Modification of chitosan with carboxyl-functionalized ionic liquid for anion adsorption

We report a novel chitosan derivative, chitosan–ionic liquid (CS–IL) conjugation for anion adsorption. Specifically, CS–IL conjugation was synthesized through the reaction of amino groups of chitosan with carboxylic groups of 1-carboxybutyl-3-methylimidazolium chloride. Due to the amphiphilic structure, CS–IL conjugation could self-assemble into nanoparticles in distilled water. This novel chitosan derivative revealed good anion adsorption performance, and the adsorption capacity of Cr2O72− and PF6− was 0.422 mmol/g and 0.840 mmol/g, respectively. The adsorption of Cr2O72− and PF6− could be improved at low pH, which was ascribed to the adsorption of protonated NH2 on chitosan. Importantly, the chitosan derivative would aggregate in the water after the adsorption and could be easily separated. The properties enable CS–IL conjugation to be used as a novel anion adsorbent for wastewater treatment.