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

R Wang and KH Shi and J Liu and RQ Snurr and JT Hupp, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 145, 13979-13988 (2023).

DOI: 10.1021/jacs.3c03708

Zirconium-basedmetal-organic frameworks (MOFs)are candidatematerials 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-MOFscan only be accessed by diffusion into the crystal interior. Therefore,the transport of nerve agents in nanopores is an important factorin the catalytic performance of Zr-MOFs. Here, we investigated thetransport 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. ConfocalRaman microscopy was used to monitor the transport of DMMP vapor throughindividual 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, assistsDMMP diffusion; indeed, the transport diffusivity (D (t)) of DMMP in NU-1008 is one order of magnitude higherat 70% than 0% RH. To understand the mechanism, magic angle spinningNMR and molecular dynamics simulations were performed and suggestedthat high water content in the channels prevents DMMP from hydrogen-bondingwith the nodes, allowing for faster diffusion of DMMP in the channels.The simulated self-diffusivity (D (s)) ofDMMP is observed to be concentration-dependent. At low loading ofDMMP, D (s) is higher at 70% RH than 0% RH,while at high loadings the trend reverses due to the DMMP aggregationin water and the reduction of free volume in channels.

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