Synthesis of palladium-modified MnS photocatalysts with enhanced photocatalytic activity in the photoreduction of CO2 to CH4

alpha-MnS and gamma-MnS photocatalysts were synthesized by the hydrothermal method and their size, structure, and appearance were determined by X-ray diffraction (XRD) patterns and scanning (SEM) and transition (TEM) electron microscopy images. mMnS behaved as a bipyramid exposed with {200} facet, while gamma-MnS behaved as a hexagonal prism exposed with {100}, {110}, and {102} facets. In addition, palladium (Pd)-modified gamma-MnS photocatalysts were prepared via a photodeposition method, and their density of states and energy band structure were studied by theoretical calculations. The introduced Pd ions, which existed on the photocatalysts surface as -S-Pd-S- active species, expanded the visible light absorption, promoted the separation of electrons and holes, and improved the photocatalytic activity for the photoreduction of CO2 to CH4, indicating surface modification as an effective method for the development of MnS-based materials with high CO2 photoreduction activity. Therefore, this study could set the basis for the design and synthesis of novel visible light photocatalysts with active surface and high application potential in diverse fields.