Interfacial Confinement Enables Dual Hosting of Sulfur Mustard and Mustard Sulfoxide in NU-1000

Abstract

Zirconium-based metal–organic frameworks have emerged as promising materials for the capture and detoxification of chemical warfare agents, but the molecular mechanism by which a hierarchical MOF differentiates a hydrophobic reactant from its oxidized product remains incompletely understood. Here, we use molecular dynamics simulations, grand-canonical Monte Carlo adsorption calculations, and periodic density functional theory to examine the dual-hosting behavior of NU-1000 toward sulfur mustard (HD) and mustard sulfoxide (HDO). Rather than treating NU-1000 only as an adsorbent or oxidation catalyst, we resolve how its internal micropore, mesopore, and c-pore interfaces impose distinct confinement environments on reactant and product species. Density functional theory (DFT) calculations show that HD binds most favorably in the c-pore region, with a binding energy of approximately −12.5 kcal/mol, and similarly favorable stabilization in confined micropore environments, whereas substantially weaker binding is observed in the mesopore. Molecular dynamics simulations also reveal sharply different pore residence patterns: HD localizes predominantly in micropores, occupying this region for ∼80% of the trajectory, while HDO samples larger pore environments more broadly, with ∼45% mesopore and ∼34% c-pore occupancy. This pore-selective behavior persists under mixed HD/HDO coadsorption conditions, demonstrating that reactant–product differentiation is intrinsic to the NU-1000 pore network rather than an artifact of isolated single-component simulations. Radial distribution functions further show that HD is stabilized by dispersion-dominated confinement and weak halogen–hydrogen contacts, whereas HDO is governed by more localized, orientation-dependent interactions with hydrated zirconium node sites. These interaction differences produce a pronounced transport asymmetry, with HDO exhibiting a self-diffusion coefficient of 10.6 ± 2.11 × 10^–10 m²/s compared with 0.5 ± 0.09 × 10^–10 m²/s for HD at comparable loading. The results identify NU-1000 as a dual-function molecular host that couples reactant retention with product mobility, providing an interface-level mechanism relevant to selective CWA detoxification and confined transport in hierarchical porous catalysts.