Transport-Relevant Pore Limiting Diameter for Molecular Separations in Metal-Organic Framework Membranes
Journal
Journal of Physical Chemistry C
Journal Volume
125
Journal Issue
37
Pages
20416-20425
Date Issued
2021
Author(s)
Abstract
Metal-organic frameworks (MOFs) are an emerging class of materials for membrane gas separations. The pore limiting diameter (PLD) of a MOF, i.e., the aperture size of the material, is often used as a key structural property to evaluate its size exclusion capability for a gas mixture. The current computation of a PLD is based on the van der Waals radii outlined by the Cambridge Crystallographic Data Centre (CCDC), and this set of van der Waals radii may fail to capture the strong repulsion exerting on a guest molecule when passing through the bottleneck of a channel. In this work, we propose a new set of van der Waals radii for the framework atoms, whose values are smaller than the existing ones to describe the repulsive adsorbent-adsorbate interaction. The PLD of a MOF computed using this more transport-relevant radius set is referred to as PLDt-r, and that computed based on the widely used set outlined by CCDC is referred to as PLDCCDC. We evaluate the relevance between PLDt-r/PLDCCDC and the transport properties of MOF compounds including their diffusivity as well as diffusive and permeative selectivities for various binary mixtures. From our investigation on approximately 400 MOF structures, the results show that PLDt-r can more effectively identify highly selective MOFs for membrane gas separations. In this work, we also demonstrate the applicability of PLDt-r when the framework flexibility is considered. ? 2021 American Chemical Society.
Subjects
Binary mixtures
Gas permeable membranes
Metal-Organic Frameworks
Organic polymers
Separation
Van der Waals forces
'current
Aperture sizes
Cambridge crystallographic data centers
Gas separations
Gases mixture
Limiting diameters
Metalorganic frameworks (MOFs)
Molecular separation
Size exclusion
Van der Waals radius
Organometallics
Type
journal article