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

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 NO 2 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 NO 2 adsorption, confirming that both NO and NO 2 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.