Application Of Polyacrylamide Gel Methods To Preparation Of Ternary Metal Oxide Materials

Nanomaterials has attracted a great of attentions due to its extensive applications in information storage medium, recording media, drug delivery, magnetic refrigeration devices, waste-water treatment, catalytic field, etc. In particular, homogenous and highly dispersed magnetic materials, especially the magnetic nanoparticles, exhibit a pronounced physicochemical properties which are usually absent in their bulk, which has attracted much interest in recent years.In this thesis a polyacrylamide gel method is used to prepare（Mg, Al, Mn, Ca, Sr,Ba）- ferrites magnetic materials and the phase purity, thermal properties, magnetic properties, optical properties and photocatalysis activity are studied. The specific research contents are listed as follows:（1） M（M=Bi, Ca, La, Sr, Y, Al, Mn）Fe O₃ powders have been prepared by a polyacrylamide gel method using tartaric acid as chelating agent. X-ray diffraction（XRD） analysis indicates that the as-synthesized M（M = Al or Mn） Fe O₃ is pure with same structure as α-Fe2O₃ or Mn2O₃. However, when the M nitrate（M= Bi, Ca, La, Sr,or Y） is used as raw material to prepare M（M= Bi, Ca, La, Sr, or Y）Fe O₃ xerogel, the XRD results of the xerogel sintered at 700 °C show the obtained product is not pure.Scanning electron microscope（SEM） observation shows that the morphology of MFe O₃ powder is significantly dependent on the sintering temperature. The thermal expansion and differential scanning calorimetry（DSC） curves of Al Fe O₃ sample analysis indicates that a phase transition near 700 ?C. The crystal growth mechanisms, coordination mechanisms, phase transformation process and luminescence mechanisms of MFe O₃ have been discussed on the basis of the experimental results. In this method, to obtain high purity MFe O₃, thus the selection of chelating agent play a crucial role. It is crucial to select proper chelating agent to obtain the pure MFe O₃ for this method.（2） The homogeneous polycrystalline（Mg, Ca, Ba）-ferrites magnetic nanoparticles have been synthesized with a phase-controllable process via the modified polyacrylamide gel route. The experimental results demonstrates that the particle size,morphology and magnetic properties of（Mg, Ca, Ba）-ferrites can be manipulated by the addition of polysaccharide and carbon. In the metal-complex structure, M2+ ions active site was coordinated by water molecule except for EDTA anions. In such a process, thepolysaccharide plays an important role in drastically shrinking the precursor gel during the gel drying process. By manipulating the sintering temperature and carbon concentration, the formation of（Mg, Ca, Ba）-ferrites phase can be suppressed to produce the intermediate phases of MCO₃（M= Mg, Ca, Ba） and Fe2O₃. In particular, the incorporation of carbon in the（Mg, Ca, Ba）-ferrite precursor improves the surface morphology and enhances the hysteresis loop squareness ratio（SQR） significantly. In addition, it is found that the SQR of Mg Fe₂O₄ nanoparticles strongly depends on the gamma ray irradiation dose. The SQR of Mg Fe₂O₄ nanoparticles increases with the increasing irradiation dose.（3） Sr Fe₁₂O₁₉ magnetic nanoparticles are synthetized by a polyacrylamide gel route and the phase transformation, powder morphology, and magnetic properties have been investigated. To obtain large SQR of Sr Fe₁₂O₁₉, a certain amount of carbon particles were introduced to the pecursor solution. The XRD results show that the carbon and sintering temperature accelerated the formation of hexagonal Sr Fe₁₂O₁₉ phase without change to the hexagonal magnetoplumbite structure. In order to obtain Sr Fe₁₂O₁₉, the formation of an intermediate phase（Sr CO₃） can be suppressed by adjusting the sintering temperature and carbon concentration. The introduce of carbon in the Sr Fe₁₂O₁₉ precursor solution improves the surface morphology and enhances the SQR. The coercivity, remanence, saturation magnetization and SQR of the Sr Fe₁₂O₁₉ are closely correlat with not only to crystallite size but also dispersion of Sr Fe₁₂O₁₉ nanoparticles.（4） Three kinds of Zn Al2O4 samples were prepared via a modified polyacrylamide gel method using a citric acid solution with different aluminum salts as starting materials, including Al Cl3?6H2O, Al2（SO4）3?18H2O, and Al（NO₃）3?9H2O under identical conditions. The influence of different aluminum salts on the morphologies, phase purity,and optical and fluorescence properties of the as-prepared Zn Al2O4 nanoparticles is studied. The experimental results demonstrate that the phase purity, particle size,morphology, and optical and fluorescence properties of Zn Al2O4 nanoparticles can be manipulated by using different aluminum salts. The energy bandgap（Eg） of Zn Al2O4 nanoparticles increases with the decreasing particle size. The fluorescence spectra show that a main blue emission band around 400 nm and two weaker side bands located at410 and 445 nm are observed when the excitation wavelength is 325 nm. The Zn Al2O4 nanoparticles prepared from Al（NO₃）3?9H2O exhibit the largest emission intensity among the three Zn Al2O4 samples, followed with the Zn Al2O4 nanoparticles preparedfrom Al2（SO4）3?18H2O and Al Cl3?6H2O in sequence. These differences are attributed to the combinational changes in Eg and the defect types of the Zn Al2O4 nanoparticles.Interestingly, similar preparation methods may be applied for the synthesis of other metal oxides nanoparticles, including fluorescence materials, multiferroic materials,oxide thermoelectric materials, photocatalytic materials, solid oxide fuel cell materials,and high-temperature superconducting materials.Although polycrystalline MFe O₃, MFe₂O₄, MFe₁₂O₁₉ and MAl2O4 prepared by the polyacrylamide gel route have been investigated, many fundamental and critical issues,such as optical, electrical, thermal, and magnetic properties, as well as formation mechanisms of these materials, are still unsolved, and further studies in this field are necessary including synthesis of high-purity multiple complex oxides and improvement of their physicochemical properties, and exploration of their industrial applications.