Metal-organic frameworks (MOFs) are known to be useful tools for adsorption and separation of gases. The diffusion processes of liquids into MOFs remain relatively less well understood. We aim to develop a model of liquid solute diffusion into MOF systems using quantitative electron paramagnetic resonance (qEPR) spectroscopy to measure diffusion rates into known MOF materials. We begin by confirming the impact of physical parameters such as powdering, washing, and washing method on particle size and crystallite size in order to correlate these properties to diffusion rates. Systematic studies of physical parameters for the preparation of HKUST-1 samples were performed and analyzed via x-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD patterns showed insignificant deviation from previously published patterns and were not dependent on powdering, washing, and washing method, confirming synthetic reproducibility. It has been determined using the Scherrer equation that the crystallite size ranged from 24-33 nm, independent of powdering and washing by sonication. In order to examine the diffusion of liquids into HKUST-1, the MOF was submerged in TEMPO solutions to allow HKUST-1 to adsorb the dissolved radical. The amount of TEMPO in various solvents adsorbed by HKUST-1 was measured using qEPR. Time-course qEPR experiments were conducted to examine the kinetics of diffusion of TEMPO into HKUST-1.

Studying diffusion processes of dissolved TEMPO into HKUST-1

ACS Spring 2022

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