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[Display omitted] Evolution of hydrogen from water by utilizing solar energy and photocatalysts is one of the most promising ways to solve energy crisis. However, designing a cost-effective and stable photocatalyst without any noble metals is of vital importance for this process. Herein, an extremely active molecular complex cocatalyst NiL 2 (Cl) 2 is successfully designed. After being covalently linked to thiophene-embedded polymeric carbon nitride (TPCN), the hybrid catalyst NiL 2 (Cl) 2 /TPCN exhibits extraordinary H 2 production activity of 95.8 μmol h−1 without Pt (λ ≥ 420 nm), together with a remarkable apparent quantum yield of 6.68% at 450 nm. In such a composite catalyst, the embedded π-electron-rich thiophene-ring not only extends the π-conjugated system to enhance visible light absorption, but also promotes the charge separation through electron-withdrawing effect. It turns out that the C N covalent bonds formed between NiL 2 (Cl) 2 and TPCN skeleton accelerate the transfer of electrons to the Ni active sites. Our finding reveals that the strategy of embedding π-electron-rich compounds to graphitic carbon nitride provides potentials to develop excellent photocatalysts. The strong covalent combination of molecular complexes cocatalyst onto organic semiconductors represents an important step towards designing noble-metal-free photocatalysts with superior activity and high stability for visible light driven hydrogen evolution. [ABSTRACT FROM AUTHOR]

Efficient solar‐to‐hydrogen (STH) energy conversion under ambient conditions (room temperature and atmospheric pressure) is important for pursuing scalable solar hydrogen generation. Modification of polymeric carbon nitride (PCN) by conjugated polymers has attracted great attention for improving photocatalytic hydrogen evolution (PHE) performance. However, the limited interfacial junction between PCN and conjugated polymers leads to a low density of free charges, resulting in unsatisfactory PHE activity. Herein, three donor‐π‐acceptor‐structured organic molecules (OMs) with different electron‐donating units (amino, N,N‐diethyl and triphenylamine) and same electron‐accepting unit (benzothiadiazole) are designed to modify PCN to enlarge the interfacial junction. The optimized PHE performance under AM 1.5G simulated sunlight and ambient conditions can maintain as high as 4.63 mmol h−1 g−1 (the highest record among all the reported PCN‐based photocatalysts to the best of the authors knowledge). The improved performance can be partially attributed to the strong visible light harvesting capability of OMs. Specifically, the triphenylamine unit in the formed type II molecule heterojunctions (MHJ) enables efficient charge separation at the interfacial junction, which prolongs the photogenerated electron lifetime for PHE. The designed MHJ photocatalysts show outstanding PHE performance under ambient conditions, which is highly promising for scalable STH conversion. [ABSTRACT FROM AUTHOR]

Polymers with a large π‐electron conjugated system have aroused extensive concern in photocatalysis due to their appropriate bandgap and high stability. In order to overcome such drawbacks as its inadequate visible light absorption and rapid recombination of the photogenerated electron‐hole pairs of graphic carbon nitride (g‐C3N4), a facile strategy is proposed to tune its electronic structure by grafting small molecules. The conjugated photocatalysts were prepared by attaching 3‐Aminobenzoic acid (AB) and 6‐Aminopyridine‐2‐carboxylic acid (APy) to the framework of g‐C3N4 via low‐temperature condensation. The obtained catalysts UCN‐AB and UCN‐APy possess higher visible light absorption that results from the modified band structure by extending π‐electron delocalization. Additionally, AB and APy worked as the electron acceptors which further enhance transport of the photogenerated electrons. The optimal UCN‐AB and UCN‐APy accomplished remarkable photocatalytic hydrogen evolution rates of 104.0 and 133.2 μmol/h, respectively, which are nearly four or five times of that over g‐C3N4. This work provides a simple and feasible modification approach to extend π‐electron delocalization in g‐C3N4 with a stronger visible light response and accelerated charge transfer for high photocatalytic hydrogen evolution. [ABSTRACT FROM AUTHOR]

In this study, a photocatalyst with a distorted skeleton and synthesized by grafting triamterene onto graphitic carbon nitride (g‐C3N4) frameworks was prepared. The pteridine ring of the triamterene‐based nitrogen‐enriched organic structure functions as a trapped electron site owing to its inductive effect. The benzene ring in triamterene plays an important role in the even dispersion of electrons by a conjugative effect. Redistribution of the intramolecular electronic potential is caused by a synergistic effect between the pteridine and benzene rings of triamterene and promotes separation and migration of the photoinduced charge carriers. After coupling with triamterene, the π electrons of g‐C3N4 are relocated; that is, the intrinsic electronic and band structures of g‐C3N4 are effectively modulated. The modified polymeric photocatalyst shows a high photocatalytic H2 evolution rate of 157.5 μmol h−1, a value that is 4.3 times higher than the H2 evolution rate of pristine g‐C3N4 (36.8 μmol h−1), with an apparent quantum efficiency of 9.7 % at λ=450 nm. The incorporation of triamterene into the g‐C3N4 frameworks significantly expands its π‐delocalized system by redistribution of the electronic potential, expands the visible‐light absorption range, and effectively promotes the separation and migration of photoinduced charge carriers. This strategy may provide a reference for promoting charge separation of g‐C3N4 through redistribution of the electronic potential and for synthesizing novel carbon nitride based semiconductors for efficient solar energy conversion into hydrogen. Moving things around: This study reports the preparation, characterization, and photocatalytic activity of triamterene‐grafted graphitic carbon nitride photocatalysts that display enhanced visible‐light absorption and improved separation of charge carriers owing to redistribution of the electronic potential of the π‐conjugated system; these photocatalysts thus show a high rate of hydrogen evolution. [ABSTRACT FROM AUTHOR]

Nitrogen deficient g-C 3 N 4 was prepared by polymerization of urea with a small amount offormamide, whichdisplays extended optical absorption and enhanced migration and separation of photogenerated charge carriers, and efficient photocatalytic hydrogen evolution. [Display omitted] • g-C 3 N 4 photocatalysts were prepared by co-polymerization of urea with formamide. • A facile approach to develop nitrogen deficient g-C 3 N 4. • The resultant samples exhibit remarkably enhanced photocatalytic H 2 evolution performance. It is noted that appropriate amount of nitrogen defects in g-C 3 N 4 are beneficial to the photocatalytic reaction. In this study, a facile approach for the preparation of nitrogen deficient g-C 3 N 4 was developed by polymerization of urea with a small amount of formamide. The obtained g-C 3 N 4 displays extended optical absorption and enhanced migration and separation of photogenerated charge carriers, which result in efficient photocatalytic hydrogen evolution. The hydrogen evolution rates of the optimized sample matched well with the extended optical absorption along with different wavelength. Density functional theory calculations further certified the proposed scheme of nitrogen defects. This work provides a feasible process using organic chemical protocols to synthesize polymeric photocatalysts. In addition, the importance of nitrogen defects on the photocatalytic performance of g-C 3 N 4 was discussed based on experimental results. The work opens a new pathway for the development of highly active g-C 3 N 4 for the application. [ABSTRACT FROM AUTHOR]

g-C 3 N 4 with distorted framework was prepared by thermal polymerization of EDTA-modified melamine. The obtained photocatalysts display high and stable activity for photocatalytic generation of hydrogen through water splitting. [Display omitted] • EDTM-modified g-C 3 N 4 was synthesized. • Extending the light harvesting. • Effective separation and transfer of charge carriers. • High visible light photocatalytic activity for H 2 evolution. Relatively narrow visible light responsive region and high recombination probability of photogenerated charge carriers are the main barriers that limit the photocatalytic activity of graphitic carbon nitride (g-C 3 N 4). In this study, modified g-C 3 N 4 was synthesized by adding minor amount of ethylenediaminetetraacetic acid (EDTA) into urea as precursors for subsequent thermal polymerization. The thermal intermediate product ethylenediaminetetramethylene (EDTM) during decarboxylation of EDTA was grafted to the framework of g-C 3 N 4 by connecting adjacent 3,s-triazine units. The special chelate structure of EDTA leads to the distortion of g-C 3 N 4 to a nonplanar structure, which is responsible for extending the light harvesting around 500 nm, and consequently promoting the generation, separation and transfer of charge carriers. The H 2 evolution rate on an optimized EDTM-grafted g-C 3 N 4 photocatalyst (UCN-10) reaches 116.4 μmol h−1, which is about 3.5 times of that on the pristine g-C 3 N 4 (UCN). The formation process of the grafted structure and the mechanism for the enhanced photocatalytic H 2 evolution over UCN-10 were proposed based on experimental results. [ABSTRACT FROM AUTHOR]

Carbonyl-grafted g-C3N4 porous nanosheets (COCNPNS) were fabricated by means of a two-step thermal process using melamine and oxalic acid as starting reagents. The combination of melamine with oxalic acid to form a melamine-oxalic acid supramolecule as a precursor is key to synthesizing carbonyl-grafted g-C3N4. The bulk carbonyl-grafted g-C3N4 (COCN) was further thermally etched onto porous nanosheets by O2 under air. In such a process, the carbonyl groups were partly removed and the obtained sample showed remarkably enhanced visible-light harvesting and promoted the separation and transfer of photogenerated electrons and holes. With its unique porous structure and enhanced light-harvesting capability, under visible-light illumination ( λ>420 nm) the prepared COCNPNS exhibited a superior photocatalytic hydrogen evolution rate of 83.6 μmol h−1, which is 26 times that of the p-CN obtained directly from thermal polycondensation of melamine. [ABSTRACT FROM AUTHOR]

This paper reports a facile one-pot synthesis strategy to prepare carbon self-doped g-C3N4 (C-g-C3N4) nanosheets by using supramolecular networks consisting of cyanuric acid, ethylene glycol (EG), and melamine (CEM) bonded through hydrogen bonding as the thermal polycondensation precursor, in which EG serves as a solvent for cyanuric acid and melamine, and as a source of the doped carbon simultaneously. The threedimensional structure of CEM resulted in the distortion of C-g-C3N4, which is capable of motivating the n-π* electronic transition involving the N lone pairs to give an additional absorption region from 450 to 600 nm. The hydrogen evolution rate of C-g-C3N4 reaches 73.09 μmol h−1, which is about 15 times of that over the g-C3N4 obtained from direct thermal polycondensation of melamine owing to its extended light harvesting and faster separation of photogenerated electrons and holes. [ABSTRACT FROM AUTHOR]

A facile and cost-effective method was developed for the synthesis of holey N-deficient graphitic carbon nitride nanosheets (FCN) using trifluoroacetic-acid-treated urea as a precursor. The role of trifluoroacetic acid on the composition, structure and photocatalytic performance of the prepared catalysts was carefully investigated. The obtained samples displayed laminated porous morphology with nitrogen defects, larger specific surface areas, extended range of spectral response and enhanced electron mobility of charge carriers. Consequently, the optimized catalyst FCN-400 exhibited superb photocatalytic performance and excellent cycling stability for hydrogen evolution. The hydrogen evolution rate over FCN-400 reached 309.3 μmol/h under visible light irradiation, which is 11.3-fold of that of urea-derived graphitic carbon nitride (27.3 μmol/h). In this study, holey N-deficient g-C 3 N x nanosheets were prepared using trifluoroacetic-acid-treated urea as a precursor. The optimized catalyst FCN-400 exhibits a hydrogen evolution rate of 309.3 μmol/h, which is 11.3-fold of that of bulk g-C 3 N 4 (27.3 μmol/h). This study provides a green and effective procedure for designing porous nanostructure and advanced photocatalysts with excellent photocatalytic activity and high stability towards solar-to-hydrogen conversion. Image 1 • Holey N-deficient g-C 3 N x nanosheets were prepared. • High and stable visible light photocatalytic activity for H 2 evolution. • Enlarged specific surface areas and extended the range of spectral response. [ABSTRACT FROM AUTHOR]

• In-plane benzene ring-incorporated graphitic carbon nitride was prepared. • Noble-metal-free photocatalysts were prepared by integrating nickel complex (NiL) onto CN-DAPS. • The optimum hydrogen generation rate is as high as 30.67 μmol·h−1. In this study, efficient visible-light-driven hydrogen evolution was achieved on novel and highly efficient photocatalysts based on nickel complex (NiL) and in-plane benzene ring-modified graphitic carbon nitride nanosheets (CN-DAPS) by copolymerization of urea and π-electron-rich 4,4′-diaminodiphenyl sulfone (DAPS). The incorporation of in-plane benzene-ring into CN not only extends the π-conjugated system, but also promotes the migration of photogenerated electrons and enhances absorption of visible light. In addition, NiL is covalently integrated onto CN-DAPS framework, enabling the intramolecular electron transfer from CN-DAPS to the coordinately-bonded nickel complex. Moreover, covalent combination of NiL with CN-DAPS framework further enables its dispersion in molecules. The novel photocatalysts NiL/CN-DAPS exhibit superior H 2 evolution activity, while the optimum hydrogen generation rate reaches 30.67 μmol·h−1. The NiL/CN-DAPS is even active for hydrogen generation even under irradiation of light with wavelength of 550 and 600 nm. The apparent quantum efficiency reaches 2.15 % at 450 nm. So to speak, the integration between the in-plane benzene-ring doped graphitic carbon nitride nanosheets aiming at high separation of charge carriers and the covalently-bonded nickel complex aiming to reduce the overpotential of photocatalytic hydrogen releasing results in a new class of photocatalysts based on non-noble-metal-based systems for efficient visible-light-driven hydrogen evolution. [ABSTRACT FROM AUTHOR]