Adsorption of catechin from aqueous solutions on polymeric resins and activated carbon

Catechin, a bioflavonoid found in green tea leaves has various applications in food and pharmaceutical industries. With a view to develop adsorptive separation process for the extraction of catechin from green tea, the batch equilibrium adsorption of catechin from aqueous solutions using commercially available activated charcoal, styrene-divinylbenzene (SDVB) and acrylic resins with different hydrophobicity, surface areas and pore radii has been studied. Adsorption isotherms were interpreted from Langmuir, Freundlich and Redlich-Peterson isotherms. However, almost in all cases, Langmuir isotherm exhibited better fit of experimental data. It appears that capacity of the adsorbate/adsorbent system depends on various interactions that occur at the solid liquid interface i.e., hydrophobic, dipole-dipole and hydrogen bonding. Physical properties of the resin such as surface area, pore radius, and porosity and the chemical characteristics of the solution i.e., solvent type and pH also play a major role in determining rates and equilibrium of adsorption. The heat of adsorption (∆Ho) was determined from Van’t Hoff plot using equilibrium data generated at different temperatures and the observed differences in ∆Ho for different adsorbents have been explained from mechanistic consideration.