Synthesis And Structure Of New Hexagonal Perovskite Intergrowth, Influence Of NiFe₂O₄ Dopant On The Photocatalytic Activity Of TiO₂

This dissertation includes two sections, the first section is mainly related to synthesis and structure of hexagonal perovskite-intergrowth compounds, details of this section is described from Chapter1 to 4; Influence of NiFe₂O₄ doping on the crystal structure and photocatalytic activity of TiO₂ is discussed in the second section.Partial substitution of Mn in La₄Ba_2.6Ca_2.4Mn₄O₁₉ with other transition metals (TM= Fe, Co, Ni, Cu) was studied by solid state reaction using citrate sol-gel precursors. A new compound has been identified, the structure was established by ab initial method and refined with Rietveld method on X-ray powder diffraction data, microstructure was observed using SEM. The main findings are as follows:1. Under the conditions we used, Mn in La₄Ba_2.6Ca_2.4Mn₄O₁₉ compound could only be substituted by other transition metals (TM= Co, Cu) with very small amount, when the substitution amount got larger or using Fe/ Ni to substitute the Mn, the structure changed greatly. A new phase was found during experiments.2. A new manganese oxide Ba2.4Ca0.6MnO5.125 was synthesized by a series of experiments. It crystallizes in the hexagonal space group with a=5.83460?,c=8.218982?,cell volume of 242.3097?3. The structure might be described as alternate stacking of 3H-type hexagonal perovskite blocks and [Ba2O2] sheets. In the hexagonal perovskite block, Mn and Ca cations occupy the octahedral sites of the face-shearing or corner-shearing octahedra, respectively. Images of SEM proved that this compound is layer-structured. The average oxidation state of manganese in this compound is +4.25.In the second part, results related to increasing the photocatalytic activity by controlling TiO₂ phase transformation using NiFe₂O₄ dopant are as follows:NiFe₂O₄, TiO₂ and NiFe₂O₄ doping TiO₂ nanoparticles were prepared by chemical precipitation and sol-gel method, respectively. Samples prepared were characterized with X-ray diffraction. Also studied were the influence of NiFe₂O₄ dopant on the anatase to rutile phase transformation of TiO₂ and the photocatalytic activity of NiFe₂O₄ doped TiO₂ nanopowders by eosin degradation under sunlight irradiation. The results showed that the phase transformation of titania from anatase to rutile were restrained by NiFe₂O₄ doping. In addition, the photocatalytic activity of TiO₂ doping with appropriate NiFe₂O₄ content could be improved obviously, and an increase in the activity by a factor of 2 relative to pure TiO₂ nanomaterials was obtained under the optimal conditions.