Removal of Cd(II) and Cr(VI) ions by highly cross-linked Thiocarbohydrazide-chitosan gel

A highly cross-linked Thiocarbohydrazide-modified chitosan (TCCS) gel was synthesized by using formaldehyde as linkage, and was used in removal of Cd(II) and Cr(VI) from aqueous solution. The results showed that TCCS could be used in a wider pH range and had higher adsorption abilities than raw chitosan for Cd(II) and Cr(VI) ions. The maximum adsorption capacities of the synthetic TCCS for two ions reached 81.26 and 144.68 mg/g at 298 K, respectively. The endothermic adsorption exhibited pseudo second-order kinetic behavior and the adsorption isotherm could be well described by Langmuir model. The Cd(II) ion adsorption mechanism was dominated by a complexation reaction process, while the Cr(VI) adsorption was governed by a multiple mechanism including electrostatic attraction, reduction and complexation process. TCCS was easy to be regenerated and had great reusability potential in Cd(II) and Cr(VI) ions capture from aqueous solution. (C) 2017 Elsevier B.V. All rights reserved.