Metal–Organic Frameworks as Catalysts and Catalysts Supports for the Detoxification of Chemical Warfare Agent Simulants

Buru, Cassandra Terez

doi:https://doi.org/10.21985/n2-c811-9b88

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Metal–Organic Frameworks as Catalysts and Catalysts Supports for the Detoxification of Chemical Warfare Agent Simulants

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The continued existence and use of chemical warfare agents (CWAs) have necessitated the development of materials which can safely and efficiently decontaminate these toxic chemicals in an environmentally benign fashion. Among the most prevalent CWAs, nerve agents (sarin, VX) and blistering agents (sulfur mustard [HD]) are considered the most toxic and most effective, respectively. Metal oxide materials have been identified as promising materials for the hydrolysis of organophosphorus nerve agents, a pathway not easily accessible for HD due to limited water solubility. Rather, the selective oxidation of HD to the sulfoxide is a more practical route. An ideal catalyst would be able to perform both reactions. To this end, we have identified multifunctional metal–organic frameworks (MOFs), composed of metal oxide-like nodes connected via organic linkers, as a promising platform for the simultaneous decontamination of nerve and blistering agents. This thesis interrogates two different approaches for installing functionality in MOFs to perform sulfide oxidation while maintaining the metal oxide-like nodes for hydrolysis. In the first approach, the linkers of the MOFs were used as photosensitizers for the generation of singlet oxygen and subsequent oxidation of HD and its simulant. By using linkers with higher quantum yield, the reactivity of the system was improved. In the second approach, encapsulated species were installed to make use of the MOF porosity. Specifically, guest polyoxometalate (POM) molecules are immobilized within the channel-type pores. POMs are discrete anionic metal oxide clusters which can undergo reversible multi-electron redox reactions for catalysis, but suffer from low-surface area and instability under catalytic conditions when used homogeneously. The hierarchical channel-type MOF allowed for POM absorption without compromising the stability or porosity of the composite, unlike previous POM@MOF examples. Dependent on the activation conditions, the POM guest was found in one of two locations within the MOF; the mechanism of this movement will be discussed. The composite POM@MOF material exhibited enhanced reactivity in the oxidation of a mustard gas simulant using hydrogen peroxide. Finally, this technique was used to immobilize an aerobically active POM in a MOF to achieve efficient aerobic sulfide oxidation.

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