (b) pseudo-first-order kinetics of BiOIO3 synthesized by 180 W microwave for 20, 40, 60, 80 and 100 min, respectively encoded as T20, T40, T60, T80 and T100, comparing with that of the blank.
visible range. The energy gap (Eg) is described by the following equation [13]
ahv ¼ Aðhv Eg Þn
ð2Þ
where a is the absorbance, h the Planck constant, m the photon frequency, A a constant and n the pure number associated with different types of electronic transition. The energy gap for absorption edge is able to be determined by extrapolating the linear portion of the plot between (ahv)2 vs hv to zero absorbance. The energy gaps of the BiOIO3 nanoplates were estimated to be 2.9, 2.7, 2.8, 2.6 and 2.5 eV for 20, 40, 60, 80 and 100 min synthesis, respectively. Generally, crystallinity, particle-size, defects and others can play the role in energy gap of solids. The photocatalytic activities of BiOIO3 catalyst were evaluated through the degradation of RhB molecules under visible radiation. Fig. 4a shows decolorization efficiency of RhB solution as model dye over the blank (catalyst-free) and BiOIO3 photocatalyst under visible light within 60 min. The photoinduced self-decomposition of RhB molecules for the blank was negligible. In the RhB solutions containing BiOIO3 photocatalyst synthesized by 180 W microwave for different lengths of time, decolorization efficiencies were increased with the increase of prolonging time within 60 min. The BiOIO3 synthesized by 180 W microwave for 60 min shows the highest decolorization efficiency of 96%. Comparing with other
materials containing TiO2, the present efficiency is higher than those of TiO2/polymer composites [14,15], TiO2 thin films [16], Ag-TiO2 [17], dahlia-like TiO2 [18] and chrysanthemum-like hierarchical anatase TiO2 [19] but is closed to those of hierarchical TiO2 [20] and hierarchical flower-like CeO2/TiO2 [21]. When visible light exposed on BiOIO3, electrons and holes were produced in the conduction and valence bands. The electrons diffused to the surface of BiOIO3 and reacted with adsorbed O2 and OH/H2O to produce O 2 and OH radicals. These radicals were responsible for the decomposition of RhB molecules by transforming them into CO2 and H2O and creating a cleaner and safer environment. The pseudo-firstorder degradation kinetics of BiOIO3 under visible light was calculated (Fig. 4b). The apparent reaction rate constant of BiOIO3 synthesized by 180 W microwave for 60 min (0.0526 min1) is higher than those of BiOIO3 synthesized for 20 min (0.0349 min1), 40 min (0.0406 min1), 80 min (0.0414 min1) and 100 min (0.0242 min1).
4. Conclusions The pure orthorhombic BiOIO3 nanoplates were successfully synthesized by 180 W microwave for 20–100 min. The photocatalytic activities were investigated through the photodegradation of RhB solutions under visible radiation. BiOIO3 synthesized by
P. Patiphatpanya et al. / Materials Letters 209 (2017) 264–267
180 W microwave for 60 min has the highest decolorization efficiency of 96% within 60 min. Acknowledgments We wish to thank Thailand Research Fund for providing financial support through the Royal Golden Jubilee Ph.D. Program, and Center of Excellence in Materials Science and Technology, Chiang Mai University, for financial support under the administration of Materials Science Research Center, Faculty of Science, Chiang Mai University. References [1] [2] [3] [4]
Y. Liu, Z. Li, H. Lv, H. Tang, X. Xing, Mater. Lett. 108 (2013) 84–87. Y. Ma, Z. Chen, D. Qu, J. Shi, Appl. Surf. Sci. 361 (2016) 63–71. H. Huang, L. Liu, Y. Zhang, N. Tian, J. Alloys Compds. 619 (2015) 807–811. H. Huang, Y. He, R. He, X. Jiang, Z. Lin, Y. Zhang, S. Wang, Inorg. Chem. Commun. 40 (2014) 215–219. [5] T. Xiong, H. Zhang, Y. Zhang, F. Dong, Chinese, J. Catal. 36 (2015) 2155–2163. [6] W. Wang, H. Cheng, B. Huang, X. Liu, X. Qin, X. Zhang, Y. Dai, J. Colloid Interf. Sci. 442 (2015) 97–102.
267
[7] X.M. Qi, M.L. Gu, X.Y. Zhu, J. Wu, H.M. Long, K. He, Q. Wu, Chem. Eng. J. 285 (2016) 11–19. [8] W. Wang, B. Huang, X. Ma, Z. Wang, X. Qin, X. Zhang, M. Whangbo, Chem. Eur. J. 19 (2013) 14777–14780. [9] T. Xiong, F. Dong, Y. Zhou, M. Fu, W. Ho, J. Colloid Interf. Sci. 447 (2015) 16–24. [10] F. Dong, T. Xiong, Y. Sun, Y. Zhang, Y. Zhou, Chem. Commun. 51 (2015) 8249– 8252. [11] H. Huang, K. Xiao, K. Liu, S. Yu, Y. Zhang, Cryst. Growth Des. 16 (2016) 221– 228. [12] S.D. Nguyen, J. Yeon, S. Kim, P.S. Halasyamani, J. Amer. Chem. Soc. 133 (2011) 12422–12425. [13] J. Tauc, A. Menth, J. Non-Cryst. Solid 8–10 (1972) 569–585. [14] K.R. Reddy, K.V. Karthik, S.B.B. Prasad, S.K. Soni, H.M. Jeong, A.V. Raghu, Polyhedron 120 (2016) 169–174. [15] Y. Ao, Y. Gao, P. Wang, C. Wang, J. Hou, J. Qian, Mater. Lett. 102–103 (2013) 36– 38. [16] F. Meng, X. Song, Z. Sun, Vacuum 83 (2009) 1147–1151. [17] F. Menga, Z. Suna, Mater. Chem. Phys. 118 (2009) 349–353. [18] Z. Fan, F. Meng, A. Li, J. Gong, H. Li, J. Mater. Sci. Mater. Electron. 27 (2016) 10454–10459. [19] Z. Fana, F. Menga, J. Gonga, H. Lia, A. Lia, Ceram. Int. 42 (2016) 6282–6287. [20] Z. Fana, F. Menga, M. Zhanga, Z. Wuc, Z. Suna, A. Li, Appl. Surf. Sci. 360 (2016) 298–305. [21] Z. Fan, F. Meng, J. Gong, H. Li, Y. Hu, D. Liu, Mater. Lett. 175 (2016) 36–39.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Microwave-assisted synthesis and characterization of BiOIO3 nanoplates for photocatalysis Panudda Patiphatpanya a,b, Anukorn Phuruangrat c,⇑, Somchai Thongtem d,e, Titipun Thongtem a,⇑ a
Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand The Graduate School, Chiang Mai University, Chiang Mai 50200, Thailand c Department of Materials Science and Technology, Faculty of Science, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand d Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand e Materials Science Research Center, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand b
a r t i c l e
i n f o
Article history: Received 19 June 2017 Received in revised form 3 August 2017 Accepted 4 August 2017 Available online 5 August 2017 Keywords: BiOIO3 XRD TEM Spectroscopy Photocatalysis
a b s t r a c t New polar BiOIO3 nanostructures were successfully synthesized by 90 and 180 W microwave for 20–100 min. X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–visible spectroscopy revealed the presence of pure orthorhombic BiOIO3 nanoplates with 2.5–2.9 eV energy gap. The photodegradation of rhodamine B (RhB) by BiOIO3 photocatalyst was tested under visible radiation for 60 min. In this research, BiOIO3 photocatalyst synthesized by 180 W microwave for 60 min has the highest activity of 96%. Ó 2017 Elsevier B.V. All rights reserved.
1. Introduction
2. Experiment
Bismuth-based photocatalytic materials such as Bi2WO6 [1,2], Bi2MoO6 [3], Bi2O2CO3 [4] and BiOIO3 [5,6] have been very excellent for photodegradation of organic pollutants under visible radiation. As newly discovered Bi-based nonlinear optical materials, bismuth oxy-iodate (BiOIO3) is an efficient photocatalyst for removal of liquid and gaseous pollutants [7] and has a remarkable catalytic activity for the degradation of dye molecules under visible light because of its heterolayered structure and internal polar field [8]. Furthermore, the nanocomposites of BiOIO3 coupled with reduced grapheme oxide (RGO) and BiOI have better visible light efficiency for removal of NO [9,10], including BiOI/BiOIO3 nanocomposites exhibit significant photoreactivity to decompose some organic dye under simulated solar light [11]. In this study, BiOIO3 was synthesized by a microwave-assisted method. The effect of microwave power and reaction time on phase, morphology and optical properties were investigated. The photocatalytic activities of the as-synthesized BiOIO3 products were investigated through the degradation of rhodamine B (RhB) solutions under visible radiation.
Typically, 0.002 mol bismuth nitrate pentahydrate (Bi(NO3)3 5H2O) was dissolved in 5 ml acetic acid, and 0.002 mol potassium iodate (KIO3) in 70 ml DI water. Each solution was mixed well by being stirred at room temperature. They were mixed together and the pH was balanced to 2. The mixture solutions were heated in a microwave oven (2.45 GHz) at 90 W for 20 min and 180 W for 20, 40, 60, 80 and 100 min. In the end, white precipitates were synthesized, washed with DI water and ethanol, and dried for further analyses. Photocatalytic activities of the as-synthesized products were tested through the degradation of RhB solutions under visible radiation of Xe lamp. Each 150 mg photocatalyst was suspended in 150 ml of 2 105 M RhB solutions which were stirred in the dark for 30 min. To initiate photocatalysis, the Xe lamp was turned on. The solutions were analyzed by UV–visible spectroscopy. Decolorization efficiency was calculated by the equation
⇑ Corresponding authors. E-mail addresses: [email protected] (A. Phuruangrat), ttpthongtem@ yahoo.com (T. Thongtem). http://dx.doi.org/10.1016/j.matlet.2017.08.019 0167-577X/Ó 2017 Elsevier B.V. All rights reserved.
Decolorization efficiency ð%Þ ¼
C0 Ct 100 C0
ð1Þ
where C0 is the initial concentration of RhB and Ct is the concentration of RhB when the photocatalysis was proceeding within the elapsed time (t).
P. Patiphatpanya et al. / Materials Letters 209 (2017) 264–267
265
3. Results and discussion
Fig. 1. XRD patterns of BiOIO3 synthesized by 90 W microwave for 20 min and 180 W microwave for 20, 40, 60, 80 and 100 min, comparing with the ICSD database.
Phase, crystallinity and purity of BiOIO3 synthesized by 90 W microwave for 20 min and 180 W microwave for 20, 40, 60, 80 and 100 min were characterized by XRD (Fig. 1). Obviously, the XRD pattern of BiOIO3 at 90 W for 20 min shows a broad peak, implying that the product has very low crystallinity. The XRD patterns of the as-synthesized BiOIO3 by 180 W microwave for 20, 40, 60, 80 and 100 min appear as narrow peaks, certified as the products with good and high crystallinity. The diffraction peaks were indexed to pure orthorhombic BiOIO3 phase with Pca21 space group (ICSD No. 262019) [12]. The diffraction intensity was increased when the prolonged reaction time was increased from 20 to 100 min, indicating that the crystallinity and particle size of BiOIO3 were increased as well. These results indicated that microwave power and reaction time played the role in improving the degree of crystallinity and promoting the growth of BiOIO3 products. The morphology and phase were investigated by TEM and SAED (Fig. 2). Their morphologies appear as nanoplates with average size ranging from 20 to 150 nm and thickness of <20 nm. The assynthesized products by 180 W microwave for 20 and 40 min were agglomerates of nanoplates. The prolonged irradiation time can lead to enlarge BiOIO3 nanoplates caused by the Ostwald ripening process. At 180 W microwave, the sizes of BiOIO3 nanoplates were enlarged from 20 to 150 nm with prolonging the reaction time from 20 to 100 min. The SAED pattern of the product synthesized by 180 W microwave for 60 min can be assigned as the (1 2 1), (0 4 0), (0 4 2) and (3 3 0) planes of orthorhombic BiOIO3 crystal system [12]. The optical properties of BiOIO3 products were characterized by UV–visible spectroscopy (Fig. 3). In this research, the as-synthesized BiOIO3 products show excellent absorption in the
Fig. 2. TEM images and SAED pattern of BiOIO3 synthesized by 180 W microwave for (a–f) 20, 40, 60, 80, 100 and 60 min, respectively.
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P. Patiphatpanya et al. / Materials Letters 209 (2017) 264–267
Fig. 3. (a) UV–visible absorption and (b) the (ahm)2 versus hm curves of BiOIO3 synthesized by 180 W microwave for 20–100 min.
Fig. 4. (a) Decolorization efficiencies and (b) pseudo-first-order kinetics of BiOIO3 synthesized by 180 W microwave for 20, 40, 60, 80 and 100 min, respectively encoded as T20, T40, T60, T80 and T100, comparing with that of the blank.
visible range. The energy gap (Eg) is described by the following equation [13]
ahv ¼ Aðhv Eg Þn
ð2Þ
where a is the absorbance, h the Planck constant, m the photon frequency, A a constant and n the pure number associated with different types of electronic transition. The energy gap for absorption edge is able to be determined by extrapolating the linear portion of the plot between (ahv)2 vs hv to zero absorbance. The energy gaps of the BiOIO3 nanoplates were estimated to be 2.9, 2.7, 2.8, 2.6 and 2.5 eV for 20, 40, 60, 80 and 100 min synthesis, respectively. Generally, crystallinity, particle-size, defects and others can play the role in energy gap of solids. The photocatalytic activities of BiOIO3 catalyst were evaluated through the degradation of RhB molecules under visible radiation. Fig. 4a shows decolorization efficiency of RhB solution as model dye over the blank (catalyst-free) and BiOIO3 photocatalyst under visible light within 60 min. The photoinduced self-decomposition of RhB molecules for the blank was negligible. In the RhB solutions containing BiOIO3 photocatalyst synthesized by 180 W microwave for different lengths of time, decolorization efficiencies were increased with the increase of prolonging time within 60 min. The BiOIO3 synthesized by 180 W microwave for 60 min shows the highest decolorization efficiency of 96%. Comparing with other
materials containing TiO2, the present efficiency is higher than those of TiO2/polymer composites [14,15], TiO2 thin films [16], Ag-TiO2 [17], dahlia-like TiO2 [18] and chrysanthemum-like hierarchical anatase TiO2 [19] but is closed to those of hierarchical TiO2 [20] and hierarchical flower-like CeO2/TiO2 [21]. When visible light exposed on BiOIO3, electrons and holes were produced in the conduction and valence bands. The electrons diffused to the surface of BiOIO3 and reacted with adsorbed O2 and OH/H2O to produce O 2 and OH radicals. These radicals were responsible for the decomposition of RhB molecules by transforming them into CO2 and H2O and creating a cleaner and safer environment. The pseudo-firstorder degradation kinetics of BiOIO3 under visible light was calculated (Fig. 4b). The apparent reaction rate constant of BiOIO3 synthesized by 180 W microwave for 60 min (0.0526 min1) is higher than those of BiOIO3 synthesized for 20 min (0.0349 min1), 40 min (0.0406 min1), 80 min (0.0414 min1) and 100 min (0.0242 min1).
4. Conclusions The pure orthorhombic BiOIO3 nanoplates were successfully synthesized by 180 W microwave for 20–100 min. The photocatalytic activities were investigated through the photodegradation of RhB solutions under visible radiation. BiOIO3 synthesized by
P. Patiphatpanya et al. / Materials Letters 209 (2017) 264–267
180 W microwave for 60 min has the highest decolorization efficiency of 96% within 60 min. Acknowledgments We wish to thank Thailand Research Fund for providing financial support through the Royal Golden Jubilee Ph.D. Program, and Center of Excellence in Materials Science and Technology, Chiang Mai University, for financial support under the administration of Materials Science Research Center, Faculty of Science, Chiang Mai University. References [1] [2] [3] [4]
Y. Liu, Z. Li, H. Lv, H. Tang, X. Xing, Mater. Lett. 108 (2013) 84–87. Y. Ma, Z. Chen, D. Qu, J. Shi, Appl. Surf. Sci. 361 (2016) 63–71. H. Huang, L. Liu, Y. Zhang, N. Tian, J. Alloys Compds. 619 (2015) 807–811. H. Huang, Y. He, R. He, X. Jiang, Z. Lin, Y. Zhang, S. Wang, Inorg. Chem. Commun. 40 (2014) 215–219. [5] T. Xiong, H. Zhang, Y. Zhang, F. Dong, Chinese, J. Catal. 36 (2015) 2155–2163. [6] W. Wang, H. Cheng, B. Huang, X. Liu, X. Qin, X. Zhang, Y. Dai, J. Colloid Interf. Sci. 442 (2015) 97–102.
267
[7] X.M. Qi, M.L. Gu, X.Y. Zhu, J. Wu, H.M. Long, K. He, Q. Wu, Chem. Eng. J. 285 (2016) 11–19. [8] W. Wang, B. Huang, X. Ma, Z. Wang, X. Qin, X. Zhang, M. Whangbo, Chem. Eur. J. 19 (2013) 14777–14780. [9] T. Xiong, F. Dong, Y. Zhou, M. Fu, W. Ho, J. Colloid Interf. Sci. 447 (2015) 16–24. [10] F. Dong, T. Xiong, Y. Sun, Y. Zhang, Y. Zhou, Chem. Commun. 51 (2015) 8249– 8252. [11] H. Huang, K. Xiao, K. Liu, S. Yu, Y. Zhang, Cryst. Growth Des. 16 (2016) 221– 228. [12] S.D. Nguyen, J. Yeon, S. Kim, P.S. Halasyamani, J. Amer. Chem. Soc. 133 (2011) 12422–12425. [13] J. Tauc, A. Menth, J. Non-Cryst. Solid 8–10 (1972) 569–585. [14] K.R. Reddy, K.V. Karthik, S.B.B. Prasad, S.K. Soni, H.M. Jeong, A.V. Raghu, Polyhedron 120 (2016) 169–174. [15] Y. Ao, Y. Gao, P. Wang, C. Wang, J. Hou, J. Qian, Mater. Lett. 102–103 (2013) 36– 38. [16] F. Meng, X. Song, Z. Sun, Vacuum 83 (2009) 1147–1151. [17] F. Menga, Z. Suna, Mater. Chem. Phys. 118 (2009) 349–353. [18] Z. Fan, F. Meng, A. Li, J. Gong, H. Li, J. Mater. Sci. Mater. Electron. 27 (2016) 10454–10459. [19] Z. Fana, F. Menga, J. Gonga, H. Lia, A. Lia, Ceram. Int. 42 (2016) 6282–6287. [20] Z. Fana, F. Menga, M. Zhanga, Z. Wuc, Z. Suna, A. Li, Appl. Surf. Sci. 360 (2016) 298–305. [21] Z. Fan, F. Meng, J. Gong, H. Li, Y. Hu, D. Liu, Mater. Lett. 175 (2016) 36–39.