Study On The Degradation Of Toluene By Non-thermal Plasma/ozone Combined With Nhotocatalvtic Oxidation

Volatile organic compounds(VOCs)are important causes of air pollution,which not only directly threaten human health and ecological environment,but also lead to the formation of PM2.5,ozone and photochemical smog.In recent years,non-thermal plasma(NTP)and photocatalytic oxidation(PCO)process have been widely studied as effective techniques for the degradation of VOCs.However,a single PCO or NTP process is generally inefficient,and difficult to meet the emission standards of government.Therefore,the combination of NTP and PCO has got a lot of attentions due to the industrial application.In this paper,the NTP+PCO combined process was adopted for the degradation of gas-phase toluene.Then the synergetic effect between NTP and PCO and the role of ozone were deeply explored.Furthermore,the influences of operating parameters and catalyst loading method for the toluene degradation performance in the ozone-assisted PCO process was deeply studied.Finally,as a novel photocatalyst,the TiO2/graphene composite was prepared to improve toluene removal efficiency.First of all,the synergetic effect of NTP+PCO combined process was studied.The performances of the single processes and the combined processes were investigated,and the role of ozone was deduced.Toluene removal efficiency of the NTP+PCO combined process was 80.2%,which was much higher than that of the single process of NTP(18.8%)and PCO(13.4%).Selectivity of CO2 and ozone consumption efficiency were also significantly improved.The amount of by-products in the gas phase and carbon-based intermediates adsorbed on the catalyst surface were dramatically decreased.The synergetic effect was mainly ascribed to the efficient consumption of ozone in the PCO process.Ozone could act as the electron acceptor to reduce the recombination rate of electron-hole pairs,and generate more hydroxyl radicals for the complete oxidation of toluene.Secondly,ozone-assisted PCO was adopted for the degradation of toluene,and the influences of operating parameters such as ozone concentration,toluene concentration,residence time,and relative humidity on the toluene degradation performance were investigated.Higher ozone concentration was beneficial to improve toluene removal efficiency,selectivity of CO2 and decrease the formation of intermediate products,but decreased the ozone consumption efficiency.Higher toluene concentration was beneficial to improve ozone consumption efficiency,but led to the decrease of toluene removal efficiency and selectivity of CO2,and more intermediates were formed during the toluene degradation process.The increase of residence time and relative humidity could greatly enhance the toluene removal efficiency,ozone consumption efficiency,selectivity of CO2 and mineralization rate of toluene.In addition,the loading of the catalyst on glass beads could greatly improve the toluene removal efficiency and ozone consumption efficiency.Finally,TiO2 was modified by graphene,and TiO2/graphene composite was prepared to further improve toluene removal efficiency in the ozone-assisted PCO process.Experimental results showed that the addition of graphene in TiO2 could effectively improve the toluene removal efficiency,and the best toluene degradation performance was obtained when the weight ratio of graphene was 0.1%.The results of UV-vis DRS,PL spectra and photocurrent measurements indicated that the addition of graphene could broaden light absorption range,enhance photogenerated electron-hole generation and separation ability,reduce the recombination of photo-generated carriers.Finally,the TiO2/graphene composite had advantages in the transfer of photo-generated carriers,so that the lifetimes of photo-generated carriers were prolonged and the photocatalytic performance was improved.TiO2/graphene achieved good performances for the degradation of toluene,acetone and ethyl acetate,indicating its potential application in the coating industry.