Halogenation effect on physicochemical properties of Ti3C2 MXenes

Halogenated MXenes have been experimentally demonstrated to be promising two-dimensional materials for a wide range of applicability. However, their physicochemical properties are largely unknown at the atomic level. In this study, we applied density functional theory (DFT) to theoretically investigate the halogenation effects on the structural, electronic, and mechanical characteristics of Ti3C2, which is the most studied MXene material. Three atomic configurations with different adsorption sites for four kinds of halogen terminals (fluorine, chlorine, bromine, and iodine) were considered. Our DFT results reveal that the adsorption site of terminals has a considerable impact on the properties of MXene. This can be ascribed to the different coordination environments of the surface Ti atoms, which change d-orbital splitting configurations of surface Ti atoms and the stabilities of systems. According to the density of states, crystal orbital Hamilton population, and charge analyses, all the considered halogenated MXenes are metallic. The electronic and mechanical properties of the halogenated MXenes are strongly dependent on the electronegativity of the halogen terminal group. The Ti–F bond has more ionic characteristics, which causes Ti3C2F2 mechanically behave in a more ductile manner. Our DFT results, therefore, suggest that the physicochemical properties of MXenes can be tuned for practical applications by selecting specific halogen terminal groups.