In Situ Nuclear Magnetic Resonance Investigation of Molecular Adsorption and Kinetics in Metal–Organic Framework UiO-66

Abstract

Thermodynamic and kinetic properties of molecular adsorption and transport in metal-organic frameworks (MOFs) are crucially important for many applications, including gas adsorption, filtration, and remediation of harmful chemicals. Using the in situ ¹H nuclear magnetic resonance (NMR) isotherm technique, we measured macroscopic thermodynamic and kinetic properties such as isotherms and rates of mass transfer while simultaneously obtaining microscopic information revealed by adsorbed molecules via NMR. Upon investigating isopropyl alcohol adsorption in MOF UiO-66 by in situ NMR, we obtained separate isotherms for molecules adsorbed at distinct environments exhibiting distinct NMR characteristics. A mechanistic view of the adsorption process is obtained by correlating such resolved isotherms with the cage structure effect on the nucleus-independent chemical shift, molecular dynamics such as the crowding effect at high loading levels, and the loading level dependence of the mass transfer rate as measured by NMR and elucidated by classical Monte Carlo simulations.