A facile method for the room-temperature synthesis of water-soluble magnetic Fe3O4 nanoparticles: Combination of in situ synthesis and decomposition of polymer hydrogel

We propose and demonstrate a facile room-temperature synthetic method for obtaining water-soluble magnetic Fe3O4 nanoparticles (NPs) by combining the in situ synthesis and decomposition of a magnetic polymer hydrogel. The Fe3O4 NPs with average diameters of 6.3–8.3 nm were synthesized in a cross-linked polyacrylamide (PAAm) hydrogel by coprecipitating iron ions. The decomposition of the magnetic polymer hydrogel by an aqueous solution of sodium hydroxide led to the transfer of Fe3O4 NPs into the aqueous medium. The NPs can be dispersed stably in water for more than three months. The Fe3O4 NPs were characterized by X-ray photoelectron spectra (XPS), X-ray powder diffraction (XRD), transmission electron microscope (TEM), and Fourier transform infrared spectroscopy (FT-IR). The saturation magnetization of the Fe3O4 NPs was 44.6 and 54.7 emu g−1 at 300 K and 5 K, respectively. The dried magnetic Fe3O4 NPs were easily dispersed in alkaline aqueous media (pH > ∼8) and kept stable for a long time. This room-temperature synthetic method for water-soluble magnetic Fe3O4 NPs can be expected for wide applications in the preparation of functional water-soluble NPs, such as those used in metals and semiconductors.