Detoxification of Chemical Warfare Agents Using a Zr 6 ‐Based Metal–Organic Framework/Polymer Mixture

Permeable Self-Association of Metal-Organic Framework 808/Ag-Based Fiber Membrane for Broad-Spectrum and Highly Efficient Degradation of Biological and Chemical War Agents

The threat posed by biological and chemical warfare agents (BCWA) to national security, the environment, and personal health underscores the need for innovative chemical protective clothing. To address the limitations of conventional activated carbon materials, which are prone to falling off and adsorption saturation, an efficient self-association approach was introduced. In this study, we proposed the immobilization of metal-organic framework (MOF) 808 and Ag nanoparticles onto a polypropylene (PP) fiber membrane using a rapid self-association method facilitated by chitosan (CS). The MOF 808/Ag-based (PP-CS/808-Ag) fiber membrane demonstrated exceptional degradation efficiency, achieving a remarkable rate of t1/2 within 2 h for the mustard simulant 2-chloroethyl ethyl sulfide (2-CEES) and a rate of t1/2 = 4.12 min for the G-series simulant dimethyl 4-nitrophenylphosphate (DMNP). A theoretical computational model was developed to determine the overall reaction mechanism, and it was verified that MOF 808 and Ag nanoparticles were mainly involved in the hydrolysis process against 2-CEES and DMNP. The PP-CS/808-Ag composite fiber film was prepared as the core layer, and the fracture strength, bending resistance, and moisture permeability were better than those specified by many countries for biochemical protective clothing, showing that it has a broad application prospect in developing a generation of broad-spectrum bioprotective clothing.

MOF magic: zirconium-based frameworks in theranostic and bio-imaging applications

Over the past two decades, metal-organic frameworks (MOFs) have garnered substantial scientific interest across diverse fields, spanning gas storage, catalysis, biotechnology, and more. Zirconium, abundant in nature and biologically relevant, offers an appealing combination of high content and low toxicity. Consequently, Zr-based MOFs have emerged as promising materials with significant potential in biomedical applications. These MOFs serve as effective nanocarriers for controlled drug delivery, particularly for challenging antitumor and retroviral drugs in cancer and AIDS treatment. Additionally, they exhibit prowess in bio-imaging applications. Beyond drug delivery, Zr-MOFs are notable for their mechanical, thermal, and chemical stability, making them increasingly relevant in engineering. The rising demand for stable, non-toxic Zr-MOFs facilitating facile nanoparticle formation, especially in drug delivery and imaging, is noteworthy. This review focuses on biocompatible zirconium-based metal-organic frameworks (Zr-MOFs) for controlled delivery in treating diseases like cancer and AIDS. These MOFs play a key role in theranostic approaches, integrating diagnostics and therapy. Additionally, their utility in bio-imaging underscores their versatility in advancing medical applications.

Hierarchically Structured Metal-Organic Framework Polymer Composites for Chemical Warfare Agent Degradation

Metal-organic frameworks (MOFs) have captured the imagination of researchers for their highly tunable properties and many potential applications, including as catalysts for a variety of transformations. Even though MOFs possess significant potential, the challenges associated with processing of these crystalline powders into usable form factors while retaining their functional properties limit their end use applications. Herein, we introduce a new approach to construct MOF-polymer composites via 3D photoprinting to overcome these limitations. We designed photoresin composite formulations that use polymerization-induced phase separation to cause the MOF catalysts to migrate to the surface of the printed material, where they are accessible to substrates such as chemical warfare agents. Using our approach, MOF-polymer composites can be fabricated into nearly any shape or architecture while retaining both the excellent catalytic activity at 10 wt % loading of the MOF components and the flexible, elastomeric mechanical properties of a polymer.

MOF-Enabled Electrochemical Sensor for Rapid and Robust Sensing of V-Series Nerve Agents at Low Concentrations

Among nerve agents, V-series nerve agents are some of the most toxic, making low-concentration detection critical for the protection of individuals, populations, and strategic resources. Electrochemical sensors are ideally suited for the real-time and in-field sensing of these agents. While V-series nerve agents are inherently nonelectroactive, they can be hydrolyzed to electroactive products compatible with electrochemical sensing. Zr(IV) MOFs are next-generation nanoporous materials that have been shown to rapidly catalyze the hydrolysis of nerve agents. This work makes use of these nanomaterials to develop, for the first time, an MOF-enabled electrochemical sensor for V-series nerve agents. Our work demonstrates that the VX thiol hydrolysis product can be electrochemically detected at low concentrations using commercially available gold electrodes. We demonstrate that low-concentration thiol oxidation is an irreversible reaction that is dependent on both mass transport and adsorption. Demeton-S-methylsulfon, a VX simulant, is used to demonstrate the full range of sensor operation that includes hydrolysis and electrochemical detection. We demonstrate that MOF-808 rapidly, selectively, and completely hydrolyzes demeton-S-methylsulfon to less-hazardous dimethyl phosphate and 2-ethylsulfonylethanethiol. Low-concentration measurements of 2-ethylsulfonylethanethiol are performed by using electrochemical techniques. This sensor has a limit of detection of 30 nM or 7.87 μg/L for 2-ethylsulfonylethanethiol, which is near the nerve agent exposure limit for water samples established by the United States military. Our work demonstrates the feasibility of rapid, robust electrochemical sensing of V-series nerve agents at low concentrations for in-field applications.

Advances in Metal-Organic Frameworks for the Removal of Chemical Warfare Agents: Insights into Hydrolysis and Oxidation Reaction Mechanisms

The destruction of chemical warfare agents (CWAs) is a crucial area of research due to the ongoing evolution of toxic chemicals. Metal-organic frameworks (MOFs), a class of porous crystalline solids, have emerged as promising materials for this purpose. Their remarkable porosity and large surface areas enable superior adsorption, reactivity, and catalytic abilities, making them ideal for capturing and decomposing target species. Moreover, the tunable networks of MOFs allow customization of their chemical functionalities, making them practicable in personal protective equipment and adjustable to dynamic environments. This review paper focuses on experimental and computational studies investigating the removal of CWAs by MOFs, specifically emphasizing the removal of nerve agents (GB, GD, and VX) via hydrolysis and sulfur mustard (HD) via selective photooxidation. Among the different MOFs, zirconium-based MOFs exhibit extraordinary structural stability and reusability, rendering them the most promising materials for the hydrolytic and photooxidative degradation of CWAs. Accordingly, this work primarily concentrates on exploring the intrinsic catalytic reaction mechanisms in Zr-MOFs through first-principles approximations, as well as the design of efficient degradation strategies in the aqueous and solid phases through the establishment of Zr-MOF structure-property relationships. Recent progress in the tuning and functionalization of MOFs is also examined, aiming to enhance practical CWA removal under realistic battlefield conditions. By providing a comprehensive overview of experimental findings and computational insights, this review paper contributes to the advancement of MOF-based strategies for the destruction of CWAs and highlights the potential of these materials to address the challenges associated with chemical warfare.

Degradation of Chemical Warfare Agent Nitrogen Mustard Using Ferrate (VI)

Chemical warfare agents (CWAs) are one of the most toxic compounds. Degradation of CWAs using decontamination agents is one of the few ways to protect human health against the harmful effects of CWAs. A ferrate (VI)-based potential chemical warfare agent decontaminant was studied for the degradation of persistent nitrogen mustard (tris(2-chloroethyl)amine, HN3). By optimizing the reaction conditions, the complete degradation of HN3 was achieved in 4 min. The degradation products contained mostly reduced Fe species, which confirmed the environmental friendliness of the proposed decontamination solution.

Water-Accelerated Transport: Vapor-Phase Nerve Agent Simulant Delivery within a Catalytic Zirconium Metal-Organic Framework as a Function of Relative Humidity

Zirconium-based metal-organic frameworks (MOFs) are candidate materials for effective nerve agent detoxification due to their thermo- and water stability as well as high density of catalytic Zr sites. However, as high-porosity materials, most of the active sites of Zr-MOFs can only be accessed by diffusion into the crystal interior. Therefore, the transport of nerve agents in nanopores is an important factor in the catalytic performance of Zr-MOFs. Here, we investigated the transport process and mechanism of a vapor-phase nerve agent simulant, dimethyl methyl phosphonate (DMMP), through a representative Zr-MOF, NU-1008, under practical conditions of varying humidity. Confocal Raman microscopy was used to monitor the transport of DMMP vapor through individual NU-1008 crystallites, where the relative humidity (RH) of the environment was tuned to understand the impact of water. Counterintuitively, water in the MOF channels, instead of blocking DMMP transport, assists DMMP diffusion; indeed, the transport diffusivity (D_t) of DMMP in NU-1008 is one order of magnitude higher at 70% than 0% RH. To understand the mechanism, magic angle spinning NMR and molecular dynamics simulations were performed and suggested that high water content in the channels prevents DMMP from hydrogen-bonding with the nodes, allowing for faster diffusion of DMMP in the channels. The simulated self-diffusivity (D_s) of DMMP is observed to be concentration-dependent. At low loading of DMMP, D_s is higher at 70% RH than 0% RH, while at high loadings the trend reverses due to the DMMP aggregation in water and the reduction of free volume in channels.

Bioinspired Framework Catalysts: From Enzyme Immobilization to Biomimetic Catalysis

Enzymatic catalysis has fueled considerable interest from chemists due to its high efficiency and selectivity. However, the structural complexity and vulnerability hamper the application potentials of enzymes. Driven by the practical demand for chemical conversion, there is a long-sought quest for bioinspired catalysts reproducing and even surpassing the functions of natural enzymes. As nanoporous materials with high surface areas and crystallinity, metal-organic frameworks (MOFs) represent an exquisite case of how natural enzymes and their active sites are integrated into porous solids, affording bioinspired heterogeneous catalysts with superior stability and customizable structures. In this review, we comprehensively summarize the advances of bioinspired MOFs for catalysis, discuss the design principle of various MOF-based catalysts, such as MOF-enzyme composites and MOFs embedded with active sites, and explore the utility of these catalysts in different reactions. The advantages of MOFs as enzyme mimetics are also highlighted, including confinement, templating effects, and functionality, in comparison with homogeneous supramolecular catalysts. A perspective is provided to discuss potential solutions addressing current challenges in MOF catalysis.

Molecularly imprinted self-buffering double network hydrogel containing bi-amidoxime functional groups for the rapid hydrolysis of organophosphates

The development of high-performance catalyst materials with high catalytic activity for the hydrolysis of organophosphorus toxicants without additional pH buffer conditions has become an urgent need for practical application. Here, a multifunctional molecularly imprinted polymer double network hydrogel (MIP-DN) material has been prepared by integrating the first polymer network containing the functional group of bi-amidoxime as the catalytic active center and the cationic polymer polyethyleneimine (PEI) with pH buffer function as the main component of the second network. Advantageously, the resultant MIP-DN hydrogel showed excellent catalytic performance without additional pH buffer conditions, exhibiting a half-life of 25 min for the hydrolysis of paraoxon in pure water. Together with multi-functions of high catalytic activity, self-buffering function and excellent processability, the MIP-DN hydrogel prepared in this work provides a new strategy for the preparation of catalytic materials with practical application value toward toxic organophosphates.

Functionalized reactive polymers for the removal of chemical warfare agents: A review

Protection from and removal of chemical warfare agents (CWAs) from the environment remains a global goal. Activated charcoal, metal oxides, metal organic frameworks (MOFs), polyoxometalates (POMs) and reactive polymers have all been investigated for CWA removal. Composite polymeric materials are rapidly gaining traction as versatile building blocks for personal protective equipment (PPE) and catalytic devices. Polymers are inexpensive to produce and easily engineered into a wide range of materials including films, electro-spun fibers, mixed-matrix membranes/reactors, and other forms. When containing reactive side-chains, hydrolysis catalysts, and/or oxidative catalysts polymeric devices are primed for CWA decontamination. In this review, recent advances in reactive polymeric materials for CWA removal are summarized. To aid in comparing the effectiveness of the different solid catalysts, particular attention is paid to the stoichiometric ratio of reactive species to toxic substrate (CWA or CWA simulant).

Feasible Detoxification Coating Material for Chemical Warfare Agents Using Poly(methyl methacrylate)-Branched Poly(ethyleneimine) Copolymer and Metal-Organic Framework Composites

Defense against chemical warfare agents (CWAs) is regarded as a top priority for the protection of humanity, but it still depends on physical protection with severe limitations such as residual toxicity and post-treatment requirement. In this study, a strategically designed functional polymeric substrate was composited with a metal-organic framework catalyst to remove toxicity immediately. A series of PMMA-BPEI copolymers exhibited high processability as a coating and accelerated the catalytic activity of Zr(IV)-based metal-organic framework catalysts (UiO-66). Among them, PMB12_40 composite coating on a cotton fabric, containing a PMMA-BPEI copolymer (PMMA/BPEI = 1/2) and 40% of UiO-66 catalyst, can efficiently decompose nerve agent simulants (methyl-paraoxon) under both liquid phase (t1/2 = 0.14 h) and humidified (t1/2 = 4.8 h) conditions. Moreover, a real agent, GD, was decomposed 100% by PMB12_40 in 4 h at 25 °C and 65% relative humidity. On the basis of superior catalytic activity, the PMB composites are anticipated to be a potential material for active chemical protection coating.

Effective Degradation of Novichok Nerve Agents by the Zirconium Metal-Organic Framework MOF-808

Novichoks are a novel class of nerve agents (also referred to as the A-series) that were employed in several poisonings over the last few years. This calls for the development of novel countermeasures that can be applied in protective concepts (e.g., protective clothing) or in decontamination methods. The Zr metal-organic framework MOF-808 has recently emerged as a promising catalyst in the hydrolysis of the V- and G-series of nerve agents as well as their simulants. In this paper, we report a detailed study of the degradation of three Novichok agents by MOF-808 in buffers with varying pH. MOF-808 is revealed to be a highly efficient and regenerable catalyst for Novichok agent hydrolysis under basic conditions. In contrast to the V- and G-series of agents, degradation of Novichoks is demonstrated to proceed in two consecutive hydrolysis steps. Initial extremely rapid P-F bond breaking is followed by MOF-catalyzed removal of the amidine group from the intermediate product. The intermediate thus acted as a competitive substrate that was rate-determining for the whole two-step degradation route. Under acidic conditions, the amidine group in Novichok A-230 is more rapidly hydrolyzed than the P-F bond, giving rise to another moderately toxic intermediate. This intermediate could in turn be efficiently hydrolyzed by MOF-808 under basic conditions. These experimental observations were corroborated by density functional theory calculations to shed light on molecular mechanisms.

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.

Utilizing Zirconium MOF-functionalized Fiber Substrates Prepared by Molecular Layer Deposition for Toxic Gas Capture and Chemical Warfare Agent Degradation

Metal-organic frameworks (MOFs) are a class of porous organic-inorganic solids extensively explored for numerous applications owing to their catalytic activity and high surface area. In this work MOF thin films deposited in a one-step, molecular layer deposition (MLD), an all-gas-phase process, on glass wool fibers are characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and their capabilities towards toxic industrial chemical (TIC) capture and chemical warfare agents (CWA) degradation are investigated. It is shown that despite low volume of the active material used, MOFs thin films are capable of removal of harmful gaseous chemicals from air stream and CWA from neutral aqueous environment. The results confirm that the MLD-deposited MOF thin films, amorphous and crystalline, are suitable materials for use in air filtration, decontamination, and physical protection against CWA and TIC.

Green MIP-202(Zr) Catalyst: Degradation and Thermally Robust Biomimetic Sensing of Nerve Agents

Rapid and robust sensing of nerve agent (NA) threats is necessary for real-time field detection to facilitate timely countermeasures. Unlike conventional phosphotriesterases employed for biocatalytic NA detection, this work describes the use of a new, green, thermally stable, and biocompatible zirconium metal-organic framework (Zr-MOF) catalyst, MIP-202(Zr). The biomimetic Zr-MOF-based catalytic NA recognition layer was coupled with a solid-contact fluoride ion-selective electrode (F-ISE) transducer, for potentiometric detection of diisopropylfluorophosphate (DFP), a F-containing G-type NA simulant. Catalytic DFP degradation by MIP-202(Zr) was evaluated and compared to the established UiO-66-NH₂ catalyst. The efficient catalytic DFP degradation with MIP-202(Zr) at near-neutral pH was validated by ³¹P NMR and FT-IR spectroscopy and potentiometric F-ISE and pH-ISE measurements. Activation of MIP-202(Zr) using Soxhlet extraction improved the DFP conversion rate and afforded a 2.64-fold improvement in total percent conversion over UiO-66-NH₂. The exceptional thermal and storage stability of the MIP-202/F-ISE sensor paves the way toward remote/wearable field detection of G-type NAs in real-world environments. Overall, the green, sustainable, highly scalable, and biocompatible nature of MIP-202(Zr) suggests the unexploited scope of such MOF catalysts for on-body sensing applications toward rapid on-site detection and detoxification of NA threats.

Product Inhibition and the Catalytic Destruction of a Nerve Agent Simulant by Zirconium-Based Metal-Organic Frameworks

Rapid degradation/destruction of chemical warfare agents, especially ones containing a phosphorous-fluorine bond, is of notable interest due to their extreme toxicity and typically rapid rate of human incapacitation. Recent studies of the hydrolytic destruction of a key nerve agent simulant, dimethyl 4-nitrophenylphosphate (DMNP), catalyzed by Zr₆-based metal-organic frameworks (MOFs), have suggested deactivation of the active sites due to inhibition by the products as the reaction progresses. In this study, the interactions of two MOFs, NU-1000 and MOF-808, and two hydrolysis products, dimethyl phosphate (DMP) and ethyl methyl phosphonate (EMP), from the hydrolysis of the simulant (DMNP) and nerve agent ethyl methylphosphonofluoridate (EMPF), resembling the hydrolysis degradation product of the G-series nerve agent, Sarin (GB), have been investigated to deconvolute the effect of product inhibition from other effects on catalytic activity. Kinetic studies via in situ nuclear magnetic resonance spectroscopy indicated substantial product inhibition upon catalyst activity after several tens to several thousand turnovers, depending on specific conditions. Apparent product binding constants were obtained by fitting initial reaction rates at pH 7.0 and pH 10.5 to a Langmuir-Freundlich binding/adsorption model. For the fits, varying amounts/concentrations of candidate inhibitors were introduced before the start of catalytic hydrolysis. The derived binding constants proved suitable for quantitatively describing product inhibition effects upon reaction rates over the extended time course of simulant hydrolysis by aqua-ligand-bearing hexa-zirconium(IV) nodes.

Preparation of UiO-66-NH2@PDA under Water System for Chemical Warfare Agents Degradation

There is an urgent need to develop catalytic degradation technologies for chemical warfare agents (CWAs) that are environmentally friendly and do not require secondary treatment. UiO-66-NH₂ and other metal–organic frameworks (MOFs) based on zirconium have been shown to promote the catalytic degradation of CWAs. At the same time, MOFs have been studied, and they have shown interesting properties in CWA removal because of their ultrahigh surface area, tunable structures, and periodically distributed abundant catalytic sites. However, MOFs synthesized by conventional methods are mostly powdery crystals that are difficult to process and have poor mechanical stability, which largely limit the development of MOFs in practical applications. An emerging trend in MOF research is hybridization with flexible materials. Polymers possess a variety of unique attributes, such as flexibility, thermal and chemical stability, and process ability, and these properties can be combined with MOFs to make a low-cost and versatile material that also provides convenience for the subsequent integration of such MOFs into independent substrates or textiles. In this article, we used a green and simple method to coat the surface of UiO-66-NH₂ with polydopamine (PDA), PDA can promote the catalytic hydrolysis of UiO-66-NH₂ to DMNP (a simulant of chemical warfare agents). Additionally, it can adsorb the toxic hydrolysis product p-nitrophenol, avoiding the trouble of secondary treatment. The half-life of UiO-66-NH₂ coated with polydopamine (UiO-66-NH₂@PDA) for catalytic hydrolysis is 8.9 min, and that of pure UiO-66-NH₂ is 20 min. We speculate that the surface coated with PDA can improve the diffusion of DMNP to the active sites of UiO-66-NH₂.

Rapid, Biomimetic Degradation of a Nerve Agent Simulant by Incorporating Imidazole Bases into a Metal-Organic Framework

Metal-organic frameworks (MOFs) are excellent catalytic materials for the hydrolytic degradation of nerve agents and their simulants. However, most of the MOF-based hydrolysis catalysts to date are reliant on liquid water media buffered by a volatile liquid base. To overcome this practical limitation, we developed a simple and feasible strategy to synthesize MOF composites that structurally mimic phosphotriesterase's active site as well as its ligated histidine residues. By incorporating imidazole and its derivative into the pores of MOF-808, the obtained MOF composites achieved rapid degradation of a nerve agent simulant (dimethyl-4-nitrophenyl phosphate, DMNP) in pure water as well as in a humid environment without liquid base. Remarkably, one of the composites Im@MOF-808 displayed the highest catalytic activity for DMNP hydrolysis in unbuffered aqueous solutions among all reported MOF-based catalysts. Furthermore, solid-phase catalysis showed that Im@MOF-808 can also rapidly hydrolyze DMNP under high-humidity conditions without bulk water or external bases. This work provides a viable solution toward the implementation of MOF materials into protective equipment for practical nerve agent detoxification.

In vitro human skin decontamination efficacy of MOF-808 in decontamination lotion following exposure to the nerve agent VX

Metal-organic frameworks (MOFs) have shown promising properties for removal of chemical warfare agents, in particular for material decontamination and functionalized fabrics. The MOF-properties could also be beneficial for skin decontamination, especially when exposed to highly toxic and low volatile nerve agents. In such exposures, efficient decontamination is crucial for adequate medical management. In the present study, seven zirconium-based MOFs were evaluated for their ability to degrade VX and subsequently tested in vitro for decontamination of VX on human dermatomed skin. Of the MOFs evaluated, MOF-808 showed the greatest ability to degrade VX in an alkaline buffer with complete degradation of VX within 5 min. PCN-777, Zr-NDC and NU-1000 displayed degradation half-lives of approximately 10 min. When including MOF-808 in a skin friendly carrier with slightly acidic pH, a decreased agent degradation rate was observed, requiring over 24 h to reach complete degradation. In skin decontamination experiments, MOF-808 enhanced the efficacy compared to the carrier alone, essentially by improved agent absorption. Adding MOF-808 to Reactive Skin Decontamination Lotion (RSDL) did not improve the high effectiveness of RSDL alone. The present study showed that including MOF in skin decontamination lotions could be beneficial. Further studies should include optimizing the particulates and formulations.

Function-Topology Relationship in the Catalytic Hydrolysis of a Chemical Warfare Simulant in Two Zr-MOFs

Owing to their high surface area, high concentration of active metal sites, and water stability, zirconium(VI)-based metal-organic frameworks (Zr-MOFs) have shown excellent activity in the hydrolysis of organophosphorus nerve agents (OPNs). In this regard, for the first time, two topologically different Zr-MOFs (Zr-fcu-tmuc and Zr-bcu-tmuc, constructed from the same organic and inorganic building blocks; fcu=face-centered cubic, bcu=body-centered cubic) have been rationally chosen to investigate the effect of network topology on the catalytic hydrolysis of the nerve agent simulant, dimethyl 4-nitrophenyl phosphate (DMNP). A remarkable enhancement in the hydrolysis rate of DMNP was observed with Zr-bcu-tmuc, reducing the half-life more than three-fold compared with Zr-fcu-tmuc. Greater accessibility of the active Zr^VI sites in the 8-connected bcu net compared with the 12-connected fcu leads to a faster hydrolysis of DMNP on Zr-bcu-tmuc. Interestingly, the higher activity of Zr-bcu-tmuc was also confirmed by its higher fluorescence sensitivity towards DMNP (limit of detection (LOD)=0.557 μm) compared with Zr-fcu-tmuc (LOD=1.09 μm). The results show that controlling the desired topology of Zr-MOFs is a useful strategy for improving their performance in the detection and catalytic detoxification of OPNs.

Continuous Flow Composite Membrane Catalysts for Efficient Decomposition of Chemical Warfare Agent Simulants

Continuous and safe decomposition of chemical warfare agents (CWAs) is a critical requirement to protect both soldiers and citizens and to eliminate the stockpiles after the cold war. The Zr-based metal-organic framework (Zr-MOF) has been known as the most effective catalyst for decomposing CWAs, especially the most fatal nerve agents, however, its low processability due to the powder form limits its expansion to actual military applications. To this end, the composite membrane catalysts (CMCs) comprising the Zr-MOF (UiO-66 catalyst) and nylon 6 nanofiber (porous supporter) are developed by the simple integration of electrospray and electrospinning, resulting in selective immobilization of UiO-66 on the surface of the nylon 6 nanofibers. These strategical benefits of CMCs gave super catalytic durability including recyclability over five times without decreasing the catalytic activity for the decomposition of methyl paraoxon (MPO), a simulant of the nerve agent, in the presence of N-ethylmorpholine (N-EM), which was not achieved in the original particulate UiO-66. Because of the excellent physical and chemical stabilities of CMCs, the CMC with 56 wt % of UiO-66 (CMC56) decomposed 198 g of MPO within an hour in the continuous flow system with a flow rate of 21.6 mL h^-1. This study highlights the important strategies in designing the feasible membrane-type catalysts with superior catalytic activity and robust durability for decomposing CWAs in the continuous flow system.

High-Throughput Screening of MOFs for Breakdown of V-Series Nerve Agents

Metal-organic frameworks (MOFs) have shown promise for the catalytic decomposition of chemical weapons. Finding the best materials for the degradation of nerve agents requires the ability to screen a high number of samples and elucidate the key parameters of effective catalysis. In this work, a high-throughput screening (HTS) method has been developed to evaluate MOFs as catalysts, specifically against the V-class of nerve agents. Over 100 MOFs have been tested using the V-class simulant, O,O-diethyl S-phenyl phosphorothioate (DEPPT), revealing good activity for some UiO-66 derivatives. A medium-throughput hydrolysis assay for the nerve agent O-ethyl S-[2-(diisopropylamino)ethyl]methylphosphonothioate (VX) was also performed using six MOFs selected from HTS and was validated by ³¹P NMR. The results demonstrated that the DEPPT-based assay is a good indicator of V-series agent reactivity and should be considered in addition to the common (4-nitrophenyl)phosphate (DMNP) assay that is used for G-series agents.

The Effect of Surface Hydroxylation on MOF Formation on ALD Metal Oxides: MOF-525 on TiO2/Polypropylene for Catalytic Hydrolysis of Chemical Warfare Agent Simulants

Metal-organic framework (MOF) fibrous composites were synthesized in a variety of methods in attempt to incorporate the highly effective reactivity of MOFs into a more facile and applicable format. Recent advances have demonstrated incorporating a metal oxide nucleation surface or reactive layer promotes conformal, well-adhered MOF growth on substrates. These materials have demonstrated promising reactivity in capturing or degrading chemical warfare agents and simulants. Here, we examine the mechanisms for MOF nucleation from metal oxide thin films to explore why some metal oxide sources are better suited for one synthesis mechanism over another. We isolate metal oxide extent of hydroxylation as an indicative factor as to whether the film serves as a nucleation promoter or may be converted directly to the MOF thin films. MOF-525 growth on Al₂O₃, TiO₂, and ZnO coated fibers is demonstrated to corroborate these findings and used to degrade chemical warfare agent simulant dimethyl-4-nitrophenyl phosphate.

Insights into Catalytic Gas-Phase Hydrolysis of Organophosphate Chemical Warfare Agents by MOF-Supported Bimetallic Metal-Oxo Clusters

Zirconium-based metal-organic frameworks (Zr-MOFs) have been reported to be efficient catalysts for the hydrolysis of organophosphate chemical warfare agents (CWAs) in buffered solutions. However, for the gas-phase reaction, which is more relevant to the situation in a battlefield gas mask application, the kinetics of Zr-MOF catalysts may be severely hindered by strong product inhibition. To improve the catalytic performance, we computationally screened a series of synthetically accessible Zr-MOF-supported bimetallic metal-oxo clusters in which the metal-oxygen-metal active motif is preserved, aiming to find catalysts that have lower binding affinities to the hydrolysis product. For the promising catalyst Al₂O₂(OH)₂@NU-1000 identified from the screening using density functional theory, we mapped out the full reaction pathway of gas-phase dimethyl p-nitrophenolphosphate (DMNP) hydrolysis and analyzed the free energy profile as well as the turnover frequency (TOF). We found that the catalytic mechanism on the new catalyst is slightly different from the one on NU-1000, which also led to a different TOF-limiting step. Additional factors that can affect the overall catalytic performance in practical application, such as the amount of ambient moisture and the existence of acid gases that may poison the catalyst, have also been evaluated.

Zirconium-Based Metal-Organic Frameworks for the Catalytic Hydrolysis of Organophosphorus Nerve Agents

Organophoshorus nerve agents are among the most toxic chemicals known to humans, and because of their unfortunate recent use despite international bans, there is an urgent need to develop materials that can effectively degrade these nerve agents. Within the past decade, zirconium-based metal-organic frameworks (Zr-MOFs) have emerged as a bioinspired class of materials capable of rapidly hydrolyzing these compounds and significantly diminishing their toxicity. Both experimental and computational insights have guided the design of Zr-MOFs, leading to the development of catalysts capable of detoxifying nerve agents and simulants, chemicals with similar functionality but lower toxicity, via hydrolysis within seconds in basic aqueous solutions. While these systems are acceptable for the elimination of stockpile weapons, translating this catalytic performance to filters incorporating Zr-MOFs that can be used in masks or protective clothing is not trivial. As such, a large area of focus recently has been targeted toward integrating these hydrolysis catalysts into protective clothing and gear while retaining the performance from solution-based catalytic systems. This Forum Article provides an overview of the development of Zr-MOFs for the catalytic hydrolysis of organophosphorus substrates, including design principles and mechanistic insights for both solution-based and textile-coated systems. Finally, we highlight the remaining challenges yet to be addressed and offer perspectives on the future directions for this field.

Swell and Destroy: A Metal-Organic Framework-Containing Polymer Sponge That Immobilizes and Catalytically Degrades Nerve Agents

Organophosphorus chemical warfare agents function as potent neurotoxins. Whilst the destruction of nerve agents is most readily achieved by hydrolysis, their storage and transport are hazardous and lethal in milligram doses, with any spillage resulting in fatalities. Furthermore, current decontamination and remediation measures are limited by a need for stoichiometric reagents, solvents, and buffered solutions, complicating the process for the treatment of bulk contaminants. Herein, we report a composite polymer material capable of rendering bulk VX unusable by immobilization within a porous polymer until a metal-organic framework (MOF) catalyst fully hydrolyzes the neurotoxin. This is an all-in-one capability that minimizes the use of multiple reagents, facilitated by a porous high internal phase emulsion-based polystyrene monolith housing an active zirconia MOF catalyst (MOF-808); the porous polymer absorbs and immobilizes the liquid agents, while the MOF enables hydrolysis. The dichotomous hierarchy of porous materials facilitates the containment and rapid hydrolysis of VX (>80% degradation in 8 h) in the presence of excess H₂O. This composite can further enable the hydrolysis of neat VX with reliance on ambient humidity (>95% in 11 days). Potentially, 4.5 kg of the composite can absorb, immobilize, and degrade the contents of a standard chemical drum/barrel (208 L, 55 gal) of the chemical warfare agent (CWA). We believe that this composite is the first example of what will be the go-to approach for CWA immobilization and degradation in the future. Furthermore, we believe that this demonstration of a catalytically reusable absorbent sponge provides a signpost for the development of similar materials where immobilization of a substrate in a catalytically active environment is desirable.

MOF-Polymer Hybrid Materials: From Simple Composites to Tailored Architectures

Metal-organic frameworks (MOFs) are inherently crystalline, brittle porous solids. Conversely, polymers are flexible, malleable, and processable solids that are used for a broad range of commonly used technologies. The stark differences between the nature of MOFs and polymers has motivated efforts to hybridize crystalline MOFs and flexible polymers to produce composites that retain the desired properties of these disparate materials. Importantly, studies have shown that MOFs can be used to influence polymer structure, and polymers can be used to modulate MOF growth and characteristics. In this Review, we highlight the development and recent advances in the synthesis of MOF-polymer mixed-matrix membranes (MMMs) and applications of these MMMs in gas and liquid separations and purifications, including aqueous applications such as dye removal, toxic heavy metal sequestration, and desalination. Other elegant ways of synthesizing MOF-polymer hybrid materials, such as grafting polymers to and from MOFs, polymerization of polymers within MOFs, using polymers to template MOFs, and the bottom-up synthesis of polyMOFs and polyMOPs are also discussed. This review highlights recent papers in the advancement of MOF-polymer hybrid materials, as well as seminal reports that significantly advanced the field.

Integration of Metal-Organic Frameworks on Protective Layers for Destruction of Nerve Agents under Relevant Conditions

Metal-organic frameworks (MOFs) are promising candidates for the catalytic hydrolysis of nerve agents and their simulants. Though highly efficient, bulk water and volatile bases are often required for hydrolysis with these MOF catalysts, preventing real-world implementation. Herein we report a generalizable and scalable approach for integrating MOFs and non-volatile polymeric bases onto textile fibers for nerve agent hydrolysis. Notably, the composite material showed similar reactivity under ambient conditions compared to the powder material in aqueous alkaline solution. This represents a critical step toward a unified strategy for nerve agent hydrolysis in practical settings, which can significantly reduce the dimensions of filters and increase the efficiency of protective suits.

Insight into organophosphate chemical warfare agent simulant hydrolysis in metal-organic frameworks

Metal-organic frameworks (MOFs) are porous 3-dimensional crystalline structures that have shown promise for a variety of applications including adsorption, catalysis, and sensing. Modern warfare has placed chemical warfare agent (CWA) destruction at the forefront of chemical applications for MOFs. However, experiments involving CWAs can only be performed by a small number of highly trained individuals as they are extremely dangerous and available only to certain laboratories. As such, it is imperative that suitable chemical simulants and reaction conditions are determined for CWAs of interest. In this work, we determine the reaction rate for heterogeneous catalytic hydrolysis of eight commonly used G-agent simulants with zirconium-based MOFs. Of the simulants tested, only dimethyl chlorophosphate (DMCP), diisopropylfluorophosphate (DFP), and dimethyl p-nitrophenylphosphate (DMNP) exhibit the ability to be catalytically hydrolyzed in a manner similar to the G-agents by the MOFs studied. Two different base-catalyzed reaction mechanisms are proposed for the hydrolysis reaction on the different MOF secondary building units, and the effect of pH and buffer properties is determined using an N-ethylmorpholine (NEM) buffer at pH 8-10 and a 3-(cyclohexylamino)-1-propanesulofinic acid (CAPS) buffer at pH 10-11.

Magnesium Exchanged Zirconium Metal-Organic Frameworks with Improved Detoxification Properties of Nerve Agents

UiO-66, MOF-808 and NU-1000 metal-organic frameworks exhibit a differentiated reactivity toward [Mg(OMe)₂(MeOH)₂]₄ related to their pore accessibility. Microporous UiO-66 remains unchanged while mesoporous MOF-808 and hierarchical micro/mesoporous NU-1000 materials yield doped systems containing exposed MgZr₅O₂(OH)₆ clusters in the mesoporous cavities. This modification is responsible for a remarkable enhancement of the catalytic activity toward the hydrolytic degradation of P-F and P-S bonds of toxic nerve agents, at room temperature, in unbuffered aqueous solutions.

Metal-Organocatalyst for Detoxification of Phosphorothioate Pesticides: Demonstration of Acetylcholine Esterase Activity

In recent years, transition metal complexes have been developed for catalytical degradation of a phosphate ester bond, particularly in RNA and DNA; however, less consideration has been given for development of complexes for the degradation of a phosphorothioate bond, as they are the foremost used pesticides in the environment and are toxic to human beings. In this context, we have developed copper complexes of benzimidazolium based ligands for catalytical degradation of a series of organophosphates (parathion, paraoxon, methyl-parathion) at ambient conditions. The copper complexes (assigned as N1-N3) were characterized using single X-ray crystallography which revealed that all three complexes are mononuclear and distorted square planner in geometry. Further, the solution state studies of the prepared complexes were carried out using UV-visible absorption, fluorescence spectroscopy, and cyclic voltametry. The complexes N1 and N2 have benzimidazolium ionic liquid as base attached with two 2-mercapto-benzimidazole pods, whereas complex N3 contains a nonionic ligand. The synthesized copper complexes were evaluated for their catalytic activity for degradation of organophosphates. It is interesting that the complex containing the ionic ligand efficiently degrades phosphorothioate pesticides, whereas complex N3 was not found to be appropriate for degradation due to a weaker conversion rate. The organophosphate degradation studies were monitored by recording absorbance spectra of parathion in the presence of catalyst, i.e., copper complexes with respect to time. The parathion was hydrolyzed into para-nitrophenol and diethyl thiophosphate. Moreover, to analyze the inhibition activity of the pesticides toward acetylcholine esterase enzyme in the presence of prepared metal complexes, Ellman's assay was performed and revealed that, within 20 min, the inhibition of acetylcholine esterase enzyme decreases by up to 13%.

Photothermally Enhanced Detoxification of Chemical Warfare Agent Simulants Using Bioinspired Core-Shell Dopamine-Melanin@Metal-Organic Frameworks and Their Fabrics

Self-detoxifying materials capable of both capture and destruction of chemical warfare agents (CWAs) are highly desirable for efficient personal protection and safe handling of contaminated materials. Developing new strategies to improve CWA removal efficiency of these materials is highly relevant to CWA purification technology. Herein, we present novel photothermally enhanced catalytic detoxification of CWA simulants and its application in self-detoxifying gas filters. The material design features a well-defined core-shell nanostructure (CSN) consisting of an inner photothermal material and an outer microporous catalyst. As a demonstration, the CSN was obtained by growing a Zr-based metal-organic framework (MOF), UiO-66-NH₂, onto bioinspired dopamine-melanin (Dpa) nanoparticles via heterogeneous nucleation induced by metal chelation. The resultant Dpa@UiO-66-NH₂ CSN has increased the turnover frequency (TOF) of a nerve agent simulant, 4-nitrophenyl phosphate (DMNP), by 2.9- and 1.7-fold in the presence of NIR laser and simulated solar light, respectively. Further incorporation of Dpa@UiO-66-NH₂ CSNs into polymer fibers by electrospinning has led to an even greater photothermal enhancement effect (5.8- and 3.2-fold TOF increase), achieving a faster DMNP degradation rate than the corresponding pure MOF powder for the first time and the shortest half-life of DMNP (1.8 min) among reported MOF-based self-detoxifying fabrics. The significant photothermal enhancement in the detoxification ability of Dpa@UiO-66-NH₂ fabrics is attributed to the instantaneous heat transfer from the photothermal core to the catalytic shell and effective heat retention enabled by the surrounding polymer matrix. The Dpa@UiO-66-NH₂ fabrics can be easily prepared on a large scale and demonstrate efficient protection against DMNP aerosols as stand-alone gas filters. This strategy of photothermally enhanced catalytic detoxification can be feasibly extended to other catalytic detoxification systems and holds promise for next-generation gas masks.

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes (II)

An updated comprehensive review to help researchers understand nanozymes better and in turn to advance the field.

Scalable, room temperature, and water-based synthesis of functionalized zirconium-based metal–organic frameworks for toxic chemical removal

An inexpensive, environmentally benign and scalable strategy was developed to synthesize UiO-66 derivatives in water at room temperature.

Rapid Capture and Hydrolysis of a Sulfur Mustard Gas in Silver-Ion-Exchanged Zeolite Y

Sulfur mustard gas, also called HD, is one of the main chemical warfare agents and has claimed thousands of lives and left many more contaminated. The development of functional materials to promptly capture and detoxify sulfur mustard within a few minutes is extremely important to save the lives of the affected people. This has motivated us to explore excellent detoxification systems that can be deployed in the field to rapidly capture and hydrolyze mustard gas in a short time. To that end, we present a silver-ion-exchanged zeolite Y [(Ag⁺) _n@Y, n = 5, 13, 21, 32, 43, and 55] that can rapidly capture mustard gas and its simulant (2-chloroethyl ethyl sulfide, CEES) in ambient conditions to enable the prompt hydrolysis of the CEES captured in its nanopores. The capture and hydrolysis ability of Ag⁺@Y positively correlated with its number of Ag⁺ ions. In addition, 70% of CEES (2.5 μL in 1 mL) was captured by (Ag⁺)₅₅@Y within 20 min at 25 °C in ambient conditions. Moreover, 100% CEES (2.5 μL in 1 mL aqueous ethanol cosolvent) was hydrolyzed in 1 min at 25 °C. The efficiency of Ag⁺@Y in capturing and hydrolyzing CEES as well as mustard gas is thus a system with high detoxification efficiency for this dangerous chemical warfare agent.

Innovative Biocatalysts as Tools to Detect and Inactivate Nerve Agents

Pesticides and warfare nerve agents are frequently organophosphates (OPs) or related compounds. Their acute toxicity highlighted more than ever the need to explore applicable strategies for the sensing, decontamination and/or detoxification of these compounds. Herein, we report the use of two different thermostable enzyme families capable to detect and inactivate OPs. In particular, mutants of carboxylesterase-2 from Alicyclobacillus acidocaldarius and of phosphotriesterase-like lactonases from Sulfolobus solfataricus and Sulfolobus acidocaldarius, have been selected and assembled in an optimized format for the development of an electrochemical biosensor and a decontamination formulation, respectively. The features of the developed tools have been tested in an ad-hoc fabricated chamber, to mimic an alarming situation of exposure to a nerve agent. Choosing ethyl-paraoxon as nerve agent simulant, a limit of detection (LOD) of 0.4 nM, after 5 s of exposure time was obtained. Furthermore, an optimized enzymatic formulation was used for a fast and efficient environmental detoxification (>99%) of the nebulized nerve agent simulants in the air and on surfaces. Crucial, large-scale experiments have been possible thanks to production of grams amounts of pure (>90%) enzymes.

Defective Metal-Organic Frameworks

The targeted incorporation of defects into crystalline matter allows for the manipulation of many properties and has led to relevant discoveries for optimized and even novel technological applications of materials. It is therefore exciting to see that defects are now recognized to be similarly useful in tailoring properties of metal-organic frameworks (MOFs). For instance, heterogeneous catalysis crucially depends on the number of active catalytic sites as well as on diffusion limitations. By the incorporation of missing linker and missing node defects into MOFs, both parameters can be accessed, improving the catalytic properties. Furthermore, the creation of defects allows for adding properties such as electronic conductivity, which are inherently absent in the parent MOFs. Herein, progress of the rapidly evolving field of the past two years is overviewed, putting a focus on properties that are altered by the incorporation and even tailoring of defects in MOFs. A brief account is also given on the emerging quantitative understanding of defects and heterogeneity in MOFs based on scale-bridging computational modeling and simulations.

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.