Fluoride removal performance and mechanism of superparamagnetic Fe3O4 nanoparticles

Fluoride contamination in drinking water is one of the major problems worldwide imposing a serious threat to human health. For fluoride removal, the superparamagnetic Fe3O4 nanoparticles (Fe3O4 NPs) were successfully synthesized in a non-aqueous medium through a simple and facile hydrothermal reduction route. These nanoparticles had a mesoporous structure with a specific surface area of 70.14 m2 g−1. Fluoride adsorption behavior was investigated and the optimization of several experimental parameters was explored. The adsorption properties of the sample were excellent. The adsorption capacity could reach up to 70.64 mg g−1 at 25°C when the initial fluoride concentration was 200 mg L−1. Kinetic data were consistent with the pseudo-second-order model and also indicated the adsorption process was limited by the pore diffusion. The adsorption isotherms were found fitting well with the Freundlich model. The presence of bicarbonate, carbonate, and phosphate adversely affected the adsorption of fluoride. The revelation of the adsorption mechanism was based on Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy analysis, and zeta potential study. The results showed the surface hydroxyl groups and sulfate anions played important roles in the fluoride removal. In the magnetic hysteresis curves, the Fe3O4 nanoparticles exhibited a superparamagnetic characteristic with a saturation magnetization of 29.86 emu g−1, which was beneficial for magnetic separation.