Porous functional metal–organic frameworks (MOFs) constructed from different N-heterocyclic carboxylic ligands for gas adsorption/separation

This review mainly summarizes the recent progress of MOFs composed of N-heterocyclic carboxylate ligands in gas sorption/separation. This work may help to understand the relationship between the structures of MOFs and gas sorption/separation.

Ionic metal-organic frameworks (iMOFs): progress and prospects as ionic functional materials

Metal-organic frameworks (MOFs) have been a research hotspot for the last two decades, witnessing an extraordinary upsurge across various domains in materials chemistry. Ionic MOFs (both anionic and cationic MOFs) have emerged as next-generation ionic functional materials and are an important subclass of MOFs owing to their ability to generate strong electrostatic interactions between their charged framework and guest molecules. Furthermore, the presence of extra-framework counter-ions in their confined nanospaces can serve as additional functionality in these materials, which endows them a significant advantage in specific host-guest interactions and ion-exchange-based applications. In the present review, we summarize the progress and future prospects of iMOFs both in terms of fundamental developments and potential applications. Furthermore, the design principles of ionic MOFs and their state-of-the-art ion exchange performances are discussed in detail and the future perspectives of these promising ionic materials are proposed.

Interpenetrated N-rich MOF derived vesicular N-doped carbon for high performance lithium ion battery

High-performance lithium ion batteries (LIBs) juggling high reversible capacity, excellent rate capability and ultralong cycle stability are urgently needed for all electronic devices. Here we report employing a vesicle-like porous N-doped carbon material (abbr. N/C-900) as a highly active anode for LIBs to balance high capacity, high rate and long life. The N/C-900 material was fabricated by pyrolysis of a designed crystal MOF LCU-104, which exhibits a graceful two-fold interpenetrating structural feature of N-rich nanocages {Zn₆(dttz)₄} linked through an N-donor ligand bpp (H₃dttz = 4,5-di(1H-tetrazol-5-yl)-2H-1,2,3-triazole, bpp = 1,3-bis(4-pyridyl)propane). The features of LCU-104 combine high N content (35.1%), interpenetration, and explosive characteristics, which endow the derived N/C material with optimized N-doping for tuning its chemical and electronic structure, a suitably thicker wall to enhance its stability, and a vesicle-like structure to improve its porosity. As an anode material for LIBs, N/C-900 delivers a highly reversible capacity of ca. 734 mA h g^-1 at a large current density of 1 A g^-1 until the 2000th cycle, revealing its ultralong cycle stability and excellent rate capability. The unique structure and preferential interaction between abundant pyridinic N active sites and Li atoms are responsible for the improved excellent lithium storage capacity and durability performances of the anode according to analysis of the results of computational modeling.

Simple synthesis of novel magnetic silver polymer nanocomposites with a good separation capacity and intrinsic antibacterial activities with high performance

Two new coordination polymers namely, [(AgCN)4LS]n (1) and [(AgCN)3LN]n (2), were successfully synthesized by the reaction of AgNO3 and cyanide as a co-anion with LS[1,1'-(hexane-1,4-diyl)bis(3-methylimidazoline-2-thione] and LN[1,1,3,3-tetrakis(3,5-dimethyl-1-pyrazole)propane] ligands in order to use them for the preparation of magnetic nanocomposites with MnFe2O4 nanoparticles by an efficient and facile method. They were then well characterized via numerous techniques, including elemental analysis, FT-IR spectroscopy, TGA, PXRD, SEM, TEM, EDX, VSM, BET, ICP, and single-crystal X-ray diffraction. The considered polymers and their magnetic nanocomposites with nearly the same antibacterial activity demonstrated a highly inhibitive effect on the growth of Gram-negative (Escherichia coli, Pseudomonas aeruginosa) and Gram-positive (Staphylococcus aureus, Bacillus subtilis) bacteria. By considering the simple separation and recyclable characters of the magnetic nanocomposites, these materials are suitable to be used in biological applications.

A Co-MOF-derived Co9S8@NS-C electrocatalyst for efficient hydrogen evolution reaction

The exploitation of efficient hydrogen evolution reaction (HER) electrocatalysts has become increasingly urgent and imperative; however, it is also challenging for high-performance sustainable clean energy applications. Herein, novel Co9S8 nanoparticles embedded in a porous N,S-dual doped carbon composite (abbr. Co9S8@NS-C-900) were fabricated by the pyrolysis of a single crystal Co-MOF assisted with thiourea. Due to the synergistic benefit of combining Co9S8 nanoparticles with N,S-dual doped carbon, the composite showed efficient HER electrocatalytic activities and long-term durability in an alkaline solution. It shows a small overpotential of -86.4 mV at a current density of 10.0 mA cm-2, a small Tafel slope of 81.1 mV dec-1, and a large exchange current density (J 0) of 0.40 mA cm-2, which are comparable to those of Pt/C. More importantly, due to the protection of Co9S8 nanoparticles by the N,S-dual doped carbon shell, the Co9S8@NS-C-900 catalyst displays excellent long-term durability. There is almost no decay in HER activities after 1000 potential cycles or it retains 99.5% of the initial current after 48 h.

Novel Systems and Membrane Technologies for Carbon Capture

Due to the global menace caused by carbon emissions from environmental, anthropogenic, and industrial processes, it has become expedient to consider the use of systems, with high trapping potentials for these carbon-based compounds. Several prior studies have considered the use of amines, activated carbon, and other solid adsorbents. Advances in carbon capture research have led to the use of ionic liquids, enzyme-based systems, microbial filters, membranes, and metal-organic frameworks in capturing CO2. Therefore, it is common knowledge that some of these systems have their lapses, which then informs the need to prioritize and optimize their synthetic routes for optimum efficiency. Some authors have also argued about the need to consider the use of hybrid systems, which offer several characteristics that in turn give synergistic effects/properties that are better compared to those of the individual components that make up the composites. For instance, some membranes are hydrophobic in nature, which makes them unsuitable for carbon capture operations; hence, it is necessary to consider modifying properties such as thermal stability, chemical stability, permeability, nature of the raw/starting material, thickness, durability, and surface area which can enhance the performance of these systems. In this review, previous and recent advances in carbon capture systems and sequestration technologies are discussed, while some recommendations and future prospects in innovative technologies are also highlighted.

A multifunctional benzothiadiazole-based fluorescence sensor for Al3+, Cr3+ and Fe3+

A benzothiadiazole-based Zn^II MOF (JXUST-3) has been synthesized, which is a good multifunctional chemosensor for the detection of Al³⁺, Cr³⁺ and Fe³⁺.

Involvement of various anions in tuning the structure of silver(i) coordination polymers based on a S-donor ligand: syntheses, crystal structure and uptake properties

Ag(i) coordination polymers based on a S-donor ligand containing of various anions were synthesized and characterized. Also, the absorption potential of the polymers was examined by the NH3 and H2S gases.

A review on production of metal organic frameworks (MOF) for CO2 adsorption

The environment sustenance and preservation of global climate are known as the crucial issues of the world today. Currently, the crisis of global warming due to CO₂ emission has turned into a paramount concern. To address such a concern, diverse CO₂ capture and sequestration techniques (CCS) have been introduced so far. In line with this, Metal Organic Frameworks (MOFs) have been considered as the newest and most promising material for CO₂ adsorption and separation. Due to their outstanding properties, this new class of porous materials a have exhibited a conspicuous potential for gas separation technologies especially for CO₂ storage and separation. Thus, the present review paper is aimed to discuss the adsorption properties of CO₂ on the MOFs based on the adsorption mechanisms and the design of the MOF structures. In addition, the main challenge associated with using this prominent porous material has been mentioned.

Combined experimental and computational studies on preferential CO2 adsorption over a zinc-based porous framework solid

Synthesis, characterization and study of selective CO₂ adsorption over other small gas molecules on a Zn-based porous framework compound.

An ionic liquid as a green solvent for high potency synthesis of 2D covalent organic frameworks

The PXRD and simulated profiles of PMDA–TAPA (a) and TFP–EB (b).

Metal-Organic Framework Materials for the Separation and Purification of Light Hydrocarbons

The separation and purification of light hydrocarbons (LHs) mixtures is one of the most significantly important but energy demanding processes in the petrochemical industry. As an alternative technology to energy intensive traditional separation methods, such as distillation, absorption, extraction, etc., adsorptive separation using selective solid adsorbents could potentially not only lower energy cost but also offer higher efficiency. The need to develop solid materials for the efficiently selective adsorption of LHs molecules, under mild conditions, is therefore of paramount importance and urgency. Metal-organic frameworks (MOFs), emerging as a relatively new class of porous organic-inorganic hybrid materials, have shown promise for addressing this challenging task due to their unparalleled features. Herein, recent advances of using MOFs as separating agents for the separation and purification of LHs, including the purification of CH₄ , and the separations of alkynes/alkenes, alkanes/alkenes, C₅ -C₆ -C₇ normal/isoalkanes, and C₈ alkylaromatics, are summarized. The relationships among the structural and compositional features of the newly synthesized MOF materials and their separation properties and mechanisms are highlighted. Finally, the existing challenges and possible research directions related to the further exploration of porous MOFs in this very active field are also discussed.

A dinuclear cobalt cluster as electrocatalyst for oxygen reduction reaction

Dinuclear metal clusters as metalloenzymes execute efficient catalytic activities in biological systems. Enlightened by this, a dinuclear {CoII 2} cluster was selected to survey its ORR (Oxygen Reduction Reaction) catalytic activities. The crystalline {CoII 2} possesses defined structure and potential catalytic active centers of {CoN4O2} sites, which was identified by X-ray single crystal diffraction, Raman and XPS. The appropriate supramolecular porosity combining abundant pyridinic-N and triazole-N sites of {CoII 2} catalyst synergistically benefit the ORR performance. As a result, this non-noble metal catalyst presents a nice ORR electrocatalytic activity and abides by a nearly 4-electron reduction pathway. Thus, this unpyrolyzed crystalline catalyst clearly provide precise active sites and the whole defined structural information, which can help researcher to design and fabricate efficient ORR catalysts to improve their activities. Considering the visible crystal structure, a single cobalt center-mediated catalytic mechanism was also proposed to elucidate the ORR process.

Direct Syntheses of Nanocages and Frameworks Based on Anderson-Type Polyoxometalates via One-Pot Reactions

A new one-step synthetic protocol of tris-functionalized Anderson polyoxomolybdates directly from heptamolybdate salts was presented in this Communication. Through this new method, we obtained the first example of Anderson-type polyoxomolybdates with vanadium as the heteroatom. Moreover, the crystals of the products exhibited interesting nanocage or framework extended structures, which were greatly affected by the trialkoxyl ligands as well as the counterions.

Facile Preparation of Porous Rod-like Cu x Co3-x O4/C Composites via Bimetal-Organic Framework Derivation as Superior Anodes for Lithium-Ion Batteries

To meet growing demand of energy, lithium-ion batteries (LIBs) are under enormous attention. The development of well-designed ternary transition metal oxides with high capacity and high stability is important and challengeable for using as electrode materials for LIBs. Herein, a new and highly reversible carbon-coated Cu-Co bimetal oxide composite material (Cu x Co3-x O4/C) with a one-dimensional (1D) porous rod-like structure was prepared through a bimetal-organic framework (BMOF) template strategy followed by a morphology-inherited annealing treatment. During the annealing process, carbon derived from organic frameworks in situ fully covered the synthesized bimetal oxide nanoparticles, and a large number of porous spaces were generated in the MOF-derived final samples, thus ensuring high electrical conductivity and fast ion diffusion. Benefiting from the synergetic effect of bimetals, the unique 1D porous structure, and conductive carbon network, the as-synthesized Cu x Co3-x O4/C delivers a high capacity retention up to 92.4% after 100 cycles, with a high reversible capacity still maintained at 900 mA h g-1, indicating an excellent cycling stability. Also, a good rate performance is demonstrated. These outstanding electrochemical properties show us a concept of synthesis of MOF-derived bimetal oxides combining both advantages of carbon incorporation and porous structure for progressive lithium-ion batteries.

Two ultramicroporous metal-organic frameworks assembled from binuclear secondary building units for highly selective CO2/N2 separation

Two novel metal-organic frameworks [Ni₂(μ₂-Cl)(BTBA)₂·DMF]·Cl·3DMF (JLU-MOF56, BTBA = 3,5-bis(triazol-1-yl)benzoic acid) and [Co₂(μ₂-Cl)(BTBA)₂·DMF]·Cl·3DMF (JLU-MOF57) have been successfully synthesized under solvothermal conditions. Crystallographic analysis indicates that the two compounds with different metal ions are isoreticular and both are constructed from binuclear [M₂(μ₂-Cl)(COO)₂N₄] (M = Co, Ni) and a 3-connected hetero-N,O donor ligand. The overall framework possesses a (3,6)-connected dag topology. Furthermore, both of them feature ultramicroporous channels of 3.5 Å× 3.4 Å, which are suitable for adsorbing smaller carbon dioxide (CO₂) gas molecules but not larger nitrogen (N₂) gas molecules. Therefore, JLU-MOF56 and JLU-MOF57 exhibit good performance for CO₂/N₂ separation, and are promising materials for gas adsorption and purification.

Two microporous CoII-MOFs with dual active sites for highly selective adsorption of CO2/CH4 and CO2/N2

Two microporous Co^II-MOFs exhibit highly CO₂/CH₄ and CO₂/N₂ selective adsorption owing to abundant dual active sites. GCMC theoretical simulations further verify the experimental results.

Unusual Moisture-Enhanced CO2 Capture within Microporous PCN-250 Frameworks

Developing metal-organic frameworks (MOFs) with moisture-resistant feature or moisture-enhanced adsorption is challenging for the practical CO₂ capture under humid conditions. In this work, under humid conditions, the CO₂ adsorption behaviors of two iron-based MOF materials, PCN-250(Fe₃) and PCN-250(Fe₂Co), were investigated. An interesting phenomenon is observed that the two materials demonstrate an unusual moisture-enhanced adsorption of CO₂. For PCN-250 frameworks, H₂O molecule induces a remarkable increase in the CO₂ uptake for the dynamic CO₂ capture from CO₂/N₂ (15:85) mixture. For PCN-250(Fe₃), its CO₂ adsorption capacity increases by 54.2% under the 50% RH humid condition, compared with that under dry conditions (from 1.18 to 1.82 mmol/g). Similarly, the CO₂ adsorption uptake of PCN-250(Fe₂Co) increases from 1.32 to 2.23 mmol/g, exhibiting a 68.9% increase. Even up to 90% RH, for PCN-250(Fe₃) and PCN-250(Fe₂Co), obvious increases of 43.7 and 70.2% in the CO₂ adsorption capacities are observed in comparison with those under dry conditions, respectively. Molecular simulations indicate that the hydroxo functional groups (μ₃-O) within the framework play a crucial role in improving CO₂ uptake in the presence of water vapor. Besides, partial substitution of Fe³⁺ by Co²⁺ ions in the PCN-250 framework gives rise to a great improvement in CO₂ adsorption capacity and selectivity. The excellent moisture stability (stable even after exposure to 90% RH humid air for 30 days), superior recyclability, as well as moisture-enhanced feature make PCN-250 as an excellent MOF adsorbent for CO₂ capture under humid conditions. This study provides a new paradigm that PCN-250 frameworks can not only be moisture resistant but can also subtly convert the common negative effect of moisture to a positive impact on improving CO₂ capture performance.

A pillar-layered porous CoII-MOF with dual active sites for selective gas adsorption

A pillar-layered microporous MOF has been constructed from linear trimeric {Co₃(COO)₆} clusters as SBUs. It exhibits preferential selective uptake of C₂H₂/C₂H₄, C₂H₂/C₂H₆ and CO₂/N₂ owing to its dual active sites.

Two Coordination Polymers Constructed from Pentanuclear Zinc Clusters with Triazolate and Benzenecarboxylate Ligands: Selective Gas Adsorption

Reactions of Zn(NO3)2·6H2O with 1,2,4-triazole (Htrz) and 1,3,5-benzenetricarboxylic acid (H3BTC) or 5-sulfoisophthalic acid (5-H3SIP) afforded two coordination polymers, {[Zn5(μ3-OH)2(trz)2(BTC)2(DMF)2]·x(solvent)}n (1) and {[Zn7(trz)8(5-SIP)2(H2O)4]·4(H2O)}n (2). Compound 1 has pentanuclear [Zn5(μ3-OH)2] clusters, which are linked by the triazolate ligands to give a 2D layer. The 2D layer is further bridged by BTC3− ligands to form a 3D framework. The 3D framework of 1 has 1D channels filled by solvent molecules. Desolvated 1 shows a moderate CO2 uptake and high CO2/CH4 and CO2/N2 adsorption selectivities due to its carboxylate oxygen decorated pore environment. Compound 2 contains a rare 3D zinc-triazolate framework constructed from a pentanuclear [Zn5(trz)8] cluster wherein the five zinc atoms are arranged linearly. The 3D zinc-triazolate substructure has 1D open channels filled by 5-SIP3− ligands, which interact with the zinc-triazolate framework through Zn–O bonds, leading to a non-porous 3D structure of 2. Introduction of BTC3− into the zinc-triazolate system gave the porous structure of 1. While a variation of BTC3−, 5-SIP3− was introduced into the zinc-triazolate system yielding a non-porous structure of 2, demonstrating that the secondary ligands play an important role in the formation of the final structures.

Design, structural diversity and properties of novel zwitterionic metal-organic frameworks

Seven new zwitterionic metal-organic frameworks (ZW MOFs) of compositions {[Cd(L1)(OH₂)]·2H₂O}_n (1), {[Mn(L1)(OH₂)₂]·H₂O}_n (2), {[Cu(HL1)₂(OH₂)₃]·9H₂O}_n (3), {[Mn₂(L2)₂(OH₂)₄]·3H₂O}_n (4), [Co(L2)(OH₂)₄]·H₂O (5), [Ni(L2)(OH₂)₃]_n (6), and {[Cd(L2)(OH₂)₃]·4H₂O}_n (7), where H₃L1Br = 3-carboxy-1-(3,5-dicarboxybenzyl)pyridinium bromide and H₃L2Br = 4-carboxy-1-(3,5-dicarboxybenzyl)pyridinium bromide, have been synthesized under hydrothermal conditions. We demonstrate that the diversity of these crystal structures suggests that the tridentate and flexible nature of ZW ligands L1 and L2 make them excellent candidates for the synthesis of new ZW MOFs. A multi-charged anionic nature is a common feature of L1 and L2, and therefore, allows the rational design of ZW MOFs without the presence of additional counterions for charge compensation. All materials were structurally characterized by single-crystal X-ray diffraction and further characterized by elemental analyses, infrared spectroscopy (IR), powder X-ray diffraction (PXRD), thermogravimetric analyses (TGA), differential scanning calorimetry (DSC) and adsorption measurements. Most interestingly, permanent porosity could be observed for 1, originated from 4 Å channel pores and confirmed by methanol adsorption experiments, which yielded an uptake of 7.43 wt% at 25 °C; and respectively, anhydrates of 1, 2, 4 and 6 can be rehydrated upon exposure to ambient air, as evidenced by TGA and PXRD measurements. In addition, we report an in-depth CSD analysis of selected structural parameters, coordination modes and topologies exhibited by MOFs based on ZW ligands L1 and L2 along with the regio-isomeric analogue L3, where H₃L3Br = N-(4-carboxybenzyl)-(3,5-dicarboxyl)pyridinium bromide.

Multishelled Nix Co3-x O4 Hollow Microspheres Derived from Bimetal-Organic Frameworks as Anode Materials for High-Performance Lithium-Ion Batteries

Metal-organic frameworks (MOFs) featuring versatile topological architectures are considered to be efficient self-sacrificial templates to achieve mesoporous nanostructured materials. A facile and cost-efficient strategy is developed to scalably fabricate binary metal oxides with complex hollow interior structures and tunable compositions. Bimetal-organic frameworks of Ni-Co-BTC solid microspheres with diverse Ni/Co ratios are readily prepared by solvothermal method to induce the Ni _x Co_3-x O₄ multishelled hollow microspheres through a morphology-inherited annealing treatment. The obtained mixed metal oxides are demonstrated to be composed of nanometer-sized subunits in the shells and large void spaces left between adjacent shells. When evaluated as anode materials for lithium-ion batteries, Ni _x Co_3-x O₄ -0.1 multishelled hollow microspheres deliver a high reversible capacity of 1109.8 mAh g^-1 after 100 cycles at a current density of 100 mA g^-1 with an excellent high-rate capability. Appropriate capacities of 832 and 673 mAh g^-1 could also be retained after 300 cycles at large currents of 1 and 2 A g^-1 , respectively. These prominent electrochemical properties raise a concept of synthesizing MOFs-derived mixed metal oxides with multishelled hollow structures for progressive lithium-ion batteries.

Structural Diversity of Three Pyrazoyl-Carboxyl Bifunctional Ligand-Based Metal-Organic Frameworks: Luminescence and Magnetic Properties

Three metal-organic frameworks (MOFs), [Cd(Hpzbpdc)(H₂ O)]⋅H₂ O (1), [Mn₂ (Hpzbpdc)₂ (dmf)₂ ] (2), and [H₂ N(CH₃ )₂ ]_0.5 [Eu(Hpzbpdc)_1.5 (HCOO)_0.5 (dmf)_0.5 ]⋅DMF⋅0.5 H₂ O (3) (H₃ pzbpdc=4'-(2 H-pyrazol-3-yl)biphenyl-3,5-dicarboxylic acid), have been solvothermally synthesized from one pyrazoyl-carboxyl bifunctional ligand and characterized by single-crystal structures. The H₃ pzbpdc ligand in 1-3 displays various coordination modes through the pyrazoyl and carboxyl groups. Both 1 and 3 contain dinuclear cluster building units and reveal a four-connected gismondine (gis) zeolite 3D framework and a 2D grid layer structure, respectively. Compound 1 shows blue luminescence, compound 3 reveals red luminescence that arises from efficient energy transfer from the organic ligand to the europium(III) ion, and compound 2 reveals an uncommon (3,8)-connected tfz-d; UO₃ net with a rare Mn₄ (COO)₆ cluster and shows antiferromagnetic interactions between the manganese(II) ions.

Solvent-induced diversity of luminescent metal–organic frameworks based on different secondary building units

New complexes with SBUs were successfully assembled based on 5′-carboxyl-(1,1′-3′,1′′-terphenyl)-4,4′′-dicarboxylic acid and the CO₂ storage properties were researched.

Two microporous Fe-based MOFs with multiple active sites for selective gas adsorption

Two Fe-based porous MOFs have been constructed from dimeric Fe-clusters and rod-shaped heterobimetallic Fe/Na-chains as SBUs, respectively. Notably, both of them exhibit highly selective CO₂ uptake over CH₄ and N₂ owing to abundant multiple active sites.

Two microporous metal–organic frameworks constructed from trinuclear cobalt(ii) and cadmium(ii) cluster subunits

This work presents two novel microporous metal–organic frameworks which are constructed from a tetracarboxylate ligand and trinuclear cobalt(ii) and cadmium(ii) cluster subunits.

Metal–organic frameworks constructed from crown ether-based 1,4-benzenedicarboxylic acid derivatives

A series of crown ether- and thiacrown ether-derivatized benzene dicarboxylic acid (H₂bdc) ligands has been synthesized and incorporated into the prototypical isoreticular metal–organic framework (IRMOF) and UiO-66 materials.