Improved Photoreduction of CO2 with Water by Tuning the Valence Band of Covalent Organic Frameworks

Superlative Porous Organic Polymers for Photochemical and Electrochemical CO2 Reduction Applications: From Synthesis to Functionality

To mimic the carbon cycle at a kinetically rapid pace, the sustainable conversion of omnipresent CO2 to value-added chemical feedstock and hydrocarbon fuels implies a remarkable prototype for utilizing released CO2. Porous organic polymers (POPs) have been recognized as remarkable catalytic systems for achieving large-scale applicability in energy-driven processes. POPs offer mesoporous characteristics, higher surface area, and superior optoelectronic properties that lead to their relatively advanced activity and selectivity for CO2 conversion. In comparison to the metal organic frameworks, POPs exhibit an enhanced tendency toward membrane formation, which governs their excellent stability with regard to remarkable ultrathinness and tailored pore channels. The structural ascendancy of POPs can be effectively utilized to develop cost-effective catalytic supports for energy conversion processes to leapfrog over conventional noble metal catalysts that have nonlinear techno-economic equilibrium. Herein, we precisely surveyed the functionality of POPs from scratch, classified it, and provided a critical commentary of its current methodological advancements and photo/electrochemical achievements in the CO2 reduction reaction.

Ambient Synthesis of Porphyrin-Based Fe-Covalent Organic Frameworks for Efficient Infected Skin Wound Healing

Reactive oxygen species (ROS) have emerged as a promising treatment option for antibacterial and biofilm eradication. However, their therapeutic efficacy is significantly hampered by the unique microenvironments of diabetic wounds. In this study, we designed and synthesized porphyrin-based Fe covalent organic frameworks (Fe-COF) through a Schiff base condensation reaction. Subsequently, Fe-COF were encapsulated with hyaluronic acid (HA) through electrostatic adsorption, resulting in a novel formulation named HA-Fe-COF for diabetic wound healing. HA-Fe-COF were engineered to respond to hyaluronidase in the infected wound, leading to the controlled release of Fe-COF. Those released Fe-COF served a dual role as photosensitizers, generating singlet oxygen and localized heating when exposed to dual light sources. Additionally, they acted as peroxidase-like nanozymes, facilitating the production of ROS through enzymatic reactions. This innovative approach enabled a synergistic therapeutic effect combining photodynamic, photothermal, and chemodynamic modalities. Furthermore, the sustained release of HA from HA-Fe-COF promoted angiogenesis, collagen deposition, and re-epithelialization during the diabetic wound healing process. This "all-in-one" strategy offers a novel approach for the development of antimicrobial and biofilm eradication strategies that minimize damage to healthy tissues in vivo.

Redox-Active Organic Materials: From Energy Storage to Redox Catalysis

Electroactive materials are central to myriad applications, including energy storage, sensing, and catalysis. Compared to traditional inorganic electrode materials, redox-active organic materials such as porous organic polymers (POPs) and covalent organic frameworks (COFs) are emerging as promising alternatives due to their structural tunability, flexibility, sustainability, and compatibility with a range of electrolytes. Herein, we discuss the challenges and opportunities available for the use of redox-active organic materials in organoelectrochemistry, an emerging area in fine chemical synthesis. In particular, we highlight the utility of organic electrode materials in photoredox catalysis, electrochemical energy storage, and electrocatalysis and point to new directions needed to unlock their potential utility for organic synthesis. This Perspective aims to bring together the organic, electrochemistry, and polymer communities to design new heterogeneous electrocatalysts for the sustainable synthesis of complex molecules.

Synthetic Leaves Based on Crystalline Olefin-Linked Covalent Organic Frameworks for Efficient CO2 Photoreduction with Water

We report, for the first time, a new synthetic strategy for the preparation of crystalline two-dimensional olefin-linked covalent organic frameworks (COFs) based on aldol condensation between benzodifurandione and aromatic aldehydes. Olefin-linked COFs can be facilely crystallized through either a pyridine-promoted solvothermal process or a benzoic anhydride-mediated organic flux synthesis. The resultant COF leaf with high in-plane π-conjugation exhibits efficient visible-light-driven photoreduction of carbon dioxide (CO2) with water (H2O) in the absence of any photosensitizer, sacrificial agents, or cocatalysts. The production rate of carbon monoxide (CO) reaches as high as 158.1 μmol g-1 h-1 with near 100% CO selectivity, which is accompanied by the oxidation of H2O to oxygen. Both theoretical and experimental results confirm that the key lies in achieving exceptional photoinduced charge separation and low exciton binding. We anticipate that our findings will facilitate new possibilities for the development of semiconducting COFs with structural diversity and functional variability.

Fully Conjugated Covalent Organic Framework Nanosheets for Visible-Light-Driven Organic Synthesis in Water

Covalent organic framework (COF) nanosheets have recently garnered great attention as a new class of functional materials. As one of the sustainable processes, however, the photocatalytic organic synthesis in water has not been investigated using COF nanosheets as a photocatalyst to date. Herein, we reported the synthesis of a fully conjugated COF nanosheets with carboxyl functional group through a cooperative strategy of chemical exfoliation and group transformation. The new COF nanosheets was found to be an efficient heterogeneous photocatalyst for a wide range of organic synthesis including selective oxidation of sulfides and oxidative coupling of benzylamines in water under visible-light illumination. This work contributes a new roadmap for the design and synthesis of functional COF-based nanosheets, but also further extends the application boundary of the ultrathin COF nanosheets.

Brominated metal phthalocyanine-based covalent organic framework for enhanced selective photocatalytic reduction of CO2

Covalent organic frameworks (COFs) have great potential for photocatalytic CO2 reduction, owing to their adjustable structures, porous characteristics, and highly ordered nature. However, poor light absorption, fast recombination of photogenerated electron-hole pairs, and suboptimal coordination conditions have contributed to the hindered efficiency and selectivity observed in photocatalytic CO2 reduction processes. In this work, the integration of bromine (Br) atoms into COFs was achieved through the synthesis process involving nickel (II) tetraaminophthalocyanine (NiTAPc) and 3,6-dibromopyromellitic dianhydride (BPMDA) using a solvothermal approach. The coupling of a porous framework structure alongside the incorporation of Br atoms yields a significant enhancement in photoelectric properties compared to bromine-free COFs. Meanwhile, X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations revealed that the introduction of Br atoms can facilitate the adjustment of the electron configuration around the phthalocyanine unit and diminish the required energy for the photocatalytic reaction. When subjected to visible light irradiation, the NiTAPc-BPMDA COF showcased a CO yield of 148.25 μmol g-1 over a 5-hour period, accompanied by an impressive selectivity of 98%. This work highlights the collaborative influence of phthalocyanines and Br atoms within COF-based photocatalysts, offering an alternative approach for designing and constructing high-performance photocatalysts with elevated yield and selectivity. The synergistic role of phthalocyanines and Br atoms within the COF-based photocatalysts provides an alternative strategy for photocatalysts with high yield and selectivity in the future.

Fabrication of a polymer brush-functionalized porphyrin-based covalent organic framework for enrichment of N-glycopeptides

A surface-initiated atom transfer radical polymerization method combining click chemistry was employed to prepare a novel porphyrin-based covalent organic framework composite grafted with polymer brushes (TAPBB@GMA@AMA@Cys) for the specific enrichment of N-glycopeptides. The material successfully realized the high efficiency enrichment of N-glycopeptides with good selectivity (1:1000), low detection limit (0.2 fmol/μL), and high loading capacity (133.3 mg·g-1). The TAPBB@GMA@AMA@Cys was successfully applied to actual sample analysis; 235 N-glycopeptides related to 125 glycoproteins and 210 N-glycopeptides related to 121 glycoproteins were recognized from the serum of normal individuals and Alzheimer's disease patients, respectively. Gene ontology studies of molecular functions, cellular components, and biological processes have revealed that identified glycoproteins are strongly associated with neurodegenerative diseases involving innate immune responses, basement membranes, calcium binding, and receptor binding. The above results confirm the surprising potential of materials in glycoproteomics research and practical sample applications.

Recent Progress of Covalent Organic Frameworks-Based Materials in Photocatalytic Applications: A Review

Covalent organic frameworks (COFs) are one type of porous organic materials linked by covalent bonds. COFs materials exhibit many outstanding characteristics such as high porosity, high chemical and thermal stability, large specific surface area, efficient electron transfer efficiency, and the ability for predesigned structures. These exceptional advantages enable COFs materials to exhibit remarkable performance in photocatalysis. Additionally, the activity of COFs materials as photocatalysts can be significantly upgraded by ion doping and the formation of heterojunctions. This paper summarizes the latest research progress on COF-based materials applied in photocatalytic systems. Initially, typical structures and preparation methods of COFs are analyzed and compared. Moreover, the essential principles of photocatalytic reactions over COFs-based materials and the latest research developments in photocatalytic hydrogen production, CO2 reduction, pollutants elimination, organic transformation, and overall water splitting are indicated. At last, the outlook and challenges of COF-based materials in photocatalysis are discussed. This review is intended to permit instructive guidance for the efficient use of photocatalysis based on COFs in the future.

A Fully Conjugated Covalent Organic Framework with Oxidative and Reductive Sites for Photocatalytic Carbon Dioxide Reduction with Water

Constructing a powerful photocatalytic system that can achieve the carbon dioxide (CO2 ) reduction half-reaction and the water (H2 O) oxidation half-reaction simultaneously is a very challenging but meaningful task. Herein, a porous material with a crystalline topological network, named viCOF-bpy-Re, was rationally synthesized by incorporating rhenium complexes as reductive sites and triazine ring structures as oxidative sites via robust -C=C- bond linkages. The charge-separation ability of viCOF-bpy-Re is promoted by low polarized π-bridges between rhenium complexes and triazine ring units, and the efficient charge-separation enables the photogenerated electron-hole pairs, followed by an intramolecular charge-transfer process, to form photogenerated electrons involved in CO2 reduction and photogenerated holes that participate in H2 O oxidation simultaneously. The viCOF-bpy-Re shows the highest catalytic photocatalytic carbon monoxide (CO) production rate (190.6 μmol g-1  h-1 with about 100 % selectivity) and oxygen (O2 ) evolution (90.2 μmol g-1 h-1 ) among all the porous catalysts in CO2 reduction with H2 O as sacrificial agents. Therefore, a powerful photocatalytic system was successfully achieved, and this catalytic system exhibited excellent stability in the catalysis process for 50 hours. The structure-function relationship was confirmed by femtosecond transient absorption spectroscopy and density functional theory calculations.

Cobalt-Porphyrin-Based Covalent Organic Frameworks with Donor-Acceptor Units as Photocatalysts for Carbon Dioxide Reduction

Covalent organic frameworks (COFs) have emerged as a promising platform for photocatalysts. Their crystalline porous nature allows comprehensive mechanistic studies of photocatalysis, which have revealed that their general photophysical parameters, such as light absorption ability, electronic band structure, and charge separation efficiency, can be conveniently tailored by structural modifications. However, further understanding of the relationship between structure-property-activity is required from the viewpoint of charge-carrier transport, because the charge-carrier property is closely related to alleviation of the excitonic effect. In the present study, COFs composed of a fixed cobalt (Co) porphyrin (Por) centered tetraamine as an acceptor unit with differently conjugated di-carbaldehyde based donor units, such as benzodithiophene (BDT), thienothiophene (TT), or phenyl (TA), were synthesized to form Co-Por-BDT, Co-Por-TT, or Co-Por-TA, respectively. Their photocatalytic activity for reducing carbon dioxide into carbon monoxide was in the order of Co-Por-BDT>Co-Por-TT>Co-Por-TA. The results indicated that the excitonic effect, associated with their charge-carrier densities and π-conjugation lengths, was a significant factor in photocatalysis performance.

Electronic Tuning of CO2 Interaction by Oriented Coordination of N-Rich Auxiliary in Porphyrin Metal-Organic Frameworks for Light-Assisted CO2 Electroreduction

The efficient CO₂ electroreduction into high-value products largely relies on the CO₂ adsorption/activation or electron-transfer of electrocatalysts, thus site-specific functionalization methods that enable boosted related interactions of electrocatalysts are much desired. Here, an oriented coordination strategy is reported to introduce N-rich auxiliary (i.e., hexamethylenetetramine, HMTA) into metalloporphyrin metal organic frameworks (MOFs) to synthesize a series of site-specific functionalized electrocatalysts (HMTA@MOF-545-M, M = Fe, Co, and Ni) and they are successfully applied in light-assisted CO₂ electroreduction. Noteworthy, thus-obtained HMTA@MOF-545-Co presents approximately two times enhanced CO₂ adsorption-enthalpy and electrochemical active surface-area with largely decreased impedance-value after modification, resulting in almost twice higher CO₂ electroreduction performance than its unmodified counterpart. Besides, its CO₂ electroreduction performance can be further improved under light-illumination and displays superior FE_CO (≈100%), high CO generation rate (≈5.11 mol m^-2  h^-1 at -1.1 V) and energy efficiency (≈70% at -0.7 V). Theoretical calculations verify that the oriented coordination of HMTA can increase the charge density of active sites, almost doubly enhance the CO₂ adsorption energy, and largely reduce the energy barrier of rate determining step for the boosted performance improvement. This work might promote the development of modifiable porous crystalline electrocatalysts in high-efficiency CO₂ electroreduction.

Porphyrin-Based Covalent Organic Frameworks: Design, Synthesis, Photoelectric Conversion Mechanism, and Applications

Photosynthesis occurs in high plants, and certain organisms show brilliant technology in converting solar light to chemical energy and producing carbohydrates from carbon dioxide (CO₂). Mimicking the mechanism of natural photosynthesis is receiving wide-ranging attention for the development of novel materials capable of photo-to-electric, photo-to-chemical, and photocatalytic transformations. Porphyrin, possessing a similar highly conjugated core ring structure to chlorophyll and flexible physical and chemical properties, has become one of the most investigated photosensitizers. Chemical modification and self-assembly of molecules as well as constructing porphyrin-based metal (covalent) organic frameworks are often used to improve its solar light utilization and electron transfer rate. Especially porphyrin-based covalent organic frameworks (COFs) in which porphyrin molecules are connected by covalent bonds combine the structural advantages of organic frameworks with light-capturing properties of porphyrins and exhibit great potential in light-responsive materials. Porphyrin-based COFs are expected to have high solar light utilization, fast charge separation/transfer performance, excellent structural stability, and novel steric selectivity by special molecular design. In this paper, we reviewed the research progress of porphyrin-based COFs in the design, synthesis, properties, and applications. We focused on the intrinsic relationship between the structure and properties, especially the photoelectric conversion properties and charge transfer mechanism of porphyrin-based COFs, and tried to provide more valuable information for the design of advanced photosensitizers. The applications of porphyrin-based COFs in photocatalysis and phototherapy were emphasized based on their special structure design and light-to-electric (or light-to-heat) conversion control.

Ingenious Artificial Leaf Based on Covalent Organic Framework Membranes for Boosting CO2 Photoreduction

Covalent organic frameworks (COFs) hold the potential in converting CO₂ with water into value-added fuels and O₂ to save the deteriorating ecological environment. However, reaching high yield and selectivity is a grand challenge under metal-, photosensitizer-, or sacrificial reagent-free conditions. Here, inspired by microstructures of natural leaves, we designed triazine-based COF membranes with the integration of steady light-harvesting sites, efficient catalytic center, and fast charge/mass transfer configuration to fabricate a novel artificial leaf for the first time. Significantly, a record high CO yield of 1240 μmol g^-1 in a 4 h reaction, approximately 100% selectivity, and a long lifespan (at least 16 cycles) were achieved under gas-solid conditions without using any metal, photosensitizer, or sacrificial reagent. Unlike the existing knowledge, the chemical structural unit of triazine-imide-triazine and the unique physical form of the COF membrane are predominant for such a remarkable photocatalysis. This work opens a new pathway to simulating photosynthesis in leaves and may motivate relevant research in the future.

Macrocycle-Based Covalent Organic Frameworks

Macrocycles with well-defined cavities and the ability to undergo supramolecular interactions are classical materials that have played an essential role in materials science. However, one of the most substantial barriers limiting the utilization of macrocycles is their aggregation, which blocks the active regions. Among many attempted strategies to prevent such aggregation, installing macrocycles into covalent organic frameworks (COFs), which are porous and stable reticular networks, has emerged as an ideal solution. The resulting macrocycle-based COFs (M-COFs) preserve the macrocycles' unique activities, enabling applications in various fields such as single-atom catalysis, adsorption/separation, optoelectronics, phototherapy, and structural design of forming single-layered or mechanically interlocked COFs. The resulting properties are unmatchable by any combination of macrocycles with other substrates, opening a new chapter in advanced materials. This review focuses on the latest progress in the concepts, synthesis, properties, and applications of M-COFs, and presents an in-depth outlook on the challenges and opportunities in this emerging field.

Regulating π-Conjugation in sp2 -Carbon-Linked Covalent Organic Frameworks for Efficient Metal-Free CO2 Photoreduction with H2 O

The development of sp² -carbon-linked covalent organic frameworks (sp² c-COFs) as artificial photocatalysts for solar-driven conversion of CO₂ into chemical feedstock has captured growing attention, but catalytic performance has been significantly limited by their intrinsic organic linkages. Here, a simple, yet efficient approach is reported to improve the CO₂ photoreduction on metal-free sp² c-COFs by rationally regulating their intrinsic π-conjugation. The incorporation of ethynyl groups into conjugated skeletons affords a significant improvement in π-conjugation and facilitates the photogenerated charge separation and transfer, thereby boosting the CO₂ photoreduction in a solid-gas mode with only water vapor and CO₂ . The resultant CO production rate reaches as high as 382.0 µmol g^-1  h^-1 , ranking at the top among all additive-free CO₂ photoreduction catalysts. The simple modulation approach not only enables to achieve enhanced CO₂ reduction performance but also simultaneously gives a rise to extend the understanding of structure-property relationship and offer new possibilities for the development of new π-conjugated COF-based artificial photocatalysts.

A CuI Cluster-Based Covalent Metal-Organic Framework as a Photocatalyst for Efficient Visible-Light-Driven Reduction of CO2

The application of solar energy to convert CO₂ into high-value chemicals and fuels has been considered a highly desirable approach to relieving the greenhouse effect and energy crisis. However, the exploration of appropriate photocatalysts remains a major challenge. Combining the respective advantages of covalent organic frameworks and metal-organic frameworks to construct covalent metal-organic frameworks (CMOFs) can be a valid strategy to provide efficient, reliable, and eco-friendly photocatalysts. In this study, a Cu^I cluster-based CMOF (JNM-2) is used as a photocatalyst for CO₂ photoreduction under visible-light irradiation. JNM-2 exhibits remarkable efficiency in photocatalytic CO₂ reduction with high production rates of HCOOH (9019 μmol g^-1  h^-1 ) and CO (835 μmol g^-1  h^-1 ). The active center, reaction intermediates, and product generation pathways are elucidated by in situ DRIFTS and DFT calculations. This work demonstrates the tremendous possibilities of CMOFs as photocatalysts for CO₂ reduction and provides profound insights into the mechanism of CO₂ conversion into HCOOH/CO by using a molecularly accurate structural model.

Design and synthesis of metal-free ethene-based covalent organic framework photocatalysts for efficient, selective, and long-term stable CO2 conversion into methane

The efficient and selective photocatalytic CO₂ conversion into higher-valued hydrocarbon products (e.g., methane and ethane) over covalent organic frameworks (COFs) remains a challenge, with all previously reported attempts producing carbon monoxide as the dominant product. Herein, we report a new ethene-based COF, through polycondensation of electron-rich (E)-1,2‑diphenylethene and 1,3,6,8‑tetraphenylpyrene units. The synthesized ethene-based COF functioned as an efficient metal-free photocatalyst for the conversion of CO₂ into methane under visible light irradiation, with a selectivity of 100 %, a production rate of 14.7 µmol g^-1h^-1, and an apparent quantum yield of c.a. 0.99 % at 489.5 nm, which are the most promising values reported for CO₂ conversion by a metal-free COF photocatalyst, without any support from a co-catalyst. The carbon origin of CH₄ product is confirmed by isotope tracer ¹³CO₂ experiment. Moreover, the photocatalytic system consistently produces methane for > 14 h with recyclability.

Porphyrins and phthalocyanines as biomimetic tools for photocatalytic H2 production and CO2 reduction

The increasing energy demand and environmental issues caused by the over-exploitation of fossil fuels render the need for renewable, clean, and environmentally benign energy sources unquestionably urgent. The zero-emission energy carrier, H₂ is an ideal alternative to carbon-based fuels especially when it is generated photocatalytically from water. Additionally, the photocatalytic conversion of CO₂ into chemical fuels can reduce the CO₂ emissions and have a positive environmental and economic impact. Inspired by natural photosynthesis, plenty of artificial photocatalytic schemes based on porphyrinoids have been investigated. This review covers the recent advances in photocatalytic H₂ production and CO₂ reduction systems containing porphyrin or phthalocyanine derivatives. The unique properties of porphyrinoids enable their utilization both as chromophores and as catalysts. The homogeneous photocatalytic systems are initially described, presenting the various approaches for the improvement of photosensitizing activity and the enhancement of catalytic performance at the molecular level. On the other hand, for the development of the heterogeneous systems, numerous methods were employed such as self-assembled supramolecular porphyrinoid nanostructures, construction of organic frameworks, combination with 2D materials and adsorption onto semiconductors. The dye sensitization on semiconductors opened the way for molecular-based dye-sensitized photoelectrochemical cells (DSPECs) devices based on porphyrins and phthalocyanines. The research in photocatalytic systems as discussed herein remains challenging since there are still many limitations making them unfeasible to be used at a large scale application before finding a large-scale application.

Rational Design of Novel COF/MOF S-Scheme Heterojunction Photocatalyst for Boosting CO2 Reduction at Gas-Solid Interface

Solar-driven photoreduction of CO₂ into valuable fuels offers a sustainable technology to relieve the energy crisis as well as the greenhouse effect. Yet the exploration of highly efficient, selective, stable, and environmental benign photocatalysts for CO₂ reduction remains a major issue and challenge. The interfacial engineering of heterojunction photocatalysts could be a valid approach to boost the efficiency of the catalytic process. Herein, we propose a novel covalent organic framework/metal organic framework (COF/MOF) heterojunction photocatalyst, using olefin (C═C) linked covalent organic framework (TTCOF) and NH₂-UiO-66 (Zr) (NUZ) as representative building blocks, for enhanced CO₂ reduction to CO. The optimized TTCOF/NUZ exhibited a superior CO yield (6.56 μmol g^-1 h^-1) in gas-solid system when irradiated by visible light and only with H₂O (g) as weak reductant, and it was 4.4 and 5 times higher than pristine TTCOF and NUZ, respectively. The photogenerated electrons transfer route was proposed to follow the typical step-scheme (S-scheme), which was affirmed by XPS, in situ XPS and EPR characterizations. The boosting CO₂ photoreduction activity could be credited to the special charge carrier separation in S-scheme heterojunction, which can accelerate photogenerated electrons transportation and improve the redox ability at the interface. This work paves the way for the design and preparation of novel COF/MOF S-scheme heterostructure photocatalysts for CO₂ reduction.

Coupling Ruthenium Bipyridyl and Cobalt Imidazolate Units in a Metal-Organic Framework for an Efficient Photosynthetic Overall Reaction in Diluted CO2

Artificial photocatalytic CO₂ reduction, using water as the reductant, is challenging mainly because it is difficult for multiple functional units to cooperate efficiently. Here, we show that the classic photosensitive and H₂O-oxidizing ruthenium bipyridyl units and CO₂-reducing cobalt imidazolate units can be incorporated into a metal-organic framework using a classic organic ligand, imidazo[4,5-f][1,10]phenanthroline. Under visible light without additional sacrificial agents and photosensitizers, the overall conversion of CO₂ and H₂O to CO and O₂ was achieved by the multifunctional photocatalyst in the CH₃CN/H₂O mixed solvent with a high CO production rate of 11.2 μmol g^-1 h^-1 and CO selectivity of ca. 100%. Thanks to its ultramicroporous structure with moderately strong CO₂ adsorption ability, the photocatalyst also exhibited high performances with CO/CH₄ production rates of 5.15/0.62 and 4.26/0.20 μmol g^-1 h^-1 in the gas phase with pure and even diluted CO₂, respectively. Photoluminescence emission spectroscopy and photoelectrochemical tests confirmed that the photosensitive and catalytic units cooperated well to give suitable photocatalytic redox potentials and fast electron-hole separation.

Covalent Microporous Polymer Nanosheets for Efficient Photocatalytic CO2 Conversion with H2 O

It is still a challenging target to achieve photocatalytic CO₂ conversion to valuable chemicals with H₂ O as an electron donor. Herein, 2D imide-based covalent organic polymer nanosheets (CoPcPDA-CMP NSs), which integrate cobalt phthalocyanine (CoPc) moiety for reduction half-reaction and 3,4,9,10-perylenetetracarboxylic diimide moiety for oxidation half-reaction, are constructed as a Z-scheme artificial photosynthesis system to complete the overall CO₂ reduction reaction. Owing to the outstanding light absorption capacity, charge separation efficiency, and electronic conductivity, CoPcPDA-CMP NSs exhibit excellent photocatalytic activity to reduce CO₂ to CO using H₂ O as a sacrificial agent with a CO production rate of 14.27 µmol g^-1 h^-1 and a CO selectivity of 92%, which is competitive to the state-of-the-art visible-light-driven organic photocatalysts towards the overall CO₂ reduction reaction. According to a series of spectroscopy experiments, the authors also verify the photoexcited electron transfer processes in the CoPcPDA-CMP NSs photocatalytic system, confirming the Z-scheme photocatalytic mechanism. The present results should be helpful for fabricating high-performance organic photocatalysts for CO₂ conversion.

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.

Porphyrin-Containing MOFs and COFs as Heterogeneous Photosensitizers for Singlet Oxygen-Based Antimicrobial Nanodevices

Visible-light irradiation of porphyrin and metalloporphyrin dyes in the presence of molecular oxygen can result in the photocatalytic generation of singlet oxygen (¹O₂). This type II reactive oxygen species (ROS) finds many applications where the dye, also called the photosensitizer, is dissolved (i.e., homogeneous phase) along with the substrate to be oxidized. In contrast, metal-organic frameworks (MOFs) are insoluble (or will disassemble) when placed in a solvent. When stable as a suspension, MOFs adsorb a large amount of O₂ and photocatalytically generate ¹O₂ in a heterogeneous process efficiently. Considering the immense surface area and great capacity for gas adsorption of MOFs, they seem ideal candidates for this application. Very recently, covalent-organic frameworks (COFs), variants where reticulation relies on covalent rather than coordination bonds, have emerged as efficient photosensitizers. This comprehensive mini review describes recent developments in the use of porphyrin-based or porphyrin-containing MOFs and COFs, including nanosized versions, as heterogeneous photosensitizers of singlet oxygen toward antimicrobial applications.

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.

Self-assembly of TiO2/ZIF-8 nanocomposites for varied photocatalytic CO2 reduction with H2O vapor induced by different synthetic methods

Photoreduction of carbon dioxide (CO₂) provides an effective perspective for solving the energy crisis and environmental problems. Herein, two types of composite photocatalysts (TiO₂/ZIF-8) based on ZIF-8 and TiO₂ have been designed and synthesized with the help of the grinding method and the solid-synthesis method. Both composite photocatalysts are employed for the photocatalytic reduction of CO₂. In composite photocatalysts prepared by the grinding method, ZIF-8 particles are distributed on the surface of TiO₂, and provide extra available spaces for storing CO₂, which is beneficial for improving their photoreduction performances. As a result, an enhanced CO formation rate of 21.74 μmol g^-1 h^-1 with a high selectivity of 99% is obtained for this family of composite photocatalysts via the solid-gas mode without photosensitizers and sacrificial agents. For comparison, the other family of composite photocatalysts synthesized via the solid-synthesis method possesses structures similar to ZIF-8, where TiO₂ is encapsulated inside the framework of ZIF-8. This structural feature obstructs the contact between the active sites of TiO₂ and CO₂, and leads to lower activities. The best CO formation rate of this family is only 10.67 μmol g^-1 h^-1 with 90% selectivity. Both the structural features of the two families of photocatalysts are described to explain their differences in photoreduction performances. The experimental finding reveals that different synthetic approaches indeed result in diversified structures and varied photocatalytic performances. This work affords a new scalable and efficient approach for the rational design of efficient photocatalysts in the area of artificial photosynthesis.

Critical Aspects of Metal-Organic Framework-Based Materials for Solar-Driven CO2 Reduction into Valuable Fuels

Photoreduction of CO2 into value-added fuels is one of the most promising strategies for tackling the energy crisis and mitigating the "greenhouse effect." Recently, metal-organic frameworks (MOFs) have been widely investigated in the field of CO2 photoreduction owing to their high CO2 uptake and adjustable functional groups. The fundamental factors and state-of-the-art advancements in MOFs for photocatalytic CO2 reduction are summarized from the critical perspectives of light absorption, carrier dynamics, adsorption/activation, and reaction on the surface of photocatalysts, which are the three main critical aspects for CO2 photoreduction and determine the overall photocatalytic efficiency. In view of the merits of porous materials, recent progress of three other types of porous materials are also briefly summarized, namely zeolite-based, covalent-organic frameworks based (COFs-based), and porous semiconductor or organic polymer based photocatalysts. The remarkable performance of these porous materials for solar-driven CO2 reduction systems is highlighted. Finally, challenges and opportunities of porous materials for photocatalytic CO2 reduction are presented, aiming to provide a new viewpoint for improving the overall photocatalytic CO2 reduction efficiency with porous materials.

Covalent organic frameworks: an ideal platform for designing ordered materials and advanced applications

Covalent organic frameworks offer a molecular platform for integrating organic units into periodically ordered yet extended 2D and 3D polymers to create topologically well-defined polygonal lattices and built-in discrete micropores and/or mesopores.

Visible-light-driven photocatalytic CO2 reduction over ketoenamine-based covalent organic frameworks: role of the host functional groups

Compared to the electron-withdrawing groups, the electron-donating groups in TpBD can accelerate the photogenerated charge separation and transfer, thereby improving the photocatalytic performance for photocatalytic CO₂ reduction.

Covalent Organic Frameworks: A Promising Materials Platform for Photocatalytic CO2 Reductions

Covalent organic frameworks (COFs) are a kind of porous crystalline polymeric material. They are constructed by organic module units connected with strong covalent bonds extending in two or three dimensions. COFs possess the advantages of low-density, large specific surface area, high thermal stability, developed pore-structure, long-range order, good crystallinity, and the excellent tunability of the monomer units and the linking reticular chemistry. These features endowed COFs with the ability to be applied in a plethora of applications, ranging from adsorption and separation, sensing, catalysis, optoelectronics, energy storage, mass transport, etc. In this paper, we will review the recent progress of COFs materials applied in photocatalytic CO₂ reduction. The state-of-the-art paragon examples and the current challenges will be discussed in detail. The future direction in this research field will be finally outlooked.