Preparation and characterization of highly water-soluble magnetic Fe₃O₄ nanoparticles via surface double-layered self-assembly method of sodium alpha-olefin sulfonate

A kind of double-layered self-assembly sodium alpha-olefin sulfonate (AOS) capped Fe₃O₄ magnetic nanoparticles (Fe₃O₄-AOS-MN) with highly water-solubility was prepared by a wet co-precipitation method with a pH of 4.8. The resulting Fe₃O₄-AOS-MN could be dispersed into water to form stable magnetic fluid without other treatments. The result of X-ray diffraction (XRD) indicated that the Fe₃O₄-AOS-MN maintained original crystalline structure and exhibited a diameter of about 7.5 nm. The iron oxide phase of nanoparticles determined by Raman spectroscopy is Fe₃O₄. Transmission electron microscopy (TEM) analysis confirmed that the Fe₃O₄-AOS-MN with spherical morphology were uniformly dispersed in water. FT-IR spectroscopy (FT-IR) and thermo-gravimetric analysis (TGA) verified the successful preparation of Fe₃O₄-AOS-MN capped with double-layered self-assembled AOS. The corresponding capacities of monolayer chemical absorption and the second-layer self-assembly absorption were respectively 4.07 and 14.71 wt% of Fe₃O₄-MN, which were much lower than those of other surfactants. Vibrating sample magnetometer (VSM) test result showed Fe₃O₄-AOS-MN possessed superparamagnetic behavior with the saturation magnetization value of about 44.45 emu/g. The blocking temperature T_B of Fe₃O₄-AOS-MN capped with double-layered AOS is 170 K. - Highlights: • Double-layered self-assembly sodium alpha-olefin sulfonate (AOS) capped Fe₃O₄ magnetic nanoparticles are prepared by a wet co-precipitation method. • Double-layered Fe₃O₄-AOS-MN exhibits highly water-solubility. • The iron oxide phase is determined by Raman spectroscopy. • Fe₃O₄-AOS-MN capped with double-layered AOS possesses super-paramagnetic behavior. • The blocking temperature T_B of Fe₃O₄-AOS-MN capped with double-layered AOS is 170 K