Green synthesis of earth-abundant metal sulfides (FeS2, CuS, and NiS2) and their use as visible-light active photocatalysts for H-2 generation and dye removal

Earth-abundant metal sulfides (for example, FeS2, CuS, and NiS2) are promising materials to be used as photocatalysts due to their suitable electronic and optical properties. In this work, we present a fast and low-cost hydrothermal method to synthesize these materials. They are integrally characterized and evaluated as photocatalysts for the H-2 evolution reaction and the degradation of indigo carmine (IC). FeS2 exhibits the highest photocatalytic efficiency (32 A mu mol g(-1) h(-1) of H-2 evolution and 88% of indigo carmine degradation) under visible light, and this activity is attributed to a larger crystallite size, smaller particle size, and lower recombination, compared to CuS and NiS2. Moreover, three different sacrificial reagents are studied for the H-2 evolution reaction, including Na2S/Na2SO3, EDTA, and ethanol. Na2S/Na2SO3 shows the highest enhancement in the activity, increasing the rate of H-2 production more than 15 times. This behavior is related to the lower oxidation potential of Na2S/Na2SO3. Moreover, we evaluate the activity of the materials for the electrochemical hydrogen evolution reaction (HER). In summary, this work provides valuable information for effective applications of these earth-abundant metal sulfides for energy and environmental photocatalytic processes.