Preparation Of TiO₂-based Thin Films And Their Photocatalytic Degradation Of Gas-phase Formic Acid

Indoor and outdoor air pollution has become a common concern in modern society.Although many policies and regulations regarding air quality have been enacted around the world over the past few decades,air pollution still has a negative impact on human health.As the main component of air pollution,the effective treatment of volatile organic compounds(VOCs)has attracted extensive attention of researchers.Titanium dioxide(TiO₂)semiconductor photocatalytic material has the advantages of high efficiency,non-toxicity,good stability,economy and environmental protection,etc.Therefore,using TiO₂ as a photocatalyst to degrade pollutants is an effective method to solve air pollution.However,TiO₂ has a wide band gap and poor absorption of visible light and single TiO₂ has a low separation efficiency of photogenerated carriers,which limits its application.In this paper,TiO₂ was modified by semiconductor compounding.With the binary heterojunction of titanium dioxide/zinc oxide(Zn O)nanorods as the main body,through the synergistic effect of ternary composite,the optical response range of the material is widened,the recombination rate of photogenerated electron holes is reduced,and the visible photocatalytic performance of a single photocatalytic material is improved.Through experiments,the structure and photocatalytic properties of the materials were characterized and tested.The main research contents of this paper are as follows:(1)First,TiO₂ thin films were prepared on stainless steel mesh by the improved pulling method,and Zn O nanorod thin films were prepared on TiO₂ by hydrothermal method.The thin films were characterized by XRD,SEM,TEM and UV-Vis techniques.Then,the photocatalytic performance of the prepared materials was evaluated by photocatalytic degradation of volatile organic compound gas-phase formic acid.The study shows that the photocatalytic degradation process of formic acid conformed to the first-order kinetic reaction model,and the reaction mechanism of photocatalytic degradation was studied.(2)Zn O nanorods with different microstructures were prepared by adjusting the growth reaction temperature,reaction time and other parameters in the chemical reaction process,and the effects of process factors on the microstructure and photocatalytic performance of Zn O were discussed.When the growth temperature is 95?and the growth time is 4 h,the TiO₂/Zn O composite film has the best photocatalytic performance under ultraviolet light,and the degradation rate reaches 94.42%.At the same time,the effects of relative humidity and light intensity on the photocatalytic degradation efficiency of gas-phase formic acid have been discussed:there is an optimum relative humidity during the degradation of formic acid,and the degradation efficiency of formic acid increases with the increase of light intensity.In repeated experiments,the prepared photocatalytic material has good stability.(3)The g-C₃N₄ material was modified on the surface of TiO₂/Zn O binary heterojunction by calcination method.It was found that the TiO₂/Zn O/g-C₃N₄ composite film had excellent photocatalytic activity in the visible light band,and the composite modified with a layer of g-C₃N₄ had the best photocatalytic performance.The degradation rate of gas-phase formic acid can reach 93.86%.This is because the narrow band gap semiconductor g-C₃N₄ can effectively broaden the light absorption range.At the same time,the formation of heterojunction reduces the recombination rate of photogenerated electron-hole pairs and enhances the photocatalytic performance of the composite film.The composite film has high stability and is conducive to recycling.