Vapor-Like Water in the NU-1000 Zr-MOF: A Molecular Level Understanding of Balanced Hydrophobicity in Humid Conditions

While the structural features and tunability of metal-organic frameworks (MOFs) make them promising materials for chemical warfare agent (CWA) hydrolysis, their stability and performance in conditions of varying humidity is an unsolved challenge. Understanding what design rules enable lasting hydrolytic functionality in evolving field conditions is consequently essential to developing practical MOFs for such applications. In this work, molecular dynamics simulations are carried out to examine the behavior of water at various loadings in the Zr-based MOF NU-1000. 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. Adsorption and residence time results reveal that while NU-1000 is hydrophilic enough to allow water to adsorb, internal hydrophobicity discourages the distribution of H2O molecules to active sites at the metal nodes. Water-water interactions take precedence in NU-1000, forming a water cluster that grows with loading and distracts individual molecules from diffusing throughout the framework. On the other hand, self-diffusion coefficients and radial distribution function patterns suggest a lack of hydrogen bonding, with the clustered molecules having faster diffusion and less ordering than that of liquid-phase water. The limited interactions between water and the metal nodes indicate a lower likelihood of competition for sites impeding target species hydrolysis in NU-1000. Additionally, the partially vapor structural state of the aggregated water molecules in the expansive NU-1000 channels indicates a lower likelihood of pore filling by water that interferes with target species adsorption and diffusion. Such results evidence a strong potential of the NU-1000 Zr-MOF for superior performance in hydrolysis applications like toxic chemical decomposition.

Automated summary

This study investigates the behavior of water in the Zr-based MOF NU-1000 under different loadings using molecular dynamics simulations. The results suggest that NU-1000, with its structural stability and hydrolytic efficiency, has the potential for effective water adsorption and decomposition of hazardous species in hydrolysis applications such as chemical warfare agent disposal.