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Graphitic carbon nitride tetragonal hollow prism (GCN-THP) with nitrogen vacancies was prepared by a simple two-step calcination method. Based on the characterizations of the as-prepared GCN-THP and the intermediate precursor, a possible mechanism was proposed for the formation of GCN-THP. The as-prepared GCN-THP exhibits superior activity and excellent stability during photocatalytic hydrogen evolution under visible light irradiation. The photocatalytic hydrogen evolution rate of GCN-THP was measured to be 1990 μmol g−1 h−1, which is 6.2 times as that of GCN. The enhanced photocatalytic activity could be attributed to unique 1D tetragonal hollow prism morphology and the presence of nitrogen vacancies in the as-prepared GCN-THP, which could increase the surface area, expand the visible light absorption, and promote the charge separation during photocatalytic hydrogen evolution. Our work could provide a new route to synthesize highly efficient photocatalysts with 1D hollow structures. Image 1 • g-C 3 N 4 tetragonal hollow prism was prepared by a two-step calcination method. • Low polymerized melamine serves as the template. • The g-C 3 N 4 hollow prism exhibits a superior HER rate of 1990 μmol g−1 h−1. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Melon with inter-triazine N-vacancies was fabricated in CCl 4 atmosphere for the first time. • Defect state is localized around the atoms adjacent to the vacancy. • Singly-occupied defect state acts as a trap for photogenerated electrons. • The vacancy site acts as the 2H+ → H 2 reduction site. • Melon with inter-triazine N-vacancies exhibits 8 times that of one without N-vacancies in photocatalytic H 2 evolution. Abstract We developed a new method to introduce N-vacancies of graphitic carbon nitride (GCN, typically in the Melon structure) at the inter-triazine sites and investigated how the visible-light photocatalytic H 2 evolution of GCN is affected by the N-vacancies at the intra- and inter-triazine sites of GCN. Theoretical and experimental results show that these N-vacancies of GCN create singly-occupied defect states within the band gap acting as a trap for photogenerated electrons and act as the reaction sites for H+ reduction. Compared with the intra-triazine N-vacancy, the inter-triazine N-vacancy exhibits stronger electron localization leading to a more efficient H 2 evolution. The photocatalytic reaction rate of GCN with inter-triazine N-vacancies is 9 times higher than that of "defect free" GCN, and 2.2 times higher normalized reaction rates than GCN with intra-triazine N-vacancies. The catalysis mechanism and the method to prepare melon with inter-triazine N-vacancies can be extended to explore new photocatalysts with high activities. [ABSTRACT FROM AUTHOR]