The influence of the degree of cross-linking on the adsorption properties of chitosan beads

The influence of the degree of cross-linking (DCL) on chitosan beads was studied. Chitosan was prepared from the exoskeleton of Cape rock-lobsters, collected from the surroundings of Cape Town, South Africa. The chitosan beads were characterized; the beads water contents and pK(a) varied in the range of 90-96% and 4.3-6.0, respectively, and were found to decrease with increasing DCL (0.0-34.0%). A pH-model, which described the reversibility of the metal adsorbed onto the beads, was used to predict the equilibrium properties of copper adsorption onto the cross-linked beads. The model accounts for the effect of pH and the important model parameters, the equilibrium adsorption constant (K-ads) and to a lesser extent the adsorbent adsorption capacity (q(max)) showed to decrease with the DCL. The adsorbent capacity and the adsorption constant were determined as 3.8-5.0 mmol/g chitosan and (9-90) x 10(-4), respectively. The adsorption kinetics could be described using a shrinking core model and the effective diffusion coefficient (D-eff) was determined as (8.0-25.8) x 10(-11) m(2)/S. It was found that D-eff. decreases with the DCL mainly due to the decreased in water content of the beads at high DCL. (C) 2008 Elsevier Ltd. All rights reserved.