Adsorption of lanthanum (III) from aqueous solution using 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester-grafted magnetic silica nanocomposites

In view of increasing attention of magnetic materials in the field of separation science and technology, we provide an effective route for fabrication of a new magnetic material with high adsorption capacity and selectivity toward metal ions, excellent acid resistance property and long service life. Silica was firstly coated on the magnetic particles, and then silane-coupling agent (3-chloropropyltryethosysilane) was used for grating 2-ethylhexyl phosphonic acid mono-2-ethylhexyl (P507), an organophosphorous acid extractant, on the surface of magnetic silica nanocomposite. The amount of P507 anchored on the particle was estimated to be 0.43 mmol/g. The P507-grafted magnetic silica nanocomposite was stable over pH range of 0-14. The maximum adsorption capacity of La (III) was 55.9 mg/g at the optimized pH 5.5. The adsorption of La (III) on our nanocomposites was found to follow the second order kinetics equation and fit Langmuir isotherm model well. The PO functional groups took an important role in the coordination and adsorption mechanism, which was confirmed by FTIR and XPS techniques. After 10 adsorption/desorption cycles, no obvious decrease in adsorption capacity or obvious loss in saturation magnetization were observed.