Facet-Dependent Performance of Microstructured SrTiO3 Particles in Photocatalytic Oxidation of Acetone

Abstract

Photocatalysis is a promising technology for purification of indoor air by oxidation of volatile organic compounds. This study provides a comprehensive analysis of the adsorption and photo-oxidation of surface-adsorbed acetone on three SrTiO₃ morphologies: cubes (for which exclusively {100} facets are exposed), {110}-truncated cubes, and {100}-truncated rhombic dodecahedrons, respectively, all prepared by hydrothermal synthesis. In situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy shows that cubic crystals contain a high quantity of surface –OH groups, enabling significant quantities of adsorbed acetone in the form of η¹-enolate when exposed to gas phase acetone. Contrary, {110} facets exhibit fewer surface –OH groups, resulting in relatively small quantities of adsorbed η¹-acetone, without observable quantities of enolate. Interestingly, acetate and formate signatures appear in the spectra of cubic, surface η¹-enolate containing, SrTiO₃ upon illumination, while besides acetate and formate, the formation of (surface) formaldehyde was observed on truncated cubes, and dodecahedrons, by conversion of adsorbed η¹-acetone. Time-Resolved Photoluminescence studies demonstrate that the lifetimes of photogenerated charge carriers vary with crystal morphology. The shortest carrier lifetime (τ₁ = 33 ± 0.1 ps) was observed in {110}-truncated cube SrTiO₃, likely due to a relatively strong built-in electric field promoting electron transport to {100} facets and hole transport to {110} facets. The second lifetime (τ₂ = 259 ± 1 ps) was also the shortest for this morphology, possibly due to a higher amount of surface trap states. Our results demonstrate that SrTiO₃ crystal morphology can be tuned to optimize performance in photocatalytic oxidation.