Prediction of 2D IV-V semiconductors: flexible monolayers with tunable band gaps and strong optical absorption as water-splitting photocatalysts.

Seeking novel photocatalysts for water splitting is one of the tasks in developing 2D materials. In the framework of density functional theory, we predict a family of 2D pentagonal sheets called penta-XY (X = Si, Ge, and Sn; Y = P, As, and Sb), and modulate their properties strain engineering. Penta-XY monolayers exhibit flexible and anisotropic mechanical properties, due to their low in-plane Young's modulus in the range of 19-42 N m. All six XY sheets are semiconductors with a band gap ranging from 2.07 eV to 2.51 eV, and the positions of their conduction and valence band edges match well with the reaction potentials of H/H and O/HO, so they are suitable for photocatalytic water splitting. Under tensile/compression strains, the band gaps, band edge positions and light absorption of GeAs, SnP and SnAs could be tuned to improve their photocatalytic performance.