Selective adsorption of Ag+ by ion-imprinted O-carboxymethyl chitosan beads grafted with thiourea–glutaraldehyde

• Synthesis of chitosan-based biosorbent by combining surface imprinting and crosslinking.
• Sorbent shows superb selectivity towards Ag+ over Cu2+ in all ranges of initial concentrations and pH 1.0–6.0.
• Selective adsorption of Ag+ occurs by chelation through >CS, amine, carboxyl and hydroxyl groups.
• Sorbent has good durability and high efficiency for repeated use.

In this study, a novel technique combining surface imprinting and polymer crosslinking was applied to synthesize the Ag+-imprinted thiourea/glutaraldehyde grafted O-carboxymethyl chitosan (ITG-OCMC) beads which demonstrate extremely good selective adsorption of Ag+ from a bimetallic aqueous solution. Results indicated that high degree of carboxymethylation and low level of crosslinking would help to achieve higher uptake capacity of Ag+. The maximum uptake of Ag+ was found to be 156.32 mg g−1 at 40 °C with an initial Ag+ concentration of 160.5 mg L−1 and the biosorbent dosage of 1.0 g L−1. Langmuir isotherm and Lagergren’s pseudo-second-order kinetic can be used to describe the sorption process of Ag+. Analyses from FT-IR and XPS confirmed that selective adsorption of Ag+ took place on the surfaces of ITG-OCMC beads by chelation through >CS, amine, carboxyl and hydroxyl groups.