Facile synthesis and enhanced photocatalytic H2-evolution performance of NiS2-modified g-C3N4 photocatalysts

Abstract

NiS2 is a promising cocatalyst to improve the photocatalytic performance of g-C3N4 for the production of H2. However, the synthesis of the NiS2 cocatalyst usually requires harsh conditions, which risks destroying the microstructures of the g-C3N4 photocatalysts. In this study, a facile and low-temperature (80 °C) impregnation method was developed to prepare NiS2/g-C3N4 photocatalysts. First, the g-C3N4 powders were processed by the hydrothermal method in order to introduce oxygen-containing functional groups (such as –OH and –CONH–) to the surface of g-C3N4. Then, the Ni2+ ions could be adsorbed near the g-C3N4 via strong electrostatic interaction between g-C3N4 and Ni2+ ions upon the addition of Ni(NO3)2 solution. Finally, NiS2 nanoparticles were formed on the surface of g-C3N4 upon the addition of TAA. It was found that the NiS2 nanoparticles were solidly and homogeneously grafted on the surface of g-C3N4, resulting in greatly improved photocatalytic H2 production. When the amount of NiS2 was 3 wt%, the resultant NiS2/g-C3N4 photocatalyst showed the highest H2 evolution rate (116.343 μmol h−1 g−1), which is significantly higher than that of the pure g-C3N4 (3 μmol h−1 g−1). Moreover, the results of a recycling test for the NiS2/g-C3N4(3 wt%) sample showed that this sample could maintain a stable and effective photocatalytic H2-evolution performance under visible-light irradiation. Based on the above results, a possible mechanism of the improved photocatalytic performance was proposed for the presented NiS2/g-C3N4 photocatalysts, in which the photogenerated electrons of g-C3N4 can be rapidly transferred to the NiS2 nanoparticles via the close and continuous contact between them; then, the photogenerated electrons rapidly react with H2O adsorbed on the surface of NiS2, which has a surficial metallic character and high catalytic activity, to produce H2. Considering the mild and facile synthesis method, the presented low-cost and highly efficient NiS2-modified g-C3N4 photocatalysts would have great potential for practical use in photocatalytic H2 production.