Computational studies on functionalized Janus MXenes MM'CT 2 , (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'CT 2 (M, M' = Zr, Ti, Hf, M ≠ M', T = -O, -F, -OH). The results of the calculations demonstrate that five stable O-terminated Janus MXenes (ZrTiCO 2 -I, ZrHfCO 2 -I, ZrHfCO 2 -III, HfTiCO 2 -I, and HfTiCO 2 -III), exhibit modest bandgaps of 1.37-1.94 eV, visible-light absorption (except for ZrHfCO 2 -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.