(501g) Chemical Warfare Agent Hydrolysis in the Nu-1000 Zr-MOF: Structure, Topology, and the Impact of Humidity

Metal organic frameworks (MOFs) are a class of catalysts characterized by high porosities and high surface areas that have been widely examined for various chemical applications. Many studies of these catalysts in the chemical engineering industry are aimed at gaining insight into the key characteristics of topology and defects crucial for optimizing accessibility, molecular mass transport, and reactivity of MOFs for adsorption, separation, and catalytic reaction operations. Specifically, due to their competitive adsorption properties, MOFs present as promising instruments for the decontamination of chemical warfare agents (CWAs).

Despite their favorable characteristics, small pore apertures (smaller or comparable to the molecular sizes of CWAs) and poor structural stability have hindered the practicality of MOFs in toxic species hydrolysis applications. A major roadblock in achieving the required performance for this application specifically comes with the exposure of these materials to realistic environmental conditions. Decreases in adsorption and diffusion capabilities of CWAs in MOFs are often attributed to environmental water that clusters in the pores or competes with CWAs for interactions on active sites. Recent breakthroughs have shown that Zr-based MOFs possess the structural and compositional stability required for effectively decontaminating nerve agents and simulants, however, it is unclear what characteristic properties enable efficient chemical breakdown in conditions of varying humidity. Consequently, studying how molecules interact inside different MOF structures is essential for determining what design rules result in optimized MOF functionality.

To elucidate design rules for the applicable success of these catalysts, the behavior of water and nerve agents in the NU-1000 Zr-MOF has been evaluated. With its strong node-linker bonds, expansive pores, and balanced hydrophobicity, pristine NU-1000 possesses the characteristic attributes for structural stability and hydrolytic efficiency in the presence of environmental water. Molecular dynamics (MD) simulations and density functional theory (DFT) calculations have been performed to study the role of these combined features on the binding, diffusivity, and active site accessibility of the nerve agents sarin (GB) and soman (GD) in NU-1000 under conditions of humidity. These results give insight into relationships between key topological and geometric structural effects and optimized functionalities, helping to pinpoint the ideal Zr-MOF design rules that lead to efficient hydrolysis reactions for decomposition of chemical warfare agents (CWAs).