Preparation And Optical/Electrical Properties Of Bismuth Vanadate-based Micro/Nano Structure Materials

With the rapid development of social economy,the energy shortage and environmental pollution caused by this have become increasingly severe.Photocatalytic technology with semiconductors as catalysts is a relatively ideal energy development and environmental treatment technology.It can not only convert solar energy into chemical energy,but also achieve catalytic degradation of pollutants under the excitation of sunlight;the reaction conditions are mild and low energy consumption.Among them,Ti O₂is one of the most widely studied photocatalysts,but its large band gap（3.2e V,which can only absorb ultraviolet light）,easily recombined photogenerated electron-hole pairs and other shortcomings restrict its practical application.Therefore,it is urgent to develop new photocatalysts with low carrier recombination rate,wide photoresponse range,and high photocatalytic efficiency.As a typical layered semiconductor,bismuth vanadate（BiVO₄）is usually orange-yellow with bright color,corrosion resistance,good acid and alkali resistance,good resistance to organic solvents and thermal stability,and is environmentally friendly,etc.Its band gap is 2.4～2.9 e V,and its absorption edge can be extended to 520 nm.BiVO₄could absorb both ultraviolet and visible light,it is an ideal visible light-responsive photocatalytic material.However,because its some shortcomings:（1）the VO tetrahedrons of BiVO₄are not in direct contact,the conversion of photo-generated carriers can only be achieved by jumping,which reduces the transmission efficiency of photo-generated carriers;（2）the specific surface area is not large enough,and the organic The adsorption efficiency of pollutants is low.After being adsorbed for a period of time,organic pollutants will leave the BiVO₄surface;（3）The energy band structure is not ideal,the conduction band potential is low,the electron-hole pair migration is difficult,and the electron and hole are difficult to transfer.Further lead to the high recombination rate;so tha the photocatalytic efficiency of the commonly prepared BiVO₄is not very satisfactory.This thesis intends to realize the adjustment of the optical properties and photocatalytic properties of BiVO₄through the control of morphology and structure.The main research contents are as follows:（1）The solvothermal method was used to prepare BiVO₄with a angleless-octahedron structure.The results of XRD,SEM and UV showed that the product had a high purity and had a monoclinic scheelite structure;the morphology is close to a chamfered octahedral structure with a size of about 2～5μm;and the band gap is 2.388 e V.Fluorescence（PL）spectroscopy test results found that if the reaction time is extended,the luminescence intensity first increases and then decreases.If the reaction time continues to increase,the intensity increases again.It can be seen that various reaction parameters have a greater impact on the morphology of the product.This in turn affects the performance of the product.（2）Without adding any surfactant,BiVO₄with mulberry-like structure was synthesized by solvothermal method.XRD and SEM results show that the diameter of the mulberry-like BiVO₄product is about 300 nm and the length is about 1μm.The results of PL and EIS show that:among the three samples（R=0.5,3,5）,the PL spectrum intensity of the product at R=0.5is the weakest,the EIS spectrum radius is the smallest,and its impedance is the lowest,which shows that its photo-generated current The electron recombination rate is the lowest and the charge transfer efficiency is the highest.The photocatalytic results showed that the degradation rate of the product to Rh B is 85.07%under UV light irradiation,and it is still80.82%after 3 cycles,and the photocatalytic reaction constantκis 0.07898 min^-1;the photodegradation efficiency of the product to MB is 76.88%,andκis 0.03683 min^-1.When the light source is a xenon lamp,the photodegradation efficiency of the product on Rh B and MB is 32.85%and 44.95%,andκis 0.1357 min^-1and 0.1997 min^-1,respectively.（3）The rice-bunch-like BiVO₄@C composite was prepared by solvothermal method,and the effects of the type of solvent and the amount of glucose added on the properties of the product were studied.The research results show that the product still has a monoclinic scheelite structure with an average length of 2μm.The optimal preparation conditions for the rice-bunch-like BiVO₄@C composites are:EG is used as the solvent,the reaction temperature and time are 180℃,24 h,and the amount of glucose added is 0.6 g.Photocatalytic degradation experiments show that under the irradiation...