Equilibrium adsorption of caffeic, chlorogenic and rosmarinic acids on cationic cross-linked starch with quaternary ammonium groups

- Adsorption of phenolic acids on cationic cross-linked starch was performed.
- Adsorption values were related to the dissociation constants of phenolic acids.
- Adsorption properties were related to the phenolic acid structure.

In the present study, the equilibrium adsorption of caffeic acid (CA) and its derivatives, namely, chlorogenic (CGA) and rosmarinic (RA) acids on cationic cross-linked starch (CCS) with degree of substitution of quaternary ammonium groups of 0.42 have been investigated in relation to the structure and acidity of phenolic acids. The Langmuir, Freundlich and Dubinin-Radushkevich adsorption models have been used to describe the equilibrium adsorption of CA, CGA and RA from their initial solutions and solutions having the equimolar amount of NaOH at different temperatures. In the case of adsorption from the initial solutions of acids the values of adsorption parameters were closely related to the dissociation constants of investigated acids. According to the increasing effectiveness of adsorption, phenolic acids could be arranged in the following order: CA < CGA < RA, i.e. in the range contrary to increasing value of pKa. At temperature of 30 °C the maximum Langmuir sorption capacity was 0.76, 1.11 and 2.68 mmol/g for CA, CGA and RA, respectively. The addition of equimolar amounts of NaOH to the acids solutions changed their sorption properties which became mostly related to the acids structure.