Adsorption of rosmarinic acid from aqueous solution on chitosan powder

Abstract

In present study the adsorption of rosmarinic acid (RA) on chitosan (CH) powder from aqueous solution have been investigated in order to obtain insoluble RA-CH complexes with high amount of RA. The pseudo-second kinetic model and the Langmuir adsorption model described the kinetic and equilibrium adsorption of RA on CH with high correlation coefficients. With the increase of adsorption temperature the rate of adsorption decreased but amount of adsorbed RA increased. It was established that adsorption of RA on CH occurred in two steps, and relevant adsorption mechanism was proposed. The formation of RA-CH with the molar ratio of RA to CH equal to 0.11, 0.22. 0.39, 0.6 and 0.8 was investigated by FT-IR and steady-state fluorescence spectroscopic techniques. By the increase of RA amount in RA-CH complexes the character of both FT-IR and fluorescence spectra changed. The antioxidant activity of RA-CH was investigated by ABTS method and showed that RA-CH having higher amount of adsorbed RA has prolonged antioxidant activity.

Keywords: Adsorption; Antioxidant activity; Chitosan; Rosmarinic acid.