Metal–Organic Framework‐Activated Carbon Composite Materials for the Removal of Ammonia from Contaminated Airstreams

Loading and thermal behaviour of ZIF-8 metal-organic framework-inorganic glass composites

Here we describe the synthesis of a compositional series of metal-organic framework crystalline-inorganic glass composites (MOF-CIGCs) containing ZIF-8 and an inorganic phosphate glass, 20Na2O-10NaCl-70P2O5, to expand the library of host matrices for metal-organic frameworks. By careful selection of the inorganic glass component, a relatively high loading of ZIF-8 (70 wt%) was achieved, which is the active component of the composite. A Zn⋯O-P interfacial bond, previously identified in similar composites/hybrid blends, was suggested by analysis of the total scattering pair distribution function data. Additionally, CO2 and N2 sorption and variable-temperature PXRD experiments were performed to assess the composites' properties.

Polyester conversion by homogeneous catalysis for separating and recycling ammonia from biogas

Biogas is being promoted as a renewable and clean energy source. However, NH3 is a precursor of NOx and PM2.5 within the biogas, threatening ecological and human health. Therein, recycling waste NH3 from the biogas as a raw material of nitrogen fertilizer was tested by optimizing polyester as a sorbent material. After homogeneous catalysis, the converted polyester significantly increased the NH3 adsorption sites within polyester nanopores; correspondingly, the NH3 adsorption capacity increased from 0.56 mg·g-1 to 84.07 mg·g-1. Based on the structural characterization of polyesters, functional groups analysis before and after adsorption, and kinetic analysis during adsorption, chemical adsorption was identified as the dominant mechanism for NH3 adsorption. Moreover, selective adsorption and the regeneration experiments to optimize polyester indicated that NH3 could be efficiently separated from biogas with good regeneration performance. The results demonstrate the efficacy of recycling waste polyester and NH3 from the biogas.

Recent progress of MOF-functionalized nanocomposites: From structure to properties

Metal-organic frameworks (MOFs) are novel crystalline porous materials assembled from metal ions and organic ligands. The adaptability of their design and the fine-tuning of the pore structures make them stand out in porous materials. Furthermore, by integrating MOF guest functional materials with other hosts, the novel composites have synergistic benefits in numerous fields such as batteries, supercapacitors, catalysis, gas storage and separation, sensors, and drug delivery. This article starts by examining the structural relationship between the host and guest materials, providing a comprehensive overview of the research advancements in various types of MOF-functionalized composites reported to date. The review focuses specifically on four types of spatial structures, including MOFs being (1) embedded in nanopores, (2) immobilized on surface, (3) coated as shells and (4) assembled into hybrids. In addition, specific design ideas for these four MOF-based composites are presented. Some of them involve in situ synthesis method, solvothermal method, etc. The specific properties and applications of these materials are also mentioned. Finally, a brief summary of the advantages of these four types of MOF composites is given. Hopefully, this article will help researchers in the design of MOF composite structures.

MOF-based heterogeneous catalysis in continuous flow via incorporation onto polymer-based spherical activated carbon supports

We present an approach to harnessing the tuneable catalytic properties of complex nanomaterials for continuous flow heterogeneous catalysis by combining them with the scalable and industrially implementable properties of carbon pelleted supports. This approach, in turn, will enable these catalytic materials, which largely currently exist in forms unsuitable for this application (e.g. powders), to be fully integrated into large scale, chemical processes. A composite heterogeneous catalyst consisting of a metal-organic framework-based Lewis acid, MIL-100(Sc), immobilised onto polymer-based spherical activated carbon (PBSAC) support has been developed. The material was characterised by focused ion beam-scanning electron microscopy-energy dispersive X-ray analysis, powder X-ray diffraction, N2 adsorption, thermogravimetric analysis, atomic absorption spectroscopy, light scattering and crush testing with the catalytic activity studied in continuous flow. The mechanically robust spherical geometry makes the composite material ideal for application in packed-bed reactors. The catalyst was observed to operate without any loss in activity at steady state for 9 hours when utilised as a Lewis acid catalyst for the intramolecular cyclisation of (±)-citronellal as a model reaction. This work paves the way for further development into the exploitation of MOF-based continuous flow heterogeneous catalysis.

Coordination Polymers from Biphenyl-Dicarboxylate Linkers: Synthesis, Structural Diversity, Interpenetration, and Catalytic Properties

The present work explores two biphenyl-dicarboxylate linkers, 3,3'-dihydroxy-(1,1'-biphenyl)-4,4'-dicarboxylic (H₄L₁) and 4,4'-dihydroxy-(1,1'-biphenyl)-3,3'-dicarboxylic (H₄L₂) acids, in hydrothermal generation of nine new compounds formulated as [Co₂(μ₂-H₂L₁)₂(phen)₂(H₂O)₄] (1), [Mn₂(μ₄-H₂L₁)₂(phen)₂]_n·4nH₂O (2), [Zn(μ₂-H₂L₁)(2,2'-bipy)(H₂O)]_n (3), [Cd(μ₂-H₂L₁) (2,2'-bipy)(H₂O)]_n (4), [Mn₂(μ₂-H₂L₁)(μ₄-H₂L₁)(μ₂-4,4'-bipy)₂]_n·4nH₂O (5), [Zn(μ₂-H₂L₁)(μ₂-4,4'-bipy)]_n (6), [Zn(μ₂-H₂L₂)(phen)]_n (7), [Cd(μ₃-H₂L₂)(phen)]_n (8), and [Cu(μ₂-H₂L₂) (μ₂-4,4'-bipy)(H₂O)]_n (9). These coordination polymers (CPs) were generated by reacting a metal(II) chloride, a H₄L₁ or H₄L₂ linker, and a crystallization mediator such as 2,2'-bipy (2,2'-bipyridine), 4,4'-bipy (4,4'-bipyridine), or phen (1,10-phenanthroline). The structural types of 1-9 range from molecular dimers (1) to one-dimensional (3, 4, 7) and two-dimensional (8, 9) CPs as well as three-dimensional metal-organic frameworks (2, 5, 6). Their structural, topological, and interpenetration features were underlined, including an identification of unique two- and fivefold 3D + 3D interpenetrated nets in 5 and 6. Phase purity, thermal and luminescence behavior, as well as catalytic activity of the synthesized products were investigated. Particularly, a Zn(II)-based CP 3 acts as an effective and recyclable heterogeneous catalyst for Henry reaction between a model substrate (4-nitrobenzaldehyde) and nitroethane to give β-nitro alcohol products. For this reaction, various parameters were optimized, followed by the investigation of the substrate scope. By reporting nine new compounds and their structural traits and functional properties, the present work further outspreads a family of CPs constructed from the biphenyl-dicarboxylate H₄L₁ and H₄L₂ linkers.

Introduction of a Zn-based metal-organic framework @ biomass porous activated carbon as a high-sensitive coating for a stainless steel SPME fiber: application to the simultaneous analysis of nonsteroidal anti-inflammatory drugs

The present study introduces a high-efficiency nanocomposite material featuring a zinc-based metal-organic framework and a novel porous activated carbon derived from bread waste. The prepared nanocomposite, namely Zn-MOF-5@BHPAC, has been synthesized by a low-temperature hydrothermal process and coated onto the surface of a stainless steel wire with epoxy glue. The fabricated fiber has been employed as an SPME fiber applied in the extraction and pre-concentration of some nonsteroidal anti-inflammatory drugs (NSAIDs) before their high-performance liquid chromatography-ultraviolet (HPLC-UV) studies. The characterization studies were performed utilizing field emission scanning electron microscopy, elemental mapping, energy-dispersive X-ray spectroscopy, elemental analyzer, Fourier-transform infrared spectroscopy, and Brunauer-Emmett-Teller surface area analysis. Under the optimal conditions, the method demonstrated low detection limits (LODs, 0.06-0.15 µg L-1), wide linear ranges (LRs, 0.20-380 µg L-1) with good linearity (R2 > 0.991), good precisions (RSDs < 6.95%), and acceptable relative recoveries (RR > 85%). Using the green and affordable biomass of bread as a novel carbon-rich source is an innovative idea provided in this study. In addition, the hybridization of the obtained carbon-based material with the MOF compound to create a new high-capacity sorbent is another strength of the proposed method. Long service lifetime, economic efficiency, environmental friendliness, and high extraction capability were some of the other advantages of the suggested procedure. Therefore, the method can utilize successfully for the simultaneous determination of NSAIDs (as model analytes) in different matrixes.

Ab Initio Study of Hydrostable Metal-Organic Frameworks for Postsynthetic Modification and Tuning toward Practical Applications

Metal-organic frameworks (MOFs), a subclass of nanoporous coordination polymers, have emerged as one of the most promising next-generation materials. The postsynthetic modification method, a strategy that provides tunability and control of these materials, plays an important role in enhancing its properties and functionalities. However, knowing adjustments which leads to a desired structure-function a priori remains a challenge. In this comprehensive study, the intermolecular interactions between 21 industrially important gases and a hydrostable STAM-17-OEt MOF were investigated using density functional theory. Substitutions on its 5-ethoxy isophthalate linker included two classes of chemical groups, electron-donating (-NH₂, -OH, and -CH₃) and electron-withdrawing (-CN, -COOH, and -F), as well as the effect of mono-, di-, and tri-substitutions. This resulted in 651 unique MOF-gas complexes. The adsorption energies at the ground state and room temperature, bond lengths, adsorption geometry, natural bond orbital analysis of the electric structure, HOMO-LUMO interactions, and the predicted zwitterionic properties are presented and discussed. This study provides a viable strategy for the functionalization, which leads to the strongest affinity for each gas, an insight into the role of different chemical groups in adsorbing various gas molecules, and identifies synthetic routes for moderating the gas adsorption capacity and reducing water adsorption. Recommendations for various applications are discussed. A custom Python script to assess and visualize the hypothetical separation of two equal gas mixtures of interest is provided. The methodology presented here provides new opportunities to expand the chemical space and physical properties of STAM-17-OEt and advances the development of other hydrostable MOFs.

In-situ detoxification of schedule-I chemical warfare agents utilizing Zr(OH)4@W-ACF functional material for the development of next generation NBC protective gears

Chemical warfare agents (CWAs) have become a pivotal concern for the global community and spurred a wide spectrum of research for the development of new generation protective materials. Herein, a highly effective self-detoxifying filter consisting of in-situ immobilized Zirconium hydroxide [Zr(OH)4] over woven activated carbon fabric [Zr(OH)4@W-ACF] is presented for the removal of CWAs. It was prepared to harness the synergistic effect of high surface area of W-ACF, leads to high dispersion of CWAs and high phosphilicity and reactivity of [Zr(OH)4]. The synthesized materials were characterized by ATR-FTIR, EDX, SEM, TEM, XPS, TGA, and BET surface area analyzer. The kinetics of  in-situ degradation of CWAs over Zr(OH)4@W-ACF were studied and found to be following the first-order reaction kinetics. The rate constant was found to be 0.244 min-1 and 2.31 × 10-2 min-1 for sarin and soman, respectively over Zr(OH)4@W-ACF. The potential practical applicability of this work was established by fabricating Zr(OH)4@W-ACF as reactive adsorbent layer for protective suit, and found to be meeting the specified criteria in terms of air permeability, tearing strength and nerve agent permeation as per TOP-08-2-501A:2013 and IS-17380:2020. The degradation products of CWAs were analyzed with NMR and GC-MS. The combined properties of dual functional textile with reactive material are expected to open up new exciting avenues in the field of CWAs protective clothing and thus find diverse application in defence and environmental sector.

Enhanced Adsorption and Mass Transfer of Hierarchically Porous Zr-MOF Nanoarchitectures toward Toxic Chemical Removal

Zirconium-based metal-organic frameworks (Zr-MOFs) have shown tremendous prospects as highly efficient adsorbents against toxic chemicals under ambient conditions. Here, we report for the first time the enhanced toxic chemical adsorption and mass transfer properties of hierarchically porous Zr-MOF nanoarchitectures. A general and scalable sol-gel-based strategy combined with facile ambient pressure drying (APD) was utilized to construct MOF-808, MOF-808-NH₂, and UiO-66-NH₂ xerogel monoliths, denoted as G808, G808-NH₂, and G66-NH₂, respectively. The resulting Zr-MOF xerogels demonstrated 3D porous networks assembled by nanocrystal aggregates, with substantially higher mesoporosities than the precipitate analogues. Microbreakthrough tests on powders and tube breakthrough experiments on engineered granules were conducted at different relative humidities to comprehensively evaluate the NO₂ adsorption capabilities. The Zr-MOF xerogels showed considerably better NO₂ removal abilities than the precipitates, whether intrinsically or under simulated respirator canister/protection filter environment conditions. Multiple physicochemical characterizations were conducted to illuminate the NO₂ filtration mechanisms. Analysis on adsorption kinetics and mass transfer patterns in Zr-MOF xerogels was further performed to visualize the underlying structure-activity relationship using the gravimetric uptake and zero length column methods with cyclohexane and acetaldehyde as probes. The results revealed that the synergy of hierarchical porosities and nanosized crystals could effectively expedite the intracrystalline diffusion for the G66-NH₂ xerogel as well as alleviate the surface resistance for the G808-NH₂ xerogel, which led to accelerated overall adsorption uptake and thus enhanced performance toward toxic chemical removal.

Modern Carbon-Based Materials for Adsorptive Removal of Organic and Inorganic Pollutants from Water and Wastewater

Currently, a serious threat for living organisms and human life in particular, is water contamination with persistent organic and inorganic pollutants. To date, several techniques have been adopted to remove/treat organics and toxic contaminants. Adsorption is one of the most effective and economical methods for this purpose. Generally, porous materials are considered as appropriate adsorbents for water purification. Conventional adsorbents such as activated carbons have a limited possibility of surface modification (texture and functionality), and their adsorption capacity is difficult to control. Therefore, despite the significant progress achieved in the development of the systems for water remediation, there is still a need for novel adsorptive materials with tunable functional characteristics. This review addresses the new trends in the development of new adsorbent materials. Herein, modern carbon-based materials, such as graphene, oxidized carbon, carbon nanotubes, biomass-derived carbonaceous matrices-biochars as well as their composites with metal-organic frameworks (MOFs) and MOF-derived highly-ordered carbons are considered as advanced adsorbents for removal of hazardous organics from drinking water, process water, and leachate. The review is focused on the preparation and modification of these next-generation carbon-based adsorbents and analysis of their adsorption performance including possible adsorption mechanisms. Simultaneously, some weak points of modern carbon-based adsorbents are analyzed as well as the routes to conquer them. For instance, for removal of large quantities of pollutants, the combination of adsorption and other methods, like sedimentation may be recommended. A number of efficient strategies for further enhancing the adsorption performance of the carbon-based adsorbents, in particular, integrating approaches and further rational functionalization, including composing these adsorbents (of two or even three types) can be recommended. The cost reduction and efficient regeneration must also be in the focus of future research endeavors. The targeted optimization of the discussed carbon-based adsorbents associated with detailed studies of the adsorption process, especially, for multicomponent adsorbate solution, will pave a bright avenue for efficient water remediation.

Layer-by-Layer Integration of Zirconium Metal-Organic Frameworks onto Activated Carbon Spheres and Fabrics with Model Nerve Agent Detoxification Properties

We report the controlled synthesis of thin films of prototypical zirconium metal-organic frameworks [Zr₆O₄(OH)₄(benzene-1,4-dicarboxylate-2-X)₆] (X = H, UiO-66 and X = NH₂, UiO-66-NH₂) over the external surface of shaped carbonized substrates (spheres and textile fabrics) using a layer-by-layer method. The resulting composite materials contain metal-organic framework (MOF) crystals homogeneously distributed over the external surface of the porous shaped bodies, which are able to capture an organophosphate nerve agent simulant (diisopropylfluorophosphate, DIFP) in competition with moisture (very fast) and hydrolyze the P-F bond (slow). This behavior confers the composite material self-cleaning properties, which are useful for blocking secondary emission problems of classical protective equipment based on activated carbon.

The reactivity of an inorganic glass melt with ZIF-8

The thermal behaviour of ZIF-8, Zn(meIm)2 in the presence of a sodium fluoroaluminophosphate glass melt was probed through differential scanning calorimetry and thermogravimetric analysis. The structural integrity of ZIF-8 was then determined by a combination of powder X-ray diffraction, Fourier transform infra-red and 1H nuclear magnetic resonance spectroscopy.

Emerging Porous Materials and Their Composites for NH3 Gas Removal

NH3, essential for producing artificial fertilizers and several military and commercial products, is being produced at a large scale to satisfy increasing demands. The inevitable leakage of NH3 during its utilization, even in trace concentrations, poses significant environmental and health risks because of its highly toxic and reactive nature. Although numerous techniques have been developed for the removal of atmospheric NH3, conventional NH3 abatement systems possess the disadvantages of high maintenance cost, low selectivity, and emission of secondary wastes. In this context, highly tunable porous materials such as metal-organic frameworks, covalent organic frameworks, hydrogen organic frameworks, porous organic polymers, and their composite materials have emerged as next-generation NH3 adsorbents. Herein, recent progress in the development of porous NH3 adsorbents is summarized; furthermore, factors affecting NH3 capture are analyzed to provide a reasonable strategy for the design and synthesis of promising materials for NH3 abatement.

Metal-organic framework and inorganic glass composites

Metal-organic framework (MOF) glasses have become a subject of interest as a distinct category of melt quenched glass, and have potential applications in areas such as ion transport and sensing. In this paper we show how MOF glasses can be combined with inorganic glasses in order to fabricate a new family of materials composed of both MOF and inorganic glass domains. We use an array of experimental techniques to propose the bonding between inorganic and MOF domains, and show that the composites produced are more mechanically pliant than the inorganic glass itself.

Recyclable Superhydrophobic, Antimoisture-Activated Carbon Pellets for Air and Water Purification

Activated carbon (AC) is a low-cost, highly porous material with large internal surface areas. It is highly efficient in absorbing moisture and a variety of chemical pollutants. Therefore, it has been widely used in air and water purification. However, the strong affinity to moisture often dominates, thus limiting AC's adsorption capacity of other pollutants in a humid environment and reducing its overall lifetime. In the study, superhydrophobic and anti-moisture AC (SA-AC) pellets are fabricated through one-step modification of commercially available AC with a solution consisting of superhydrophobic silica nanoparticles. The SA-AC pellets exhibit excellent water repellency with a static water contact angle reaching 160.3°. More importantly, they are moisture-resistant and air-permeable. Therefore, they preferably adsorb organic gases at humid conditions. The absorbed organic vapor can be released when they are transferred back to the dry atmosphere, for example, releasing approximately 35% of absorbed ethanol. The recoverability significantly reduces energy requirement compared to calcination or conventional extraction. Great adsorption capacity of organic dyes such as methylene blue, removal of oil-in-water microemulsions, and recyclability of SA-AC pellets are demonstrated. The morphology of the microporous structures of the SA-AC pellets is characterized against processing conditions, surface functional groups, and hierarchical structures tailored by the deposition of low-surface energy silica nanoparticles. The resulting micro-/sub-micropores on the pellet surface promote droplet condensation, thus displaying greater damp-proof performance than those treated by traditional modification. The study here presents a promising alternative for the efficient purification on large-scale air/water treatment.

MOFs-carbon hybrid nanocomposites in environmental protection applications

The demand for green engineering environmentally friendly nanomaterials had made carbon nanotube a suitable material to keep metal-organic frameworks (MOFs) in the application of wastewater treatment and air pollution monitoring systems. This review summarizes many of the recent research accomplishments in the synthesis of MOFs and MOFs-carbon hybrid nanocomposites for various applications such as wastewater treatment and removal of hazardous gases (CO, SO₂, H₂S and NH₃) with emphasis on MOF/CNTs composites. This review focuses on the efficient removal of pollutants from the environment using adsorption techniques. Another important application of MOFs composite discussed in this review is sensor materials for environmental pollution.

H-Bonded and metal(ii)-organic architectures assembled from an unexplored aromatic tricarboxylic acid: structural variety and functional properties

This study reports the application of an aromatic tricarboxylic acid, 2,5-di(4-carboxylphenyl)nicotinic acid (H3dcna) as a versatile and unexplored organic building block for assembling a new series of metal(ii) (M = Co, Ni, Zn, Fe, and Mn) complexes and coordination polymers, namely [M(Hdcna)(phen)2(H2O)]·H2O (M = Co (1), Ni (2)), [Zn(μ-Hdcna)(phen)]n (3), [Co(μ-Hdcna)(bipy)(H2O)2]n·nH2O (4), [Zn2(μ-Hdcna)2(bipy)2(H2O)4]·6H2O (5), [Zn(μ3-Hdcna)(H2biim)]n (6), [Ni2(Hdcna)2(μ-bpb)(bpb)2(H2O)4] (7), [Fe(μ4-Hdcna)(μ-H2O)]n·nH2O (8), and [Mn3(μ5-dcna)2(bipy)2(H2O)2]n·2nH2O (9). Such a diversity of products was hydrothermally prepared from the corresponding metal(ii) salts, H3dcna as a principal multifunctional ligand, and N-donor mediators of crystallization (1,10-phenanthroline, phen; 2,2'-bipyridine, bipy; 2,2'-biimidazole, H2biim; or 1,4-bis(pyrid-4-yl)benzene, bpb). The obtained products 1-9 were fully characterized by standard methods (elemental analysis, FTIR, TGA, PXRD) and the structures were established by single-crystal X-ray diffraction. These vary from the discrete monomers (1, 2) and dimers (5, 7) to the 1D (3, 4, 6) and 2D (8, 9) coordination polymers (CPs). Structural and topological characteristics of hydrogen-bonded or metal-organic architectures in 1-9 were highlighted, revealing that their structural multiplicity depends on the type of metal(ii) source and crystallization mediator. Thermal stability as well as luminescent, magnetic, or catalytic properties were explored for selected compounds. In particular, the zinc(ii) derivatives 3, 5, and 6 were applied as efficient heterogeneous catalysts for the cyanosilylation of aldehydes with trimethylsilyl cyanide at room temperature. The catalytic reactions were optimized by tuning the different reaction parameters (solvent composition, time, catalyst loading) and the substrate scope was also explored. Compound 5 revealed superior catalytic activity leading to up to 75% product yields, while maintaining its original performance upon recycling for at least four reaction cycles. Finally, the obtained herein products represent the unique examples of coordination compounds derived from H3dcna, thus opening up the use of this multifunctional tricarboxylic acid for generating complexes and coordination polymers with interesting structures and functional properties.

A multi-stimuli-responsive metallohydrogel applied in chiral recognition, adsorption of poisonous anions, and construction of various chiral metal-organic frameworks

The design of stimuli-responsive hydrogels is attractive but challenging. A multi-stimuli-responsive chiral metallohydrogel was constructed using a rational approach to design a functional metallohydrogel using chiral organic gelators. The as-synthesized metallohydrogel reported here performed remarkably as a visual sensor for discriminating between (R)-phenylglycinol and (S)-phenylglycinol. Furthermore, the metallohydrogel showed a significant capacity for adsorption and enrichment of Cr(vi) in aqueous solution. Besides this, by utilizing anion-induced transformation, the metallohydrogel could be controllably directed to synthesize different types of chiral metal-organic frameworks.