F/N co-doped SrTiO₃ for enhanced photocatalytic water oxidation under visible light

Strontium titanate (SrTiO₃) holds promise for photocatalytic applications, but suffers from a wide bandgap that limits visible-light absorption. This work explores a synergistic fluorine-nitrogen (F/N) co-doping strategy to engineer the electronic structure of SrTiO₃ for enhanced photocatalytic water oxidation performance. Through solid-state synthesis followed by ammonia treatment, F/N co-doped SrTiO₃ (SrTiO₃-F-N) is successfully fabricated. The pre-doping of F atoms into the SrTiO₃ effectively weakens the Ti-O bond and compensates for the charge difference between N^3- and O^2-, which promotes the subsequent doping process of N atoms and increases the doping concentration, leading to an enhanced visible-light absorption intensity. Therefore, it forms a high density of localized energy levels above the valence band maximum of SrTiO₃, extending the absorption range beyond 500 nm. Compared to N-doped SrTiO₃, the photovoltage response wavelength of the F/N co-doped SrTiO₃ is extended to around 525 nm, meaning a broader spectral response range for photocatalysis. The photocatalytic oxygen evolution activity in half-reactions under visible light is increased by 4.1 and 1.7 times, respectively, compared to SrTiO₃ and SrTiO₃-N.