Dissociative scavenging of toxic sulfur chloride gases on Mo2C and O-terminated Mo2CO2 MXenes: A comprehensive DFT investigation.

Sulfur chloride gases, including S2Cl2, SOCl2, and SO2Cl2, are highly toxic and reactive industrial chemicals that pose significant environmental and safety risks. In this work, density functional theory (DFT) calculations were employed to systematically investigate the structural stability, electronic properties, adsorption behaviour, and optical response of pristine Mo2C and oxygen-functionalized Mo2CO2 MXenes toward these hazardous gases. Structural analysis confirms the high intrinsic stability of Mo2C, which is further enhanced upon O-termination. Electronic structure calculations reveal semiconducting characteristics with moderate energy gap modulation induced by surface functionalization. Adsorption energy results demonstrate exceptionally strong and spontaneous interactions between sulfur chloride molecules and Mo2C, with highly exothermic values indicative of dissociative chemisorption. Although oxygen termination moderates the adsorption strength, Mo2CO2 maintains substantial binding energies while providing improved structural robustness. Optimized geometries confirm bond elongation and cleavage of S-Cl and S-S bonds, highlighting irreversible capture mechanisms rather than reversible physisorption. Comprehensive electronic analyses, including PDOS, HOMO-LUMO distributions, natural bond orbital (NBO) charge transfer, and noncovalent interaction (NCI) analysis, reveal pronounced orbital hybridization, significant charge redistribution, and cooperative attractive interactions at the gas-surface interface. Time-dependent DFT calculations further show that gas adsorption induces controlled modulation of optical absorption without disrupting the intrinsic spectral characteristics of the MXene substrates. Overall, the results identify Mo2C and Mo2CO2 MXenes as highly promising scavenging materials for the effective capture and neutralization of toxic sulfur chloride gases, offering potential applications in environmental remediation and hazardous gas mitigation technologies. Future studies involving experimental validation, defect engineering, and realistic environmental conditions are expected to further optimize the practical performance of these MXene-based scavenging systems.