Adsorption of fluoride ions onto non-thermal plasma-modified CeO2/Al2O3 composites

The CeO2/Al2O3 composites were synthesized by different synthesis methods and applied to remove excessive fluoride ions from water. The resulting materials were examined by scanning electron microscope (SEM), N-2 adsorption/desorption, and X-ray diffraction (XRD) analysis. In order to improve fluoride removal efficiency, non-thermal plasma (NTP) was used to modify the surface structure of the composites. Effects of calcination temperature, loading, solution pH, adsorption time, and coexisting anions on adsorption capacity were investigated in detail. The results indicated that the composites synthesized by co-precipitation method exhibit excellent removal efficiency in low-concentration fluoridated water. The appropriate adsorption capacity was achieved in the pH range of 3-10. The NTP-modified composites show high binding capacity for fluoride, where the maximum adsorption capacity of 37.0 mg/g was reached at the initial concentration of 120 mg/L. The kinetics of the fluoride adsorption processes were well described by the pseudo-second-order kinetic model. The equilibrium adsorption data, obtained from the experiment using adsorbents with and without NTP treatment, were analyzed by Redlich-Peterson, Temkin, and Dubinin-Radushkevich isotherm models. It was found that the Redlich-Peterson model provides the best correlation for the experimental data.