(199f) Pore Level Decomposition of Adsorption Isotherms in Metal Organic Frameworks

Metal Organic Frameworks (MOFs) demonstrate a variety of unique features due to their ability to selectively adsorb and retain guest molecules from gas and liquid phases. Adsorption properties are directly related to the specifics of the pore structure. A better understanding between the MOF structural parameters and adsorption properties is required for the guided design of novel MOFs and their modifications for advanced applications. MOFs are considered as nanoporous crystals processing regular 3-dimensional pore networks composed of pore compartments than differ in size, shape and chemistry. Here, we present a Monte Carlo (MC) simulation methodology for decomposition of the adsorption isotherm into the fingerprint isotherms, which reflect adsorption in individual pore compartments [1]. We consider two characteristic MOF structures, PCN-224 and ZIF-412, for which the distribution of adsorbate between the individual pore compartments was studied experimentally using adsorption crystallography based on in-situ XRD [2]. The pore network in PCN-224 represents a cubic network of alternating micropore channels and junctions of size 1.5 and 2.5 nm. The pore network in ZIF-412 has a complex micro-mesopore structure with three type, with pores of ca. 2.1, 2.5, and 3.9 nm. Employing MC simulation, we constructed the adsorption isotherms of three most common adsorbate probes (argon, carbon dioxide and nitrogen) in the ideal crystallographic models of PCN-224 and ZIF-412 and decomposed them into the fingerprint isotherms for the individual pore compartments. The results of simulation are found in qualitative agreement with the experimental data [2]. This work is motivated by the need of novel pore structure characterization methods, which account for the multiplicity of morphologies of different families of MOFs. Comparison of the reference fingerprint isotherms with the experimental adsorption isotherms allows to assess to what extend the structure of the practical sample differs from that of the ideal crystal due various types of defects, residual solvents, degree of hydration, pore blockage, etc.

This work is supported by the National Science Foundation (CBET grant no. 1834339)

1. Dantas, S.; Neimark, A. V., Coupling Structural and Adsorption Properties of Metal-Organic Frameworks: From Pore Size Distribution to Pore Type Distribution. ACS Appl Mater Interfaces 2020, 12 (13), 15595-15605.
2. Cho, H. S.; Yang, J.; Gong, X.; Zhang, Y. B.; Momma, K.; Weckhuysen, B. M.; Deng, H.; Kang, J. K.; Yaghi, O. M.; Terasaki, O., Isotherms of individual pores by gas adsorption crystallography. Nature Chemistry 2019.