Water defluoridation using Al2O3 nanoparticles synthesized by flame spray pyrolysis (FSP) method

In the present study, Al2O3 nanoparticles (synthesized by flame spray pyrolysis (FSP)) method were used for the defluoridation of aqueous solutions in batch tests under different experimental conditions. The point of zero charge (pHpzc) of Al2O3 nanoparticles was found to be 5.64. The role of functional groups in fluoride adsorption was discussed based on the data obtained from Fourier transform infrared (FTIR) analysis. The effects of different parameters such as solution pH, contact time, adsorbent dosage, temperature, initial fluoride concentration and presence of common competing anions were investigated on the defluoridation by Al2O3 nanoparticles. Results of this study show that the optimum pH for fluoride removal was 5.56. Kinetic data revealed that the uptake rate of fluoride was rapid in the beginning and equilibrium was achieved in 120 min. The adsorption data fitted reasonable well with pseudo-second-order kinetic model. Also, the Sips isotherm model was found to fit well with experimental data of defluoridation by Al2O3 nanoparticles. The maximum adsorption capacity for fluoride was 9.73 mg g−1 by Al2O3 nanoparticles. The fluoride adsorption was decreased in the presence of phosphate followed by carbonate and sulfate ions, while chloride and nitrate ions did not show significant effect on fluoride adsorption by Al2O3 nanoparticles.