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Graphical abstract Highlights • Bifunctionalized chitosan(C4) was synthesized for removal of both Cu2+ and Cr6+. • C4 was insoluble in water in a pH range of 1–10. • The maximum adsorption capacity of C4 for Cu2+ adsorption at pH 5.5 was 2.60 mmol/g. • The maximum adsorption capacity of C4 for Cr6+ adsorption at pH 2.0 was 3.50 mmol/g. • The re-adsorption efficiency of C4 was 106% for Cu2+ and 44% for oxyanions of Cr6+. Abstract 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. [ABSTRACT FROM AUTHOR]

This study describes the synthesis of a new chitosan derivative (C2) with zwitterionic characteristics and its use for the removal of cationic species Cu 2+ , Co 2+ , and Ni 2+ and anionic species of Cr 6+ in a single aqueous solution. The new adsorbent was synthesized by quaternization of the amine group of chitosan and esterification of hydroxyl groups with EDTA dianhydride. These combined reactions gave both cationic and anionic characteristics to C2 with the release of quaternary ammonium groups and carboxylic groups. The capacity of C2 to adsorb Cu 2+ , Co 2+ , Ni 2+ , and oxyanions of Cr 6+ was evaluated in a batch process with different contact times, pH values, and initial concentrations. Adsorption isotherms were best fitted to the Langmuir and Sips models. The maximum adsorption capacities ( Q max ) of C2 for adsorption of Cu 2+ , Co 2+ , Ni 2+ , and Cr 6+ were 0.698, 1.125, 0.725, and 1.910 mmol/g, respectively. The Δ ads G ° values were in the range from −20 to −28 kJ/mol. These values suggest a mixed mechanism controlling adsorption. Desorption studies using an aqueous solution consisting of 0.1 mol/L HNO 3 were carried out. The reusability of the recovered C2 adsorbent after desorption was also evaluated. [ABSTRACT FROM AUTHOR]