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Sorption: a statistical thermodynamic fluctuation theory

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Publication details

DateSubmitted - 17 Mar 2021
DateAccepted/In press - 23 May 2021
DatePublished (current) - 14 Jun 2021
Issue number24
Number of pages12
Pages (from-to)7380–7391
Original languageEnglish


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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© 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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