Adsorbate-adsorbate interactions on microporous materials

Shimizu, Seishi; Matubayasi, Nobuyuki

doi:10.1016/j.micromeso.2021.111254

Cited by 24 publications

(42 citation statements)

References 67 publications

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“…N 22 + 1 tending to 0 reflects the liquid-like nature of sorbates at saturation, which has been inferred from experiments. 89,90 Previously, we have estimated N 22 + 1 for the PIT-type porous carbons around the peaks of N 22 + 1, 65 which shows a good agreement with the adsorption lines in Figures 3 and 4, whereas a discrepancy is seen for the desorption lines. Note that the maximum gradient of ⟨n 2 ⟩ was detected visually without using any fitting model 65 and that the deviation of our fitting function from the data may have also exaggerated the gradient for the desorption lines.…”

Section: ■ Results and Discussionsupporting

confidence: 75%

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Cooperative Sorption on Porous Materials

2021

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The functional shape of a sorption isotherm is determined by underlying molecular interactions. However, doubts have been raised on whether the sorption mechanism can be understood in principle from analyzing sorption curves via a range of competing models. We have shown recently that it is possible to translate a sorption isotherm to the underlying molecular interactions via rigorous statistical thermodynamics. The aim of this paper is to fill the gap between the statistical thermodynamic theory and analyzing experimental sorption isotherms, especially of microporous and mesoporous materials. Based on a statistical thermodynamic approach to interfaces, we have derived a cooperative isotherm, as a generalization of the Hill isotherm and our cooperative solubilization model, without the need for assumptions on adsorption sites, layers, and pore geometry. Instead, the statistical characterization of sorbates, such as the sorbate-interface distribution function and the sorbate number distribution, as well as the existence of statistically independent units of the interface, underlies the cooperative sorption isotherm. Our isotherm can be applied directly to literature data to reveal a few key system attributes that control the isotherm: the cooperative number of sorbates and the free energy of transferring sorbates from the saturated vapor to the interface. The sorbate− sorbate interaction is quantified also via the Kirkwood−Buff integral and the excess numbers.

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Section: ■ Results and Discussionsupporting

confidence: 75%

“…At the high end of a 2 , N 22 is low (Figures and ) despite the high population of sorbates as seen from the large ⟨ n 2 ⟩ (Figures and ). N 22 + 1 tending to 0 reflects the liquid-like nature of sorbates at saturation, which has been inferred from experiments. , …”

Section: Resultsmentioning

confidence: 75%

Cooperative Sorption on Porous Materials

2021

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“…The deliquescence point of sucrose is around a 2 = 0.85. , The discontinuity of n 2 at this point is not captured by the Oswin model which can exhibit divergence only at a 2 → 1 (see Appendix B). The increase of N 22 with a 2 shows that sorbates, despite their increase in quantity, do not behave like bulk water (in which case, N 22 ≃ −1).…”

Section: Resultsmentioning

confidence: 99%

“…Both justifications assume that the structure of adsorbates is identical to that of the bulk solvent . For a bulk solvent, the Kirkwood–Buff theory yields N 22 ≃ −1, which is equivalent to the Gurvitsch rule for adsorbate density . This is satisfied only at D = 3 (eq ) when the adsorbate dimension is the same as that of the embedding system.…”

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confidence: 99%

Sorption: A Statistical Thermodynamic Fluctuation Theory

2021

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Can the sorption mechanism be proven by fitting an isotherm model to an 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 Brunauer−Emmett−Teller (BET) and Guggenheim− Anderson−de Boer (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 planar 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 vapor 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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“…Understanding how sorption depends on temperature is an important question in basic and applied sciences alike. − This paper aims to answer this question on a molecular scale via statistical thermodynamics. − This question may seem simple yet has been made complicated. We have identified the three areas of difficulty in the previous attempts to answer this question.…”

Section: Introductionmentioning

confidence: 99%

Temperature Dependence of Sorption

Shimizu

Matubayasi

2021

Langmuir

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Understanding how sorption depends on temperature on a molecular basis has been made difficult by the coexistence of isotherm models, each assuming a different sorption mechanism and the routine application of planar, multilayer sorption models (such as Brunauer–Emmett–Teller (BET) and Guggenheim–Anderson–de Boer (GAB)) beyond their premises. Furthermore, a common observation that adsorption isotherms measured at different temperatures fall onto a single “characteristic curve” when plotted against the adsorption potential has not been given a clear explanation, due to its ambiguous foundation. Extending our recent statistical thermodynamic fluctuation theory of sorption, we have generalized the classical isosteric theory of sorption into a statistical thermodynamic fluctuation theory and clarified how sorption depends on temperature. We have shown that a characteristic curve exists when sorbate number increment contributes purely energetically to the interface, whereas the correlation between sorbate number and entropy drives the temperature dependence of an isotherm. This theory rationalizes the opposite temperature dependence of water vapor sorption on activated carbons with uniform versus broad pore size distributions and can be applied to moisture sorption on starch gels. The adsorption potential is a convenient variable for sorption in its ability to unify sorbate–sorbate fluctuation and the isosteric thermodynamics of sorption.

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Adsorbate-adsorbate interactions on microporous materials

Cited by 24 publications

References 67 publications

Cooperative Sorption on Porous Materials

Cooperative Sorption on Porous Materials

Sorption: A Statistical Thermodynamic Fluctuation Theory

Temperature Dependence of Sorption

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