Despite broad condemnation across the globe and international agreements prohibiting their use, organophoshpate-based chemical warfare agents (CWAs) remain a danger. Recently, some zirconium-based members of the class of porous, crystalline materials known as metal-organic frameworks (MOFs) have demonstrated efficient catalytic degradation of CWAs. Two approaches have been used to enhance CWA hydrolysis by MOFs: synthesizing MOFs with different ligands or metal centers that improve hydrolysis, or by promoting defective sites at the secondary building unit where catalytic conversion takes place. Density functional theory (DFT) calculations indicate the mechanism involves binding of the CWA to the metal center followed by hydrolysis of the phosphoester bond resulting in agent degradation. Herein, we report three studies on the degradation of the CWA simulant dimethyl-4-nitrophenyl phosphate (DMNP) using the Zr<sup>IV</sup> based MOF UiO-66 (UiO = University of Oslo). First, we utilize iodine functionalized UiO-66 where the iodine atom creates a halogen bonding interaction with the phosphoester linkage allowing for four times more rapid hydrolysis compared to native UiO-66. A second method involves incorporation of multivariate functional groups into the same MOF (MTV-UiO-66) and through a synergistic ligand effect, these materials degrade the CWA simulant at a rate of three times faster than the parent single ligand MOFs. Third, we hybridize UiO-66 and polyamides into composites that display the CWA catalytic degradation property of MOFs and the robustness of the polymers. Given their utility, ubiquity, and facile preparation, polyamides are a natural choice for preparation of covalent composites with MOFs. The covalent hybrid material demonstrated nearly an order of magnitude higher catalytic activity for the breakdown of a chemical warfare simulant DMNP compared to MOFs that are non-covalently, physically entrapped in PA-66, highlighting the importance of MOF-polymer hybridization.

Metal-organic frameworks and the degradation of chemical warfare agent simulants

2019 Fall National Meeting

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