Theoretical Study On Photocatalytic Water Splitting Of Two-dimensional MoS₂ With Defects

Monolayer MoS₂ whose structure is stable has illuminated many promising applications in field effect transistors, nano-electronic, light-emitting diodes and solar cells with its exotic electrical, mechanical as well as optical properties. In addition, the single-layer MoS₂ possesses excellent charge carrier mobility, as good as that of a carbon nanotube, and a superior surface-to-volume ratio that could be an advantage for a photoelectrocatalyst. Catalytically active center of a single-layer MoS₂ is relevant with the unsaturated S edge sites, but not with the intact MoS₂ plane site. Therefore, it is necessary to destroy the lattice structure of the plane to increase its active sites, improving the overall photocatalytic ability. Point defects are the most common crystal defects, mainly in the form of vacancies and substitute doping. The instructional computing about monolayer MoS₂ in terms of photocatalytic aspects is rarely reported in the literature, especially in terms of photocatalytic decomposition of water. Therefore, it is imperative to explore the influence of point defects on the performance of photocatalytic decomposition water.In this paper, the CASTEP module implemented in MS software package which was based on density functional theory was used to investigate the photocatalytic performance of monolayer MoS₂ with vacancies?Mo vacancy and S vacancy?, non-metallic C element as well as transition metal element?Cr and W? doping. The electron-electron interaction was treated with the PBE functional of the generalized gradient approximation?GGA?. We mainly focused on the effects of vacancies as well as dopings on the structural stability, band structures, density of states and photocatalytic properties for monolayer MoS₂. The conclusions as follows:Firstly, it demonstrated that monolayer MoS₂ with different structure defects could be prepared by controlling the reaction conditions, with the help of vacancy formation energy calculations. Monolayer MoS₂ still maintained a direct band gap after Mo as well as S vacancies, with a presented p-type properties of Mo vacancies and n-type properties of S vacancies. It was obtained from the optical absorption that the absorption peak were shifted to the infrared band after Mo and S vacancies, improving the solar energy utilization. With the help of calculations about photocatalytic oxidation-reduction potential, it was indicated that S vacancies were more favorable to improve the overall photocatalytic water splitting activity of monolayer MoS₂.Secondly, C-doped monolayer MoS₂ possessed thermodynamic stability. With the increasing C doping concentrations, it presented phenomena that decreasing bandgap, more and more shallow donor level, red-shifted light absorption wavelength, indicating the increasing solar energy utilization. With the help of calculations about photocatalytic oxidation-reduction potential, the conclusion drawn was that it was more conductive to the overall photocatalytic water splitting reaction at doping concentration 3.7%.For the last one, monolayer MoS₂ with Cr doping was easier than the W doping thermodynamically, and the structure was more stable. W doping led to the expansion of the lattice structure and a slightly wider band gap. However, Cr doping resulted in the shrinkage of lattice structure and a narrower bandgap. Thence, the solar energy utilization of Cr doping was higher than W doping. With the help of calculations about photocatalytic oxidation-reduction potential, the conclusion made was that it was more favorable to improve the overall photocatalytic water splitting activity of monolayer MoS₂ after Cr doping.With comprehensive analysis of solar energy utilization as well as photocatalytic oxidation-reduction capability, for C doping, it was more conductive to the overall photocatalytic water splitting reaction at doping concentration 3.7%. For vacancy and W as well as Cr doping, it was more favorable to the overall photocatalytic water splitting reaction after S vacancy and Cr doping.