(30d) Design of Stratified Metal Organic Frameworks for Chemical Warfare Agent Concentration and Destruction
There is a pressing need for next generation materials for protection against chemical warfare agents and other toxic chemicals. The ideal material would be capable of rapidly detecting and destroying toxic species. Stratified metal-organic frameworks (MOFs) containing catalytic particles may be able to meet this need. Stratified MOFs consist of layered materials having different functional groups in each layer. This creates a gradient to direct transport of dilute target analytes to the center of the MOF, where an embedded catalyst particle could destroy it. The goal of our work is to develop a detailed understanding of the fundamental properties of sorption and transport of target chemical species in stratified MOF-nanocatalyst systems. The first step to achieve this is to design, synthesize, and evaluate functionalized MOFs that exhibit differential binding of analytes. We use quantum mechanical methods to identify functional groups for binding target species, Monte Carlo methods to perform fluid adsorption isotherms, and ab initio molecular dynamics to explore various binding sites. We use classical molecular dynamics to characterize the mobility of analytes in the MOF strata. In complimentary experiments, we synthesize robust UiO-67 based MOFs with specific functional groups, measure isotherms of target molecules to compare with calculations, and use temperature programmed desorption to verify loading and binding energies of target molecules. Our calculations accurately predict sorption energies for dimethyl methylphosphonate (a common chemical warfare agent simulant) on the MOFs, as verified by temperature programmed desorption. We observe no reactions between dimethyl methylphosphonate and the MOFs in contrast to previous literature accounts.