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Pure and In-doped orthorhombic Bi2WO6 are synthesized by sol-gel method through using raw materials Bi(NO3)3·5H2O, In(NO3)3·6H2O, (NH4)2WO4 and surfactants citric acid, polyethylene glycol. All samples are in pure phase without impurity phase as indicated by X-ray diffraction characterization. The In-doped sample degradation efficiency for rhodamine B is higher than that for pure phase with the optimal content 7% mole ratio. Because indium impurity adhering to Bi2WO6 nucleus surface may affect the crystallization range, the sample morphology gradually becomes fluffy and regular, which is reveled through scanning electron microscopy analysis. This morphology change plays an important role in electron-hole transport process as well as contact area of carrier and organic molecule. Using X-ray photoelectron spectroscopy (XPS) characterization and Gaussian fitting, it is found that the O 1s XPS peak of pure and In-doped sample each contain three peak sites. The low energy peak around 530 eV originates from W—O and Bi—O bond. The high peak is ascribed to lattice oxygen defect and its intensity is enhanced gradually with the increase of In content. Thus the increase of oxygen vacancies is the main reason for this photocatalytic performance improvement. Comparing with the impurity-free sample, the visible absorption of In-doped Bi2WO6 is enhanced and the corresponding band gap slightly decreases, which is indicated by diffraction reflection spectroscopy measurement. The reduction of forbidden band width further enhances the photocatalytic performance. After configuration relaxation and self-consistence calculation, the formation energy obtained from a single oxygen vacancy model is less than those from the Bi1In + VO and the Bi2In + VO co-doping models, and greater than the WIn + VO formation energy. This result indicates that indium replacing W site can promote the generating of oxygen vacancies. The calculation of the 18%-hybridization function electronic structure shows that the Bi2WO6 has indirect band gap semi-conduction with energy gap 2.76 eV, which is consistent with the experimental value 2.79 eV. A series of new local states appears in the band gap and near conduction band bottom based on the oxygen vacancy model. These local states promote light absorption and enhance photocatalytic performance. In conclusion, the enhanced photocatalytic performance of Bi2WO6 is attributed to the indium entering into the tungsten site rather than the bismuth site as indicated by the experimental and theoretical result.
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Keywords:
- bismuth tungstate /
- indium doping /
- oxygen vacancy /
- formation energy
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图 1 溶胶-凝胶法制备钨酸铋粉体实验流程图
Figure 1. Schematic diagram of sol-gel method for bismuth tungstate powder preparation.
图 2 ICSD模拟和不同浓度铟掺杂钨酸铋XRD图谱(a)和优化完正交钨酸铋结构模型(b)
Figure 2. XRD patterns of the ICSD simulation and different concentration In-doped bismuth tungstate (a), as well as optimized orthogonal bismuth tungstate structure model (b).
图 3 样品微观形貌结构图 (a)纯相, (b) 5 at%, (c) 7 at%, (d) 10 at% In-Bi2WO6
Figure 3. Microscopic morphology of samples: (a) Pure phase, (b) 5 at%, (c) 7 at%, and (d) 10 at% In-Bi2WO6
图 4 不同铟掺杂钨酸铋的降解效率(a)和一级反应速率常数柱状图(b)
Figure 4. Degradation efficiency of In-doped bismuth tungstate (a) and the first-order reaction rate constant (b).
图 5 纯相(a)和7%铟掺杂(b) Bi2WO6的O 1 s XPS光谱以及Gaussian分峰
Figure 5. O1 s XPS spectra and Gaussian peaks of pure phase (a) and 7% In-doped Bi2WO6 (b).
图 6 纯的和7 at%铟掺杂样品的漫反射光谱(a)和K-M方程拟合的带隙值(b)
Figure 6. Diffuse reflectance spectra of pure and 7 at% In-doped samples (a) and band gap values fitted by K-M equation (b).
图 7 (a)四种模型结构示意图及其(b)相应形成能变化趋势
Figure 7. Schematic diagram of four model structures (a) and corresponding formation energy variation (b).
图 8 纯相(a), (b)和单一氧空位(c), (d)模型电子结构 (a), (c) 能带图; (b), (d) 态密度图
Figure 8. Pure phase (a), (b) and single oxygen vacancy (c), (d) model electronic structure: (a), (c) Energy band diagram; (b), (d) density of states (DOS).
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[1] Ait Ahsaine H, Ezahri M, Benlhachemi A, Bakiz B, Villain S, Guinneton F, Gavarri J R 2016 Ceram. Int. 42 8552
Google Scholar
[2] Ait Ahsaine H, El Jaouhari A, Slassi A, Ezahri M, Benlhachemi A, Bakiz B, Guinnetonc F, Gavarric J R 2016 RSC Adv. 6 101105
Google Scholar
[3] Song X C, Zheng Y F, Ma R, Zhang Y Y, Yin H Y 2011 J. Hazard. Mater. 192 186
[4] 盛珈怡, 李晓金, 许宜铭 2014 物理化学学报 30 508
Google Scholar
Sheng J Y, Li X J, Xu Y M 2014 Acta Phys. Chim. Sin. 30 508
Google Scholar
[5] Wang J J, Tang L, Zeng G G, Liu Y N, Zhou Y Y, Deng Y C, Wang J J, Peng B 2017 ACS Sustainable Chem. Eng. 5 1062
Google Scholar
[6] Kong X Y, Choo Y Y, Chai S P, Soh A K, Mohamedc A R 2016 Chem. Commun. 52 14242
Google Scholar
[7] 卢青, 华罗光, 陈亦琳, 高碧芬, 林碧洲 2015 无机材料学报 30 413
Lu Q, Hua L G, Chen Y L, Gao B F, Lin B Z 2015 J. Inorg. Mater. 30 413
[8] 许雪棠, 王凡, 黄恒俊, 季璐璐, 蒙晶棉, 邓鸿骥 2017 中国专利 CN 106390992 A
Xu X T, Wang F, Huang H J, Ji L L, Meng J M, Deng H J 2017 Chinese Patent CN 106390992 A (in Chinese)
[9] Lü Y H, Yao W Q, Zong R L, Zhu Y F 2016 Sci. Rep. 6 19347
Google Scholar
[10] Liu Y, Wei B, Xu L L, Gao H, Zhang M Y 2015 Chem. Cat. Chem. 7 4076
[11] Gu H, Ding J, Zhong Q, Zeng Y Q, Song F J 2019 Inter. J. Hydrogen. Energ. 44 11808
Google Scholar
[12] 郝亮, 张慧娜, 闫建成, 程丽君, 关苏军, 鲁云 2018 天津科技大学学报 33 1
Hao L, Zhang H N, Yan J C, Cheng L J, Guan S J, Lu Y 2018 J. Tianjin Univ. Sci. Tech. 33 1
[13] Zhang Z J, Wang W Z, Gao E P, Shang M, Xu J H 2011 J. Hazard. Mater. 196 255
Google Scholar
[14] Tan G Q, Huang J, Zhang L L, Ren H J, Xia A 2014 Ceram. Inter. 40 11671
Google Scholar
[15] Ding B F, Han C, Zheng L R, Zhang J Y, Wang R M, Tang Z L 2015 Sci. Rep. 5 9443
Google Scholar
[16] Shannon R D 1976 Acta Cryst. A 32 751
Google Scholar
[17] 李洪全, 郑树凯, 丁帮福, 闫小兵 2018 中国粉体技术 24 19
Li H Q, Zheng S K, Ding B F, Yan X B 2018 Chin. Powder. Sci. Tech. 24 19
[18] Nie Z P, Ma D K, Fang G Y, Chen W, Huang S M 2016 J. Mater. Chem. A 4 2438
Google Scholar
[19] Zhou Y, Tian Z P, Zhao Z Y, Liu Q, Kou J H, Chen X Y, Gao J, Yin S C, Zou Z G 2011 ACS Appl. Mater. Interface 3 3594
[20] 王亚军, 于海洋, 李泽雪, 郭梁 2018 材料研究学报 32 149
Google Scholar
Wang Y J, Yu H Y, Li Z X, Guo L 2018 Chin. J. Mater. Res. 32 149
Google Scholar
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