Research On Improving The Performance Of BiVO₄ In HCHO Degradation By Regulating The Energy And Transport Of Photogenerated Carriers

Formaldehyde as a common indoor organic pollutant,with a characteristic of low concentration and continuous release,which is extremely harmful to the human body.Photocatalytic oxidation is an ideal technology to deal with low-concentration gas pollution.Among many photocatalytic materials,the monoclinic scheelite phase bismuth vanadate（BiVO₄）has attracted people’s attention for its reasonable energy band structure,stable chemical properties and strong oxidation ability.However,it has two shortcomings（limiting factors）in practical applications:1.the lower conduction band position leads to poor reduction of the photo-generated electrons;2.the transmission distance of photogenerated carriers is short and easy to recombine.In this work,we have developed two strategies to effectively solve the above problems and greatly improve the performance of BiVO₄ photocatalytic degradation of formaldehyde.（1）Strategies on particle size control.The photo-generated charge properties of BiVO₄ were improved by preparing BiVO₄ quantum dots（BiVO₄-QD）with band broadening effect and short photo-generated carrier transport distance.BiVO₄-QD were successfully prepared by continuous ion layer adsorption reaction method and with an average particle size of about 5 nm.Rutile Ti O₂ nanorod array（RTA）was selected as the substrate,and the prepared nanocomposites have better formaldehyde degradation performance under visible light irradiation.The excellent photocatalytic activity is mainly attributed to the wider band gap of BiVO₄-QD,which enables the photogenerated electrons to have higher energy and can be effectively transferred to the RTA as an electron acceptor and transport medium.Hence the separation of charges is efficiency enhanced and prolongs its charge life.In addition,the nanocomposite material loaded with Au nanoparticles further enhances the photocatalytic activity due to the plasmon resonance effect.（2）Strategies on piezoelectric electric field control.We promote the energy and transport of photogenerated electrons in BiVO₄-QD by means of an applied electric field.BiVO₄-QDs were modified on ZnO nanorods to construct a piezoelectric potential assisted photocatalyst.The results show that the negative electric field generated by the top of the ZnO nanorods significantly increases the formaldehyde degradation rate of BiVO₄-QD under visible light.This is mainly because when ZnO nanorods are deformed under compressive stress,the negative electric field generated in the top can elevate the conduction band of BiVO₄,so that the photogenerated electrons have higher energy.Moreover,under the influence of the negative electric field,photogenerated electrons and holes transfer in opposite directions,which significantly improves the separation efficiency of photogenerated carriers,thereby greatly improving the photocatalytic activity of BiVO₄ quantum dots.Through the above strategies,we have solved the problems of low energy of photogenerated electrons and easy recombination of BiVO₄ material,and provided a feasible reference for the performance improvement of other photocatalysts with low conductivity band position.