First-principles Calculation On Photocatalytic Performance Of BiVO₄

Semiconductor photocatalysts had drawn increasing attention in the application ofeliminating aqueous and atmospherical pollutants with the development of economyand the destruction of earth. The monoclinic BiVO4(Eg=2.4eV) which was chemicallystable, non-toxic and cheap could split water in visible light and degrade organicpollutants in visible light region. Because people had different opinions about themechanism of the visible light catalytic activity, the photocatalytic properties ofdifferent crystalline phases of BiVO4, doped and loaded monoclinic BiVO4were studiedby CASTEP of MS-5.5software under PWPP based on density function theory (DFT)in this paper. Results were as follows:1. BiVO4appeared mainly in three crystalline forms which were tetragonal zircon,monoclinic scheelite, and tetragonal scheelite structures. Among them, thephotocatalytic properties of monoclinic BiVO4and tetragonal BiVO4were better. Theanalysis of calculated results from MS shows that: the photocatalytic properties ofmonoclinic BiVO4were the best of the three crystalline forms. Because of the band gapof monoclinic BiVO4was narrow than tetragonal BiVO4, in theory, the narrower theband gap, the less the energy of electrons from the valence band transited to theconduction band, then the more easy to produced photo-generated electron-hole pair.The results of absorption spectrum shown that, the visible-light response of monoclinicBiVO4was stronger than tetragonal BiVO4. To sum up, the photocatalytic properties ofmonoclinic BiVO4were better than tetragonal BiVO4. So took monoclinic BiVO4as theresearch object on first-principles study.2. W doped BiVO4with different doping concentration was calculated by CASTEP ofMS-5.5software under PWPP based on density function theory (DFT) in this paper. Allcalculated samples with different doping concentration could improve the photocatalyticactivity of BiVO4crystallites. When the doping concentration was of6.25%, W-BiVO4has the most stable state, the narrowest band gap and the maximum red shift ofabsorption edge.3. The photocatalytic properties of monoclinic BiVO4with two different transitionmetal (Mo, W) doping calculated from MS. The results showed that: firstly, with theband gap narrowed, photo-generated electron-hole pair effectively separated and theabsorption edge red shifted after W or Mo doping, which could effectively improve thephotocatalytic activity of BiVO4crystallites. Among them, the structure of Mo-BiVO4 was more stable, the band structure was narrower and the absorption spectrum red shiftis more obvious. Secondly, d orbit has an outstanding contribution in improving thephotocatalytic performance.4. The photocatalytic properties of monoclinic BiVO4with metal oxide CuO loadingcalculated from MS. The result showed that the band gap narrowed to1.031eV, and themiddle of the band gap appeared the impurity level, it was completely hybridized thatthe bottom of the conduction band and the top of the valence band. The results of theelectron density difference showed that with the photo-generated electron of CuOmoved to the conduction band of BiVO4, and the photo-generated hole of BiVO4movedto the valence band of CuO, which could effectively restrained the recombination ofphoto-generated electron-hole pair and improved the photocatalytic activity.