Adsorption properties of tea polyphenols onto three polymeric adsorbents with amide group.

Macroporous crosslinked poly(N-methyl-N-p-vinylbenzylacetamide) (PMVBA), poly(N-methyl-N-p-vinylbenzylurea) (PMVBU), and poly(N-methylacrylamide) (PMA) were prepared and their adsorption behaviors for tea polyphenols (TP) were investigated in aqueous solution. The results indicated that their adsorption capacities for TP followed an order as: PMVBU>PMVBA>PMA. The adsorption isotherms were fitted to Freundlich isotherm and adsorption enthalpies were calculated. It was found that Freundlich isotherm was suitable to characterize the adsorption process and their adsorption enthalpies for TP gave the same order as: PMVBU>PMVBA>PMA. Surface energy heterogeneity was analyzed by Do's model and the surface of PMVBU was shown to be the most homogeneous. Analysis of adsorption mechanism suggested that multiple hydrogen bonding, hydrophobic interaction, and pi-pi stacking were responsible for the adsorption of TP onto the adsorbents.