Abstract
Using a hydrothermal process in FeCl2 solution, γ-Fe2O3/Ni2O3/FeCl3(FeCl2) composite nanoparticles were obtained from the FeOOH/Ni(OH)2 precursor prepared by coprecipitation. The precursor and the as-prepared nanoparticles were investigated by vibrating sample magnetometer (VSM), X-ray diffraction (XRD), energy disperse X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The experimental results showed that the paramagnetic amorphous precursor, in which Ni(OH)2 is formed outside FeOOH, is transformed to ferrimagnetic γ-Fe2O3/Ni2O3 composite when it is processed in FeCl2 solution (0.25, 0.50, 1.00 M) in an autoclave at 100°C for 1 hr. In addition, the dismutation reaction of FeCl2 produces FeCl3 and Fe. Some FeCl3 and little FeCl2 can be absorbed to form γ-Fe2O3/Ni2O3/FeCl3(FeCl2) composite nanoparticles in which Ni2O3 forms outside the γ-Fe2O3 core and the outermost layer is FeCl3 (FeCl2). The content of FeCl3 (FeCl2) in the particles increased, and the magnetization of the particles decreased with the concentration of FeCl2 solution increasing in the hydrothermal process. The FeCl3 (FeCl2) surface is chemically passive and nonmagnetic (paramagnetic). Accordingly, the composite nanoparticles are chemically stable, and their aggregation is prevented. The specific saturation magnetization of such composite nanoparticles can get to 57.4–62.2 emu/g and could be very suitable for synthesizing ferrofluids.
Highlights
Magnetic nanoparticles with diameters less than 100 nm have attracted increasing interest in the fields of basic science and technology [1,2,3]
The particles prepared by the hydrothermal process in 0.25 M, 0.50 M, and 1.00 M FeCl2 solution give σs values of 62.2, 59.2, and 57.4 emu/g, respectively
Since the ratio of Fe to Ni measured by X-ray photoelectron spectroscopy (XPS) is less than that of the starting reagents and the energy disperse X-ray spectroscopy (EDX) measurement is in agreement, it can be concluded that the Ni(OH)2 species has formed outside the FeOOH species in the precursor because the XPS information comes from the surface layer, less than 3 nm thick, but the EDX information comes from a depth of about 1 μm
Summary
Magnetic nanoparticles with diameters less than 100 nm have attracted increasing interest in the fields of basic science and technology [1,2,3]. Studies of magnetic nanoparticles have focused on the development of novel synthetic technology [2]. A nanocomposite is a material composed of two or more phases where the combination of different physical or chemical properties may lead to completely novel materials [4]. Magnetic nanocomposites have applications ranging from ferrofluids to separation science and technology [5]. The precursor, synthesized by chemical coprecipitation, needs to be further processed (by drying, calcinations, etc.) to form oxide nanoparticles [6]. For the synthesis of ferrofluids, nanoparticles prepared by calcination could be unsuitable
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
