The Effect Of Environmental Factors On Photooxidation And Photocatalytic Of Toluene

With the improvement of people’s living standards, indoor air quality (IAQ) has gradually become the focus of attention.Toluene,as a typical indoor air po llutant,was widely studiedbecause of the simple detection method and low toxic ity. Currently, many researches aspects of the removal of toluene using photoca talytic method were reported, but most of these researcheswere concentrated on improving the efficiency of photocatalyst. Few researchesstudied on the impact of environmental factors(temperature, relative humidity, light intensity, and the gas-phase reaction medium) on the degradation of toluene were reported. Mea nwhile, few researches were concentrated on the mass transfer in the photocata lyticprocess, although toluene were adsorbed to the catalyst surface was the firs t step of the degradation of toluene.For address these deficiencies, this paper c arried out severalexperiments to obtain more reaction mechanism of toluene.The photooxidation of gaseous toluene using low-pressure mercury UV la mp as the irradiation source is described in this study. The influence of enviro nmental factors such as relative humidity (RH), temperature (T), light intensity (I), and aerobic/anaerobic atmosphere on the photooxidation efficiency of toluen e with low concentration (10-20mg/L) were studied in a quartz tube reactor usi ng a dynamic experiment system. The intermediate products generated during t he photooxidation of toluene were studied in the Teflon reactor using a static experimental system. The experimental results indicated that:1) RH had a sign ificant effect on the toluene photooxidation. The removal rate of toluene was b etween 8% and 9% under the drying condition (RH=0%～5%). When water vap or was introduced into the air, the removal rate of toluene reduced to 7%(RH =20%). With the increase of RH, the photooxidation removal rate of toluene al so increased, and the peak removal rate of toluene was between 9% and 12% under RH=60%. When RH increased to 80%, the removal rate of toluene rapid ly reduced to 4% to 6%.2) The photooxidation removal rate of toluene tended to improve with the increasing of environmental temperature or the light inten sity.3) The removal rate of toluene in the aerobic atmosphere (air) were highe r than that in the anaerobic atmosphere (nitrogen) in both dry environment (R H=0%-5%) and humid environment (RH=60%). The intermediate of photooxidat ion of toluene in the nitrogen medium was benzene, while the intermediates in the air medium were benzene and benzaldehyde.4) Under the aerobic dry at mosphere, the active species of photooxidation of toluene maybe O (1D), while it was ·OH in humid environment. Under the anaerobic atmosphere, the remo ve of toluene was mainly derived from the directly degradation by UV (185nm) irradiation.Influence of environmental factors on photocatalytic oxidation of toluene u sing activated carbon fibers coated TiO2 (TiO2/ACF, prepared by impregnation method) was investigated. The remnant of toluene and the accumulation of inte mediates on the TiO2/ACF catalyst under different experimental conditions wer e determined by GC-FID.Toluene conversion efficiency increased with the incr easing of environmental temperature and light intensity. Toluene conversion effi ciency also gradually increasedwhen RH increasedfrom 0～5% to 80%, and it m eaned humidity played a positive effect on the photocatalytic degradation of tol uene. Benzaldehyde is the only intermediate found on the TiO2/ACF catalyst u nder a dry environment (RH= 0～5%), while two intermediates(benzaldehyde an d benzylalcohol)were detectedunder a moist environment(RH=20%-80%). The a ccumulation amount of benzaldehyde and benzyl alcohol on the TiO2/ACF catal yst increased with the increasing of RH.Usingan adsorbent as the carrier to load photocatalyst is onenew photocatalyst preparation technique.For these photocatalyst, VOC transferred to the catalyst surface is an important condition for the photocatalytic degradation of VOC, while few papers studied on the diffusion problems during the photocatalytic process. Influence of the mass transfer process on photocatalytic oxidation of toluene using TiO2/ACF was studied in this paper.The results showed that:the diffusion migration of toluene on the surface of ACF was detected and the mobileabilitywas improved with the increasing ofenvironmental temperature.The degradation rates of toluene weredetermined by the diffusion amount oftoluene from dark area to UV light area.