Synthesis and Macrodynamics of Water-based Magnetic Fluid

Abstract: In this paper, preparation of water-based magnetic fluid by using nanometer Fe_3O_4,synthesized by different methods, as basic substance was systematically studied.1. Fe_3O_4 magnetic nanoparticles (MNPs) were prepared by the coprecipitation of Fe~(2+)and Fe~(3+) using ammonium hydroxide (NH_4OH) as precipitating agent. Transmissionelectronic microscopy (TEM) showed that the particle size is around 10 nm. X-raypowder diffraction (XRD) indicated the sole existence of inverse cubic spinel phase ofFe_3O_4. The surface of MNPs was coated with oleate sodium as the primary layer andpolyethylene glycol 4000 (PEG-4000) as the secondary layer to improve the stabilityof water-based ferrofluids (FFs). The dosages of oleate sodium and PEG-4000 werefound to have an important effect on increasing the solid content. Gouy magneticbalance showed that the saturation magnetization could be as high as 1.44×10~5 A/m.Laser particle-size analyzer determined the aggregate size in FFs. The Fe_3O_4 MNPsdid not change through the preparation of FFs. Differential scanningcalorimetry-thermogravimetry (DSC-TG) and Fourier transform infrared spectroscopy(FT-IR) analysis showed existence of two distinct surfactants on the particle surface.The concentrated and diluted FFs were characterized by UV-vis spectrophotometerand excellent stability was found. The rheological measurements indicated thatviscosity increased with the increase of solid content and applied magnetic field, butdecreased with the increase of temperature. The FFs showed the non-Newtonianbehavior of shear-thinning when the solid content was high. The mechanical propertiesof polyvinylalcohol (PVA) thin film can be greatly improved by adding FFs.2. Fe_3O_4 magnetic nanoparticles (MNPs) were synthesized by the co-precipitation of Fe~(3+)and Fe~(2+) with ammonium hydroxide under an antioxidant, hydrazine hydrate. Thesodium citrate-modified Fe_3O_4 MNPs were prepared under Ar protection and were characterized by Fourier transform infrared spectroscopy (FT-IR), transmissionelectron microscopy (TEM), X-ray powder diffraction (XRD) and vibrating samplemagnetometer (VSM). The sedimentation experiment was carried out to compare thedispersibility of modified MNPs with that of unmodified ones. To improve theantioxygenic property of Fe_3O_4 MNPs, a silica layer was coated onto the modified andunmodified MNPs by the hydrolysis of tetraethoxysilane (TEOS) at 50℃and pH=9.The resultant silica-coated Fe_3O_4 MNPs were characterized by FT-IR, XPS, XRD,TEM and VSM. Afterwards, the silica-coated Fe_3O_4 composite MNPs were modifiedby oleic acid (OA) and were tested by IR and VSM. IR results revealed that the OAwas successfully grafted onto the silica shell. The Fe_3O_4/SiO_2 MNPs modified by OAwere used to prepare water-based ferrofluid (FF), which was prepared by adding PEGas surfactant to form bilayer surfactant-stabilized FF. The properties of FFs werecharacterized using UV-vis spectrophotometer, Gouy magnetic balance, laserparticle-size analyzer and a Brookfield LVDV-Ⅲ+ rheometer. The FF was used toprepare polyvinylalcohol (PVA) thin film, and the mechanical properties of the filmcan be greatly improved.3. Fe_3O_4 magnetic nanoparticles (MNPs) were synthesized by the co-precipitation of Fe~(3+)and Fe~(2+) with a precipitating agent (ammonium hydroxide) and an antioxidant(hydrazine hydrate). Transmission electronic microscopy (TEM) showed that theparticle size is around 10 nm. X-ray powder diffraction (XRD) indicated the soleexistence of inverse cubic spinel phase of Fe_3O_4. The sodium citrate treated Fe_3O_4nanoparticles were prepared under Ar protection and were characterized bytransmission electron microscopy (TEM), X-ray powder diffraction (XRD) andvibrating sample magnetometer (VSM). The coating of Fe_3O_4 magnetic nanoparticleswas carried out by the direct precipitation using zinc acetate and ammonium carbonate.The obtained solids were firstly dried under vacuum for 12h, and then calcined at 350℃for 3h to obtain Fe_3O_4/ZnO composite MNPs. The resultant Fe_3O_4/ZnO MNPswere characterized by FT-IR, XRD, TEM and VSM. Afterwards, photocatalytic degradation of methyl orange in aqueous solution was performed using differentnanoparticles as photocatalyst. Fe_3O_4/ZnO composite MNPs had different molar ratioof Fe_3O_4 to ZnO. The separation of composite MNPs from the aqueous suspension wasalso carried out using a magnet. The results showed that the Fe_3O_4/ZnO compositeMNPs had better catalytic activity than that of bare ZnO nanoparticles, and themagnetic properties of composite MNPs provided an easy and efficient way toseparate Fe_3O_4/ZnO MNPs from a suspension. Therefore, the composite MNPs couldbe used repeatedly.4. A system composed of a self-made experimental apparatus and a high-speed CCDcamera was used to study the macrodynamics of water-based ferrofluid. It was foundthat the model used to simulate the interface can well match the shape of interfacesurface obtained by CCD camera whether there is applied magnetic field or not…
Key words: Fe_3O_4 nanoparticles; surface modification; magnetic fluid; photocatalytic activity; macrodynamics

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