【作者】 杨加栋；

【导师】 别利剑；

【作者基本信息】 天津理工大学 ， 材料物理与化学， 2008， 硕士

【摘要】 本论文主要包括两部分内容,第一部分是新型六方层状钙钛矿化合物的合成及结构研究,内容包括论文第一至第四章;第二部分内容为铁酸镍掺杂对TiO₂结构及光催化性能的影响。采用柠檬酸盐热解法制备前驱物,以固相烧结工艺探索了六方层状钙钛矿化合物La₄Ba_2.6Ca_2.4Mn₄O₁₉中锰元素的取代,在掺杂过程中发现了由Ba、Ca、Mn、O组成的新物相,通过反复探索合成条件合成了新的化合物。利用多晶X射线衍射、电子衍射等方法研究了该化合物的结构;通过SEM观察并分析了样品的表面形貌。主要研究结果如下:1.通过一系列实验发现,在我们所选取的实验条件下,化合物La₄Ba_2.6Ca_2.4Mn₄O₁₉中Mn元素可以被少量的Cu、Co取代,随着Cu、Co相对含量的增加,化合物中出现了其它的物相,当Cu、Co的相对含量达到一定值时,化合物的结构平衡被破坏,形成了另外的物相;用Fe、Ni取代La₄Ba_2.6Ca_2.4Mn₄O₁₉中的Mn,在掺入量较少时,样品中有第二相存在,取代量较多时,化合物原有的结构平衡被打破,形成了未知的新物相。2.在研究新物相时,我们发现了一个由Ba、Ca、Mn、O四种元素共同构成的新化合物,通过实验合成了该化合物的纯相,此化合物组成为Ba2.4Ca0.6MnO5.125。该化合物属于六方晶系,晶胞参数为a=5.83460?,c=8.218982?,v=242.3097?3。化合物的结构是利用粉末X射线衍射数据和直接法推测出的,结构拟合使用了X射线衍射数据。结构可能是由3H型六方钙钛矿结构单元和[Ba2O2]层交替排列形成。在六方钙钛矿结构单元中,Mn离子和Ca离子分别占据八面体格位,八面体分别通过共面或共顶点连接,Ca离子占据了1/3的八面体格位,钙钛矿结构单元层中的A位离子格位由Ba离子占据。在[Ba2O2]层中,10%的Ba原子被Ca取代。SEM图像显示此化合物为层状结构,这与结构解析结果是一致的。在该化合物中Mn平均氧化态为+4.25。通过掺杂铁酸镍控制二氧化钛相变以提高其光催化性能的主要研究如下:分别采用共沉淀法和溶胶-凝胶法制备铁酸镍和二氧化钛纳米粉体,探讨了铁酸镍纳米掺杂对二氧化钛“锐钛矿”→“金红石”的晶体结构转变及其光催化活性的影响。结果表明,铁酸镍的掺杂可抑制二氧化钛由“锐钛矿”到“金红石”的结构相变,显著提高其光催化活性,在最佳掺杂浓度时,其光催化降解曙红的效率可提高约2倍。更多还原

【Abstract】 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.更多还原