Crystal Facets Modification And Photocatalytic Performance Of BiVO₄

Semiconductor photocatalysis technology has broad application prospects in solving environmental pollution and energy shortage problems.Among them,the BiVO4 exposed active crystal facets not only responds to visible light and has a narrow band gap,but also forms a surface heterojunction between different crystal facets,which promotes the migration of carriers on the surface.However,the BiVO4 exposed active facets still has the problems of electron hole pair recombination in the body and low reduction potential.The subject prepared Ag/(010)BiVO4 photocatalysts with different Ag particle sizes by changing the energy of incident light,TiO2/BiVO4 direct Z-type heterojunction,Ag/TiO2/BiVO4 indirect Z-type heterojunction,and Ag/BiVO4/MnOx multi-stage interface heterojunction were constructed by hydrothermal method and photodeposition method,respectively.The optical response range of the semiconductor is enhanced,and the carrier separation is improved.The main conclusions are as follows:(1)The Schottky heterojunction with Ag deposited on BiVO4(010)crystal facets were prepared by changing the energy of incident light.Among them,the Ag element deposited under ultraviolet light is the most and the largest,and the Ag element deposited under visible light is the least and the smallest.Ag element not only has a surface plasmon resonance effect,but also forms a Schottky junction at the interface of BiVO4,which promotes the separation of carriers,thereby improving the photocatalytic activity.(2)Direct Z-type TiO2/BiVO4 heterojunction photocatalyst is synthesized by hydrothermal method.Due to the different work functions,the electrons of TiO2 flow to BiVO4,so that the two change from type Ⅰ heterojunction to type Ⅱheterojunction,and then into direct Z type heterojunction.This can not only promote the separation of electron-hole pairs,but also maintain strong redox ability.Among them,15%TiO2/BiVO4 composite photocatalyst can remove rhodamine B by 74.7%after simulating sunlight for 180min,which is 2.83 times that of pure BiVO4.(3)The Ag/TiO2/BiVO4 indirect Z-type heterojunction photocatalyst was prepared by two-step photodeposition method,and Ag and TiO2 were deposited on the surface of BiVO4.The SPR effect of the precious metal Ag extends the response range to near-infrared light.At the same time,due to its good conductivity,Ag acts as a bridge for charge transfer between TiO2 and BiVO4 semiconductors,forming an indirect Z-type heterojunction,which increases the carrier separation rate.The removal rate of rhodamine B by 20%Ag/TiO2/BiVO4 photocatalyst can reach 86.16%after simulating sunlight for 180min,which is 3.26 times that of pure BiVO4.(4)Under ultraviolet light,amorphous MnOx and metal Ag are deposited on the(110)and(010)crystal facets of BiVO4 in sequence to form an Ag/BiVO4/MnOx photocatalyst.A multi-level interface heterojunction was successfully constructed in the Ag/BiVO4/MnOx photocatalyst.At the interface of p-n junction,surface heterojunction and Schottky junction,three built-in electric fields in the same direction are formed.The three electric fields work together to promote the migration of photogenerated carriers and inhibit the recombination of electron-hole pairs.Plasma Ag has the LSPR effect,which can not only improve light absorption,but also generate a local magnetic field,and cooperate with the electric field generated by the multi-stage interface heterojunction to improve photocatalytic activity.Under visible light,the removal rate of Ag/BiVO4/MnOx photocatalyst for RhB is up to 96.5%,which is 5.9 times that of pure phase BiVO4.