Uptake of fluoride by nano-hydroxyapatite/chitosan, a bioinorganic composite

A bioinorganic composite namely nano-hydroxyapatite/chitosan (n-HApC) composite which could be employed for technology development was prepared and studied for its defluoridation efficiency. It has been observed that there was a slight enhancement in the defluoridation capacity (DC) of n-HApC composite (1560 mg F−/kg) than nano-hydroxyapatite (n-HAp) which has a DC of 1296 mg F−/kg. The sorbents were characterized with XRD and TEM studies. The fluoride sorption was explained with Freundlich and Langmuir isotherms. Thermodynamic parameters such as ΔG°, ΔH°, ΔS° and Ea were calculated in order to understand the nature of sorption. The sorption process was found to be controlled by pseudo-second-order and pore diffusion models. Field studies were carried out with the fluoride containing water sample collected from a fluoride-endemic area in order to test the suitability of the sorbents at field conditions.