Boosting Photocatalytic Hydrogen Evolution Achieved by NiSx Coupled with g-C3N4@ZIF-67 Heterojunction

g-C3N4@ZIF-67 composite photocatalyst-supported NiSx are successfully prepared by a hydrothermal method using g-C3N4 and ZIF-67 as carriers. The synthesized composite catalyst has an efficient photocatalytic H2 production effect. Under visible light irradiation, the maximum H2 production within 5 h over the [g-C3N4@ZIF-67/(10%wt)NiSx] photocatalyst is 208 μmol, which is 8.32 times higher than that of pure g-C3N4. Based on the analysis of scanning electron microscopy and transmission electron microscopy, it is not only known that g-C3N4 and ZIF-67 provide space for the loading of NiSx nanoparticles but also that ZIF-67 as a carrier framework can effectively reduce the particle size of NiSx nanoparticles and increase the dispersion of NiSx. Further studies of photoluminescence (PL), time-resolved PL, i–t, linear scanning voltammetry, electrochemical impedance spectroscopy, and Mott–Schottky curves, we can not only know that the modification of NiSx nanoparticles do enhance the electron transfer ability but also that the matched conduction band position between g-C3N4 and ZIF-67 provides a feasible thermodynamic path for the transmission of electrons. Based on the DFT calculations, both NiS2 and Ni3S4 show the metallic characteristics, which means the outstanding electrical conductivity of them and implies the excellent capability to transport electrons. The work function of NiSx with metallic properties is more negative than that of the semiconductor, which indicates that the loading of NiSx can further promote the separation of electrons, thereby improving the H2 production efficiency.