In Situ IR Study On The Surface Adsorption And Photocatalysis Of TiO₂

TiO₂film has wider application in environmental cleanup and preparation ofmulti-functional materials due to its high stability， innocuity and excellentphotocatalytic properties. But low quantum efficiency and easy deactivation of TiO₂seriously block the large-scale application of photocatalytic technology. Both ofthese depend on the further understanding of the structure of catalyst （crystal structure,electronic structure, surface structure） and structure-activity relationships.Theproperties of the TiO₂surface are decisive for its catalytic reaction. Studies the surfacechemistry （includeing surface structure, surface hydroxyl groups and surface acidity）and their action in photocatlytic reaction are very important. On the one hand, ithelps to understand the catalytic activity and selectivity of TiO₂, on the other hand,provides significant insight into adsorption behaviors of reactants and photocatalyticmechanism at the molecular level.In this work, the nature, categories, and distributions of surface hydroxyl groupsand acidity on TiO₂and sulfate-modified TiO₂are studied. The actions of hydroxylgroups and surface acidity in photoctalytic reaction are determined by thecharacteristics （stability and spectral） of adsorbed toluene and their interaction withhydroxyl groups under UV illumination. The main conclusions obtained from thepresent research are as follows:（1） P25and anatase TiO₂have six isolate hydroxylwith bands at3731,3715,3688,3669，3656and3640cm^-1. The six hydroxyl arethermal stable even evacuated the sample at higher temperature.（2） Rutile TiO₂hasfour hydroxyl with bands at3730,3720,3696and3658cm^-1which are lost whenevacuated at550℃.（3） The six isolate hydroxyls (3731,3712,3688,3669，3656and3640cm^-1) on TiO₂surface are excellent adsorption site for toluene, in which the3669and3688cm^-1band adsorbs toluene prior to the other four bands. In additation, thecoordinatively unsaturated surface （c.u.s） ions and the c.u.s oxygen anions areadsorption site when the sample evacuation at high temperature.（4） During thephotooxidation process of toluene, the3731and3712cm^-1are more active than3688,3669and3640cm^-1. When illuminated the adsorbed toluene in the absence of O₂, themain partial oxidation product is benzyl alchol. Illuminated the adsorbed toluene inthe presence of O₂, toluene is oxidized into benzaldeyde and futher into benzoics.（5） The sulfur-modified TiO₂show strong band at1370cm^-1which corresponds to S=Ostretching modes and exhibits Br nsted acidity. The presence of Br nsted acidityprevents the formation of benzoics that appears to be reponssible for the deactivationof catalysts。...