Tuning the optoelectronic and photocatalytic properties of SrTiO3 via S/Zr co-doping: A DFT study

Abstract

Strontium titanate (SrTiO 3 ) is acknowledged for its photocatalytic potential; however, its broad band gap considerably restricts its efficiency under visible light irradiation. To address this challenge, we explore the effect of co-doping with zirconium (Zr) on the Ti site and sulfur (S) at the O site on the electronic and optical characteristics of SrTiO 3 , aiming to improve its photocatalytic activity in the visible-light spectrum. According to our calculations, co-doping SrTiO 3 with Zr and S causes a significant change in its electronic structure, resulting in a shift from indirect to direct band gap. This change, combined with a significant reduction in band gap energy, increases visible-light absorption while also improving photogenerated charge carrier mobility and separation. In addition, the calculated band edge positions of the co-doped system meet the thermodynamic conditions for overall water splitting. Nevertheless, under particular pH conditions, only the co-doped materials exhibit appropriate band edge alignment for solar-driven photocatalytic hydrogen production, specifically, Sr 8 Ti 7 Zr 1 O 23 S 1 at 1 ≤pH ≤ 10 and Sr 8 Ti 6 Zr 2 O 22 S 2 at 1 ≤ pH ≤ 7. The chemicals investigated have photocatalytic activity at various pH levels and can reduce CO 2 effectively. In particular, electrical conductivity and thermal conductivity evolve differently with temperature, directly influencing the figure of merit (ZT) of thermoelectric materials. The results suggest that, due to their high thermal conductivity and the low density of states near the Fermi level (E F ), Sr 8 Ti 7 Zr 1 O 23 S 1 and Sr 8 Ti 6 Zr 2 O 22 S 2 stand out with moderate improvement in thermoelectric properties. These findings demonstrate the efficacy of the S/Zr co-doping strategy and offer important theoretical guidance for developing high-performance SrTiO 3 -based photocatalysts for solar-powered applications.