A universal route for synthesizing nearly monodisperse MxOy (M=Zn, In, Co, Fe) nanocrystals

In this work, we successfully synthesized nearly monodisperse ZnO, In2O3, CoO, and Fe3O4 nanocrystals by using a universal route. The designed synthetic route is a two-step chemical process, based on the hot reduction of metal oleate ((C18H33O2)xM, M=Zn, In, Co, Fe) with metal sodium in liquid paraffin followed by the rapid oxidation of the resulting products. During the reaction, the byproduct sodium oleate is used as the capped surfactant. XRD and XPS results display that the as-obtained products are ZnO, In2O3, CoO, and Fe3O4 rather than metal/metal oxides core/shell nanocomposites. TEM images of these products show that they are nearly monodisperse nanoparticles with relatively uniform size distribution. On the basis of our experimental results, the possible formation mechanism for nearly monodisperse MxOy nanocrystals was proposed. In our performance tests, ZnO and In2O3 nanocrystals display good optical behavior, while CoO and Fe3O4 nanocrystals show good ferromagnetism and superparamagnetism behavior at room temperature, respectively.