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Dye/polymeric carbon nitride (PCN) systems exhibit great potential for photocatalytic hydrogen evolution (PHE), due to the broad light-harvesting region and optimized charge separation ability. However, charge recombination due to the unmatched photogenerated carrier lifetimes (ns level) of organic dyes and photocatalytic reaction rates (s level) is a major hindrance, which afforded a big challenge to modulate electronic processes by prolongation of carrier lifetimes of dyes. Herein, the excited triplet states of organic dyes with longer carrier lifetimes (ms level) were employed in PHE systems for the first time, which are stabilized by the adjustment of π–π interactions of conjugation skeletons with alkyl chain engineering. By utilizing the increased isolation effect of alkyl chains, from linear to branched ones with prolonged lengths, higher PHE activities were achieved by branched chain-substituted dyes due to their longer lifetimes, accompanied by the improved phosphorescence properties, and suppressed charge recombination. Accordingly, a relationship among properties of triplet excited states, alkyl chains, and PHE activity has been roughly built, providing valuable information for further promoting PHE activities by adjustment of dye–dye and dye–PCN interactions. [ABSTRACT FROM AUTHOR]

Towards green production and efficient utilization of hydrogen, developing renewable clean energy technologies based on hydrogen and oxygen electrocatalysis, especially water electrolysis, zinc–air batteries, and fuel cells, is of vital significance. To promote their energy conversion efficiency, low-cost and high-efficiency electrocatalysts are highly desired to accelerate the sluggish kinetics of hydrogen and oxygen electrocatalytic reactions. The emergence of metal–organic frameworks (MOFs) provides new opportunities to obtain high-performance hydrogen and oxygen electrocatalysts with desired composition and structures. However, most of these MOF-based electrocatalysts are powders, resulting in limited active sites, blocked mass/charge transport, and insufficient stability. In this context, we present an up-to-date investigation of self-supporting MOF-based hydrogen and oxygen electrocatalysts with a focus on the synthesis strategy and application. Finally, some personal insights into the current challenges and potential solutions are presented, aiming at providing some guidance for the design and synthesis of advanced self-supporting MOF-based materials in hydrogen/oxygen-related energy technologies. [ABSTRACT FROM AUTHOR]

Photocatalytic H2 production via water splitting holds great potential for the conversion of solar energy into renewable and storable chemical fuels in a sustainable manner, but this up-hill reaction is mainly hindered by the water oxidation process. This reaction is sluggish and relies on high overpotentials (wasted energy), while only oxygen is generated as a low value oxidation by-product. Coupling hydrogen generation to a less unfavorable oxidation reaction creating higher value products is therefore a recommendable issue. Here we found that poly(heptazine imide) (PHI), a stable and reactive allotrope of crystalline carbon nitride, supported with highly dispersed Pt nanoparticles (PtNPs) could achieve efficient and persistent H2 and CH4 production by photocatalytic reforming of biomass derived alcohols under visible light irradiation. The results reveal that PHI with low grain boundary defects restrains the bulk charge carrier recombination and largely promotes photocatalytic efficiency. The apparent quantum efficiency (AQE) of the optimized material for visible light H2 evolution could reach values as high as 15% at 420 nm. The DFT results reveal that the activity is associated with the Tafel step rather than the Volmer–Tafel step. This study highlights the development of a new covalent scaffold for the simultaneous generation of storable and valuable chemical fuels (H2 and CH4) in a feasible photocatalytic manner. [ABSTRACT FROM AUTHOR]

A metal-free protocol is established for the decarboxylative N–H or C(sp2)–H functionalization of acids via metal-free boron carbon nitride (BCN) photocatalysis, delivering the desired products under ambient conditions. This methodology is applicable to the late-stage modification of pharmaceutical molecules and gram-scale experiments as well as in the recovery and reuse of the photocatalysts without the loss of reactivity. The developed photochemical reaction system fulfills the requirements of green and sustainable chemistry. [ABSTRACT FROM AUTHOR]

Single-atom catalysis has become the most active new frontier in energy conversion applications due to its remarkable catalytic activity and low material consumption. However, the issue of atom aggregation during the synthesis process or catalytic reaction must be overcome. In this work, we have developed a one-step photo-deposition process to fabricate Pt single-atom catalysts (SACs) on nitrogen doped carbon dots (NCDs). The Pt–NCDs were then hybridized with TiO2 to achieve high hydrogen generation activity and to understand the fundamentals at the Pt/NCD/TiO2 interface. The synergistic effect of Pt SAC and NCDs with maximized atomic efficiency of Pt and improved charge transfer capability provides a new strategy to rationally design a multi-scale photocatalyst structure to achieve high H2 evolution efficiency. The facile synthesis process also holds great potential for various applications such as electrocatalysis, heterogeneous catalysis and drug delivery, providing a promising way to reduce the high cost of noble metals. [ABSTRACT FROM AUTHOR]

Metal-free photocatalysis has evoked broad research interest in green energy applications. Herein, two-dimensional (2D) carbon-doped BN (C-BN) nanosheets are vertically aligned on a conductive substrate by low-temperature plasma enhanced chemical vapor deposition (PE-CVD) and are demonstrated to be a photoelectrocatalytic device for water oxidation under sunlight irradiation. By virtue of this geometry, the unique 2D material presents advantages for the catalytic reaction. In addition, adjusting the carbon concentration can facilely control the structure and optoelectronic properties of the C-BN nanosheets to improve light harvesting in the solar spectrum. As a result, the photocurrent density exhibits a 60-fold enhancement over that of the C-BN films achieved by traditional deposition of C-BN powder. Experimental and theoretical studies of band structures are performed and the results are in agreement with each other. This 2D C-BN nanofilm based device could stimulate interest in advanced applications in many fields such as catalysis, sensors, transistors and others. [ABSTRACT FROM AUTHOR]

Atomic-level boron carbon nitride nanosheets (BCNNS) have been prepared by a molten salt assisted assembly growth strategy, which effectively promotes the solvation of precursors, minimizes the surface energy and prevents the aggregation of layers. The as-synthesized BCNNS have atomic layered thickness and large lateral size, and show enhanced visible light H2 evolution activity compared to bulk BCN. [ABSTRACT FROM AUTHOR]

Efficient biomimetic catalases have been broadly explored for free-radical scavenging and antioxidative stress. Herein, we introduce a non-toxic Se-modified carbon nitride (CN) nanosheet for this bioapplication, and it presents efficient catalase activity, high fluorescence properties, and good biocompatibility. These properties indicate that this material has potential for use as an artificial enzyme against oxidative stress. [ABSTRACT FROM AUTHOR]

A new type of base catalyst was designed and prepared by metalation of carbon nitrides with alkali metal ions. The as-prepared metalated carbon nitride composites showed enhanced basicity and efficient catalytic hydrolysis of carbonyl sulfide. The results of this study demonstrate that the metalation of carbon nitrides holds great promise for base catalysis applications. [ABSTRACT FROM AUTHOR]

Herein, a facile reorganization of a triazine-based conjugated polymer structure was adopted to optimize the optical, electronic, and photocatalytic properties of the polymer. The optimal photocatalyst presents enhanced performance as compared to the pristine photocatalyst by a factor of 3. This demonstration provides a new strategy for the optimization of conjugated polymers for various photoredox applications. [ABSTRACT FROM AUTHOR]

Employing palygorskite (Pal) as a moderate alkaline regulator, herein we report the construction of a novel heterogeneous cobalt-based cocatalyst via an in situ electrostatic adsorption deposition process for its application to the photoreduction of CO2 to CO. Characterization results reveal that the negatively charged layer and relatively large specific surface area of Pal could mainly account for the high dispersity of cobalt on the surface of the fibrous support, thus endowing it with feasible CO2 adsorption and transformation. [ABSTRACT FROM AUTHOR]

CO2 is a vital compond for life, and its concentration significantly affects the living environment of the Earth. Extensive effort has been devoted to balance its concentration. Among the developed approaches, photocatalytic CO2 conversion is considered as an ideal option. Previous reports suggest polymeric carbon nitride (PCN) can be effectively used as a metal-free photocatalyst to convert CO2. Herein, the recent developments of PCN and the related photocatalysts for CO2 conversion are summarized from the fundamental of using PCN, and their extended applications through molecular modification and physical/chemical coupling with other substances. The concluding remarks finally indicate the future challenges of using PCN materials for relevant solar-driven applications. [ABSTRACT FROM AUTHOR]

We report the first use of polymeric carbon nitride (CN) for the catalytic selective oxidation of H2S. The as-prepared CN with unique ultrathin “nanomeshes” structure exhibits excellent H2S conversion and high S selectivity. In particular, the CN nanomesh also displays better durability in the desulfurization reaction than traditional catalysts, such as carbon- and iron-based materials. [ABSTRACT FROM AUTHOR]

As a unique class of functional materials, perovskite oxides have shown great opportunities in various energy storage and conversion applications. However, their performance for boosting photocatalytic CO2 reduction is seldom reported. Herein, we report a facile synthesis of coralline-like LaCoO3 perovskite materials and their use as highly efficient and stable cocatalysts for splitting CO2 into CO with visible light. [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]

The synthesis of boron carbon nitride (BCN) with special morphologies via a simple pathway is still a major challenge. A novel and facile biotemplating method has been presented to synthesize boron carbon nitride tubes (BCNTs) by using kapok fibers (KFs) as both biotemplates and carbonaceous sources. The BCNT photocatalysts can catalyse hydrogen evolution from water under visible light illumination. [ABSTRACT FROM AUTHOR]

Large pore three-dimensional cage-type mesoporous carbon nitride semiconductors were successfully synthesized by employing SBA-16 templates which are prepared by hydrothermal methods at higher temperatures. These samples were characterized by using various techniques, and their photocatalytic H2 production properties were investigated under visible light (λ ＞ 420 nm) irradiation. The results have shown that the textural parameters of the carbon nitride semiconductors can be easily tuned by simple adjustment of the synthesis temperature of the template SBA-16 silica, and carbon nitride semiconductors can be truly reversely replicated from the cubic structure of the template silica synthesized at a temperature of 180 and 200 °C. The large pore cage-type mesoporous carbon nitride semiconductor cast from mesoporous silica at the hydrothermal temperature of 200 °C exhibits a remarkably enhanced photocatalytic activity towards hydrogen evolution, as compared to either disordered mesoporous g-CN or bulk g-CN prepared by our previous synthetic approaches. [ABSTRACT FROM AUTHOR]

Photocatalyst surface restructuration is of immense practical importance for solar energy utilization. Herein, we present an ingenious strategy to bridge π-conjugated molecules into the framework of a polymeric semiconductor. This endows the catalyst with increased charge transfer and separation efficiency, resulting in an improved photoactivity. Moreover, the modified photocatalysts exhibit high structural stability and photoactivity. These results illustrate a novel method of integrating functional units to construct new photocatalysts for sustainable photocatalysis. [ABSTRACT FROM AUTHOR]

Porous hematite photoanodes with wormlike networks were prepared by microwave-assisted rapid annealing of β-FeOOH grown directly on a FTO glass. The enhanced electrochemical characteristics such as large surface area and good permeation of an electrolyte lead to the excellent photoelectrochemical performance toward the solar-driven water splitting for hydrogen production. [ABSTRACT FROM AUTHOR]

A ternary photocatalyst has been successfully constructed through the integration of Au, CdS and hollow carbon nitride nanospheres (HCNS), where Au nanoparticles were designed to shuttle interparticle transfer of charge carriers between CdS and HCNS photosensitizers to establish two-photon (Z-scheme) photocatalytic tandem systems for solar fuel production. The solid-state CdS–Au–HCNS Z-scheme nanocomposites were efficient for H2 evolution (with a quantum yield of 8.7% at 420 nm) and CO2 reduction catalysis with visible light irradiation. This work further proves the feasibility of employing hollow conjugated polymer photocatalysts in the function-led design of artificial Z-type photosynthetic machinery on soft material interfaces. [ABSTRACT FROM AUTHOR]

A simple one-step procedure for the preparation of cobalt oxide–carbon nitride composites by carrying out the thermal condensation reaction of carbon nitride precursors in cobalt(ii) chloride-containing salt melts is developed. This method enables us to control the structure of the polymer constituent by the proper selection of the second eutectic component. In this respect, alkali metal chlorides and zinc chloride give rise to poly(triazine imides), while tin(ii) chloride delivers melon-based polymers. The crystallinity of the carbon nitride polymer phase can be influenced by varying the concentration of the precursor in the melt. On the other hand, cobalt oxide loading in the final products can be increased by decreasing the precursor concentration in the melt. The products are highly active photocatalysts for Rhodamine B degradation as exemplified by SnCl2/CoCl2-derived solids, and the water oxidation reaction (WOR). The activity of the products in the WOR is comparable with that of the bench composite photocatalyst prepared by using the three-step procedure that includes the synthesis of Co3O4 nanoparticles as a separate step, thus illustrating the advantages of the developed salt melt assisted approach. [ABSTRACT FROM AUTHOR]

Cobalt selenide has been developed as an effective cocatalyst to decorate visible light photocatalysts, including WO3, BiVO4 and g-C3N4, establishing intense surface contact with substrates for the photocatalytic water oxidation reaction. Compared with CoOx and CoSx, CoSe2 is superior for improving the photocatalytic water oxidation activity due to the lower anionic electronegativity, which leads to dense adhesion and enables fast interfacial charge transfer for the water oxidation reaction. [ABSTRACT FROM AUTHOR]

Incorporation of aromatic motifs into the nanosized shells of hollow carbon nitride nanospheres has been reported to develop functional photosynthetic structures for solar energy application. This modification results in an extended π-conjugation system, red-shift of the optical absorption, and an improved charge separation in the shell, while still retaining the unique hollow polymeric nanoarchitectures. This strategy enables the tuning of the semiconductor properties of the shell substance in the hollow carbon nitride nanostructures to generate the redox species to enhance photocatalytic activity for hydrogen evolution using visible light. [ABSTRACT FROM AUTHOR]

Carbon nitride (C3N4) polymers work as a vital component in a photocatalytic CO2 reduction assembly that operates under visible light when modified with a ruthenium complex, trans(Cl)-[Ru{4,4'-(CH2PO3H2)2-2,2'-bipyridine}(CO)2Cl2], (Ru) as a catalyst. Here we examined the effects of structural properties of carbon nitride on the photocatalytic performance for CO2 reduction into formic acid. Introduction of mesoporosity into the graphitic carbon nitride structure increased the specific surface area, leading to significant enhancement in activity. However, higher surface area (in other words, lower crystallinity) that originated from excessively introduced mesopores had a negative impact on activity, although it is a prerequisite to allow for adsorption of Ru on the carbon nitride surface. Thus, the activity was sensitive to specific surface area and crystallinity of carbon nitride, but is largely insensitive to the pore size and the volume. [ABSTRACT FROM AUTHOR]

A noble-metal-free system for photochemical reduction of CO2 has been developed by integrating graphitic carbon nitride (g-C3N4) with a cobalt-containing zeolitic imidazolate framework (Co-ZIF-9). g-C3N4 acts as a semiconductor photocatalyst, whereas Co-ZIF-9 is a cocatalyst that facilitates the capture/concentration of CO2 and promotes light-induced charge separation. The two materials cooperate efficiently to catalyze CO2-to-CO conversion upon visible light illumination under mild reaction conditions. A 13C-labelled isotropic experiment proved that CO2 is the carbon source of the produced CO. Even without noble metals, the system still achieved an apparent quantum yield of 0.9 percent. The system displayed high photocatalytic stability, without noticeable alterations in the chemical and crystal structures of g-C3N4 and Co-ZIF-9 after the reaction. [ABSTRACT FROM AUTHOR]

A cheap and easily-available organosulfur compound, guanidine thiocyanate, has been used to synthesize graphitic carbon nitride (g-C3N4) by a thermally-induced desulfurization and polymerization of the precursor. Photocatalytic activity experiments demonstrated that the g-C3N4 synthesized from guanidine thiocyanate exhibited a much higher H2 evolution rate than the reference sample prepared from dicyanamide. Further improvement in the activity was achieved by optimization of the condensation temperature. Based on X-ray photoelectron spectroscopy analysis, the samples synthesized at a high temperature of 700 °C feature a high crystallinity and a low density of surface defects, with an enhanced optical absorbance extending to the visible light region. As a result, the sample prepared at 700 °C has been found to be 7 times more reactive towards photocatalytic hydrogen evolution than the sample polymerized at the normal temperature of 550 °C. Other guanidine halides have also been applied to synthesize g-C3N4 materials, and the structure and activity of the resultant g-C3N4 were compared to the carbon nitride polymer from guanidine thiocyanate. [ABSTRACT FROM AUTHOR]

TaON nanoparticles with low surface reduction defect sites were successfully constructed by a simple nitridation approach using Ta2O5·nH2O as a precursor. Large amounts of crystal water in Ta2O5·nH2O are considered as a parclose to prohibit Ta5+ from being reduced in the nitridation process with NH3 gas. Urea was also used in the synthesis, acting as a co-nitridation agent together with NH3 but also as a porogen for creating nanopores in TaON frameworks. The as-prepared TaON catalyst was evaluated by environmental purification of organic pollutants in water, as exemplified here by mineralization of phenol and its chloroderivatives in aqueous phase under visible light irradiation. Results revealed that a lower defect density of TaON, as well as its nanopore structure and smaller particle size, contribute to the promotion in both electron–hole separation and interfacial charge-transfer in materials surface/interface, being the main reasons for the enhanced photocatalytic performance. [ABSTRACT FROM AUTHOR]

Spectral sensitization of a mesoporous graphite carbon nitride (mpg-C3N4) photocatalyst was investigated by depositing magnesium phthalocyanine (MgPc) to expand the absorption to wavelengths longer than those of the principal mpg-C3N4. The obtained sample, MgPc/Pt/mpg-C3N4(Pt as a cocatalyst) showed stable photocatalytic evolution of hydrogen from aqueous solution in the presence of sacrificial reagents (triethanolamine), even under irradiation at wavelengths longer than 600 nm. Increasing the amount of MgPc led to ordered MgPc aggregation on the photocatalyst surfaces. The rate of photocatalytic hydrogen evolution was highest on a sample with an amount of MgPc corresponding to a monolayer on the Pt/mpg-C3N4photocatalyst surface. The obtained action spectra of hydrogen evolution and the observation that the amount of evolved hydrogen substantially surpassed the amount of MgPc, confirm that the introduced MgPc functioned as a photocatalytic sensitizer. [ABSTRACT FROM AUTHOR]

Spinel ZnCo2O4 nanostructures have shown great opportunities in energy related areas. However, the applications of ZnCo2O4 for the conversion of CO2 are much less reported. Herein, we present the use of mesoporous ZnCo2O4 nanorods as efficient and high stable cocatalysts for the photochemical reduction of CO2 under mild reaction conditions. [ABSTRACT FROM AUTHOR]

Three-dimensional conjugated poly(azomethine) networks were found to be promising candidates for applications in photocatalytic water splitting. Straightforward synthetic protocols lead to fully organic photocatalysts that showed enhanced long-time stability. Furthermore, the catalytic performance of these materials was correlated to the molecular composition and the optoelectronic properties of the samples. [ABSTRACT FROM AUTHOR]

Iron-doped titanium dioxide nanoarchitectures with ordered mesopore periodicity and enhanced photocatalytic activity have been developed as photofunctional materials for environmental purification. [ABSTRACT FROM AUTHOR]

We report the direct splitting of pure water by light-excited graphitic carbon nitride (g-C 3 N 4 ) modified with Pt, PtO x , and CoO x as redox cocatalysts, while pure g-C 3 N 4 is virtually inactive for overall water splitting by photocatalysis. The novelty is in the selective creation of both H 2 and O 2 cocatalysts on surface active sites of g-C 3 N 4 via photodeposition triggering the splitting of water for the simultaneous evolution of H 2 and O 2 gases in a stoichiometric ratio of 2 : 1, irradiated with light, without using any sacrificial reagents. The photocatalyst was stable for 510 hours of reaction.

A noble-metal-free system for photochemical reduction of CO2 has been developed by integrating graphitic carbon nitride (g-C3N4) with a cobalt-containing zeolitic imidazolate framework (Co-ZIF-9). g-C3N4 acts as a semiconductor photocatalyst, whereas Co-ZIF-9 is a cocatalyst that facilitates the capture/concentration of CO2 and promotes light-induced charge separation. The two materials cooperate efficiently to catalyze CO2-to-CO conversion upon visible light illumination under mild reaction conditions. A (13)C-labelled isotropic experiment proved that CO2 is the carbon source of the produced CO. Even without noble metals, the system still achieved an apparent quantum yield of 0.9 percent. The system displayed high photocatalytic stability, without noticeable alterations in the chemical and crystal structures of g-C3N4 and Co-ZIF-9 after the reaction.

Covalent carbon nitride polymers were applied as metal-free robust catalysts for the inactivation of Escherichia coli K-12 (E. coli), a common Gram-negative bacterium, under visible light illumination. The results demonstrated that the creation of antibacterial function on the surface of conjugated polymers has now become possible.

Semiconducting carbon nitride materials were successfully prepared via a thermal poly-condensation of dicyandiamide as a precursor at >500 °C. The resulting materials were investigated as metal-free catalysts for the activation of H(2)O(2) with visible light under mild conditions, using the decomposition of Rhodamine B (RhB) in aqueous solution as a model reaction. Results revealed that carbon nitride catalysts can activate H(2)O(2) to generate reactive oxy-radicals under visible light irradiation without employment of any metal additives, leading to the mineralization of the dye. Factors affecting the degradation of organic compounds are pH values and the concentration of H(2)O(2). Recycling of the catalyst indicated no obvious deactivation during the entire catalytic reaction, indicating good (photo)chemical stability of metal-free polymeric carbon nitride photocatalysts for environmental purification. This study demonstrated a promising approach for the activation of green oxidant, hydrogen peroxide, by the newly-developed polymer photocatalysts for environmental remediation and oxidation catalysis.