Synthesis And Magnetic Properties Of Mesoporous Metal Oxide Use Nanocasting

Abstract： Mesoporous metal oxides possess excellent catalytic, photovoltaic,electromagnetic properties due to the diversity of the valence state, and haveapplications in many fields, such as solid catalytic, magnetic materials and lithiumbatteries. Synthesis of the ordered structure of the metal oxide based on nanocastingroute is arousing increasing interests in recent years. Many researches have beenfocused on mesoporous metal oxide to investigate the relationship between theregulation of the fine structure of magnetic metal oxides and magnetic behavior.To acheave highly ordered mesoporous metal oxides structure, it is of crucialimportant to adjust the regulation of the hard template pores. Herein, the synthesiesof the hard templates （FDU-12and SBA-16） were first studied. By controlling of thehydrothermal temperature, the synthesis temperature and the TEOS concentration,the pore stuctrues were finely adjusted.Then, face centered cubic ordered mesoporous Co₃O₄magnetic material wereprepared via the nanocasting route using FDU-12as hard template with differentpore size. The replicas show ordering from sub-nanometer size to micrometer size:1)the walls are highly crystalline;2) a highly ordered3D pore structure is observed;3)the particles are several micrometers in size which compose of nano-spheres. It wasdemonstrated that the sphere diameter （wall thickness） and the distance between thespheres （pore size） in the mesoporous Co₃O₄can be varied systematically within therange18.2-24.8nm and12.2-9.1nm. We have also studied their rmagnetic behaviorby using the temperature dependence of the magnetization and the applied magneticfield dependence of the magnetization. It was found that that the factors which affectthe magnetic behavior in our Co₃O₄nano-sphere system are not only the size effectbut also the distance between the spheres at the nanoscale.Thirdly, a series of hollow structure of mesoporous iron oxide nanospheresM-α-Fe₂O₃, M-Fe₃O₄and M-γ-Fe₂O₃were synthesized using concentrated H₂SO₄treated FDU-12as hard template by impregnation method. Differnet with Co₃O₄ samples, hollow α-Fe₂O₃spheres rather then mesoporous solid sphere were obtainedafter the replicating process. The hollow α-Fe₂O₃spheres were then transformed intoM-Fe₃O₄in reduction atmospheres （H₂/Ar,5/95） and further transformed intoγ-Fe₂O₃through oxidation. The results show high specific surface area of107.9and91.5and88m²/g for M-α-Fe₂O₃, M-Fe₃O₄and M-γ-Fe₂O₃respectively. Magneticmeasurement showed that remanent magnetization of the M-α-Fe₂O₃wasMs=0.02283emu/g. The Tbof the M-Fe₃O₄and γ-Fe₂O₃were190°C and185°C,the specific saturation magnetization were53.8emu/g and36.1emu/g, and thecoercivity were1.8Oe and11Oe which can emerge superparamagnetic and class ofthe superparamagnetic effect.