Dynamic adsorption behaviors between Cu²⁺ ion and water-insoluble amphoteric starch in aqueous solutions

Dynamic adsorption behavior between Cu²⁺ ion and water-insoluble amphoteric starch was investigated. The sorption process occurs in two stages: external mass transport occurs in the early stage and intraparticle diffusion occurs in the long-term stage. The diffusion rate of Cu²⁺ ion in both stages is concentration dependent. In the external mass-transport process, the diffusion coefficient (D₁) increases with increasing initial concentration in the low- (1 × 10⁻³-4 × 10⁻³M) and high-concentration regions (6 × 10⁻³-10 × 10⁻³M). The values of adsorption activation energy (k_d1) in the low- and high-concentration regions are 15.46–24.67 and −1.80 to −11.57 kJ/mol, respectively. In the intraparticle diffusion process, the diffusion coefficient (D₂) increases with increasing initial concentration in the low-concentration region (1 × 10⁻³-2 × 10⁻³M) and decreases with increasing initial concentration in the high-concentration region (4 × 10⁻³-10 × 10⁻³M). The k_d2 values in the low- and high-concentration regions are 9.96–15.30 and −15.53 to −10.71 kJ/mol, respectively. These results indicate that the diffusion process is endothermic in the low-concentration region and is exothermic in the high-concentration region for both stages. The external mass-transport process is more concentration dependent than the intraparticle diffusion process in the high-concentration region, and the dependence of concentration for both processes is about equal in the low-concentration region. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2849–2855, 2001