PVP modified Fe3O4@SiO2 nanoparticles as a new adsorbent for hydrophobic substances

Abstract

In this work, superparamagnetic Fe3O4@SiO2 nanoparticles (NPs) with high saturation magnetization (Ms) were synthesized. The NPs had core-shell structures with magnetic Fe3O4 as the core and SiO2 as the shell. The magnetic core was firstly prepared with miniemulsion method, then SiO2 shell was synthesized by Stöber method. Polyvinylpyrrolidone (PVP) modified Fe3O4@SiO2 NPs were a new adsorbent material for hydrophobic substances in water environments. The original and PVP modified Fe3O4@SiO2 NPs were characterized with transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometry (FT-IR), atomic force microscopy (AFM), as well as Brunauer–Emmet–Teller (BET). The Ms of the original and modified Fe3O4@SiO2 NPs were 30.78 emu·g−1 and 30.89 emu·g−1, respectively. XPS certified that PVP molecules were embedded in the shell of Fe3O4@SiO2 NPs, owing to PVP used in preparation of Fe3O4 nanocluster as a protective agent. After modification, besides in SiO2 shell, PVP was also found on the surface of Fe3O4@SiO2 NPs. AFM images showed that column-shaped admicelles formed upon the surface of Fe3O4@SiO2 NPs. Fe3O4@SiO2 NPs surface area reduced considerably from 88.74 to 60.82 m2 g−1, which verified large aggregations formed on the surface of Fe3O4@SiO2 NPs. Hydrophobic interaction helped phenanthrene (as a representative of hydrophobic substance) to be adsolubilized in PVP admicelles. The equilibrium adsorption capacity of PVP modified Fe3O4@SiO2 NPs for phenanthrene was 18.84 mg g−1, 2.01 times as that of Fe3O4@SiO2 NPs.