Adsorption and Potential CO Gas-Sensing Performance of the Fe-Doped Ti₂CO₂-MXenes: A First-Principles Study

The adsorption behaviors and electronic properties of five gas molecules (CO, H₂O, NH₃, NO, and C₂H₆O) on the intrinsic Ti₂CO₂ and Fe-doped Ti₂CO₂ were calculated and studied based on first principles. The adsorption height, bond length change, adsorption energy, charge transfer, band structure, differential charge, work function, and recovery time of the two gas adsorption systems were discussed, and their sensing performance was evaluated. The results show that the CO gas molecules have the best adsorption energy and charge transfer on Ti₂CO₂ modified by the Fe atom (Ti₂CO₂-Fe). The electrical conductivity obviously increases with the decrease of the band gap, which changes from semiconductor to conductor behavior. The reduction of the work function in the Ti₂CO₂-Fe system weakens the binding of the electron, which improves the electron flow between the substrate and the gas molecules. In addition, the Ti₂CO₂-Fe system with H₂O molecule participation remained the best adsorption effect on CO gas, and the fast recovery time was 625 s at 398 K. Therefore, Ti₂CO₂-Fe is a prospective material for the advancement of CO gas-sensitive sensors.