Browsing by Author "Plonka, Anna M."

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    Atomic resolution tracking of nerve-agent simulant decomposition and host metal-organic framework response in real space
    Terban, Maxwell W.; Ghose, Sanjit K.; Plonka, Anna M.; Troya, Diego; Juhas, Pavol; Dinnebier, Robert E.; Mahle, John J.; Gordon, Wesley O.; Frenkel, Anatoly I. (2021-01-04)
    Gas capture and sequestration are valuable properties of metal-organic frameworks (MOFs) driving tremendous interest in their use as filtration materials for chemical warfare agents. Recently, the Zr-based MOF UiO-67 was shown to effectively adsorb and decompose the nerve-agent simulant, dimethyl methylphosphonate (DMMP). Understanding mechanisms of MOF-agent interaction is challenging due to the need to distinguish between the roles of the MOF framework and its particular sites for the activation and sequestration process. Here, we demonstrate the quantitative tracking of both framework and binding component structures using in situ X-ray total scattering measurements of UiO-67 under DMMP exposure, pair distribution function analysis, and theoretical calculations. The sorption and desorption of DMMP within the pores, association with linker-deficient Zr6 cores, and decomposition to irreversibly bound methyl methylphosphonate were directly observed and analyzed with atomic resolution. Metal-organic frameworks have been shown to adsorb and decompose chemical warfare agents, but their mechanism of action is not completely understood. Here the authors quantitatively track the binding and decomposition product structures of nerve-agent simulant dimethyl methylphosphonate in host UiO-67 through in situ X-ray total scattering measurements, pair distribution function analysis, and density functional theory calculations.
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    Atomic-Level Structural Dynamics of Polyoxoniobates during DMMP Decomposition
    Wang, Qi; Chapleski, Robert C. Jr.; Plonka, Anna M.; Gordon, Wesley O.; Guo, Weiwei; Thuy-Duong Nguyen-Phan; Sharp, Conor H.; Marinkovic, Nebojsa S.; Senanayake, Sanjaya D.; Morris, John R.; Hill, Craig L.; Troya, Diego; Frenkel, Anatoly I. (Springer Nature, 2017-04-10)
    Ambient pressure in situ synchrotron-based spectroscopic techniques have been correlated to illuminate atomic-level details of bond breaking and formation during the hydrolysis of a chemical warfare nerve agent simulant over a polyoxometalate catalyst. Specifically, a Cs-8[Nb6O19] polyoxoniobate catalyst has been shown to react readily with dimethyl methylphosphonate (DMMP). The atomic-level transformations of all reactant moieties, the [Nb6O19](8)-polyanion, its Cs+ counterions, and the DMMP substrate, were tracked under ambient conditions by a combination of X-ray absorption fine structure spectroscopy, Raman spectroscopy, and X-ray diffraction. Results reveal that the reaction mechanism follows general base (in contrast to specific base) hydrolysis. Together with computational results, the work demonstrates that the ultimate fate of DMMP hydrolysis at the Cs-8[Nb6O19] catalyst is strong binding of the (methyl) methylphosphonic acid ((M) MPA) product to the polyanions, which ultimately inhibits catalytic turnover.