Hydrothermal synthesis of a mineral-substituted hydroxyapatite nanocomposite material for fluoride removal from drinking water

This work deals with the fluoride removal studies of a mineral-substituted hydroxyapatite (mHAp) nanocomposite. The developed hybrid mHAp nanocomposite displays a high fluoride removal capacity of 8.36 mg g(-1). Batch sorption experiments were performed to determine the effect of various influencing parameters such as pH, contact time, competitor co-anions, initial fluoride concentration, and temperature. The structure, surface morphological changes, and elements present in the sorbent were studied by Fourier-transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy with energy-dispersive X-ray analysis. The particle size of the adsorbent is observed as similar to 220 nm for mHAp and it is slightly higher than that of HAp (similar to 205 nm). The equilibrium isotherm study was fitted using the Langmuir isotherm model. The thermodynamic parameter values indicate the spontaneous and endothermic nature of fluoride sorption. The proposed mechanism indicates that the enhanced fluoride removal capacity of the mHAp nanocomposite is mainly due to electrostatic adsorption and complexation between the fluoride ions and the composites in addition to ion exchange. Regeneration and reusability studies were performed to enable the effective utilization of the mHAp nanocomposite. The performance of the mHAp nanocomposite under field conditions was evaluated with water samples collected from a nearby fluoride-prevalent area.