Abstract: The number of photogenerated carriers involved in the photocatalytic reaction is one of the main factors influencing the photocatalytic activity, and constructing S-scheme heterojunctions can significantly enhance the migration of photogenerated carriers, which is regarded as an effective method. In this study, Au nanoparticles (NPs)-supported crystallized heptazine/triazine-based carbon nitride (AHTCN) S-scheme heterojunction photocatalysts are successfully prepared by photoreduction methods. Except for the Au NPs function as an electron mediator, the experiment results and DFT calculations demonstrate that the Fermi energy level of crystallized heptazine/triazine-based heterojunction (HTCN) is pulled down after anchoring Au NPs, and thus the electron transfer path of HTCN changed from Type II-scheme to S-scheme. Owing to S-scheme heterojunction, the optimal AHTCN-2 (2 wt.% Au loaded) exhibits the best photocatalytic hydrogen evolution with a production rate of 715.2 μmol h^-1 g^-1, which significantly outperforms that of the HTCN. This work delivers a new strategy for the construction of S-scheme heterojunctions.

Key words: Photocatalytic hydrogen evolution, Graphitic carbon nitride, S-scheme heterojunction, Au nanoparticles, Crystalline