Acid-Stable Magnetic Core-Shell Nanoparticles for the Separation of Rare Earths

Coreshell Fe3O4@SiO2 nanoparticles were prepared with a modified Stober method and functionalized with N-[(3-trimethoxysilyl)propyl]ethylenediamine triacetic acid (TMS-EDTA). The synthesis was optimized to make coreshell nanoparticles with homogeneous and thin SiO2 shells (4.8 +/- 0.5 nm) around highly superparamagnetic Fe3O4 cores (14.5 +/- 3.0 nm). The coreshell Fe3O4@SiO2(TMS-EDTA) nanoparticles were then used for the extraction and separation of rare-earth ions. By comparing them with previously published results for Fe3O4(TMS-EDTA) and SiO2(TMS-EDTA) nanoparticles, it was clear that the coreshell nanoparticles combine the advantage of magnetic retrieval observed for Fe3O4(TMS-EDTA) nanoparticles with the higher selectivity observed for SiO2(TMS-EDTA). The advantages of the SiO2 shell include a lower specific weight and a larger grafting density compared to Fe3O4 surfaces, but also the improved resistance to acidic environments required for the stripping of rare-earth ions.