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A porphyrinic metal-organic framework (PMOF) known as PCN-222(Zn) was chemically doped with a molecular Re(I) catalyst-bearing carboxylate anchoring group to form a new type of metal-organic framework (MOF)-Re(I) hybrid photocatalyst. The porphyrinic MOF-sensitized hybrid (PMOF/Re) was prepared with an archetypical CO2 reduction catalyst, (L)ReI(CO)3Cl (Re(I); L = 4,4'-dicarboxylic-2,2'-bipyridine), in the presence of 3 vol % water produced CO with no leveling-off tendency for 59 h to give a turnover number of ≥1893 [1070 ± 80 μmol h-1 (g MOF)-1]. The high catalytic activity arises mainly from efficient exciton migration and funneling from photoexcited porphyrin linkers to the peripheral Re(I) catalytic sites, which is in accordance with the observed fast exciton (energy) migration (≈1 ps) in highly ordered porphyrin photoreceptors and the effective funneling into Re(I) catalytic centers in the Re(I)-doped PMOF sample. Enhanced catalytic performance is convincingly supported by serial photophysical measurements including decisive Stern-Volmer interpretation.

The targeted synthesis of an efficient, visible light active, recyclable, freestanding covalent organic framework thin film photocatalyst for multi-faceted photocatalysis is the essence of the proposed work. A simple, scalable, reagent free synthesis of a thin film at the interface of 5,10,15,20-tetra-(4-aminophenyl)porphyrin, 2-vinylbenzene-1,4-dicarbaldehyde in nitrobenzene and aqueous glyoxal affords centimetre sized continuous 2D thin film with substantial stability, flexibility and efficient visible light activity. Strikingly different from the regular imine based COF, the incorporation of the glyoxal unit as a modulator helps in band gap tuning and induces flexibility within the thin film. An interplay between time and concentration helps in achieving a thin film photocatalyst with efficient photocatalytic activity for 1,4-NADH regeneration and selective formic acid formation from CO2. The optimum band edge position of the thin film photocatalyst also enables solar fine chemical synthesis via reductive dehalogenation under visible light illumination with excellent recyclability. The present work gives insight into visible light active thin film formation en route to metal-free sustainable photocatalysis.

Mimicking natural photosynthesis is a promising way to produce fine chemicals, yet there is a need for efficient catalysts. Here, we synthesized a photocatalyst made of self-assembled graphitic carbon nitride/sulfur/cobalt (III) tetraphenyl porphyrin, and we used this photocatalyst for production of the l-glutamate amino acid in 93.6% yield. Regeneration of the 1,4-dihydronicotinamide adenine dinucleotide cofactor under visible light reached 88.3%.

Herein, we report the in situ single-step hydrothermal synthesis of hierarchical 2D SnS@ZnIn2S4 nano-heterostructures and the examination of their photocatalytic activity towards hydrogen generation from H2S and water under sunlight. The photoactive sulfides rationally integrate via strong electrostatic interactions between ZnIn2S4 and SnS with two-dimensional ultrathin subunits, i.e. nanopetals. The morphological study of nano-heterostructures revealed that the hierarchical marigold flower-like structure is self-assembled via the nanopetals of ZnIn2S4 with few layers of SnS nanopetals. Surprisingly, it also showed that the SnS nanopetals with a thickness of ∼25 nm couple in situ with the nanopetals of ZnIn2S4 with a thickness of ∼25 nm to form a marigold flower–like assembly with intimate contact. Considering the unique band gap (2.0–2.4 eV) of this SnS@ZnIn2S4, photocatalytic hydrogen generation from water and H2S was performed under sunlight. SnS@ZnIn2S4 exhibits enhanced hydrogen evolution, i.e. 650 μmol h−1 g−1 from water and 6429 μmol h−1 g−1 from H2S, which is much higher compared to that of pure ZnIn2S4 and SnS. More significantly, the enhancement in hydrogen generation is 1.6–2 times more for H2S splitting and 6 times more for water splitting. SnS@ZnIn2S4 forms type I band alignment, which accelerates charge separation during the surface reaction. Additionally, this has been provoked by the nanostructuring of the materials. Due to the nano-heterostructure with hierarchical morphology, the surface defects increased which ultimately suppresses the recombination of the electron–hole pair. The above-mentioned facts demonstrate a significant improvement in the interface electron transfer kinetics due to such a unique 2D nano-heterostructure semiconductor which is responsible for a higher photocatalytic activity.

Solar light-driven fuel production from carbon dioxide using organic photocatalysts is a promising technique for sustainable energy sources. Band gap engineering in sustainable organic photocatalysts for improving efficiency and fulfilling the requirements is highly anticipated. Here, we present a new strategy to engineer the band gap in covalent organic framework (COF) photocatalysts by varying the push-pull electronic effect. To implement this strategy, we have designed and synthesized four different COFs using a tripodal amine 4,4',4″-(1,3,5-triazine-2,4,6-triyl)tris(([1,1'-biphenyl]-4-amine)) [Ttba] with 1,3,5-triformylbenzene (COF-1), 2,4,6-triformylphloroglucinol (COF-2), 2,4,6-triformylphenol (COF-3), and 2,4,6-triformylresorcinol (COF-4). On varying the number of hydroxyl units in the aldehyde precursor, the resulting COFs allow the fine-tuning of their band gap and band edge positions and result in different morphologies with varying surface areas. The enhanced optical properties of COF-3 and COF-4 with very suitable band gaps of 2.02 and 1.95 eV, respectively, enable them to demonstrate a high-efficiency photobiocatalytic system for NADH photoregeneration and enhanced visible light-driven formic acid production at a rate of 226.3 μmol g-1 in 90 min. The triazine core enables efficient charge separation, while the hydroxyl groups induce an electronic push-pull effect, regulating their photocatalytic efficiency. The results demonstrated the morphology-guided enhanced surface area and dual keto-enol tautomerism-induced push-pull effect in asymmetrical charge distribution as key features in the fine-tuning of the photocatalysts.

The efficient and selective light-driven conversion of carbon dioxide to formate is a scientific challenge for green chemistry and energy science, especially utilizing visible-light energy and earth-abundant catalytic materials. In this report, two mononuclear Ni(II) complexes of pyridylbenzimidazole (pbi) and pyridylbenzothiazole (pbt), such as Ni(pbt)(pyS)2 (1) and Ni(pbi)(pyS)2 (2) (pyS = pyridine-2-thiolate), were prepared and their reactivities studied. The two Ni complexes were examined for CO2 conversion using eosin Y as a photosensitizer upon visible-light irradiation in a H2O/ethanol solvent. The photoreaction of CO2 catalyzed by complexes 1 and 2 selectively affords formate with a high efficiency (14 000 turnover number) and a high catalytic selectivity of ∼99%. Undesirable proton reduction pathways were completely suppressed in the photocatalytic reactions with these sulfur-rich Ni catalysts under CO2. Hydrogen photoproduction was also studied under argon. Their kinetic isotope effects and influence of solution pH for formate and H2 production in the photocatalytic reactions are described in relation to the reaction mechanisms. These bioinspired Ni(II) catalysts with N/S ligation in relation to [NiFe]-hydrogenases are the first examples of early transition metal complexes affording such high selectivity and efficiencies, providing a future path to design solar-to-fuel processes for artificial photosynthesis.

The selective production of fine chemicals using inexpensive solar light continues to be a challenge. As a means to achieve this we report herein the synthesis and development of a perylene-based solar-light-driven photocatalyst (PDA–DAA) obtained by the covalent bonding of perylene tetracarboxylic dianhydride (PDA) with a 2,6-diamino-anthraquinone (DAA) molecule. The photocatalyst/biocatalyst coupled system developed using PDA–DAA as a photocatalyst functions in a highly efficient manner, leading to high NADH regeneration (80.12%), followed by its consumption in exclusive production of l-glutamate (94.16%) from α-ketoglutarate. The present research highlights the development and application of the PDA–DAA photocatalyst for direct formation of l-glutamate under solar light.

A novel BODIPY functionalized ruthenium-nitrogen doped graphene nanosheet photocatalyst is reported herein for the regioselective direct C–H arylation of imidazo-pyrimidines at the C-3 position with excellent functional-group tolerance. Organic transformation is achieved under visible light irradiation in high yields and selectivity (∼99%) using this photocatalyst. The results are a benchmark example for the use of functionalized graphene nanosheets as a highly practical and efficient visible light active photocatalyst for carrying out regioselective direct C–H arylation.

The synthesis of pharmaceutically active 1,2,3-triazoles has been continuously scrutinized in the search for unique and effective catalysts to make the process efficient, green, and sustainable. Here, we are presenting a new visible light active Ni(II) cyclam-integrated triazole-linked organic polymer (Ni-TLOP) photocatalyst for the synthesis of 1,2,3-triazole compounds with excellent efficiency and regioselectivity. The reaction was studied for a series of substrates and the absolute regioselectivity of a representative triazole product has also been confirmed by X-ray crystallography. The proficiency and chemical orthogonality of the Ni-TLOP are remarkable and it shows enhanced efficiency and regioselectivity. The use of a recyclable photocatalyst and non-hazardous reagents makes the catalytic system sustainable and environmentally friendly. This photocatalyzed click reaction technique has been successfully applied to the expedient synthesis of one of the most sold anti-epileptic drugs rufinamide.

Our growing energy demands must be met by a sustainable supply with reduced carbon intensity. One of the most exciting prospects to realize this goal is the photocatalyst-biocatalyst integrated artificial photosynthesis system which affords solar fuel/chemicals in high selectivity from CO2. Graphene based photocatalysts are highly suitable for the system, but their industrial scale use requires immobilization for improved separation and recovery of the photocatalyst. Therefore for practical purposes, design and fabrication of film type graphene photocatalyst with higher solar energy conversion efficiency is an absolute necessity. As a means to achieve this, we report herein the successful development of a new type of flexible graphene film photocatalyst that leads to >225% rise in visible light harvesting efficiency of the resultant photocatalyst-biocatalyst integrated artificial photosynthesis system for highly selective solar fuel production from CO2 compared to conventional spin coated graphene film photocatalyst. It is an important step towards the design of a new pool of graphene film based photocatalysts for artificial photosynthesis of solar fuels from CO2.

Novel in situ Se-doped carbon nitride (C3N4) nanosheets are synthesized for the first time by a facile one-pot two-step strategy. The as-prepared Se-doped C3N4 nanosheets show a high visible light driven formic acid production rate of 1.001 × 105 μmol gcat–1 h–1. It represents the highest value reported in literature for formic acid production from CO2 by visible light harvesting C3N4 photocatalysts. The exceptional photocatalytic activity is largely attributed to selenium-doped conjugated system besides porous nanosheet morphology of the photocatalyst. The presence of midgap state in carbon nitride (−0.35 V vs standard hydrogen electrode) due to Se doping is found to significantly extend the light absorption up to 570 nm thereby further enhancing light harvesting ability of the photocatalyst. The current work not only provides a facile and scalable route to synthesize highly efficient Se-doped carbon nitride (C3N4) nanosheet photocatalysts but also sheds light on devising new avenues for rational design ...

Photocatalytic CO2 reduction for solar fuel production has attracted considerable attention as it can simultaneously reduce the effects of worldwide fossil-fuel shortage and global warming. As a means to achieve this we herein report the facile and eco-friendly synthesis of highly active carbon nanodots-silica hybrid photocatalyst (CNDSH) by a reverse microemulsion method with a nonionic surfactant. The photocatalyst-biocatalyst coupled system developed using CNDSH as photocatalyst functions efficiently to carry out high NADH regeneration (74.10 ± 0.17 %) followed by its consumption in exclusive formic acid production (203.33 ± 1.9 µmol) from CO2. This research work is a benchmark example of carbon nanodots-silica hybrid photocatalyst system for solar fuel production and expected to trigger further interest in the development of efficient and eco-friendly CO2 reduction systems.

Herein, we report visible light active mesoporous cadmium bismuth niobate (CBN) nanospheres as a photocatalyst for hydrogen (H 2 ) generation from copious hydrogen sulfide (H 2 S). CBN has been synthesized by solid state reaction (SSR) and also using combustion method (CM) at relatively lower temperatures. The as-synthesized materials were characterized using different techniques. X-ray diffraction analysis shows the formation of single phase orthorhombic CBN. Field emission scanning electron microscopy and high resolution-transmission electron microscopy showed the particle size in the range of ∼0.5–1 µm for CBN obtained by SSR and 50–70 nm size nanospheres using CM, respectively. Interestingly, nanospheres of size 50–70 nm self assembled with 5–7 nm nanoparticles were observed in case of CBN prepared by CM. The optical properties were studied using UV–visible diffuse reflectance spectroscopy and showed band gap around ∼3.0 eV for SSR and 3.1 eV for CM. The slight shift in band gap of CM is due to nanocrystalline nature of material. Considering the band gap in visible region, the photocatalytic activity of CBN for hydrogen production from H 2 S has been performed under visible light. CBN prepared by CM has shown utmost hydrogen evolution i.e. 6912 µmol/h/0.5 g which is much higher than CBN prepared using SSR. The enhanced photocatalytic property can be attributed to the smaller particle size, crystalline nature, high surface area and mesoporous structure of CBN prepared by combustion method. The catalyst was found to be stable, active and can be utilized for water splitting.

We have demonstrated the controlled synthesis of hierarchical nanostructured ZnIn₂S₄ using a facile template free hydrothermal/solvothermal method. The effect of solvents on the morphology and microstructure of ZnIn₂S₄ has been studied by using water, methanol and ethylene glycol as a solvents. The hierarchical nanostructure, i.e., rose-like morphology composed of very thin (5–6 nm) nanoplates of length ˜1 μm which was obtained in aqueous mediated ZnIn₂S₄. The porous structure (distorted flowers) and agglomerated nanoparticles were obtained using methanol-and ethylene glycol-mediated ZnIn₂S₄. Considering the band gap in the visible region, ZnIn₂S₄ is used as a solar light driven photocatalyst. An ecofriendly photocatalytic process for the conversion of poisonous H₂S into H₂ which is a green unconventional energy source has been demonstrated. The nanostructured ZnIn₂S₄ is employed as a photocatalyst for hydrogen production from H₂S via a solar light-driven eco-friendly approach. The stable photocatalytic activity of hydrogen evolution, i.e., 3964 μmol ⁻¹ was obtained using 0.5 gm of such hierarchical nanostructured ZnIn₂S₄ under visible light irradiation. The unique hierarchical nanostructured ZnIn₂S₄ ternary semiconductor having hexagonal layer is expected to have potential applications in solar cells, LEDs, charge storage, electrochemical recording, thermoelectricity, other prospective electronic and optical devices.

Photocatalysis is one of the most promising ways for the production of organic chemicals with renewable energy source. For the development of cost-effective and metal-free catalysts, two-dimensional covalent organic framework (COF) has been emerged as a photocatalyst. Here, we report the synthetic method of two-dimensional covalent porphyrin framework (2D CPF) and the fabrication procedure of highly active flexible film. 2D CPF were constructed from tetrakis-(4-amino-phenyl)-porphyrin (TAPP) and tetrakis-(4-nitro-phenyl)-porphyrin (TNPP) monomers through the poly-condensation reaction and the resultant composite showed the superb harvesting ability of solar light, the suitable optical band-gap, and the highly ordered π-electron channels which facilitates efficient charge migrations. The 2D CPF photocatalyst deposited on the thin film was readily applicable to light-induced activation of C H bond between p-position of substituted aryl diazonium salts and heteroarenes, and exhibited the high selectivity (~99%) as well as high production yield. Our results show an experimental benchmark for the use of flexible COF film as a highly practical and efficient solar light responsive photocatalyst for the selective C H bond formation in between substituted aryl diazonium salts and heteroarenes derivatives.

Developing stable semiconducting oxides that are active in the visible region for photocatalytic reactions is a major technological challenge. Herein, we report a facile co-precipitation based synthesis of PbCrO4 nanostructures with the aim to study their hitherto unreported hydrogen production potential. It has been observed that monoclinic PbCrO4 nanorods have been generated using a simple co-precipitation method in the presence of water and methanol as solvents while spherical nanostructures are produced using an ultrasonication assisted co-precipitation method. The nanorods synthesized by the aqueous co-precipitation method have yielded the highest rate of hydrogen production (3214 μmol h−1 0.5 g−1) by splitting hydrogen sulfide (H2S) gas.

Two-dimensional covalent organic frameworks (2D COFs) are a class of crystalline polymers with a design controllable platform that may be developed into a new type of metal-free photocatalyst. The exploration of new frameworks is, however, critical for further progress in this emerging field. To realize their full potential in practical light harvesting applications, the fabrication of a film type photocatalyst is equally essential. Here, we report the successful development of a triazine based covalent organic framework (2D CTF) as an inexpensive and highly efficient visible light active flexible film photocatalyst for solar fuel production from CO2. For this research work, the condensation polymerization between cyanuric chloride and perylene diimide has been exploited for the first time as a new synthetic approach to the construction of 2D CTFs. The visible light-harvesting capacity, suitable band gap and highly ordered π electron channels contribute to the excellent performance of the film photocatalyst. The current study is a benchmark example of COF based photocatalysts for solar fuel production from CO2 and is expected to trigger further interest in potential solar energy conversion applications such as wearable devices.

In situ synthesis of the orthorhombic Bi2S3 nanowires decorated with hexagonal CdS nanoparticles (nano-heterostructure) has been demonstrated by a facile solvothermal method. The tiny 5–7 nm CdS spherical nanoparticles are decorated on the surfaces of 30–40 nm Bi2S3 nanowires, successfully. Structural, morphological and optical studies clearly show the existence of CdS on the nanowires. A possible sequential deposition growth mechanism is proposed on the basis of experimental results to reveal the formation of the nano heterostructure. The heterostructures have been used as a photocatalyst for hydrogen production as well as degradation of methylene blue under solar light. The maximum hydrogen evolution i.e. 4560 and 2340 μmol h−1 0.5 g was obtained from H2S splitting and glycerol degradation for Bi2S3 NWs decorated with CdS nanoparticles (nano-heterostructure) which is higher than that of the Bi2S3 NWs (3000 and 1170 μmol h−1 0.5 g, respectively). The enhanced photocatalytical hydrogen evolution efficiency of the heterostructures is mainly attributed to its nanostructure. In the nano heterostructure, the CdS nanoparticles control the charge carrier transition, recombination, and separation, while the Bi2S3 nanowire serves as a support for the CdS nanoparticles. The photogenerated electron's migration is faster than the holes from the inside of a CdS nanoparticle to its surface or to the phase interface, resulting in a relatively higher hole density inside the CdS nanoparticle leaving electron density at surface of the Bi2S3 NWs. This influences the photocatalytic activity under solar light. Such nano-heterostructures may have potential in other photocatalytic reactions.

Conductive metal–organic frameworks are an emerging class of three-dimensional architectures with degrees of modularity, synthetic flexibility and structural predictability that are unprecedented in other porous materials. However, engendering long-range charge delocalization and establishing synthetic strategies that are broadly applicable to the diverse range of structures encountered for this class of materials remain challenging. Here, we report the synthesis of K x Fe2(BDP)3 (0 ≤ x ≤ 2; BDP2− = 1,4-benzenedipyrazolate), which exhibits full charge delocalization within the parent framework and charge mobilities comparable to technologically relevant polymers and ceramics. Through a battery of spectroscopic methods, computational techniques and single-microcrystal field-effect transistor measurements, we demonstrate that fractional reduction of Fe2(BDP)3 results in a metal–organic framework that displays a nearly 10,000-fold enhancement in conductivity along a single crystallographic axis. The attainment of such properties in a K x Fe2(BDP)3 field-effect transistor represents the realization of a general synthetic strategy for the creation of new porous conductor-based devices. A conducting metal–organic framework with charge delocalization by reductive potassium insertion is demonstrated. Integration into a field-effect transistor shows similar mobilities to semiconductors, with a mobility estimated to be at least 0.84 cm2 V–1 s–1.

Artificial photosynthesis process is a nature inspired process that can convert solar energy to important value added chemicals. Here, we report the synthesis of a self-assembled protein and carbon nitride/sulfur hydrogel (Fmoc- d -PheA/g-C3N4/S) as a visible light active hydrogel photocatalyst for 86.78% reduced nicotinamide adenine dinucleotide (NADH) regeneration and 90.0% l -Glutamate production under solar light irradiation. The present work represents a new benchmark example for NADH regeneration and solar chemical production.

Natural photosynthesis is the primary route that supplies energy required for the endurance of all living things. The initial step in this process is the absorption of solar light by an organic-inorganic molecular organization called a light harvesting complex. This complicated natural solar energy conversion platform has inspired scientists to create artificial counter parts. As a means to achieve this, a self-assembled light harvesting carbon nitride/cobalt tetra-phenyl-porphyrin (CN/Co(III)TPP) material as a highly selective solar light active photocatalyst has been developed. The system exhibited excellent NADH regeneration (87.87%) and L-glutamate (94.30%) production under visible light irradiation. The current research endeavor highlights the development and application of a self-assembled CN/Co(III)TPP photocatalyst for the selective production of L-glutamate from α-ketoglutarate.