Synthesis And Characterization Of Iron Doped Hydroxyapatite For Defluoridation Of Water

Abstract

According to the World Health Organization the maximum acceptable concentration of fluoride ions in drinking water lies below 1.5 mg/L. Fluoride if taken in small amount is usually beneficial, but the beneficial fluoride concentration range for human health is very small. For this reason the development of materials for the removal of fluoride from aqueous solution is in progress. This study was focused on the synthesis of Iron doped hydroxyapatite (Fe-HAp) from diammonium hydrogen phosphate (DAP), Calcium and Iron precursors using urea as fuel for defluoridation of water and antibacterial activities. The synthesized pure hydroxyapatite (HAp) and Fe-HAp were characterized by using thermogravimetric analysis; scanning electron microscopy, X-ray diffraction, and Fourier transform Infrared spectroscopic techniques. Average crystallite size of HAp and Fe-HAp were 32.54 nm and 27.91 nm, respectively. Batch experiments were performed to investigate the adsorption capacity of Fe-HAp such as the initial pH of the solution, contact time, adsorbent dose and initial fluoride concentration. Accordingly, the optimum adsorption capacity was observed at pH 3, contact time 3 hr, adsorbent dose 0.7 g, and initial fluoride concentration of 10 mg/L. The correlation coefficients of Langmuir isotherm (R2 = 0.9796) and the Freundlich isotherm (R2 = 0.9968) kinetic studies, show that adsorption was fitted with Freundlich isotherm model. Also the correlation coefficients of pseudo first order (R2 = 0.874) and pseudo second order (R2 = 0.9969), show that the adsorption was fitted with pseudo second order kinetic model. The maximum fluoride removal efficiency of synthetic water and groundwater obtained by using the material developed, Fe-HAp, to be 98 % and 82.9 %, respectively, under the optimum conditions. The maximum adsorption capacity of synthesized Fe-HAp was 4.2 mg/g. The antibacterial activities of the synthesized HAp4 and Fe0.05HAp tested against gram-negative bacterial strains E. coli by disc diffusion method was about 11 mm for both HAp4 and Fe0.05HAp. The maximum inhibition zone of gram-positive bacterial S. aureus was found to be 8 mm for HAp4 and Fe0.05HAp.