Study On The Photocatalytic Oxidation Of Formaldehyde By Bismuth-based Oxide Doped Titanium Oxide Composite

In recent years,the problem of indoor environmental pollution has seriously affected human life,and long-term exposure to volatile organic compounds（VOCs）can cause damage to human health,which is an urgent problem to be solved at present.Photocatalytic technology has attracted much attention as a new method with moderate reaction conditions,high removal efficiency,no secondary pollution,and good economy.Selecting suitable photocatalytic materials generates a variety of active species under the excitation of light to convert pollutant molecules into H₂O and CO₂.Based on the many advantages of photocatalysis technology,this paper prepares a variety of excellent Bi-based oxide-doped TiO₂composite functional materials based on TiO₂for the efficient removal of HCHO,a common gaseous pollutant in indoor environment,for the efficient photocatalytic oxidation of formaldehyde gas to H₂O and CO₂under simulated indoor visible light irradiation.The study employed XRD,SEM,BET,UV-vis,and XPS to characterize and analyze the prepared catalysts,and various methods were used to improve the catalyst performance in order to enhance the catalytic degradation activity and selectivity for indoor low concentration gaseous HCHO under visible light and powerless conditions.The details of the study are as follows:（1）Composite photocatalytic materials of Bi-modified TiO₂were successfully constructed by sol-gel method.According to the characterization,partially Bi-doped TiO₂can be transformed into a unique crystalline phase of Bi₄Ti₃O₁₂,which can improve the photocatalytic degradation performance of HCHO.Excessive doping of Bi₂O₃into TiO₂,such as Bi₂O₃-N/TiO₂and Bi₂O₃-C/TiO₂,produced the generation of mixed oxides of Bi₂O₃and Bi₄Ti₃O₁₂,which is not conducive to improving the oxidation activity of HCHO,while Bi/TiO₂composed of TiO₂and Bi₄Ti₃O₁₂showed higher activity and good stability.Bi/TiO₂could reduce the HCHO concentration from 1.059 to 0.315 mg/m³within 48 h under visible light irradiation.due to the homogeneous particles,high surface area and strong interaction between TiO₂and Bi₄Ti₃O₁₂,Bi/TiO₂exhibited high photocatalytic activity,which was attributed to the generation of superoxide radical anions（·O₂^-）and hydroxyl groups（·OH）.（2）The Ag Bi/TiO₂photocatalyst co doped with silver and bismuth was prepared by hydrothermal method and sol gel method based on the Bi/TiO₂photocatalyst with the best activity mentioned above,The effects of preparation methods,silver bismuth doping amount,and calcination temperature on the visible light catalytic oxidation performance of the catalyst were investigated.It was found that the Ag-Bi/TiO₂-H catalyst made by hydrothermal method had the best effect in degrading HCHO,which could reduce the HCHO concentration of1.076 mg/m³to 0.093 mg/m³within 48 h.It significantly improved the catalytic oxidation performance of TiO₂and had excellent stability performance.The synergistic interaction between Ag₂O/Ag,Bi³⁺and TiO₂improves the microstructure of the catalyst,enhances its absorption of visible light,and promotes the formation and transfer of photogenerated electrons.The surface hydroxyl groups and the adsorbed oxygen formed by coupling enhance the adsorption and catalytic oxidative degradation of HCHO at low concentrations.BiVO₄/TiO₂and BiVO₄-TiO₂catalysts were prepared by hydrothermal and physical mixing methods to investigate the effects of four surfactants on BiVO₄-TiO₂composite structure photocatalysts.The photocatalytic performance of the prepared samples was tested and the samples were characterized physically by controlling the reaction time,compounding method and loading amount to change the morphology and arrangement of BiVO₄-TiO₂nanostructures.BiVO₄-TiO₂with surfactant as Na OH prepared by ultrasonic physical mixing could reduce formaldehyde concentration from 1.050 mg/m³to 0.03 mg/m³in 48 hours,and the degradation ability of formaldehyde was significantly higher than that of BiVO₄and TiO₂.The monoclinic phase BiVO₄was successfully compounded onto the anatase phase TiO₂,and the active substance that plays a major role in the photocatalytic degradation of formaldehyde by BiVO₄（Na OH）-TiO₂photocatalyst is·O₂^-,followed by·OH.