Performance Regulation And Reaction Mechanism Of SrTiO₃-based Photocatalyst For Toluene Purification

As a highly toxic and refractory volatile organic compound（VOC）,toluene widely exists in human life,which has a serious influence on the human health and the ecological environment.Photocatalytic oxidation is considered to be an effective environmental purification technology with the advantages of wide application range,strong mineralization ability,mild reaction conditions,simple operating conditions and less secondary pollutant.It has a broad application prospect in toluene degradation.After absorbing photon energy larger than the band gap,semiconductors produce photogenerated holes and electrons in the valence band and conduction band,which can participate in the activation reaction of surface oxygen species.The generated active species have strong redox ability,so as to achieve the effect of toluene degradation and mineralization.SrTiO₃,a wide band gap semiconductor material with a relatively positive valence band position,has great potential in toluene degradation.In this work,the photocatalytic degradation of toluene by SrTiO₃ was enhanced by two means of forming solid solutions and adjusting the crystal plane.The mechanism of enhanced photocatalytic activity and the deep mineralization were discussed from the aspects of electronic structure,charge transfer,reactant activation,intermediate products transformation and mineralization path.（1）Sr_1-xBa_xTi O₃ solid solution was successfully prepared by hydrothermal method,and the substitution of Sr by Ba created new active sites on the surface.The electron localization center was established on the substituted Ba site,which enhanced the charge transfer between the catalyst surface and the adsorbed molecules.SrTiO₃ with（110）exposure and SrTiO₃ with（100）exposure were synthesized by adjusting the feeding sequence of precursors.（100）surface was more conducive to the activation of H₂O and the formation of·OH,and then enhanced the oxidation ability of SrTiO₃.（2）Through the dynamic monitoring and reaction intermediates tracking,we obtained the evidence of adsorption and activation of toluene and its intermediates experimentally.And the reaction path of toluene degradation was deduced.Combined with DFT calculation,the charge transfer behavior between adsorbed molecules and catalyst surface were revealed.It was confirmed that the surface structure of catalyst and the adsorption of key intermediates were two key factors affecting toluene mineralization.More reactive oxygen species and stronger adsorption and activation of intermediates were observed on Sr_1-xBa_xTi O₃ solid solution and SrTiO₃ with（100）exposure,which confirmed to be the direct reason for the increase of toluene degradation rate.（3）It was revealed that the smooth transformation of key products played an important role in improving the mineralization rate of toluene.The stronger charge exchange with benzoic acid in Sr_1-xBa_xTi O₃ solid solution promoted the ring opening reaction of benzoic acid and braked the stable C=C conjugate structure,which greatly improved the mineralization efficiency.SrTiO₃ with（100）exposure improved the adsorption and activation ability of benzaldehyde,so that benzaldehyde was continuously oxidized and converted to benzoic acid,and finally converted to CO₂.