The pollution of the atmospheric environment has significantly increased due to the rapid growth of population and industrial development. To prevent environmental disasters caused by such deterioration, it is imperative to control and monitor such pollutants. This study investigates the structural, electronic, and optical characteristics of the CdS monolayer nanosheets, and evaluates their gas adsorption behavior for various gas molecules (CO₂, SO₂, H₂S, CO, and SO) using DFT calculations. SO₂, H₂S, and CO are found to show weak adsorption suggesting the physisorption behavior, whereas CO₂ and SO adsorption systems are found to undergo chemical adsorption on the CdS surface, suggesting it as a promising sensing material for the latter gasses. The electronic structure and geometrical positions of the gas molecules on monolayer CdS surface have been analyzed, revealing a significant alteration in the band gap of CdS upon the the adsorption of gas molecules. We also investigated the optical properties of the monolayer CdS in the presence of the gasses, indicating that the real and imaginary components of the dielectric function are crucial for sensing applications, and changes in the absorption spectrum of the CdS monolayer upon adsorption of the different gasses can be attributed to the specific electronic and chemical properties of each gas and their interaction with the CdS surface.

The analysis of the electron localization function (ELF) and charge density differences (CDD) is shown here for CO/CdS and SO/CdS systems. The high degree of ELF and CDD indicates chemisorption (SO/CdS system), while a low degree (or negligible) of ELF and CDD suggests physisorption (CO/CdS system)