Effect of Al-Doping of Faceted SrTiO3 on Surface Chemistry in Photocatalytic Oxidation of Acetone.

We have investigated how Al3+ doping affects the facet-specific performance of SrTiO3 in gas-phase photocatalytic oxidation of acetone, comparing cubic and truncated structures. In situ Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS) indicates that Al-doping suppresses facet-specific adsorption of acetone and results in very similar relatively weakly adsorbed states of acetone on both, cubic and truncated structures. Oxidation of adsorbed acetone on both Al3+ doped SrTiO3 structures proceeds via α-cleavage, yielding acetaldehyde and formaldehyde, followed by the formation of surface-bound acetate and formate. The absence of CO2 suggests these species deactivate the surface leading to rapid termination of the oxidation process. Interestingly, the rate at which surface bound products are formed appears higher for the Al3+-doped truncated SrTiO3 than for the cubic morphologycontrary to the undoped analogues showing higher rates for the cubic structure. Time-resolved Photoluminescence (TRPL) analysis shows that Al3+ doping enhances charge carrier lifetimes in both morphologies, compared to undoped SrTiO3 having the same morphologies. Importantly, the Al-doped cubic STO shows shorter carrier lifetimes (τ1 = 86 ± 0.1 ps; τ2 = 709 ± 1 ps) compared to the Al-doped truncated material (τ1 = 116 ± 0.1 ps; τ2 = 1070 ± 1 ps)which is consistent with the observed faster acetone transformations for the latter. This study shows Al3+ doping of SrTiO3 induces a transition from crystallographically controlled, to defect-dominated surface chemistry upon illumination, prohibiting complete mineralization of acetone, despite a doping induced lengthening of charge carrier lifetimes of cubic and truncated SrTiO3 structures.