Preparation And Characterization Of Magnetic Nanoparticles

The properties of magnetic nanoparticles are very different from bulk materials. It has been widely used in catalysis, magnetic data storage and other fields. However, these properties are highly dependent on the size of the particles. So preparation of monodisperse magnetic nanoparticles is of fundamental and technological interest.Iron, nickel, and core-shell Fe3O4@Ni magnetic nanoparticles were produced by thermal decomposition of Fe(acac)3 and Ni(acac)2 in the autoclave reactor. Nanoparticles were characterized by XRD, TEM, HRTEM, EDS, AGM, and IR.During the processes of iron nanoparticles preparation, the influences of ambience, reducing agent, stabilizer and reaction media were studied. The results confirmed that some key points are necessary to get iron metal nanoparticles. Firstly it must be in reducing ambience like H2 and CO atmosphere. Then the reducing agent should be oil-soluble. At last, all of the reaction media and stabilizer molecules should be molecules without O atom. Monodisperse iron nanoparticles with mean sizes 10nm were prepared. These nanoparticles are superparamagnetic, with saturation intensity of 121 emu·g-1. The result of IR showed that stabilizer molecules adsorb on the surface nanoparticles to prevent aggregation. Nickel nanoparticles were not successfully prepared in the same way like preparation of iron. As Iron nanoparticles is an excellent catalyst for the reaction of Ni(acac)2 thermal decomposition, Nickel nanoparticles were ultimately prepared in the presence of 5% iron nanoparticles. At the end, core-shell Fe3O4@Ni nanoparticles were prepared, the size of core is 8.3nm and the thickness of shell is 2.6nm . The results showed that these particles are superparamagnetic, with saturation intensity of 121 emu·g-1.The stability of nanoparticles, the forming process of core-shell nanoprarticles and the protection mechanism of stabilizer were studied by molecule simulation method. The results showed that the specific surface energy increasees rapidly as the size of nanopartilces decrease, when size less than 4nm. These nanoparticles with size less than 4nm, are not stable even in the presence of stabilizer. The results of Molecular Dynamics(MD) simulation shows the forming process of core-shell structure nanoparticles: firstly formation of the core nanoparticle of iron, then nickel atoms diffuse to the nuclear surface, at last nickel and iron atoms mutual penetrate and form chemical bond. The adsorption mechanism of ole in the iron (1 1 0) face and iron nanopartilces surface was investigated by dynamic simulation method. It showed that ole adsorb in the surface of nanoparticle through–N- and–C=C- double chelating. This chelation reduces the surface energy and makes nanoparticles stable. The calculation frequency and IR result consistent well, the result further confirm this adsorption mechanism.