【作者】 俞晓晶；

【导师】 姚奎鸿；

【作者基本信息】 浙江理工大学 ， 材料加工工程， 2010， 硕士

【摘要】 以形貌和尺寸剪裁为目的的材料合成研究,是材料研究领域的一个重要方向。现代的材料应用已经不仅仅取决于材料的物相组分,而对材料的精细结构提出了更高的要求。过渡金属氧化物具有优异的电磁、光电以及催化等性能,广泛应用在固体催化、光催化、择形分离、微型电磁装置、光致变色材料、电极材料以及信息储存等领域。近年来,由纳米次级颗粒聚集而成的各种过渡金属氧化物形貌体的调控合成成为研究热点。纳米颗粒聚集体材料一方面秉承了块体材料的宏观性能优势,有序的组装次级纳米颗粒,避免纳米尺寸材料的无序团聚;其宏观形貌结构特征可以根据实际应用进行剪裁调节。另一方面其特殊的结构层次兼有纳米颗粒的表面效应、体积效应、量子尺寸效应等,拥有一系列新颖的物理和化学特性。在合成过程中,过渡金属氧化物晶体趋向于异向生长,容易形成大晶体而失去纳米颗粒的特性,且难以聚集成形。本论文设想采用PMMA聚合物微球为模板,利用PMMA分子中螯合基团的功能,在高分子微球表面富集过渡金属离子,并诱导生成氧化物纳米晶粒;这些晶粒在合适的结晶环境中生长并自组装,形成具有球壳层结构的聚集体形貌。这种对称弧形结构的球壳形貌聚集体有望产生基于材料结构特点的特殊性能。论文中首先对PMMA微球进行表面活化处理,强化微球表面对过渡金属离子的配位作用。选择合适的沉淀剂,使结晶中心趋向于在PMMA微球表面优先成核。最后经陈化反应,在PMMA微球表面形成由次级颗粒聚集而成的过渡金属氧化物晶体壳层。采用SEM、XRD、TEM、TGA、IR、XPS等现代分析测试手段,对材料的微观结构、物相、物理性质等进行表征。用UV测试表征了材料的光吸收性能。初步探讨了基于PMMA微球为模板、过渡金属氧化物壳层聚集体的形成机理。氧化锌是材料研究领域的热点。它是一种性能优异的宽带半导体材料,具有特殊的光、电、催化性能。氧化铜作为一种重要的过渡金属氧化物,具有多种催化活性,在C₁化学合成、NO_x还原和气敏材料、锂离子电池、场发射器、氧电极催化等领域显示出良好的应用前景。论文以这两种过渡金属氧化物为目标产物进行研究。研究发现,通过常温常压的溶液法可以在PMMA微球表面合成过渡金属氧化物颗粒紧密聚集的壳层结构。不同的阳离子反应物、沉淀剂、陈化反应温度、溶液pH值、陈化反应时间等是影响壳层颗粒尺寸、形貌、聚集形态和致密度的主要因素。形成的核壳结构复合材料,壳层由过渡金属氧化物颗粒紧密组装而成。其中氧化锌颗粒尺寸约100 nm,氧化铜颗粒尺寸200 nm-300 nm。复合物显示出特殊的UV-Vis吸收特性,内核PMMA的热分解温度延后50℃-100℃。通过放大的电镜照片可以看出,壳层聚集体有明显的孔结构特征,富于材料高比表面积的同时,还有一定的择形透过性。对壳结构聚集体的形成机理研究表明,PMMA微球的表面活化处理是表面优先成核结晶的前提。氮、氧等原子的协同配位作用,以及功能基团在高分子链上的序列排列,对过渡金属阳离子在PMMA微球表面的富集提供了电荷与空间构型基础。沉淀剂的选择是诱导晶体在PMMA表面异相结晶,避免晶体体相结晶的关键。研究结果显示:对氧化锌而言,氢氧化钠是较好的沉淀剂;而对氧化铜而言,以氨水作为沉淀剂得到的产物较优。合适的沉淀剂与阳离子容易形成稳定的络合产物,增加阳离子在体相中的溶解度,减小浓度积,有效的缓解了晶体在体相溶液中直接成核结晶,客观上有利于在PMMA表面的优先成核。后续的陈化反应则遵循典型的奥斯特瓦尔德（Ostwald）晶体熟化理论,晶体自组装在PMMA微球表面形成致密、完整的壳层聚集体。更多还原

【Abstract】 Researches on the morphology and size tailoring during the synthesis process of materials are quite necessary for the development of material. Nowadays, phase composition is not the only factor that should be considered during the application of materials. Microstructures, such as the shape, size and texture, are even more important. The oxides of transitional metal exhibit highly desirable optical, electronic, magnetic and catalytic properties, which have been widely applied in field such as solid catalysis, photocatalysis, shape-selective separation, micro electromagnetic device, photochromic materials, electrode materials and information storage device. In recent years, shaped aggregations by nanoparticles of transitional metal oxides attract more interests. Such shaped aggregations perform the properties of the bulk materials. What’s more, the sub-building block units exhibit unique properties such as surface effect, little size effect and quantum measure effect, due to their nanoscaled size.However, anisotropic growth and structure collapse are two problems during the fabrication of the aggregations of transitional metal oxides. As a result, nanoparticles might grow into bulk particles which are hard to aggregate. In this thesis, spherical shell shaped aggregation of transitional metal oxides is supposed to be obtained using polymethylmethacrylate (PMMA) as core template. Particles of transitional metal oxides are induced to grow preferably on the surface of the PMMA microspheres, based on the electrostatic and stereochemical interactions at the inorganic-organic interface. Then, spherical shell shaped aggregation is supposed to finally be constructed by these building blocks through self- assembling. Such 3-D hierarchical organization with curved symmetry results in special surface properties.ZnO and CuO crystals were selected as the shell materials, since both of these two oxides are important semiconductor oxides. During our experimental process, PMMA microspheres were pretreated by NH3.H2O first. Solution route was then used to prepare the transitional metal oxides crystals. Precipitation agent in this step was crucial. After that, an aging reaction was carried out to obtain spherical shell shaped aggregation with well crystallinity. SEM, XRD, TEM, TGA, UV and IR measurements were used to investigate the morphology, size, texture and structure of the products. Furthermore, formation mechanism of such spherical shell shaped aggregation was explored.The results show that shape and size of the sub-crystallites, as well as the form of the aggregations can be tuned by many parameters, such as the zince/copper source, precipitation agent, aging temperature, aging time and pH value of the solution. The final core-shell composites contain integral spherical shell aggregated by ZnO crystals with the size of 100 nm, or CuO crystals with size of 200 nm-300 nm. The composites exhibit novel UV adsorption in the range of ultra-violet band. The decomposition temperature of the PMMA core increase for about 50℃-100℃with the protection of the oxide shell. High-resolution observation shows that the shell aggregation has porous character. More interestingly, porous ZnO aggregation with hollow interior are obtained after the removing of the PMMA core, implying that the shell aggregation depends on certain binding and interpenetrating among its building units.XPS analysis shows that a trace of N was detected on the surface of NH3.H2O treated PMMA microspheres. Ammonolysis is believed to take place at the surface of the PMMA microspheres. Since O and N are preferable ligands to Zn ions and Cu ions, the cations tended to bind to the surface of the PMMA cores. The crystal growth centers are thus supplied to induce the preferable crystallization of ZnO crystal on the surface of PMMA. It is found that NaOH is the optimal precipitation agent for ZnO crystal aggregated on the PMMA surface, and NH3.H2O for CuO crystal. Both the precipitation can react with the cation to form coordination structure, correspondingly. Formation of the complex restrains the crystal growth homogeneously, and the heterogeneous nucleation on the PMMA surface becomes preferable. With the growth of the nuclei during the aging reaction following a typical Ostwald ripening process, the constructional shell aggregations composed of transitional metal oxide particles are finally formed.更多还原