Engineering Preparation Of BiVO₄ Crystal Plane And Regulation Of Photocatalytic Hydrogen Evolution Performance

Photocatalytic materials have sparked a lot of interest in wastewater treatment for printing and dyeing as well as photocatalytic hydrogen evolution（HER）and oxygen evolution due to their benefits of high efficiency and fast recovery（OER）.With a small band gap of 2.4-2.6 e V,bismuth vanadate（BiVO₄）is able to absorb visible light and respond favorably to it.The low photocatalytic effect of pure BiVO₄ photocatalyst is due to a high photoelectron-hole recombination rate,which severely reduces the photocatalytic activity.This work examined the modification of BiVO₄ in order to facilitate the separation of photogenerated electrons and holes,enlarge the light absorption of modified BiVO₄,and address the aforementioned issues to enhance the photocatalytic performance.The main results are as follows:（1）Flake BiVO₄ was prepared by hydrothermal method,and bismuth vanadate(Bi_1-xVO₄)containing bismuth vacancy(Bi_vac)was prepared by a new deep eutectic solvent（CCG）.Raman spectra show that Bivac promotes the red shift of V-O bond of BiVO₄ and X-ray photoelectron spectroscopy（XPS）shows that the production of Bi_vacreduces the Bi 4f binding energy of BiVO₄.The results of photocatalysis showed that the H₂O₂ production of Bi_1-xVO₄ was up to 1.37 mg/L and the hydrogen evolution was70.5μmol/g.The cycle experiment also showed that Bi_1-xVO₄had good stability.In addition,the electrochemical results showed that Bi_1-xVO₄has more negative potential,lower impedance and lower overpotential.Compared with BiVO₄,the band gap of Bi_1-xVO₄ is narrower than that of 0.13 e V,and the conduction band shifts negatively to0.32e V.Density functional theory（DFT）calculation showed that there are more electrons on the V atom around Bi_vac in Bi_1-xVO₄,which provided a theoretical basis for hydrogen production in Bi_1-xVO₄.（2）Using BiVO₄ nanosheets prepared by hydrothermal method as substrate,Ag was deposited on BiVO₄ by photo-deposition（Ag-BiVO₄）.Scanning electron microscopy（SEM）and transmission electron microscopy（TEM）can clearly observe that Ag nanoparticles（Ag NPs）were successfully loaded on BiVO₄ nanosheets.The photocatalytic results showed that Ag-BiVO₄ has good hydrogen evolution ability（72.1μmol/g）and oxygen evolution capacity（107.3μmol/g）,as well as excellent photocatalytic degradation efficiency and reuse performance for rhodamine B（Rh B）（the degradation rate reaches 90%within 2.5 h and can still maintain more than 90%photocatalytic performance after 30 cycles）.Electrochemical characterization showed that the conduction band of Ag-BiVO₄ shifted negative 0.19V relative to BiVO₄ under light condition.DFT showed that electrons mainly concentrated on silver atoms attract water molecules to reduce around Ag.Combined with electrochemistry,DFT calculation and free radical capture experiment,the possible photocatalytic mechanism was proposed.