Design of graphene-like gallium nitride and WS2/WSe2 nanocomposites for photocatalyst applications

The geometric, electronic and optical properties of the graphene-like gallium nitride (GaN) monolayer paired with WS2 or WSe2 were studied systematically using the first-principles calculations. GaN interacts with WS2 or WSe2 via van der Waals interaction and all the most stable configurations of these two nanocomposites exhibit direct band gap characteristics. Meanwhile, the type-II heterojunctions are formed because the conduction band minimums and valence band maximums are respectively contributed by WS2 (or WSe2) and GaN. The imaginary parts of the dielectric function and the absorption spectra of the heterostructures were also calculated and the relatively improved optical properties were observed because of the new interband transitions. In addition, the band offsets as well as the intrinsic electric fields resulting from the interlayer charge transfer indicate that the electron-hole pairs recombination can be effectively inhibited, which is conducive for the photocatalysis process. Moreover, the band gaps of the heterostructures can be modulated by applying biaxial strains and even shift away the conduction band edge potential from the H+/H-2 potential in a certain range, which further enhances the photocatalyst performance. The results indicate that GaN/WS2 or GaN/WSe2 nanocomposites are good candidate materials for photocatalyst or photoelectronic applications.