Application of a new bifunctionalized chitosan derivative with zwitterionic characteristics for the adsorption of Cu2+, Co2+, Ni2+, and oxyanions of Cr6+ from aqueous solutions: Kinetic and equilibrium aspects

• A new bifunctionalized chitosan (C2) with zwitterionic characteristics was prepared.
• Trimethylation of amine and esterification of hydroxyls with EDTAD was performed.
• C2 was used for the adsorption of Cu2+, Co2+, Ni2+, and Cr6+ in aqueous solutions.
• Qmax of C2 for Cu2+, Co2+, Ni2+, and Cr6+ were 0.698, 1.125, 0.725, and 1.91 mmol/g.
• Desorption (0.1 mol/L HNO3) and reusability of the C2 adsorbent was also evaluated.

This study describes the synthesis of a new chitosan derivative (C2) with zwitterionic characteristics and its use for the removal of cationic species Cu2+, Co2+, and Ni2+ and anionic species of Cr6+ 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 Cu2+, Co2+, Ni2+, and oxyanions of Cr6+ 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 (Qmax) of C2 for adsorption of Cu2+, Co2+, Ni2+, and Cr6+ were 0.698, 1.125, 0.725, and 1.910 mmol/g, respectively. The ΔadsG° 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 HNO3 were carried out. The reusability of the recovered C2 adsorbent after desorption was also evaluated.

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