Performance of molybdenum carbide MXenes for pollutant abatement and sensing

The adsorption of H₂S, NH₃, and HCN pollutants on Mo-derived MXenes with different thicknesses and functionalizations is systematically investigated by means of density functional theory (DFT) combined with transition state theory (TST). The calculated results indicate that all pollutants interact favorably with all Mo-derived MXenes regardless of their composition. The number of atomic layers of the investigated MXenes has a minor impact on the interaction strength, while the MXene functionalization significantly influences not only the adsorption strength but also the selectivity towards certain pollutants. Analysis based on adsorption and desorption rates allows one to identify the temperature at a constant partial pressure above which pollutants desorb. Additionally, the recovery time evaluated at different temperatures reveals a wide spectrum of behaviors dictated by functionalization. Our calculations show that pristine Mo-derived MXenes interact favorably with HCN above 526 °C, while O-terminated Mo-derived MXenes adsorb only NH₃ at room temperature. On the other hand, HCN and NH₃ anchor on O-terminated Mo-MXenes at 227 °C. Finally, the OH-terminated MXenes are found to be nonselective due to analogous affinity for all pollutants. Crucially, recovery time analysis reveals that pristine Mo-MXenes act as single-use adsorbents at room temperature; H-terminated MXenes exhibit recovery times ranging from seconds to hours and O- and OH-terminated MXenes have recovery times in the nanoseconds to milliseconds range, qualifying them as genuine regenerable sensor materials. These findings may help experimentalists synthesize functionalized MXenes ad hoc with preferential affinities to pollutants by controlling the termination of MXenes during the synthesis process.