Efficient defluoridation of water by Monetite nanorods

Novel Monetite nanorods were successfully prepared for fluoride removal for the first time. The fluoride adsorption on the Monetite nanorods was studied by the batch adsorption technique. The Monetite nanorods were characterized by transmission electron microscope (TEM), X-ray powder diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR), and the point of zero charge (pH_PZC) measurement. The results revealed that the Monetite nanorods transformed to fluorapatite after adsorbing fluoride. The adsorption kinetics followed the pseudo-second-order model, and the adsorption isotherms could be well described by the Sips model. The maximum adsorption capacity was 222.88 mg g⁻¹ at pH 7, 328 K when the initial fluoride concentration was 300 mg L⁻¹ and the Monetite dose was 1 g L⁻¹. The thermodynamic parameters revealed that the adsorption of fluoride onto Monetite nanorods was spontaneous and endothermic. The effects of different parameters including adsorbent dosage, pH, initial fluoride concentration and co-existing anions were investigated to understand the adsorption behaviour of Monetite nanorods under various conditions. Their adsorption capacities decreased with the increase of adsorbent dosage, and also decreased with the increase of pH. Electrostatic attraction and ion exchange were found to be the major mechanisms governing the adsorption of fluoride onto Monetite nanorods. Furthermore, a field study was conducted with the water from a fluoride endemic area in Tanzania. This study demonstrated that the synthesized Monetite nanorods were very effective adsorbents for defluoridation applications.