BiVO₄ Composite Catalyst And Its Photocatalytic Activity Under Visible-light Irradiation

Cu/BiVO₄ and tourmaline/BiVO₄ composite photocatalysts are prepared by hydrothermal synthesis of BiVO₄,followed impregnation and TEOS sol-gol hydrolysis method respectively.Then the photocatalysts are separately immobilized onto stainless steel meshes and/or nylon.Common indoor pollutants toluene and formaldehyde are used as the target chemicals.The removal of these two pollutant molecules in air affectd by catalysts composition and property under visible light irradiation is investigated.The composite photocatalysts are characterized by X-ray diffraction(XRD) scanning electron microscope (SEM),X-ray photoelectron spectroscopy(XPS)and ultraviolet-visible absorption spectra (UV-vis).The mechanisms of enhanced activity in oxidizing pollutants were explored.Cu/BiVO₄ composite thin film photocatalysts are prepared via hydrothermal synthesis, impregnation and followed loading via sol gel process onto metal meshes.In which,BiVO₄ is the monoclinic phase structure and high crystallinity.Copper species form heterostructure p-n with BiVO₄ in the form of Cu²⁺.Composite of copper significantly improves the absorption ability of the photocatalysts towards visible light,the absorption band edge has a red shift from 530nm to 650nm.It proves that Cu/BiVO₄ composite has narrowed the band width. Compared to pure BiVO₄ samples,Cu/BiVO₄ catalysts have substantial increase in the visible light activity.The results showed that two layers coated catalyst with 5.0%Cu has the highest catalytic activity.After 5h,the removal rate of toluene at 80 mg/m³ initial concentration goes up to 90%.Tourmaline/BiVO₄ photocatalysts are prepared by hydrothermal and sol-gel method, this composite catalyst shows good activity under visible light irradiation.In the best conditions(3.5%tourmaline doping,two film layers load),the removal rate of toluene at 80 mg/m³ initial goes up to 78%after five hours of visible light irradiation.Doping of tourmaline increases the roughness of catalyst surface,is good for the adsorption of toluene and the existence of a weak electric field also increases the catalytic activity. Photocatalytic activity of photocatalyts modified withβ-CD has changed.The photocatalytic activity of Cu/BiVO₄ and tourmaline/BiVO₄ is weakened afterβ-CD modification,and the catalyst activity of BiVO₄ is greatly enhanced,from 34%to 82%.Chitosan-modified nylon supported Cu/BiVO₄ photocatalysts have a notable photocatalytic activity on formaldehyde removal at 10-11 mg/m³ initial concentration under visible light irradiation,the removal rate can get up to 50%.Compared with the samples without chitosan modification,the results show that surface modification can enhance the adsorption of pollutants and purifying effect.This study is carried out in conditions that simulating natural convection and diffusion of indoor air.The contaminants reaching the surface of catalyst is oxidized,no extra light,no noise and a small secondary pollution.The catalyst immobilization conditions used is at room temperature,thus expands the range of the substrate materials,enables new indoor decoration that features air cleaning effect,thus has the potential to be used for air purification purposes.