Linker Engineering of High-Nuclearity {V12@P8W48}-Based Metal-Organic Frameworks for Green-Light-Driven Oxidative Coupling of Amines

The development of long-wavelength visible-light-responsive and reusable photocatalysts for organic transformation is of significant interest. Herein, we report the design and synthesis of high-nuclearity {V12@P8W48}-based metal-organic frameworks, POMOF1 and POMOF2, as heterogeneous photocatalysts for long-wavelength light-triggered oxidation. Linker engineering, by tuning from visible-light-inactive triazole (L1) to a photosensitive anthraquinone-derived ligand (L2), not only leads to the generation of porous 1D open channels within POMOF2 but also imparts a strong peak absorption centered at 500 nm. Moreover, the integration of {V12@P8W48} and Cu2+ ions together with L2 into POMOF2 enables the continued and broad absorption ranging from the ultraviolet to near-infrared region. Consequently, POMOF2 exhibited excellent activity in the green-light-driven oxidative coupling of benzylamines, affording a series of imines with high conversions of up to 99% under mild conditions. In contrast, POMOF1 could barely promote the reaction under the same conditions, further confirming the advantage of linker modulation. POMOF2 is stable and can be reused for three cycles with little loss of catalytic activity and structural integrity. This work highlights the potential of linker engineering as an efficient approach for designing long-wavelength photocatalysts, which can further push forward photoredox catalysis.

Gram-Scale Synthesis of an Ultrastable 38-Nuclei Copper(I) Alkynide Nanocluster for Unraveling Bifunctional Photocatalysis

Developing earth-abundant single catalysts capable of simultaneously driving redox reactions is highly desirable, yet it remains elusive due to band gap engineering complexity and rapid charge recombination. Herein, gram-scale synthesis of an ultrastable copper(I) alkynyl nanocluster (Cu38) was realized, and its bifunctionalization was comprehensively studied. Cu38 features a sandwiched structure comprising two Cu10 units and a peanut-like Cu18 unit at the waist. Two types of in-situ reactions involving the oxidization of phenylphosphinic acid and the release of C22- ions from alkynol, occur in this assembly system. The stepwise assembly process of Cu38 was revealed through mass spectrometry. Catalysis studies reveal that Cu38 realizes synchronous photocatalysis disposal in the binary CrVI/dye system due to its appropriate band gap and efficient carrier separation, which are further corroborated by density functional theory (DFT) calculations. This work provides strategic guidance for constructing ultrastable high-nuclearity CuI nanoclusters and new insights into achieving multiple catalytic half-reactions using redox-type nanoclusters.

Hierarchical Co9S8/CdS Hollow Nanocages for Efficient and Robust Cooperative Coupling Photoredox Synthesis

The elaborate development of photocatalysts that can maximize the utility of solar energy with simultaneous photocatalytic H2 evolution and high-quality chemicals production holds great promise in the field of selective photoredox synthesis. Herein, the in situ growth of CdS nanowires on the outside surface of Co9S8 hollow nanocages is reported to create a hierarchical CdS/Co9S8 hollow photocatalyst for efficient photochemical coupling of amines to produce imines and H2. This ingenious hierarchical photocatalyst has a unique hollow structure and dense interfacial contact with a type-I band orientation, which facilitates the interfacial transfer of charge carriers. The photocatalytic activity of this hierarchical hollow catalyst is significantly enhanced in comparison to CdS and Co9S8, and distinctively exhibits excellent recycling stability. Mechanistic studies have shown that the carbon-centered radical Ph(•CH)NH2 is essential for the reaction. Additionally, the CdS/Co9S8 hollow hybrid also exhibits outstanding performance in coupling various primary amines to the corresponding imines, highlighting the broad applicability of this photocatalyst for C-N coupling reactions. This work offers a new strategy for the efficient design of heterostructured hollow semiconductor-based photocatalysts for the cooperative coupling of clean fuel production and fine chemical synthesis.

Photo-responsive antibacterial metal organic frameworks

The misuse and overuse of antibiotics have caused the emergence of antibiotic-resistant bacteria, making bacterial infections more challenging. The increasing prevalence of multidrug-resistant pathogens has driven researchers to explore novel therapeutic strategies. Phototherapy strategies that utilize photo-responsive biomaterials for their antibacterial properties have gained widespread attention due to their capability of precisely controlling bacterial inactivation with minimal side effects. Despite their potential, photodynamic therapies suffer from phototoxicity and low efficiency of photosensitizers, while photothermal therapy risks overheating, which may harm healthy tissues, thus restricting its broader application. Metal organic frameworks (MOFs) have unique physicochemical properties, which provide a promising way to deal with these challenges. MOFs can function as reservoirs, loading and releasing antibacterial agents, such as antibiotics or metal ions, upon light illumination by virtue of their metastable coordination bonds. Their porous structures enable controlled drug release and encapsulation of photosensitizers. Furthermore, MOFs' tunable composition and pore structure allow for the light-triggered generation of heat and reactive oxygen species, enhancing their antibacterial effectiveness. By doping MOFs with functional materials, it is possible to achieve multi-mode antibacterial effects. In this review, we will outline recent advancements of photo-responsive antibacterial MOFs, categorize their underlying mechanisms of action and highlight their prospects in addressing bacterial resistance.

Solar-Driven Massive Production of Dimerized Imine in Aqueous Phase via an Atomically Engineered Photocatalyst

Photocatalytic selective oxidation of organics coupled with green H2 evolution represents a promising avenue for the sustainable production of value-added chemicals, but suffers from sluggish charge separation and difficult selectivity manipulation. In particular, the Schottky barrier-induced adsorption of expected organic products at reduction sites tends to trigger the hydrogenation side reaction, which is more pronounced in the ideal aqueous environment due to distinct polarity. Here, we report a precise cocatalyst strategy on ZnIn2S4 (ZIS) photocatalyst at the atomic level to eliminate the Schottky barrier between ZIS and cocatalyst, thus achieving exceptional activity (565 µmol h-1) and selectivity (99%) for photocatalytic dimerized imine production in aqueous media, which is five times more effective than ZIS loaded with Pt nanoparticles. The excellent performance is achieved by effectively attenuating the accumulation of photogenerated holes near the Pt sites and then suppressing the unwanted hydrogenation side reaction. We further demonstrate that our system can be directly scaled up to 0.5 m2 for scalable outdoor experiment and achieve solar-driven production of benzylimine with 125 mL yield and 97 wt% purity for two weeks under solar irradiation. This study presents an interfacial atomical design strategy for photocatalysts to efficiently produce high-value imine coupled with H2 under mild and green conditions.

Visible-light harvesting 2D copper-cluster-based MOFs as efficient ROS generators for selective oxidation of amines

We have designed and synthesized an aesthetically appealing two-dimensional copper-cluster-based organic framework material named Cu-BPYC. This material exhibits superior charge separation and transfer efficiency, as well as reactive oxygen species (ROS) generation capability under visible-light irradiation. Through the synergistic mechanisms of photo-induced energy and charge transfer, it effectively promotes the oxidation of amines to imines. Additionally, Cu-BPYC demonstrates excellent structural stability and reusability in heterogeneous catalytic systems.

Highly Efficient Yolk-Shell Photocatalyst Constructed by Integration of Ni2P and Cu2O Nanoparticles to Defective Metal-Organic Frameworks for Visible-Light-Driven Amine Oxidation

Realizing the directional migration of photogenerated carriers plays an important role in improving the photocatalytic performance. Meanwhile, light-driven oxidative coupling of benzylamine under ambient conditions with an inexpensive catalyst is highly desirable for the industrial field. Herein, via in situ synthesis, defect engineering, and photodeposition, a yolk-shell nanostructured photocatalyst, Ni2P@OH-NH2-UiO-66@Cu2O, featuring nickel phosphide (Ni2P) nanoparticles (NPs) trapped inside a defect engineered metal-organic framework (MOF, namely OH-NH2-UiO-66) and Cu2O NPs adhering on the surface of MOFs, has been rationally fabricated for the achievement of spatial separation of oxidation/reduction cocatalyst in photocatalytic reaction systems. The yolk-shell structure can effectively avoid the aggregation of the Ni2P and Cu2O NPs. Remarkably, the separation of electron collector Ni2P and hole collector Cu2O regulates the directional movement of the photogenerated carriers and effectively improves the electron-hole separation efficiency to generate abundant reactive superoxide radicals (•O2-) and hydroxyl radicals (•OH). Ni2P@OH-NH2-UiO-66@Cu2O achieves a conversion of 99% for the oxidative coupling of benzylamine into imine within 1 h at ambient temperature under visible-light irradiation. The present study provides an economical method to construct a MOF-based yolk-shell photocatalyst for the oxidative coupling of amines.

Electrocatalytic Hydrogenation and Deuteration of Unsaturated C-N Bonds to Amines with Vacancy-Rich Cu3P Nanowires as Catalysts in Aqueous Solution

Renewable energy driven electrochemically hydrogenation of unsaturated C-N bonds with water as a hydrogen source provides an eco-friendly route for amine production. However, the potential commercial applications of this strategy were limited by the lack of relevant extended research. Here we demonstrate an efficient electrochemical hydrogenation system for the formation of amines from nitriles by a vacancy-rich copper phosphide catalyst. The catalytic system achieves a yield of 99 % and a Faraday efficiency of 99 % for the hydrogenation of benzonitrile. Mechanism study shows that benzonitrile is spontaneously adsorbed on the electrode surface and the electrogenerated active adsorbed hydrogen is the key reactive intermediate for hydrogenation. Theoretical calculation results show that vacancy-induced active sites chemisorb the N atom, thus accelerating C≡N bond activation for hydrogenation. Encouragingly, good yields of amines (≥99 %) are obtained when benzonitrile is replaced by a series of aromatic nitriles, heterocyclic nitriles, aliphatic nitriles, and imines. These results show the general applicability of this method for the synthesis of various amines.

Efficient Photocatalytic Oxidative Coupling of Amines under Visible Light Using a Trioporphyrins-Based Covalent Triazine Framework

Porphyrins-based porous organic polymers (POP) were widely used in photocatalytic oxidation under visible light owing to their superiority in the activation of oxygen. In contrast, the efficiency is usually limited due to the fast recombination and slow electron transfer. Herein, we report the use of a trioporphyrins-based covalent triazine framework (Por-CTF) as visible-light-active photocatalyst for the coupling oxidative of amines to imines at room temperature. By incorporating the π-conjugated porphyrin building block led to the enhanced electron transport between molecules, and the extended recombination time of excited electrons. The photocatalytic efficiency of Por-CTF is superior to that of polymer in absence of triazine framework (POP-TSP), which was prepared by radical polymerization using tetra-(4-vinylphenyl) porphyrin (TSP) as monomer. Por-CTF catalyst presented excellent efficiency for various primary amines and stability. This work provides a reasonable guidance of catalyst molecular structure design for enhancing efficiency in the photocatalytic oxidation.

Regulated Charge Transfer in Donor-Acceptor Metal-Organic Frameworks for Highly-Sensitive Photodetectors

In photo-induced charge separation, organic thin films with donor and acceptor chromophores are vital for uses such as artificial photosynthesis and photodetection. The main challenges include optimizing charge separation efficiency and identifying the ideal acceptor/donor ratio. Achieving this is difficult due to the variability in molecular configurations within these typically amorphous organic aggregates. Metal-organic frameworks (MOFs) provide a structured solution by enabling systematic design of donor/acceptor blends with adjustable ratios within a crystalline lattice. We demonstrate this approach by incorporating donor and acceptor naphthalenediimide (NDI) chromophores as linkers in a highly oriented, monolithic MOF thin film. By adjusting the NDI acceptor linker concentration during the layer-by-layer assembly of surface-anchored MOF thin films (SURMOFs), we significantly enhanced charge separation efficiency. Surprisingly, the optimum acceptor concentration was only 3 %, achieving a forty-fold increase in photodetection efficiency compared to baseline NDI donor-based SURMOFs. This unexpected behaviour was clarified through theoretical analysis enabled by the well-defined crystalline structure of the SURMOFs. Using density functional theory and kinetic Monte Carlo simulations, we identified two opposing effects from acceptors: the positive effect of suppressing undesirable charge carrier recombination is offset at high concentrations by a reduction in charge-carrier mobility.

Reticular Materials for Photocatalysis

Photocatalysis leverages solar energy to overcome the thermodynamic barrier, enabling efficient chemical reactions under mild conditions. It can greatly reduce reliance on traditional energy sources and has attracted significant research interest. Reticular materials, including metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), represent a class of crystalline materials constructed from molecular building blocks linked by coordination and covalent bonds, respectively. Reticular materials function as heterogeneous catalysts, combining well-defined structures and high tailorability akin to homogeneous catalysts. In this review, the regulation of light absorption, charge separation, and surface reactions in the photocatalytic process through precise molecular-level design based on the features of reticular materials is elaborated. Notably, for MOFsmicroenvironment modulation around catalytic sites affects photocatalytic performance is delved, with emphasis on their unique dynamic and flexible microenvironments. For COFs, the inherent excitonic effects due to their fully organic nature is discussed and highlight the strategies to regulate excitonic effects for charge- and/or energy-transfer-mediated photocatalysis. Finally, the current challenges and future directions in this field, aiming to provide a comprehensive understanding of how reticular materials can be optimized for enhanced photocatalysis is discussed.

Growing large single crystals of two- or three-dimensional covalent organic polymers through unconventional Te-O-P linkages

Understanding precise structures of two-/three- dimensional (2D/3D) covalent organic polymers (COPs) through single-crystal X-ray diffraction (SCXRD) analysis is important. However, how to grow high-quality single crystals for 2D/3D COPs is of challenge due to poor reversibility and difficult self-correction of covalent bonds. In addition, the success of introducing tellurium into the backbone to construct 2D/3D COPs and obtaining their single crystals is rare. Here, utilizing the strategy that a heavy element (e.g., tellurium) can form dynamic linkages with a self-correction function, we develop a fast and universal method for growing large-sized single crystals (up to 500 µm) for 2D/3D COPs, especially for 2D COPs. Three 2D COPs and one 3D COP are harvested through dynamic -Te-O-P- bonds in two days, with structures clearly uncovered via the SCXRD analysis. These 2D/3D COPs also show promising photocatalytic activities (nearly 100% selectivity and 100% yield) in superoxide anion radical-mediated coupling of (arylmethyl)amines.

Photocatalytic Hydrogenation of Alkenes Using Water as Both the Reductant and the Proton Source

Utilization of clean and low-cost water as the reductant to enable hydrogenation of alkenes is highly attractive in green chemistry. However, this research subject is considerably challenging due to the sluggish kinetics of the water oxidation half-reaction. It is also very difficult to avoid the undesired oxidation of alkenes because that this oxidation is far easier to occur than the desired oxidation of water from thermodynamic standpoint. Herein, this challenge is overcome by applying a cooperative catalysis where HCl is used as the cocatalyst to accelerate Pt/g-C3N4-catalyzed water oxidation and suppress the undesired oxidation of the alkene. This provides an example for using water as the reductant and the proton source to enable the photocatalytic hydrogenation of alkenes. The present method exhibits broad substrate applicability, and allows various arylethenes and aliphatic alkenes to undergo the hydrogenation smoothly.

Metal-organic frameworks for organic transformations by photocatalysis and photothermal catalysis

Organic transformation by light-driven catalysis, especially, photocatalysis and photothermal catalysis, denoted as photo(thermal) catalysis, is an efficient, green, and economical route to produce value-added compounds. In recent years, owing to their diverse structure types, tunable pore sizes, and abundant active sites, metal-organic framework (MOF)-based photo(thermal) catalysis has attracted broad interest in organic transformations. In this review, we provide a comprehensive and systematic overview of MOF-based photo(thermal) catalysis for organic transformations. First, the general mechanisms, unique advantages, and strategies to improve the performance of MOFs in photo(thermal) catalysis are discussed. Then, outstanding examples of organic transformations over MOF-based photo(thermal) catalysis are introduced according to the reaction type. In addition, several representative advanced characterization techniques used for revealing the charge reaction kinetics and reaction intermediates of MOF-based organic transformations by photo(thermal) catalysis are presented. Finally, the prospects and challenges in this field are proposed. This review aims to inspire the rational design and development of MOF-based materials with improved performance in organic transformations by photocatalysis and photothermal catalysis.

All-in-One: Plasmonic Janus Heterostructures for Efficient Cooperative Photoredox Catalysis

Janus heterostructures consisting of multiple jointed components with distinct properties have gained growing interest in the photoredox catalytic field. Herein, we have developed a facile low-temperature method to gain anisotropic one-dimensional Au-tipped CdS (Au-CdS) nanorods (NRs), followed by assembling Ru molecular co-catalyst (RuN5) onto the surface of the NRs. The CdS NRs decorated with plasmonic Au nanoparticles and RuN5 complex harness the virtues of metal-semiconductor and inorganic-organic interface, giving directional charge transfer channels, spatially separated reaction sites, and enhanced local electric field distribution. As a result, the Au-CdS-RuN5 can act as an efficient dual-function photocatalyst for simultaneous H2 evolution and valorization of biomass-derived alcohols. Benefiting from the interfacial charge decoupling and selective chemical bond activation, the optimal all-in-one Au-CdS-RuN5 heterostructure shows greatly enhanced photoactivity and selectivity as compared to bare CdS NRs, along with a remarkable apparent quantum yield of 40.2 % at 400 nm. The structural evolution and working mechanism of the heterostructures are systematically analyzed based on experimental and computational results.

Metal-Organic Framework-Based Photodetectors

The unique and interesting physical and chemical properties of metal-organic framework (MOF) materials have recently attracted extensive attention in a new generation of photoelectric applications. In this review, we summarized and discussed the research progress on MOF-based photodetectors. The methods of preparing MOF-based photodetectors and various types of MOF single crystals and thin film as well as MOF composites are introduced in details. Additionally, the photodetectors applications for X-ray, ultraviolet and infrared light, biological detectors, and circularly polarized light photodetectors are discussed. Furthermore, summaries and challenges are provided for this important research field.

Covalent Bonding of Salen Metal Complexes with Pyrene Chromophores to Porous Polymers for Photocatalytic Hydrogen Evolution

The development of low-cost and efficient photocatalysts to achieve water splitting to hydrogen (H2) is highly desirable but remains challenging. Herein, we design and synthesize two porous polymers (Co-Salen-P and Fe-Salen-P) by covalent bonding of salen metal complexes and pyrene chromophores for photocatalytic H2 evolution. The catalytic results demonstrate that the two polymers exhibit excellent catalytic performance for H2 generation in the absence of additional noble-metal photosensitizers and cocatalysts. Particularly, the H2 generation rate of Co-Salen-P reaches as high as 542.5 μmol g-1 h-1, which is not only 6 times higher than that of Fe-Salen-P but also higher than a large amount of reported Pt-assisted photocatalytic systems. Systematic studies show that Co-Salen-P displays faster charge separation and transfer efficiencies, thereby accounting for the significantly improved photocatalytic activity. This study provides a facile and efficient way to fabricate high-performance photocatalysts for H2 production.

Crystal-Defect-Induced Longer Lifetime of Excited States in a Metal-Organic Framework Photocatalyst to Enhance Visible-Light-Mediated CO2 Reduction

We report the structural defects in Zr-metal-organic framework (MOFs) for achieving highly efficient CO2 reduction under visible light irradiation. A series of defective Zr-MOF-X (X = 160, 240, 320, or 400) are synthesized by acid-regulated defect engineering. Compared to pristine defect-free Zr-MOF (NNU-28), N2 uptake increases for Zr-MOF-X synthesized with the HAc modulator, producing a larger pore space and Brunauer-Emmett-Teller surface area. The pore size distribution demonstrates that defective Zr-MOF-X exhibits mesoporous structures. Electrochemistry tests show that defective Zr-MOF-X possesses a more negative reduction potential and a higher photocurrent responsive signal than that of pristine NNU-28. Consequently, the defective samples exhibit a significantly higher efficiency in the photoreduction of CO2 to formate. Transient absorption spectroscopies manifest that structural defects modulate the excited-state behivior of Zr-MOF-X and improve the photogenerated charge separation of Zr-MOF-X. Furthermore, electron paramagnetic resonance and in-suit X-ray photoelectron spectroscopy provide additional evidence of the high photocatalytic performance exhibited by defective Zr-MOF-X. Results demonstrate that structural defects in Zr-MOF-X also improve the charge transfer, producing abundant Zr(III) catalytically active sites, exhibiting a slower decay process than defect-free Zr-MOF. The long-lifetime Zr(III) species in defective Zr-MOF-X are fully exposed to a high-concentration CO2 atmosphere, thereby enhancing the photocatalytic efficiency of CO2 reduction.

Regulating the Transfer of Photogenerated Carriers for Photocatalytic Hydrogen Evolution Coupled with Furfural Synthesis

How to simultaneously utilize photogenerated electrons and holes still remains a critical challenge in the field of artificial photosynthesis, especially in the process of photocatalytic hydrogen (H2) evolution coupled with biomass oxidation to value-added chemicals. Herein, a series-parallel photocatalyst (Cu NPs/CdS/In2O3) that can intrinsically regulate the transfer of photogenerated carriers is ingeniously designed for photocatalytic H2 evolution synergized with furfural alcohol (FFA) selective oxidation to furfural (FF). Accordingly, the desired H2 and FF evolution rates with near 100% selectivity toward FF are achieved on Cu NPs/CdS/In2O3 in a sealed atmospheric system. Experimental and theoretical analyses confirm that the localized surface plasmon resonance (LSPR) effect induced by Cu NPs accelerates the reduction of protons (H+) to H2 efficiently, while the photogenerated holes from In2O3 preferentially activate the α-C-H bond of FFA adsorbed on Lewis acid sites to generate FF. This work provides a reference for regulating the transfer of photogenerated carriers for H2 evolution coupled with FF synthesis.

Building Co16-N3-Based UiO-MOF to Expand Design Parameters for MOF Photosensitization

The construction of secondary building units (SBUs) in versatile metal-organic frameworks (MOFs) represents a promising method for developing multi-functional materials, especially for improving their sensitizing ability. Herein, we developed a dual small molecules auxiliary strategy to construct a high-nuclear transition-metal-based UiO-architecture Co16-MOF-BDC with visible-light-absorbing capacity. Remarkably, the N3 - molecule in hexadecameric cobalt azide SBU offers novel modification sites to precise bonding of strong visible-light-absorbing chromophores via click reaction. The resulting Bodipy@Co16-MOF-BDC exhibits extremely high performance for oxidative coupling benzylamine (~100 % yield) via both energy and electron transfer processes, which is much superior to that of Co16-MOF-BDC (31.5 %) and Carboxyl @Co16-MOF-BDC (37.5 %). Systematic investigations reveal that the advantages of Bodipy@Co16-MOF-BDC in dual light-absorbing channels, robust bonding between Bodipy/Co16 clusters and efficient electron-hole separation can greatly boost photosynthesis. This work provides an ideal molecular platform for synergy between photosensitizing MOFs and chromophores by constructing high-nuclear transition-metal-based SBUs with surface-modifiable small molecules.

Design and synthesis of broadband absorption covalent organic framework for efficient artificial photocatalytic amine coupling

Developing highly active materials that efficiently utilize solar spectra is crucial for photocatalysis, but still remains a challenge. Here, we report a new donor-acceptor (D-A) covalent organic framework (COF) with a wide absorption range from 200 nm to 900 nm (ultraviolet-visible-near infrared light). We find that the thiophene functional group is accurately introduced into the electron acceptor units of TpDPP-Py (TpDPP: 5,5'-(2,5-bis(2-ethylhexyl)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo [3,4-c]pyrrole-1,4-diyl)bis(thiophene-2-carbaldehyde), Py: 1,3,6,8-tetrakis(4-aminophenyl)pyrene) COFs not only significantly extends its spectral absorption capacity but also endows them with two-photon and three-photon absorption effects, greatly enhancing the utilization rate of sunlight. The selective coupling of benzylamine as the target reactant is used to assess the photocatalytic activity of TpDPP-Py COFs, showing high photocatalytic conversion of 99% and selectivity of 98% in 20 min. Additionally, the TpDPP-Py COFs also exhibit the universality of photocatalytic selective coupling of other imine derivatives with ~100% conversion efficiency. Overall, this work brings a significant strategy for developing COFs with a wide absorption range to enhance photocatalytic activity.

Strong Second-Harmonic Generation Induced by a Triphenylamine-Based Bismuth-Organic Framework for Photocatalytic Activity Enhancement

Taking advantage of the well-defined geometry of metal centers and highly directional metal-ligand coordination bonds, metal-organic frameworks (MOFs) have emerged as promising candidates for nonlinear optical (NLO) materials. In this work, taking a photoresponsive carboxylate triphenylamine derivative as an organic ligand, a bismuth-based MOF, Bi-NBC, NBC = 4',4‴,4‴″-nitrilotris(([1,1'-biphenyl]-4-carboxylic acid)) is obtained. Structure determination reveals that it is a potential NLO material derived from its noncentrosymmetric structure, which is finally confirmed by its rarely strong second harmonic generation (SHG) effect. Theoretical calculations reveal that the potential difference around Bi atoms is large; therefore, it leads to a strong local built-in electric field, which greatly facilitates the charge separation and transfer and finally improves the photocatalytic performance. Our results provide a reference for the exploration of MOFs with NLO properties.

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.

Three-Motif Molecular Junction Type Covalent Organic Frameworks for Efficient Photocatalytic Aerobic Oxidation

Covalent organic frameworks (COFs), with the features of flexible structure regulation and easy introduction of functional groups, have aroused broad interest in the field of photocatalysis. However, due to the low light absorption intensity, low photoelectron conversion efficiency, and lack of suitable active sites, it remains a great challenge to achieve efficient photocatalytic aerobic oxidation reactions. Herein, based on reticular chemistry, we rationally designed a series of three-motif molecular junction type COFs, which formed dual photosensitizer coupled redox molecular junctions containing multifunctional COF photocatalysts. Significantly, due to the strong light adsorption ability of dual photosensitizer units and integrated oxidation and reduction features, the PY-BT COF exhibited the highest activity for photocatalytic aerobic oxidation. Especially, it achieved a photocatalytic benzylamine conversion efficiency of 99.9% in 2.5 h, which is much higher than that of the two-motif molecular junctions with only one photosensitizer or redox unit lacking COFs. The mechanism of selective aerobic oxidation was studied through comprehensive experiments and density functional theory calculations. The results showed that the photoinduced electron transfer occurred from PY and then through triphenylamine to BT. Furthermore, the thermodynamics energy for benzylamine oxidation on PY-BT COF was much lower than that for others, which confirmed the synergistic effect of dual photosensitizer coupled redox molecular junction COFs. This work provided a new strategy for the design of functional COFs with three-motif molecular junctions and also represented a new insight into the multifunctional COFs for organic catalytic reactions.

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.

Visible-Light-Driven NO Release from Postmodified MOFs via Photoinduced Electron Transfer for Antibacterial Application

Photoresponsive nitric oxide (NO)-releasing materials (NORMs) enable the spatiotemporal delivery of NO to facilitate their potential applications in physiological conditions. Here two novel metal-organic frameworks (MOFs)-based photoactive NORMs achieved by the incorporation of prefunctionalized NO donors into the photosensitive Fe-MOFs via a postmodification strategy is reported. The modified Fe-MOFs display superior photoactivity of NO release when exposed to visible light (up to 720 nm). Significantly, the visible-light-driven NO release properties are further corroborated by their efficient antibacterial performance.

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.

Versatile Structural Engineering of Metal-Organic Frameworks Enabling Switchable Catalytic Selectivity

The structure engineering of metal-organic frameworks (MOFs) forms the cornerstone of their applications. Nonetheless, realizing the simultaneous versatile structure engineering of MOFs remains a significant challenge. Herein, a dynamically mediated synthesis strategy to simultaneously engineer the crystal structure, defect structure, and nanostructure of MOFs is proposed. These include amorphous Zr-ODB nanoparticles, crystalline Zr-ODB-hz (ODB = 4,4'-oxalyldibenzoate, hz = hydrazine) nanosheets, and defective d-Zr-ODB-hz nanosheets. Aberration-corrected scanning transmission electron microscopy combined with low-dose high-angle annular dark-field imaging technique vividly portrays these engineered structures. Concurrently, the introduced hydrazine moieties confer self-reduction properties to the respective MOF structures, allowing the in situ installation of catalytic Pd nanoparticles. Remarkably, in the hydrogenation of vanillin-like biomass derivatives, Pd/Zr-ODB-hz yields partially hydrogenated alcohols as the primary products, whereas Pd/d-Zr-ODB-hz exclusively produces fully hydrogenated alkanes. Density functional theory calculations, coupled with experimental evidence, uncover the catalytic selectivity switch triggered by the change in structure type. The proposed strategy of versatile structure engineering of MOFs introduces an innovative pathway for the development of high-performance MOF-based catalysts for various reactions.

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.

Metal-organic frameworks (MOFs) for energy production and gaseous fuel and electrochemical energy storage applications

The increasing energy demands in society and industrial sectors have inspired the search for alternative energy sources that are renewable and sustainable, also driving the development of clean energy storage and delivery systems. Various solid-state materials (e.g., oxides, sulphides, polymer and conductive nanomaterials, activated carbon and their composites) have been developed for energy production (water splitting-H2 production), gaseous fuel (H2 and CH4) storage and electrochemical energy storage (batteries and supercapacitors) applications. Nevertheless, the low surface area, pore volume and conductivity, and poor physical and chemical stability of the reported materials have resulted in higher requirements and challenges in the development of energy production and energy storage technologies. Thus, to overcome these issues, the development of metal-organic frameworks (MOFs) has attracted significant attention. MOFs are a class of porous materials with extremely high porosity and surface area, structural diversity, multifunctionality, and chemical and structural stability, and thus they can be used in a wide range of applications. In the present review, we precisely discuss the interesting properties of MOFs and the various methodologies for their synthesis, and also the future dependence on the valorization of solid waste for the recovery of metals and organic ligands for the synthesis of new classes of MOFs. Subsequently, the utilization of these interesting characteristics for energy production (water splitting), storage of gaseous fuels (H2 and CH4), and electrochemical storage (batteries and supercapacitors) applications are described. However, although MOFs are efficient materials with versatile uses, they still have many challenges, limiting their practical applications. Therefore, finally, we highlight the challenges associated with MOFs and show the way forward in overcoming them for the development of these highly porous materials with large-scale practical utility.

Reticular framework materials for photocatalytic organic reactions

Photocatalytic organic reactions, harvesting solar energy to produce high value-added organic chemicals, have attracted increasing attention as a sustainable approach to address the global energy crisis and environmental issues. Reticular framework materials, including metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), are widely considered as promising candidates for photocatalysis owing to their high crystallinity, tailorable pore environment and extensive structural diversity. Although the design and synthesis of MOFs and COFs have been intensively developed in the last 20 years, their applications in photocatalytic organic transformations are still in the preliminary stage, making their systematic summary necessary. Thus, this review aims to provide a comprehensive understanding and useful guidelines for the exploration of suitable MOF and COF photocatalysts towards appropriate photocatalytic organic reactions. The commonly used reactions are categorized to facilitate the identification of suitable reaction types. From a practical viewpoint, the fundamentals of experimental design, including active species, performance evaluation and external reaction conditions, are discussed in detail for easy experimentation. Furthermore, the latest advances in photocatalytic organic reactions of MOFs and COFs, including their composites, are comprehensively summarized according to the actual active sites, together with the discussion of their structure-property relationship. We believe that this study will be helpful for researchers to design novel reticular framework photocatalysts for various organic synthetic applications.

Modulating Photoinduced Electron Transfer between Photosensitive MOF and Co(II) Proton Reduction Sites for Boosting Photocatalytic Hydrogen Production

Photocatalytic hydrogen production via water splitting is the subject of intense research. Photoinduced electron transfer (PET) between a photosensitizer (PS) and a proton reduction catalyst is a prerequisite step and crucial to affecting hydrogen production efficiency. Herein, three photoactive metal-organic framework (MOF) systems having two different PET processes where PS and Co(II) centers are either covalently bonded or coexisting to drive photocatalytic H2 production are built. Compared to these two intramolecular PET systems including CoII -Zn-PDTP prepared from the post-synthetic metalation toward uncoordinated pyridine N sites of Zn-PDTP and sole cobalt-based MOF Co-PDTP, the CoII (bpy)3 @Zn-PDTP system impregnated by molecular cocatalyst possessing intermolecular PET process achieves the highest H2 evolution rate of 116.8 mmol g-1 h-1 over a period of 10 h, about 7.5 and 9.3 times compared to CoII -Zn-PDTP and Co-PDTP in visible-light-driven H2 evolution, respectively. Further studies reveal that the enhanced photoactivity in CoII (bpy)3 @Zn-PDTP can be ascribed to the high charge-separation efficiency of Zn-PDTP and the synergistic intermolecular interaction between Zn-PDTP and cobalt complexes. The present work demonstrates that the rational design of PET process between MOFs and catalytic metal sites can be a viable strategy for the development of highly efficient photocatalysts with enhanced photocatalytic activities.

Incorporating a D-A-D-Type Benzothiadiazole Photosensitizer into MOFs for Photocatalytic Oxidation of Phenylsulfides and Benzylamines

Oxidation and removal of highly toxic sulfides and amines are particularly important for environmental and human security but remain challenging. Here, incorporating an excellent photosensitizer, donor-acceptor-donor (D-A-D)-type 4,4'-(benzo[c][1,2,5]thiadiazole-4,7-diyl)dibenzoic (H2L), into metal-organic frameworks (MOFs) has been manifested to promote the charge separation, affording four three-dimensional (3D) MOFs (isostructural 1-Co/1-Zn with Co2/Zn2 units, and 2-Gd/2-Tb with Gd/Tb-cluster chains) as photocatalysts in the visible light-driven air-O2-mediated catalytic oxidation and removal of hazardous phenylsulfides and benzylamines. Impressively, structure-property correlation illustrated that the transition metal centers assembled in MOFs play an important role in the photocatalytic activity, and we can conclude that 1-Zn can be a robust heterogeneous catalyst possessing good light adsorption and fast charge separation in oxidation removal reactions of both benzylamines and phenylsulfides under visible light irradiation and room temperature with excellent activity/selectivity, stability, and reusability.

HCR/DNAzyme-triggered cascaded feedback cycle amplification for self-powered dual-photoelectrode detection of femtomolar HPV16

For high-performance dual-photoelectrode assay, developing a pair of photoactive materials with well-matched band structure and the design of a powerful sensing strategy are highly desirable. Herein, the Zn-TBAPy pyrene-based MOF and BiVO4/Ti3C2 Schottky junction were employed as photocathode and photoanode to form an efficient dual-photoelectrode system. The integration of the cascaded hybridization chain reaction (HCR)/DNAzyme-assisted feedback amplification with DNA walker-mediated cycle amplification strategy realizes femtomolar HPV16 dual-photoelectrode bioassay. Through the activation of the HCR cascaded with the DNAzyme system in the presence of HPV16, plentiful HPV16 analogs are generated that leads to exponential positive feedback signal amplification. Meanwhile on the Zn-TBAPy photocathode, the NDNA hybridizes with the bipedal DNA walker followed by circular cleavage by Nb.BbvCI NEase, producing a dramatically enhanced PEC readout. The achieved ultralow detection limit of 0.57 fM and a wide linear range of 10-6 nM-103 nM showcase the excellent performance of the developed dual-photoelectrode system.

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.

Coupling Benzylamine Oxidation with CO2 Photoconversion to Ethanol over a Black Phosphorus and Bismuth Tungstate S-Scheme Heterojunction

Photoconversion of CO2 and H2 O into ethanol is an ideal strategy to achieve carbon neutrality. However, the production of ethanol with high activity and selectivity is challenging owing to the less efficient reduction half-reaction involving multi-step proton-coupled electron transfer (PCET), a slow C-C coupling process, and sluggish water oxidation half-reaction. Herein, a two-dimensional/two-dimensional (2D/2D) S-scheme heterojunction consisting of black phosphorus and Bi2 WO6 (BP/BWO) was constructed for photocatalytic CO2 reduction coupling with benzylamine (BA) oxidation. The as-prepared BP/BWO catalyst exhibits a superior photocatalytic performance toward CO2 reduction, with a yield of 61.3 μmol g-1  h-1 for ethanol (selectivity of 91 %).In situ spectroscopic studies and theoretical calculations reveal that S-scheme heterojunction can effectively promote photogenerated carrier separation via the Bi-O-P bridge to accelerate the PCET process. Meanwhile, electron-rich BP acts as the active site and plays a vital role in the process of C-C coupling. In addition, the substitution of BA oxidation for H2 O oxidation can further enhance the photocatalytic performance of CO2 reduction to C2 H5 OH. This work opens a new horizon for exploring novel heterogeneous photocatalysts in CO2 photoconversion to C2 H5 OH based on cooperative photoredox systems.

Linker Engineering for Reactive Oxygen Species Generation Efficiency in Ultra-Stable Nickel-Based Metal-Organic Frameworks

Interfacial charge transfer on the surface of heterogeneous photocatalysts dictates the efficiency of reactive oxygen species (ROS) generation and therefore the efficiency of aerobic oxidation reactions. Reticular chemistry in metal-organic frameworks (MOFs) allows for the rational design of donor-acceptor pairs to optimize interfacial charge-transfer kinetics. Herein, we report a series of isostructural fcu-topology Ni8-MOFs (termed JNU-212, JNU-213, JNU-214, and JNU-215) with linearly bridged bipyrazoles as organic linkers. These crystalline Ni8-MOFs can maintain their structural integrity in 7 M NaOH at 100 °C for 24 h. Experimental studies reveal that linker engineering by tuning the electron-accepting capacity of the pyrazole-bridging units renders these Ni8-MOFs with significantly improved charge separation and transfer efficiency under visible-light irradiation. Among them, the one containing a benzoselenadiazole unit (JNU-214) exhibits the best photocatalytic performance in the aerobic oxidation of benzylamines with a conversion rate of 99% in 24 h. Recycling experiments were carried out to confirm the stability and reusability of JNU-214 as a robust heterogeneous catalyst. Significantly, the systematic modulation of the electron-accepting capacity of the bridging units in donor-acceptor-donor MOFs provides a new pathway to develop viable noble-metal-free heterogeneous photocatalysts for aerobic oxidation reactions.

Mesoporous Mixed-Metal-Organic Framework Incorporating a [Ru(Phen)3]2+ Photosensitizer for Highly Efficient Aerobic Photocatalytic Oxidative Coupling of Amines

[Ru(Phen)₃]²⁺ (phen = phenanthroline) as a very classical photosensitizer possesses strong absorption in the visible range and facilitates photoinduced electron transfer, which plays a vital role in regulating photochemical reactions. However, it remains a significant challenge to utilize more adequately and exploit more efficiently the ruthenium-based materials due to the uniqueness, scarcity, and nonrenewal of the noble metal. Here, we integrate the intrinsic advantages of the ruthenium-based photosensitizer and mesoporous metal-organic frameworks (meso-MOFs) into a [Ru(Phen)₃]²⁺ photosensitizer-embedded heterometallic Ni(II)/Ru(II) meso-MOF (LTG-NiRu) via the metalloligand approach. LTG-NiRu, with an extremely robust framework and a large one-dimensional (1D) channel, not only makes ruthenium photosensitizer units anchored in the inner wall of meso-MOF tubes to circumvent the problem of product/catalyst separation and recycling of catalysts in heterogeneous systems but also exhibits exceptional activities for the aerobic photocatalytic oxidative coupling of amine derivatives as a general photocatalyst. The conversion of the light-induced oxidative coupling reaction for various benzylamines is ∼100% in 1 h, and more than 20 chemical products generated by photocatalytic oxidative cycloaddition of N-substituted maleimides and N,N-dimethylaniline can be synthesized easily in the presence of LTG-NiRu upon visible light irradiation. Moreover, recycling experiments demonstrate that LTG-NiRu is an excellent heterogeneous photocatalyst with high stability and excellent reusability. LTG-NiRu represents a great potential photosensitizer-based meso-MOF platform with an efficient aerobic photocatalytic oxidation function that is convenient for gram-scale synthesis.

Enhanced Photocatalytic Coupling of Benzylamine to N-Benzylidene Benzylamine over the Organic-Inorganic Composites F70-TiO2 Based on Fullerenes Derivatives and TiO2

The organic-inorganic composites F70-TiO₂, based on fullerene with carboxyl group derivatives and TiO₂ semiconductor, have been designed and constructed to become an optical-functional photocatalyst via the facile sol-gel method. The composite photocatalyst obtained shows excellent photocatalytic activity for the high-efficiency conversion of benzylamine (BA) to N-benzylidene benzylamine (NBBA) with air pressure at a normal temperature under visible light irradiation. By optimizing the composition, the composites with the 1:15 mass ratio of F70 and TiO₂, denoted as F70-TiO₂(1:15), demonstrated the highest reaction efficiency for benzylamine (>98% conversion) to N-benzylidene benzylamine (>93% selectivity) in this study. However, pure TiO₂ and fullerene derivatives (F70) exhibit decreased conversion (56.3% and 89.7%, respectively) and selectivity (83.8% and 86.0%, respectively). The UV-vis diffuse reflectance spectra (DRS) and Mott-Schottky experiment's results indicate that the introduction of fullerene derivatives into anatase TiO₂ would greatly broaden the visible light response range and adjust the energy band positions of the composites, enhancing the sunlight utilization and promoting the photogenerated charge (e^--h⁺) separation and transfer. Specifically, a series of results on the in situ EPR tests and the photo-electrophysical experiment indicate that the separated charges from the hybrid could effectively activate benzylamine and O₂ to accelerate the formation of active intermediates, and then couple with free BA molecules to form the desired production of N-BBA. The effective combination, on a molecular scale, between fullerene and titanium dioxide has provided a profound understanding of the photocatalysis mechanism. This work elaborates and makes clear the relationship between the structure and the performance of functional photocatalysts.

A Stable Triphenylamine-Based Zn(II)-MOF for Photocatalytic H2 Evolution and Photooxidative Carbon-Carbon Coupling Reaction

Efficient charge transfer has always been a challenge in heterogeneous MOF-based photoredox catalysis due to the poor electrical conductivity of the MOF photocatalyst, the toilless electron-hole recombination, and the uncontrollable host-guest interactions. Herein, a propeller-like tris(3'-carboxybiphenyl)amine (H₃TCBA) ligand was synthesized to fabricate a 3D Zn₃O cluster-based Zn(II)-MOF photocatalyst, Zn₃(TCBA)₂(μ₃-H₂O)H₂O (Zn-TCBA), which was applied to efficient photoreductive H₂ evolution and photooxidative aerobic cross-dehydrogenation coupling reactions of N-aryl-tetrahydroisoquinolines and nitromethane. In Zn-TCBA, the ingenious introduction of the meta-position benzene carboxylates on the triphenylamine motif not only promotes Zn-TCBA to exhibit a broad visible-light absorption with a maximum absorption edge of 480 nm but also causes special phenyl plane twists with dihedral angles of 27.8-45.8° through the coordination to Zn nodes. The semiconductor-like Zn clusters and the twisted TCBA^3- antenna with multidimensional π interaction sites facilitate photoinduced electron transfer to render Zn-TCBA a good photocatalytic H₂ evolution efficiency of 27.104 mmol·g^-1·h^-1 in the presence of [Co(bpy)₃]Cl₂ under visible-light illumination, surpassing many non-noble-metal MOF systems. Moreover, the positive enough excited-state potential of 2.03 V and the semiconductor-like characteristics of Zn-TCBA endow Zn-TCBA with double oxygen activation ability for photocatalytic oxidation of N-aryl-tetrahydroisoquinoline substrates with a yield up to 98.7% over 6 h. The durability of Zn-TCBA and the possible catalytic mechanisms were also investigated by a series of experiments including PXRD, IR, EPR, and fluorescence analyses.

Oxidation of N-Alkyl(iso)quinolinium Salts Over TEMPO@Metal-Organic Framework Heterogeneous Photocatalyst†

Quinolones and isoquinolones are of particular importance to pharmaceutical industry due to their diverse biological activities. However, their synthetic protocols were limited by high toxicity, high energy consumption, poor functional group tolerance and noble metal catalyst. This study concerns the development of a series of TEMPO@PCN-222 (TEMPO: 2,2,6,6-tetramethylpiperidinyl-1-oxy; PCN: porous coordination network) composite photocatalysts by coordinating different amount of 4-carboxy-TEMPO with the secondary building units of PCN-222. Upon visible-light irradiation, photogenerated holes in the highest occupied molecular orbital of PCN-222 can smoothly transfer to TEMPO, which can significantly boost the photosynthesis of bioactive (iso)quinolones from readily available N-alkyl(iso)quinolinium salts. TEMPO@PCN-222 exhibits an outstanding catalytic stability and substrate tolerance with a 1-methyl-2-quinolinone yield of 86.7 %, over four times that with PCN-222 (21.4 %). This work provides a new route to construct composite photocatalysts from abundant starting materials for efficient photosynthesis of high value-added chemicals.

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.

Zr- and Ti-based metal-organic frameworks: synthesis, structures and catalytic applications

Recently, Zr- and Ti-based metal-organic frameworks (MOFs) have gathered increasing interest in the field of chemistry and materials science, not only for their ordered porous structure, large surface area, and high thermal and chemical stability, but also for their various potential applications. Particularly, the unique features of Zr- and Ti-based MOFs enable them to be a highly versatile platform for catalysis. Although much effort has been devoted to developing Zr- and Ti-based MOF materials, they still suffer from difficulties in targeted synthesis, especially for Ti-based MOFs. In this Feature Article, we discuss the evolution of Zr- and Ti-based MOFs, giving a brief overview of their synthesis and structures. Furthermore, the catalytic uses of Zr- and Ti-based MOF materials in the previous 3-5 years have been highlighted. Finally, perspectives on the Zr- and Ti-based MOF materials are also proposed. This work provides in-depth insight into the advances in Zr- and Ti-based MOFs and boosts their catalytic applications.

Enzyme-Inspired Coordination Polymers for Selective Oxidization of C(sp3)-H Bonds via Multiphoton Excitation

Nature's blueprint provides the fundamental principles for expanding the use of abundant metals in catalysis; however, mimicking both the structure and function of copper enzymes simultaneously in one artificial system for selective C-H bond oxidation faces marked challenges. Herein, we report a new approach to the assembly of artificial monooxygenases utilizing a binuclear Cu₂S₂Cl₂ cluster to duplicate the identical structure and catalysis of the Cu_A enzyme. The designed monooxygenase Cu-Cl-bpyc facilitates well-defined redox potential that initially activated O₂via photoinduced electron transfer, and generated an active chlorine radical via a ligand-to-metal charge transfer (LMCT) process from the consecutive excitation of the in situ formed copper(II) center. The chlorine radical abstracts a hydrogen atom selectively from C(sp³)-H bonds to generate the radical intermediate; meanwhile, the O₂^•- species interacted with the mimic to form mixed-valence species, giving the desired oxidization products with inherent product selectivity of copper monooxygenases and recovering the catalyst directly. This enzymatic protocol exhibits excellent recyclability, good functional group tolerance, and broad substrate scope, including some biological and pharmacologically relevant targets. Mechanistic studies indicate that the C-H bond cleavage was the rate-determining step and the cuprous interactions were essential to stabilize the active oxygen species. The well-defined structural characters and the fine-modified catalytic properties open a new avenue to develop robust artificial enzymes with uniform and precise active sites and high catalytic performances.

Tipping Gold Nanobipyramids with Titania for the Use of Plasmonic Hotspots to Drive Amine Coupling

Designing plasmonic photocatalysts with spatially controlled catalytic sites is an effective strategy to boost the sunlight-driven chemical transformation efficiency through plasmonic enhancement. Herein, we describe a facile method for the synthesis of TiO₂-tipped Au nanobipyramids (NBPs) to give (Au NBP)/t-TiO₂ nanodumbbells. The surfactant cetyltrimethylammonium bromide concentration is the key factor in the construction of this type of unique nanostructure. The photocatalytic aerobic oxidative coupling of amines using the plasmonic photocatalysts with the dumbbell-like and core@shell structures indicates that the TiO₂-tipped ends for the photo-reduction and the exposed adjacent Au surface for the photo-oxidation on (Au NBP)/t-TiO₂ can significantly improve the photocatalytic activity. The underlying mechanism of the photocatalytic oxidative coupling of benzylamine over (Au NBP)/t-TiO₂ has been thoroughly investigated. Both experimental and simulation results for (Au NBP)/t-TiO₂ and (Au nanorod)/t-TiO₂ confirm the important effect of the plasmonic hotspots on the enhancement of the photocatalytic activity.