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• CCl 4 assisted method was firstly applied to construct free-standing g-C 3 N 4 films. • Metal cations can be in-situ extracted from the substrates and serve as nucleate sites. • The physicochemical properties of the g-C 3 N 4 films can be easily adjusted. • The g-C 3 N 4 film exhibited an excellent visible-light hydrogen evolution rate of 74.98 μmol g−1 h−1. Developing a simple and general method to fabricate graphitic carbon nitride (g-CN) film is crucial for the application of devices. Herein, we report a CCl 4 -assisted method for the fabrication of continuous g-CN films on various substrates with in-situ extracted metal cations as nucleate sites. The g-CN film exhibits continuous wrinkles-like graphene structure, and can be completely exfoliated as a free-standing film. In the g-CN film, the metallic cations are bonded with the electron-rich nitrogen as the nucleate sites for connecting molecular structure. By changing the synthesis temperature and the flow rate of CCl 4 , the thickness and the band structure of the g-CN films can be successfully adjusted. Under visible light illumination, the g-CN films exhibit efficient hydrogen evolution with a rate of 74.98 μmol g−1 h−1. We believe that the precise controlled free-standing g-CN film will shed light on many opportunities in the utilization of graphitic carbon nitride for catalysis, sensor, electronic and energy-related applications. This method may open a new avenue to fabricate other two-dimensional films on different substrates. [ABSTRACT FROM AUTHOR]

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]

Carbon bridged graphitic carbon nitride (g-C 3 N 4 ) was prepared by a facile supramolecular self-assembly method. Experimental results and theoretical calculations indicate C atoms were introduced into the g-C 3 N 4 lattice by substituting the bridged N atoms. As a result, the delocalized big π bonds can be formed among the adjacent heptazine rings, which could both enhance the light absorption and promote the charge separation. Beneficial from the efficient charge separation and enhanced light absorption, the carbon bridged g-C 3 N 4 exhibits high efficient photocatalytic activity, where the H 2 evolution rate is about 7 times as high as that of pristine g-C 3 N 4 . This work demonstrates carbon bridged C 3 N 4 can be fabricated by a simple supramolecular self-assembly process, which could be useful for the further development of high efficient g-C 3 N 4 photocatalysts. [ABSTRACT FROM AUTHOR]