Removal of fluoride from aqueous media by Fe3O4@Al(OH)3 magnetic nanoparticles

A novel magnetic nanosized adsorbent using hydrous aluminum oxide embedded with Fe3O4 nanoparticle (Fe3O4@Al(OH)3 NPs), was prepared and applied to remove excessive fluoride from aqueous solution. This adsorbent combines the advantages of magnetic nanoparticle and hydrous aluminum oxide floc with magnetic separability and high affinity toward fluoride, which provides distinctive merits including easy preparation, high adsorption capacity, easy isolation from sample solutions by the application of an external magnetic field. The adsorption capacity calculated by Langmuir equation was 88.48 mg g−1 at pH 6.5. Main factors affecting the removal of fluoride, such as solution pH, temperature, adsorption time, initial fluoride concentration and co-existing anions were investigated. 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 6.836 kJ mol−1 and 41.65 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@Al(OH)3 NPs as adsorbent could reach 0.3 mg L−1 with an initial concentration of 20 mg L−1, which met the standard of World Health Organization (WHO) norms for drinking water quality. All of the results suggested that the Fe3O4@Al(OH)3 NPs with strong and specific affinity to fluoride could be excellent adsorbents for fluoride contaminated water treatment.