(560fs) Advancement of Nerve-Agent Filters, Polyoxometalates, By Utilizing a Correlated Multimodal Approach

Development of technologies for efficient protection against nerve agents is critically important. Recently, polyoxometalates (POMs) have attracted attention as potential catalysts for nerve-agent decomposition. The improvement of their effectiveness in real operating conditions requires an atomic-level understanding of nerve-agent decomposition at the gas-solid interface. Several challenges limit our understandings, including 1) dynamic changes of the structures of both catalysts and agents, 2) uncertainty in the nature of structural/functional units where the reactions occur, 3) scarcity of experimental methods that are sensitive to changes that may occur in the several interacting parts of these complex systems, and 4) the need to bring this research to relevant environmental conditions, where the sensitivity of many characterization techniques is particularly limited. We tackled these challenges by utilizing a multi-modal approach specific for gas surface reactions, combining synchrotron X-ray absorption and scattering with electron and vibrational spectroscopies and density functional theory calculations, to investigate a reaction of gaseous DMCP, a nerve agent simulant, with a Zr-based POM. We were able to detect the changes both in the Zr-POM and agent/simulant, determine the active sites or structural/functional units responsible for the agent/simulant decomposition, and address the question of the quality of DMCP as a GB simulant, by comparing results of their multimodal investigation by complementary techniques. We also present our findings on a one-dimensional polymeric polyniobate (P-PONb), K₁₂[Ti₂O₂][SiNb₁₂O₄₀]·19H₂O (KSiNb) for the decomposition of DMCP. Raman spectroscopy and DRIFTS data indicate the adsorption and decomposition of DMCP on KSiNb. Ti K-edge and Nb K-edge XAFS data of DMCP exposed KSiNb samples shows that while the Ti linkage keeps intact, the shortest Nb-O bonds are the ones most responsive to the interaction with DMCP. These measurements provide further information for theoretical modeling. Results of the in situ XAFS, Raman, and DRIFTS data, aimed at studying kinetics of the simulant-POM interaction, will be presented.