Characteristics of Cyclodextrin Adsorption onto Activated Carbons

Area of Science:

• Adsorption Science
• Materials Chemistry
• Physical Chemistry

Background:

• Cyclodextrins (CDs) are cyclic oligosaccharides with diverse applications.
• Activated carbons (ACs) are widely used adsorbents with varying pore structures.
• Understanding adsorption mechanisms is crucial for optimizing separation processes.

Purpose of the Study:

• Investigate the adsorption behavior of cyclodextrins on activated carbons with different pore sizes.
• Determine the factors influencing cyclodextrin adsorption, distinguishing between pore size effects and chemical interactions.
• Develop a more accurate method for estimating cyclodextrin adsorbability in aqueous solutions.

Main Methods:

• Adsorption experiments using cyclodextrins and two types of activated carbon (large-pore AC-A and small-pore AC-B).
• Analysis of adsorption isotherms and application of Freundlich adsorption models.
• Characterization of activated carbon pore structure before and after adsorption.
• Development of a novel method to estimate relative chemical potential of CDs based on molecular composition.

Main Results:

• Adsorption of cyclodextrins on AC-A increased with glucose units, while AC-B showed the opposite trend, indicating molecular exclusion.
• Freundlich adsorption models fit AC-A data well, but deviated significantly for AC-B due to pore size limitations.
• Adsorption on AC-A was not solely explained by solubility, suggesting chemical potential is a key factor.
• A new method based on carbon and oxygen atom counts provided a better estimation of CD adsorbability than solubility.
• AC-A pore diameter increased post-adsorption, while AC-B showed minimal change.

Conclusions:

• Molecular exclusion significantly impacts cyclodextrin adsorption on activated carbons, particularly with small pores.
• Chemical potential, rather than solubility, is a more critical parameter for predicting cyclodextrin adsorption onto activated carbons.
• The developed method offers a more accurate approach for estimating cyclodextrin adsorbability, aiding in adsorbent selection and process design.