Adsorption process of fluoride from drinking water with magnetic core-shell Ce-Ti@Fe₃O₄ and Ce-Ti oxide nanoparticles

Synthesized magnetic core-shell Ce-Ti@Fe₃O₄ nanoparticles were tested, as an adsorbent, for fluoride removal and the adsorption studies were optimized. Adsorption capacity was compared with the synthesized Ce-Ti oxide nanoparticles. The adsorption equilibrium for the Ce-Ti@Fe₃O₄ adsorbent was found to occur in <15min and it was demonstrated to be stable and efficient in a wide pH range of 5-11 with high fluoride removal efficiency over 80% of all cases. Furthermore, isotherm data were fitted using Langmuir and Freundlich models, and the adsorption capacities resulted in 44.37 and 91.04mg/g, at pH7, for Ce-Ti oxides and Ce-Ti@Fe₃O₄ nanoparticles, respectively. The physical sorption mechanism was estimated using the Dubinin-Radushkevich model. An anionic exchange process between the OH^- group on the surface of the Ce-Ti@Fe₃O₄ nanomaterial and the F^- was involved in the adsorption. Moreover, thermodynamic parameters proved the spontaneous process for the adsorption of fluoride on Ce-Ti@Fe₃O₄ nanoparticles. The reusability of the material through magnetic recovery was demonstrated for five cycles of adsorption-desorption. Although the nanoparticles suffer slight structure modifications after their reusability, they keep their adsorption capacity. Likewise, the efficiency of the Ce-Ti@Fe₃O₄ was demonstrated when applied to real water to obtain a residual concentration of F^- below the maximum contaminated level, 1.5mg/L (WHO, 2006).