Simple and compelling biomimetic metal-organic framework catalyst for the degradation of nerve agent simulants

Significant enhancement in hydrolytic degradation of sulfur mustard promoted by silver nanoparticles in the Ag NPs@HKUST-1 composites

The Ag NPs@HKUST-1 composites have been successfully prepared with different loading amounts of silver nanoparticles in HKUST-1 featuring a three-dimensional system of channels constructed by benzene-1,3,5-tricarboxylate and dimeric cupric units by a simple one-pot hydrothermal method, and characterized by various microscopy and spectroscopy analysis techniques. The average particle size of Ag NPs increased with the increase of the loading amount of Ag NPs. The experimental results showed that the degradation of sulfur mustard (HD) under ambient conditions followed pseudo-first order reaction kinetics. Additionally, the optimized Ag NPs@HKUST-1 (wherein Ag is l6.67 wt%) exhibited the highest degradation efficacy with an equilibrium rate constant and half-life for HD of 0.0450 min^-1 and 15.34 min, respectively. These values were significantly higher than those for pure HKUST-1 with an equilibrium rate constant and half-life for HD of 0.0168 min^-1 and 41.29 min, under the same experimental conditions. Gas chromatography-mass spectrometry (GC-MS) analysis on the product of 2-chloroethylethyl sulfide (2-CEES) degraded by Ag NPs@HKUST-1 showed that 2-hydroxyethyl ethyl sulfide (2-HEES) is the sole product, indicating that the remarkable enhancement of the degradation of HD must be due to the Ag NPs, which can promote hydrolysis of the chemical war agent in the composite.

Stable Metal-Organic Frameworks: Design, Synthesis, and Applications

Metal-organic frameworks (MOFs) are an emerging class of porous materials with potential applications in gas storage, separations, catalysis, and chemical sensing. Despite numerous advantages, applications of many MOFs are ultimately limited by their stability under harsh conditions. Herein, the recent advances in the field of stable MOFs, covering the fundamental mechanisms of MOF stability, design, and synthesis of stable MOF architectures, and their latest applications are reviewed. First, key factors that affect MOF stability under certain chemical environments are introduced to guide the design of robust structures. This is followed by a short review of synthetic strategies of stable MOFs including modulated synthesis and postsynthetic modifications. Based on the fundamentals of MOF stability, stable MOFs are classified into two categories: high-valency metal-carboxylate frameworks and low-valency metal-azolate frameworks. Along this line, some representative stable MOFs are introduced, their structures are described, and their properties are briefly discussed. The expanded applications of stable MOFs in Lewis/Brønsted acid catalysis, redox catalysis, photocatalysis, electrocatalysis, gas storage, and sensing are highlighted. Overall, this review is expected to guide the design of stable MOFs by providing insights into existing structures, which could lead to the discovery and development of more advanced functional materials.

Toxic Organophosphate Hydrolysis Using Nanofiber-Templated UiO-66-NH2 Metal-Organic Framework Polycrystalline Cylinders

Metal organic frameworks (MOFs), the UiO series in particular, have attracted much attention because of the high surface area and ability to capture and decontaminate chemical warfare agents. Much work has been done on incorporating these MOFs into or onto textile materials while retaining the desirable properties of the MOF. Many different techniques have been explored to achieve this. Atomic layer deposition (ALD) of TiO₂ followed by solvothermal synthesis of MOF has become one of the most adaptable techniques for growing MOFs on the surface of many different polymer fabric materials. However, little work has been done with using this technique on polymer composite materials. In this work, UiO-66-NH₂ was grown onto the surface of poly(methyl methacrylate) (PMMA)/Ti(OH)₄ and poly(vinylidene fluoride) (PVDF)/Ti(OH)₄ composite fibers by first modifying the surface with ALD of TiO₂ (@TiO₂) followed by solvothermal synthesis of MOF (@MOF). The catalytic activity of these materials was then evaluated using the simulant paraoxon-methyl (DMNP). These new MOF-functionalized composite fabrics were compared to polyamide-6 (PA-6)@TiO₂@MOF- and polypropylene (PP)@TiO₂@MOF-functionalized fabrics. PMMA/Ti(OH)₄@TiO₂@MOF fibers resulted in unique hollowed fibers with high surface area of 264 m²/g and fast catalytic activity. The catalytic activity of these samples was found to be related to the active MOF mass fraction on the MOF-functionalized composite fabric, with the hollowed PMMA/Ti(OH)₄@TiO₂@MOF having the highest weight percent of active MOF and a DMNP t_1/2 of 26 min followed by PA-6@TiO₂@MOF with 45 min, PVDF/Ti(OH)₄@TiO₂@MOF with 61 min, and PP@TiO₂@MOF with 83 min.

Water-Stable Nanoscale Zirconium-Based Metal-Organic Frameworks for the Effective Removal of Glyphosate from Aqueous Media

Two water-stable zirconium-based metal-organic frameworks (MOFs) (NU-1000 and UiO-67) have been synthesized in various size scales (100-2000 nm) for the adsorptive removal of glyphosate from the aqueous media. Both NU-1000 and UiO-67 possess a three-dimensional structure; NU-1000 consists of triangular micropores and wide mesoporous channels (31 Å), whereas UiO-67 has cage-like pores [octahedral (16 Å) and tetrahedral (14 Å) cages]. NU-1000 comprises Zr6(μ3-O)4(μ3-OH)4(H2O)4(OH)4, and UiO-67 contains Zr6O4(OH)4 as secondary building units. These units act as Lewis acid nodes and can interact with the Lewis base phosphate group of the glyphosate. The time taken for reaching equilibrium is found to be reduced considerably as the size of the MOF decreases. The smaller the particle size, the lesser is the diffusion barrier for the analyte, which enhances the interaction between Lewis acidic metal nodes and the Lewis basic center of the glyphosate molecule. NU-1000 was found to be better compared to UiO-67, both in terms of efficiency and reusability. This might be due to the larger pore diameters of the NU-1000. Theoretical calculations revealed that the interaction energy of glyphosate with the nodes of NU-1000 is higher (-37.63 KJ mol-1) compared to UiO-67 (-17.37 KJ mol-1), which might be the possible reason for the higher efficiency of NU-1000.

Determination of carbamazepine in urine and water samples using amino-functionalized metal-organic framework as sorbent

A stable and porous amino-functionalized zirconium-based metal organic framework (Zr-MOF-NH₂) containing missing linker defects was prepared and fully characterized by FTIR, scanning electron microscopy, powder X-ray diffraction, and BET surface area measurement. The Zr-MOF-NH₂ was then applied as an adsorbent in pipette-tip solid phase extraction (PT-SPE) of carbamazepine. Important parameters affecting extraction efficiency such as pH, sample volume, type and volume of eluent, amount of adsorbent, and number of aspirating/dispensing cycles for sample solution and eluent solvent were investigated and optimized. The best extraction efficiency was obtained when pH of 100 µL of sample solution was adjusted to 7.5 and 5 mg of the sorbent was used. Eluent solvent was 10 µL methanol. Linear dynamic range was found to be between 0.1 and 50 µg L⁻¹ and limit of detection for 10 measurement of blank solution was 0.05 µg L⁻¹. This extraction method was coupled to HPLC and was successfully employed for the determination of carbamazepine in urine and water samples. The strategy combined the advantages of fast and easy operation of PT-SPE with robustness and large adsorption capacity of Zr-MOF-NH₂.

Fast and Sustained Degradation of Chemical Warfare Agent Simulants Using Flexible Self-Supported Metal-Organic Framework Filters

Self-detoxification filters against lethal chemical warfare agents (CWAs) are highly desirable for the protection of human beings and the environment. In this report, flexible self-supported filters of a series of Zr(IV)-based metal-organic frameworks (MOFs) including UiO-66, UiO-67, and UiO-66-NH₂ were successfully prepared and exhibited fast and sustained degradation of CWA simulants. A half-life as short as 2.4 min was obtained for the catalytic hydrolysis of dimethyl 4-nitrophenyl phosphate, and the percent conversion remained above 90% over a long-term exposure of 120 min, well exceeding those of the previously reported composite MOF filters and the corresponding MOF powders. The outstanding detoxification performance of the self-supported fibrous filter comes from the exceptionally high surface area, excellent pore accessibility, and hierarchical structure from the nano- to macroscale. This work demonstrates, for the first time, MOF-only filters as efficient self-detoxification media, which will offer new opportunities for the design and fabrication of functional materials for toxic chemical protection.

Anchored Aluminum Catalyzed Meerwein-Ponndorf-Verley Reduction at the Metal Nodes of Robust MOFs

Catalytic Meerwein-Ponndorf-Verley reductions of ketones and aldehydes in the presence of isopropyl alcohol were performed at aluminum alkoxide sites that were postsynthetically introduced into robust metal-organic frameworks (MOFs). The aluminum was anchored at the bridging hydroxyl sites inherent in some MOFs. MOFs in the UiO-66/67 family as well as DUT-5 were successfully adapted to this strategy. Incorporation of catalytically active aluminum species greatly enhanced the reactivity of the native MOF at 80 °C in the case of both UiO-66, and was almost solely responsible for catalytic activity in the case of metalated UiO-66 and DUT-5. The site isolation of the catalyst prevented aggregation and complete deactivation of the molecular aluminum catalyst, allowing it to be recovered and recycled in the case of UiO-67. This catalyst also proved to be moderately tolerant to wet isopropyl alcohol.

Dual Role of Water in Heterogeneous Catalytic Hydrolysis of Sarin by Zirconium-Based Metal-Organic Frameworks

Recent experimental studies on Zr^IV-based metal-organic frameworks (MOFs) have shown the extraordinary effectiveness of these porous materials for the detoxification of phosphorus-based chemical warfare agents (CWAs). However, pressing challenges remain with respect to characterizing these catalytic processes both at the molecular and crystalline levels. We here use theory to compare the reactivity of different zirconium-based MOFs for the catalytic hydrolysis of the CWA sarin, using both periodic and cluster modeling. We consider both hydrated and dehydrated secondary building units, as well as linker functionalized MOFs, to more fully understand and rationalize available experimental findings as well as to enable concrete predictions for achieving higher activities for the decomposition of CWAs.

Stable Metal-Organic Frameworks with Group 4 Metals: Current Status and Trends

Group 4 metal-based metal-organic frameworks (M^IV-MOFs), including Ti-, Zr-, and Hf-based MOFs, are one of the most attractive classes of MOF materials owing to their superior chemical stability and structural tunability. Despite being a relatively new field, M^IV-MOFs have attracted significant research attention in the past few years, leading to exciting advances in syntheses and applications. In this outlook, we start with a brief overview of the history and current status of M^IV-MOFs, emphasizing the challenges encountered in their syntheses. The unique properties of M^IV-MOFs are discussed, including their high chemical stability and strong tolerance toward defects. Particular emphasis is placed on defect engineering in Zr-MOFs which offers additional routes to tailor their functions. Photocatalysis of M^IV-MOF is introduced as a representative example of their emerging applications. Finally, we conclude with the perspective of new opportunities in synthesis and defect engineering.

A Chromium Hydroxide/MIL-101(Cr) MOF Composite Catalyst and Its Use for the Selective Isomerization of Glucose to Fructose

A metal-organic framework (MOF)-based catalyst, chromium hydroxide/MIL-101(Cr), was prepared by a one-pot synthesis method. The combination of chromium hydroxide particles on and within Lewis acidic MIL-101 accomplishes highly selective conversion of glucose to fructose in the presence of ethanol, matching the performance of optimized Sn-containing Lewis acidic zeolites. Differently from zeolites, NMR spectroscopy studies with isotopically labeled molecules demonstrate that isomerization of glucose to fructose on this catalyst, proceeds predominantly via a proton transfer mechanism.

Metal-Organic Framework Modified Glass Substrate for Analysis of Highly Volatile Chemical Warfare Agents by Paper Spray Mass Spectrometry

Paper spray mass spectrometry has been shown to successfully analyze chemical warfare agent (CWA) simulants. However, due to the volatility differences between the simulants and real G-series (i.e., sarin, soman) CWAs, analysis from an untreated paper substrate proved difficult. To extend the analytical lifetime of these G-agents, metal-organic frameworks (MOFs) were successfully integrated onto the paper spray substrates to increase adsorption and desorption. In this study, several MOFs and nanoparticles were tested to extend the analytical lifetimes of sarin, soman, and cyclosarin on paper spray substrates. It was found that the addition of either UiO-66 or HKUST-1 to the paper substrate increased the analytical lifetime of the G-agents from less than 5 min detectability to at least 50 min.

Impact of ambient gases on the mechanism of [Cs8Nb6O19]-promoted nerve-agent decomposition

Polyoxoniobate catalyst, nerve agent decomposition, reaction mechanism, impact of ambient gases on the stability and reactivity of the polyoxoniobate.

The impact of ambient gas molecules (X), NO₂, CO₂ and SO₂ on the structure, stability and decontamination activity of Cs₈Nb₆O₁₉ polyoxometalate was studied computationally and experimentally. It was found that Cs₈Nb₆O₁₉ absorbs these molecules more strongly than it adsorbs water and Sarin (GB) and that these interactions hinder nerve agent decontamination. The impacts of diamagnetic CO₂ and SO₂ molecules on polyoxoniobate Cs₈Nb₆O₁₉ were fundamentally different from that of NO₂ radical. At ambient temperatures, weak coordination of the first NO₂ radical to Cs₈Nb₆O₁₉ conferred partial radical character on the polyoxoniobate and promoted stronger coordination of the second NO₂ adsorbent to form a stable diamagnetic Cs₈Nb₆O₁₉/(NO₂)₂ species. Moreover, at low temperatures, NO₂ radicals formed stable dinitrogen tetraoxide (N₂O₄) that weakly interacted with Cs₈Nb₆O₁₉. It was found that both in the absence and presence of ambient gas molecules, GB decontamination by the Cs₈Nb₆O₁₉ species proceeds via general base hydrolysis involving: (a) the adsorption of water and the nerve agent on Cs₈Nb₆O₁₉/(X), (b) concerted hydrolysis of a water molecule on a basic oxygen atom of the polyoxoniobate and nucleophilic addition of the nascent OH group to the phosphorus center of Sarin, and (c) rapid reorganization of the formed pentacoordinated-phosphorus intermediate, followed by dissociation of either HF or isopropanol and formation of POM-bound isopropyl methyl phosphonic acid (i-MPA) or methyl phosphonofluoridic acid (MPFA), respectively. The presence of the ambient gas molecules increases the energy of the intermediate stationary points relative to the asymptote of the reactants and slightly increases the hydrolysis barrier. These changes closely correlate with the Cs₈Nb₆O₁₉–X complexation energy. The most energetically stable intermediates of the GB hydrolysis and decontamination reaction were found to be Cs₈Nb₆O₁₉/X-MPFA-(i-POH) and Cs₈Nb₆O₁₉/X-(i-MPA)-HF both in the absence and presence of ambient gas molecules. The high stability of these intermediates is due to, in part, the strong hydrogen bonding between the adsorbates and the protonated [Cs₈Nb₆O₁₉/X/H]⁺-core. Desorption of HF or/and (i-POH) and regeneration of the catalyst required deprotonation of the [Cs₈Nb₆O₁₉/X/H]⁺-core and protonation of the phosphonic acids i-MPA and MPFA. This catalyst regeneration is shown to be a highly endothermic process, which is the rate-limiting step of the GB hydrolysis and decontamination reaction both in the absence and presence of ambient gas molecules.

Decoration of Cotton Fibers with a Water-Stable Metal-Organic Framework (UiO-66) for the Decomposition and Enhanced Adsorption of Micropollutants in Water

We report on the successful functionalization of cotton fabrics with a water-stable metal-organic framework (MOF), UiO-66, under mild solvothermal conditions (80 °C) and its ability to adsorb and degrade water micropollutants. The functionalized cotton samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). UiO-66 crystals grew in a uniform and conformal manner over the surface of the cotton fibers. The cotton fabrics functionalized with UiO-66 frameworks exhibited an enhanced uptake capacity for methylchlorophenoxypropionic acid (MCPP), a commonly used herbicide. The functionalized fabrics also showed photocatalytic activity, demonstrated by the degradation of acetaminophen, a common pharmaceutical compound, under simulated sunlight irradiation. These results indicate that UiO-66 can be supported on textile substrates for filtration and photocatalytic purposes and that these substrates can find applications in wastewater decontamination and micropollutant degradation.

Mimic Carbonic Anhydrase Using Metal-Organic Frameworks for CO2 Capture and Conversion

Carbonic anhydrase (CA) is a zinc-containing metalloprotein, in which the Zn active center plays the key role to transform CO₂ into carbonate. Inspired by nature, herein we used metal-organic frameworks (MOFs) to mimic CA for CO₂ conversion, on the basis of the structural similarity between the Zn coordination in MOFs and CA active center. The biomimetic activity of MOFs was investigated by detecting the hydrolysis of para-nitrophenyl acetate, which is a model reaction used to evaluate CA activity. The biomimetic materials (e.g., CFA-1) showed good catalytic activity, and excellent reusability, and solvent and thermal stability, which is very important for practical applications. In addition, ZIF-100 and CFA-1 were used to mimic CA to convert CO₂ gas, and exhibited good efficiency on CO₂ conversion compared with those of other porous materials (e.g., MCM-41, active carbon). This biomimetic study revealed a novel CO₂ treatment method. Instead of simply using MOFs to absorb CO₂, ZIF-100 and CFA-1 were used to mimic CA for in situ CO₂ conversion, which provides a new prospect in the biological and industrial applications of MOFs.

Sensing and capture of toxic and hazardous gases and vapors by metal–organic frameworks

This review summaries recent progress in the luminescent detection and adsorptive removal of harmful gases and vapors by metal–organic frameworks, as well as the principles and strategies guiding the design of these materials.

Degradation of chemical warfare agents over cotton fabric functionalized with UiO-66-NH2

Herein, cotton fabric was treated with an alkaline solution to increase the content of surface hydroxyl groups and then functionalized with UiO-66-NH₂, a nanoporous metal–organic framework. Instrumental analysis of the thus treated fabric revealed that its surface was covered with UiO-66-NH₂ crystals in a uniform manner. The ability of the functionalized fabric to degrade two chemical warfare agents (soman and sulfur mustard) was probed by testing its permeability to these two agents (swatch testing), and the excellent degradation performance was concluded to be well suited for a broad range of filtration and decontamination applications.

We develop a very efficient modification method of cotton fabric to be functionalized with a MOF via mercerization.

An integrated nanocatalyst combining enzymatic and metal–organic framework catalysts for cascade degradation of organophosphate nerve agents

An integrated nanocatalyst that combined a metal–organic framework-based catalyst and a biocatalyst was developed for cascade degradation of organophosphate nerve agents.

Rational design of CNTs with encapsulated Co nanospheres as superior acid- and base-resistant microwave absorbers

A Co@CNT material with a specific coating structure displays good EM wave absorption, even after treatment with concentrated acid or base.

H5PV2Mo10O40 encapsulated in MIL-101(Cr): facile synthesis and characterization of rationally designed composite materials for efficient decontamination of sulfur mustard

A newly synthesized composite H₅PV₂Mo₁₀O₄₀@MIL-101(Cr) can decontaminate HD quickly and efficiently owing to the synergetic combination of the components.

Cobalt complexes of Biginelli derivatives as fluorescent probes for selective estimation and degradation of organophosphates in aqueous medium

Bonding between metal complexes of Biginelli derivatives and organophosphates leads to enhancement of emission intensity.

Stable metal–organic frameworks as a host platform for catalysis and biomimetics

Recent years have witnessed the exploration and synthesis of an increasing number of metal–organic frameworks (MOFs). The utilization of stable MOFs as a platform for catalysis and biomimetics is discussed.

Effect of surface acidity of cyano-bridged polynuclear metal complexes on the catalytic activity for the hydrolysis of organophosphates

Heterogeneous catalysis of cyano-bridged polynuclear metal complexes was examined for the hydrolysis of toxic organophosphates. The surface acidity of cyano-bridged polynuclear metal complexes strongly effects on the catalytic activity.

Smart textiles of MOF/g-C3N4 nanospheres for the rapid detection/detoxification of chemical warfare agents

Smart textiles consisting of cotton, Cu-BTC MOF and oxidized graphitic carbon nitride, g-C₃N₄-ox, nanospheres were synthesized and tested as nerve agent detoxification media and colorimetric detectors. Combining Cu-BTC and g-C₃N₄-ox resulted in a nanocomposite (MOFgCNox) of heterogeneous porosity and chemistry. Upon the deposition of MOFgCNox onto cotton textiles, a stable fabric with a supreme photocatalytic detoxification ability towards the nerve gas surrogate, dimethyl chlorophosphate, was obtained. The detoxification process was accompanied by a visible and gradual color change, which can be used for the selective detection of chemical warfare agents and for monitoring their penetration inside a protective layer. These smart textiles adsorbed almost 7 g of CWA surrogate/its detoxification products per gram of Cu. The superior performance was linked to the high dispersion of the MOF crystals on the fibers, and a specific texture promoting the availability of the active copper centers.

Synthesis of a Zr-Based Metal-Organic Framework with Spirobifluorenetetrabenzoic Acid for the Effective Removal of Nerve Agent Simulants

A new microporous Zr(IV)-based metal-organic framework (MOF) containing 4,4',4″,4‴-(9,9'-spirobi[fluorene]-2,2',7,7'-tetrayl)tetrabenzoic acid (Spirof-MOF) was synthesized, characterized, and size-controlled for the adsorption and decomposition of a nerve agent simulant, dimethyl 4-nitrophenylphosphate (DMNP). Spirof-MOF showed a hydrolysis half-life (t_1/2) of 7.5 min to DMNP, which was confirmed by using in situ ³¹P NMR spectroscopy. Additionally, size-controlled Spirof-MOFb (∼1 μm) exhibited a half-life of 1.8 min and 99% removal within 18 min for DMNP. The results show that Spirof-MOF is a new active material in removing nerve agent simulants by adsorption and hydrolytic decomposition.

Degradation of Paraoxon and the Chemical Warfare Agents VX, Tabun, and Soman by the Metal-Organic Frameworks UiO-66-NH2, MOF-808, NU-1000, and PCN-777

In recent years, Zr-based metal-organic frameworks (MOFs) have been developed that facilitate catalytic degradation of toxic organophosphate agents, such as chemical warfare agents (CWAs). Because of strict regulations, experiments using live agents are not possible for most laboratories and, as a result, simulants are used in the majority of cases. Reports that employ real CWAs are scarce and do not cover the whole spectrum of agents. We here present a comparative study in which UiO-66-NH₂, NU-1000, MOF-808, and PCN-777 are evaluated for their effectiveness in the degradation of paraoxon and the chemical warfare agents tabun, VX, and soman, in N-ethylmorpholine buffer (pH 10) as well as in pure water. All MOFs showed excellent ability to degrade the agents under basic conditions. It was further disclosed that tabun is degraded by different mechanisms depending on the conditions. The presence of an amine, either as part of the MOF structure (UiO-66-NH₂) or in the agent itself (VX, tabun), is the most important factor governing degradation rates in water. The results show that MOFs have great potential in future protective applications. Although the use of simulants provides valuable information for initial screening and selection of new MOFs, the use of live agents revealed additional mechanisms that should aid the future development of even better catalysts.

Chemical Warfare Agents Detoxification Properties of Zirconium Metal-Organic Frameworks by Synergistic Incorporation of Nucleophilic and Basic Sites

The development of protective self-detoxifying materials is an important societal challenge to counteract risk of attacks employing highly toxic chemical warfare agents (CWAs). In this work, we have developed bifunctional zirconium metal-organic frameworks (MOFs) incorporating variable amounts of nucleophilic amino residues by means of formation of the mixed ligand [Zr₆O₄(OH)₄(bdc)_6(1-x)(bdc-NH₂)_6x] (UiO-66-xNH₂) and [Zr₆O₄(OH)₄(bpdc)_6(1-x)(bpdc-(NH₂)₂)_6x] (UiO-67-x(NH₂)₂) systems where bdc = benzene-1,4-dicarboxylate; bdc-NH₂= benzene-2-amino-1,4-dicarboxylate; bpdc = 4,4'-biphenyldicarboxylate; bpdc-(NH₂)₂ = 2,2'-diamino-4,4'-biphenyldicarboxylate and x = 0, 0.25, 0.5, 0.75, 1. In a second step, the UiO-66-xNH₂ and UiO-67-x(NH₂)₂ systems have been postsynthetically modified by introduction of highly basic lithium tert-butoxide (LiO^tBu) on the oxohydroxometallic clusters of the mixed ligand MOFs to yield UiO-66-xNH₂@LiO^tBu and UiO-67-x(NH₂)₂@LiO^tBu materials. The results show that the combination of pre and postsynthetic modifications on these MOF series gives rise to fine-tuning of the catalytic activity toward the hydrolytic degradation of both simulants and real CWAs in unbuffered aqueous solutions. Indeed, UiO-66-0.25NH₂@LiO^tBu is able to hydrolyze both CWAs simulants (diisopropylfluorophosphate (DIFP), 2-chloroethylethylsulfide (CEES), and real CWAs (soman (GD), sulfur mustard (HD)) quickly in aqueous solution. These results are related to a suitable combination of robustness, nucleophilicity, basicity, and accessibility to the porous framework.

Tailoring the Adsorption and Reaction Chemistry of the Metal-Organic Frameworks UiO-66, UiO-66-NH2, and HKUST-1 via the Incorporation of Molecular Guests

Metal-organic frameworks (MOFs) are versatile materials highly regarded for their porous nature. Depending on the synthetic method, various guest molecules may remain in the pores or can be systematically loaded for various reasons. Herein, we present a study that explores the effect of guest molecules on the adsorption and reactivity of the MOF in both the gas phase and solution. The differences between guest molecule interactions and the subsequent effects on their activity are described for each system. Interestingly, different effects are observed and described in detail for each class of guest molecules studied. We determine that there is a strong effect of alcohols with the secondary building unit of UiO MOFs, while Lewis bases have an effect on the reactivity of the -NH₂ group in UiO-66-NH₂ and adsorption by the coordinatively unsaturated copper sites in HKUST-1. These effects must be considered when determining synthesis and activation methods of MOFs toward various applications.

Metal-organic and covalent organic frameworks as single-site catalysts

Heterogeneous single-site catalysts consist of isolated, well-defined, active sites that are spatially separated in a given solid and, ideally, structurally identical. In this review, the potential of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) as platforms for the development of heterogeneous single-site catalysts is reviewed thoroughly. In the first part of this article, synthetic strategies and progress in the implementation of such sites in these two classes of materials are discussed. Because these solids are excellent playgrounds to allow a better understanding of catalytic functions, we highlight the most important recent advances in the modelling and spectroscopic characterization of single-site catalysts based on these materials. Finally, we discuss the potential of MOFs as materials in which several single-site catalytic functions can be combined within one framework along with their potential as powerful enzyme-mimicking materials. The review is wrapped up with our personal vision on future research directions.

Atomic-Level Structural Dynamics of Polyoxoniobates during DMMP Decomposition

Ambient pressure in situ synchrotron-based spectroscopic techniques have been correlated to illuminate atomic-level details of bond breaking and formation during the hydrolysis of a chemical warfare nerve agent simulant over a polyoxometalate catalyst. Specifically, a Cs₈[Nb₆O₁₉] polyoxoniobate catalyst has been shown to react readily with dimethyl methylphosphonate (DMMP). The atomic-level transformations of all reactant moieties, the [Nb₆O₁₉]^8- polyanion, its Cs⁺ counterions, and the DMMP substrate, were tracked under ambient conditions by a combination of X-ray absorption fine structure spectroscopy, Raman spectroscopy, and X-ray diffraction. Results reveal that the reaction mechanism follows general base (in contrast to specific base) hydrolysis. Together with computational results, the work demonstrates that the ultimate fate of DMMP hydrolysis at the Cs₈[Nb₆O₁₉] catalyst is strong binding of the (methyl) methylphosphonic acid ((M)MPA) product to the polyanions, which ultimately inhibits catalytic turnover.

Particle size studies to reveal crystallization mechanisms of the metal organic framework HKUST-1 during sonochemical synthesis

Systematic studies of key operating parameters for the sonochemical synthesis of the metal organic framework (MOF) HKUST-1(also called CuBTC) were performed including reaction time, reactor volume, sonication amplitude, sonication tip size, solvent composition, and reactant concentrations analyzed through SEM particle size analysis. Trends in the particle size and size distributions show reproducible control of average particle sizes between 1 and 4μm. These results along with complementary studies in sonofragmentation and temperature control were conducted to compare these results to kinetic crystal growth models found in literature to develop a plausible hypothetical mechanism for ultrasound-assisted growth of metal-organic-frameworks composed of a competitive mechanism including constructive solid-on-solid (SOS) crystal growth and a deconstructive sonofragmentation.

Electrospun metal–organic framework polymer composites for the catalytic degradation of methyl paraoxon

Electrospun polymer fibers containing poly(methyl methacrylate) (PMMA), Ti(OH)₄, and UiO-66 convert a chemical warfare agent simulant to non-toxic product via catalytic hydrolysis.

Metal–organic frameworks for the removal of toxic industrial chemicals and chemical warfare agents

Toxic gases can be captured or degraded by metal–organic frameworks.

Effective removal of chemical warfare agent simulants using water stable metal–organic frameworks: mechanistic study and structure–property correlation

Water stable zirconium based MOFs are used for the efficient adsorptive removal of chemical warfare agent simulants from aqueous medium.

Assembly of the active center of organophosphorus hydrolase in metal–organic frameworks via rational combination of functional ligands

Mimicking the total coordination sphere of the active center of organophosphorus hydrolase in MOFs to destruct nerve agents without co-catalysts.