【作者】 薛斌；

【导师】 徐铸德；

【作者基本信息】 浙江大学 ， 化学， 2009， 博士

【摘要】 由低维纳米结构作为构筑单元组装而成的分等级三维纳米结构是当前纳米结构和纳米材料研究领域的热点。探索分等级三维纳米结构新的合成方法,深入研究分等级三维纳米结构的物理化学性质,对于进一步理解纳米结构的自组装行为和开发纳米结构的应用价值具有重要意义。新奇形貌碳纳米管因其独特的结构和形貌,在诸多应用方面表现出了潜在的价值,制备具有优势性和高比例的新奇形貌碳纳米管将促进对其物理化学性质和应用性能的深入研究。本论文采用新的易于实现、环境友好的合成方法,制备了一系列分等级三维金属氧化物纳米结构,诸如球状α-Fe₂O₃、球状TiO₂、中空TiO₂、核桃状CeO₂,以及竹节状碳纳米管。利用X射线衍射（XRD）、透射电子显微镜（TEM）、场发射扫描电子显微镜（FESEM）、高分辨透射电子显微镜（HRTEM）、选区电子衍射（SAED）、Raman光谱、氮气吸附分析、热重分析（TG）、示差扫描量热分析（DSC）、紫外—可见漫反射光谱（UV-Vis DRS）、紫外—可见吸收光谱（UV-Vis）、光致发光（PL）光谱和多功能物理性质测量系统（PPMS）等表征手段对产物的结构、形貌、磁性质、光学性质以及光催化活性进行了系统研究。采用聚丙烯酰胺（PAM）作为辅助物质结合微波加热回流以及焙烧处理制备了分等级球状α-Fe₂O₃纳米结构。这种分等级球状α-Fe₂O₃纳米结构由纳米粒子作为构筑单元组装而成,具有介孔结构,在300K下剩磁为0.08947 emu g^-1,矫顽力为2 301.5 Oe。PAM在分等级球状α-Fe₂O₃纳米结构形成中起到重要作用。采用PAM作为辅助物质,以TiCl₃为钛源,通过水热反应以及焙烧处理制备了由纳米粒子组装而成的分等级球状TiO₂纳米结构。这种分等级球状TiO₂纳米结构以锐钛矿相为主,同时含有部分金红石相,具有介孔结构,并且UV-Vis DRS吸收带边产生了红移。紫外光照射下降解甲基橙水溶液的探针反应表明这种分等级球状TiO₂纳米结构具有较好的光催化活性。对PAM在制备分等级球状TiO₂纳米结构过程中的作用进行了讨论。采用无模板合成策略,以TiCl₃作为Ti源,H₂O₂作为氧化剂,KBF₄作为矿化剂,通过水热反应简便制备了分等级中空TiO₂纳米结构。这种TiO₂纳米结构为锐钛矿相,由纳米粒子作为构筑单元组装而成,具有介孔结构。对比实验表明这种分等级中空TiO₂纳米结构通过奥斯瓦尔德熟化过程形成。H₂O₂和KBF₄的协同效应在分等级中空TiO₂纳米结构的形成过程中发挥着重要作用。在紫外光下甲基橙水溶液降解反应中这种分等级中空TiO₂纳米结构具有较好的光催化活性。采用β-环糊精辅助水热反应制备了具有纯粹六方晶相的分等级核桃状介晶CeOHCO₃纳米结构,这种分等级核桃状CeOHCO₃纳米结构由纳米粒子作为构筑单元组装而成,具有单分散特征和单晶性质。在形成过程中,CeOHCO₃纳米结构经历了独特的晶相转变和形貌转变。β-环糊精在这种CeOHCO₃纳米结构形成过程中起到重要作用。这种六方相CeOHCO₃纳米结构表现出了明显的光致发光特性。分等级核桃状介晶CeOHCO₃纳米结构热分解后得到了保持了单分散核桃状形貌特征和单晶性质的介晶CeO₂纳米结构。这种CeO₂纳米结构具有介孔结构,在紫外光区域存在强烈的吸收,并且有明显的红移。在常压下以乙醇作为碳源,采用化学气相沉积方法,在Cu/Al₂O₃催化剂上制备了竹节状碳纳米管。明显不同于通常得到的竹节状碳纳米管和传统碳纳米管混杂的情形,本论文得到的碳纳米管具有优势性、高比例的竹节状形貌。对比实验表明,800℃是制备较高质量竹节状碳纳米管的最佳温度,Cu/Al₂O₃催化剂和乙醇的组合对于竹节状碳纳米管的生长具有关键作用。对竹节状形貌形成的原因也进行了讨论。更多还原

【Abstract】 Currently,the study on hierarchical three-dimensional nanostructures assembled by low-dimensional nanostructures as building units is a hot area in research of nanostructures and nanomaterials.To explore new synthesis methods and research on physico-chemical properties of hierarchical three-dimensional nanostructures is of great significance for better understanding of their self-assembly behavior.Carbon nanotubes（CNTs） with novel morphology represent potential values in many application areas because of their particular structures and morphology.Fabrication of dominant and high proportion CNTs with novel morphology may promote further research of their physico-chemical properties and application performance.The preparations of a series of hierarchical three-dimensional metal oxide nanostructures such asα-Fe₂O₃ spheres,TiO₂ spheres,hollow TiO₂ and walnut-like CeO₂ and bamboo-like carbon nanotubes have been achieved adopting new,facile, and environmentally friendly methods.The structure,morphology,magnetic,optical properties and photocatalytic activity of the products are systematically characterized by X-ray diffraction（XRD）,transmission electron microscopy（TEM）,field emission scanning electron microscopy（FESEM）,high resolution transmission electron microscopy（HRTEM）,selected area electron diffraction（SAED）,Raman spectroscopy,nitrogen sorption analysis,thermogravimetry（TG）,differential scanning calorimetry（DSC）,UV-Vis diffuse relectance spectroscopy（UV-Vis DRS）, UV-Vis absorption spectroscopy（UV-Vis）,photoluminescence（PL） spectroscopy and physical property measurement system（PPMS）.The hierarchical sphericalα-Fe₂O₃ nanostructures have been prepared by polyacrylamide（PAM）-assisted microwave heating reflux as well as calcination process.The hierarchical sphericalα-Fe₂O₃ nanostructures are assembled by nanoparticles,exhibit mesoporous structures,display a remanent magnetization of 0.08947 emu g^-1 and a coercivity of 2 301.5 Oe in 300 K.PAM plays an important role in the formation of the hierarchical sphericalα-Fe₂O₃ nanostructures.The hierarchical spherical TiO₂,nanostructures assembled by nanoparticles as building units have been prepared via PAM-assisted hydrothermal route using TiCl₃ as Ti source.The hierarchical spherical TiO₂ nanostructures remain with dominant anatase phase and partial rutile phase,exhibit mesoporous structures and display red shift in UV-Vis DRS.The hierarchical spherical TiO₂ nanostructures have preferable photocatalytic activity in the photodegradation of methyl orange（MO） in aqueous solution under UV light.The role of PAM in the prepration of the hierarchical spherical TiO₂ nanostructures was discussed.The hierarchical hollow TiO₂ nanostructures have been prepared via a facile hydrothermal route using TiCl₃ as Ti source,H₂O₂ as oxidation agent and KBF₄ as mineralizer through template-free synthesis strategy.The hierarchical hollow TiO₂ nanostructures are assembled by nanoparticles,possess anatase phase and mesoporous structure.Control experiments show that the hierarchical hollow TiO₂ nanostructures formed in accordance with the Oswald ripening.Synergy of H₂O₂ and KBF₄ in the formation of the hierarchical hollow TiO₂ nanostructures plays an important role.The hierarchical hollow TiO₂ nanostructures exhibit better photocatalytic activity in the photodegradation of MO in aqueous solution under UV light.The hierarchical walnut-like mesocrystal CeOHCO₃ nanostructures with hexagonal phase have been prepared via a hydrothermal route usingβ-cyclodextrin as assistant agent.The hierarchical walnut-like CeOHCO₃ nanostructures are assembled by nanoparticles as building units,exhibit monodisperse characteristic and single-crystalline nature.In the formation process,unique crystal phase and morphology transitions of CeOHCO₃ nanostructures occurred.β-cyclodextrin plays an important role in the formation of the hierarchical walnut-like CeOHCO₃ nanostructures.The CeOHCO₃ nanostructures with hexagonal phase show an evident PL property.The mesocrystal CeO₂ nanostructures with unchanged monodisperse walnut-like morphology and single-crystalline nature are obtained after thermal conversion of the hierarchical walnut-like mesocrystal CeOHCO₃ nanostructures.The CeO₂ nanostructures display mesoporous structure,strong absorption phenomenon in UV light region with clear red shift.The CNTs with dominant bamboo-like morphology were obtained by chemical vapor deposition over Cu/Al₂O₃ catalyst using ethanol as carbon source under atmospheric pressure.The majority bamboo-like structure obviously differs from the past situation in which generally a mixture of bamboo-like and conventional straight CNTs was obtained.Control experiments show that 800℃is the optimum temperature for the growth of bamboo-like CNTs with higher quality.The combination of Cu/Al₂O₃ catalyst and ethanol played a critical role in the growth of bamboo-like CNTs.The possible causes of the formation of bamboo-like morphology were also discussed.更多还原