Single-layer Group-IVB nitride halides as promising photocatalysts

In order to construct efficient solar-driven devices, many potential materials have been explored in search of desirable photocatalyts for water splitting. Layered structure nitride halides have received significant attention from different fields because of their unusual electronic properties. In this work, we have systematically studied the electronic structures and potential photocatalytic properties of single-layer Group-IVB nitride halides (MNX, M = Ti, Zr, Hf; X = Cl, Br, I) in different forms using first-principles calculations. The results show that the single-layer nitride halides have very low formation energies, which indicates that the isolation of these single-layer MNX materials should not be difficult. The calculated band structures reveal that all of the single-layer MNX are semiconductors, while each of them shows a distinct type of electronic properties. Among these semiconducting nitride halides, ten members of the single-layer MNX family are feasible photocatalysts for splitting water. Interestingly, single-layer alpha-ZrNX (X = Cl, Br, I) and alpha-HfNI are direct band gap semiconductors with desirable band gaps (2.23-2.83 eV), and the calculated optical adsorption spectra further confirm their excellent light absorption in visible light region. Finally, the electronic properties and optical absorption in visible light region of single-layer MNX can be easily tuned through hybridisation or doping between them because of the similarity of the MNXs. Their high stability, versatile electronic properties, and high optical absorption make single-layer Group-IVB nitride halides promising candidates for application in photocatalytic water splitting.