Functionalized Metal-organic Frameworks for Chemical Warfare Agent Mitigation

Abstract

Chemical warfare agents (CWAs), including nerve and blister agents, pose persistent threats due to their extreme toxicity and environmental stability. The development of structurally-defined, tunable materials capable of rapid and selective detoxification remains a critical challenge. Organophosphate simulants such as dimethyl p-nitrophenyl phosphate (DMNP) and sulfur mustard simulants such as 2-chloroethyl ethyl sulfide (CEES) provide accessible and representative platforms for probing degradation pathways under controlled laboratory conditions. DMNP undergoes hydrolytic degradation at metal-oxo active sites, whereas CEES primarily interacts through adsorption and surface-mediated processes, with photooxidation emerging as an additional robust pathway in photoactive MOF systems. Metal-organic frameworks (MOFs), with their tunable structure and accessible active sites, provide a platform to investigate how these pathways can be modulated through targeted structural design. This dissertation examines the role of metal node composition and linker photophysics in controlling reactivity across both hydrolysis and photooxidation pathways. In solvent-free DMNP hydrolysis, catalytic performance is highly sensitive to metal identity and composition. Multi-metal functionalization of MOF-808 reveals that reactivity does not show a trend with individual metals but instead suggest cooperative interactions with certain metals. For example, Cu@MOF-808 (~81% conversion) and Mo@MOF-808 (~41% conversion) individually exhibit moderate activity, while the bimetallic CuMo@MOF-808 system achieves significantly enhanced performance (~95% conversion), suggesting synergistic effects between metal centers. In contrast, CEES reactivity across these systems is primarily governed by adsorption and surface-mediated interactions, with performance more closely linked to framework accessibility than to metal identity. Further investigation of Ag incorporation demonstrates that catalytic performance is controlled by the balance between metal-induced functionality and accessibility. Low Ag loading (~0.4 wt%) enhances DMNP hydrolysis (~85% conversion) without restricting access to active sites, whereas higher loadings lead to reduced activity due to pore blockage and aggregation. Partial recovery at the highest loadings suggests a transition from framework-confined reactivity to contributions from externally accessible metal domains. CEES removal across this series follows a similar non-linear trend, reflecting changes in accessibility rather than catalytic enhancement. Extension to photoactive MOFs highlights a distinct mechanistic contrast. CEES photooxidation is governed by linker excited-state properties, where heavy-atom functionalization enhances intersystem crossing and singlet oxygen generation. Pd@PCN-222 exhibits significantly faster kinetics (t1/2 ~4.6 min) compared to PCN-222 (t1/2 ~58 min), and similar enhancements are observed for Pd-functionalized Al-PMOF relative to its pristine analogue. Pyrene-based systems show intermediate behavior, while variations across frameworks emphasize the importance of spectral overlap between the light source and linker absorption. In contrast, DMNP hydrolysis under solvent/base-free conditions remains limited across MOF platforms, suggesting that restricted mass transport and limited accessibility to active sites play a significant role in constraining reactivity. Finally, chapter 5 presents a comprehensive review of MOFs for chemical warfare agent detoxification, integrating mechanistic insights into hydrolysis and photooxidation with advances in active-site engineering and processable material formats for practical applications. Overall, the results from chapters 2‒4 demonstrate that MOF reactivity is likely influenced by the interplay between catalytic site composition, pore accessibility, and linker photophysics, depending on the targeted degradation pathway. These findings provide guidance for design principles for integrating multiple detoxification mechanisms within a single material platform and provide a foundation for the rational development of MOFs for chemical agent mitigation under realistic conditions.