Photocoupled Electroreduction of CO2 over Photosensitizer-Decorated Covalent Organic Frameworks

Low-Coordination Triangular Cu3 Motif Steers CO2 Photoreduction to Ethanol

Photoreduction of CO2 using copper-based multi-atom catalysts (MACs) offers a potential approach to achieve value-added C2+ products. However, achieving MACs with high metal contents and suppressing the thermodynamically favored competing ethylene production pathway remain challenging, thus leading to unsatisfactory performance in ethanol production. Herein, we developed a "pre-locking and nanoconfined polymerization" strategy for synthesis of an ultra-high-density Cu MAC with low-coordination triangular Cu3 motifs (Cu3 MAC) on polymeric carbon nitride mesoporous nanofibers. The Cu3 MAC with Cu contents of 36 wt% achieves a high reactivity of 117 µmol g-1 h-1 for ethanol production from CO2 and H2O, with a remarkable selectivity of 98% under simulated sunlight irradiation, representing one of the highest performances in ambient conditions without sacrificial reagents. The superior catalytic efficiency is attributed to the triangular Cu3 configuration, in which both Cu(I) and Cu(II) coexist, predominantly as Cu(I). Such Cu3 motifs act as strong alkaline sites that effectively chemisorb and activate CO2, extend visible-light absorption range, while accumulating high-density electrons and favoring 12-electron-transfer products. An accelerated asymmetric C─C coupling with adsorption configuration of the bridge-adsorbed *CO at paired Cu sites and atop-adsorbed *CO at adjacent single Cu atom was observed, enabling preferential formation of *CHCHOH intermediates to produce ethanol.

Cascaded Metalation of Two-Dimensional Covalent Organic Frameworks for Boosting Electrochemical CO Reduction

The electrochemical CO reduction reaction (CORR) to high-value methanol requires the delicate design of catalysts due to the large overpotential. Especially, achieving precise modification of electrocatalysts while preserving the periodic alignment of active sites to optimize performance remains a significant challenge. Here, we report the cascaded metalation of phthalocyanine-based COFs for selective reduction of CO to methanol. After implanting the secondary metal (Ni), CityU-35 achieves a Faradaic efficiency (FE) of 48.4% at -0.85 V versus RHE, significantly surpassing that of CityU-34 (2.1%) with only Co atoms. Enhanced methanol production originates from the optimization of electronic structure with improved *CO adsorption, as substantiated by the in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). Theoretical calculations have demonstrated that the cascaded metalation with the introduction of secondary Ni sites not only strengthens *CO adsorption but also accelerates proton generation for the hydrogenation of *CO toward CH3OH. The cascaded metalation with synergistic effects between Co and Ni sites reduces the energy barriers and improves the overall electroactivity. Our results demonstrate cascaded metalation as an effective strategy to tailor the catalytic activities of 2D COFs, extending the functional design of reticular frameworks in electrocatalysis.

Application of COF Materials in Carbon Dioxide Electrocatalytic Reduction

COFs have become the most attractive frontier research area in heterogeneous catalysis. Since the geometry and electronic structure of COFs are largely determined by their microenvironment, which in turn determines the performance in electrocatalytic processes, the precise integration of atoms of COF building blocks to achieve pre-designed composition, components and functions is the core. This paper focuses on the structural design, synthesis, electrocatalytic mechanism and application of COFs in electrocatalytic CO2RR (types of COFs in electrocatalytic CO2RR, performance evaluation indicators of COFs in electrocatalytic CO2RR, and the relationship between the structure of COFs and electrocatalytic performance). In addition, we also explore the challenges faced by COFs in CO2RR and the corresponding solution strategies. Finally, by highlighting the prospects and challenges of COFs structural regulation, we hope to provide inspiration for the further development of COFs in electrocatalytic applications.

Modulating Active Center Microenvironment in Phthalocyanine-Based Covalent Organic Frameworks for Enhanced Electrocatalytic CO2 to CH3OH

Developing catalysts for electrocatalytic CO2 to CH3OH still faces great challenge due to the involvement of multiple proton-coupled electron transfer (PCET) processes. Molecular phthalocyanine electrocatalysts on carbon nanotubes have achieved production of methanol as the sole liquid-phase product but with the activity and stability far from meeting industrial demands. Herein, phthalocyaninato cobalt is fabricated into covalent organic frameworks PE-COF via polymerization with ellagic acid. Subsequent hydrolyzation of the ester groups in this framework affords COOH/OH-containing PEH-COF, resulting in the successful modulation over the local microenvironment of Co as electrochemical active center and in turn rendering the production of CH3OH with high yield and durability. Experimental and theoretical investigations reveal that construction of the COOH group and H2O participated catalytic cages in PEH-COF can effectively fix hydrated potassium ions, which efficiently enhances the PCET kinetics and lowers the energy barriers for the conversion of CO2 to CH3OH. The partial current density (j) and Faraday efficiency of methanol for PEH-COF could reach 100.9 mA cm-2 and 38.5%, respectively. Moreover, thej C H 3 O H $\mathrm{j}_{{CH}_3OH}$ of PEH-COF can be maintained at 100.4 mA cm-2 after 9 h of electrocatalysis, superior to the thus far reported catalysts.

Ionic-Fence Effect in Au Nanoparticle-Loaded UiO-66 Metal-Organic Frameworks for Highly Chemoselective Hydrogenation

The chemoselective reaction are vital for fine chemicals, which requires economical and environmentally friendly catalysts. In order to improve the selectivity of multi-reaction competition, herein, we propose a novel ionic-fence strategy to synthesize heterogeneous catalyst for efficient hydrogenation. Practically, UIO-66 metal-organic frameworks (MOF) modified with pyridinium-linker has been constructed through post-synthetic chains with paired anion via quaternization and ion exchange to form ionic-fence MOF (IFMOF-Cl), which can manage the adsorption mode of nitro substrate, further confine the formation of metal nanoparticles with high dispersity. The optimal Au@IFMOF-Cl catalyst demonstrates satisfactory selectivity for hydrogenation of nitro group compared to acetylene group in 4-nitrophenylacetylene. Specifically, it owns a high yield of 4-aminophenylacetylene (~97 %) with ultra-high catalytic efficiency (3880 h-1 TOF) and long stability, far superior to other catalysts without ionic fence effect. Adsorption experiments and density functional theory studies reveal that the incorporation of ionic fence could modulate the adsorption energy of nitro group, which is responsible for the high selectivity enhancement. Notably, this ionic-fence strategy exhibits comprehensive universality towards a wide range of substrates (23 kinds in total), providing a promising avenue for precisely engineering the internal microenvironments of catalysts to achieve highly selective synthesis of fine chemicals.

Staggered ABC-Stacking Cobalt-Triptycene Framework for Accelerating CO2 Photoreduction

Metal-organic frameworks (MOFs) are highly efficient photocatalysts due to their highly tunable structures and favorable electronic properties. However, achieving control over framework stacking arrangements, such as the staggered ABC-stacking, presents significant challenges. This difficulty arises from the inherently unfavorable energetics of the ABC arrangement and weaker π-π interactions compared to other stacking modes. Herein, a cobalt-triptycene framework with a staggered ABC-stacking arrangement was successfully synthesized in the aqueous phase, achieving a 90% yield. Experimental evaluations revealed that this framework achieved a CO production rate of 4.43 mmol g-1 h-1, which is comparable to the most reported MOF-based photocatalysts for CO2 reduction. Moreover, density functional theory (DFT) calculations and molecular dynamics (MD) simulations indicated that the ABC-stacking cobalt-triptycene framework exhibits lower activation energy (0.079 eV) for water molecules, reduced Gibbs free energies for key intermediates *COOH (0.76 eV) and *H (0.73 eV), and the highest reaction rate increment (7.488 times). Furthermore, principal component analysis (PCA) reveals a strong correlation between the CO production rate and factors such as the Ik value, optical bandgap, and ΔG*H, revising the previous held notion that ΔG*COOH is the primary determinant of catalytic performance. These results offer valuable insights into the design principles of advanced photocatalysts for CO2 reduction.

Photocatalytic Reduction of Carbon Dioxide: Designing the Active Sites and Tracking the Pathways

Photocatalytic reduction of carbon dioxide (CO2) realizes the recycling of carbon emissions and storage of solar energy into the bonding of organics at the same time, and thus attract great interest in the field of energy and environment. However, the current photocatalytic performance of CO2 reduction cannot match the industrial application. The design of highly efficient photocatalysts with precise selectivity and reliable long-term stability is still a big challenge, partially because the mechanism of photocatalytic CO2 reduction to guide the design and fabrication, is not completely clear yet. The reduction can involve at most eight electrons for each CO2 molecule, during which several pathways might be opened up at the active sites to consume photocarriers to influence the selectivity and stability. The reduction pathways are dependent on the electronic structure and property of active sites, and the photocatalytic performance can be optimized if those pathways are thermodynamically or kinetically compatible for the target production. This review will summarize the strategy for designing the active sites on the surface of photocatalysts and the investigation on the relation between the active sites and pathways for photocatalytic CO2 reduction, looking ahead at the future development of the photocatalysts and devices for CO2 reduction.

Synergistic Bifunctional Covalent Organic Framework for Efficient Photocatalytic CO2 Reduction and Water Oxidation

The scientific community has been actively researching artificial photosynthesis to promote ecologically sustainable living and address environmental issues. However, designing photocatalysts with active sites that are effective for both CO2 reduction and water oxidation remains a significant challenge. Thus, we present the development of a donor-acceptor covalent organic framework (D-A COF), that integrates two distinct metal coordination environments through structure-activity relationships. Either cobalt or nickel ion is anchored on the D-A COF backbone to create N-metal-nitrogen and N-metal-sulfur coordination configurations, serving as bifunctional reduction and oxidation active sites, respectively. Remarkably, the as-synthesized Co-Btt-Bpy COF generated CO at a rate of 9,800 μmol g-1 h-1 and O2 at 242 μmol g-1 h-1 under visible light irradiation. The CO generation rate was 127 times higher than that of pristine D-A COF. More importantly, Co-Btt-Bpy COF facilitates artificial photosynthesis with a CO release rate of 7.4 μmol g-1 h-1. The outstanding photocatalytic performance can be attributed to the synergistic interaction between the dispersed single-atom sites and Btt-Bpy COF, as well as the rapid migration of photogenerated electrons. In situ attenuated total reflection Fourier transform infrared (ATR FT-IR) spectra and theoretical calculations indicated that introducing Co sites effectively lowered the reaction energy barriers for the crucial intermediates *COOH and *OH. This work provides state-of-the-art designs of photocatalysts at the molecular level and in-depth insights for efficient artificial photosynthesis.

Porphyrin-based Vinylene-linked 3D Covalent Organic Framework with Unprecedented cya Topology for Photocatalytic H2O2 Production

Designing and realizing new topologies represent one of the most important ways toward developing new structures and functionalities for molecule-based frameworks including SOFs, MOFs, and COFs. Herein, Aldol condensation between 5,10,15,20-tetrayl(tetrakis(([1,1':3',1''-terphenyl]-4,4''-dicarbaldehyde)))-porphyrin (TTEP) and 2,4,6-trimethyl-1,3,5-triazine (TMT) affords the vinylene-linked 3D covalent organic framework Por-COF-cya. Powder X-ray diffraction (PXRD) in combination with structural simulation reveals its high crystalline structure with an unprecedented cya topology in the molecule-based frameworks reported thus far. Por-COF-cya displayed polycrystallinity and possessed high permanent porosity. Especially, the incorporation of light-harvesting porphyrin unit and vinylene linkages in Por-COF-cya enables a conjugation effect within the framework, endowing it with a photocatalytic H2O2 production rate of 2209 μmol g-1h-1 in pure aqueous solution under visible-light irradiation (λ >420 nm). Inclusion of the guest molecules TTF into the pores of Por-COF-cya results in a donor-acceptor system TTF@Por-COF-cya, enhancing the photocatalytic activity with H2O2 production rate of 6994 μmol g-1h-1. This work paves a new way for the development of new topological functional molecule-based frameworks toward diverse application potentials.

Porphyrin-Based Covalent Organic Frameworks for CO2 Photo/Electro-Reduction

Photo/electro-catalytic CO2 reduction into high-value products are promising strategies for addressing both environmental problems and energy crisis. Duo to their advantageous visible light absorption ability, adjustable optic/electronic properties, definite active center, post-modification capability, and excellent stability, porphyrin-based covalent organic frameworks (COFs) have emerged as attractive photo/electro-catalysts towards CO2 reduction. In this review, the research progress of the porphyrin-based COFs for photo/electro-catalytic CO2 reduction is summarized including the design principles, catalytic performance, and reaction mechanism. In addition, this review also presents some challenges and prospects for the application of porphyrin-based COFs in photo/electro-catalytic CO2 reduction, laying the base for both fundamental research and application efforts.

In/Outside Catalytic Sites of the Pore Walls in One-Dimensional Covalent Organic Frameworks for Oxygen Reduction Reaction

Pore channels play a decisive role in mass transport in catalytic systems. However, the influences of the location of catalytic sites inside or outside of the pore walls on the performance were still under-explored due, because it is difficult to construct sites anchored in or outside of pore walls. Herein, one-dimensional covalent organic frameworks with precisely anchored active sites were used to explore the effects of channels on a typical oxygen reduction reaction (ORR) catalysis. Electrocatalytic evaluations showed that single Pt sites located inside of the channels exhibited higher kinetic activity compared to those anchored outside. The in situ spectroscopic analysis revealed that local reconstruction of Pt-Cl breaking and potential-induced anion transport occurred more effectively inside the channels. The superior anion transportability and kinetic activity of the inside-channel active sites also facilitated *OH desorption during the ORR process outperforming their outside-channel counterparts. The results of this study provide strategies for designing active sites in porous catalysts for heterogeneous catalysis.

Self-sensitized Cu(ii)-complex catalyzed solar driven CO2 reduction

Developing a self-sensitized catalyst from earth-abundant elements, capable of efficient light harvesting and electron transfer, is crucial for enhancing the efficacy of CO2 transformation, a critical step in environmental cleanup and advancing clean energy prospects. Traditional approaches relying on external photosensitizers, comprising 4d/5d metal complexes, involve intermolecular electron transfer, and attachment of photosensitizing arms to the catalyst necessitates intramolecular electron transfer, underscoring the need for a more integrated solution. We report a new Cu(ii) complex, K[CuNDPA] (1[K(18-crown-6)]), bearing a dipyrrin amide-based trianionic tetradentate ligand, NDPA (H3L), which is capable of harnessing light energy, despite having a paramagnetic Cu(ii) centre, without any external photosensitizer and photocatalytically reducing CO2 to CO in acetonitrile : water (19 : 1 v/v) with a TON as high as 1132, a TOF of 566 h-1 and a selectivity of 99%. This complex also shows hemilability in the presence of water, which not only plays a role in the proton relay mechanism but also helps stabilize a crucial Cu(i)-NDPA intermediate. The hemilability was justified by the formation of N3O (2) and N2O2 (3) coordinated congeners of the N4 bound complex 1. The overall mechanism was further investigated via spectroscopic techniques such as EPR, UV-vis, and spectroelectrochemistry, culminating in the justification of a single electron-reduced Cu(i)NDPA species as a proposed intermediate. In the next step, the binding of CO2 to the Cu(i) complex and subsequent electron transfer to form Cu(ii)-COO·- was indirectly probed by a radical trapping experiment via the addition of p-methoxy-2,6-di-tert-butylphenol that led to the formation of a phenoxyl radical. This work provides new strategies for designing earth-abundant robust molecular catalysts that can function as photocatalysts without the aid of any external photosensitizers.

Modulation of Electrochemical Reactions through External Stimuli: Applications in Oxygen Evolution Reaction and Beyond

Electrochemical water splitting is a promising method for generating green hydrogen gas, offering a sustainable approach to addressing global energy challenges. However, the sluggish kinetics of the anodic oxygen evolution reaction (OER) poses a great obstacle to its practical application. Recently, increasing attention has been focused on introducing various external stimuli to modify the OER process. Despite significant enhancement in catalytic performance, an in-depth understanding of the origin of superior OER activity contributed by the external stimuli remains elusive, which significantly hinders the further development of highly efficient and durable water electrolyzed devices. Herein, this review systematically summarizes the recent advancements in the understanding of various external stimuli, including photon irradiation, applied magnetic field, and thermal heating, etc., to boost OER activities. In particular, the underlying mechanisms of external stimuli to promote species transfer, modify the electronic structure of electrocatalysts, and accelerate structural reconstruction are highlighted. Additionally, applications of external stimuli in other electrocatalytic reactions are also presented. Finally, several remaining challenges and future opportunities are discussed, providing insights that could further the study of external stimuli in electrocatalytic reactions and support the rational design of highly efficient energy storage and conversion devices.

Photocatalytic applications of covalent organic frameworks: synthesis, characterization, and utility

Photocatalysis has emerged as an energy efficient and safe method to perform organic transformations, and many semiconductors have been studied for use as photocatalysts. Covalent organic frameworks (COFs) are an established class of crystalline, porous materials constructed from organic units that are easily tunable. COFs importantly display semiconductor properties and respectable photoelectric behaviour, making them a strong prospect as photocatalysts. In this review, we summarize the design, synthetic methods, and characterization techniques for COFs. Strategies to boost photocatalytic performance are also discussed. Then the applications of COFs as photocatalysts in a variety of reactions are detailed. Finally, a summary, challenges, and future opportunities for the development of COFs as efficient photocatalysts are entailed.

Drug-phospholipid conjugate nano-assembly for drug delivery

Phospholipid-based liposomes are among the most successful nanodrug delivery systems in clinical use. However, these conventional liposomes present significant challenges including low drug-loading capacity and issues with drug leakage. Drug-phospholipid conjugates (DPCs) and their assemblies offer a promising strategy for addressing these limitations. In this review, we summarize recent advances in the design, synthesis, and application of DPCs for drug delivery. We begin by discussing the chemical backbone structures and various design strategies such as phosphate head embedding and mono-/bis-embedding in the sn-1/sn-2 positions. Furthermore, we highlight stimulus-responsive designs of DPCs and their applications in treating diseases such as cancer, inflammation, and malaria. Lastly, we explore future directions for DPCs development and their potential applications in drug delivery.

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.

Delocalized Orbitals over Metal Clusters and Organic Linkers Enable Boosted Charge Transfer in Metal-Organic Framework for Overall CO2 Photoreduction

The conversion of CO2 to C2 through photocatalysis poses significant challenges, and one of the biggest hurdles stems from the sluggishness of the multi-electron transfer process. Herein, taking metal-organic framework (MOF, PFC-98) as a model photocatalyst, we report a new strategy to facilitate charge separation. This strategy involves matching the energy levels of the lowest unoccupied node and linker orbitals of the MOF, thereby creating the lowest unoccupied crystal orbital (LUCO) delocalized over both the node and linker. This feature enables the direct excitation of electrons from photosensitive linker to the catalytic centers, achieving a direct charge transfer (DCT) pathway. For comparison, an isoreticular MOF (PFC-6) based on analogue components but with far apart frontier energy level was synthesized. The delocalized LUCO caused the presence of an internal charge-separated (ICS) state, prolonging the excited state lifetime and further inhibiting the electron-hole recombination. The presence of ICS state prolongs the excited state lifetime and further inhibits the electron-hole recombination. Moreover, it also induced abundant electrons accumulating at the catalytic sites, enabling the multi-electron transfer process. As a result, the material featuring delocalized LUCO exhibits superior overall CO2 photocatalytic performance with high C2 production yield and selectivity.

Microenvironment Engineering of Heterogeneous Catalysts for Liquid-Phase Environmental Catalysis

Environmental catalysis has emerged as a scientific frontier in mitigating water pollution and advancing circular chemistry and reaction microenvironment significantly influences the catalytic performance and efficiency. This review delves into microenvironment engineering within liquid-phase environmental catalysis, categorizing microenvironments into four scales: atom/molecule-level modulation, nano/microscale-confined structures, interface and surface regulation, and external field effects. Each category is analyzed for its unique characteristics and merits, emphasizing its potential to significantly enhance catalytic efficiency and selectivity. Following this overview, we introduced recent advancements in advanced material and system design to promote liquid-phase environmental catalysis (e.g., water purification, transformation to value-added products, and green synthesis), leveraging state-of-the-art microenvironment engineering technologies. These discussions showcase microenvironment engineering was applied in different reactions to fine-tune catalytic regimes and improve the efficiency from both thermodynamics and kinetics perspectives. Lastly, we discussed the challenges and future directions in microenvironment engineering. This review underscores the potential of microenvironment engineering in intelligent materials and system design to drive the development of more effective and sustainable catalytic solutions to environmental decontamination.

Covalent Organic Framework Catalyzed Amide Synthesis Directly from Alcohol Under Red Light Excitation

The dehydrogenative coupling of alcohols and amines to form amide bonds is typically catalysed by homogeneous transition metal catalysts at high temperatures ranging from 130-140 °C. In our pursuit of an efficient and recyclable photocatalyst capable of conducting this transformation at room temperature, we report herein a COF-mediated dehydrogenative synthesis. The TTT-DHTD COF was strategically designed to incorporate a high density of functional units, specifically dithiophenedione, to trap photogenerated electrons and effectively facilitate hydrogen atom abstraction reactions. The photoactive TTT-DHTD COF, synthesized using solvothermal methods showed high crystallinity and moderate surface area, providing an ideal platform for heterogeneous amide synthesis. Light absorption by the COF across the entire visible range, narrow band gap, and valence band position make it well-suited for the efficient generation of excitons necessary for targeted dehydrogenation. Utilizing red light irradiation and employing extremely low loading of the COF, we have successfully prepared a wide range of amides, including challenging secondary amides, in good to excellent yields. The substrates' functional group tolerance, very mild reaction conditions, and the catalyst's significant recyclability represent substantial advancements over prior methodologies.

Covalent Organic Frameworks for Photocatalytic Reduction of Carbon Dioxide: A Review

Covalent organic frameworks (COFs) are crystalline networks with extended backbones cross-linked by covalent bonds. Due to the semiconductive properties and variable metal coordinating sites, along with the rapid development in linkage chemistry, the utilization of COFs in photocatalytic CO2RR has attracted many scientists' interests. In this Review, we summarize the latest research progress on variable COFs for photocatalytic CO2 reduction. In the first part, we present the development of COF linkages that have been used in CO2RR, and we discuss four mechanisms including COFs as intrinsic photocatalysts, COFs with photosensitive motifs as photocatalysts, metalated COF photocatalysts, and COFs with semiconductors as heterojunction photocatalysts. Then, we summarize the principles of structural designs including functional building units and stacking mode exchange. Finally, the outlook and challenges have been provided. This Review is intended to give some guidance on the design and synthesis of diverse COFs with different linkages, various structures, and divergent stacking modes for the efficient photoreduction of CO2.

Recent Advances and Challenges in Efficient Selective Photocatalytic CO2 Methanation

Solar-driven carbon dioxide (CO2) methanation holds significant research value in the context of carbon emission reduction and energy crisis. However, this eight-electron catalytic reaction presents substantial challenges in catalytic activity and selectivity. In this regard, researchers have conducted extensive exploration and achieved significant developments. This review provides an overview of the recent advances and challenges in efficient selective photocatalytic CO2 methanation. It begins by discussing the fundamental principles and challenges in detail, analyzing strategies for improving the efficiency of photocatalytic CO2 conversion to CH4 comprehensively. Subsequently, it outlines the recent applications and advanced characterization methods for photocatalytic CO2 methanation. Finally, this review highlights the prospects and opportunities in this area, aiming to inspire CO2 conversion into high-value CH4 and shed light on the research of catalytic mechanisms.

Ferrocene-modified covalent organic framework for efficient oxygen evolution reaction and CO2 electroreduction

A ferrocene-modified COF, namely Ni-Tph-COF-Fc, was synthesized and applied in OER. Compared with Ni-Tph-COF-OH, Ni-Tph-COF-Fc shows improved performance with a current density of 99.6 mA cm-2, an overpotential of 450 mV, and a Tafel slope of 73.1 mV dec-1, which may be attributed to a synergy between introduced ferrocene and metalloporphyrin in the COFs. Moreover, the enhanced OER performance leads to an improved CO2RR performance with an FECO of 93.1%. This work represents an effective strategy to enhance the anodic OER performance and realize efficient CO2RR.

Electrocatalytic Reduction of Carbon Dioxide in Acidic Electrolyte with Superior Performance of a Metal-Covalent Organic Framework over Metal-Organic Framework

CO2 electroreduction (CO2RR) to generate valuable chemicals in acidic electrolytes can improve the carbon utilization rate in comparison to that under alkaline conditions. However, the thermodynamically more favorable hydrogen evolution reaction under an acidic electrolyte makes the CO2RR a big challenge. Herein, robust metal phthalocyanine(Pc)-based (M = Ni, Co) conductive metal-covalent organic frameworks (MCOFs) connected by strong metal tetraaza[14]annulene (TAA) linkage, named NiPc-NiTAA and NiPc-CoTAA, are designed and synthesized to apply in the CO2RR in acidic electrolytes for the first time. The optimal NiPc-NiTAA exhibited an excellent Faradaic efficiency (FECO) of 95.1% and a CO partial current density of 143.0 mA cm-2 at -1.5 V versus the reversible hydrogen electrode in an acidic electrolyte, which is 3.1 times that of the corresponding metal-organic framework NiPc-NiN4. The comparison tests and theoretical calculations reveal that in-plane full π-d conjugation MCOF with a good conductivity of 3.01 × 10-4 S m-1 accelerates migration of the electrons. The NiTAA linkage can tune the electron distribution in the d orbit of metal centers, making the d-band center close to the Fermi level and then activating CO2. Thus, the active sites of NiPc and NiTAA collaborate to reduce the *COOH formation energy barrier, favoring CO production in an acid electrolyte. It is a helpful route for designing outstanding conductive MCOF materials to enhance CO2 electrocatalysis under an acidic electrolyte.

Elaborate Modulating Binding Strength of Intermediates via Three-component Covalent Organic Frameworks for CO2 Reduction Reaction

The catalytic performance for electrocatalytic CO2 reduction reaction (CO2RR) depends on the binding strength of the reactants and intermediates. Covalent organic frameworks (COFs) have been adopted to catalyze CO2RR, and their binding abilities are tuned via constructing donor-acceptor (DA) systems. However, most DA COFs have single donor and acceptor units, which caused wide-range but lacking accuracy in modulating the binding strength of intermediates. More elaborate regulation of the interactions with intermediates are necessary and challenge to construct high-efficiency catalysts. Herein, the three-component COF with D-A-A units was first constructed by introducing electron-rich diarylamine unit, electron-deficient benzothiazole and Co-porphyrin units. Compared with two-component COFs, the designed COF exhibit elevated electronic conductivity, enhanced reducibility, high efficiency charge transfer, further improving the electrocatalytic CO2RR performance with the faradic efficiency of 97.2 % at -0.8 V and high activity with the partial current density of 27.85 mA cm-2 at -1.0 V which exceed other two-component COFs. Theoretical calculations demonstrate that catalytic sites in three-component COF have suitable binding ability of the intermediates, which are benefit for formation of *COOH and desorption of *CO. This work offers valuable insights for the advancement of multi-component COFs, enabling modulated charge transfer to improve the CO2RR activity.

Covalent Organic Frameworks: Opportunities for Rational Materials Design in Cancer Therapy

Nanomedicines are extensively used in cancer therapy. Covalent organic frameworks (COFs) are crystalline organic porous materials with several benefits for cancer therapy, including porosity, design flexibility, functionalizability, and biocompatibility. This review examines the use of COFs in cancer therapy from the perspective of reticular chemistry and function-oriented materials design. First, the modification sites and functionalization methods of COFs are discussed, followed by their potential as multifunctional nanoplatforms for tumor targeting, imaging, and therapy by integrating functional components. Finally, some challenges in the clinical translation of COFs are presented with the hope of promoting the development of COF-based anticancer nanomedicines and bringing COFs closer to clinical trials.

Oxygen-tolerant CO2 electroreduction over covalent organic frameworks via photoswitching control oxygen passivation strategy

The direct use of flue gas for the electrochemical CO2 reduction reaction is desirable but severely limited by the thermodynamically favorable oxygen reduction reaction. Herein, a photonicswitching unit 1,2-Bis(5'-formyl-2'-methylthien-3'-yl)cyclopentene (DAE) is integrated into a cobalt porphyrin-based covalent organic framework for highly efficient CO2 electrocatalysis under aerobic environment. The DAE moiety in the material can reversibly modulate the O2 activation capacity and electronic conductivity by the framework ring-closing/opening reactions under UV/Vis irradiation. The DAE-based covalent organic framework with ring-closing type shows a high CO Faradaic efficiency of 90.5% with CO partial current density of -20.1 mA cm-2 at -1.0 V vs. reversible hydrogen electrode by co-feeding CO2 and 5% O2. This work presents an oxygen passivation strategy to realize efficient CO2 electroreduction performance by co-feeding of CO2 and O2, which would inspire to design electrocatalysts for the practical CO2 source such as flue gas from power plants or air.

Spin Polarization: A New Frontier in Efficient Photocatalysis for Environmental Purification and Energy Conversion

As a promising strategy to improve photocatalytic efficiency, spin polarization has attracted enormous attention in recent years, which could be involved in various steps of photoreaction. The Pauli repulsion principle and the spin selection rule dictate that the behavior of two electrons in a spatial eigenstate is based on their spin states, and this fact opens up a new avenue for manipulating photocatalytic efficiency. In this review, recent advances in modulating the photocatalytic activity with spin polarization are systematically summarized. Fundamental insights into the influence of spin-polarization effects on photon absorption, carrier separation, and migration, and the behaviors of reaction-related substances from the photon uptake to reactant desorption are highlighted and discussed in detail, and various photocatalytic applications for environmental purification and energy conversion are presented. This review is expected to deliver a timely overview of the recent developments in spin-polarization-modulated photocatalysis for environmental purification and energy conversion in terms of their practical applications.

Two-Dimensional Porphyrinic Metal-Organic Framework Composites as a Photocatalytic Platform for Chemoselective Hydrogenation

Chemoselective hydrogenation with high efficiency under ambient conditions remains a great challenge. Herein, an efficient photocatalyst, the 2D porphyrin metal-organic framework composite AmPy/Pd-PPF-1(Cu), featuring AmPy (1-aminopyrene) sitting axially on a paddle-wheel unit, has been rationally fabricated. The 2D AmPy/Pd-PPF-1(Cu) composite acts as a photocatalytic platform, promoting the selective hydrogenation of quinolines to tetrahydroquinolines with a yield up to 99%, in which ammonia borane serves as the hydrogen donor. The AmPy molecules coordinated on a 2D MOF not only enhance the light absorption capacity but also adjust the layer spacing without affecting the network structure of 2D Pd-PPF-1(Cu) nanosheets. Through deuterium-labeling experiments, in situ X-ray photoelectron spectroscopy, electron paramagnetic resonance studies, and density functional theory calculations, it is disclosed that Cu paddle-wheel units in 2D AmPy/Pd-PPF-1(Cu) nanosheets behave as the active site for transfer hydrogenation, and metalloporphyrin ligand and axial aminopyrene molecules can enhance the light absorption capacity and excite photogenerated electrons to Cu paddle-wheel units, assisting in photocatalysis.