Study On Photocatalytic Degradation Of Gaseous Formaldehyde By TiO₂/ACF Composite Photocatalytic Material

With the increasing attention of indoor VOCs pollution,photocatalytic technology with good degradation effect is becoming a new hot spot in the field of indoor air purification.By using the load technique,the TiO₂ has been loaded to the adsorption type vector ACF to form TiO₂/ACF composite photocatalytic materials.The complex shows strong adsorption ability and high photocatalytic activity,which has a high degradation efficiency for indoor VOCs.However,there are still some problems in the degradation of indoor VOCs using TiO₂/ACF composite photocatalytic materials: Most of the degradation reaction cabin have limited size and simple equipment,it is difficult to accurately simulate the real indoor environment degradation process;The load effect is poor;The effects of various factors on the adsorption photocatalytic degradation process,the related mechanism and the kinetic analysis are not clear;And the impact of adsorption photocatalytic degradation process on environmental parameters are inadequate,etc.In this paper,based on the full summary of the relevant research,a closed loop system with photocatalytic reactor has been designed and built,which is more closer to the real conditions of indoor pollutant diffusion model.Using AlPO₄ as binder,TiO₂/ACF composite photocatalytic material was prepared by and impregnation method.The samples were characterized by XRD,BET and thermogravimetric analysis,and a series of adsorption photocatalytic degradation experiments has been carried out in the closed cycle system.TiO₂/ACF composite photocatalytic materials with different TiO₂ loading were prepared,and the adsorption and photocatalytic degradation of formaldehyde in the closed cycle system has been studied to find out the degradation effect;The effect of the interference of other kinds of VOCs on the degradation of formaldehyde was studied by adding gaseous xylene in the reaction system;The effects of environmental factors on the degradation of formaldehyde were investigated by changing the initial concentration,reaction temperature and relative humidity.The conclusions can be obtained as following:（1）According to the characterization of XRD,the crystal of TiO₂ particles after the loading process has not changed,TiO₂ has successfully loaded onto the ACF surface;Before and after the loading process,the grain size of TiO₂ are 24 nm and 17 nm.（2）According to the N₂ isotherm desorption spectra,the adsorption isotherms of TiO₂,ACF and TiO₂/ACF composite photocatalytic materials are classified as type III,type I and type IV.It can be seen that the adsorption capacity of TiO₂/ACF is lower than ACF,but is much higher than TiO₂.（3）By comparing the specific surface area and pore structure parameters of ACF,TiO₂ and TiO₂/ACF,it was found that the specific surface area of ACF decreased with the loading of TiO₂.However,compared with TiO₂,TiO₂/ACF still maintained a very large specific surface and strong adsorption capacity;Adding Al PO4 as binder has no significant effect on the pore structure of TiO₂/ACF.（4）According to the TG spectra of TiO₂ and TiO₂/ACF,the optimal heat treatment temperature of the composite photocatalytic material is about 400℃,and the composite photocatalyst material has higher thermal stability than ACF.The thermal stability of the composites with different loads is approximately the same.（5）The ACF loading process was carried out by using TiO₂ suspension emulsion with mass fraction of 1%,2% and 3%.Using three types of TiO₂/ACF composite photocatalytic materials to study the adsorption and photocatalytic degradation of gaseous formaldehyde in closed cycle system.The experimental results show that when the load is small,the adsorption of ACF is good,but the photocatalytic rate is limited.When the load is large,the adsorption process is blocked,but the photocatalytic effect is good.（6）Under certain conditions,the adsorption and photocatalytic degradation experiments of two components VOCs（formaldehyde and xylene）were carried out.The results show that the presence of xylene in the closed cycle system can VIIIinhibit the adsorption and photocatalytic degradation of formaldehyde.（7）With formaldehyde as the target pollutant,there was no significant difference in the rate of photocatalytic degradation at different initial concentrations,and the final degradation rate could reach more than 80%.The degradation rate of formaldehyde can reach more than 65%,while the photocatalytic degradation rate of formaldehyde is from 15% to 32%.There was no significant relationship between the rate of photocatalytic degradation and the initial concentration of formaldehyde.The reaction kinetics of photocatalytic degradation of formaldehyde under different initial concentrations of analysis found that the this degradation process accords with the first-order reaction kinetics model of L-H.In the adsorption phase,the relative humidity increases,and the adsorption of formaldehyde on the composites decreases;In the photocatalytic phase,because of the dual effect of water molecules on the photocatalytic process,with the increase of relative humidity,the photocatalytic reaction rate of formaldehyde increased first and then decreased.When the relative humidity is in the range of 50%-60%,the photocatalytic reaction rate reaches the maximum.In the adsorption stage,the temperature will decrease the adsorption amount.In the photocatalytic stage,the photocatalytic degradation rate was no significant difference between the different reaction temperature,formaldehyde photocatalytic degradation rate and reaction temperature have no significant relationship.（8）Under different reaction conditions,the whole system humidity difference before and after the reaction is not more than 5%,and the temperature difference is not more than 1.3℃.The degradation process has little effect on the comfort of human body.