Synthesis of SrFe_xTi_1-xO_3-Δ nanocubes with tunable oxygen vacancies for selective and efficient photocatalytic NO oxidation

Oxygen vacancies of metal oxides play critical roles in tunning activity and selectivity for many photocatalysis mediated reactions, yet the mechanism of NO oxidation on defect enriched photocatalyst surface is seldomly discussed. Herein, we provide detailed insight into the relationship between oxygen vacancy manipulation by extrinsic Fe³⁺ substitution in SrTiO₃ host lattice and the photocatalytic performance of NO abatement. In particular, the hydrothermal synthesized SrFe_xTi_1-xO_3-δ nanocubes (denoted as SFTO-hyd sample) rather than the impregnated-post annealing sample, enabled oxygen vacancy formation, and promoted O₂ adsorption and superoxide anion radicals ([rad]O₂ ⁻) formation. The SFTO-hyd (x = 5%) sample showed remarkably higher NO removal activity and selectivity under Xe lamp (λ > 420 nm), in comparison with the pristine SrTiO₃, P25 and impregnation-doped SFTO sample, underlining the important roles played by coexisted Fe³⁺ sites and oxygen vacancies. The in situ diffuse reflectance IR spectroscopy (DRIFTS) mechanically revealed that SrTiO₃ provided Lewis acidic sites for NO dark adsorption and photoreaction with nitrates as final products; the substitutional Fe³⁺ sites provided more active sites for NO adsorption and photoreaction with enhanced number of radicals. This study deepens the understanding of photocatalytic NO abatement on defective surface, and may also provide a simple and cost effective strategy for synthesizing efficient and selective photocatalysts for environmental remediation.