Experiments combined with theoretical research on the effect of hydrogen evolution by the nanosheet of NiS–CdS–CN catalyst

A ternary composite photocatalyst of nickel sulfide supported on the heterojunction of ultrathin cadmium sulfide-carbon based on g-C3N4 nanosheets was prepared by aqueous-phase in low-temperature innovatively, and its chemical compositions were confirmed by XRD, FT-IR and XPS. The morphology of two-dimensional nanosheet heterojunction was verified by SEM, TEM, HRTEM and BET, and the addition of nickel is beneficial to improve the specific surface area of the catalyst. The larger surface area was more beneficial to accelerate the carrier migration and reactant diffusion. Meanwhile, the electron structures were analyzed by UV–vis, work function, bader charge and ELF charge calculated by GGA-PBE, which proved that the electrons at heterojunction interface of CdS–C3N4 were transferred from g-C3N4 to CdS, and the strong interaction existed in two layers between CdS and g-C3N4 by reformed the bonds of Cd–N, and the doping Ni can regulate the interface electron transport mechanism of CdS–C3N4 heterojunction. The hydrogen evolution performance showed that the ternary composite photocatalyst was better than both of the single system of cadmium sulfide or carbon nitride and the binary system containing NiS–CdS or CdS–C3N4. Through the characterization and theoretical calculation of the results, we found that the synergistic effect of NiS–CdS–C3N4 system could solve the problems of high recombination rate of photo-electrons and holes, and insufficient active sites existing in single materials of g-C3N4 or CdS during the photocatalytic reaction.