Textural Characterization by Using an Alternative Langmuir Isotherm and a New Thickness Function

Area of Science:

• Materials Science
• Physical Chemistry
• Surface Science

Background:

• The Langmuir isotherm, based on a monolayer assumption, is inadequate for describing adsorption in microporous materials.
• Micropores present challenges for traditional adsorption models due to their small size and high surface area.

Purpose of the Study:

• To develop a modified isotherm model that accurately describes adsorption in microporous materials.
• To introduce a corrective parameter accounting for sample porosity and a new adsorbate layer thickness function.

Main Methods:

• Modification of the Langmuir isotherm by incorporating a porosity-related parameter.
• Development of a novel thickness function for the adsorbate layer as a function of relative pressure.
• Validation of the modified model using experimental adsorption data from diverse materials (aluminas, clays, silicas, zeolites, zirconias).

Main Results:

• The modified isotherm successfully describes experimental adsorption data across low and full relative pressure ranges for various materials.
• The new thickness function improves the characterization of external surface areas, mesopores, and micropores.
• The VBS model, enhanced with the new thickness function, provides a superior description of pore size distribution.

Conclusions:

• The proposed modified isotherm overcomes the limitations of the Langmuir model for microporous systems.
• The enhanced model offers a more accurate method for characterizing the porous structure of diverse materials.
• This approach provides a better understanding of adsorption phenomena in materials with complex pore architectures.