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Single-atom catalysts anchoring offers a desirable pathway for efficiency maximization and cost-saving for photocatalytic hydrogen evolution. However, the single-atoms loading amount is always within 0.5% in most of the reported due to the agglomeration at higher loading concentrations. In this work, the highly dispersed and large loading amount (>1 wt%) of copper single-atoms were achieved on TiO 2 , exhibiting the H 2 evolution rate of 101.7 mmol g −1  h −1 under simulated solar light irradiation, which is higher than other photocatalysts reported, in addition to the excellent stability as proved after storing 380 days. More importantly, it exhibits an apparent quantum efficiency of 56% at 365 nm, a significant breakthrough in this field. The highly dispersed and large amount of Cu single-atoms incorporation on TiO 2 enables the efficient electron transfer via Cu 2+ -Cu + process. The present approach paves the way to design advanced materials for remarkable photocatalytic activity and durability. In this work, the highly dispersed and large loading amount (>1 wt%) of copper single-atoms were achieved on TiO 2 , resulting into an apparent quantum efficiency of 56% at 365 nm, in addition to an excellent thermal stability as proved after storing 380 days.

Production of hydrogen fuel from sunlight and water, two of the most abundant natural resources on Earth, offers one of the most promising pathways for carbon neutrality 1 – 3 . Some solar hydrogen production approaches, for example, photoelectrochemical water splitting, often require corrosive electrolyte, limiting their performance stability and environmental sustainability 1 , 3 . Alternatively, clean hydrogen can be produced directly from sunlight and water by photocatalytic water splitting 2 , 4 , 5 . The solar-to-hydrogen (STH) efficiency of photocatalytic water splitting, however, has remained very low. Here we have developed a strategy to achieve a high STH efficiency of 9.2 per cent using pure water, concentrated solar light and an indium gallium nitride photocatalyst. The success of this strategy originates from the synergistic effects of promoting forward hydrogen–oxygen evolution and inhibiting the reverse hydrogen–oxygen recombination by operating at an optimal reaction temperature (about 70 degrees Celsius), which can be directly achieved by harvesting the previously wasted infrared light in sunlight. Moreover, this temperature-dependent strategy also leads to an STH efficiency of about 7 per cent from widely available tap water and sea water and an STH efficiency of 6.2 per cent in a large-scale photocatalytic water-splitting system with a natural solar light capacity of 257 watts. Our study offers a practical approach to produce hydrogen fuel efficiently from natural solar light and water, overcoming the efficiency bottleneck of solar hydrogen production. Photocatalytic water splitting with a high solar-to-hydrogen efficiency of more than nine per cent is achieved using pure water, concentrated solar light and an indium gallium nitride photocatalyst.

Mimicking natural photosynthesis to convert CO 2 with H 2 O into value-added fuels achieving overall reaction is a promising way to reduce the atmospheric CO 2 level. Casting the catalyst of two or more catalytic sites with rapid electron transfer and interaction may be an effective strategy for coupling photocatalytic CO 2 reduction and H 2 O oxidation. Herein, based on the MOF ∪ COF collaboration, we have carefully designed and synthesized a crystalline hetero-metallic cluster catalyst denoted MCOF-Ti 6 Cu 3 with spatial separation and functional cooperation between oxidative and reductive clusters. It utilizes dynamic covalent bonds between clusters to promote photo-induced charge separation and transfer efficiency, to drive both the photocatalytic oxidative and reductive reactions. MCOF-Ti 6 Cu 3 exhibits fine activity in the conversion of CO 2 with water into HCOOH (169.8 μmol g −1 h −1 ). Remarkably, experiments and theoretical calculations reveal that photo-excited electrons are transferred from Ti to Cu, indicating that the Cu cluster is the catalytic reduction center. A crystalline hetero-metallic cluster catalyst based on a covalent organic framework strategy is reported. The catalyst can facilitate both photocatalytic oxidative and reductive reactions leading to efficient production of HCOOH from CO2 and H2O.

For more than one century, photochemical [2+2]-cycloadditions have been used by synthetic chemists to make cyclobutanes, four-membered carbon-based rings. In this reaction, typically two olefin subunits (two π -electrons per olefin) cyclize to form two new C–C σ -bonds. Although the development of photochemical [2+2]-cycloadditions has made enormous progress within the last century, research has been focused on such [2 π +2 π ]-systems, in which two π -bonds are converted into two new σ -bonds 1 , 2 . Here we report an intermolecular [2+2]-photocycloaddition that uses bicyclo[1.1.0]butanes as 2 σ -electron reactants 3 – 7 . This strain-release-driven [2 π +2 σ ]-photocycloaddition reaction was realized by visible-light-mediated triplet energy transfer catalysis 8 , 9 . A simple, modular and diastereoselective synthesis of bicyclo[2.1.1]hexanes from heterocyclic olefin coupling partners, namely coumarins, flavones and indoles, is disclosed. Given the increasing importance of bicyclo[2.1.1]hexanes as bioisosteres—groups that convey similar biological properties to those they replace—in pharmaceutical research and considering their limited access 10 , 11 , there remains a need for new synthetic methodologies. Applying this strategy enabled us to extend the intermolecular [2+2]-photocycloadditions to σ -bonds and provides previously inaccessible structural motifs. A strain-release approach, realized by visible-light-mediated triplet energy transfer catalysis, enabled an intermolecular [2 π +2 σ ]-photocycloaddition.

Photocatalytic air purification is a promising technology that mimics nature’s photochemical process, but its practical applications are still limited despite considerable research efforts in recent decades. Here, we briefly discuss the progress and challenges associated with this technology.

Photocatalytic two-electron oxygen reduction to produce high-value hydrogen peroxide (H 2 O 2 ) is gaining popularity as a promising avenue of research. However, structural evolution mechanisms of catalytically active sites in the entire photosynthetic H 2 O 2 system remains unclear and seriously hinders the development of highly-active and stable H 2 O 2 photocatalysts. Herein, we report a high-loading Ni single-atom photocatalyst for efficient H 2 O 2 synthesis in pure water, achieving an apparent quantum yield of 10.9% at 420 nm and a solar-to-chemical conversion efficiency of 0.82%. Importantly, using in situ synchrotron X-ray absorption spectroscopy and Raman spectroscopy we directly observe that initial Ni-N 3 sites dynamically transform into high-valent O 1 -Ni-N 2 sites after O 2 adsorption and further evolve to form a key *OOH intermediate before finally forming HOO-Ni-N 2 . Theoretical calculations and experiments further reveal that the evolution of the active sites structure reduces the formation energy barrier of *OOH and suppresses the O=O bond dissociation, leading to improved H 2 O 2 production activity and selectivity. Here, the authors explore how Ni single-atom sites on carbon nitride evolve under photocatalytic conditions. They show that this evolution plays a pivotal role in enhancing photocatalytic H 2 O 2 production.

Covalent organic frameworks (COFs) are an emerging type of crystalline and porous photocatalysts for hydrogen evolution, however, the overall water splitting activity of COFs is rarely known. In this work, we firstly realized overall water splitting activity of β -ketoamine COFs by systematically engineering N-sites, architecture, and morphology. By in situ incorporating sub-nanometer platinum (Pt) nanoparticles co-catalyst into the pores of COFs nanosheets, both Pt@TpBpy-NS and Pt@TpBpy-2-NS show visible-light-driven overall water splitting activity, with the optimal H 2 and O 2 evolution activities of 9.9 and 4.8 μmol in 5 h for Pt@TpBpy-NS, respectively, and a maximum solar-to-hydrogen efficiency of 0.23%. The crucial factors affecting the activity including N-sites position, nano morphology, and co-catalyst distribution were systematically explored. Further mechanism investigation reveals the tiny diversity of N sites in COFs that induces great differences in electron transfer as well as reaction potential barriers. Covalent organic frameworks (COFs) are an emerging type of crystalline and porous photocatalysts for hydrogen evolution. Here, the authors report a β-ketoamine COF by systematically engineering N-sites, architecture, and morphology for improved water splitting activity.

The active center for the adsorption and activation of carbon dioxide plays a vital role in the conversion and product selectivity of photocatalytic CO 2 reduction. Here, we find multiple metal sulfides CuInSnS 4 octahedral nanocrystal with exposed (1 1 1) plane for the selectively photocatalytic CO 2 reduction to methane. Still, the product is switched to carbon monoxide on the corresponding individual metal sulfides In 2 S 3 , SnS 2 , and Cu 2 S. Unlike the common metal or defects as active sites, the non-metal sulfur atom in CuInSnS 4 is revealed to be the adsorption center for responding to the selectivity of CH 4 products. The carbon atom of CO 2 adsorbed on the electron-poor sulfur atom of CuInSnS 4 is favorable for stabilizing the intermediates and thus promotes the conversion of CO 2 to CH 4 . Both the activity and selectivity of CH 4 products over the pristine CuInSnS 4 nanocrystal can be further improved by the modification of with various co-catalysts to enhance the separation of the photogenerated charge carrier. This work provides a non-metal active site to determine the conversion and selectivity of photocatalytic CO 2 reduction. The product selectivity of photocatalytic carbon dioxide reduction from carbon monoxide to methane is determined by the active center from metal to sulfur site in metal sulfides. Non-metal sulfur in CuInSnS4 octahedral nanocrystal acts as carbon dioxide activation center for switching selectivity to methane.

Constructing photocatalytically active and stable covalent organic frameworks containing both oxidative and reductive reaction centers remain a challenge. In this study, benzotrithiophene-based covalent organic frameworks with spatially separated redox centers are rationally designed for the photocatalytic production of hydrogen peroxide from water and oxygen without sacrificial agents. The triazine-containing framework demonstrates high selectivity for H 2 O 2 photogeneration, with a yield rate of 2111 μM h −1 (21.11 μmol h −1 and 1407 μmol g −1 h −1 ) and a solar-to-chemical conversion efficiency of 0.296%. Codirectional charge transfer and large energetic differences between linkages and linkers are verified in the double donor-acceptor structures of periodic frameworks. The active sites are mainly concentrated on the electron-acceptor fragments near the imine bond, which regulate the electron distribution of adjacent carbon atoms to optimally reduce the Gibbs free energy of O 2 * and OOH* intermediates during the formation of H 2 O 2 . In this study, benzotrithiophene-based covalent organic frameworks with spatially separated oxidative and reductive reaction centers are rationally designed for photocatalytic production of H 2 O 2 from water and oxygen without sacrificial agents.

Achieving CO 2 reduction with H 2 O on metal photocatalysts and understanding the corresponding mechanisms at the molecular level are challenging. Herein, we report that quantum-sized Au nanoparticles can photocatalytically reduce CO 2 to CO with the help of H 2 O by electron-hole pairs mainly originating from interband transitions. Notably, the Au photocatalyst shows a CO production rate of 4.73 mmol g −1 h −1 (~100% selectivity), ~2.5 times the rate during CO 2 reduction with H 2 under the same experimental conditions, under low-intensity irradiation at 420 nm. Theoretical and experimental studies reveal that the increased activity is induced by surface Au–O species formed from H 2 O decomposition, which synchronously optimizes the rate-determining steps in the CO 2 reduction and H 2 O oxidation reactions, lowers the energy barriers for the *CO desorption and *OOH formation, and facilitates CO and O 2 production. Our findings provide an in-depth mechanistic understanding for designing active metal photocatalysts for efficient CO 2 reduction with H 2 O. While plasmonic metals show some activity for photocatalysis, they often must be paired with semiconductors or sacrificial reagents. Here, authors find quantum-sized Au nanoparticles can achieve photocatalytic CO 2 -to-CO conversion with H 2 O by charge carriers generated from interband transitions.