A Covalent Organic Framework Bearing Single Ni Sites as a Synergistic Photocatalyst for Selective Photoreduction of CO2 to CO

Integrating Single Co Sites into Crystalline Covalent Triazine Frameworks for Photoreduction of CO2

Bipyridine-containing covalent triazine framework (CTF-Bpy) was proved can accomplish the atomic-level distribution of Co2+. The cobalt-loaded CTF-Bpy-Co produced 120 µmol CO with a selectivity of 83.8 % (CO to H2)...

Rational Design of Dot-on-Rod Nano-Heterostructure for Photocatalytic CO2 Reduction: Pivotal Role of Hole Transfer and Utilization

Inspired by green plants, artificial photosynthesis has become one of the most attractive approaches toward carbon dioxide (CO₂ ) valorization. Semiconductor quantum dots (QDs) or dot-in-rod (DIR) nano-heterostructures have gained substantial research interest in multielectron photoredox reactions. However, fast electron-hole recombination or sluggish hole transfer and utilization remains unsatisfactory for their potential applications. Here, the first application of a well-designed ZnSe/CdS dot-on-rods (DORs) nano-heterostructure for efficient and selective CO₂ photoreduction with H₂ O as an electron donor is presented. In-depth spectroscopic studies reveal that surface-anchored ZnSe QDs not only assist ultrafast (≈2 ps) electron and hole separation, but also promote interfacial hole transfer participating in oxidative half-reactions. Surface photovoltage (SPV) spectroscopy provides a direct image of spatially separated electrons in CdS and holes in ZnSe. Therefore, ZnSe/CdS DORs photocatalyze CO₂ to CO with a rate of ≈11.3 µmol g^-1 h^-1 and ≥85% selectivity, much higher than that of ZnSe/CdS DIRs or pristine CdS nanorods under identical conditions. Obviously, favored energy-level alignment and unique morphology balance the utilization of electrons and holes in this nano-heterostructure, thus enhancing the performance of artificial photosynthetic solar-to-chemical conversion.

A metal-free hydroxyl functionalized quaternary phosphine type ionic liquid polymer for cycloaddition of CO2 and epoxides

Quaternary phosphine type hypercrosslinked polymer catalysts were successfully prepared using the Friedel-Crafts alkylation reactions, which benefit from the synergistic effects between the Brønsted acidity of the hydroxyl group and nucleophilicity of the Br^- group as well as the CO₂ capture of the ionic liquids. The as-obtained metal-free catalysts facilitate the cycloaddition and synthesis of high value-added fine chemicals.

Dual-Single-Atom Tailoring with Bifunctional Integration for High-Performance CO2 Photoreduction

Single-atom photocatalysis has been demonstrated as a novel strategy to promote heterogeneous reactions. There is a diversity of monoatomic metal species with specific functions; however, integrating representative merits into dual-single-atoms and regulating cooperative photocatalysis remain a pressing challenge. For dual-single-atom catalysts, enhanced photocatalytic activity would be realized through integrating bifunctional properties and tuning the synergistic effect. Herein, dual-single-atoms supported on conjugated porous carbon nitride polymer are developed for effective photocatalytic CO₂ reduction, featuring the function of cobalt (Co) and ruthenium (Ru). A series of in situ characterizations and theoretical calculations are conducted for quantitative analysis of structure-performance correlation. It is concluded that the active Co sites facilitate dynamic charge transfer, while the Ru sites promote selective CO₂ surface-bound interaction during CO₂ photoreduction. The combination of atom-specific traits and the synergy between Co and Ru lead to the high photocatalytic CO₂ conversion with corresponding apparent quantum efficiency (AQE) of 2.8% at 385 nm, along with a high turnover number (TON) of more than 200 without addition of any sacrificial agent. This work presents an example of identifying the roles of different single-atom metals and regulating the synergy, where the two metals with unique properties collaborate to further boost the photocatalytic performance.

Controllable Synthesis and Performance Modulation of 2D Covalent-Organic Frameworks

Covalent-organic frameworks (COFs) are especially interesting and unique as their highly ordered topological structures entirely built from plentiful π-conjugated units through covalent bonds. Arranging tailorable organic building blocks into periodically reticular skeleton bestows predictable lattices and various properties upon COFs in respect of topology diagrams, pore size, properties of channel wall interfaces, etc. Indeed, these peculiar features in terms of crystallinity, conjugation degree, and topology diagrams fundamentally decide the applications of COFs including heterogeneous catalysis, energy conversion, proton conduction, light emission, and optoelectronic devices. Additionally, this research field has attracted widespread attention and is of importance with a major breakthrough in recent year. However, this research field is running with the lack of summaries about tailorable construction of 2D COFs for targeted functionalities. This review first covers some crucial polymeric strategies of preparing COFs, containing boron ester condensation, amine-aldehyde condensation, Knoevenagel condensation, trimerization reaction, Suzuki CC coupling reaction, and hybrid polycondensation. Subsequently, a summary is made of some representative building blocks, and then underlines how the electronic and molecular structures of building blocks can strongly influence the functional performance of COFs. Finally, conclusion and perspectives on 2D COFs for further study are proposed.

Single PEDOT Catalyst Boosts CO2 Photoreduction Efficiency

Atmospheric pollution demands the development of solar-driven photocatalytic technologies for the conversion of CO₂ into a fuel; state-of-the-art cocatalyst systems demonstrate conversion efficiencies currently unattainable by a single catalyst. Here, we upend the status quo demonstrating that the nanofibrillar conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) is a record-breaking single catalyst for the photoreduction of CO₂ to CO. This high catalytic efficiency stems from a highly conductive nanofibrillar structure that significantly enhances surface area, CO₂ adsorption and light absorption. Moreover, the polymer's band gap is optimized via chemical doping/dedoping treatments using hydrochloric acid, ammonia hydroxide, and hydrazine. The hydrazine-treated PEDOT catalyst exhibits 100% CO yield under a stable regime (>10 h) with a maximum rate of CO evolution (3000 μmol g_cat ^-1 h^-1) that is 2 orders of magnitude higher than the top performing single catalyst and surpassed only by three other cocatalyst systems. Nanofibrillar PEDOT provides a new direction for designing the next generation of high-efficiency photoreduction catalysts.

Donor-Acceptor Pairs in Covalent Organic Frameworks Promoting Electron Transfer for Metal-Free Photocatalytic Organic Synthesis

The donor-acceptor-type covalent organic frameworks (COFs) have recently gained increasing interest in photocatalysis, but the photoinduced electron-transfer regimes in the COFs are underexplored. Herein, we demonstrate a designed porphyrinic COF possessing a donor-acceptor structure together with its photocatalytic performance in aerobic coupling of primary amines. The COF could be photoexcited by the full range of visible light to generate electron-hole pairs that could be separated by donor-acceptor pairs. Electron transfer as the mechanism of the reaction from anthracene unit to porphyrin unit was revealed by natural transition orbitals analyses. The electrons migrate to the adsorbed O₂ to generate reactive oxidative species. The COF displays remarkable photocatalytic activities in the coupling of amines to imines, which can be explained mainly by the sufficient charge separation and mobility, benefiting from the donor-acceptor pairs in the COF and their interactions to the reactants and intermediates.

Porous Organic Polymers for Catalytic Conversion of Carbon Dioxide

To overcome the challenges of global warming and environmental pollution, it is necessary to reduce the concentration of carbon dioxide (CO₂ ) in the atmosphere, which is mainly accumulated in the air through the burning of fossil fuels. Therefore, the development of environmentally friendly strategies to capture carbon dioxide and convert it into value-added products offers a promising way forward for reducing carbon dioxide concentration in the atmosphere. In this context, POPs (porous organic polymers) have shown great potential as CO₂ selective adsorbents due to their high specific surface area, chemical stability, nanoscale porosity and structural diversity, as well as POPs based heterogeneous catalysts for CO₂ conversion. This review provides a concise account of preparation methods of various POPs, challenges and current development trends of POPs in photocatalytic CO₂ reduction, electrocatalytic CO₂ reduction and chemical CO₂ conversion.

Photoredox Heterobimetallic Dual Catalysis Using Engineered Covalent Organic Frameworks

The functionalization of an imine-based layered covalent organic framework (COF), containing phenanthroline units as ligands, has allowed the obtention of a heterobimetallated material. Photoactive Ir and Ni fragments were immobilized within the porous structure of the COF, enabling heterogeneous light-mediated Csp3-Csp2 cross-couplings. As radical precursors, potassium benzyl- and alkoxy-trifluoroborates, organic silicates, and proline derivatives were employed, which brings out the good versatility of Ir,Ni@Phen-COF. Moreover, in all the studied cases, an enhanced activity and stability have been observed in comparison with analogous homogenous systems.

Hierarchical Double-Shelled CoP Nanocages for Efficient Visible-Light-Driven CO2 Reduction

Visible-light-driven photocatalytic CO₂ reduction is considered an appealing strategy to mitigate the energy crisis and environmental issues, whereas the reactivity is limited due to the difficulties in activation of inert CO₂ molecule and efficient transportation of photoinduced carriers. Herein, we report the design of novel Fe doped CoP hierarchical double-shelled nanocages (Fe-CoP HDSNC) via a MOF-templated approach for highly efficient visible-light-driven CO₂ reduction. The unique hierarchical double-shelled hollow architectures can greatly shorten the charge transfer distances and also expose abundant reactive sites. Moreover, Fe atoms doping is able to reduce the CO₂ activation energy barrier through stabilizing the *COOH intermediates and promote the CO desorption by destabilizing the CO* adduct. As expected, the Fe-CoP HDSNC achieves an unprecedented catalytic efficiency in visible-light-driven CO₂ reduction with an up to 3.25% apparent quantum yield and 90.3% CO selectivity, superior to most of the state-of-the-art photocatalysts under comparable conditions. More importantly, the Fe-CoP HDSNC is also highly effective under diluted CO₂ atmosphere, suggesting the practicability of the present photocatalytic system.

Atomically Dispersed Catalytic Sites: A New Frontier for Cocatalyst/Photocatalyst Composites toward Sustainable Fuel and Chemical Production

Photocatalysis delivers a promising pathway toward the clean and sustainable energy supply of the future. However, the inefficiency of photon absorption, rapid recombination of photogenerated electron-hole pairs, and especially the limited active sites for catalytic reactions result in unsatisfactory performances of the photocatalytic materials. Single-atom photocatalysts (SAPCs), in which metal atoms are individually isolated and stably anchored on support materials, allow for maximum atom utilization and possess distinct photocatalytic properties due to the unique geometric and electronic features of the unsaturated catalytic sites. Very recently, constructing SAPCs has emerged as a new avenue for promoting the efficiency of sustainable production of fuels and chemicals via photocatalysis. In this review, we summarize the recent development of SAPCs as a new frontier for cocatalyst/photocatalyst composites in photocatalytic water splitting. This begins with an introduction on the typical structures of SAPCs, followed by a detailed discussion on the synthetic strategies that are applicable to SAPCs. Thereafter, the promising applications of SAPCs to boost photocatalytic water splitting are outlined. Finally, the challenges and prospects for the future development of SAPCs are summarized.

Efficient Photocatalytic Reduction of CO2 to CO Using NiFe2O4@N/C/SnO2 Derived from FeNi Metal-Organic Framework

Use of light is considered an effective approach to convert CO₂ into usable chemical energy. In the present study, an iron- and nickel-containing bimetallic metal-organic framework (MOF) was synthesized via a simple solvothermal route. SnO₂ was then composited with the said MOF, and the obtained material was calcined and annealed to fabricate a series of nanophotocatalysts. The annealed sample displayed superior photocatalytic activity to the calcined sample, possibly due to the carbon-nitrogen layer formed after annealing mediating the charge-transfer process. The results of photocatalytic experiments indicated that using [Ru(bpy)₃]Cl₂·6H₂O as a photosensitizer and triethanolamine (TEOA) and acetonitrile (MeCN) as sacrificial agents, the catalyst sample was annealed at 450 °C (NiFe₂O₄@N/C/SnO₂-450) to afford the highest CO yield from CO₂ (2057.41 μmol g^-1 h^-1). The increase in the photocatalytic ability of the nanocomposites is basically attributed to multiple synergistic effects between NiFe₂O₄ and SnO₂, which reduce the recombination probability of the photo-induced electrons and holes. Ultimately, a photocatalytic reaction mechanism is proposed for NiFe₂O₄@N/C/SnO₂ in the reduction of CO₂.

Self-assembly of anthraquinone covalent organic frameworks as 1D superstructures for highly efficient CO2 electroreduction to CH4

The design of selective and efficient covalent organic frameworks (COFs) based electrocatalysts with tunable morphology for efficient CO₂ reduction reaction (CO₂RR) to CH₄ is highly desirable. Here, two kinds of anthraquinone-based COFs (i.e., AAn-COF and OH-AAn-COF) with tunable 1D superstructures (e.g., nanofibers (NF) and hollow tubes (HT)) have been produced via Schiff-base condensation reaction. Interestingly, a rarely reported nanosheet-based self-template mechanism and a nanosheet-crimping mechanism have been demonstrated for the production of COF-based nanofibers and hollow tubes, respectively. Besides, the obtained COF-based superstructures can be post-modified with transition metals for efficient CO₂RR. Specifically, AAn-COF-Cu (NF) and OH-AAn-COF-Cu (HT) exhibit superior faradaic-efficiency with CH₄ (FE_CH4) of 77% (-128.1 mA cm^-2, -0.9 V) and 61% (-99.5 mA cm^-2, -1.0 V) in a flow-cell, respectively. Noteworthy, the achieved FE_CH4 of AAn-COF-Cu (NF) (77%) the is highest one among reported crystalline COFs. This work provides a general methodology in exploring morphology-controlled COFs for electrocatalytic CO₂RR.

Structural and Morphological Engineering of Benzothiadiazole-Based Covalent Organic Frameworks for Visible Light-Driven Oxidative Coupling of Amines

Covalent organic frameworks (COFs) are appealing platforms for photocatalysts because of their structural diversity and adjustable optical band gaps. The construction of efficient COFs for heterogeneous photocatalysis of organic transformations is highly desirable. Herein, we constructed a photoactive COF containing benzothiadiazole and triazine (BTDA-TAPT), for which the morphology and crystallinity might be easily tuned by slight synthetic variation. To unveil the relationship of photocatalytic properties between the structure and morphology, analogous COFs were synthesized by precisely tailoring building blocks. Systematic investigations indicated that tuning the structure and morphology might greatly impact photoelectric properties. The BTDA-TAPT featuring ordered alignment and perfect crystalline nature was more beneficial for promoting charge transfer and separation, which exhibited superior photocatalytic activity for visible light-driven oxidative coupling of amines. Outcomes from this study reveal the intrinsic synergy effects between the structure and morphology of COFs for photocatalysis.

Design of Crystalline Reduction-Oxidation Cluster-Based Catalysts for Artificial Photosynthesis

Metal cluster-based compounds have difficulty finishing the photocatalytic carbon dioxide reduction reaction (CO₂RR) and water oxidation reaction (WOR) simultaneously because of the big challenge in realizing the coexistence of independently and synergistically reductive and oxidative active sites in one compound. Herein, we elaborately designed and synthesized one kind of crystalline reduction-oxidation (RO) cluster-based catalysts connecting reductive {M ₃ L ₈ (H ₂ O) ₂ } (M = Zn, Co, and Ni for RO-1, 2, 3 respectively) cluster and oxidative {PMo₉V₇O₄₄} cluster through a single oxygen atom bridge to achieve artificial photosynthesis successfully. These clusters can all photocatalyze CO₂-to-CO and H₂O-to-O₂ reactions simultaneously, of which the CO yield of RO-1 is 13.8 μmol/g·h, and the selectivity is nearly 100%. Density functional theory calculations reveal that the concomitantly catalytically reductive and oxidative active sites (for CO₂RR and WOR, respectively) and the effective electron transfer between the sites in these RO photocatalysts are the key factors to complete the overall photosynthesis.

A Porphyrin-Based Covalent Organic Framework for Metal-Free Photocatalytic Aerobic Oxidative Coupling of Amines

Imine is an important intermediate in drug synthesis. Photocatalytic aerobic oxidative coupling of amines has been considered as a clean and promising way to produce imine and attracted great attentions. Herein, we designed and synthesized a novel two-dimensional porphyrin-based COF (Por-BC-COF) which adopts an AA stacking mode with excellent crystallinity, high Brunauer-Emmett-Teller surface areas (1200 m 2 g -1 ), wide light absorption range (200-1300 nm) and good stability in a variety of organic solvents. Por-BC-COF can be used as a metal-free heterogeneous photocatalyst for the photocatalytic oxidation of amines to imines under visible light and red light with a high yield (97%). This work presents a novel and efficient COF photocatalyst in the application of light-driven organic synthesis.

Rational Design of Single-Atom Site Electrocatalysts: From Theoretical Understandings to Practical Applications

Atomically dispersed metal-based electrocatalysts have attracted increasing attention due to their nearly 100% atomic utilization and excellent catalytic performance. However, current fundamental comprehension and summaries to reveal the underlying relationship between single-atom site electrocatalysts (SACs) and corresponding catalytic application are rarely reported. Herein, the fundamental understandings and intrinsic mechanisms underlying SACs and corresponding electrocatalytic applications are systemically summarized. Different preparation strategies are presented to reveal the synthetic strategies with engineering the well-defined SACs on the basis of theoretical principle (size effect, metal-support interactions, electronic structure effect, and coordination environment effect). Then, an overview of the electrocatalytic applications is presented, including oxygen reduction reaction, hydrogen evolution reaction, oxygen evolution reaction, oxidation of small organic molecules, carbon dioxide reduction reaction, and nitrogen reduction reaction. The underlying structure-performance relationship between SACs and electrocatalytic reactions is also discussed in depth to expound the enhancement mechanisms. Finally, a summary is provided and a perspective supplied to demonstrate the current challenges and opportunities for rational designing, synthesizing, and modulating the advanced SACs toward electrocatalytic reactions.

Integrating Single Atoms with Different Microenvironments into One Porous Organic Polymer for Efficient Photocatalytic CO2 Reduction

The precise identification of single-atom catalysts (SACs) activity and boosting their efficiency toward CO₂ conversion is imperative yet quite challenging. Herein, for the first time a series of porous organic polymers is designed and prepared simultaneously, containing well-defined M-N₄ and M-N₂ O₂ single-atom sites. Such a strategy not only offers multiactive sites to promote the catalytic efficiency but also provides a more direct chance to identify the metal center activity. The CO₂ photoreduction results indicate that the introduction of salphen unit with Ni-N₂ O₂ catalytic centers into pristine phthalocyanine-based Ni-N₄ framework achieves remarkable CO generation ability (7.77 mmol g^-1 ) with a high selectivity of 96% over H₂ . In combination with control experiments, as well as theoretical studies, the Ni-N₂ O₂ moiety is evidenced as a more active site for CO₂ RR compared with the traditional Ni-N₄ moiety, which can be ascribed to the M-N₂ O₂ active sites effectively reducing the energy barrier, facilitating the adsorption of reaction radicals *COOH, and improving the charge transportation. This work might shed some light on designing more efficient SACs toward CO₂ reduction through modification of their coordination environments.

Highly Dispersive Ni@C and Co@C Nanoparticles Derived from Metal-Organic Monolayers for Enhanced Photocatalytic CO2 Reduction

The metal/carbon composites prepared by direct pyrolysis of metal-organic frameworks (MOFs) are regarded as ideal catalysts. However, conventional MOFs show a three-dimensional bulk structure. For bulk MOF-derived catalysts, most active metal sites are confined in the interior and not fully utilized. In this work, metal-organic monolayers (MOLs) are used as the starting precursors to prepare carbon-wrapped metal nanoparticles, which are further employed as catalysts for photocatalytic CO₂ reduction. The as-prepared Ni-MOLs and Co-MOLs have an ultrathin thickness of ∼1 nm. It is interestingly found that their derived Ni@C and Co@C nanoparticles are highly dispersive and connected with each other like a piece of paper. As compared with bulk MOF-derived counterparts, MOL-derived catalysts increase the accessibility of active metal sites, which can accelerate electron transfer from photosensitizers to Ni@C and Co@C nanoparticles. In this way, the catalytic activity can be greatly improved. Besides, the magnetic nature of Ni@C and Co@C nanoparticles enables the easy separation and recycling of catalysts. It is expected that this work will provide instructive guidelines for the rational design of MOL-derived catalysts.

Differences and Similarities of Photocatalysis and Electrocatalysis in Two-Dimensional Nanomaterials: Strategies, Traps, Applications and Challenges

Photocatalysis and electrocatalysis have been essential parts of electrochemical processes for over half a century. Recent progress in the controllable synthesis of 2D nanomaterials has exhibited enhanced catalytic performance compared to bulk materials. This has led to significant interest in the exploitation of 2D nanomaterials for catalysis. There have been a variety of excellent reviews on 2D nanomaterials for catalysis, but related issues of differences and similarities between photocatalysis and electrocatalysis in 2D nanomaterials are still vacant. Here, we provide a comprehensive overview on the differences and similarities of photocatalysis and electrocatalysis in the latest 2D nanomaterials. Strategies and traps for performance enhancement of 2D nanocatalysts are highlighted, which point out the differences and similarities of series issues for photocatalysis and electrocatalysis. In addition, 2D nanocatalysts and their catalytic applications are discussed. Finally, opportunities, challenges and development directions for 2D nanocatalysts are described. The intention of this review is to inspire and direct interest in this research realm for the creation of future 2D nanomaterials for photocatalysis and electrocatalysis.

Regulating Utilization Efficiency of the Photogenerated Charge Carriers by Constructing Donor-π-Acceptor Polymers for Upgrading Photocatalytic CO2 Reduction

Photocatalytic CO₂ reduction offers a promising approach for managing global carbon balance. The smooth delivery of the photoexcited electrons to the active sites without the extra photosensitizers is still challenging. Herein, a series of donor-π-acceptor conjugated organic polymers (COPs) were produced using anthracene, cobalt-coordinated bipyridyl, and benzene as donor, acceptor, and π linker units, respectively. The introduction of phenyl linker significantly improved the activities of photocatalytic CO₂ reduction upon visible light illumination. Structure-performance relationship examinations uncovered that donor-π-acceptor structure promotes mobility of charge carriers and utilization efficiency on the catalytically active sites, resulting in high photocatalytic activity and durability for CO₂ photoreduction. The in-depth insights into the electron transport processes open new perspectives for further optimization and rational design of photoactive polymers with high efficiency for solar-energy conversion.

Atom-Anchoring Strategy with Metal-Organic Frameworks for Highly Efficient Solid-State Electrochemiluminescence

A chemical fixation strategy originating from single-atom-anchoring with metal-organic frameworks as a carrying matrix was proposed for solid-state electrochemiluminescence (ECL). Herein, UiO-67(N) with the exposure of 2,2'-bipyridine (bpy) ligands could coordinate with Ru²⁺ to form a local structure of [Ru(bpy)₃]²⁺ (Ru-UiO). The influence of the steric effect induced with different Ru sources was discussed. The as-obtained Ru-UiO exhibits high ECL intensity and outstanding stability in the presence of a coreactant at low concentrations. The proposed synthesis strategy may hold great potential for the synthesis of solid-state ECL materials and their further utilization in ECL analysis.

Atomically Dispersed Pt-N3C1 Sites Enabling Efficient and Selective Electrocatalytic C-C Bond Cleavage in Lignin Models under Ambient Conditions

Selective cleavage of C-C linkages is the key and a challenge for lignin degradation to harvest value-added aromatic compounds. To this end, electrocatalytic oxidation presents a promising technique by virtue of mild reaction conditions and strong sustainability. However, the existing electrocatalysts (traditional bulk metal and metal oxides) for C-C bond oxidative cleavage suffer from poor selectivity and low product yields. We show for the first time that atomically dispersed Pt-N₃C₁ sites planted on nitrogen-doped carbon nanotubes (Pt₁/N-CNTs), constructed via a stepwise polymerization-carbonization-electrostatic adsorption strategy, are highly active and selective toward C_α-C_β bond cleavage in β-O-4 model compounds under ambient conditions. Pt₁/N-CNTs exhibits 99% substrate conversion with 81% yield of benzaldehyde, which is exceptional and unprecedented compared with previously reported electrocatalysts. Moreover, Pt₁/N-CNTs using only 0.41 wt % Pt achieved a much higher benzaldehyde yield than those of the state-of-the-art bulk Pt electrode (100 wt % Pt) and commercial Pt/C catalyst (20 wt % Pt). Systematic experimental investigation together with density functional theory (DFT) calculation suggests that the superior performance of Pt₁/N-CNTs arises from the atomically dispersed Pt-N₃C₁ sites facilitating the formation of a key C_β radical intermediate, further inducing a radical/radical cross-coupling path to break the C_α-C_β bond. This work opens up opportunities in lignin valorization via a green and sustainable electrochemical route with ultralow noble metal usage.

Rational construction of Ni(OH)2 nanoparticles on covalent triazine-based framework for artificial CO2 reduction

Artificial photoreduction of CO₂ to chemical fuel is an intriguing and reliable strategy to tackle the issues of energy crisis and climate change simultaneously. In the present study, we rationally constructed a Ni(OH)₂-modified covalent triazine-based framework (CTF-1) composites to serve as cocatalyst ensemble for superior photoreduction of CO₂. In particular, the optimal Ni(OH)₂-CTF-1 composites (loading ratio at 0.5 wt%) exhibited superior photocatalytic activity, which surpassed the bare CTF-1 by 33 times when irradiated by visible light. The mechanism for the enhancement was systematically investigated based on various instrumental analyses. The origin of the superior activity was attributable to the enhanced CO₂ capture, more robust visible-light response, and improved charge carrier separation/transfer. This study offers an innovative pathway for the fabrication of noble-metal-free cocatalysts on CTF semiconductors and deepens the understanding of photocatalytic CO₂ reduction.

Aptamer-Regulated Gold Nanosol Plasmonic SERS/RRS Dimode Assay of Trace Organic Pollutants Based on TpPa-Loaded PdNC Catalytic Amplification

As with excellent catalytic performance, palladium nanoclusters (PdNCs) have a wide range of applications. However, the traditional PdNCs are easy to agglomerate in the analysis system and lose their catalytic activity. A covalent organic framework (COF) has a definite structure, good stability, and easy surface functionalization. So, it is of great significance to develop stable PdNCs with high catalytic activity and then combine with advanced analysis techniques to analyze ultratrace small-molecule pollutants in the environment. In this research, a stable PdNC dispersed on a COF (PdTpPa) catalyst is prepared and we find it with strong catalysis for the NaH2PO2-HAuCl4 catalytic reaction. Furthermore, this nanocatalytic indicator reaction can be tracked by surface-enhanced Raman spectroscopy (SERS) and resonance Rayleigh scattering (RRS) dual-mode. Combined with a highly specific aptamer-modifying technique, a highly sensitive and selective SERS/RRS dimode assay platform for trace organic pollutants has been developed. The detection limits of oxytetracycline (OTC), glyphosate (GLY), tetracycline (TEC), and bisphenol A (BPA) are 0.64, 0.03, 6.2 × 10-3, and 0.53 × 10-3 ng/mL, respectively. This work also provides ideas for the application of COF materials and Pd nanocatalysts in the molecular spectral detection of trace pollutants.

Single-atom catalysts for high-energy rechargeable batteries

Clean and sustainable electrochemical energy storage has attracted extensive attention. It remains a great challenge to achieve next-generation rechargeable battery systems with high energy density, good rate capability, excellent cycling stability, efficient active material utilization, and high coulombic efficiency. Many catalysts have been explored to promote electrochemical reactions during the charge and discharge process. Among reported catalysts, single-atom catalysts (SACs) have attracted extensive attention due to their maximum atom utilization efficiency, homogenous active centres, and unique reaction mechanisms. In this perspective, we summarize the recent advances of the synthesis methods for SACs and highlight the recent progress of SACs for a new generation of rechargeable batteries, including lithium/sodium metal batteries, lithium/sodium-sulfur batteries, lithium-oxygen batteries, and zinc-air batteries. The challenges and perspectives for the future development of SACs are discussed to shed light on the future research of SACs for boosting the performances of rechargeable batteries.

Metal-organic framework membranes with single-atomic centers for photocatalytic CO2 and O2 reduction

The demand for sustainable energy has motivated the development of artificial photosynthesis. Yet the catalyst and reaction interface designs for directly fixing permanent gases (e.g. CO₂, O₂, N₂) into liquid fuels are still challenged by slow mass transfer and sluggish catalytic kinetics at the gas-liquid-solid boundary. Here, we report that gas-permeable metal-organic framework (MOF) membranes can modify the electronic structures and catalytic properties of metal single-atoms (SAs) to promote the diffusion, activation, and reduction of gas molecules (e.g. CO_2, O₂) and produce liquid fuels under visible light and mild conditions. With Ir SAs as active centers, the defect-engineered MOF (e.g. activated NH₂-UiO-66) particles can reduce CO₂ to HCOOH with an apparent quantum efficiency (AQE) of 2.51% at 420 nm on the gas-liquid-solid reaction interface. With promoted gas diffusion at the porous gas-solid interfaces, the gas-permeable SA/MOF membranes can directly convert humid CO₂ gas into HCOOH with a near-unity selectivity and a significantly increased AQE of 15.76% at 420 nm. A similar strategy can be applied to the photocatalytic O₂-to-H₂O₂ conversions, suggesting the wide applicability of our catalyst and reaction interface designs.

Photoreduction of permanent gas faces challenges in reactant diffusion and activation at the three-phase interface. Here the authors showed porous metal-organic framework membranes decorated by metal single atoms can boost the photoreduction of CO₂ and O₂ at the high-throughput gas-solid interface.

Probe metal binding mode of imine covalent organic frameworks: cycloiridation for (photo)catalytic hydrogen evolution from formate

Metalation of covalent organic frameworks (COFs) is a critical strategy to functionalize COFs for advanced applications yet largely relies on the pre-installed specific metal docking sites in the network, such as porphyrin, salen, 2,2'-bipyridine, etc. We show in this study that the imine linkage of simple imine-based COFs, one of the most popular COFs, readily chelate transition metal (Ir in this work) via cyclometalation, which has not been explored before. The iridacycle decorated COF exhibited more than 10-fold efficiency enhancement in (photo)catalytic hydrogen evolution from aqueous formate solution than its molecular counterpart under mild conditions. This work will inspire more functional cyclometallated COFs to be explored beyond catalysis considering the large imine COF library and the rich metallacycle chemistry.

Ag/Ultrathin-Layered Double Hydroxide Nanosheets Induced by a Self-Redox Strategy for Highly Selective CO2 Reduction

The carbon-neutral photocatalytic CO₂ reduction reaction (CO₂RR) enables the conversion of CO₂ into hydrocarbon fuels or value-added chemicals under mild conditions. Achieving high selectivity for the desired products of the CO₂RR remains challenging. Herein, a self-redox strategy is developed to construct strong interfacial bonds between Ag nanoparticles and an ultrathin CoAl-layered double hydroxide (U-LDH) nanosheet support, where the surface hydroxyl groups associated with oxygen vacancies of U-LDH play a critical role in the formation of the interface structure. The supported Ag@U-LDH acts as a highly efficient catalyst for CO₂ reduction, resulting in a high CO evolution rate of 757 μmol g_cat^-1 h^-1 and a CO selectivity of 94.5% under light irradiation. Such a high catalytic selectivity may represent a new record among current photocatalytic CO₂RR to CO systems. The Ag-O-Co interface bonding is confirmed by Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and FTIR CO₂ adsorption studies. The in situ FTIR measurements indicate that the formation of the *COOH intermediate is accelerated and the mass transfer is improved during the CO₂RR. Density functional theory calculations show that the Ag-O-Co interface reduces the formation energy of the *COOH intermediate and accumulates localized charge. Experimental and theoretical analysis collectively demonstrates that the strong interface bonding between Ag and U-LDH activates the interface structure as catalytically CO₂RR active sites, effectively optimizing the binding energies with reacted intermediates and facilitating the CO₂RR performance.

A Visible-Light-Harvesting Covalent Organic Framework Bearing Single Nickel Sites as a Highly Efficient Sulfur-Carbon Cross-Coupling Dual Catalyst

Covalent Organic Frameworks (COFs) have recently emerged as light-harvesting devices, as well as elegant heterogeneous catalysts. The combination of these two properties into a dual catalyst has not yet been explored. We report a new photosensitive triazine-based COF, decorated with single Ni sites to form a dual catalyst. This crystalline and highly porous catalyst shows excellent catalytic performance in the visible-light-driven catalytic sulfur-carbon cross-coupling reaction. Incorporation of single transition metal sites in a photosensitive COF scaffold with two-component synergistic catalyst in organic transformation is demonstrated for the first time.

Review on the hazardous applications and photodegradation mechanisms of chlorophenols over different photocatalysts

Chlorophenols are very important environmental pollutants, which have created huge problems for both aquatic and terrestrial lives. Therefore, their removal needs urgent, effective, and advanced technologies to safeguard our environment for future generation. This review encompasses a comprehensive study of the applications of chlorophenols, their hazardous effects and photocatalytic degradation under light illumination. The effect of various factors such as pH and presence of different anions on the photocatalytic oxidation of chlorophenols have been elaborated comprehensively. The production of different oxidizing agents taking part in the photodegradation of chlorophenols are given a bird eye view. The photocatalytic degradation mechanism of different chlorophenols over various photocatalyts has been discussed in more detail and elaborated that how different photocatalysts degrade the same chlorophenols with the aid of different oxidizing agents produced during photocatalysis. Finally, a future perspective has been given to deal with the effective removal of these hazardous pollutants from the environment.

N-Heterocyclic Carbene Functionalized Covalent Organic Framework for Transesterification of Glycerol with Dialkyl Carbonates

The development of a heterogeneous catalyst through the combination of novel carrier and powerful catalytic active sites is of particular interest. Herein, the successful integration of an N-Heterocyclic carbene (NHC) moiety into a covalent organic framework (COF) was achieved by coupling 4,4′,4′′,4′′′-(pyrene-1,3,6,8-tetrayl) tetraaniline (PyTTA) and equimolar 4,7-bis(4-formylphenyl)-1-methyl-1H-benzimidazole (IM) and 2′3′5′6′-tetrafluoro-[1,1′:4′,1′′-terphenyl]-4,4′-dicarbaldehyde (4F) followed by ionization with 1-bromobutane (C4H9Br) and then deprotonation upon addition of a base. The resulting material exhibited promising heterogeneous catalytic activity towards transesterification reaction of glycerol with dialkyl carbonate. Moreover, good recyclability granted no substantial loss of activity upon five cycles. Combination of COFs and NHCs might synergize their characteristics, thus providing more possibilities for creating new patterns of catalytic reactivity.

Rational design of isostructural 2D porphyrin-based covalent organic frameworks for tunable photocatalytic hydrogen evolution

Covalent organic frameworks have recently gained increasing attention in photocatalytic hydrogen generation from water. However, their structure-property-activity relationship, which should be beneficial for the structural design, is still far-away explored. Herein, we report the designed synthesis of four isostructural porphyrinic two-dimensional covalent organic frameworks (MPor-DETH-COF, M = H₂, Co, Ni, Zn) and their photocatalytic activity in hydrogen generation. Our results clearly show that all four covalent organic frameworks adopt AA stacking structures, with high crystallinity and large surface area. Interestingly, the incorporation of different transition metals into the porphyrin rings can rationally tune the photocatalytic hydrogen evolution rate of corresponding covalent organic frameworks, with the order of CoPor-DETH-COF < H₂Por-DETH-COF < NiPor-DETH-COF < ZnPor-DETH-COF. Based on the detailed experiments and calculations, this tunable performance can be mainly explained by their tailored charge-carrier dynamics via molecular engineering. This study not only represents a simple and effective way for efficient tuning of the photocatalytic hydrogen evolution activities of covalent organic frameworks at molecular level, but also provides valuable insight on the structure design of covalent organic frameworks for better photocatalysis.