Year: 2026
Type: preprint
Abstract: For analytic determination of the isosteric heats of adsorption, Qst, in microporous crystalline materials such as metal-organic frameworks (MOFs) and zeolites, it is common practice to fit experimental data of unary isotherms at different temperatures using Virial fits, with a total of 12 parameters. The Virial fits of unary isotherms, however, do not allow calculations of adsorption selectivities using the Ideal Adsorbed Solution Theory (IAST). The main objective of this article is to demonstrate that a better approach is to fit the unary isotherms at different temperatures using the Dual-Site Langmuir-Freundlich (DSLF) model in which the saturation capacities and Freundlich exponents are constrained to be T-independent, and requiring a total of 8 parameters. The DSLF fits allow analytic determination of Qst, and may also be used in IAST calculations. Examination of published experimental data on unary isotherms for several guest/host combinations shows that the Virial and DSLF fits are of comparable accuracy, despite the fact that significantly fewer parameters are required for DSLF fits. Also, the Qst vs loading characteristics of the Virial and DSLF fits are distinctively different. The overall conclusion to be drawn is that DSLF fits with T-independent saturation capacities, and Freundlich exponents are generally to be preferred to Virial fits.
Source: ChemRxiv
Author: Rajamani Krishna
Institution: University of Amsterdam
Language: English
Subfield: Inorganic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7204956033