First principle calculation and photocatalytic performance of BixWO6 (1.81 ≤ x ≤ 2.01) with oxygen vacancies

Semiconductor photocatalyst Bi2WO6 has an extensive application prospect in organic contaminant degradation.But its energy band is relatively large and the recombination rate of photon-generated carriers is high,which prohibit its rapid development and applications.Many methods such as ion doping,non-stoichiometry,semiconductor heterojunction have been used to improve the photocatalytic activity of Bi2WO6.But the improvement mechanism is still not very clear.In this paper,by using first principle density functional theory (DFT) calculation,we study the influences of oxygen vacancy on the bond length,charge population,band structure,defect formation energy,and density of states of Bi2WO6.On the basis of DFT calculation results,different non-stoichiometric BixWO6 (x=1.81,1.87,1.89,1.92,2.01) products with oxygen vacancies are synthesized through the solvothermal method.The products are characterized by X-ray diffraction,scanning electron microscopy,X-ray photoelectron spectroscopy,UV-vis diffuse reflectance spectra photoluminescence spectroscopy,and X-ray Fluorescence.The effects of non-stoichiometric Bi element on crystal structure,chemical composition,the number of oxygen vacancies,microstructure,and photocatalytic properties are investigated and the improvement mechanism of the photocatalytic property is explored.The DFT calculation results reveal that the formation energies of Bi16W8O48 are different for the three kinds of oxygen vacancies and the bond lengths of Bi–O and W–O with one oxygen vacancy decrease a little and the bond populations decrease significantly for the Bi and W atoms adjacent to oxygen vacancy.The existence of oxygen vacancies forms O 2p impurity energy level and significantly reduces the band gap of Bi2WO6. The absorption spectra indicate that the absorption intensities in the visible light increase for the Bi16W8O48 cell with oxygen vacancy defects increasing.The DFT calculation results show that oxygen vacancy defects promote the formation of photoelectrons and enhance the photocatalytic performance of Bi2WO6.The experimental results show that non-stoichiometric Bi element makes the crystal structure slightly deformed and significantly affects the number of oxygen vacancies,photoabsorption capacity and the electron-hole recombination of Bi2WO6.The Bi1.89WO6 product has the best photocatalytic performance,and the rhodamine B is degraded by 98% after being irradiated for 180 min by visible light.Therefore,non-stoichiometric semiconductor with oxygen vacancy is testified to be an efficient method of obtaining high activity photocatalyst.