Temperature Dependence of Sorption.

Area of Science:

• Physical Chemistry
• Thermodynamics
• Materials Science

Background:

• Classical sorption models like BET and GAB have limitations and are often misapplied.
• The phenomenon of adsorption isotherms forming a single characteristic curve at different temperatures lacks a clear molecular explanation.

Purpose of the Study:

• To generalize classical isosteric sorption theory into a statistical thermodynamic fluctuation theory.
• To clarify the molecular basis of temperature dependence in sorption processes.
• To provide a theoretical framework for understanding the characteristic curve phenomenon.

Main Methods:

• Extension of a recent statistical thermodynamic fluctuation theory of sorption.
• Generalization of classical isosteric sorption theory.
• Analysis of energetic and entropic contributions to sorption.

Main Results:

• A generalized statistical thermodynamic fluctuation theory of sorption is presented.
• The existence of a characteristic curve is explained by purely energetic contributions to the interface.
• The temperature dependence of isotherms is linked to the correlation between sorbate number and entropy.

Conclusions:

• The developed theory rationalizes the opposing temperature dependence of water vapor sorption on activated carbons with different pore size distributions.
• The theory is applicable to moisture sorption on starch gels.
• Adsorption potential serves as a unifying variable for sorption thermodynamics and fluctuations.