A facile method for the room-temperature synthesis of water-soluble magnetic Fe 3O 4 nanoparticles: Combination of in situ synthesis and decomposition of polymer hydrogel

Abstract

We propose and demonstrate a facile room-temperature synthetic method for obtaining water-soluble magnetic Fe 3O 4 nanoparticles (NPs) by combining the in situ synthesis and decomposition of a magnetic polymer hydrogel. The Fe 3O 4 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 Fe 3O 4 NPs into the aqueous medium. The NPs can be dispersed stably in water for more than three months. The Fe 3O 4 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 Fe 3O 4 NPs was 44.6 and 54.7 emu g −1 at 300 K and 5 K, respectively. The dried magnetic Fe 3O 4 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 Fe 3O 4 NPs can be expected for wide applications in the preparation of functional water-soluble NPs, such as those used in metals and semiconductors.