| Magnetic nanomaterials have attracted particular attention for their wide application potentials in various fields, such as catalyst supports, biomedicine, ferrofluid and high-density information storage. Recently, extensive research has been carried out on the synthesis, functionalization and applications of magnetic nanomaterials. Great research achievements have been made. However, how to design magnetic nanomaterials according to the practical applications is still a great challenge. In this thesis, based on the research background of carbon, silica and magnetic materials in our group, we have developed the design synthesis and application of different types of iron-based magnetic nanomaterials, described as follows.(1) In order to improve the stability of manetic nanoparticles, we present a novel method to synthesize carbon protected highly stable, discrete, dispersible and superparamagnetic Fe3O4@C nanospheres. The synthesis involves the follow steps:first, Fe3O4nanoparticles synthesized by modified co-precipitation method were successfully coated with phenol-formaldehyde resin through a hydrothermal method, forming Fe3O4@PF nanospheres; the silica layer was then deposited on the surface of Fe3O4@PF forming monodisperse Fe3O4@PF@SiO2composites; at last, the monodisperse, Fe3O4@C nanospheres can be obtained after pyrolysis and subsequent removal of the silica layer. By varying synthetic conditions, we have successeded in tailoring the size of Fe3O4@C nanospheres ranging from100to500nm, the number of encapsulated Fe3O4nanoparticles and the saturation magnetization values (in the range of1-24emu·g-1). It has been found that pyrolysis temperature has significant influence on the states of the Fe3O4nanoparticles in the carbon matrix. At pyrolysis temperature of500℃, the Fe3O4nanoparticles in the carbon matrix have no change compared with their polymer precursors. At600℃, the Fe3O4nanoparticles aggregate into larger single-crystal. Above700℃, the Fe3O4nanoparticles start to react with carbon forming Fe, Fe3C and graphitic carbon. The stability test has confirmed that the products carbonized at600℃show perfect stabilities in concentrated hydrochloric acid and under350℃in air.(2) Synthesis of shape-and size-controlled a-Fe2O3nanoparticles was performed through a hydrothermal method assisted with amino acids. It was found that the type and the amount of amino acids as well as the reaction temperatures have significant influence on the shape and size of the obtained a-Fe2O3nanoparticles. The use of acidic amino acids (always contain C=O in the side chain) typically leads to the formation of a-Fe2O3nanoparticles with spindle shape. However, rhombohedrally shaped a-Fe2O3nanoparticles were formed in presence of basic amino acids (always contain-NH2in the side chain). Increasing the amount of amino acid generally results in a-Fe2O3nanoparticles with decreasing particle sizes. The as-obtained spindle a-Fe2O3nanoparticles were successfully coated with phenol-formaldehyde resin forming a-Fe2O3@PF nanospheres through a hydrothermal method. In addition, cubic a-Fe2O3nanoparticles with a size of40nm were synthesized according to the methods published previously. Then, phenol-formaldehyde resin was also successfully coated on the surface of cubic a-Fe2O3nanoparticles through the hydrothermal method. So, the hydrothermal method can be regarded as a general mechanism to design other FexOy@PF core/shell structure products, no mater what shapes and sizes of iron oxide particles.(3) We have developed a novel synthesis for hollow polymer and carbon nanospheres, by utilization of the weak acid-base interaction (-COO-/NH4+/-COO-) induced self-assembly under hydrothermal conditions. The diameter of hollow polymer nanospheres and the core sizes can be adjusted by changing the reaction conditions. Consequently, the sizes of the hollow carbon are also variable. Owing to the presence of functional groups, the hollow polymer nanospheres can be converted to magnetic analogues after ion-exchange (Fe3+) and carboniztion process. In addition, we successfully introduced Fe3O4nanoparticles into the hollow polymer spheres. Then, the noble metal nanoparticles were doped into the carbon shell through ion-exchange and pyrolysis processes. Finally, we can obtain difunctional products composed of carbon shell dopped with noble metal nanoparticles and embedded Fe3O4nanoparticles in the hollow core.(4) The recovery and reuse of catalysts become more and more important for the development of green chemistry. In this part, we design a novel rattle-type nanospheres composed of a hollow mesoporous silica shell and entrapped Fe/noble metal nanoparticles based on the synthesis of Fe3O4@C nanospheres. First, Fe2O3@PF@SiO2was prepared using the method mentioned in chapter2. Subsequently, the as-synthesized Fe2O3@PF@SiO2was calcinated under air to remove polymer, then reduced by H2to form Fe@/h-SiO2. At last, the final Fe/noble metal@h-SiO2was obtained through replacement reaction between Fe and noble metal precursors. The activities of as-obtained Fe/Ag@h-SiO2and Fe/Pd@h-SiO2were tested in styrene epoxidation reaction and nitrobenzene reduction reaction. It was found that both catalysts were catalytically active. |
