Graphite carbon nitride (g-C 3 N 4 ) is a potential photocatalyst for decomposing aquatic H 2 . However, the H 2 production activity of g-C 3 N 4 is limited by its small specific surface area and sluggish electron−hole pair separation. To improve the photocatalytic H 2 production performance of g-C 3 N 4 , the g-C 3 N 4 was treated by acid and then self-assembled with carboxylated graphene oxide (GO-COOH) to obtain H + /g-C 3 N 4 /GO-COOH in this work. The acid treatment facilitated the structure change of g-C 3 N 4 and increased its specific surface area. Functionalization of GO resulted in a considerable number of carboxyl groups (−COOH) grafted on the surface of GO. −COOH groups possess a strong electron-withdrawing property and can speed up the H 2 production reactions. Meanwhile, the high absorbance of H + /g-C 3 N 4 /GO-COOH in the visible light region separated the photogenerated charges efficiently. The H 2 production efficiency of H + /g-C 3 N 4 /GO-COOH was calculated as1091 μmol•g −1 •h −1 , approximately 5.42-fold of the efficiency of g-C 3 N 4 . This research might bring a fresh opinion in the field of photocatalytic H 2 evolution of g-C 3 N 4 .

Co3O4 is an attractive semiconductor in the photocatalytic field due to its proper band gap; however, its energy level structure is mismatched for H2 evolution. Herein, the Co3O4-based photocatalysts, Co3O4 nanosheet/g-C3N4 hybrids, were successfully prepared by an ultrasonic self-assembly method for enhanced photocatalytic H2 evolution. The optimized hybrid with 20 wt % g-C3N4, 20-CNCo, displayed the best photocatalytic performances, and the average H2 evolution rate was 134.6 μmol·g–1·h–1. The enhanced photocatalytic H2 evolution activities of 20-CNCo were due to the formation of heterojunctions between Co3O4 nanosheets and g-C3N4, which can increase the optical absorption ability, promote the separation of photogenerated charges, accelerate the electron transfer, and prolong the lifetime of the excited electrons. Moreover, following the unique step-scheme (S-scheme) charge transfer mechanism, the strong redox ability of the Co3O4 nanosheet/ g-C3N4 hybrid was retained, which was beneficial to the H2 evolution. This work provides strategies for designing active catalysts for photocatalytic reactions.

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