EPR study of charge separation associated states and reversibility of surface bound superoxide radicals in SrTiO3 photocatalyst

Understanding the processes of charge generation, transfer and capture is important for the design and synthesis of efficient photocatalysts. In this work, light-induced charge separation and effect of O2 on electron transfer processes in SrTiO3 were investigated by electron paramagnetic resonance (EPR). It was found that photoinduced electron transfer from O2− to Ti4+ produced Ti3+ and O− redox radical pairs under vacuum condition. Under oxygen atmosphere, however, surface bound superoxide radicals O2− were formed by electron reduction of adsorbed oxygen at initial photoirradiation stage, and quenched by the reverse electron transfer to Ti4+ upon further photoirradiation. Formation of long-lived charge separation associated [Ti3+---O−] species and the reversibility of surface bound superoxide radicals mediating the processes of photogenerated electrons may be accountable for the high activity of SrTiO3 in photocatalytic water splitting reaction.