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 2 (X = Si, Ge, and Sn; Y = P, As, and Sb), and modulate their properties via strain engineering. Penta-XY 2 monolayers exhibit flexible and anisotropic mechanical properties, due to their low in-plane Young's modulus in the range of 19-42 N m -1 . All six XY 2 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 2 and O 2 /H 2 O, so they are suitable for photocatalytic water splitting. Under tensile/compression strains, the band gaps, band edge positions and light absorption of GeAs, SnP 2 and SnAs 2 could be tuned to improve their photocatalytic performance.