Preparation And Characterization Of Magnetic Nanoparticles Comprised Of Nickel And Cobalt

The properties of magnetic nanoparticles which have been widely used in catalysis, magnetic data storage and other fields are very different from bulk materials. However, these properties are highly dependent on the size of the particles. Therefore preparation of mono-disperse magnetic nanoparticles is of fundamental and technological interest.Firstly, the transition metal acetylacetonates precursors were prepared. Secondly, Nickel, Cobalt and alloy Fe-Ni, Ni-Co, Fe-Co magnetic nanoparticles were prepared by thermal decomposition of Ni(acac)2, Co (acac)2 and Fe (acac)3 in the autoclave reactor. Nanoparticles were characterized by XRD, TEM and HRTEM.The metal acetylacetonates are very important precursors for making the nanoparticals. Up to now, the acetylacetonates have to be purchased from the foreign agent companies, which will improve the cost in making the nanoparticals. Now the complex nature, the applications, as well as the synthesis and characterization methods for the Ni(acac)2, Co (acac)2 and Fe (acac)3 have been researched. Through a series of experiments, the influences of pH, reactants, reactant ratios and temperature were studied. Then infrared spectra, XRD and elemental analysis are used to analyse the structures and properties of the products. At the end, the optimized synthesis conditions for the preparation of Ni(acac)2, Co (acac)2 and Fe (acac)3 can be obtained.During the preparation of nickel nanoparticles, the influences of temperature, protective gas, reducing agent and stabilizer for different reaction mediums should be considered. The results demonstrated that some key points are necessary to get Nickel metal nanoparticles. Firstly the reaction must take place in reducing ambience like H2. Secondly the reducing agent should be oil-soluble. Thirdly suitable chain stabilizers are necessary. Monodisperse Nickle nanoparticles with mean sizes of 6.8nm and 6.1nm were prepared by using liquid paraffin or n-heptane as reaction mediums comparatively. As iron nanoparticles is an excellent catalyst for the thermal decomposition of Ni(acac)2, Nickel nanoparticles were prepared in the presence of 5% iron nanoparticles. In this condition, the magnetic and disperse properties of nickel nanoparticles are unconverted, but the mean size of nickel nanoparticles decreases from 6.8nm to 4.1nm.According to the conditions for the preparation of Nickel nanoparticles and the properties of Co(acac)2, Cobalt nanoparticles with mean size 12.5nm after a large number of experiments, which coalesce slightly and have high degree of crystallinity can be obtained. The results confirmed that Cobalt nanoparticles with stronger magnetism are easier to aggregate in comparison with Nickel nanoparticles. This is because that the molecular polar force and the coupling force between the Cobalt nanoparticles are much stronger. According to the properties of alloy magnetic nanoparticles and optimizing the reactant ratios, Fe-Ni alloy nanoparticles with mean size 13.2nm, Ni-Co alloy nanoparticles with mean size 18.4nm and Fe-Co alloy nanoparticles with mean size from 78.8 to 87.5nm were also prepared successfully.The preparation of nanoparticles is the precondition for their application. By using nickel nanoparticles and alloy Ni-Co nanoparticles as catalyzers respectively, the selective hydrogenation of parachloronitrobenzene to produce p-chloroaniline are studied. The results showed that the transformation ratio of parachloronitrobenzene is 21.1% and the selectivity is 95%-98% when the nickel nanoparticles are used as catalyst. If Ni-Co nanoparticles are used as catalyst, the transformation ratio is 100% and the selectivity is 99%. The transformation ratio of the Ni-Co nanoparticle catalyst is higher than that of the nickel nanoparticle catalyst, however both of the two kinds nanoparticles are of a high selectivity.