Manipulation of the Nanoarchitecture of Porous Media Determines Water Mobility: NMR Experiments using Metal–Organic Framework (MOF)-Functionalized Track-Etched Solid-State Nanochannels (SSNs)

Abstract

Transport in hierarchically porous membranes depends on pore organization at the mesoscale, yet how this organization shapes local dynamics remains poorly understood. Herein, we employ single-sided nuclear magnetic resonance (SS-NMR) to probe the in situ diffusion dynamics of water within solid-state nanochannels (SSNs) functionalized with UiO-66 metal–organic framework (MOF). We systematically compare two distinct synthetic protocols: a one-pot (OP) interfacial growth and a counter-diffusion (CD) method. By deconvoluting the NMR signal attenuation, we isolate a minor slow diffusion component corresponding to intraparticle micropores and a dominant fast diffusion component representing interparticle constructional porosity. Our results show that OP growth produces large particle agglomerates and poorly connected pores with narrow bottlenecks, forcing water along highly tortuous paths. Furthermore, leveraging the pH-responsive surface charge of UiO-66, we find that water mobility in the well-connected CD nanoarchitecture varies measurably with pH, consistent with a surface-charge effect, whereas OP membranes show a weaker, nonmonotonic variation, consistent with dominant geometric obstruction. These findings link nanochannel architecture directly to local water mobility and identify constructional porosity as a structural parameter to consider in MOF-based nanofluidic membranes.