Photoimmobilized Ni Clusters Boost Photodehydrogenative Coupling of Amines to Imines via Enhanced Hydrogen Evolution Kinetics

Specific Photocatalytic C-C Coupling of Benzyl Alcohol to Deoxybenzoin or Benzoin by Precise Control of Cα-H Bond Activation or O-H Bond Activation by Adjusting the Adsorption Orientation of Hydrobenzoin Intermediates

Benzyl alcohol (BA) is a major biomass derivative and can be further converted into deoxybenzoin (DOB) and benzoin (BZ) as high-value products for industrial applications through photocatalytic C-C coupling reaction. The photocatalytic process contains two reaction steps, which are (1) the C-C coupling of BA to hydrobenzoin (HB) intermediates and (2) either dehydration of HB to DOB or dehydrogenation of HB to BZ. We found that generation of DOB or BZ is mainly determined by the activation of Cα-H or O-H bonds in HB. In this study, phase junction CdS photocatalysts and Ni/CdS photocatalysts were elaborately designed to precisely control the activation of Cα-H or O-H bonds in HB by adjusting the adsorption orientation of HB on the photocatalyst surfaces. After orienting the Cα-H groups in HB on the CdS surfaces, the Cα-H bond dissociation energy (BDE) at 1.39 eV is lower than the BDE of the O-H bond at 2.69 eV, therefore improving the selectivity of the DOB. Conversely, on Ni/CdS photocatalysts, the O-H groups in HB orient toward the photocatalyst surfaces. The BDE of the O-H bonds is 1.11 eV to form BZ, which is lower than the BDE of the Cα-H bonds to the DOB (1.33 eV), thereby enhancing the selectivity of BZ. As a result, CdS photocatalysts can achieve complete conversion of BA to 80.4% of the DOB after 9 h of visible light irradiation, while 0.3% Ni/CdS photocatalysts promote complete conversion of BA to 81.5% of BZ after only 5 h. This work provides a promising strategy in selective conversion of BA to either DOB or BZ through delicate design of photocatalysts.

Incorporation of Pd Single-Atom Sites in Perovskite with an Excellent Selectivity toward Photocatalytic Semihydrogenation of Alkynes

Semihydrogenation is a crucial industrial process. Noble metals such as Pd have been extensively studied in semihydrogenation reactions, owing to their unique catalytic activity toward hydrogen activation. However, the overhydrogenation of alkenes to alkanes often happens due to the rather strong adsorption of alkenes on Pd active phases. Herein, we demonstrate that the incorporation of Pd active phases as single-atom sites in perovskite lattices such as SrTiO3 can greatly alternate the electronic structure and coordination environment of Pd active phases to facilitate the desorption of alkenes rather than further hydrogenation. Furthermore, the incorporated Pd sites can be well stabilized without sintering by a strong host-guest interaction with SrTiO3 during the activation of H species in hydrogenation reactions. As a result, the Pd incorporated SrTiO3 (Pd-SrTiO3) exhibits an excellent time-independent selectivity (>99.9 %) and robust durability for the photocatalytic semihydrogenation of phenylacetylene to styrene. This strategy based on incorporation of active phases in perovskite lattices will have broad implications in the development of high-performance photocatalysts for selective hydrogenation reactions.

Synthetic Chemistry in Flow: From Photolysis & Homogeneous Photocatalysis to Heterogeneous Photocatalysis

Photocatalytic synthesis of value-added chemicals has gained increasing attention in recent years owing to its versatility in driving many important reactions under ambient conditions. Selective hydrogenation, oxidation, coupling, and halogenation with a high conversion of the reactants have been realized using designed photocatalysts in batch reactors with small volumes at a laboratory scale; however, scaling-up remains a critical challenge due to inefficient utilization of incident light and active sites of the photocatalysts, resulting in poor catalytic performance that hinders its practical applications. Flow systems are considered one of the solutions for practical applications of light-driven reactions and have experienced great success in photolytic and homogeneous photocatalysis, yet their applications in heterogeneous photocatalysis are still under development. In this perspective, we have summarized recent progress in photolytic and photocatalytic synthetic chemistry performed in flow systems from the view of reactor design with a special focus on heterogeneous photocatalysis. The advantages and limitations of different flow systems, as well as some practical considerations of design strategies are discussed.

Hollow structured CdS@ZnIn2S4 Z-scheme heterojunction for bifunctional photocatalytic hydrogen evolution and selective benzylamine oxidation

Photocatalytic hydrogen evolution (PHE) is frequently constrained by inadequate light utilization and the rapid combination rate of the photogenerated electron-hole pairs. Additionally, conventional PHE processes are often facilitated by the addition of sacrificial reagents to consume photo-induced holes, which makes this approach economically unfavorable. Herein, we designed a spatially separated bifunctional cocatalyst decorated Z-scheme heterojunction of hollow structured CdS (HCdS) @ZnIn2S4 (ZIS), which was prepared by a sacrificial hard template method followed by photo-deposition. Consequently, PdOx@HCdS@ZIS@Pt exhibited efficient PHE (86.38 mmol·g-1·h-1) and benzylamine (BA) oxidation coupling (164.75 mmol·g-1·h-1) with high selectivity (97.34 %). The unique hollow core-shelled morphology and bifunctional cocatalyst loading in this work hold great potential for the design and synthesis of bifunctional Z-scheme photocatalysts.

P-N Heterojunction Embedded CuS/TiO2 Bifunctional Photocatalyst for Synchronous Hydrogen Production and Benzylamine Conversion

The coupling of photocatalytic hydrogen production and selective oxidation of benzylamine is a topic of significant research interest. However, enhancing the bifunctional photocatalytic activity in this context is still a major challenge. The construction of Z-scheme heterojunctions is an effective strategy to enhance the activity of bifunctional photocatalysts. Herein, a p-n type direct Z-scheme heterojunction CuS/TiO2 is constructed using metal-organic framework (MOF)-derived TiO2 as a substrate. The carrier density is measured by Mott-Schottky under photoexcitation, which confirms that the Z-scheme electron transfer mode of CuS/TiO2 is driven by the diffusion effect caused by the carrier concentration difference. Benefiting from efficient charge separation and transfer, photogenerated electrons, and holes are directedly transferred to active oxidation and reduction sites. CuS/TiO2 also exhibits excellent bifunctional photocatalytic activity without noble metal cocatalysts. Among them, the H2 evolution activity of the CuS/TiO2 is found to be 17.1 and 29.5 times higher than that of TiO2 and CuS, respectively. Additionally, the yields of N-Benzylidenebenzylamine (NBB) are 14.3 and 47.4 times higher than those of TiO2 and CuS, respectively.

Accurate assembly of thiophene-bridged titanium-oxo clusters with photocatalytic amine oxidation activity

Designing and synthesizing well-defined crystalline catalysts for the photocatalytic oxidative coupling of amines to imines remains a great challenge. In this work, a crystalline dumbbell-shaped titanium oxo cluster, [Ti10O6(Thdc)(Dmg)2(iPrO)22] (Ti10, Thdc = 2,5-thiophenedicarboxylic acid, Dmg = dimethylglyoxime, iPrOH = isopropanol), was constructed through a facile one-pot solvothermal strategy and treated as a catalyst for the photocatalytic oxidative coupling of amines. In this structure, Thdc serves as the horizontal bar, while the {Ti5Dmg} layers on each side act as the weight plates. The molecular structure, light absorption, and photoelectrochemical properties of Ti10 were systematically investigated. Remarkably, the inclusion of the Thdc ligand, with the assistance of the Dmg ligand, broadens the light absorption spectrum of Ti10, extending it into the visible range. Furthermore, the effective enhancement of charge transfer within the Ti10 was achieved with the successful incorporation of the Thdc ligand, as opposed to PTC-211, where terephthalic acid replaces the Thdc ligand, while maintaining consistency in other aspects of Ti10. Building on this foundation, Ti10 was employed as a heterogeneous molecular photocatalyst for the catalytic oxidative coupling reaction of benzylamine (BA), demonstrating very high conversion activity and selectivity. Our study illustrates that the inclusion of ligands derived from Thdc enhances the efficiency of charge transfer in functionalized photocatalysts, significantly influencing the performance of photocatalytic organic conversion.

Rational design of bimetallic sites in covalent organic frameworks for efficient photocatalytic oxidative coupling of amines

The conversion of organic compounds by photocatalysis under mild conditions is an environment-friendly alternative for organic transformations. In this work, the bimetallic covalent organic framework coordinated by Sr2+ and Fe2+ in the porphyrin centers with molar ratio of 2:1 (COF-Sr2Fe1) was synthesized through a two-step reaction. Under the synergistic regulation of Sr2+ and Fe2+, the separation of photogenerated charges and visible light absorption for COF-Sr2Fe1 were significantly promoted, and thus COF-Sr2Fe1 exhibited efficient photocatalytic performance towards benzylamine oxidative coupling reaction with a yield of 97 %, much higher than that of the nonmetallic covalent organic framework COF-366. Moreover, it was found that the Fe site displayed higher dehydrogenation ability and the Sr site displayed higher CN coupling ability through the density functional theory (DFT) calculations, thereby making the dehydrogenation and CN coupling steps more controllable for benzylamine oxidative coupling reaction by COF-Sr2Fe1. This work provides a strategy for designing efficient covalent organic frameworks photocatalysts, and helps to understand the oxidative coupling of amines more deeply.

Nanoscale Metal Particle Modified Single-Atom Catalyst: Synthesis, Characterization, and Application

Single-atom catalysts (SACs) have attracted considerable attention in heterogeneous catalysis because of their well-defined active sites, maximum atomic utilization efficiency, and unique unsaturated coordinated structures. However, their effectiveness is limited to reactions requiring active sites containing multiple metal atoms. Furthermore, the loading amounts of single-atom sites must be restricted to prevent aggregation, which can adversely affect the catalytic performance despite the high activity of the individual atoms. The introduction of nanoscale metal particles (NMPs) into SACs (NMP-SACs) has proven to be an efficient approach for improving their catalytic performance. A comprehensive review is urgently needed to systematically introduce the synthesis, characterization, and application of NMP-SACs and the mechanisms behind their superior catalytic performance. This review first presents and classifies the different mechanisms through which NMPs enhance the performance of SACs. It then summarizes the currently reported synthetic strategies and state-of-the-art characterization techniques of NMP-SACs. Moreover, their application in electro/thermo/photocatalysis, and the reasons for their superior performance are discussed. Finally, the challenges and perspectives of NMP-SACs for the future design of advanced catalysts are addressed.

Electronic configuration inversion in CdIn2S4 for efficient photocatalytic hydrogen peroxide generation coupled with selective benzylamine oxidation

Vacancies engineering has sparked a huge interest in enhancing photocatalytic activity, but monovacancy simultaneously conducts as either electron or hole acceptor and redox reaction, worsening charge transfer and catalytic performance. Here, the concept of electronic inversion has been proposed through the simultaneous introduction of surface oxygen and S vacancies in CdIn2S4 (OSv-CIS). Consequently, under mild conditions, the well-designed OSv-CIS-200 demonstrated a strong rate of N-benzylidenebenzylamine production (2972.07 µmol g-1 h-1) coupled with Hydrogen peroxide (H2O2) synthesis (2362.33 µmol g-1 h-1) (PIH), which is 12.4 times higher than that of CdIn2S4. Density functional theory (DFT) simulation and characterization studies demonstrate that oxygen is introduced into the lattice on the surface of the material, reversing the charge distribution of the S vacancy and enhancing the polarity of the total charge distribution. It not only provides a huge built-in electric field (BEF) for guiding the orientation of the charge transfer, but also acts as a long-distance active site to accelerate reaction and prevent H2O2 decomposition. Our work offers a straightforward connection between the atomic defect and intrinsic properties for designing high-efficiency materials.

Versatile synthesis of nano-icosapods via cation exchange for effective photocatalytic conversion of biomass-relevant alcohols

Branched metal chalcogenide nanostructures with well-defined composition and configuration are appealing photocatalysts for solar-driven organic transformations. However, precise design and controlled synthesis of such nanostructures still remain a great challenge. Herein, we report the construction of a variety of highly symmetrical metal sulfides and heterostructured icosapods based on them, in which twenty branches were radially grown in spatially ordered arrangement, with a high degree of structure homogeneity. Impressively, the as-obtained CdS-PdxS icosapods manifest a significantly improved photocatalytic activity for the selective oxidation of biomass-relevant alcohols into corresponding aldehydes coupled with H2 evolution under visible-light irradiation (>420 nm), and the apparent quantum yield of the benzyl alcohol reforming can be achieved as high as 31.4% at 420 nm. The photoreforming process over the CdS-PdxS icosapods is found to be directly triggered by the photogenerated electrons and holes without participation of radicals. The enhanced photocatalytic performance is attributed to the fast charge separation and abundant active sites originating from the well-defined configuration and spatial organization of the components in the branched heterostructures.

Surface anchoring of nickel sulfide clusters as active sites and cocatalysts for photocatalytic antibiotic degradation and bacterial inactivation

Achieving photocatalytic antibiotic degradation and bacterial inactivation with high efficiency remains a challenging mission to originate a clean environment. In this work, ultra-small NiS clusters were in-situ grew on photoactive ZnIn₂S₄ nanoflower supports to form a NiS/ZnIn₂S₄ heterojunction, in which a strong and surface-limited binding was formed between the NiS clusters and ZnIn₂S₄ supports. The in-situ formed NiS clusters not only appeased interfacial charge transfer resistance of the heterojunction but also eventuated a strong built-in electric field, resulting a fast electron migration from ZnIn₂S₄ to NiS clusters functioned as cocatalyst and active sites to boost the separation efficiency of photogenerated carriers. As a result, the optimal 2NiS/ZnIn₂S₄ heterojunction expressed a higher photocatalytic Escherichia inactivation activity (99.23 % for 3 h) and a raised antibiotic degradation performance, including tetracycline (60 % for 20 min), ofloxacin (62 % for 20 min), oxytetracycline (63 % for 20 min) compared to that of pure ZnIn₂S₄ (39.14 % for Escherichia inactivation and 44 % for tetracycline degradation). This work furnishes a great promise to develop inorganic clusters coupled photocatalysts for light-driven environmental application.

Alternatives to water oxidation in the photocatalytic water splitting reaction for solar hydrogen production

The photocatalytic water splitting process to produce H₂ is an attractive approach to meet energy demands while achieving carbon emission reduction targets. However, none of the current photocatalytic devices meets the criteria for practical sustainable H₂ production due to their insufficient efficiency and the resulting high H₂ cost. Economic viability may be achieved by simultaneously producing more valuable products than O₂ or integrating with reforming processes of real waste streams, such as plastic and food waste. Research over the past decade has begun to investigate the possibility of replacing water oxidation with more kinetically and thermodynamically facile oxidation reactions. We summarize how various alternative photo-oxidation reactions can be combined with proton reduction in photocatalysis to achieve chemical valorization with concurrent H₂ production. By examining the current advantages and challenges of these oxidation reactions, we intend to demonstrate that these technologies would contribute to providing H₂ energy, while also producing high-value chemicals for a sustainable chemical industry and eliminating waste.

Enhanced Photocatalytic Activity of Hyper-Cross-Linked Polymers Toward Amines Oxidation Coupled with H2 O2 Generation through Extending Monomer's Conjugation Degree

Visible-light-driven amines oxidation coupled with hydrogen peroxide (H₂ O₂ ) generation is a promising way to convert solar energy to chemical energy. Herein, a series of hyper-cross-linked polymers (HCPs) photocatalysts with different arenes monomers, including benzene (BE), diphenyl (DP), p-terphenyl (TP), or p-quaterphenyl (QP), were synthesized by simple Friedel-Crafts alkylation reaction. Owing to the maximum monomer's conjunction degree and excellent oxygen (O₂ ) adsorption capacity, QP-HCPs exhibited highest photocatalytic activity for benzylamine oxidation coupled with H₂ O₂ generation under the irradiation of 455 nm Blue LED lamp. More than 99 % of benzylamine could be converted to N-benzylidenebenzylamine within 60 min. In addition, nearly stoichiometric H₂ O₂ was synchronously obtained with a high production rate of 9.3 mmol g_cat ^-1 h^-1 . Our work not only demonstrated that the photocatalytic activity of HCPs photocatalysts significantly depends on monomer's conjunction degree, but also provided a new strategy for converting solar energy to chemical energy.

Photocatalytic co-production of hydrogen gas and N-benzylidenebenzylamine over high-quality 2D layered In4/3P2Se6 nanosheets

The concurrent photocatalytic synthesis of hydrogen gas and high-valued chemicals over two-dimensional semiconductors is extremely attractive to alleviate global energy and environmental concerns through directly using sunlight. Herein, a novel layered In_4/3P₂Se₆ nanosheet is synthesized by a space confined chemical vapor conversion method, and it acts as a dual-functional photocatalyst to deliver the co-production of hydrogen gas and N-benzylidenebenzylamine from water reduction and selective benzylamine oxidation. The simultaneous yield of hydrogen gas and N-benzylidenebenzylamine is 895 μmol g^-1 and 681 μmol g^-1, respectively, within 16-hour continuous reaction involving a small amount of water in acetonitrile solvent. Moreover, 97.4% N-benzylidenebenzylamine selectivity from benzylamine oxidation can be achieved with continuous 10 hour-reaction only in acetonitrile solvent under ambient conditions. Further in situ electron paramagnetic resonance measurements and reaction optimization tests reveal that the reaction mechanism strongly relies on the conditions over the In_4/3P₂Se₆ nanosheet photocatalyst.

Engineering Semiconductor Quantum Dots for Selectivity Switch on High-Performance Heterogeneous Coupling Photosynthesis

Semiconductor-based photoredox catalysis brings an innovative strategy for sustainable organic transformation (e.g., C-C/C-X bond formation), via radical coupling under mild conditions. However, since semiconductors interact with photogenerated radicals unselectively, the precise control of selectivity for such organic synthesis by steering radical conversion is extremely challenging. Here, by the judicious design of a structurally well-defined and atomically dispersed cocatalyst over semiconductor quantum dots, we demonstrate the precise selectivity switch on high-performance selective heterogeneous coupling photosynthesis of a C-C bond or a C-N bond along with hydrogen production over the Ni-oxo cluster and single Pd atom-decorated CdS quantum dots crafted onto the SiO₂ support. Mechanistic studies unveil that the Ph(^•CH)NH₂ and PhCH₂NH₂^•+ act as dominant radical intermediates for such divergent organic synthesis of C-C coupled vicinal diamines and C-N coupled imines, as respectively enabled by Ni-oxo clusters assisted radical-radical coupling and single Pd atom-assisted radical addition-elimination. This work overcomes the pervasive difficulties of selectivity regulation in semiconductor-based photochemical synthesis, highlighting a vista of utilizing atomically dispersed cocatalysts as active sites to maneuver unselective radical conversion by engineering quantum dots toward selective heterogeneous photosynthesis.

Sandwich-Structured Hybrid of NiCo Nanoparticles-Embedded Carbon Nanotubes Grafted on C3N4 Nanosheets for Efficient Photodehydrogenative Coupling Reactions

Exploring cheap and efficient hybrid catalysts offers exciting opportunities for enhancing the performance of photocatalysts in the green organic synthesis field. Herein, a facile and effective approach is designed for the synthesis of a sandwich-structured hybrid in which NiCo bimetallic nanoparticles are embedded in the tip of nitrogen-doped carbon nanotubes (N-CNTs) grafted on both sides of a nitrogen deficient C₃N₄ (N_v-C₃N₄) nanosheet for photodehydrogenative coupling reactions. Such a brand-new type of sandwich-structured hybrid comprises N_v-C₃N₄ nanosheets and surrounding N-CNTs embedded with NiCo nanoparticles at their tips. Remarkably, the resultant hybrid exhibits integrated functionalities, abundant active sites, enhanced visible light absorption, and excellent interfacial charge transfer ability. As a result, the optimized NiCo@N-CNTs@N_v-C₃N₄ photocatalyst shows significantly improved photodehydrogenative coupling performance of amines to imines compared to the control single-metal-based catalysts (Ni@N-CNTs@N_v-C₃N₄ and Co@N-CNTs@N_v-C₃N₄). The mechanistic investigation through experimental and computational study demonstrates that, compared with single-metal-based hybrids, the NiCo bimetallic hybrid exhibits stronger amine adsorption and weaker photogenerated hydrogen atom adsorption, thus promoting the dehydrogenative activation of primary amines and fast generation of imines. This work presents a promising insight for designing and preparing efficient photocatalysts to trigger organic synthesis in high yields.

Near-infrared light photocatalysis enabled by a ruthenium complex-integrated metal–organic framework via two-photon absorption

Photocatalysis under UV/visible light irradiation has emerged as one of the green methodologies for solar energy utilization and organic synthesis. These photocatalytic processes are typically initiated by one-photon-absorbing metal complexes or organic dyes. Nevertheless, the intrinsic restrictions of UV/visible light irradiation, such as shallow penetration in reaction solutions, competing absorption by substrates, and limited coverage of the solar spectrum, call for the development of innovative photocatalysts functioning under longer wavelength irradiation. Herein, we report a ruthenium complex containing a metal-organic framework, MOF-Ru1, which can drive diverse organic reactions under 740 nm light irradiation following the two-photon absorption (TPA) process. Various organic transformations such as energy transfer, reductive, oxidative, and redox neutral reactions were realized using this heterogeneous hybrid photocatalyst. Overall, MOF-Ru1 represents an intriguing TPA photocatalyst active under near-infrared light irradiation, paving a way for the efficient utilization of low-energy light and convenient photocatalyst recycling because of phase separation.

•

Ru complexes with π-conjugation ligands show two-photon absorption of NIR photons

•

Hybrid MOF-Ru has NIR light-driven photocatalytic performance with recyclability

•

A variety of organic reactions were photocatalyzed by MOF-Ru under 740 nm irradiation

Dual-Functional Photocatalysis for Cooperative Hydrogen Evolution and Benzylamine Oxidation Coupling over Sandwiched-Like Pd@TiO2 @ZnIn2 S4 Nanobox

Photocatalytic hydrogen evolution (PHE) over semiconductor photocatalysts is usually constrained by the limited light-harvesting and separation of photogenerated electron-hole pairs. Most of the reported systems focusing on PHE are facilitated by consuming the photoinduced holes with organic sacrificial electron donors (SEDs). The introduction of the SEDs not only causes the environmental problem, but also increases the cost of the reaction. Herein, a dual-functional photocatalyst is developed with the morphology of sandwiched-like hollowed Pd@TiO₂ @ZnIn₂ S₄ nanobox, which is synthesized by choosing microporous zeolites with sub-nanometer-sized Pd nanoparticles (Pd NPs) embedded as the sacrificial templates. The ternary Pd@TiO₂ @ZnIn₂ S₄ photocatalyst exhibits a superior PHE rate (5.35 mmol g^-1 h^-1 ) and benzylamine oxidation conversion rate (>99%) simultaneously without adding any other SEDs. The PHE performance is superior to the reported composites of TiO₂ and ZnIn₂ S₄ , which is attributed to the elevated light capture ability induced by the hollow structure, and the enhanced charge separation efficiency facilitated by the ultrasmall sized Pd NPs. The unique design presented here holds great potential for other highly efficient cooperative dual-functional photocatalytic reactions.

Construction of reduced graphene oxide coupled with CoSe2-MoSe2 heterostructure for enhanced electrocatalytic hydrogen production

It is important to develop novel energy to solve energy shortage and environmental problems. Hydrogen evolution reaction (HER) is envisaged as a viable technology that can be used to develop sustainable clean energy. Herein, we report a catalyst with CoSe₂-MoSe₂ heterostructure grown on reduced graphene oxide with an optimum Co/Mo proportion of 1:1 (CoSe₂-MoSe₂(1-1)/rGO). It exhibits good HER activities in both acidic and alkaline conditions. The CoSe₂-MoSe₂(1-1)/rGO shows an overpotential of 107 mV at 10 mA cm^-2 with a Tafel slope of 56 mV dec^-1 under acidic condition. Meanwhile, CoSe₂-MoSe₂(1-1)/rGO also presents an overpotential of 182 mV at 10 mA cm^-2 and with a Tafel slope of 89 mV dec^-1 under alkaline condition. These impressive performances of the catalyst are mainly due to the excellent electronic transmission capability of rGO and the abundant active sites of CoSe₂-MoSe₂ heterostructure as well as the optimized hydrogen adsorption energy of CoSe₂-MoSe₂ interface. The design of CoSe₂-MoSe₂(1-1)/rGO provides a meaningful guide for manufacturing electrode in energy storage and conversion.

Light-Induced Hypoxia in Carbon Quantum Dots and Ultrahigh Photocatalytic Efficiency

Carbon quantum dots (CQDs) represent a class of carbon materials exhibiting photoresponse and many potential applications. Here, we present a unique property that dissolved CQDs capture large amounts of molecular oxygen from the air, the quantity of which can be controlled by light irradiation. The O₂ content can be varied between a remarkable 1 wt % of the CQDs in the dark to nearly half of it under illumination, in a reversible manner. Moreover, O₂ depletion enhances away from the air-solution interface as the nearby CQDs quickly regain them from the air, creating a pronounced concentration gradient in the solution. We elucidate the role of the CQD functional groups and show that excitons generated under light are responsible for their tunable adsorbed-oxygen content. Because of O₂ enrichment, the photocatalytic efficiency of the CQDs toward oxidation of benzylamines in the air is the same as under oxygen flow and far higher than the existing photocatalysts. The findings should encourage the development of a new class of oxygen-enricher materials and air as a sustainable oxidant in chemical transformations.

Ordered Macroporous Carbonous Frameworks Implanted with CdS Quantum Dots for Efficient Photocatalytic CO2 Reduction

Solar-driven photocatalytic CO₂ reduction is regarded as a promising way to simultaneously mitigate the energy crisis and CO₂ pollution. However, achieving high efficiency of photocatalytic CO₂ reduction, especially without the assistance of sacrifice reagents or extra alkaline additives, remains a critical issue. Herein, a photocatalyst of 3D ordered macroporous N-doped carbon (NC) supported CdS quantum dots (3DOM CdSQD/NC) is successfully fabricated toward photocatalytic CO₂ reduction via an in situ transformation strategy. Additionally, an amines oxidation reaction is introduced to replace the H₂ O oxidation process to further boost the photocatalytic CO₂ reduction efficiency. Impressively, 3DOM CdSQD/NC exhibits superior activity and selectivity in photocatalytic CO₂ reduction coupled with amines oxidation, affording a CO production rate as high as 5210 µmol g^-1 h^-1 in the absence of any sacrificial agents and alkaline additives. Moreover, 3DOM CdSQD/NC achieves an apparent quantum efficiency of 2.9% at 450 nm. Mechanism studies indicate that the 3D ordered macropores in the NC matrix are beneficial to the transfer of photogenerated carriers. Furthermore, the highly dispersed CdS QDs on the NC skeleton are able to significantly promote the adsorption of both CO₂ and amine molecules and depress the CO₂ activation energy barriers by stabilizing the *COOH intermediate, directly contributing to the high activity.

Cooperative Coupling of Oxidative Organic Synthesis and Hydrogen Production over Semiconductor-Based Photocatalysts

Merging hydrogen (H₂) evolution with oxidative organic synthesis in a semiconductor-mediated photoredox reaction is extremely attractive because the clean H₂ fuel and high-value chemicals can be coproduced under mild conditions using light as the sole energy input. Following this dual-functional photocatalytic strategy, a dreamlike reaction pathway for constructing C-C/C-X (X = C, N, O, S) bonds from abundant and readily available X-H bond-containing compounds with concomitant release of H₂ can be readily fulfilled without the need of external chemical reagents, thus offering a green and fascinating organic synthetic strategy. In this review, we begin by presenting a concise overview on the general background of traditional photocatalytic H₂ production and then focus on the fundamental principles of cooperative photoredox coupling of selective organic synthesis and H₂ production by simultaneous utilization of photoexcited electrons and holes over semiconductor-based catalysts to meet the economic and sustainability goal. Thereafter, we put dedicated emphasis on recent key progress of cooperative photoredox coupling of H₂ production and various selective organic transformations, including selective alcohol oxidation, selective methane conversion, amines oxidative coupling, oxidative cross-coupling, cyclic alkanes dehydrogenation, reforming of lignocellulosic biomass, and so on. Finally, the remaining challenges and future perspectives in this flourishing area have been critically discussed. It is anticipated that this review will provide enlightening guidance on the rational design of such dual-functional photoredox reaction system, thereby stimulating the development of economical and environmentally benign solar fuel generation and organic synthesis of value-added fine chemicals.

Synthesis of Ni modified Au@CdS core-shell nanostructures for enhancing photocatalytic coproduction of hydrogen and benzaldehyde under visible light

The development of visible light responsive photocatalysts for simultaneous production of hydrogen (H₂) fuel and value-added chemicals is greatly promising to solve the energy and environmental issues by improving the utilization efficiency of solar energy. Herein, the three-component Ni/(Au@CdS) core-shell nanostructures were constructed by the hydrothermal synthesis followed with photodeposition. The intimate integration of plasmonic Au nanospheres and visible-light responsive CdS shells modified with Ni cocatalyst facilitated the generation and separation of electron-hole pairs as well as reduced the overpotential of hydrogen evolution. The Ni/(Au@CdS) photocatalyst exhibited excellent performance toward the selective transformation of benzyl alcohol under anaerobic conditions, and the yields of H₂ and benzaldehyde reached up to 3882 and 4242 μmol·g^-1·h^-1, respectively. The apparent quantum efficiency (AQE) was determined to be 4.09% under the irradiation of 420 nm. The systematic studies have verified the synergy of plasmonic effect and metal cocatalyst on enhancing the photocatalysis. This work highlights the desirable design and potential application of plasmonic photocatalysts for solar-driven coproduction of H₂ fuel and high-value chemicals.

Photocatalytic Hydrogen Evolution Coupled with Production of Highly Value-Added Organic Chemicals by a Composite Photocatalyst CdIn2 S4 @MIL-53-SO3 Ni1/2

Photocatalytic water splitting coupled with the production of highly value-added organic chemicals is of significant importance, which represents a very promising pathway for transforming green solar energy into chemical energy. Herein, we report a composite photocatalyst CdIn₂ S₄ @MIL-53-SO₃ Ni_1/2 , which is highly efficient on prompting water splitting for the production of H₂ in the reduction half-reaction and selective oxidation of organic molecules for the production of highly value-added organic chemicals in the oxidation half-reaction under visible light irradiation. The superior photocatalytic properties of the composite photocatalyst CdIn₂ S₄ @MIL-53-SO₃ Ni_1/2 should be ascribed to coating suspended ion catalyst (SIC), consisting of redox-active Ni^II ions in the anionic pores of coordination network MIL-53-SO₃ ^- , on the surface of photoactive CdIn₂ S₄ , which endows photogenerated electron-hole pairs separate more efficiently for high rate production of H₂ and selective production of highly value-added organic products, demonstrating great potential for practical applications.

Synergistic Pd Single Atoms, Clusters, and Oxygen Vacancies on TiO2 for Photocatalytic Hydrogen Evolution Coupled with Selective Organic Oxidation

Developing efficient photocatalysts for synchronously producing H₂ and high value-added chemicals holds great promise to enhance solar energy conversion. Herein, a facile strategy of simultaneously engineering Pd cocatalyst and oxygen vacancies (V_O s) on TiO₂ to promote H₂ production coupled with selective oxidation of benzylamine is demonstrated. The optimized Pd_SA+C /TiO₂ -V_O photocatalyst containing Pd single atoms (SAs), clusters (C), and V_O s exhibits much superior performance to those of TiO₂ -V_O and Pd_SA /TiO₂ -V_O counterparts. The production rates of H₂ and N-benzylidenebenzylamine over Pd_SA+C /TiO₂ -V_O are 52.7 and 1.5 times those over TiO₂ -V_O , respectively. Both experimental and theoretical studies have elucidated the synergistic effect of Pd SAs, clusters, and V_O s on TiO₂ in boosting the photocatalytic reaction. The presence of Pd SAs facilitates the generation and stabilization of abundant V_O s by the formation of PdOTi³⁺ atomic interface, while Pd clusters promote the photogenerated charge separation and afford the optimum active sites for H₂ evolution. Surface V_O s of TiO₂ guarantee the efficient adsorption and dissociation/activation of reactant molecules. This study reveals the effect of active-site engineering on the photocatalysis and is expected to shed substantial light on future structure design and modulation of semiconductor photocatalysts.