Bifunctionalized chitosan: A versatile adsorbent for removal of Cu(II) and Cr(VI) from aqueous solution

This study describes the chemical modification of chitosan to produce a novel bifunctionalized adsorbent material (C4) for the removal of Cu²⁺ and oxyanions of Cr⁶⁺ from a single aqueous solution. The chemical modifications allowed C4 to be insoluble under acidic conditions, improving the chemical properties of the modified chitosan in aqueous solution. C4 adsorbent was synthesized by reaction of the amino group of chitosan with 2-pyridinecarboxaldehyde, a reduction of imine group, followed by esterification with EDTA dianhydride (EDTAD). C4 was characterized by solid-state ¹³C nuclear magnetic resonance, infrared spectroscopy, and elemental analysis. The adsorption studies of Cu²⁺ and oxyanions of Cr⁶⁺ in a batch mode were evaluated as a function of the contact time (kinetics), solution pH, and initial metal ion concentration. The maximum adsorption capacities (Q_max) of C4 for the adsorption of Cu²⁺ (pH 5.5) and Cr⁶⁺ (pH 2.0) were 2.60 and 3.50 mmol/g, respectively. The reusability of the recovered C4 adsorbent was also evaluated.