Synthesis of iron oxyhydroxide nanoparticles and its application for fluoride removal from water

Iron oxyhydroxide nanoparticles were synthesized from natural clay to remove fluoride from aqueous medium. Natural clay was leached in acid solution to obtain iron precursor consist of ferrous and ferric ions to prepare the iron oxyhydroxide nanoparticles. The various process parameters like pH, iron concentration in the precursor, surfactant co-surfactant ratio and critical micelle concentration of surface active agent were optimized to obtain smaller sizes nanoparticles. The synthesized nanoparticles were characterized using, X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and BET surface area analyzer. Nanoparticles of average diameters of 6-20 nm were revealed through TEM analyses. The specific surface area and total pore volume of the nanoparticles sample obtained under optimized process conditions were 312 m²/g and 0.2 mL/g, respectively. Experimental data were fitted the Freundlich adsorption isotherm more satisfactorily compared to the Langmuir isotherm. The pseudo second order kinetic model was shown better fit to the experimental data compared to first order kinetic model. Thus, the rate controlling factors involved in the adsorption process may be both fluoride concentration and adsorbent's active sites concentration. Batch adsorption isotherm study reveals that with an initial fluoride concentration of 100 mg/L and adsorbent dosing 0.2 g/L, the adsorption of fluoride was observed 111.1 ± 4.32 mg/g within the 45 min of agitation time at pH ∼7.5.