ADSORPTION AND MECHANISTIC STUDIES OF DIMETHYL METHYLPHOSPHONATE FOR CWA DEFEAT
Huynh, Kim Lien
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This thesis work systematically investigated carefully designed ASZM- TEDA deconstruction–reconstruction experiments. Our objective is to understand the role of each impregnant, the factors that influence filter performance, and filter lifetime. Chemical warfare agent simulant, dimethyl methylphosphonate (DMMP), is used to evaluate the adsorption properties and reactivity of different materials using a temperature programmed desorption (TPD)/quantitative 1H-NMR method, combined with inductively coupled plasma-atomic emission spectroscopy (ICP- AES) bulk analysis. Our investigation begins with a full analysis of the current commercial gas mask filter, ASZM-TEDA. In Chapter 2, studies with ordered mesoporous carbons (OMCs) and a disordered microporous carbon (BPL) reveal that surface area and pore volume dictate total adsorption loading. It was also discovered that an ordered pore network would lead to higher DMMP desorption energies by 30–40%, confirming stronger binding to the carbon surface in pores ≤2.4 nm. In Chapter 3, our investigation of an ASZM-TEDA deconstructed analog, carbon/CuO, further our understanding of CuO functionality within the adsorbent. Our study reveals that CuO impregnation increases adsorption capacity (up to 64%) in comparison to native carbon adsorbents. The CuO surface activity (reported as DMMP area capacity) was over 3.5 times higher in comparison to the OMCs (0.075–0.078 m2 g-1), and 17 times higher than BPL (0.016 m2 g-1). In addition, the extent of DMMP decomposition is greater for nano sized endo-pore CuO relative to larger exo-pore CuO particles. In Chapter 4, ordered mesoporous metal oxides (OMMs) are described with more reactive sites and designed to presumably have better mass transfer into the pores in comparison to impregnated carbons. DMMP chemisorption to the metal oxide reactive sites allow for greater decomposition (reported as the decomposed DMMP capacity), which is 2 to 4 times higher for the OMMs in comparison to OMC. TPD measurements for meso-Al2O3 and meso-Fe2O3 suggest that DMMP conversion to methanol is roughly one-to-one, whereas meso-TiO2 undergoes greater decomposition with the cleavage of a second methoxy group. It was also discovered that meso-Al2O3 achieved the highest DMMP total volume capacity in comparison to the other materials, making it the most efficient adsorbent studied for CWA defeat.