Adsorption of iodine on cationic cross-linked starches

The influence of the degree of substitution (DS) on the equilibrium adsorption of iodine on cationic cross-linked starch chlorides (CCSCl) and cationic cross-linked starch iodides (CCSI) from aqueous iodine - potassium iodide solutions at different temperatures has been investigated and compared with iodine adsorption on only cross-linked starch (CS). The Langmuir, Freundlich and Dubinin-Radushkevich adsorption models have been used to describe iodine adsorption on CCSCl and CCSI. With increasing the DS, both the sorption capacity of CCSCl and CCSI and the value of effectiveness of cationic groups in iodine binding were increasing. The thermodynamic characteristics of iodine adsorption on CCSCI, CCSI and CS have been evaluated. Iodine adsorption on CCSCl and CCSI proceeded spontaneously as indicated by the calculated values of the Gibbs free energy (Delta G(0)). On the contrary, iodine adsorption on CS was accompanied by a positive value of Delta G(0).