Sorption: A Statistical Thermodynamic Fluctuation Theory.

Area of Science:

• Physical Chemistry
• Thermodynamics
• Materials Science

Background:

• Traditional isotherm models (e.g., BET, GAB) often fit experimental data well but do not accurately reflect underlying sorption mechanisms.
• Some empirical isotherm equations lack a clear theoretical basis for mechanism elucidation.
• Discrepancies arise when models are applied to isotherms that violate their core assumptions.

Purpose of the Study:

• To develop a universal method for directly elucidating sorption mechanisms from experimental isotherms, independent of specific models.
• To overcome the ambiguity and limitations associated with fitting various isotherm models to experimental data.
• To establish a robust approach applicable across diverse sorption systems.

Main Methods:

• Utilized statistical thermodynamic fluctuation theory to derive a universal isotherm equation.
• Focused on the dependence of sorbate-sorbate interaction on activity as the primary determinant of sorption mechanism.
• Developed a model free from assumptions about adsorption sites and planar layers.

Main Results:

• A novel isotherm equation was derived, encompassing Langmuir, BET, and GAB models as special cases.
• Demonstrated that sorbate-sorbate interaction dependence on activity is crucial for understanding sorption mechanisms.
• Successfully applied the universal approach to the humidity sorption isotherm of sucrose.

Conclusions:

• The proposed method offers a direct and reliable route to elucidate sorption mechanisms without relying on model fitting.
• The statistical thermodynamic fluctuation theory provides a powerful framework for understanding sorption phenomena.
• The universal approach is broadly applicable to various adsorption/absorption scenarios and sorbate/sorbent types.