First-Principles Study of the Electronic Properties and NOx (x = 1,2) Adsorption Characteristics of Al and Cr Doped CdS Materials

Abstract

This study uses first-principles calculations to investigate the structural, electronic, and NOx adsorption properties of monolayer CdS. The results show that pristine CdS is a direct-bandgap semiconductor with a bandgap of 1.628 eV, while Al and Cr doping induce an indirect bandgap and enhance charge transfer. In addition, Cr-doped CdS exhibits a magnetic moment of 4.00 μ_B. Doping significantly strengthens the interaction between CdS and gas molecules. For NO adsorption, the adsorption height decreases from 3.0 Å (pristine) to 1.894 Å (Al-CdS) and 1.644 Å (Cr-CdS), with corresponding adsorption energies of −1.670 eV and −2.470 eV, respectively. For NO₂ adsorption, the adsorption height is 1.966 Å (Al-CdS) and 1.959 Å (Cr-CdS), with adsorption energies of −2.794 eV and −2.067 eV, respectively, indicating stronger binding compared to the pristine system. Bader charge analysis further quantifies the charge-transfer behavior, revealing net charge transfers of 0.648 |e| (Al-CdS) and 0.501 |e| (Cr-CdS) for NO adsorption, and 0.849 |e| (Al-CdS) and 0.624 |e| (Cr-CdS) for NO₂ adsorption, confirming that both NO and NO₂ act as strong electron acceptors. The formation of NAl and NCr bonds further enhances the adsorption strength. These results demonstrate that Al- and Cr-doped CdS monolayers exhibit significantly improved gas adsorption performance, with larger absolute adsorption energies indicating stronger gas–surface interactions, which are crucial for enhancing gas capture and sensing-related properties.