Preparation And Characterization Of Silica-coated Fe_3o_4 Nanoparticles Used As Precursor Of Ferrofluids

摘要

Fe_3O_4 magnetic nanoparticles (MNPs) were synthesized by the co-precipitation of Fe~(3+) and Fe~(2+) with ammonium hydroxide. The sodium citrate-modified Fe_3O_4 MNPs were prepared under Ar protection and were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and vibrating sample magnetometer (VSM). To improve the oxidation resistance of Fe_3O_4 MNPs, a silica layer was coated onto the modified and unmodified MNPs by the hydrolysis of tetraethoxysilane (TEOS) at 50 ℃ and pH 9. Afterwards, the silica-coated Fe_3o_4 core/ shell MNPs were modified by oleic acid (OA) and were tested by IR and VSM. IR results revealed that the OA was successfully grafted onto the silica shell. The Fe_3O_4/SiO_2 core/shell MNPs modified by OA were used to prepare water-based ferrofluids (FFs) using PEG as the second layer of surfactants. The properties of FFs were characterized using a UV-vis spectrophotometer, a Gouy magnetic balance, a laser particle size analyzer and a Brookfield LVDV-III+ rheometer.