Impact of Molecular Clustering inside Nanopores on Desorption Processes

Abstract

Understanding the sorption kinetics of nanoporous systems is crucial for the development and design of novel porous materials for practical applications. Here, using a porous coordination polymer/quartz crystal microbalance (PCP/QCM) hybrid device, we investigate the desorption of various vapor molecules featuring different degrees of intermolecular (hydrogen bonding) or molecule-framework interactions. Our findings reveal that strong intermolecular interactions lead to the desorption process proceeding via an unprecedented metastable state, wherein the guest molecules are clustered within the pores, causing the desorption rate to be temporarily slowed. The results demonstrate the considerable impact of the chemical nature of an adsorbate on the kinetics of desorption, which is also expected to influence the efficiency of certain processes, such as desorption by gas purge.

Langmuir–Blodgett Films of the Metal–Organic Framework MIL-101(Cr): Preparation, Characterization, and CO2 Adsorption Study Using a QCM-Based Setup

“…Previous studies also showed that QCM experiments performed with drop-cast films (deposited MOF mass 3-7 g) could be used to study the kinetics of the desorption processes of guest molecules from the pores of different MOFs. 31 LB films obtained at the best working conditions tested (MIL-101(Cr) + 1% BA) were then deposited onto QCM substrates at 12 mN·m -1 for CO 2 adsorption studies. The change in the resonant frequency after the deposition of the film was first used to determine the mass of MOF deposited using the Sauerbrey equation, 32 f = -C f ·m, where f is the observed frequency change in Hz, C f is the sensitivity factor of the QCM crystal (0.1834 Hz·ng -1 ·cm 2 ) provided by Inficon and m is the change in mass per unit area.…”

Influence of adsorption thermodynamics on guest diffusivities in nanoporous crystalline materials

“…78 A further consequence of molecular clustering is that in concentration regions where 1/G i > 1, eqn (4) and (6) would yield the hierarchy of this unusual hierarchy is found for diffusion of methanol and ethanol in ZIF-8. 88 Tsotsalas et al 89 have investigated the kinetics of desorption of 1-butanol, diethyl ether, and n-pentane in CuBTC and found that molecular clustering effects, along with 1/G i > 1, provide an explanation for unusual desorption behaviours.…”

Theoretical model estimation of guest diffusion in metal–organic frameworks (MOFs)

“…These applications involve a process whereby the guest molecules diffuse in a spatial confinement on a length-scale below 1 nm and in a full flexible framework with breathing and gate-opening effects [1]. The diffusion rate influences the exchange phenomena between the host materials and the surroundings and influences the performance of MOFs' in their various applications [2][3][4]. Therefore, investigating guest diffusion within a MOF framework is an in demand research focus.…”