Dicarbon nitride and Janus transition metal chalcogenides van der Waals heterojunctions for photocatalytic water splitting.

Two-dimensional graphene-like dicarbon nitride (CN) is a newly synthesized metal-free material, which has attracted significant research interest owing to the direct band gap, high carrier mobility, thermal stability, and great tunable properties. However, their application in photocatalytic water splitting has not been well explored. In this work, the properties of photocatalytic water decomposition in heterojunctions composed of CN and transition metal dichalcogenides (TMDs) with Janus structure MoXY (X, Y = S, Se, Te) are systematically studied by the first-principles calculations based on density functional theory. The results show that except for MoTeS/CN, the other five heterojunctions have type-Ⅱ band alignment, which causes electrons and holes to gather in the CN and MoXY layer separately. Because the coupled built-in electric field at the intra-layer and inter-layer of asymmetric TMDs with Janus structure forms van der Waals heterojunction, the external electric field is an effective means of modulating the electronic properties of the heterojunction. Under the imposition of an external electric field, the MoSeS/CN, MoTeSe/CN, and MoTeS/CN heterojunctions meet the band edge requirements for the photocatalytic decomposition of water. Detailed analysis demonstrates that the MoSeS/CN heterojunction could effectively improve the optical absorption properties of monolayer CN, making it a potential photocatalytic water decomposition material.