Oxygen vacancies promote sulfur species accumulation on TiO2 mineral particles

Abstract

In this study, we investigated the heterogeneous SO2 oxidation catalyzed by defective TiO2 mineral particles at molecular scale. Theoretical DFT calculations revealed that O2 favorably attached to oxygen vacancies, while SO2 adsorption more likely took place over the unsaturated Ti5c and O2c or hydroxyl sites of TiO2 bearing surface oxygen vacancies (TiO2-OV). In the dark, the amount of sulfite species formed on TiO2-OV surface via the SO2 adsorption was 8 times that on pristine TiO2 due to the increased charges of the undercoordinated Ti and O sites around OVs. Although solar light irradiation could promote the sulfate accumulation on both pristine TiO2 and TiO2-OV, OVs facilitated molecular oxygen activation to generate O2− capable of photochemically converting interfacial SO2, accounting for higher sulfate accumulation of TiO2-OV than that of pristine TiO2. These findings provide in-depth understanding of sulfur species identification and sulfate aerosol formation on defective metal oxide minerals in atmosphere.