Integrating Levels of Hierarchical Organization in Porous Organic Molecular Materials

Porous organic molecular materials(POMMs)are an emergent class of molecular-based materials characterized by the formation of extended porous frameworks,mainly held by non-covalent interactions.POMMs represent a variety of chemical families,such as hydrogen-bonded organic frameworks,porous organic salts,porous organic cages,C-H···πmicroporous crystals,supramolecular organic frameworks,π-organic frameworks,halogen-bonded organic framework,and intrinsically porous molecular materials.In some porous materials such as zeolites and metal organic frameworks,the integration of multiscale has been adopted to build materials with multifunctionality and optimized properties.Therefore,considering the significant role of hierarchy in porous materials and the growing importance of POMMs in the realm of synthetic porous materials,we consider it appropriate to dedicate for the first time a critical review covering both topics.Herein,we will provide a summary of literature examples showcasing hierarchical POMMs,with a focus on their main synthetic approaches,applications,and the advantages brought forth by introducing hierarchy.

Rational design of new in situ reduction of Ni(II)catalytic system for low-cost and large-scale preparation of porous aromatic frameworks

Porous aromatic framework 1(PAF-1)is an extremely representative nanoporous organic framework owing to its high stability and exceptionally high surface area.Currently,the synthesis of PAF-1 is catalyzed by the Ni(COD)2/COD/bpy system,suffering from great instability and high cost.Herein,we developed an in situ reduction of the Ni(II)catalytic system to synthesize PAF-1 in low cost and high yield.The active Ni(0)species produced from the NiCl_(2)/bpy/NaI/Mg catalyst system can effectively catalyze homocoupling of tetrakis(4-bromophenyl)methane at the room temperature to form PAF-1 with high Brunauer-Emmett-Teller(BET)-specific surface area up to 4948 m^(2) g^(−1)(Langmuir surface area,6785 m2 g−1).The possible halogen exchange and dehalogenation coupling mechanisms for this new catalytic process in PAF's synthesis are discussed in detail.The efficiency and universality of this innovative catalyst system have also been demonstrated in other PAFs'synthesis.This work provides a cheap,facile,and efficient method for scalable synthesis of PAFs and explores their application for high-pressure storage of Xe and Kr.

Visible-light degradation of azo dyes by imine-linked covalent organic frameworks

Covalent organic frameworks(COFs)are nanoporous crystalline polymers with densely conjugated structures.This work discovers that imine-linked COFs exhibit remarkable photodegradation efficiency to azo dyes dissolved in water.Visible light generates different types of radicals from COFs,and superoxide radicals break N=N bonds in dye molecules,resulting in 100%degradation of azo dyes within 1 h.In contrast,these dyes cannot be degraded by conventionally used photocatalysts,for example,TiO2.Importantly,the COF photocatalysts can be recovered from the dye solutions and re-used to degrade azo dyes for multiple times without loss of degradation efficiency.This work provides an efficient strategy to degrade synthetic dyes,and we expect that COFs with designable structures may use as new photocatalysts for other important applications.

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.

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.

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.

Metal–organic framework derived hierarchical porous TiO_2 nanopills as a super stable anode for Na-ion batteries

Hierarchical porous TiOnanopills were synthesized using a titanium metal-organic framework MIL-125（Ti） as precursor. The as-synthesized TiOnanopills owned a large specific surface area of 102 m/g and unique porous structure. Furthermore, the obtained TiOnanopills were applied as anode materials for Na-ion batteries for the first time. The as-synthesized TiOnanopills achieved a high discharge capacity of 196.4 m Ah/g at a current density of 0.1 A/g. A discharge capacity of 115.9 m Ah/g was obtained at a high current density of 0.5 A/g and the capacity retention was remained as high as 90% even after 3000 cycles. The excellent electrochemical performance can be attributed to its unique hierarchical porous feature.

Covalent organic frameworks as heterogeneous catalysts

Covalent organic frameworks （COFs）, established as an emerging class of crystalline porous polymers with high surface area, structural diversity, and esignability, attract much interest and exhibit potential applications in catalysis. In this review, we summarize the use of COFs as a versatile platform to develop heterogeneous catalysts for a variety of chemical reactions. Catalytic COFs are categorized in accordance with the types of active sites, involving single functional active sites, bifunctional active sites, and metal nanoparticles （NPs） embedded in pores. Special emphasis is placed on the deliberate or incidental synthesis strategies, the stability, the heterogeneity, and the shape/size selectivity for COF catalysis. Moreover, a description of the application of COFs as photocatalysts and electrocatalysts is presented. Finally, the prospects of COFs in catalysis and remaining issues in this field are indicated.

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.

MOF‐derived 1D/3D N‐doped porous carbon for spatially confined electrochemical CO2 reduction to adjustable syngas

Electrochemical reduction of CO_(2)to syngas(CO and H_(2))offers an efficient way to mitigate carbon emissions and store intermittent renewable energy in chemicals.Herein,the hierarchical one‐dimensional/three‐dimensional nitrogen‐doped porous carbon(1D/3D NPC)is prepared by carbonizing the composite of Zn‐MOF‐74 crystals in situ grown on a commercial melamine sponge(MS),for electrochemical CO_(2)reduction reaction(CO_(2)RR).The 1D/3D NPC exhibits a high CO/H_(2)ratio(5.06)and CO yield(31 mmol g^(−1)h^(−1))at−0.55 V,which are 13.7 times and 21.4 times those of 1D porous carbon(derived from Zn‐MOF‐74)and N‐doped carbon(carbonized by MS),respectively.This is attributed to the unique spatial environment of 1D/3D NPC,which increases the adsorption capacity of CO_(2)and promotes electron transfer from the 3D N‐doped carbon framework to 1D carbon,improving the reaction kinetics of CO_(2)RR.Experimental results and charge density difference plots indicate that the active site of CO_(2)RR is the positively charged carbon atom adjacent to graphitic N on 1D carbon and the active site of HER is the pyridinic N on 1D carbon.The presence of pyridinic N and pyrrolic N reduces the number of electron transfer,decreasing the reaction kinetics and the activity of CO_(2)RR.The CO/H_(2)ratio is related to the distribution of N species and the specific surface area,which are determined by the degree of spatial confinement effect.The CO/H_(2)ratios can be regulated by adjusting the carbonization temperature to adjust the degree of spatial confinement effect.Given the low cost of feedstock and easy strategy,1D/3D NPC catalysts have great potential for industrial application.

Amide-linked covalent organic frameworks as efficient heterogeneous photocatalysts in water

Semiconductor photocatalysts play an indispensable role in the photocatalytic process.Two-dimensional covalent organic frameworks(2D-COFs),as a kind of innovative photocatalyst,have garnered tremendous attention.Herein,we report an amide-linked 2D-COF(COF-JLU19)with outstanding photocatalytic performance in water,designed through a multi-synergistic approach.The synergistic effects of the high porosity,photoactive framework,high wettability,and stability of COF-JLU19 led to an unprecedented enhancement in the photocatalytic activity and recyclability in water upon illumination by visible light.More importantly,amide-linked 2D-COF based electrospinning membranes were prepared,which also exhibited superior photocatalytic activity for the degradation of Rhodamine B in water with sunlight.This study highlights the potential of the multi-synergistic approach as a universal rule for developing COF-based photocatalysts to address environmental and energy challenges.

Covalent organic frameworks:Design,synthesis,characterization,and applications

Covalent organic frameworks(COFs)have emerged as an interesting class of crystalline porous materials with desirable properties(such as highly ordered porosity,structural versatility,high chemical and thermal stabilities,and facile surface modification)and a broad range of potential applications.This critical review is aimed at providing insight into design strategies and synthetic methodologies for COFs.Unlike previous reviews on COFs,this article also focuses on the characterization of COFs,which is important for understanding the physical and chemical properties of COFs that are essential for practical applications.Furthermore,this review highlights the applications of COFs in various fields,including catalysis,photovoltaic devices,sensors,supercapacitors,wastewater treatment,biomedicine,chromatographic and spectroscopic analyses,and gas separation and storage.Lastly,perspectives on future directions and challenges associated with COFs are provided.

Recent Advances in Multifunctional Reticular Framework Nanoparticles:A Paradigm Shift in Materials Science Road to a Structured Future

Porous organic frameworks(POFs)have become a highly sought-after research domain that offers a promising avenue for developing cutting-edge nanostructured materials,both in their pristine state and when subjected to various chemical and structural modifications.Metal–organic frameworks,covalent organic frameworks,and hydrogen-bonded organic frameworks are examples of these emerging materials that have gained significant attention due to their unique properties,such as high crystallinity,intrinsic porosity,unique structural regularity,diverse functionality,design flexibility,and outstanding stability.This review provides an overview of the state-of-the-art research on base-stable POFs,emphasizing the distinct pros and cons of reticular framework nanoparticles compared to other types of nanocluster materials.Thereafter,the review highlights the unique opportunity to produce multifunctional tailoring nanoparticles to meet specific application requirements.It is recommended that this potential for creating customized nanoparticles should be the driving force behind future synthesis efforts to tap the full potential of this multifaceted material category.

Fully Conjugated Covalent Organic Frameworks:Synthesis,Structures and Applications

This review presents a comprehensive examination of fully conjugated covalent organic frameworks(COFs),which constitute an emerging class of porous materials with immense potential for diverse applications.This article focuses on diversified fully conjugated COFs,including sp2 carbon-carbon linkages,pyrazine linkages,benzobisoxazole linkages,dioxin linkages,β-aminoalkenone linkages,etc.The synthesis techniques and structural attributes of these COFs are expounded upon in great detail,along with their potential applications in various fields.The review thus provides a valuable resource for researchers keen on delving into the synthesis and applications of fully conjugated COFs,thereby highlighting their potential for developing novel functional materials with distinctive properties.

Synthesis and applications of MOF-derived porous nanostructures

Metal organic frameworks(MOFs) represent a class of porous material which is formed by strong bonds between metal ions and organic linkers. By careful selection of constituents, MOFs can exhibit very high surface area, large pore volume, and excellent chemical stability.Research on synthesis, structures and properties of various MOFs has shown that they are promising materials for many applications, such as energy storage, gas storage, heterogeneous catalysis and sensing. Apart from direct use, MOFs have also been used as support substrates for nanomaterials or as sacrificial templates/precursors for preparation of various functional nanostructures. In this review, we aim to present the most recent development of MOFs as precursors for the preparation of various nanostructures and their potential applications in energy-related devices and processes. Specifically, this present survey intends to push the boundaries and covers the literatures from the year 2013 to early 2017,on supercapacitors, lithium ion batteries, electrocatalysts, photocatalyst, gas sensing, water treatment, solar cells, and carbon dioxide capture.Finally, an outlook in terms of future challenges and potential prospects towards industrial applications are also discussed.

Enhanced stability of highly-dispersed copper catalyst supported by hierarchically porous carbon for long term selective hydrogenation

Copper based catalysts have high potential for the substituent of noble-metal based catalysts as their high selectivity and moderate activity for selective hydrogenation reaction;however,achieving further high catalytic stability is very difficult.In this work,the carbonization process of Cu-based organic frameworks was explored for the synthesis of highly-dispersed Cu supported by hierarchically porous carbon with high catalytic performance for selective hydrogenation of 1,3-butadiene.The porous hierarchy of carbon support and the dispersion of copper nanoparticles can be precisely tuned by controlling the carbonization process.The resultant catalyst carbonized at 600°C exhibits a rather low reaction temperature at 75°C for 100%butadiene conversion with 100%selectivity to butenes,due to its reasonable porous hierarchy and highly-dispersed copper sites.More importantly,unprecedentedly stability of the corresponding Cu catalyst was firstly observed for selective 1,3-butadiene hydrogenation,with both 100%butadiene conversion and 100%butenes selectivity over 120 h of reaction at 75°C.This study verifies that a simply control the carbonization process of metal organic frameworks can be an effective way to obtain Cu-based catalysts with superior catalytic performance for selective hydrogenation reaction.

Impregnated Sulfur in Carbonized Nitrogen-containing Porous Organic Frameworks as Cathode with High Rate Performance and Long Cycle Life for Lithium-sulfur Batteries

The undesirable cycling performance caused by soluble poly sulfides shuttling between anode and cathode has been considered as the main challenge that has hindered its practical applications for lithium-sulfiir(Li-S) batteries. To solve tliis issue effectively, a nitrogen-containing porous carbon, namely JUC-Z2-900,developed from a porous organic framework, namely JUC-Z2, bearing a high surface area(805 m^2/g),small pore size(0.5 mil) and nitrogen doping(2.15%, mass fraction), has been used as a host material for Li-S batteries. The micropores of JUC-Z2-900 can confine the smaller sulfur molecules S2-4, which can essentially alleviate the critical problem of poly sulfide dissolution.Furthermore, nitrogen-containing JUC-Z2-900 can promote chemical adsorption of sulfur. The above two factors can improve the electrochemical performance of Li-S batteries effectively. To compare the eftects of sulfur contents and melt-difiusion strategy in JUC-Z2-900/S composites, a series of JUC-Z2-900/S composites was synthesized and tlieir electrochemical perfbnnances were explored, indicating good rate performance and excellent cycling stability of the composites contributed by both appropriate mass percentage of sulfiir and its confinement in the micropores.

Co_(1-x)S embedded in porous carbon derived from metal organic framework as a highly efficient electrocatalyst for oxygen evolution reaction

Developing active, robust, and cost-efficient electrocatalysts is critical for oxygen evolution reaction(OER). Here, a novel composite catalyst of Co_(1-x)S embedded in porous dodecahedron carbon hybrid was synthesized by a two-step conversion protocol of a cobalt-based metal-organic framework(ZIF-67). The porous dodecahedron Co_(1-x)S@C composite catalyst was prepared by direct oxidation of ZIF-67 followed by sulfurization reaction. The Co_(1-x)S@C composite exhibit superior OER performance, including a low overpotential of 260 mV for 10 mA/cm2, a small Tafel slope of ~85 mV/dec, outstanding stability over 80 h and almost 100% Faradaic efficiency. The various material characterizations indicate that the excellent activity and strong stability of Co_(1-x)S@C might be attributed to good conductivity of Co_(1-x)S, mesoporous nanostructure, and synergistic effect of Co_(1-x)S encapsulated within porous carbon. This work provides a novel strategy for designing and synthesizing advanced composite

An Ultrastable π-π Stacked Porous Organic Molecular Framework as a Crystalline Sponge for Rapid Molecular Structure Determination

The crystalline sponge method is a pragmatic and promising strategy for molecular structure determination.However,the dominant metal-organic framework crystal sponge platforms always face poor chemical stability,especially solvent instability,hampering their application in a vaster domain.Herein,we report an ultrastable π-π stacked porous organic molecular framework which exhibits permanent porosity,high thermal stability,and good chemical resistance.It can efficiently implement an approach to molecular structure determination via a single-crystal-to-single-crystal transformation.This is the first example utilizing π-π stacked porous organic molecular framework as“crystalline sponge”to determine a wide variety of guests,ranging from hydrophilic to hydrophobic,and from aliphatic to aromatic,which complements the crystalline sponges based on the famous metal-organic frameworks.More importantly,it can achieve rapid structure determination of small molecules within 3 h.

Porous Organic Frameworks-derived Porous Carbons with Outstanding Gas Adsorption Performance

A series of porous carbon materials was synthesized via high temperature pyrolysis from well-defined and thermally stable precursors, namely porous organic frameworks（POFs）, in inert atmosphere. The porous carbon materials showed enhanced gas adsorption capacities together with increased heat of adsorption and stronger affinity between the frameworks and the gases as compared to the precursor materials. To exemplify, sample C-POF-TBBP-1000 with a high BET surface area of 1290 m^2/g can adsorb 2.8 mmol/g CH4（273 K, 101.325 kPa）, 5.4 mmol/g CO2（273 K, 101.325 kPa） and 2.2% H2（mass fraction, 77 K, 101.325 kPa）, thereby surpassing most other porous adsorbent materials reported till date. The study highlights the potential of porous carbons derived from novel porous organic framework structures for gas adsorption applications.