Biopolymer based nanocomposite (Fe3O4/GONR/SA) for targeted fluoride removal: Facile synthesis, adsorption mechanism and regeneration potential

Excessive fluoride in water poses potential health risks. This study developed a Fe₃O₄/GONR/SA nanocomposite hydrogel to address fluorosis challenges. Herein, we used the free radical polymerization method to synthesize a novel nanocomposite hydrogel, namely as Fe₃O₄/GONR/SA nanocomposite hydrogel. Nanocomposite hydrogel was characterized using SEM, XRD, FTIR, and EDX analysis to examine its morphology, crystalline structure, and elemental composition, respectively. Defluoridation properties were evaluated under varying pH, contact time, and fluoride concentration conditions. The results suggested that Fe₃O₄/GONR/SA nanocomposite hydrogel had a fast capture rate for fluoride. The nanocomposite hydrogel demonstrated an impressive maximum defluoridation capacity (Q_o) of 90.0 mg g⁻¹ within 12 min at pH 6, which surpasses conventional adsorbents and shows superiority. Isotherm and kinetic data analyses revealed that the Langmuir adsorption isotherm and pseudo-second-order (PSO) models best described chemisorption and the rate of the fluoride adsorption process. The primary defluoridation mechanism was identified as chemisorption involving both electrostatic interactions and ion exchange, where protonated hydroxyl and carboxyl groups attract fluoride ions, and ion exchange, wherein fluoride ions replace surface-bound hydroxyl groups. Additional renewal and field investigations assessed the nanocomposite’s regeneration ability and practical applicability.