| As a class of air pollutants,volatile organic pollutants（VOCs）,which have the characteristics of toxicity,irritation and volatility,seriously threaten the eco-logical environment and human health.How to economically and efficiently re-move VOCs has become a hot topic in the field of current environmental prob-lems.Compared with the traditional heat treatment method,photocatalytic oxida-tion method has the advantages of simple process,mild reaction condition and low energy consumption.It is considered as one of the most promising technolo-gies.Toluene is a typical toxic gas in VOCs.At present,the research on photo-catalytic degradation of gaseous toluene is mainly focused on the degradation of a certain amount of waste gas in the catalyst,and there is less research on continu-ous flow into the exhaust gas.In this paper,toluene is selected as the target pollu-tant,and the effect of different factors on the photocatalytic performance of con-tinuous toluene waste gas is investigated from two aspects:catalyst modification and coating method.The high efficiency photocatalyst was first studied.The pho-tocatalytic activity of toluene was investigated by using the modification of com-mercial TiO2（P25）and then put into self-made photocatalytic reactor.Then,the coated TiO2 photocatalytic material was prepared,and the effect of the material on the removal efficiency of toluene was investigated under different environmental factors such as light source,initial concentration of reactant and relative humidity.The main research contents are as follows:（1）The elements Fe and Cu were selected as modifying elements respec-tively,and TiO2 was modified by impregnation method.The doping amount of each element was 0.1%,0.5%and 1.0%respectively.The modified samples were characterized by XRD,SEM,BET and UV-Vis.The results are as follows:The doping of elements Fe and Cu does not change the crystalline phase of Ti O2,but makes the grain surface produce different number of processes.The surface area of the modified sample increases as compared with the base TiO2,and the uv region and visible region of light absorption rate increased too.The modified samples were sprayed onto the foil paper,then put into the self-made photocata-lytic reactor,and toluene was used as the target degradation material to verify its photocatalytic activity.The effects of doping elements,doping amount and amount of catalyst on photocatalytic activity were investigated.The experimental results show that the doping effect of element Cu is better than that of Fe,and the photocatalytic activity of the modified sample is the highest when the Cu content is 1.0%.In photocatalytic reaction,the optimum dosage of catalyst is 1.5 g.（2）The TiO2 was prepared by sol-gel method.The influence of calcination temperature on TiO2 crystal phase was investigated first.The characterization re-sults of XRD,SEM and TEM show that when the calcination temperature was500℃,the crystalline of TiO2 was pure anatase with the highest crystallinity and crystal content.The shape of TiO2 is granular,with the particle diameter of 1020 nm and the specific surface area of 56.02 m2/g.Therefore,it is determined that the optimum calcination temperature is 500℃.A new type of coated TiO2 photo-catalyst was prepared by sol-gel method and impregnation method.The alumina ball was used as the carrier and calcined at 500℃.The characterization results of BET,XRD,SEM and UV-Vis show that alumina ball has larger specific surface area of 225.27 m2/g,which is suitable as a carrier.The surface of alumina ball be-fore coating is coarse and flaky,and its surface is smooth and even after coating,indicates that the surface of alumina ball is coated with a pure anatase TiO2.（3）Using toluene as the degradation object,and loading it into a self-made photocatalytic reactor for experiment,the effects of light source,initial concentra-tion of reactants,relative humidity,residence time and loading mode on the effi-ciency of photocatalytic degradation of toluene were investigated,so that the best experimental conditions for photocatalytic degradation of toluene is obtained.Meanwhile,the change of CO2 concentration in import and export and the Inter-mediate products of photocatalysis degradation for toluene were analyzed.The experimental results show that the removal rate of toluene with coated TiO2 pho-tocatalyst can reach about 80%when the light source is 254 nm,the toluene inlet concentration is about 43 mg/m3,the residence time is 117 s,and the relative hu-midity is about 70%.Under the same conditions,the removal efficiency of the coated TiO2 is about 20%higher than that of the spray Ti O2 due to the more full contact area of the toluene and the catalyst.The ring-opening product of photo-catalytic degradation of toluene is 3,4-two methyl-2-amyl and the ring-closing product is benzene.The CO2 outlet concentration is higher than the inlet concen-tration,indicating that toluene will generate CO2 during the photocatalytic oxida-tion process. |
