The Improvement Of The Photocatalytic Performance Of The Bi 2 WO 6 Semiconductor By Halogen Element Doping

Energy is an important factor in the development of modern society. However, earth has been suffering from an astonishing decline in energy, an increased awareness of energy and environmental issues has led to a new focus on the development of clean and renewable energy sources. Nowadays, the photocatalytic properties of some ternary oxides such as ZnWO₄?SrTiO₃?AgNbO₃?NaNbO₃?BiVO₄?Bi₂WO₆ and so on, have been attracted extensive attention. It has been confirmed that tungstate materials, such as ZnWO₄ and AgInW₂O₈, present high photo-catalytic activity on decontamination. Meanwhile, Bi₂WO₆ as one of the tungstate family has been identified with an Aurivillius layered structure composing of MO6 octahedron and Bi-O-Bi layers, shows promising photocatalytic activity. It has been put forward, doping with halogen maybe a good way to improve the photoelectric properties of semiconductor such as TiO2 and obtained prospective consequence. In this paper, we present a systemic study the electronic and photocatalytic properties of a series halogen-doped Bi₂WO₆ structure by using first-principles projector argumented wave potential within the generalized gradient approximation.In the third chapter, we present an experimental study on photocatalysis of pure and Br-doped Bi₂WO₆ powders, including photo-degradation of Rhodamine B, UV-vis absorption spectra and photo-luminescence spectrum. The obtained results indicate that Br-doped Bi₂WO₆ powders exhibit preferable photocatalytic activity than pure Bi₂WO₆. Then, the structural stability and the electronic properties of Br-doped Bi₂WO₆ are studied by employing the first-principles method, and a promising improvement of photo-catalytic activity is found in the visible-light region after doping, which is consistent with the experimental results. The Bru-doped structure is found to be more preferred, nevertheless all the three types of doping can narrow the band gap of Bi₂WO₆ pronouncedly, and thus the availability of solar energy increases consequently with the doping. On the other hand, the doping of Br results to smaller electron effective mass and induces impurity levels in gap, which is in favor of the carrier's transfer and the decrease of electron-hole recombination respectively.In the fourth chapter, we consummate the halogen-doped content. Our work shows that the doping becomes more difficult in the order F<Cl<Br<I and the halogen-doping are present as F^-1, Cl^-1, Br^-1 and I⁺³ ions for halogen-doped Bi₂WO₆. Halogen-doped Bi₂WO₆ significantly reduce the optical band gaps with respect to that of pure Bi₂WO₆.