Kinetics of Water Adsorption in UiO-66 MOF

Abstract

The diffusion mechanism and the concentration dependence of the mass transfer rate of water vapor adsorbing in the zirconium-based metal organic framework (MOF) UiO-66 has been determined using a concentration swing frequency response (CSFR) apparatus. The mechanism that best describes the adsorption of water in UiO-66 is micropore diffusion and the rate is dependent on the gas phase concentration of the water. Moreover, the results show that as the gas phase water concentration increases, a minimum in the water adsorption rate occurs near 4 mol/kg of water loading. Although the Darken relationship is unable to predict the concentration dependence, it agreed qualitatively with the experimental diffusivity data extracted from the CSFR analysis. The results demonstrate the ability of the concentration-swing frequency response technique to accurately determine adsorption rate mechanisms and quantify the adsorption kinetics of a slow to moderately fast diffusing component in MOFs.

A computational study of water in UiO‐66 Zr‐MOFs: Diffusion, hydrogen bonding network, and confinement effect

“…Despite available insights from water adsorption studies, the dynamics properties of water in UiO-66 are scattered. 26 In this work, a series of density functional theory (DFT) calculations, ab initio molecular dynamics (AIMD) and force field based classical molecular dynamics (MD) simulations have been performed to reveal the structural and diffusion properties of water in the pristine defectfree UiO-66, and their dependence on water loadings. This article is organized as following: Section 2 presents a brief introduction to the models and details to performed calculations.…”

“…Further increasing the loading could lead to the formation of water cubane clusters, 25 and water condensation in the framework. Despite available insights from water adsorption studies, the dynamics properties of water in UiO‐66 are scattered 26 . In this work, a series of density functional theory (DFT) calculations, ab initio molecular dynamics (AIMD) and force field based classical molecular dynamics (MD) simulations have been performed to reveal the structural and diffusion properties of water in the pristine defect‐free UiO‐66, and their dependence on water loadings.…”

Identification of mass transfer resistances in microporous materials using frequency response methods

“…They found more extensive modulation can be applied for the flow system, based on the excellent agreement between two experiments with very different amplitude modulation, one was the usual 5% and another was much larger, approximately 80%. Based on these approaches, a more general CSFR method has been developed theoretically and experimentally for mixture diffusion [63] and pure components (either gas or vapor) mixing with an inert gas [18,20,22,23,65,66].…”

“…By optimizing the flow rate, system volume, and adsorbent weight, the maximum frequency should not limit the kinetic measurement for moderately short-time scale systems. This apparatus was also applied to perform single-particle experiments, yielding dynamic measurements for short-time scale systems in zeolites and MOFs without the interference of heat effects and axial dispersion [22,65,79].…”

“…Also, it has the advantage of minimizing measurement errors because of its periodic process and non-dependence on initial conditions. Thus, FR has proven to be very useful for characterizing the transport of gases in adsorbent materials, such as zeolites [3][4][5][6][7][8][9][10][11][12][13][14], carbons [15][16][17][18][19][20], silicas [21], metal organic frameworks (MOFs) [22][23][24], and catalysts [25][26][27][28][29][30].…”