Self-assembled heterojunction of metal sulfides for improved photocatalysis

Due to its high redox potential, zinc sulfide (ZnS) is considered an excellent semiconductor photocatalyst. However, the rapid recombination rate of the photogenerated electron-hole pairs limits the efficiency of ZnS for photocatalytic reactions. Herein, we suggest a design rule of heterojunction structure of ZnS for improvement of its photocatalytic performance. Two specific properties are specially emphasized: phase immiscibility and the different growth rates of the component materials. The phase immiscibility not only guarantees a well-separated interface, it also enables the technical convenience of one-pot synthesis. The different growth rates help form wide heterojunctions that foster the efficient consumption of materials. We found that the ZnS/Ni_xS_y composite not only meets the aforementioned requirements but also has proper band alignment. Ready-to-use heterojunction photocatalysts (ZnS/Ni_xS_y) were obtained via one-pot synthesis, thanks to the different growth rates and the immiscibility of the two sulfides. Combining ZnS with Ni_xS_y resulted in substantially improved photocatalytic activity in regard to dye decomposition and H₂ production via water splitting. Both band position measurements and DFT simulations indicated that Ni_xS_y is a co-catalyst for ZnS, allowing sufficient band offset for electron-hole separation. Abundant and mass-producible, the ZnS/Ni_xS_y composite can effectively substitute for noble metal photocatalysis when it comes to organic pollutant degradation and water splitting.