Preparation,Modification,Photocatalytic Performance And Application Of BiVO₄

As visible-light driven photocatalyst,bismuth vanadate?BiVO₄?is used to photodegrade organic pollutants widely,to solve the serious environmental problems.However,the photo-excited carries transport characteristics of BiVO₄ photocatalyst is poor,which is a disadvantage of photocatalytic performance.And the state of BiVO₄photocatalyst used during the photodegradation process is powder,it is difficult to be separated from the treated target degradation content solution,which is a limitation to meet the requirement of practical environmental application.In this thesis,the methods for preparing the BiVO₄ and improving the photocatalytic performance and new used state were explored to overcome the drawbacks of BiVO₄ photocatalyst,which can produce a new route for application.It also reveals the relationship between the physical chemical properties and photocatalytic performance,and photocatalytic mechanism.The main contents are as following:?1?The influences of temperatures,holding times,and pH values of precursor solution upon the structure and photocatalytic activity have been studied using template-free hydrothermal method with Bi?NO3?3?5H2O and NH4VO3 as metal source,NH₃?H₂O as pH adjustor.The photocatalytic activity was evaluated for the degradation of the methylene blue?MB?under visible light irradiation.It is shown that all the samples present monoclinic phase,the temperatures,holding times,and pH values of precursor solution can influence crystallinity,unique morphology,BET specific surface area,band gap energy,surface charge and adsorption capacity of BiVO₄ photocatalyst,and these factors influenced the photocatalytic activities together.The best photocatalytic activity was obtained when sample synthesized at T=180°C,t=15 h,and pH=6.87,even 9.2 times higher than that of the reference P25.?2?BiVO₄ photocatalyst was synthesized via a facile aqueous solution method with Bi?NO3?3?5H2O and NH4VO3 as metal source,the samples are heterophase comprising monoclinic-scheelite and tetragonal-zircon phase.The heat treatment or adjusting the pH values of precursor solution influenced the crystal structures,crystallinity,morphologies,local structure,band gap energy,and BET specific surface area,etc..Effects of factors on the photocatalytic performance were investigated,and when heat treatment temperature was 700°C or the pH value of precursor solution was 9,the obtained samples showed the highest photocatalytic performance,promoting 100%degradation of MB in 60 min under visible light irradiation,even10 times higher than that of the reference P25.?3?S-doped BiVO₄ photocatalysts were synthesized using a template-free hydrothermal method or facile aqueous solution method with Bi?NO₃?₃?5H₂O and NH₄VO₃ as metal source,CH₄N₂S as S source without any further treatments.S-doped BiVO₄ photocatalysts exhibit much higher photocatalytic activity,because S ions can be doped into the BiVO4 crystal lattices,which can increase the BiVO4lattice parameters,increase the number of defects and oxygen vacancy density,and cause a narrow of band gap energy,in addition,S ions can act as electrons or holes'traps,and inhibit their recombination.For S-doped BiVO₄ photocatalysts synthesized by hydrothermal method,the amount of CH₄N₂S greatly affects the photocatalytic performance,the best performance achieves when molar ratio of CH₄N₂S to BiVO₄ is0.5 for it could degrade MB totally in 25 min under visible light irradiation,4.8 times higher than that of the undoped BiVO₄ and 16 times higher than that of the reference P25;For S-doped BiVO₄ photocatalysts synthesized by aqueous solution method,the amount of CH4N2S has little effect on the photocatalytic performance,the best performance achieves when molar ratio of CH₄N₂S to BiVO₄ is 0.3 for it could degrade MB totally in 40 min under visible light irradiation.?4?BiVO₄ ceramics balls have been successfully fabricated by low temperature sintering with S-doped BiVO₄ powder synthesized by template-free hydrothermal method and BiVO₄ powder synthesized by aqueous solution method as raw material,respectively.The balls have excellent photocatalytic performance and outstanding stability.This work could provide new insights into fabricating highly efficient and stable semiconductor ceramics balls for practical application in environmental remediation.?5?The BiVO₄,S-doped BiVO₄ photocatalysts and BiVO₄ ceramics balls involved in the thesis have excellent photo-stability during the degradation process.The study of MB photocatalytic degradation mechanism under visible light irradiation indicates that in all the BiVO₄ systems of this thesis,photogenerated h⁺and·O₂^-radicals are the dominant oxidative species that can degrade MB effectively,but·OH radicals are not involved.