Effects of S Doping and Oxygen Vacancy on the Physical Properties of Rutile TiO2 for Photocatalysis Applications Based on Density Functional Theory Study

This study explores the effects of sulfur (S) doping and oxygen vacancy (OV) creation on the fundamental properties of TiO₂, which plays a crucial role in photocatalysis applications. Using density functional theory (DFT + U), we investigate how S doping and OV impact the structural, electronic, mechanical, and optical properties of rutile TiO₂. The structural results reveal that the lattice constants of undoped rutile TiO₂ are a = b = 4.63 Å and c = 2.98 Å, which are consistent with reported values. Upon S doping at concentrations of 6.25%, 12.5%, and 18.75%, the lattice constants expand to a = b = 4.89 Å, 5.14 Å, and 5.31 Å, and c = 3.27 Å, 3.69 Å, and 3.82 Å, respectively. This expansion is attributed to the difference in atomic radii between sulfur and oxygen atoms. In contrast, the presence of OV leads to a reduction in the lattice constants, with values of a = b = 4.17 Å and c = 2.82 Å. Our findings on the electronic properties indicate that both S doping and OV contribute to an improvement in the electronic structure, notably shifting the electronic bandgap toward the visible spectrum. Moreover, the mechanical properties show that S doping increases the material's rigidity, while the introduction of OV results in a reduction of mechanical strength. This highlights a trade-off between improved photocatalytic activity and material durability. Lastly, the optical properties exhibit a red-shift in absorption due to S doping and the formation of OV, offering valuable insights for designing efficient photocatalysts for visible-light-driven applications.