Cross-linked amino konjac glucomannan as an eco-friendly adsorbent for adsorption of Cr(VI) from aqueous solution

A new eco-friendly adsorbent (ACKGM) derived from konjac glucomannan was prepared and used for Cr(VI) adsorption from aqueous solution. The ACKGM was synthesized by amino-modification of cross-linked konjac glucomannan through nucleophilic substitution approach. The adsorbent was characterized by scanning electron microscopy and Fourier Transform Infrared spectroscopy. The ACKGM possessed property of fast adsorption and over 92% of Cr(VI) was adsorbed in the first 10 min. The adsorption equilibrium was reached in 45 min. The ACKGM removed 99.98%-85.93% of Cr(VI) when initial Cr(VI) concentration varied in 20-150 mg/L. It was found the absorption depended on pH and the optimum adsorption took place at pH = 2. The maximum adsorption capacity was 34.1 mg/g, when the dosage of ACKGM was 2.0 g/L at 30 degrees C. The adsorption kinetics followed the pseudo-second order kinetics equation and the activation energy (E-a) of the adsorption was 32.72 kJ/mol.Different isotherm models were used to analyze the isotherms of the adsorption. The adsorption isotherms fitted best with the Redlich-Peterson isotherm equation. The enthalpy change (Delta H-0) of adsorption was -23.21 kJ/mol. The thermodynamic parameters showed the adsorption of Cr(VI) onto ACKGM was a spontaneous and exothermic process. The adsorption mechanism study showed that electrostatic attraction, affinity interaction and polymer inclusion and net trapping mechanisms were involved in the process. The present study suggests that the ACKGM is an effective adsorbent for the removal of Cr(VI) from aqueous solution. (C) 2017 Elsevier B.V. All rights reserved.