Preparation Of Magnetic Transition Metal Nanoparticles In W/O Microemulsion

Synthesis of nanoparticles is in the frontier of researches and an issue of general interest of multi-disciplines now. Various techniques have been fruitfully employed in the preparation of nanoparticles. The microemulsion-processing method seems to be particularly promising and undergo rapid improvement in the past few years as it does not require special instruments or extreme conditions.In W/O microemulsion, the droplets provide perfect media as microreactor for preparation of nanoparticles, and due to the compartimentalized droplets, the monodispersed namoparticle size can be easily controlled in such media. Nanoparticles can nucleate, grow and aggregate in the water pool under the confinement of the water-in-oil interface, so the flexibility of the interface, the size of the water pool and also the ratio of reactants can affect the chateteristics of the resultant particles.Three different types surfactant (anion- surfactant is SDS, nonion- surfactant is TX-100, cation- surfactant is CTAB) were chosed as surfactants. The pseudo-ternary phase diagrams were drawed and used to be a standard of excellent microemulsion.The structure types of these microemulsions were characterized by the shapes of conductivity curves. The results showed that all the three systems had obvious microemulsion area. The stability of the W/O microemulsion was investigated by the conductivity curves, the microemulsion of CTAB- butanol- heptane-solution was used as the reactor system.A W/O microemulsion was prepared with CTAB as surfactant, butanol as cosurfactant, heptane as oil phase and FeCl2 solution as water phase. The optimal microemulsion conditions were found from pseudo-ternary phase diagrams. The average particle size is less than 10 nm, and magnetic particles are well-dispersed in methanetrichloride. The Fe3O4 nanoparticals obtained was investigated by means of TEM, XRD, FTIR and AGM. The XRD and EDS shows that the Fe3O4 nanoparticles are Fe3O4 and little Fe .TEM shows that the nanoparticals are mainly average spherical. The FTIR shows that the Fe3O4 nanoparticals are packaged by CTAB very well. The AGM analyzing results shows the nanoparticals exhibit superparamagnetic behavior and their magnetic saturation moments are 70emu/g, which are only～22% less than that of bulk Fe3O 4.The same system of microemulsion where the solution was changed to FeCl₂+NiCl₂ was used to prepare Fe-Ni alloy nanoparticles. The Fe-Ni alloy nanoparticals obtained was investigated by means of TEM, XRD, FTIR and AGM. The XRD and EDS results shows that the FeNi alloy nanoparticles are pure Fe-Ni alloy without any impurity.The TEM and HRTEM shows that the FeNi alloy particles are mainly average spherical, but have the tendency to form chain,it also have perfect crystal.The FTIR analysis shows that the Fe-Ni alloy nanoparticals are entraped by CTAB very well. The AGM analysis results show the nanoparticals exhibit superparamagnetic behavior and their magnetic saturation moments are as stronger as the amount of Fe.