Uniformly Dispersed Metal Sulfide Nanodots on g-C3N4 as Bifunctional Catalysts for High-Efficiency Photocatalytic H2 and H2O2 Production under Visible-Light Irradiation

Loading transition metal as a cocatalyst to a photocatalyst is a promising and mainstream way to improve the photocatalytic H2 evolution reaction (HER) of a semiconductor. However, transition metal cocatalysts are rarely reported to enhance photocatalytic oxygen reduction (ORR) to generate H2O2. In this work, a light-induced deposition approach was adopted to precisely load nickel sulfide nanodots onto the surface of g-C3N4, and the resultant composite photocatalysts enhanced both photocatalytic HER and ORR performances. In the typical case of NiS@g-C3N4, NiS@g-C3N4-30 displayed a H2 evolution rate of 3297 μmol g–1 h–1 under visible-light irradiation, which showed 74 and 1.23 times activity for pure g-C3N4 and classical Pt (3%) modified g-C3N4, respectively. NiS@g-C3N4-30 also exhibited the best photocatalytic efficiency with a H2O2 production of 400 μM in 1 h, which was 12.6 times that of pure g-C3N4. The remarkable activity and stability of this bifunctional catalyst can be attributed to the accurate loading of intimately contacted NiS nanodots at the electron transfer sites of g-C3N4 nanosheets, which can boost the separation of photogenerated charge carriers and accelerate the chemical reaction on the surface of the photocatalyst. This work opens a new pathway for the precise preparation of bifunctional cocatalysts for solar to chemical energy conversion.