Synthesis and Research of Oil-based Magnetic Fluid

Abstract: In this paper, two parts, including synthesis and surface modification of ZnO nanoparticles and preparation of oil-based magnetic fluid by using nanometer Fe_3O_4 as basic substance, were systematically studied.In the first part- synthesis and surface modification of ZnO nanoparticles, four systems were studied as follows:1. Employing ZnSO_4·7H_2O and urea as raw materials, ZnO nanoparticles were synthesized by homogeneous precipitation method. And the obtained ZnO nanoparticles were characterized by XRD and TEM, respectively. Afterwards, the surfaces of ZnO nanoparticles were modified with stearic acid. And the synthesized sample was tested by IR. It was concluded that a covalent bond was formed by chemical reaction between the surface hydroxylic groups that were present on the surface of nanometer ZnO powders and organic long-chain molecules such as stearic acid, the surface of ZnO powder was coated with a monomolecular layer of aliphatic chains, the polarity of nanometer ZnO powders was changed to non-polarity. In addition, the effects of concentration, reaction temperature and reaction time on the surface-modified ZnO nanoparticles were discussed.2. ZnO nanoparticles were prepared by the precipitation method, employed ZnSO_4·7H_2O and NaOH as materials. Moreover, the surface of ZnO nanoparticles was coated by SiO_2, which was synthesized by the hydrolysis of Na_2SiO_3. The obtained ZnO nanoparticles were characterized by many methods such as IR, TEM, XRD, SEM and XPS. It was clearly shown that there was the formation of an interfacial bond between ZnO and SiO_2 by comparison of IR and XPS of ZnO and ZnO/ SiO_2 In addition, photodegradation of methyl orange in aqueous solution was investigated by using the powder of ZnO nanoparticles and ZnO/ SiO_2 nanoparticls as photocatalyst. The results showed that the ZnO nanoparticles have better performance of photocatalysis than that of ZnO/ SiO_2 nanoparticles, which further illustrated that SiO_2 was coated on the surface of ZnO nanoparticles as a thin layer.3. The precursor of the ZnO nanoparticles was synthesized by precipitation from zinc acetate and ammonium carbonate. Afterwards, two different routines were used to prepare the ZnO nanoparticles. The obtained ZnO nanoparticles were characterized by the methods of transmission electron microscope and X-ray diffraction. It was concluded that the heterogeneous azeotropic distillation process of the precursor, which made 1-butanol molecular substitute water surrounding the precursor particle, effectively reduced the formation of hard agglomeration between nanoparticles and decreased the mean size of ZnO nanoparticles. Furthermore, the surface of ZnO nanoparticles was capped by oleic acid. Existence of the organic layer can beconfirmed by the results of FT-IR Spectrums, which also indicated that the inorganic nuclei and organic surface layer were linked with chemical bond. The mechanism of formation was also proposed.4. To improve the interfacial interaction between ZnO nanoparticles and polymer matrix, an effective surface modification method was proposed by grafting PMMA onto the particles. That is, the surface of ZnO nanoparticles was firstly treated with a KH570 silane coupling agent, which introduced functional double bonds onto the surface of ZnO nanoparticles, followed by radical grafting polymerization in non-aqueous system. The obtained samples were characterized by Fourier-transform infrared spectra (FTTR), thermogravimetric analysis (TGA), sedimentation test in solvents, scanning electron microscope (SEM), x-ray powder diffraction (XRD), and gel permeation chromatography (GPC). Results of FTIR, TGA and GPC showed that the desired polymer chains have been covalently bonded to the surface of the ZnO nanoparitles. In addition, effects of concentrations of monomer on the percentage of MMA grafting and dispersion in solvents were investigated. It was found that the growing concentrations of monomer could increase the percentage of MMA grafting and promote the dispersion in solvents. Moreover, the ZnO/PS composites were prepared by adding surface PMMA grafted ZnO into styrene monomer, followed by radical grafting polymerization. The resulted composites were characterized by TGA, DSC and XRD. The testing results indicated that thermal behaviors of PS were obviously changed in the presence of surface PMMA grafted ZnO.In the second part- preparation of oil-based magnetic fluid by using nanometer as basic substance, four systems were studied as follows:1. Magnetic Fe_3O_4 nanoparticles were prepared by the co-precipitation of Fe~(3+) and Fe~(2+). NH_3·H_2O was used as the precipitating agent to control the pH value. The synthesized magnetic nanoparticles were characterized by HRTEM and XRD. The primary size of Fe_3O_4 nanoparticles is around 10 nm. Afterwards, to enhance the interfacial interaction between the magnetic Fe_3O_4 nanoparticles and polymer matrix, an effective surface modification method was developed by grafting styrene onto the nanoparticle surface. That is, the surface of magnetic Fe_3O_4 nanoparticles was firstly treated with the coupling agent, KH-570, which introduced reactive groups onto the surface of Fe_3O_4 particles, followed by radical grafting polymerization in non-aqueous system. The testing results of IR and TG indicated that the ploystyrene chains had been covalently bonded to the surface of the magnetic Fe_3O_4 nanoparticles. After the surface graft polymerization, Fe_3O_4 nanoparticles were varied from non-polarity to polarity. In additon, the effects of initiator dosage, monomer concentration and reaction temperature on the surface-modified Fe_3O_4 nanoparticles were discussed.2. The influence of microwave aging on the crystalline form of Fe_3O_4 magnetic nanoparticles was studied. Moreover, the surface of Fe_3O_4 magneticnanoparticies was modified by stearic acid. The obtained sample was characterized by IR. The testing results of IR indicated that a covalent bond was formed by chemical reaction between the hydroxyl groups on the surface of nano-Fe_3O_4 and carboxyl groups of stearic acid. After modification, the polarity of nano-Fe_3O_4 is changed to non-polarity. Moreover, effects of reaction time, reaction temperature, and concentration of stearic acid on surface modification were investigated.3. The oil-based magnetic fluid in oxy-iron was synthesized by employing magnetic Fe_3O_4 nanoparticies as basic substance and toluene as mediated fluid. The obtained magnetic fluid was characterized by UV-vis, Gouy magnetic balance and laser particle sizer. The testing results showed that the synthesized magnetic fluid had good stability, its susceptibility was 3.7 ×10~(-8) and its saturated magnetization was 2.91mT. In addition, the mean size d(0.99) of magnetic FesQ* nanoparticies was 39.55nm.4. The silicon-oil-based magnetic fluid was synthesized by employing magnetic Fe3O4 nanoparticies as basic substance and silicon-oil as mediated fluid. The obtained magnetic fluid was characterized by UV-Vis, Gouy magnetic balance. The testing results showed that the resulted magnetic fluid had excellent stability, its susceptibility was 3.4X10"6 and its saturated magnetization was 21.95 mT…
Key words: ZnO; Fe_3O_4; nanoparticies; surface modification; grafting polymerization; nanocomposites; magnetic fluid

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