Theoretical study of adsorption of gas (CO, CO2, NH3) by metal (Au, Ag, Cu)-doped single-layer WS2.

Context: The adsorptions of gas (CO, CO₂, NH₃) by metal (Au, Ag, Cu)-doped single layer WS₂ are studied by density functional theory. The doping of metal atoms makes WS₂ behave as n-type semiconductors. The final adsorption sites for CO, CO₂, and NH₃ are close to the atomic sites of the doped metal. The adsorptions of CO and NH₃ gases on Cu/WS₂, Ag/WS₂, and Au/WS₂ are dominated by chemisorption. The doped metal atoms enhance the hybridization of the substrate with the gas molecular orbitals, which contributes to the charge transfer and enhances the adsorption of the gas with the material surface. The adsorptions of CO and NH₃ on Cu/WS₂ and Ag/WS₂ allow favorable desorption in a short time after heating. The single-layer Cu/WS₂ is proved to have the potential to be used as a reliable recyclable sensor for CO. This work provides a theoretical basis for developing high-performance WS₂-based gas sensors.

Methods: In this paper, the adsorption energy, electronic structure, charge transfer, and recovery time of CO, CO₂, and NH₃ in the doped system have been investigated based on the CASTEP code of density functional theory. The exchange correlation function used is the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA). The TS (Tkatchenko-Scheffler) dispersion correction method was used to involve the effects of van der Waals interaction on the adsorption energies for all adsorption system. The ultrasoft pseudopotentials are chosen and the plane-wave cut-off energies are set to 500 eV. The k-point mesh generated by the Monkhorst package scheme is used to perform the numerical integration of the Brillouin zone and 5 × 5 × 1 k-point grid is used. The tolerances of total energy convergence, maximum ionic force, ionic displacement, and stress component are 1.0 × 10^-5 eV/atom, 0.03 eV/Å, 0.001 Å, and 0.05 GPa, respectively.