Critical role of oxygen vacancies in SnO2 for enhanced photocatalytic degradation of toluene.

The low density of active sites, poor light absorption and rapid recombination of photogenerated carriers often suppress photocatalytic activity and impede practical applications. Oxygen vacancies (OVs), as unique crystal defects, can improve the performance of photocatalysts for refractory pollutant purification. Herein, a series of SnO2 photocatalysts with tunable OVs concentrations were synthesized via a facile hydrothermal method. Under 50 % relative humidity, an initial toluene concentration of 50 ppm and 60 min of UV irradiation, SnO2 prepared hydrothermally for 24 h with abundant OVs achieved excellent toluene removal efficiency of 92.6 %. The remarkable photocatalytic performance of the catalyst was attributed to the modulation of local electronic structure by OVs. In particular, OVs not only narrowed the bandgap of SnO2, enhancing absorption of longer wavelength light, but also served as trapping sites that hindered recombination of photogenerated charge carriers. Moreover, density functional theory calculations revealed that electron migration in SnO2 was facilitated by OVs, promoting subsequent photocatalytic redox reactions. During toluene elimination, the accelerated formation of ·OH radicals driven by OVs played an important role in increasing the yield of various intermediate products. This work provides valuable insights for developing efficient photocatalysts for pollutant abatement.