Modification of Fe3O4 superparamagnetic nanoparticles with zirconium oxide; preparation, characterization and its application toward fluoride removal

Abstract

Fe₃O₄ superparamagnetic nanoparticles (NPs) modified with zirconia (ZrO₂) were synthesized (Fe₃O₄@ZrO₂) using a chemical co-precipitation method and used as a nanoadsorbent in the removal of excessive fluoride from aqueous solutions. This adsorbent combines the advantages of magnetic nanomaterial and F⁻ sorbent floc, with magnetic separability and high affinity toward fluoride, which provides distinctive merits including easy preparation, high adsorption capacity, and easy isolation from sample solutions by the application of an external magnetic field. The prepared Fe₃O₄@ZrO₂ magnetic nanoparticles were characterized by XPS, XRD, SEM, EDXA, TEM, BET, FTIR, and VSM techniques. Affecting parameters on the removal of fluoride, such as mass ratio of Fe₃O₄ to ZrO₂, solution pH, adsorption time, initial fluoride concentration, and co-existing anions were investigated. The high adsorption capacity calculated by the Langmuir equation was 158.6 mg g⁻¹ for Fe₃O₄@ZrO₂ (2 : 5) in pH 2.5. The adsorption capacity increased with temperature and the kinetics followed a pseudo-second-order rate equation. The enthalpy change (ΔH⁰) and entropy change (ΔS⁰) was 25.02 kJ mol⁻¹ and 3.76 J mol⁻¹ K⁻¹, which substantiates the endothermic and spontaneous nature of the fluoride adsorption process. Furthermore, the residual concentration of fluoride using Fe₃O₄@ZrO₂ NPs as adsorbents could reach 0.3 mg L⁻¹ with an initial concentration of 20 mg L⁻¹. Also application of Fe₃O₄@ZrO₂ NPs for the removal of fluoride from real samples was tested. All of the results suggested that the Fe₃O₄@ZrO₂ NPs with a strong and specific affinity toward fluoride could be an excellent adsorbent for treatment of fluoride contaminated water.