Nanostructured oxide stabilized by chitosan: hybrid composite as an adsorbent for the removal of chromium (VI)

Abstract

The surface of iron oxides can be modified by treatments using organic components, which is an alternative for the production of new materials. Chitosan (CT) is a polymer that has been widely used as a protective and stabilizing agent, which can functionalize and improve adsorbent properties of iron oxides. In this study, the synthesis of chitosan-stabilized nanostructured iron oxide was carried out for application and the optimization of Cr(VI) removal. The material was synthesized by the direct incorporation of Fe(II) into the chitosan gel, producing CT-Fe beads. The chemical, morphological and structural characterizations of the materials were performed using SEM, XRD, FTIR, TGA and DSC. The magnetic iron oxide produced together with chitosan was identified as magnetite (Fe3O4). In the formation of the CT-Fe composite, chitosan chains became less ordered, providing the formation of low-crystalline magnetic iron oxide capable of increasing the adsorption capacity. CT-Fe composite showed higher capacity for the removal of Cr(VI), relative when compared to pure magnetite. Kinetic studies showed that chromium adsorption follows the pseudo-second order model, indicating chemical adsorption. The removal of Cr(VI) was pH-dependent and the highest removal was obtained in acid medium, in which the groups present on the surface of the materials are fully protonated, facilitating the electrostatic attraction of HCrO4−. Furthermore, the reduction of Cr(VI) by Fe(II) can cause Cr(III) to return to the aqueous medium and being readsorbed. The CT-Fe composite has promising adsorption capacity with remarkable reuse for the removal of chromium from solution.