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Poly (triazine imide) (PTI/Li+Cl−), one of the crystalline versions of polymeric carbon nitrides, holds great promise for photocatalytic overall water splitting. In principle, the photocatalytic activity of PTI/Li+Cl− is closely related to the morphology, which could be reasonably tailored by the modulation of the polycondensation process. Herein, we demonstrate that the hexagonal prisms of PTI/Li+Cl− could be converted to hexagonal nanosheets by adjusting the binary eutectic salts from LiCl/KCl or NaCl/LiCl to ternary LiCl/KCl/NaCl. Results reveal that the extension of in‐plane conjugation is preferred, when the polymerisation was performed in the presence of ternary eutectic salts. The hexagonal nanosheets bears longer lifetimes of charge carriers than that of hexagonal prisms due to lower intensity of structure defects and shorter hopping distance of charge carriers along the stacking direction of triazine nanosheets. The optimized hexagonal nanosheets exhibits a record apparent quantum yield value of 25 % (λ=365 nm) for solar hydrogen production by one‐step excitation overall water splitting. [ABSTRACT FROM AUTHOR]

Broadening the visible light absorption range and accelerating the separation and migration process of charge carriers are effective ways to improve photocatalytic quantum efficiencies. In this study, we show that poly heptazine imides with enhanced optical absorption and promoted charge carrier separation and migration could be obtained by means of a rational design of the band structures and crystallinity of polymeric carbon nitride. Copolymerization of urea with monomers such as 2‐aminothiophene‐3‐carbonitrile would first generate amorphous melon with enhanced optical absorption, while further ionothermal treatment of melon in eutectic salts would increase the polymerization degree and create condensed poly heptazine imides as final products. Accordingly, the optimized poly heptazine imide presents an apparent quantum yield of 12 % at 420 nm for photocatalytic hydrogen production. [ABSTRACT FROM AUTHOR]

Conjugated polymers (CPs) have garnered increasing attention in the field of photocatalysis due to their stability and molecular tunability. Understanding the structure–property relationship in CPs and addressing appropriate molecular design strategies are pivotal to improving the photocatalytic performance of CPs. Herein, a new efficient cyano (CN) engineering approach was proposed to promote the photocatalytic performance of CPs, and three representative CP‐based photocatalysts with different CN contents were tailor‐made to investigate the relationship between CN functionalization and photocatalytic activity. A series of systematically experimental and theoretical studies reveal that CN functionalization contributes to strengthening the donor‐acceptor (D‐A) interaction, enhancing the light absorption ability, charge separation/transfer efficiency, and hydrophilicity of CPs, and also facilitating the output of separated photoinduced electrons from CPs to Pt cocatalyst. Thus, the dicyano‐functionalized polymer (P‐2CN) manifests an attractive photocatalytic performance in hydrogen production. This study provides a facile strategy to develop excellent CP‐based photocatalysts for solar fuel production. [ABSTRACT FROM AUTHOR]

Poly(heptazine imide) (PHI), one of the attractive allotropes of polymeric carbon nitride, has recently received extensive attention in photocatalysis due to its extended conjugation for fast separation and transfer of the charges. However, pristine PHI bears an intrinsic optical absorption band edge at 460 nm, which largely restrains the visible light utilization. Herein, the narrow‐bandgap PHI (N‐PHI) with an ordered‐distorted interface was fabricated from polycondensation of the mixture of NaSCN, cyanuric chloride, and LiCl. Results revealed that the enhanced optical absorption and the promoted separation and transfer of the charge carriers at the interface greatly improved the photocatalytic performance, which endowed N‐PHI with an apparent quantum yield of 20 % for hydrogen production at 450 nm. [ABSTRACT FROM AUTHOR]

The construction of heterojunctions is a promising manner to accelerate the separation and transfer of the charge carriers at the interface. Herein, a binary poly(heptazine‐triazine) imides (PHI/PTI) with semi‐coherent interfaces was fabricated via a facile two‐step salt‐melt synthetic process. The built‐in electric fields at the semi‐coherent interface endow prompt exciton splitting and charge carrier separation. Hence, the optimized PHI/PTI‐based copolymer presents a high apparent quantum yield (AQY=64 %) for visible‐light driven hydrogen production, by the aids of K2HPO4 as charge transfer mediator. This study provides physical insights for the rational promotion of the photocatalytic performance from the viewpoint of interfacial engineering of photocatalytic junctions on crystalline carbon nitride based semiconductors. [ABSTRACT FROM AUTHOR]

Covalent triazine‐based frameworks (CTFs) are typically produced by the salt‐melt polycondensation of aromatic nitriles in the presence of ZnCl2. In this reaction, molten ZnCl2 salt acts as both a solvent and Lewis acid catalyst. However, when cyclotrimerization takes place at temperatures above 300 °C, undesired carbonization occurs. In this study, an ionothermal synthesis method for CTF‐based photocatalysts was developed using a ternary NaCl‐KCl‐ZnCl2 eutectic salt (ES) mixture with a melting point of approximately 200 °C. This temperature is lower than the melting point of pure ZnCl2 (318 °C), thus providing milder salt‐melt conditions. These conditions facilitated the polycondensation process, while avoiding carbonization of the polymeric backbone. The resulting CTF‐ES200 exhibited enhanced optical and electronic properties, and displayed remarkable photocatalytic performance in the hydrogen evolution reaction. [ABSTRACT FROM AUTHOR]

Construction of local donor–acceptor architecture is one of the valid means for facilitating the intramolecular charge transfer in organic semiconductors. To further accelerate the interface charge transfer, a ternary acceptor–donor–acceptor (A1‐D‐A2) molecular junction is established via gradient nitrogen substituting into the polymer skeleton. Accordingly, the exciton splitting and interface charge transfer could be promptly liberated because of the strong attracting ability of the two different electron acceptors. Both DFT calculations and photoluminescence spectra elucidate the swift charge transfer at the donor‐acceptor interface. Consequently, the optimum polymer, N3‐CP, undergoes a remarkable photocatalytic property in terms of hydrogen production with AQY405 nm=26.6 % by the rational design of asymmetric molecular junctions on organic semiconductors. [ABSTRACT FROM AUTHOR]

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Abstract: Polymeric carbon nitride (PCN), in either triazine or heptazine form, has been regarded as a promising metal‐free, environmentally benign, and sustainable photocatalyst for solar hydrogen production. However, PCN in most cases only exhibits moderate activity owing to its inherent properties, such as rapid charge carrier recombination. Herein we present a triazine–heptazine copolymer synthesized by simple post‐calcination of PCN in eutectic salts, that is, NaCl/KCl, to modulate the polymerization process and optimize the structure. The construction of an internal triazine–heptazine donor–acceptor (D‐A) heterostructure was affirmed to significantly accelerate interface charge transfer (CT) and thus boost the photocatalytic activity (AQY=60 % at 420 nm). This study highlights the construction of intermolecular D‐A copolymers in NaCl/KCl molten salts with higher melting points but in the absence of lithium to modulate the chemical structure and properties of PCN. [ABSTRACT FROM AUTHOR]

The photocatalytic activity of protonated ordered mesoporous carbon nitride (pom-CN) was significantly improved by assembling anionic [Mo3S13]2− clusters as cocatalysts onto the surface and channel of pom-CN via electrostatic interactions. This work demonstrates the feasibility of employing solution chemistry to assemble co-catalysts in the form of ionic clusters as building blocks into a photosynthetic architecture. [ABSTRACT FROM AUTHOR]

Polymeric or organic semiconductors are promising candidates for photocatalysis but mostly only show moderate activity owing to strongly bound excitons and insufficient optical absorption. Herein, we report a facile bottom-up strategy to improve the activity of a carbon nitride to a level in which a majority of photons are really used to drive photoredox chemistry. Co-condensation of urea and oxamide followed by post-calcination in molten salt is shown to result in highly crystalline species with a maximum π-π layer stacking distance of heptazine units of 0.292 nm, which improves lateral charge transport and interlayer exciton dissociation. The addition of oxamide decreases the optical band gap from 2.74 to 2.56 eV, which enables efficient photochemistry also with green light. The apparent quantum yield (AQY) for H2 evolution of optimal samples reaches 57 % and 10 % at 420 nm and 525 nm, respectively, which is significantly higher than in most previous experiments. [ABSTRACT FROM AUTHOR]

The delamination of layered crystals that produces single or few-layered nanosheets while enabling exotic physical and chemical properties, particularly for semiconductor functions in optoelectronic applications, remains a challenge. Here, we report a facile and green approach to prepare few-layered polymeric carbon nitride (PCN) semiconductors by a one-step carbon/nitrogen steam reforming reaction. Bulky PCN, obtained from typical precursors including urea, melamine, dicyandiamide, and thiourea, are exfoliated into few-layered nanosheets, while engineering its surface carbon vacancies. The unique sheet structures with strengthened surface properties endow PCNs with more active sites, and an increased charge separation efficiency with a prolonged charge lifetime, drastically promoting their photoredox performance. After an assay of a H2 evolution reaction, an apparent quantum yield of 11.3 % at 405 nm was recorded for the PCN nanosheets, which is much higher than those of PCN nanosheets. This delamination method is expandable to other carbon-based 2D materials for advanced applications. [ABSTRACT FROM AUTHOR]

The search for metal-free organic photocatalysts for H2 production from water using visible light remains a key challenge. Reported herein is a molecular structural design of pure organic photocatalysts, derived from conjugated polybenzothiadiazoles, for photocatalytic H2 evolution using visible light. By alternating the substitution position of the electron-withdrawing benzothiadizole unit on the phenyl unit as a comonomer, various polymers with either one- or three-dimensional structures were synthesized and the effect of the molecular structure on their catalytic activity was investigated. Photocatalytic H2 evolution efficiencies up to 116 μmol h−1 were observed by employing the linear polymer based on a phenyl-benzothiadiazole alternating main chain, with an apparent quantum yield (AQY) of 4.01 % at 420 nm using triethanolamine as the sacrificial agent. [ABSTRACT FROM AUTHOR]

The article talks about sustainable energy and hydrogen production by solar water splitting techniques focusing on the production of an alternative energy resource and increasing demands for energy. Topics include Honda-Fujishima effect, application of photocatalysis for conversion of solar energy, and use of metal oxynitrides. Also discussed are strategies for designing a tantalum based photocatalyst dealing with electronic structure, band-gap energy, and prevention of photocorrosion.

Graphical abstract The main processes and the principle of visible light-driven photocatalytic water splitting in a suspension system. Abstract In order to solve the shortage of sustainable energy and the related concern about combustion of fossil fuels, converting the most abundant solar energy into chemical fuels becomes one of the most promising choices to provide the everlasting and environmentally friendly energy vector along with the minimum impact on environment. Among the methods of converting solar energy into chemical fuels, there is a significant interest in the renewable hydrogen production by photocatalysts from abundant water under visible light irradiation. Therefore, the development of efficient photocatalysts for water reduction and oxidation in a suspension system is the footstone for the development of solar energy conversion. In this review, the fundamental theory of photocatalysis and key factors affecting photocatalysis will be introduced first. Then the new materials development covering inorganic materials (oxides, nitrides and sulfides), carbon-based photocatalysts, and semiconductor-coordination compound photocatalysts developed over the past 10 years will be addressed with discussion about dominating factors in the photochemical process. This review would provide a comprehensive reference to exploring the efficient and novel materials working for the solar energy conversion to affordable and sustainable fuels. Finally, the perspective of the technology is also discussed. [ABSTRACT FROM AUTHOR]

Carbon nitride (CN) polymer has been widely investigated as a photocatalyst for solar hydrogen production in recent years due to its unique properties. However, the pristine CN typically shows moderate photocatalytic performance. An important reason is its high-density defects in CN framework, and it could play the role as a recombination center of photogenerated electron-hole pair. Therefore, increasing the crystallinity can be one of efficient way to enhance its photocatalytic activity. Recently, we have report a new heptazine-based crystalline CN synthesized by ionothermal method, and the as-prepared sample has been exhibited high activity toward photocatalytic hydrogen production. Herein, we systematically investigated influences of the synthetic temperature on the properties and photocatalytic activity of the as-prepared crystalline CN polymer. Our results demonstrate that the crystalline CN synthesized by using 550 °C pre-heated precursor shows the highest activity in photocatalytic hydrogen production, and achieving an apparent quantum yield of 6.8%@420 nm with MeOH as sacrificial agent. When compared to the reference photocatalyst P25, the CCN 550 shows remarkable photocatalytic hydrogen production under visible light irradiation, while P25 is virtually inactive. In addition, the amount of produced hydrogen gas by CCN 550 is closed to P25 under full arc irradiation of Xe lamp, which highlights the potential solar energy utilization of such crystalline conjugated polymer in the future development. [ABSTRACT FROM AUTHOR]

p -Si nanowire (Si-NW) arrays are successfully decorated with molybdenum–sulfur (MS) clusters by a drop-casting method. The composited photocathode (MS/Si-NW) demonstrated an enhanced photoelectrochemical (PEC) hydrogen production performance, with a photocurrent density of −14.3 mA/cm 2 at a potential of 0 V vs . RHE under the illumination of the red part of simulated solar light (λ > 590 nm, 27.3 mW/cm 2 ). The photocathode also showed a good stability in the long-term photocatalytic hydrogen evolution measurement, and the Faradaic efficiency of hydrogen production was close to 100%. Additionally, the morphological, optical and wetting properties of the photoelectrodes were investigated in detail. On the basis of the results, it could be concluded that the enhanced PEC performance is attributed to the high surface area, low light reflection and good wetting property of Si-NW, together with a low overpotential for hydrogen evolution reaction (HER) of the molybdenum–sulfur clusters. [ABSTRACT FROM AUTHOR]

Highlights: [•] Mesoporous graphitic carbon nitride (mpg-CN) was loaded with WS2 via an impregnation–sulfidation approach. [•] WS2/mpg-CN showed enhanced photocatalytic activity for H2 evolution. [•] WS2 played an important role in catalyzing H2 production. [•] The reaction mechanism of photocatalytic H2 production over WS2/mpg-CN was proposed. [Copyright &y& Elsevier]