Predicted stable two-dimensional semiconductor TiOS materials with promising photocatalytic properties: First-principles calculations

Abstract TiO 2 is a well-known photocatalyst with a band gap of 3.2 eV, yet its ability to absorb light is limited to the short wavelengths of ultraviolet light. To achieve a more effective photocatalytic material, we have designed two-dimensional semiconductor TiOS materials using swarm intelligence algorithms combined with first-principles calculations. Three stable low-energy structures with space groups of P 2 1 / m , P 3 m 1 and P 2 1 / c are identified. Among these structures, the Janus P 3 m 1 phase is a direct bandgap semiconductor, while the P 2 1 / m and P 2 1 / c phases are indirect bandgap semiconductors. Utilizing the accurate hybrid density functional HSE06 method, the band gaps of the three structures are calculated to be 2.34 eV ( P 2 1 / m ), 2.24 eV ( P 3 m 1) and 3.22 eV ( P 2 1 / c ). Optical calculations reveal that TiOS materials exhibit a good light-harvesting capability in both visible and ultraviolet spectral ranges. Moreover, the photocatalytic calculations also indicate that both P 2 1 / m and P 3 m 1 TiOS can provide a strong driving force for converting H 2 O to H 2 and O 2 in an acidic environment with pH = 0. The structural stabilities, mechanical properties, electronic structures and hydrogen evolution reaction activities are also discussed in detail. Our research suggests that two-dimensional TiOS materials have potential applications in both semiconductor devices and photocatalysis.