Computational studies on functionalized Janus MXenes MM′CT2, (M, M′ = Zr, Ti, Hf, M ≠ M′; T = –O, –F, –OH): photoelectronic properties and potential photocatalytic activities

Motivated by the successful synthesis of Janus monolayers of transition metal dichalcogenides (i.e., MoSSe), we computationally investigated the structural, electronic, optical, and transport properties of functionalized Janus MXenes, namely MM'CT2 (M, M' = Zr, Ti, Hf, M ≠ M', T = -O, -F, -OH). The results of the calculations demonstrate that five stable O-terminated Janus MXenes (ZrTiCO2-I, ZrHfCO2-I, ZrHfCO2-III, HfTiCO2-I, and HfTiCO2-III), exhibit modest bandgaps of 1.37-1.94 eV, visible-light absorption (except for ZrHfCO2-I), high carrier mobility, and promising oxidization capability of photoinduced holes. Additionally, their indirect-gap, spatially separated electron-hole pairs, and the dramatic difference between the mobilities of electrons and holes could significantly limit the recombination of photoinduced electron-hole pairs. Our results indicate that the functionalized Janus MXene monolayers are ideal and promising materials for application in visible light-driven photocatalysis.