A sandwich model of Cr(VI) adsorption and detoxification by Fenton modified chitosan

The Fenton reaction has the advantages of short reaction time, low cost, no toxicity, and straightforward application and control. The Fenton reaction generates highly reactive HO•, which has been applied effectively. However, the effect of the generated Fe³⁺ has not been investigated widely. In this study, the Fenton reaction was used to improve the Cr(VI) adsorption and detoxification capacities of chitosan. After the Fenton modification, chitosan efficiently adsorbed Cr(VI) and transformed it into the less toxic Cr(III) in a wide pH range as a result of layer formation, which was described by a sandwich model. The adsorption of Cr(VI) onto the Fenton modified chitosan was in good agreement with the Freundlich adsorption model, and the adsorption capacity exceeded 120 mg/g. During the Fenton reaction, H₂ O₂ and HO• with high oxidative activity broke the hydrogen bonds in the chitosan structure, resulting in the release of free amine groups for Fe³⁺ to form metal-binding biopolymers. The distance between the chitosan polymers increased, and additional adsorption sites were created. HCrO₄ ^- entered the gap between the chitosan polymer and was adsorbed on the newly created adsorption sites. The sandwich adsorption model indicated that the Fenton modified chitosan provided a high concentration of active sites for Cr(VI) capture and detoxification. PRACTITIONER POINTS: Fenton reaction was used to improve the adsorption ability of chitosan. The formed Fe³⁺ in Fenton reaction was utilized. HO· broke the hydrogen bonds and Fe³⁺ ions chelated with chitosan in modification. Cr(VI) could be adsorbed and reduced efficiently by Fenton modified chitosan. The Fenton modified chitosan provided a high concentration of active sites for Cr(VI) capture and detoxification.