Reducing the size of metal nanoparticle (NP) cocatalyst down to single-atom level to improve photocatalytic efficiency is inevitably accompanied by the changes of its coordination environment, geometric configuration, electronic structure and active site. Thus, the construction of single metal atom (SA) photocatalyst is not necessarily a panacea for activity improvement toward target catalytic reactions. Herein, we report a critical and benchmark comparison in a reasonable framework of ZnIn2S4/Pt 2 S 4 /Pt NP (ZIS/Pt NP) and ZnIn2S4/Pt 2 S 4 /Pt SA (ZIS/Pt SA) towards photocatalytic hydrogen (H2) 2 ) evolution, aiming to demonstrate which is better between Pt NP and Pt SA as cocatalyst in boosting photoredox catalysis. Mechanism study proves that the higher charge separation/ transfer and weaker H* adsorption strength over ZIS/Pt NP than ZIS/Pt SA promote the more effective reduction of protons to H2, 2 , leading to the higher activity of ZIS/Pt NP than ZIS/Pt SA. Our work is expected to timely inspire the critical and rational thinking on the function and intrinsic mechanism of SA and NP cocatalysts in enhancing the photoredox catalysis performance.

The precise design of the charge carrier relay channel and active sites of semiconductor-based photocatalysts is highly crucial for target selective photoredox synthesis. In this context, we report an atomic-level catalyst design strategy based on depositing Pt single atoms (SAs) onto Cu-doped ultrathin cadmium sulfide nanosheets (CdS/Cu/Pt) to enable an optimized band structure, a directional charge transfer channel, and favorable catalytic sites for efficient and selective dehydrocoupling of amines to imines and hydrogen (H2). The Cu dopant acts as a unique electron bridge to construct a directional Cu-Pt electron transfer channel with the assistance of atomically dispersed Pt sites, thereby promoting charge separation and transfer kinetics. The introduction of Pt SAs not only facilitates the H2 generation by decreasing the overpotential of proton reduction but also improves the selectivity of imines synthesis because the weak adsorption of imines on Pt SAs prevents further hydrogenation of imines to secondary amines. This work is anticipated to inspire a further rational design of semiconductor-based photocatalysts with atomic precision for the coproduction of renewable fuels and value-added fine chemicals.

Coupling photocatalytic hydrogen (H-2) evolution with selective organic synthesis in one redox cycle showcases great potential for the coinstantaneous utilization of photoexcited electrons and holes toward sustainable production of value-added fuels and chemicals. Herein, we construct one-dimensional/two-dimensional (1D/2D) WO3/ZnIn2S4 (WO3/ZIS) hierarchical Z-scheme composites for bifunctional integrated light-driven H-2 production and biomass-derived aromatic alcohol conversion. The superior photoactivity and selectivity over WO3/ZIS composites compared with that over bare WO3 nanorods (NRs) and ZIS nanosheets (NSs) can be attributed to the assembly of the Z-scheme heterostructure. The construction of WO3/ZIS direct Z-scheme composites not only facilitates the charge separation dynamics by transporting photoinduced electrons and holes to spatially separated redox sites but also steers the selectivity of targeted products by tuning the energy band potentials to endow electrons and holes with stronger reduction and oxidation abilities. The mechanistic studies combining the control experiments and electron paramagnetic resonance spectroscopy validate the free radical mechanism of the benzyl alcohol photooxidation reaction. It is anticipated that this work would offer a conducive paradigm for the ingenious design of high-performance Z-scheme heterostructured catalysts toward the solar light-driven collaborative redox of H-2 production and selective organic synthesis.

Graphene (GR), a single-layer carbon sheet with a hexagonal packed lattice structure, has displayed attractive potential and demonstrably become the research focus in artificial photocatalysis due to its enchanting properties in enhancing light absorption, electron transfer dynamics, and surface reactions. Currently, numerous efforts have shown that the properties of GR, which are closely correlated to the photocatalytic performance of GR-based composites are significantly affected by the synthesis methods. Herein, we first introduce the optimization strategies of GR-based hybrids and then elaborate the synthesis of GR-based composite photocatalysts oriented by manifold roles of GR in photoredox catalysis, containing photoelectron mediator and acceptor, improving adsorption capacity, regulating light absorption range and intensity, as well as macromolecular photosensitizer. Beyond that, a brief outlook on the challenges in this burgeoning research field and potential evolution strategies for enhancing the photoactivity of GR-based hybrids is presented and we anticipate that this review could provide some enlightenments for the rational construction and application of multifunctional GR-based composite photocatalysts.

Owing to the simultaneous utilization of photogenerated electrons and holes, coupling light-driven hydrogen (H2) evolution reaction (HER) and biomass-derived alcohol conversion reactions in one photoredox cycle has aroused many interests for the coproduction of valuable chemical products and renewable fuels. In this study, a facile photochemical reduction approach has been used to decorate MoS2 cocatalyst on ZnIn2S4 nanoflowers (NFs) for photocatalytic coupling reactions of selective benzyl alcohol (BA) oxidation and HER. The results reveal that 1%MoS2/ZnIn2S4 composite photocatalyst displays the best visible-light-induced photoactivity for BA conversion (3.69 mmol g−1 h−1) and H2 evolution (3.88 mmol g−1 h−1), exhibiting 6 times as high as the photoactivity over bare ZnIn2S4. The MoS2 cocatalyst markedly improves charge separation and mitigates the overpotential of HER, thereby accelerating H2 production kinetics for the coproduction reactions. The photoreduction of Cr (VI) and 4-nitroaniline (4-NA) is also investigated to verify the universality of MoS2 as high-performance cocatalyst. The carbon-centered radical is identified in BA conversion over MoS2/ZnIn2S4 composite photocatalyst. This work could contribute to the rational construction of ZnIn2S4-based cooperative photoredox-catalyzed system toward efficient coproduction of value-added fine chemicals and clean fuels.

Utilizing photocatalytic technology to reduce water or carbon dioxide to solar fuels and to selectively or non-selectively oxidize organics to their respective target products, is a promising and sustainable way to increase the supply of energy and chemical feedstocks, reduce greenhouse gas emissions, and solve environmental pollution. However, photoredox reaction proceeding efficiently and stably is often a challenge in the absence of scavengers. A recent development surge is integrating solar fuels production and organic oxidation into a light-driven photoredox system, so as to realize the simultaneous utilization of electrons and holes, which is desirable from the consideration of economic benefits of photocatalytic technology application. In this review, we briefly recap the recent advances concerning dual-function cooperative photoredox catalytic systems integrating solar fuels production with organic oxidation. Firstly, the dual-functional reaction systems combining hydrogen production and organic oxidation are discussed, which includes hydrogen evolution coupled with non-selective organic oxidation to degrade pollutants, and hydrogen evolution integrated with selective organic conversion to produce value-added chemicals. After that, we discuss the emerging system combining carbon dioxide reduction and organic conversion. Finally, we cast a personal prospect on the opportunities and challenges for the future development of this booming and cooperative dual-function photoredox catalysis field.

The fabrication of efficient catalysts to reduce nitrogen (N2) to ammonia (NH3) is a significant challenge for artificial N2 fixation under mild conditions. In this work, we demonstrated that the simultaneous introduction of oxygen vacancies (OVs) and Mo dopants into Bi5O7Br nanosheets can significantly increase the activity for photocatalytic N2 fixation. The 1 mol% Mo-doped Bi5O7Br nanosheets exhibited an optimal NH3 generation rate of 122.9 μmol g−1 h−1 and durable stability, which is attributed to their optimized conduction band position, suitable absorption edge, large number of light-switchable OVs, and improved charge carrier separation. This work provides a promising approach to design photocatalysts with light-switchable OVs for N2 reduction to NH3 under mild conditions, highlighting the wide application scope of nanostructured BiOBr-based photocatalysts as effective N2 fixation systems.

Semiconductor photocatalysis is considered as a cutting-edge research topic for the production of value-added fuels and chemicals to confront the global energy crisis. In order to improve the solar-to-chemical conversion efficiency of pristine semiconductors, combining them with cocatalysts to form heterostructures has been extensively investigated. Among studied formulations, bimetallic nanoparticles (NPs), featuring enhanced light harvesting, efficient capture of photogenerated electrons and abundant surface active sites are ideal cocatalysts to improve the photocatalytic performance of semiconductor-based photocatalysts. In this review, we begin with a concise overview of representative synthesis and characterization methods of bimetallic NPs. Then, we predominantly summarize the typical applications of semiconductor/bimetallic NPs-based composites in photoredox catalysis, including hydrogen evolution, carbon dioxide reduction, selective organic synthesis and environmental remediation. In particular, we highlight the regulatory effects of parameters of bimetallic NPs (composition, structure, morphology, size, atomic arrangement, loading position, etc.) on the photocatalytic activity and selectivity. Finally, the remaining challenges and future perspectives for the utilization of bimetallic NPs in photoredox catalysis are discussed and anticipated to stimulate the sparkling ideas in the construction of high-efficiency semiconductor/bimetallic NPs-based photocatalytic systems.

Solar-driven syngas production by CO2 reduction provides a sustainable strategy to produce renewable feedstocks. However, this promising reaction often suffers from tough CO2 activation, sluggish oxidative half-reaction kinetics and undesired by-products. Herein, we report a function-oriented strategy of deliberately constructing black phosphorus quantum dots-ZnIn2 S4 (BP/ZIS) heterostructures for solar-driven CO2 reduction to syngas, paired with selectively oxidative C-N bond formation, in one redox cycle. The optimal BP/ZIS heterostructure features the enhanced charge-carrier separation and enriched active sites for cooperatively photocatalytic syngas production with a tunable ratio of CO/H2 and efficient oxidation of amines to imines with high conversion and selectivity. This prominent catalytic performance arises from the efficient electronic coupling between black phosphorus quantum dots and ZnIn2 S4 , as well as the optimized adsorption strength for key reaction intermediates, as supported by both experimental and theoretical investigations. We also demonstrate a synergistic interplay between CO2 reduction and amine dehydrogenation oxidation, rather than simply collecting these two single half-reactions in this dual-functional photoredox system.

Harnessing solar power to convert carbon dioxide (CO2) into fuels is a crucial channel to alleviate the global energy shortage and environment pollution. Photothermal catalytic conversion of CO2 into value-added fuels or chemicals, e.g., carbon monoxide (CO), methane (CH4), and methanol (CH3OH), offers an effective, economical, and eco-friendly solution to obtain “sunshine” feedstocks by coupling renewable solar energy with heat energy. In this review, we begin by briefly describing the fundamentals for photothermal catalytic CO2 reduction. Subsequently, we summarize the types of nanocatalysts for photothermal catalysis and their design strategies, where we propose two major photothermal catalytic mechanisms based on semiconductors and plasmonic metals, followed by three key design strategies of nanomaterials for photothermal catalytic CO2 reduction. Then, we expatiate the recent typical applications of photothermal catalytic CO2 reduction. Finally, we present our vision of the future developments and challenges in this exciting research field.

Achieving substantial light harvesting typically in visible light region is crucial to further improve the performance and their practical applications of photocatalysts in solar energy utilization. Recently, enormous attention has been paid to the gold (Au) clusters in the field of photocatalysis because they are a unique type of novel visible photosensitizer and catalytic center. So far, a wide variety of Au clusters-based photocatalysts have been designed to drive diverse photoredox reactions under light irradiation with suitable wavelengths. The special focus of this minireview is on overviewing various applications of Au clusters-based composites in heterogeneous photocatalysis with selected recent representative examples. Subsequently, the latest advances about the strategies for improving the photostability of Au clusters are elaborated. At last, we end with casting a personal prospect on the possible opportunities and challenges for future development of Au clusters-based photocatalysis. Graphic abstract

Artificial photocatalytic N-2 reduction to NH3 under ambient conditions represents a promising alternative way for the industrial N-2 fixation by Haber - Bosch process. This work reports the simultaneous engineering of BiOBr nanosheets with exposed {102} facets by means of transition metal (Fe, Mo, Ni) doping and oxygen vacancies (OVs) that aid to expose internal metal dopants toward efficient visible light N-2 fixation. The synergy of transition metal doping and OVs results in the modulated band structures, improved charge carrier separation as well as electron transfer to N-2, thereby leading to enhanced N-2 adsorption and activation ability over modified BiOBr nanosheets. In particular, the Fe-doped BiOBr with OVs possesses the optimal photocatalytic activity of NH3 yield of 46.1 mu mol g(-1) h(-1) without any sacrificial agent, which is 6-fold that of pristine BiOBr. The findings will shed new light on rational engineering of adsorption, activation sites and charge carrier separation for designing efficient N-2 fixation photocatalysts.

Graphene oxide (GO) has been widely utilized as the precursor of graphene (GR) to fabricate GR-based hybrid photocatalysts for solar-to-chemical energy conversion. However, until now, the properties and roles that GO played in heterogeneous photocatalysis have remained relatively elusive. In this Review, we start with a brief discussion of synthesis and structure of GO. Then, the photocatalysis-related properties of GO, including electrical conductivity, surface chemistry, dispersibility, and semiconductor properties, are concisely summarized. In particular, we have highlighted the fundamental multifaceted roles of GO in heterogeneous photocatalysis, which contain the precursor of GR, cross-linked framework for constructing aerogel photocatalyst, macromolecular surfactant, two-dimensional growth template, and photocatalyst by itself. Furthermore, the future prospects and remaining challenges on developing effective GO-derived hybrid photocatalysts are presented, which is expected to inspire further research into this promising research domain.

Highly-efficient oxygen evolution reaction (OER) and reduction of carbon dioxide (CO2RR) represent the two biggest scientific challenges in artificial photosynthesis. Many efficient and cost-affordable electrocatalysts have been reported in the development of electrochemical OER and CO2RR; however, during the electro-derived oxidation or reduction processes, a critical fact that, most catalysts tend to undergo structural reconstruction and/or surface rearrangement, has been widely observed, which greatly subverts the traditional conception of "catalysts". In this respect, the research trends have gradually transferred from optimizing catalyst materials to elucidating the real active sites of the catalysts as well as understanding the underlying mechanisms behind these complex reactions. Most importantly, the in situ/operando characterization techniques are powerful tools to achieve this goal. Herein, recent advances in the in situ X-ray diffraction and absorption spectroscopy that have provided a unique opportunity to investigate the structural reconstruction and/or surface rearrangement of catalysts under realistic OER and CO2RR conditions are thoroughly reviewed. Finally, the challenges of the material design are discussed, and the future perspective for developing next-generation catalysts with imperative requirements of material nature is provided.

Artificial CO2 photoreduction to solar fuels represents an ecofriendly and sustainable solution to obtain "sunshine" feedstocks by using renewable energy media. Herein, we report that single cobalt atoms anchored on two-dimensional Ti3C2Tx-MXene nano-sheets act as an efficient photocatalytic ensemble for visible-light CO2 reduction, wherein the Ti3C2Tx nanosheets bridge visible-light absorbers (ruthenium complex) with cobalt active sites. The single cobalt atoms build strong interactions with Ti(3)C(2)T(x )by forming metal-oxygen/carbon bonds, resulting in the formation of the Co-Ti3C2Tx ensemble. As a result, the production rate of CO reaches a high value of 6.06 mmol h(-1) g(-1) over the optimal Co-Ti3C2Tx which markedly exceeds previous MXene-based catalysts for CO2 photoreduction. Theoretical calculation manifests that the isolated Co atoms coordinated with Ti3C2Tx can effectively facilitate the generation of CO. This work may provide a new line of thought into the rational design of high-activity MXene-based photocatalysts toward artificial CO2 conversion.

The photocatalytic coupling reaction can be conducted in one pot to realize the simultaneous utilization of electrons and holes, thereby obtaining value-added fine chemicals and fuels. Herein, we report a binary nickel modified ZnIn2S4 (Ni:ZIS) for highly efficient photocatalytic selective oxidation of benzyl alcohol (BA) to benzaldehyde (BAD) integrated with hydrogen (H-2) evolution, in which Ni can promote photogenerated charge transfer for enhancing photoactivity. Particularly, the products of converting BA to aromatic compounds over blank ZnIn2S4 (ZIS) and Ni:ZIS show a marked difference under the same reaction conditions. Hydrobenzoin (HB) is the primary product over blank ZIS. After the introduction of Ni, the formation of HB is dramatically suppressed, resulting in higher selectivity of BAD, because the introduction of Ni facilitates the alpha-H abstraction. In addition, an analogous phenomenon has been observed on Ni-based compounds modified ZIS, such as NixP and NiS. It is hoped that this work would provide a feasible paradigm for modifying the surface of photocatalysts to tune the selectivity of product-oriented alcohols oxidation coupled with H-2 evolution in water.

Incorporating different materials, such as metal sulfides, with metal-organic frameworks (MOFs) to develop MOF-based multifunctional composites with enhanced performance is an important area of research. However, the intrinsically high interfacial energy barrier significantly restricts the heterogeneous nucleation and nanoassembly of metal sulfides onto MOFs during the wet chemistry synthesis process. Herein, taking advantage of the natural tailorability of MOFs, the precise and controllable growth of metal sulfide nanoparticles (NPs) (CdS, ZnS, CuS and Ag2S) at the coordinatively unsaturated metal sites (CUSs) of MOFs to form MOF@metal sulfide composites under mild conditions is achieved via a cysteamine-assisted coordination-driven route. During the process, the molecular linker of cysteamine, possessing one amino group for chelating with the CUSs of the MOF and one thiol group as a docking site to anchor metal ions, plays a prominent role in enhancing interfacial interactions between the MOF and metal ions. The subsequent S2- anion exchange process leads to intimate surface-attached nucleation and epitaxial growth of metal sulfide NPs on the surface of the MOF. The as-formed composites exhibit enhanced charge separation and transfer capability, and thus boost photocatalytic performance. This general and simple approach provides a new avenue for the design of MOF-metal sulfide hybrids.

Carbonaceous materials (CMs), such as carbon nanotubes, fullerenes, graphene, carbon quantum dots, graphdiyne, and their derivatives, have sparked enormous excitement because of their attractive properties and great potential for solar energy conversion applications. Although pristine CMs are known for their unique electronic structure, optical properties, and thermal conductivity, many research fields and applications require functionalized CMs with integrated physicochemical properties and tunable dimensionality. Structurally modifying CMs through various surface/interface engineering reveals the numerous possibilities for tuning their architectures and properties. This Review mainly focuses on the basic surface/interface engineering issues of diverse CMs. The effects of surface/interfacial engineering in versatile systems as well as the excellent mechanical, electronic, optical properties and applications of the functionalized CMs‐based composites are highlighted. Some ongoing challenges and possible solutions for future exploration of CMs‐based functional composites are critically discussed.

The performance of transition metal hydroxides, as cocatalysts for CO2 photoreduction, is significantly limited by their inherent weaknesses of poor conductivity and stacked structure. Herein, we report the rational assembly of a series of transition metal hydroxides on graphene to act as a cocatalyst ensemble for efficient CO2 photoreduction. In particular, with the Ru-dye as visible light photosensitizer, hierarchical Ni(OH)2 nanosheet arrays-graphene (Ni(OH)2-GR) composites exhibit superior photoactivity and selectivity, which remarkably surpass other counterparts and most of analogous hybrid photocatalyst system. The origin of such superior performance of Ni(OH)2-GR is attributed to its appropriate synergy on the enhanced adsorption of CO2, increased active sites for CO2 reduction and improved charge carriers separation/transfer. This work is anticipated to spur rationally designing efficient earth-abundant transition metal hydroxides-based cocatalysts on graphene and other two-dimension platforms for artificial reduction of CO2 to solar chemicals and fuels.

Harvesting solar energy to drive highly efficient photocatalytic conversion of renewable biomass and its derivatives to value-added chemicals with the concomitant formation of hydrogen (H2) is a green and promising strategy to cope with the global energy dilemma. In this context, we have reported the facile assembly of uniformly distributed CdS nanoparticles (NPs) on the two-dimensional (2D) platform of Ti3C2Tx MXene nanosheets (NSs) via a low-temperature wet chemistry process, during which tight interfacial contact between CdS and Ti3C2Tx has been realized. The Ti3C2Tx/CdS composites feature remarkable enhancement in the aqueous-phase photoredox conversion of furfural alcohol to furfural and H2 by simultaneously utilizing photoexcited holes and electrons. Mechanistic studies reveal that the Ti3C2Tx MXene acts as an “electron sink” to capture the electrons generated from CdS and the close interfacial connection expedites the separation and transport of photoexcited charge carriers, thereby accelerating the photocatalytic performance of the Ti3C2Tx/CdS composites. We anticipate that this work would provide an instructive paradigm for further rational design of MXene/semiconductor hybrids for photoredox-catalyzed production of value-added products and H2 from biomass intermediates.