Sorption: a statistical thermodynamic fluctuation theory

Seishi Shimizu; Nobuyuki Matubayasi

doi:10.1021/acs.langmuir.1c00742

Sorption: a statistical thermodynamic fluctuation theory

Seishi Shimizu, Nobuyuki Matubayasi

Chemistry

Research output: Contribution to journal › Article › peer-review

Abstract

Can the sorption mechanism be proven by fitting an isotherm model to experiment? Such a question arises because (i) multiple isotherm models, with different assumptions on sorption mechanisms, often fit an experimental isotherm equally well, (ii) some isotherm models (such as BET and GAB) fit experimental isotherms that do not satisfy the underlying assumptions of the model, and (iii) some isotherms (such as Oswin and Peleg) are empirical equations that do not have a well-defined basis on sorption mechanisms. To overcome these difficulties, we propose a universal route of elucidating the sorption mechanism directly from an experimental isotherm without an isotherm model, based on the statistical thermodynamic fluctuation theory. We have shown that how sorbate-sorbate interaction depends on activity is the key to understanding the sorption mechanism. Without assuming adsorption sites and planer layers, an isotherm can be derived which contains the Langmuir, BET, and GAB models as its special cases. We have constructed a universal approach applicable to adsorption and absorption, solid and liquid sorbents, and vapour and liquid sorbates, and demonstrated its efficacy using the humidity sorption isotherm of sucrose from both the solid and liquid sides.

Original language	English
Pages (from-to)	7380–7391
Number of pages	12
Journal	Langmuir
Volume	37
Issue number	24
DOIs	https://doi.org/10.1021/acs.langmuir.1c00742
Publication status	Published - 14 Jun 2021

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© 2021 American Chemical Society. This is an author-produced version of the published paper. Uploaded in accordance with the publisher’s self-archiving policy. Further copying may not be permitted; contact the publisher for details

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Cite this

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title = "Sorption: a statistical thermodynamic fluctuation theory",

abstract = "Can the sorption mechanism be proven by fitting an isotherm model to experiment? Such a question arises because (i) multiple isotherm models, with different assumptions on sorption mechanisms, often fit an experimental isotherm equally well, (ii) some isotherm models (such as BET and GAB) fit experimental isotherms that do not satisfy the underlying assumptions of the model, and (iii) some isotherms (such as Oswin and Peleg) are empirical equations that do not have a well-defined basis on sorption mechanisms. To overcome these difficulties, we propose a universal route of elucidating the sorption mechanism directly from an experimental isotherm without an isotherm model, based on the statistical thermodynamic fluctuation theory. We have shown that how sorbate-sorbate interaction depends on activity is the key to understanding the sorption mechanism. Without assuming adsorption sites and planer layers, an isotherm can be derived which contains the Langmuir, BET, and GAB models as its special cases. We have constructed a universal approach applicable to adsorption and absorption, solid and liquid sorbents, and vapour and liquid sorbates, and demonstrated its efficacy using the humidity sorption isotherm of sucrose from both the solid and liquid sides. ",

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