The role of accessibility in the characterization of porous solids and their adsorption properties

Abstract

This paper addresses the role of accessibility for adsorption in porous solids on the adsorption properties including Henry constant, adsorption isotherms and isosteric heat of adsorption. The relevant parameters are the accessible volume, the accessible geometrical surface area and the accessible pore size and its associated volume. This concept will be demonstrated to be important and calls for the need to consider adsorption characteristics in the most coherent and consistent manner. It is particularly reinforced by the limitations inherent in the conventional ways in determining the void volume, surface area and pore size. We provide a number of examples to support this; the challenge that faces us is the development of consistent experimental procedures to determine these accessible quantities. We define the accessible pore size as the size of the largest sphere that rests on three closest solid atoms in such a manner that any probe particle residing in that sphere would have a non-positive solid-fluid potential energy. For each accessible pore size there is an associated accessible pore volume, giving rise to a new accessible pore size distribution (APSD). This is distinct from the classical pore size distribution commonly used in the literature, and in our definition of accessible pore size, a zero pore size is possible. It is also emphasized that the accessible quantities that we introduce here are dependent on the choice of molecular probe, which is entirely consistent with the concept of molecular sieving.

Computational structure characterisation tools in application to ordered and disordered porous materials

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A comprehensive analysis of the BET area for nanoporous materials

“…Surface area characterization using the BET method is essentially an empirical procedure that is dependent not only on the theoretical assumptions but also on the selection of empirical parameters such as the cross‐section area ( ) of adsorbed gas molecules. Even for nitrogen adsorption, the model parameters might be altered for adsorption in micropores with different surface structures and interactions . The purpose of this work is, by extensive Monte Carlos simulations, to provide a comprehensive analysis of the relation between the BET and the geometric surface areas for both the conventional models of amorphous porous materials and for a large number of MOF materials promising for gas storage.…”

Sorbate densities on 5A zeolite above and below the critical conditions: n alkane data evaluation and modeling

“…The theoretical saturation loading of n alkanes in 5A zeolite may be calculated from first principles for zeolite crystals and pellets of crystals and binder, assuming 100% accessibility for the alkanes (Do et al 2009), as:…”