Photocatalytic Degradation Of Toluene In Air Using Modified TiO₂ Film

Photocatalysis is a new technology extensively studied for the degradation of VOCs in the house recently.The research efforts of this field are focused on improving the efficiency of photocatalytic VOC removal by preparing high activity catalysts or combining adsorbents with photocatalyst.So,this rearch using Ag or Ce modification and tourmaline composite photocatalyst,as well as beta-CD modification to increase adsorption of low concentration toluene,and increase toluene removal efficiency from air.The photocatalysts were prepared, characterized with XRD,TEM,SEM,and the influencing factors for the toluene-removal were investigated.(1) TiO₂-photocatalysts doped with Ag⁺ is prepared with sol-gel method on stainless steel net.The results of XRD and TEM show that the crystal structure of catalysts are of anatase type,and the average size of TiO₂ particles is about 8nm.The oxidation and reduction capability of the thin film have been studied from the removal of toluene in the flowing reactor.Some important factors such as different doping concentration of Ag⁺,different initial concentration of toluene are discussed.The result show that the removal of toluene is 54.99% when the 4%-Ag⁺/TiO₂ is used.To initial concentration of toluene at 226mg·m^-3,70mg·m^-3,the removal of toluene are 54.99%and 37.02%with a better result in the flowing reactor.(2) The tourmaline powders is either mixed to the sol during sol-gel preparation or with P-25 suspension to coat stainless steel net.By using the sol-gel -prepared catalyst,more than 80%toluene removal is obtained when initial concentration either high or low after 4 hours reaction;and the removal of toluene were 60.02%,and 48.06%when the mixed- prepared catalyst is used.Tourmaline addition in the sol gel stage affected crystal size of the prepared composite catalyst,thus increased photocatalytic activity,while the weak electric field effect of the composite catalyst containing tourmaline increased oxidation rate of toluene.(3) Ce-1%-TiO₂ is prepard in sol-gel method;then the immobilized catalyst is dipped in theβ-cyclodextrin(CD) solution to adsorbβ-CD.With the CD modified catalyst,in about 4-5 hours reaction time,100%toluene removal was obtained when the initial toluene concentration was 70mg·m^-3 and the removal rate was still 100%when the catalyst is used repeatedly for a third time.To initial concentration of toluene at 97mg·m^-3,100%toluene removal is obtained and to the high initial concentration of toluene(～208mg·m^-3),80% toluene removal was also obtained usingβ-CD modified Ce-1%-TiO₂.The results indicate CD modified photocatalyst had higher activity in photocatalytic oxidation of toluene,than the un-modified catalyst.