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

Abstract

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-NH, 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-NH) 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.

Screening for Improved Nerve Agent Simulants and Insights into Organophosphate Hydrolysis Reactions from DFT and QSAR Modeling

“…Note that the above analysis was focused entirely on Δ G TS1 as an indicator of kinetic similarity, but the relative thermodynamics (Δ G rxn ) compared to nerve agents is also relevant . If translating these results for experimental catalysis, simulant size would be another factor to consider, as smaller molecules may experience less difficulty accessing catalyst active sites . A bulky simulant such as dibenzyl chlorophosphonate (CAS RN: 538‐37‐4, Table ) may have significant difficulty diffusing into microporous catalysts, such as the UiO class of MOFs with relatively small pore diameters, and thus the degradation reaction may be limited to the exterior catalyst surface.…”

“…Further, there is little reason to believe that the current simulants used in the literature will have identical degradation behavior to all types of agents. Sometimes, using actual agents can reveal additional mechanisms not observed with simulants . For example, dimethyl methylphosphonate (DMMP) is commonly used as a simulant for GB because it exhibits similar adsorption behavior.…”

“…Sometimes, using actual agents can reveal additionalm echanisms not observed with simulants. [12] For example,dimethyl methylphosphonate (DMMP) is commonly used as as imulant [13,14] for GB becausei t exhibits similar adsorption behavior.H owever,i td oes not contain the PÀFb ond that is broken during sarin hydrolysis, and is therefore not as effective for mimicking reactivity. [15] Choosing the most appropriate simulanti sn on-trivial because it dependso nt he physical or chemical applicationo fi nterest(e.g., degradation, adsorption,o rd iffusion), but there are still many cases where researchers claim materials are activet owards CWAs based on extrapolationo fs imulantd ata alone.…”

Creation of Active Sites in MOF‐808(Zr) by a Facile Route for Oxidative Desulfurization of Model Diesel Oil

“…MOF‐808(Zr) as one member of them has received much attention due to its advantages such as high specific surface area (∼2000 m 2 /g), large pore opening, good stability and rich metal sites . These advantages make it a potential candidate in many applications such as gas storage and catalysis . As for the structure of MOF‐808(Zr), the coordination of the secondary building units (SBUs) is completed with six formate ligands, which accounts for the charge balance .…”

Air Activated Self‐Decontaminating Polydicyclopentadiene PolyHIPE Foams for Rapid Decontamination of Chemical Warfare Agents

“…Research motivated by self‐cleaning filtration media has included investigations into catalytic technologies such as polyoxometallates (POMs), metal–organic frameworks (MOFs), metal oxides, and, more recently, nucleophilic polymers . POMs, MOFs, and metal oxides are all limited in application as powders or require incorporation into a supportive structure that limits the reactive surface area.…”