In Situ Probes of Capture and Decomposition of Chemical Warfare Agent Simulants by Zr-Based Metal Organic Frameworks

Abstract

New materials for the rapid decomposition of chemical warfare agents (CWAs) are in high demand for protecting military and civilian populations from these weapons of mass destruction. The need for novel sorbents and decontamination catalysts has gained great urgency as terrorists groups demonstrate the ability to synthesize and deploy agents in chemical attacks. Although many new materials, such as metal-organic frameworks (MOFs), have been proposed to use as CWA filtration media, their eventual transition requires a detailed understanding of the atomic-scale reaction mechanisms. Zr-based MOFs were recently shown to be among the fastest catalysts of nerve-agent hydrolysis reaction in solution. We show the results of a detailed study of the adsorption and decomposition of a nerve-agent simulant, dimethyl methylphosphonate (DMMP), on UiO-66, UiO-67, MOF-808 and NU-1000 MOFs (that have different pore sizes and connectivities) using synchrotron-based X-ray powder diffraction, X-ray absorption and infrared spectroscopies, which reveals key aspects of the reaction mechanism.[1] This study describes the implementation of a newly developed experimental setup for delivering vaporized DMMP to a reaction cell containing a MOF sample. The diffraction measurements indicate that all four MOFs adsorb DMMP (introduced at atmospheric pressures through a flow of helium or in air) within the pore space. In addition, the combination of X-ray absorption and infrared spectra suggests direct coordination of DMMP to the Zr 6 cores of all MOFs and its subsequent decomposition to phosphonate products. Further, we show that DMMP is actively adsorbed from air with good selectivity, even in the presence of humidity or other ambient gases, demonstrating that Zr 6-based MOFs may serve as effective sorbents for CWAs under ambient conditions. These experimental probes into the mechanism of adsorption and decomposition of chemical warfare agent simulants on Zr-based MOFs open new opportunities for rational design of new and superior decontamination materials.

Presence versus Proximity: The Role of Pendant Amines in the Catalytic Hydrolysis of a Nerve Agent Simulant

“…In addition to the promising activity demonstrated by UiO‐66 and its amino functionalized derivative, we have also shown that using UiO‐67 (Figure ), a MOF which is isostructural to UiO‐66 but contains 4,4′‐biphenyldicarboxylic acid linkers and larger pores, results in a further enhancement in hydrolysis reaction rate compared to UiO‐66 (Figure and Table ) . This reaction rate enhancement is to be expected given that diffusion of the simulant DMNP in UiO‐67 is expected to be faster compared to that in UiO‐66 . Since primary amines have been shown to have a favorable effect on DMNP hydrolysis and the apertures of UiO‐67 are known to promote DMNP diffusion, the next step was to test the activity of amine functionalized UiO‐67 against DMNP.…”

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

“…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. However, it does not contain the P−F bond that is broken during sarin hydrolysis, and is therefore not as effective for mimicking reactivity .…”

Presence versus Proximity: The Role of Pendant Amines in the Catalytic Hydrolysis of a Nerve Agent Simulant

“…[13] Among the linker-appended functional groups screened, primary amine bearing MOFs have shown unprecedented activity in the hydrolysis of DMNP.W eh ave demonstrated that, while keeping other factors constant, installing aprimary amine group on the benzene-1,4-dicarboxylic acid (BDC) linkers of UiO-66 ( Figure 1) can accelerate the catalytic hydrolysis of DMNP by 20 times compared to the parent UiO-66 ( Figure 2a nd Table 1). [14] Since primary amines have been shown to have af avorable effect on DMNP hydrolysis and the apertures of UiO-67 are known to promote DMNP diffusion, the next step was to test the activity of amine functionalized UiO-67 against DMNP.I ts hould be noted that we previously tested the activity of UiO-67m-NH 2 for DMNP hydrolysis at ac atalyst loading of 6mol %. [9, 12a] This reaction rate enhancement is to be expected given that diffusion of the simulant DMNP in UiO-67 is expected to be faster compared to that in UiO-66.…”