First-principles calculations of 0D/2D GQDs-MoS2 mixed van der Waals heterojunctions for photocatalysis: a transition from type I to type II

The fabrication of type II heterojunctions is an efficient strategy to facilitate charge separation in photocatalysis. Here, mixed dimensional 0D/2D van der Waals (vdW) heterostructures (graphene quantum dots (GQDs)-MoS₂) for generating hydrogen from water splitting are investigated based on density functional theory (DFT). The electronic and photocatalytic properties of three heterostructures, namely, C₆H₆-MoS₂, C₂₄H₁₂-MoS₂ and C₃₂H₁₄-MoS₂ are estimated by analyzing the density of states, charge density difference, work function, Bader charge, absorption spectra and band alignment. The results indicated that the built-in electric fields from GQDs to MoS₂ boost charge separation. Meanwhile, all the GQDs-MoS₂ exhibit strong absorption in the visible light region. Surprisingly, the transition of heterojunctions from type I to type II is realized by tuning the size of GQDs. In particular, C₃₂H₁₄-MoS₂ with enhanced visible-light absorption and an appropriate band edge position, as a type II heterostructure, may be a promising photocatalyst for generating hydrogen from water splitting. Thus, in this work a novel type II 0D/2D nanocomposite as a photocatalyst is constructed that provides a strategy to regulate the type of heterostructure from the perspective of theoretical calculation.