Nitrogen ligands in two-dimensional covalent organic frameworks for metal catalysis

We introduced bipyridine ligands into a series of two‐dimensional （2D） covalent organic frame‐works （COFs） using 2,2’‐bipyridine‐5,5’‐dicarbaldehyde （2,2’‐BPyDCA） as a component in the mixed building blocks. The framework of the COFs was formed by the linkage of imine groups. The ligand content in the COFs was synthetically tuned by the content of 2,2’‐BPyDCA, and thus the amount of metal, palladium（II） acetate, bonded to the nitrogen ligands could be manipulated. Both the bipyri‐dine ligands and imine groups can coordinate with Pd（II） ions, but the loading position can be var‐ied, with one ligand favoring binding in the space between adjacent COFs’ layers and the other lig‐and favoring binding within the pores of the COFs. The Pd（II）‐loaded COFs exhibited good catalytic activity for the Heck reaction.

Mo_(3)(C_(6)X_(6))_(2)(X=NH,S,O)monolayers:two-dimensional conductive metal-organic frameworks as effective electrocatalysts for the nitrogen reduction reaction

As a constituent element of amino acids,nitrogen plays an important role in nourishing plants,animals and other forms of life.Although the atmosphere is rich in nitrogen gas(N_(2)),the highly inert N≡N bond makes it difficult for most organisms to directly utilize N_(2).The supply of nitrogen in the biological chain mainly depends on the slow conversion of N_(2) to ammonia(NH3)by biological nitrogen fixation[1].

Ultrathin two-dimensional metal–organic framework nanosheets for efficient electrochemical CO_(2) reduction

Electrochemical CO_(2) reduction into CO or high-value products is regarded as a feasible pathway for energy conversion,which has attracted universal attention in recent years [1-3].However,the reduction of CO_(2) molecule is a thermodynamically uphill process,which involves multiple elemental steps and the competition of hydrogen evolution reaction(HER) in aqueous solution.

Three-dimensional porous bimetallic metal–organic framework/gelatin aerogels: A readily recyclable peroxymonosulfate activator for efficient and continuous organic dye removal

As promising catalysts for the degradation of organic pollutants,metal–organic frameworks(MOFs)often face limitations due to the particle agglomeration and challenging recovery in liquid-catalysis application,stemming from their powdery nature.Engineering macroscopic structures from pulverous MOF is thus of great importance for broadening their practical applications.In this study,three-dimensional porous MOF aerogel catalysts were successfully fabricated for degrading organic dyes by activating peroxymonosulfate(PMS).MOF/gelatin aerogel(MOF/GA)catalysts were prepared by directly integrating bimetallic FeCo-BDC with gelatin solutions,followed by freeze-drying and low-temperature calcination.The FeCo-BDC-0.15/GA/PMS system exhibited remarkable performance in degrading various organic dyes,eliminating 99.2%of rhodamine B within a mere 5 min.Compared to the GA/PMS system,there was over a 300-fold increase in the reaction rate constant.Remarkably,high removal efficiency was maintained across varying conditions,including different solution pH,co-existing inorganic anions,and natural water matrices.Radical trapping experiments and electron paramagnetic resonance analysis revealed that the degradation involved radical(SO_(4)^(-)·)and non-radical routes(^(1)O_(2)),of which ^(1)O_(2) was dominant.Furthermore,even after a continuous 400-min reaction in a fixed-bed reactor at a liquid hourly space velocity of 27 h^(-1),the FeCo-BDC/GA composite sustained a degradation efficiency exceeding 98.7%.This work presents highly active MOF-gelatin aerogels for dye degradation and expands the potential for their large-scale,continuous treatment application in organic dye wastewater management.

Metal-Organic Framework Enabling Poly(Vinylidene Fluoride)-Based Polymer Electrolyte for Dendrite-Free and Long-Lifespan Sodium Metal Batteries

Sodium dentrite formed by uneven plating/stripping can reduce the utilization of active sodium with poor cyclic stability and,more importantly,cause internal short circuit and lead to thermal runaway and fire.Therefore,sodium dendrites and their related problems seriously hinder the practical application of sodium metal batteries(SMBs).Herein,a design concept for the incorporation of metal-organic framework(MOF)in polymer matrix(polyvinylidene fluoride-hexafluoropropylene)is practiced to prepare a novel gel polymer electrolyte(PH@MOF polymer-based electrolyte[GPE])and thus to achieve high-performance SMBs.The addition of the MOF particles can not only reduce the movement hindrance of polymer chains to promote the transfer of Na^(+)but also anchor anions by virtue of their negative charge to reduce polarization during electrochemical reaction.A stable cycling performance with tiny overpotential for over 800 h at a current density of 5 mA cm^(-2)with areal capacity of 5 mA h cm^(-2)is achieved by symmetric cells based on the resulted GPE while the Na_(3)V_(2)O_(2)(PO_(4))_(2)F@rGO(NVOPF)|PH@MOF|Nacell also displays impressive specific cycling capacity(113.3 mA h g^(-1)at 1 C)and rate capability with considerable capacity retention.

Imide-pillared covalent organic framework protective films as stable zinc ion-conducting interphases for dendrite-free Zn metal anodes

The notorious growth of zinc dendrite and the water-induced corrosion of zinc metal anodes(ZMAs)restrict the practical development of aqueous zinc ion batteries(AZIBs).In this work,a zinc metallized,imide-pillared covalent organic framework(ZPC)protective film has been engineered as a stable Zn^(2+)ion-conducting interphase to modulate interfacial kinetics and suppress side reactions for ZMAs.Compared to bare Zn,ZPC@Zn exhibits a higher Zn^(2+)ionic conductivity,a larger Zn^(2+)transference number,a lower electronic conductivity,a smaller desolvation activation energy and correspondingly a significant suppression of corrosion,hydrogen evolution and Zn dendrites.Impressively,the ZPC@Zn||ZPC@Zn symmetric cell obtains a cycling lifespan over 3000 h under 5 mA cm^(-2)for 1 mA h cm^(-2).The ZPC@Zn||NH_(4)V_(4)O_(10)coin-type full battery delivers a specific capacity of 195.8 mA h g^(-1)with a retention rate of78.5%at 2 A g^(-1)after 1100 cycles,and the ZPC@Zn||NH_(4)V_(4)O_(10) pouch full cell shows a retention of70.1%in reversible capacity at 3 A g^(-1)after 1100 cycles.The present incorporation of imide-linked covalent organic frameworks in the surface modification of ZMAs will offer fresh perspectives in the search for ideal protective films for the practicality of AZIBs.

Recent Progress on Engineering Highly Efficient Porous Semiconductor Photocatalysts Derived from Metal–Organic Frameworks

Porous structures o er highly accessible surfaces and rich pores, which facilitate the exposure of numerous active sites for photocatalytic reactions, leading to excellent performances. Recently, metal–organic frameworks(MOFs) have been considered ideal precursors for well-designed semiconductors with porous structures and/or heterostructures, which have shown enhanced photocatalytic activities. In this review, we summarize the recent development of porous structures, such as metal oxides and metal sulfides, and their heterostructures, derived from MOF-based materials as catalysts for various light-driven energy-/environment-related reactions, including water splitting, CO_2 reduction, organic redox reaction, and pollution degradation. A summary and outlook section is also included.

Metal-organic frameworks for electrochemical reduction of carbon dioxide: The role of metal centers

Direct electrochemical reduction of CO2 into valuable chemicals and fuel is one of the most promising approaches to address the current energy crisis and lower CO2 emission.Recently,numerous metal-organic framework(MOF)and their derived materials have extensively been developed as electrocatalysts for CO2 reduction owing to their unique structure including porosity,large specific surface area,and tunable chemical structures.In this review,the recent progress of MOF-based electrocatalysts for CO2 reduction was summarized and discussed.Detailed discussions mainly focus on the synthesis and mechanism of pristine MOFs and MOF-derived materials for electrocatalytic CO2 reduction.These examples are expected to provide clues to rational design and synthesis of stable and high-performance MOFs-based electrocatalysts for CO2 reduction.

Applications of metal–organic frameworks for green energy and environment: New advances in adsorptive gas separation, storage and removal

The separation of gas molecules with similar physicochemical properties is of high importance but practically entails a substantial energy penalty in chemical industry. Meanwhile, clean energy gases such as H_2 and CH_4 are considered as promising candidates for the replacement of traditional fossil fuels. However, the technologies for the storage of these gases are still immature. In addition, the release of anthropogenic toxic gases into the atmosphere is a worldwide threat of growing concern. Both in academia and industry, considerable research efforts have been devoted to developing advanced porous materials for the effective and energy-efficient separation, storage, or capture of the related gases. In contrast to conventional inorganic porous materials such as zeolites and activated carbons, metal–organic frameworks(MOFs) are considered as a type of promising materials for gas separation and storage. In this contribution, we review the recent research advance of MOFs in some relevant applications, including CO_2 capture, O_2 purification, separation of light hydrocarbons, separation of noble gases, storage of gases(CH_4,H_2, and C_2 H_2) for energy, and removal of some gaseous air pollutants(NH_3, NO_2, and SO_2). Finally, an outlook regarding the challenges of the future research of MOFs in these directions is given.

Tuning Atomically Dispersed Fe Sites in Metal–Organic Frameworks Boosts Peroxidase‑Like Activity for Sensitive Biosensing

Although nanozymes have been widely developed,accurate design of highly active sites at the atomic level to mimic the electronic and geometrical structure of enzymes and the exploration of underlying mechanisms still face significant challenges.Herein,two functional groups with opposite electron modulation abilities(nitro and amino)were introduced into the metal–organic frameworks(MIL-101(Fe))to tune the atomically dispersed metal sites and thus regulate the enzymelike activity.Notably,the functionalization of nitro can enhance the peroxidase(POD)-like activity of MIL-101(Fe),while the amino is poles apart.Theoretical calculations demonstrate that the introduction of nitro can not only regulate the geometry of adsorbed intermediates but also improve the electronic structure of metal active sites.Benefiting from both geometric and electronic effects,the nitro-functionalized MIL-101(Fe)with a low reaction energy barrier for the HO*formation exhibits a superior POD-like activity.As a concept of the application,a nitro-functionalized MIL-101(Fe)-based biosensor was elaborately applied for the sensitive detection of acetylcholinesterase activity in the range of 0.2–50 mU mL−1 with a limit of detection of 0.14 mU mL−1.Moreover,the detection of organophosphorus pesticides was also achieved.This work not only opens up new prospects for the rational design of highly active nanozymes at the atomic scale but also enhances the performance of nanozyme-based biosensors.

Recent advances in the synthesis of nanoscale hierarchically porous metal–organic frameworks

Nanoscale hierarchically porous metal–organic frameworks(NHP-MOFs)have received unprecedented attention in many fields owing to their integration of the strengths of nanoscale size(<1μm)and hierarchical porous structure(micro-,meso-and/or macro-pores)of MOFs.This review focuses on recent advances in the main synthetic strategies for NHP-MOFs based on different metal ions(e.g.,Cu,Fe,Co,Zn,Al,Zr,and Cr),including the template method,composite technology,post-synthetic modification,in situ growth and the grind method.In addition,the mechanisms of synthesis,regulation techniques and the advantages and disadvantages of various methods are discussed.Finally,the challenges and prospects of the commercialisation of promising NHP-MOFs are also presented.The purpose of this review is to provide a road map for future design and development of NHP-MOFs for practical application.

Design of metal-organic frameworks(MOFs)-based photocatalyst for solar fuel production and photo-degradation of pollutants

Metal organic frameworks(MOFs)is a research hotspot in the solar fuel production and photo-degradation of pollutants field due to high surface area,rich metal/organic species,large pore volume,and adjustability of structures and compositions.Therefore,in this review,we first summarized the design factors of photocatalytic materials based on MOF from the perspective of"star"MOF.The modification strategies of MOFs-based photocatalysts were discussed to improve its photocatalytic activity and specific applications were summarized as well,including photocatalytic CO_(2)reduction,photocatalytic water splitting and photo-degradation of pollutants.Finally,the advantages and disadvantages of MOFs-based photocatalysts were discussed,the current challenges were highlighted,and suggestions for future research directions were proposed.

Pyridinic nitrogen enriched porous carbon derived from bimetal organic frameworks for high capacity zinc ion hybrid capacitors with remarkable rate capability

Aqueous zinc ion hybrid capacitors(ZIHCs)hold great potential for large-scale energy storage applications owing to their high safety and low cost,but suffer from low capacity and energy density.Herein,pyridinic nitrogen enriched porous carbon(nPC)was successfully synthesized via the growth,subsequent annealing and acid etching of bimetal organic frameworks for high capacity and safe ZIHCs with exceptional rate capability.Benefiting from the mesopores for easy ion diffusion,high electrical conductivity enabled by in-situ grown carbon nanotubes matrix and residual metal Co nanoparticles for fast electron transfer,sufficient micropores and high N content(8.9 at%)with dominated pyridinic N(54%)for enhanced zinc ion storage,the resulting nPC cathodes for ZIHCs achieved high capacities of 302 and137 m Ah g^(-1) at 1 and 18 A g^(-1),outperforming most reported carbon based cathodes.Theoretical results further disclosed that pyridinic N possessed larger binding energy of-4.99 eV to chemically coordinate with Zn2+than other N species.Moreover,quasi-solid-state ZIHCs with gelatin based gel electrolytes exhibited high energy density of 157.6 Wh kg^(-1) at 0.69 kW kg^(-1),high safety and mechanical flexibility to withstand mechanical deformation and drilling.This strategy of developing pyridinic nitrogen enriched porous carbon will pave a new avenue to construct safe ZIHCs with high energy densities.

Advanced metal–organic frameworks for aqueous sodium-ion rechargeable batteries

Inexpensive and abundant sodium resources make energy storage systems using sodium chemistry promising replacements for typical lithium-ion rechargeable batteries(LIBs).Fortuitously,aqueous sodium-ion rechargeable batteries(ASIBs),which operate in aqueous electrolytes,are cheaper,safer,and more ionically conductive than batteries that operate in conventional organic electrolytes;furthermore,they are suitable for grid-scale energy storage applications.As electrode materials for storing Na~+ ions in ASIBs,a variety of multifunctional metal-organic frameworks(MOFs) have demonstrated great potential in terms of having porous 3 D crystal structures,compatibility with aqueous solutions,long cycle lives(≥1000 cycles),and ease of synthesis.The present review describes MOF-derived technologies for the successful application of MOFs to ASIBs and suggests future challenges in this area of research based on the current understanding.

Nanoengineering Metal–Organic Frameworks and Derivatives for Electrosynthesis of Ammonia

Electrocatalytic synthesis under mild conditions has become increasingly important as one of the practical alternatives for industrial applications,especially for the green ammonia(NH_(3))industry.A properly engineered electrocatalyst plays a vital role in the realization of superior catalytic performance.Among various types of promising nanomaterials,metal–organic frameworks(MOFs)are competitive candidates for developing efficient electrocatalytic NH_(3) synthesis from simple nitrogen-containing molecules or ions,such as N_(2) and NO_(3)^(−).In this review,recent advances in the development of electrocatalysts derived from MOFs for the electrosynthesis of NH_(3) are collected,categorized,and discussed,including their application in the N_(2) reduction reaction(NRR)and the NO_(3)^(−)reduction reaction(NO3RR).Firstly,the fundamental principles are illustrated,such as plausible mechanisms of NH_(3) generation from N_(2) and NO_(3)^(−),the apparatus of corresponding electrocatalysis,parameters for evaluation of reaction efficiency,and detection methods of yielding NH_(3).Then,the electrocatalysts for NRR processes are discussed in detail,including pristine MOFs,MOF-hybrids,MOF-derived N-doped porous carbons,single atomic catalysts from pyrolysis of MOFs,and other MOF-related materials.Subsequently,MOF-related NO3RR processes are also listed and discussed.Finally,the existing challenges and prospects for the rational design and fabrication of electrocatalysts from MOFs for electrochemical NH_(3) synthesis are presented,such as the evolution of investigation methods with artificial intelligence,innovation in synthetic methods of MOF-related catalysts,advancement of characterization techniques,and extended electrocatalytic reactions.

Machine learning and high-throughput computational screening of hydrophobic metal–organic frameworks for capture of formaldehyde from air

Aiming to efficiently capture the formaldehyde(HCHO)with low content in the air exceeding the standard,31,399 hydrophobic metal–organic frameworks(MOFs)were first selected from 137,953 hypothetical MOFs to calculate their formaldehyde adsorption performance,namely,adsorption capacity(NHCHO)and selectivity(SHCHO=N^(2+)O_(2))by molecular simulation and machine learning(ML).To combine the SHCHO=N^(2+)O_(2) and NHCHO,a new performance metric,the tradeoff between selectivity and capacity(TSC)was proposed to identify more reasonably the top-performing MOFs.The MOFs were divided into three datasets(i.e.,all of the MOFs(AM),MOFs with top 5%of SHCHO=N^(2+)O_(2)(PS)and MOFs with top 5%of NHCHO(PN))to scrutinize and explore the characteristics of different materials capturing formaldehyde from the air(N2 and O_(2)).Furthermore,after four ML algorithms(the back propagation neural network(BPNN),support vector machine(SVM),extreme learning machine(ELM),and random forest(RF))are applied to quantitatively assess the prediction effects of performance indexes in different datasets,RF algorithm with the most accurate prediction revealed that the TSC has strong correlations with the MOF descriptors in PS dataset.In view of 14.10%of the promising MOFs occupied PN,the design paths of excellent adsorbents for six MOF descriptors were quantitatively determined,especially for the Henry's coefficient(KHCHO)and heat of adsorption of formaldehyde(Q0 st).Their probabilities of obtaining excellent MOFs could reach 100%and 77.42%,respectively,and both the relative importance and the trends of univariate analysis coherently confirm the important positions of KHCHO and Q0 st.Finally,20 best MOFs were identified for the single-step separation of formaldehyde with low concentration.The microscopic insights and structure-performance relationship predictions from this computational and ML study are useful toward the development of new MOFs for the capture of formaldehyde from air.

Hierarchical Metal-Organic Frameworks with Macroporosity:Synthesis, Achievements,and Challenges

Introduction of multiple pore size regimes into metalorganic frameworks(MOFs)to form hierarchical porous structures can lead to improved performance of the material in various applications.In many cases,where interactions with bulky molecules are involved,enlarging the pore size of typically microporous MOF adsorbents or MOF catalysts is crucial for enhancing both mass transfer and molecular accessibility.In this review,we examine the range of synthetic strategies which have been reported thus far to prepare hierarchical MOFs or MOF composites with added macroporosity.These fabrication techniques can be either pre-or post-synthetic and include using hard or soft structural template agents,defect formation,routes involving supercritical CO2,and 3D printing.We also discuss potential applications and some of the challenges involved with current techniques,which must be addressed if any of these approaches are to be taken forward for industrial applications.

Metal-organic frameworks for highly efficient oxygen electrocatalysis

Metal‐organic frameworks(MOFs)are a series of highly porous crystalline materials,which are built from inorganic metal nodes and organic linkers through coordination bonds.Their unique porous structural features(such as high porosity,high surface areas,and highly ordered nanoporous structures)and designable structures and compositions have facilitated their use in gas capture,separation,catalysis,and energy storage and conversion.Recently,the design and synthesis of pure MOFs and their derivatives have opened new routes to develop highly efficient electrocatalysts toward oxygen reduction reactions(ORR)and oxygen evolution reactions(OER),which are the core electrode reactions in many energy storage and conversion techniques,such as metal‐air batteries and fuel cells.This review first discusses recent progress in the synthesis and the electrocatalytic applications of pure MOF‐based electrocatalysts toward ORR or OER,including pure MOFs,MOFs decorated with active species,and MOFs incorporated with conductive materials.The following section focuses on the advancements of the design and preparation of various MOF‐derived materials-such as inorganic nano‐(or micro‐)structures/porous carbon composites,pure porous carbons,pure inorganic nano‐(or micro‐)structured materials,and single‐atom electrocatalysts-and their applications in oxygen electrocatalysis.Finally,we present a conclusion and an outlook for some general design strategies and future research directions of MOF‐based oxygen electrocatalysts.

Metal‐organic frameworks‐derived novel nanostructured electrocatalysts for oxygen evolution reaction

Engineering cost‐effective catalysts with exceptional performance for theelectrochemical oxygen evolution reaction (OER) remains crucial for theaccelerated development of renewable energy techniques, and especially so,given the pivotal role of OER in water electrolysis. On the basis of the metalnodes (clusters) and organic linkers, metal‐organic frameworks (MOFs) andtheir derivatives are rapidly gaining ground in the fabrication of electrocatalysts,with promising catalytic activity and sound durability in OER, thanksto their controllable pore structures, abundant unsaturated active sites of metalion, extensive specific surface area, as well as easily functionalized/modifiedsurfaces. This review presents an in‐depth understanding of the establishedprogress of MOFs‐derived materials for OER electrocatalysis. The materialdesigning strategies of the pristine, monometallic, and multimetallic MOFsbasedcatalysts are summarized to indicate the infinite possibilities of themorphology and the composition of MOF‐derived materials. While emphasisis laid on the essential features of MOF‐derived materials for the electrocatalysisof the corresponding reactions, insights about the applications in OERare discussed. Finally, this paper is concluded by presenting challengesand perspectives for MOF‐derived materials’ future applications in OERelectrocatalysis.

Adsorption behavior and mechanism of Hg(Ⅱ)on highly stable Zn-based metal organic frameworks

A novel adsorbent(MTZ-MOFs)was synthesized by a one-step reaction of zinc nitrate hexahydrate and 1-(2-dimethylaminoethyl)-1H-5-mercaptotetrazole to remove mercury from waste water.The results showed that MTZ-MOFs had excellent selectivity and repeatability for Hg(Ⅱ),the optimum pH was 3.0,the maximum adsorption capacity was 872.8 mg/g,and the process was a spontaneous exothermic reaction.The adsorption behavior was chemisorption,which conformed to the pseudo-second-order kinetic and Freundlich isothermal model.Moreover,the adsorption mechanism showed that the adsorption process mainly depended on ion exchange and chelation,and the synergistic action of S and N atoms played a key role.So,MTZ-MOFs were an efficient adsorbent for mercury ion removal.