Ion-imprinted chitosan gel beads for selective adsorption of Ag+ from aqueous solutions

In this study, the Ag+-imprinted chitosan gel beads were synthesized to selectively adsorb Ag+ from bimetallic aqueous solutions containing the same molar concentration of Ag+ and Cu2+. The Ag+-imprinting not only helps to achieve extremely high selectivity of Ag+, but also enhances the uptake capacity of the target Ag+ by protecting some amine groups, the primary binding sites of metal ions from cross-linking. The maximum uptake of Ag+ by the ion-imprinted chitosan beads was found to be 89.20 mg g−1 at 25.0 °C with an initial Ag+ concentration of 352.95 mg L−1 and the biosorbent dosage of 1.0 g L−1. The adsorption equilibrium and kinetics of Ag+ by the ion-imprinted chitosan beads can be better described by Langmuir isotherm and the intraparticle diffusion model. FTIR and XPS analyses suggested that amine functional groups involve the binding of Ag+ via complexation at higher solution pH (3.0 ≤ pH ≤ 5.0) and ion exchange at lower solution pH (1.0 ≤ pH < 3.0).