Cooperative Sorption on Heterogeneous Surfaces.

Area of Science:

• Physical Chemistry
• Materials Science
• Chemical Engineering

Background:

• Heterogeneous adsorbents with multiple surface/pore types exhibit complex stepwise adsorption isotherms.
• Existing models often rely on empirical equations or make unrealistic assumptions, limiting their applicability and physical insight.

Purpose of the Study:

• To develop a physically meaningful and universally applicable model for stepwise adsorption isotherms.
• To provide a rigorous statistical thermodynamic framework for understanding adsorption on heterogeneous materials.

Main Methods:

• Developed a statistical thermodynamic approach based on two postulates: finite interface range and independent microscopic subsystems.
• Utilized a superposition scheme combining simple (Langmuir-type) and cooperative isotherms.
• Applied the model to various adsorbent systems including micro-mesoporous carbons, gate-opening adsorbents, and hydrogen-bonded organic frameworks.

Main Results:

• Successfully modeled stepwise isotherms, including those with initial rise-sigmoid or multiple sigmoidal steps.
• Demonstrated the model's applicability across diverse heterogeneous adsorbent types.
• Ensured all fitting parameters are interpretable within statistical thermodynamics, offering clear mechanistic insights.

Conclusions:

• The presented statistical thermodynamic model offers a universal and physically grounded approach to modeling stepwise adsorption isotherms.
• This method overcomes limitations of empirical models by providing interpretable parameters and clear insights into sorption mechanisms on heterogeneous adsorbents.