Porous Crystalline Structure Research Articles

Metal‐organic frameworks‐based nanomedicines to promote cancer immunotherapy: Recent advances and future directions

AbstractCancer immunotherapy uses the body's immune system to fight tumors by restoring natural antitumor responses. Metal‐organic frameworks (MOFs), characterized by their unique crystalline porous structures formed from metal ions linked by organic ligands, offer a promising solution. Recent studies have unveiled the potential of MOFs in cancer immunotherapy. The exceptional porosity and surface area, coupled with their extraordinary thermal and chemical stability, bring significant advantages for efficient drug loading and delivery of immunotherapeutic agents. The adaptability of MOFs further enhances the controlled release of immunotherapeutic drugs within target cells and increases tumor sensitivity to other therapies such as photodynamic, photothermal, and radiotherapy. This multifunctional carrier contributes to modulating the tumor microenvironment and reactivating antitumor immunity, providing a comprehensive strategy for cancer treatment. In this review, we summarize the applications of MOFs in immune checkpoint blockade, immunomodulator delivery, and cancer vaccine delivery, and discuss existing challenges in their use for immunotherapy. This discussion aims to offer insights for developing better treatments and enhancing the efficacy of immunotherapy.

Design and synthesis of pillared metal-organic frameworks featuring olefinic fragments.

While metal-organic frameworks (MOFs) are known primarily for their well-defined crystalline porous structures that make them desirable for a myriad of applications, they also distinguish themselves with their chemical tunability. One strategy for chemical tailoring of MOF structures is post-synthetic modification (PSM) targeting moieties present in their organic building blocks (linkers). In this context, alkene (olefinic) fragments are underrepresented in the realm of MOFs despite their extremely well-established and versatile chemistry. With the majority of reported olefinic MOFs falling into the microporous regime, the PSM opportunities involving bulkier reagents are severely limited. Herein, we report a family of UofT (University of Toronto) pillared MOFs constructed around olefinic 1,4-bis(2-(pyridin-4-yl)vinyl)benzene (BPVB) and tetrakis(4-carboxyphenyl)porphyrin (TCPP) linkers. By utilizing a variety of M(II) [M = Zn, Ni, Co] precursors, three structurally distinct frameworks were synthesized and characterized. Most notably, the nickel-based framework represents the first reported example of a stable mesoporous olefinic pillared MOF. In addition to the de novo formation of a stable pillared MOF, Ni(II) is also used in a cation exchange process to structurally reinforce zinc-based frameworks.

From Nanozymes to Multi-Purpose Nanomaterials: The Potential of Metal-Organic Frameworks for Proteomics Applications.

Metal-organic frameworks (MOFs) have the potential to revolutionize the biotechnological and medical landscapes due to their easily tunable crystalline porous structure. Herein, the study presents MOFs' potential impact on proteomics, unveiling the diverse roles MOFs can play to boost it. Although MOFs are excellent catalysts in other scientific disciplines, their role as catalysts in proteomics applications remains largely underexplored, despite protein cleavage being of crucial importance in proteomics protocols. Additionally, the study discusses evolving MOF materials that are tailored for proteomics, showcasing their structural diversity and functional advantages compared to other types of materials used for similar applications. MOFs can be developed to seamlessly integrate into proteomics workflows due to their tunable features, contributing to protein separation, peptide enrichment, and ionization for mass spectrometry. This review is meant as a guide to help bridge the gap between material scientists, engineers, and MOF chemists and on the other side researchers in biology or bioinformatics working in proteomics.

Keggin type polyoxometalate-based metal-organic frameworks with electrocatalytive activity as effective multifunctional amperometric sensors for metal ions and ascorbic acid

Polyoxometalates (POMs) based metal-organic frameworks (POMOFs) integrate the merits of POMs with excellent redox properties and MOFs with highly ordered porous crystalline structures, which show potential electrochemical applications relying on the synergistic catalytic effect. Here, two new Keggin-type POMOFs [Cd(btbu)2(H2O)2(PMo12O40)] (CUST-636), [Cd(btbu)2(H2O)(SiW12O40)0.5](CUST-638) are synthesized using flexible ligand of 1,4-bis(1,2,4-triazol-1-yl)butane (abbreviated as btbu) as a ligand by hydrothermal method. PXRD, IR, and TG analysis were carried out on CUST-636 and CUST-638. Then, they were prepared into electrode materials (referred to as 636-GCE and 638-GCE), to explore the electrocatalytic properties. 636-GCE and 638-GCE show good electrocatalytic redox performance against KBrO3, KNO2, K2Cr2O7 and AA. Furthermore, detection of trace Cr(VI) was conducted using electrochemical sensors 636-GCE and 638-GCE. The low detection limits (LODs) of CUST-636 and CUST-638 were 0.32 and 0.45 μM, respectively, which were lower concentrations of Cr(VI) in drinking water than the maximum allowable concentration specified by the World Health Organization (WHO).

Vapor/Vapor‐Solid Interfacial Growth of Covalent Organic Framework Membranes on Alumina Hollow Fiber for Advanced Molecular Separation

AbstractCovalent organic frameworks (COFs), known for their chemical stability and porous crystalline structure, hold promises as advanced separation membranes. However, fabricating high‐quality COF membranes, particularly on industrial‐preferred hollow fiber substrates, remains challenging. This study introduces a novel vapor/vapor‐solid (V/V−S) method for growing ultrathin crystalline TpPa‐1 COF membranes on the inner lumen surface of alumina hollow fibers (TpPa‐1/Alumina). Through vapor‐phase monomer introduction onto polydopamine‐modified alumina at 170 °C and 1 atm, efficient polymerization and crystallization occur at the confined V−S interface. This enables one‐step growth within 8 h, producing 100 nm thick COF membranes with strong substrate adhesion. TpPa‐1/Alumina exhibits exceptional stability and performance over 80 h in continuous cross‐flow organic solvent nanofiltration (OSN), with methanol permeance of about 200 L m−2 h−1 bar−1 and dye rejection with molecular weight cutoff (MWCO) of approximately 700 Da. Moreover, the versatile V/V−S method synthesizes two additional COF membranes (TpPa2Cl/Alumina and TpHz/Alumina) with different pore sizes and chemical environments. Adjusting the COF membrane thickness between 100–500 nm is achievable easily by varying the growth cycle numbers. Notably, TpPa2Cl/Alumina demonstrates excellent OSN performance in separating the model active pharmaceutical ingredient glycyrrhizic acid (GA) from dimethyl sulfoxide (DMSO), highlighting the method's potential for large‐scale industrial applications.

Vapor/Vapor-Solid Interfacial Growth of Covalent Organic Framework Membranes on Alumina Hollow Fiber for Advanced Molecular Separation.

Covalent organic frameworks (COFs), known for their chemical stability and porous crystalline structure, hold promises as advanced separation membranes. However, fabricating high-quality COF membranes, particularly on industrial-preferred hollow fiber substrates, remains challenging. This study introduces a novel vapor/vapor-solid (V/V-S) method for growing ultrathin crystalline TpPa-1 COF membranes on the inner lumen surface of alumina hollow fibers (TpPa-1/Alumina). Through vapor-phase monomer introduction onto polydopamine-modified alumina at 170 °C and 1 atm, efficient polymerization and crystallization occur at the confined V-S interface. This enables one-step growth within 8 h, producing 100 nm thick COF membranes with strong substrate adhesion. TpPa-1/Alumina exhibits exceptional stability and performance over 80 h in continuous cross-flow organic solvent nanofiltration (OSN), with methanol permeance of about 200 L m-2 h-1 bar-1 and dye rejection with molecular weight cutoff (MWCO) of approximately 700 Da. Moreover, the versatile V/V-S method synthesizes two additional COF membranes (TpPa2Cl/Alumina and TpHz/Alumina) with different pore sizes and chemical environments. Adjusting the COF membrane thickness between 100-500 nm is achievable easily by varying the growth cycle numbers. Notably, TpPa2Cl/Alumina demonstrates excellent OSN performance in separating the model active pharmaceutical ingredient glycyrrhizic acid (GA) from dimethyl sulfoxide (DMSO), highlighting the method's potential for large-scale industrial applications.

Enhanced photocatalytic hydrogen generation using UiO-66(Zr) MOF with tailored modifications: A review

The utilization of UiO-66 MOF-based photocatalytic materials has achieved significant attention for their potential in hydrogen generation, owing to their remarkable stability and porous crystalline structure. Recent studies have disclosed enhanced light absorption capabilities in UiO-66 through both pre and post-synthetic modifications. These modifications also play a significant role in mitigating the recombination of photogenerated charge carriers by facilitating electron transfer in hybrid or derived materials. Designing of MOF-based modified improved photocatalyst includes, integration with other low band gap semiconductors, incorporation of noble metals as co-catalysts, surface engineering, inclusion of defects or introduction of heteroatom in the framework. MOF-COF hybridization, dye sensitization etc., further reinforced photocatalytic hydrogen yield. The above-mentioned comprehensive investigations have researched into aspects such as morphology, hydrogen generation efficiency, and the underlying mechanisms. It reveals that the creation of heterojunctions at interface channelizes the separation and smooth flow of electrons resulting in suppression of recombination reaction and favorable photocatalytic properties. The synergy between the components often results in enhanced performance. The present article provides a comprehensive review of modified UiO-66 MOF-based materials investigated for photocatalytic hydrogen generation.

An overview of Metal–Organic Frameworks as potential platform: Sensing for detection environmental pollutants and drug delivery applications

Metal Organic Frameworks (MOFs) represent a novel class of materials, characterized by their ability to form extended porous crystalline structures through the linkage of inorganic clusters or metallic ions with organic ligands. The availability of broad range of metal centres and type of organic linkers gives us opportunity for tailoring physical and chemical properties of MOFs. These modified MOFs opens up new channels for the customization of new devices needed for specific purposes. Though MOFs have been explored for significant applications in different sectors such as gas storage, proton conduction, biotechnological, biomedical sciences, catalysis, and separation, but drug delivery and the sensing applications has been taken exclusively at the manuscript. So, this article entails an overview of various synthetic methodology of low dimensional MOFs such as 1D and 2-D MOFs, and also focuses on their applications in sensing and drug delivery. This stems from their remarkable catalytic chemistry and their compatibility with a broad spectrum of materials. Furthermore, the 2-D layered structure of MOFs and their distinctive coordination of metal ions with organic ligands have emerging interest in the recent years.

Exogenous Co-Reactant-Free Electrochemiluminescent Biosensor for Ratiometric Measurement of α-Glucosidase Based on a ZIF-67-Regulated Hydrogen-Bonded Organic Framework.

The development of highly sensitive and selective analytical approaches for monitoring enzymatic activity is critical for disease diagnosis and biomedical research. Herein, we develop an exogenous co-reactant-free electrochemiluminescence (ECL) biosensor for the ratiometric measurement of α-glucosidase (α-Glu) based on a zeolitic imidazolate framework (ZIF-67)-regulated pyrene-based hydrogen-bonded organic framework (HOF-101). Target α-Glu can hydrolyze maltose to α-d-glucose, which can subsequently react with GOx to produce gluconic acid. The resultant gluconic acid can dissolve ZIF-67, leading to the recovery of the HOF-101 cathodic ECL signal and the decrease of the luminol anodic ECL signal. The long-range ordered structure of HOF-101 can speed up charge transfer, resulting in a stable and strong cathodic ECL signal. Moreover, ZIF-67 can not only efficiently quench the ECL signal of HOF-101 due to ECL resonance energy transfer between HOF-101 and ZIF-67 as well as the steric hindrance effect of ZIF-67 but also enhance the anodic ECL emission of luminol in dissolved O2 system because of its ordered and porous crystalline structure and the atomically dispersed Co2+. Notably, HOF-101 possesses a higher ECL efficiency (32.22%) compared with the Ru(bpy)32+ standard. Importantly, this ratiometric ECL biosensor shows high sensitivity (a detection limit of 0.19 U L-1) and a broad linear range (0.2-50 U L-1). This biosensor can efficiently eliminate systematic errors and enhance detection reliability without the involvement of exogenous co-reactants, and it displays good assay performance in human serum samples, holding great promise in biomedical research studies.

A theoretical study of hybrid hydrogen adsorption: Mg nanoparticle-inserted Mg-MOF-74

Metal-organic frameworks (MOFs) provide highly selective catalytic activity due to their porous crystalline structure. There is particular interest in metal nanoparticle-MOF composites (M NP@MOF) that could take advantage of synergistic effects for enhanced catalytic properties. We present an investigation into the local structure and electronic properties of Mg NP@Mg-MOF-74, which is composed of Mg nanoparticles and Mg-MOF-74. A theoretical study on the adsorption of multiple Mg2–Mg10 clusters at one pore in a 1 × 1 × 2 Mg-MOF-74 supercell is conducted, clearly showing that the small clusters tend to aggregate together when stabilized by bonds between Mg and O in the MOF. Considering the size and shape of the pore in the MOF, HCP-Mg nanoparticles with 60 Mg atoms are embedded in one pore of 1 × 1 × 2 Mg-MOF-74 to form nanowires. Results show that the mixture Mg NP@Mg-MOF-74 exhibits a better hydrogen adsorption performance than the isolated Mg nanoparticle, with a considerable estimated theoretical hydrogen storage capacity of 3.98 wt. %. The corresponding electronic structure analysis reveals that the accumulation of charges on H in the hybrid system is clearly enhanced with respect to the isolated Mg nanoparticles.

Preparation and properties of antibacterial food‐preservative paper incorporating ceramic pigments

AbstractAg@ceramic composite papermaking pigment was prepared by coating silver onto red ceramic powder using the electroless plating method. SEM and XRD showed that the ceramic pigments have a porous crystalline structure and that silver particles had been successfully loaded onto the surface and into the pores of the Ag@ceramic. Untreated ceramic pigment and Ag@ceramic pigment were incorporated into paper sheets by coating, filling and filling‐coating. Using spinach as an example, the ability of the different papers to preserve food was then evaluated. Four indicators were used to assess the preservative effect of the papers: inhibition of growth of Staphylococcus aureus and Escherichia coli, weight loss of the spinach and retention of vitamin C and chlorophyll in the spinach. Although the ceramic preservative paper has no antibacterial properties, it reduced weight loss from the spinach and increased retention of vitamin C and chlorophyll. The antibacterial preservative papers inhibited the growth of E. coli and S. aureus by >99%, and because of their additional antibacterial activity, these papers preserved the spinach more effectively. The experimental results showed that the antibacterial food‐preservative paper incorporating ceramic pigments had great potential in food packing applications.

ROSPECTS FOR THE USE OF WILD BERRY PROCESSING PRODUCTS AS FUNCTIONAL FOOD INGREDIENTS

The aim of this study is to substantiate the feasibility of processing wild berries (Viburnum opulus, Sorbus, Hippophae, Sambucus nigra) into functional food ingredients. The paper analyses the structure of powders from wild berries Viburnum opulus, Sorbus, Hippophae, Sambucus nigra, and investigates the content of micro- and macroelements in the powders; physicochemical parameters of wild berry powders (dry matter, mass fraction of moisture, dispersibility, mass fraction of reducing sugars, solubility, acidity) and dietary fibre content in Viburnum opulus, Sorbus, Hippophae, Sambucus nigra powders. The prototypes were made from high-quality fruit and berry raw materials not damaged by diseases and pests. To make the powders, the berries were dehydrated by osmotic dehydration, then dried in infrared dryers for 2 hours at 50°C to a mass fraction of moisture of 6–8 %. The dried berries were ground in a laboratory mill LZM-1. The structure of the berry powders was studied by electron microscopy. It was found that the powders have a crystalline porous structure and, accordingly, hydrophilic properties. This makes it possible to use them in food production as structure stabilisers, emulsifiers and moisture retainers. The content of some minerals in the samples was studied using a microscope-based SEM and EDS detector. It was found that the powders contain macronutrients (K, Ca, P, Cl, S, N), essential trace elements (Mg) and the conditionally vital trace element Si, which was found in powders from viburnum and sea buckthorn. The obtained powders from wild berries Hippophae rhamnoides L., Viburnum opulus, Sambucus nigra and Sorbus aucuparia contain a significant amount of vitamin C. According to all physicochemical parameters, the samples of plant powders from viburnum, elderberry, sea buckthorn, and mountain ash berries meet the requirements of DSTU 8498:2015. These results indicate the feasibility of processing Viburnum opulus, Sorbus, Hippophae, Sambucus nigra into functional food ingredients.

MOFGalaxyNet: a social network analysis for predicting guest accessibility in metal–organic frameworks utilizing graph convolutional networks

Metal–organic frameworks (MOFs), are porous crystalline structures comprising of metal ions or clusters intricately linked with organic entities, displaying topological diversity and effortless chemical flexibility. These characteristics render them apt for multifarious applications such as adsorption, separation, sensing, and catalysis. Predominantly, the distinctive properties and prospective utility of MOFs are discerned post-manufacture or extrapolation from theoretically conceived models. For empirical researchers unfamiliar with hypothetical structure development, the meticulous crystal engineering of a high-performance MOF for a targeted application via a bottom-up approach resembles a gamble. For example, the precise pore limiting diameter (PLD), which determines the guest accessibility of any MOF cannot be easily inferred with mere knowledge of the metal ion and organic ligand. This limitation in bottom-up conceptual understanding of specific properties of the resultant MOF may contribute to the cautious industrial-scale adoption of MOFs.Consequently, in this study, we take a step towards circumventing this limitation by designing a new tool that predicts the guest accessibility—a MOF key performance indicator—of any given MOF from information on only the organic linkers and the metal ions. This new tool relies on clustering different MOFs in a galaxy-like social network, MOFGalaxyNet, combined with a Graphical Convolutional Network (GCN) to predict the guest accessibility of any new entry in the social network. The proposed network and GCN results provide a robust approach for screening MOFs for various host–guest interaction studies.

“Bridging hydrogen bonds” from guanidine and amidoxime groups on natural bamboo strips as a superantibacterial and knitted adsorbent to efficiently adsorb uranium from simulated seawater

Uranium adsorption from seawater can provide a sustainable development path for the future raw material supply of nuclear energy. However, in the process of uranium extraction from seawater, biofouling adheres to the surface of the adsorbent, wasting the adsorption sites and seriously affecting the adsorption capability of the adsorbent. Herein, inspired by the superanti-biofouling property of guanidine groups, a superantibacterial and knitted adsorbent with guanidine and amidoxime groups cografted on natural bamboo strips (G-AOBS) is synthesized to adsorb uranium from simulated seawater. The intrinsic structure of bamboo is not destroyed by the whole grafting process, and G-AOBS still maintains the porous and cellulose crystalline structure. The grafting of guanidine groups improves the hydrophilicity and significantly enhances the anti-biofouling performance, thereby increasing the adsorption capacity for uranium (qe = 201.4 ± 13.23 mg g−1 at pH = 4 with C0 = 100 mg L−1 and qe = 1.04 ± 0.12 mg g−1 in simulated seawater with C0 = 500 μg L−1). According to the results of DFT, the guanidine and amidoxime groups can not only replace one carbonate in uranyl tricarbonate alone to form a more stable coordination structure but also have a synergistic effect between the two, that is, using three “bridging hydrogen bonds” to form the most stable chelation mode with uranyl dicarbonate.

Influence of binder concentration in zeolitic ZSM-5/bentonite 3D-printed monoliths manufactured through robocasting for catalytic applications

In this work, a 3D printing method, robocasting was utilized to manufacture zeolite ZSM-5-based woodpile monolith catalysts of approximately 10-mm diameter, using bentonite clay as binding matrix. The effect of three different binder concentrations, in the 40–60 wt.% range, on the rheological, physicochemical, and mechanical properties was examined. The rheometer measurements showed that the printing pastes have identical shear thinning behavior and demonstrate sufficient storage modulus, irrespective of the binder concentration. The printed monoliths had high BET surface areas and porosity. The results showed that the ZSM-5 crystals retained their porous structure, textural characteristics, and crystalline structure during the additive manufacturing process. Pyridine FTIR measurements demonstrated reduced total acidity and number of Brønsted acid sites in the final specimens due to the dilution with the bentonite powder. However, the acidity reduction was roughly proportional to the binder concentration, signifying that the ZSM-5 crystallites also retain their acidity during the robocasting printing. Finally, the mechanical reliability of the thermally treated monoliths was determined by calculating the Weibull modulus values through linear regression of the Weibull equation. The increase in the binder concentration increased the compression strength by a factor of 4.5 and achieved superior mechanical reliability.Graphical abstract

Multilayer structure covalent organic frameworks (COFs) linking by double functional groups for advanced K+ batteries

Covalent organic frameworks (COFs) are regarded as the potential and promising anode materials for potassium ion batteries (PIBs) on account of their robust and porous crystalline structure. In this work, multilayer structural COF connected by double functional groups, including imine and amidogent through a simple solvothermalprocess, have been successfully synthesized. The multilayer structure of COF can provide fast charge transfer and combine the merits of imine (the restraint of irreversible dissolution) and amidogent (the supply of more active sites). It presents superior potassium storage performance, including the high reversible capacity of 229.5 mAh g−1 at 0.2 A g−1 and outstanding cycling stability of 106.1 mAh g−1 at the high current density of 5.0 A g−1 after 2000 cycles, which is superior to the individual COF. The structural advantages of the covalent organic framework linking by double functional groups (d-COF) can develop a new road for that COF anode material for PIBs in further research.

Biomedical Applications of Titanium Alloys Modified with MOFs—Current Knowledge and Further Development Directions

MOFs (Metal–Organic Frameworks) are so-called coordination polymers with a porous crystalline structure. In this review, the main emphasis was placed on these compounds’ use in modifying titanium implants. The article describes what MOFs are, gives examples of ligands used in the synthesis of MOFs, and describes a subgroup of these materials, i.e., Zeolitic imidazolate frameworks. The article also lists the basic biomedical applications of these compounds. This review shows the significant impact of titanium surface modification with Metal–Organic Frameworks. These modifications make it possible to obtain layers with antibacterial properties, better corrosion resistance, increasing cell proliferation, faster bone growth in vivo, and much more. The presented work shows that the modification of titanium with MOFs is a very promising method of improving their properties. We hope that the prepared review will help research groups from around the world in the preparation of implants modified with Metal–Organic Frameworks with enhanced properties and utility applications.

Electron Storage Performance of Metal–Organic Frameworks Based on Tetrathiafulvalene–Tetrabenzoate as Cathode Active Materials in Lithium- and Sodium-Ion Batteries

Tetrathiafulvalene (TTF) derivatives are well-known molecular-based conductors. They are used to prepare porous crystalline structures with efficient charge transport properties and suitable chemical design, such as metal–organic frameworks (MOFs), covalent organic frameworks (COFs), and hydrogen-bonded organic frameworks (HOFs). MOFs based on TTF derivatives have attracted attention as electrode-active materials for rechargeable metal-ion batteries owing to multielectron redox reactions, resulting in improved battery capacity. This study focuses on TTF–tetrabenzoate (H4TTFTB), which exhibits good redox and mechanical properties as the ligand of MOFs. We evaluated the battery performance using MOFs based on H4TTFTB with three types of core metals ([M2(TTFTB)], where M = Zn, Co, and Mn) as cathode active materials for rechargeable lithium-ion and sodium-ion batteries (LIBs and SIBs). The cycle stability and battery capacity at high current densities were improved by MOF formation in both LIBs and SIBs, indicating that MOF formation has the potential to achieve improved charging/discharging rates. In addition, the battery capacities and cycle stability of SIBs were larger than those of LIBs for all materials. These results demonstrate the interesting battery performance of MOFs based on H4TTFTB as cathode active materials for LIBs and SIBs. This implies that the application of redox-active and rigid H4TTFTB as the ligand of MOFs is an effective method for realizing high-performance energy storage devices. These findings can contribute to an improved design of cathode active materials for high-performance rechargeable metal-ion batteries for sustainable energy storage.

Metal-Free Triazine-Based Porous Organic Polymer-Derived N-Doped Porous Carbons as Effective Electrocatalysts for Oxygen Reduction Reaction

In recent years, porous heteroatom-doped carbon materials have been very promising for energy conversion. A newly designed porous organic polymer (POPQ) has been synthesized using two organic monomers, i.e., 2,6-diaminoanthraquinone and cyanuric chloride, under reflux conditions for 72 h in an inert atmosphere. The triazine-containing porous organic polymers undergo pyrolysis, which produces two nitrogen-doped porous carbon materials, N/POPQ600 and N/POPQ800, at 600 and 800 °C temperatures, respectively. Since the resultant N-doped porous materials have a higher surface area than the parent porous organic polymer and the materials have a synergistic effect due to the enriched nitrogen content throughout the matrix, the metal-free N/POPQ600 and N/POPQ800 materials exhibit good electrocatalytic activity toward oxygen reduction reaction (ORR). Among these, the N/POPQ800 material shows excellent ORR activity with a nearly four-electron oxygen reduction pathway where the half-wave potential is estimated to be 0.728 V vs reversible hydrogen electrode (RHE), comparable with the commercially available Pt/C catalyst. Most interestingly, the N/POPQ800 catalyst displays outstanding long-lasting stability. It shows a better methanol tolerance capability than Pt/C, which can be attributed to the high specific surface area and N-doped well-defined crystalline porous structure. Also, the homogeneously distributed active sites throughout the carbon framework are the most precious for the electrochemical oxygen reduction reaction.

Engineering Covalent Organic Frameworks as Heterogeneous Photocatalysts for Organic Transformations.

Covalent organic frameworks (COFs) are an emerging category of organic polymers with highly porous crystalline structures. In the last decade, reports on the use of COFs as heterogeneous photocatalysts for organic transformations have shown significant progress. Still, comprehensive reviews on the mechanisms of the photocatalytic organic transformations using COFs are lacking. This Review provides a comprehensive and systematic overview of COF-based photocatalysts for organic transformations. Firstly, we discuss the photophysical properties and the characterization methods of COF-based photocatalysts. Then, the general photocatalytic mechanism, the advantages, and the strategies to improve the photocatalytic efficiency of COF-based photocatalysts are summarized. After that, advanced examples of COF-based photocatalysts for organic transformations are analyzed with regard to the underlying mechanisms. The Review ends with a critical perspective on the challenges and prospects.