Fabrication of covalent organic frameworks incorporated hydroxyapatite based chitosan–gelatin hybrid magnetic beads for fluoride removal

Abstract

The developed biocompatible materials like covalent organic frameworks (COFs) and hydroxyapatite acquire significant defluoridation capacity (DC). But because of their powder nature, creates column blockage, pressure drop during field investigations and difficult in separation after fluoride adsorption. To address these problems, COFs and hydroxyapatite were fabricated in the usable form of beads using chitosan, gelatin and iron oxide materials as magnetic chitosan–gelatin/hydroxyapatite/covalent organic frameworks (MCGHCOF) bio-beads were developed and it was potentially applied for the removal of fluoride from water. The MCGHCOF bio-beads surface and their properties were described with FTIR, EDAX, SEM and XRD analysis. The adsorption studies were performed under the batch method. The HCO3– ion has a vital inhibitory effect on DC and this may be because of the similar ionic size of fluoride and HCO3–. The enhanced DC of MCGHCOF beads was found to be 4992 mgF-.kg−1 in 30 min at pH 7. Isotherm experimental data of fluoride adsorption was apt with Langmuir isotherm than Fruendlich and D-R isotherm models. The defluoridation system is endothermic and its spontaneous nature was demonstrated with thermodynamic studies. Kinetic studies of experimental data of fluoride adsorption were well-fitted with pseudo-second-order and intraparticle diffusion. The complexation and electrostatic interaction play a predominant role in fluoride adsorption by MCGHCOF beads. The MCGHCOF bio-beads are stable and are reusable upto six cycles. The collected field water sample was examined using MCGHCOF beads and it reduced the fluoride concentration to the tolerable drinking water threshold as recommended by WHO (1.5 mg L−1).