Removal of Cr6+ from aqueous solution using thiourea-glutaraldehyde double-crosslinked chitosan/sodium alginate composites

Abstract

In this study, a thiourea-glutaraldehyde double-crosslinked sodium alginate/chitosan alginate (GL-STC) was meticulously designed and synthesized through electrostatic and covalent interactions. The structure and morphologies of GL-STC were thoroughly characterized using SEM-EDS, FT-IR and XPS. The results revealed that GL-STC exhibited a layered and porous structure, which was achieved by incorporating thiourea and glutaraldehyde (GL) as crosslinking agents. The adsorption of Cr6+ by GL-STC was found to be a spontaneous endothermic process. The removal efficiency of Cr6+ exceeded 60% within the pH range of 2–6, with the highest removal rate reaching 98% at pH = 3. The maximum adsorption capacity was determined to be 271.83 mg·g−1. Anions were found to significantly inhibit the removal of Cr6+. The Langmuir isotherm model and pseudo-first-order kinetic model were deemed more appropriate for describing the equilibrium adsorption of Cr6+ by GL-STC. Furthermore, the possible mechanisms underlying the removal of Cr6+ by GL-STC primarily involved electrostatic attraction, ion exchange, reduction and complexation. This research contributes to the field of environmental material science and offers novel water treatment technologies, holding significant practical value. Highlights: A highly crosslinked polyelectrolyte hydrogel complex (GL-STC) was synthesized. The maximum adsorption capacity up to 271.83 mg·g−1. The adsorption mechanism of GL-STC for Cr6+ was studied. The adsorption process of Cr6+ on GL-STC was a spontaneous endothermic.