【作者】 徐正侠；

【导师】 胡国新；

【作者基本信息】 上海交通大学 ， 工程热物理， 2013， 博士

【摘要】 随着纳米科技的发展，人们可以通过纳米材料的组成、结构和形貌等来控制它们的基本性质。纳米功能材料表现出不同于其块体材料的性质，并可被应用于某些特定场合。通过对纳米材料进行一定的自组装，可以得到性质不同于单个纳米颗粒和块体样品的纳米结构复合物。本文首先制备出了几种纳米结构材料（石墨烯片、银纳米颗粒、氧化铁纳米颗粒和腐植酸纳米胶粒），从而为这些纳米材料的各种自组装做好了铺垫。利用层层自组装、流动定向自组装和溶液相自组装方法，将这些纳米材料自组装成复合物或薄膜，从而研究了复合物或薄膜的性质与形貌、结构之间的关系。此外，将绿色化学基本原理和纳米材料制备相结合，努力实现使用原料的低廉性、实验过程的绿色化、工艺过程的普适性和可控性以及材料形貌的可控性等目标。本文的主要内容包括以下几点：1.采用层层自组装技术，构建了由带负电的腐植酸和带正电的聚二烯二甲基溴化铵组成的多层纳米结构薄膜。紫外可见光分光光度计的测量显示薄膜的吸收率随着双层数的增加而线性的增加。傅里叶变换红外光谱的结果表明薄膜中既含有未离解的腐植酸胶体也含有离解的腐植酸。浸渍溶液中NaCl摩尔浓度为0.0到0.2M时，层层自组装得到的（PDDA/HA）10薄膜的厚度为6.0±0.5到64.9±0.5nm。薄膜的厚度与浸渍溶液中NaCl摩尔浓度的平方根成线性增加关系，而薄膜的折射率也与浸渍溶液的离子强度有关。这些都是由于随着溶液离子强度的增加，溶液中的聚合电解质的链状结构从伸展的棒状构型变为无规则的卷曲状构型并在薄膜中保持而导致的。根据薄膜的电化学测试，氢离子还原的峰值电流与扫描速度的平方根成线性关系，这说明在电极表面发生的氧化还原过程是扩散限制的。将在氧化铝纤维上的(Fe³⁺/HA)40薄膜碳化后，薄膜的石墨化和有序程度随碳化温度升高而提高。2.水溶性石墨烯的制备及其流动定向自组装方法构建薄膜。将石墨氧化制得氧化石墨，接着氧化石墨被超声剥离得到氧化石墨烯分散液。在氨水存在的情况下用肼还原，得到依靠静电排斥作用而稳定的石墨烯胶体分散液。这种分散液可以在没有聚合物稳定剂和表面活性剂的情况下稳定存在达一个月以上，从而使石墨烯的液相大规模加工成为可能。鉴于层层自组装方法效率低，采用流动定向自组装方法将石墨烯分散液加工成厚度在几十纳米到十几微米范围的均匀薄膜，并将薄膜转移到各种基体之上。与氧化石墨烯薄膜相比，石墨烯薄膜具有高的金属光泽和反射性、以及改善的电化学性能。用循环伏安法表征了薄膜的电化学电容性质，结果显示其质量比电容可达121F/g，可潜在的用于柔性超级电容器的电极材料。利用Fe（CN）₆^3-/4-氧化还原系统，对比了氧化石墨烯薄膜/电解液界面处和石墨烯薄膜/电解液界面处的电子传输性能，得到了还原对性能改善的作用，并理解了电化学性能和结构的关系。3.水溶性银纳米颗粒-石墨烯复合物的制备及其流动定向自组装方法构建薄膜。采用靠静电作用的溶液相自组装方法，通过分步还原氧化石墨烯和银离子制备了银纳米颗粒-石墨烯复合物。依靠氨吸附的静电排斥作用，使产物可以水中稳定存在达两周。透射电子显微镜测试显示银纳米颗粒很好的分散于石墨烯片之中，且复合物的形貌和复合物中银纳米颗粒的含量有密切关系。利用流动定向自组装方法，可以制得具有闪亮的金属光泽、高的反射性和很好的柔性的均匀薄膜。与单纯的石墨烯薄膜的拉曼信号相比，复合物薄膜的拉曼信号强度随着银纳米颗粒在复合物中含量的增加而增强了三到八倍，说明拉曼信号的强度增加量可以通过改变复合物中银纳米颗粒的密度来调节。这种信号增强是由银纳米颗粒和石墨烯之间形成的电荷转移配合物引起的，是化学拉曼增强作用。对于Fe（CN）₆^3-/4-氧化还原系统，复合物薄膜/电解液界面处具有快速的电子转移速度。4.通过溶液相自组装方法,制备了氧化铁纳米颗粒-石墨烯复合物。预制好的憎水性氧化铁纳米颗粒被转移到水相，接着与氧化石墨烯分散液混合。在还原过程中，直径约为10nm的氧化铁纳米颗粒通过静电作用被自组装到石墨烯片之上。X射线衍射和选取电子衍射显示复合物中的氧化铁纳米颗粒是反尖晶石结构的。由磁化曲线可知,随着氧化铁纳米颗粒含量的降低,复合物的比饱和磁化强度值由38.3emu/g降低到19.5emu/g和7.7emu/g,并都表现出磁滞较小的铁磁行为。复合物的介电常数和磁导率在测试的频率范围内有明显的波动，这主要归因于由交换共振（小尺寸效应、表面效应和自旋波激发的结果）和自然共振引起的多重磁共振。5.将绿色化学基本原理和金属纳米颗粒的制备相结合，描述了一种环境友好的制备单分散银纳米颗粒的方法。将预制好的油酸银前驱体在油酸中热还原，可以制备平均直径在4.0到5.0nm范围内、直径的标准差最低可达0.3nm（多分散性：5.5%）的银纳米颗粒。在整个制备过程,需要的反应物只有硝酸银、油酸钠和油酸,这充分显示了该方法在简单和环境可持续性方面的优势。在相同的初始前驱体摩尔浓度情况下，银纳米颗粒的平均直径可以通过反应时间来粗略控制，也可以通过反应温度来更精细的调节。利用成核/扩散成长模型，解释了各种情况下制备的银纳米颗粒的尺寸和形貌差异。得到的单分散银纳米颗粒很容易自组装成单层纳米颗粒紧密排列的六角形阵列。利用石墨烯作为分析物，银纳米颗粒组成的表面增强拉曼散射活性涂层使其拉曼散射信号增强。具有活性层的石墨烯拉曼散射信号强度是纯石墨烯拉曼散射信号强度的十五倍以上。银纳米颗粒的表面增强拉曼散射活性是在银纳米颗粒结合处（活性位置）的强烈的局域性磁场的结果，并且可以用粒子间耦合诱导的拉曼增强来解释。更多还原

【Abstract】 With the development of nanosciance and nanotechnology, the properties ofnanostructure materials were controlled by their composition, structure andmorphology. These functional nanomaterials can have properties that differ fromthose of the same bulk materials and can be used in certain circumstances. Thecomposites obtained from the self-assembly of nanomaterials display properties thatare different to those displayed by the individual nanoparticles and bulk materials.Several nanostructure materials, namely, graphene, silver nanoparticles, iron oxideand humic acid nanoparticles, were prepared to pave the way for variousself-assembly. These nanostructure materials were self-assembled into compositesand films to study the relationship of their properties and the morphology, structure.Furthermore, with the integration of green chemistry principles into the synthesis ofnanostructure materials, the goals, such as, the low cost of raw materials, the greenexperiment, the process of universality and controllability, as well as materialmorphology controllability, were sought achieve with efforts. The main contents andresults are summarized as follows:1. Multilayer films consisting of negatively charged humic acid and positivelycharged polyelectrolyte have been fabricated on various substrates using thelayer-by-layer self-assembly technique. The thickness （linearly increasing with thesquare root of NaCl concentration） and refractive index of the films determined byellipsometry can be regulated by ionic strength through adjusting the coiling of thepolyelectrolyte chains for assembly. The cone-shaped features on surface obtainedby atomic force microscope are derived from the negatively charged colloidal humicacid binding with polyelectrolyte cation. The smooth features are corresponding to the dissociated humic acid with carboxylate ion （―COO） electrostatically attractedon polyelectrolyte cation. These results are verified by Fourier transform infraredspectra. The linear dependence of the peak current on the square root of the scan raterevealed by the cyclic voltammetry indicates that the redox process at the electrodesurface is diffusion-limited and the charge transport does not involve the film itself.2. The aqueous graphene dispersions can be readily formed by reduction ofgraphene oxide colloids modified with ammonia. The dispersion can be stable overone month without the need for either polymer or surfactant stabilizers. Uniformfilms with thickness ranging from dozens of nanometers to more than a dozenmicrometers were prepared by flow directed self-assembly method and transferredto various substrates. As comparison to graphene oxide film, graphene film displaysa shiny metallic luster, high reflectivity and improved electrochemical properties.This graphene film electrode shows a specific electrochemical capacitance of121F/g, and is particularly promising for flexible supercapacitors. The electron transferreaction at the graphene film/solution interface is faster than that at the grapheneoxide film/solution interface using the Fe（CN）₆^3-/4-redox system due to therelationship of electrochemical properties and structure.3. A solution-based chemical approach has been used to prepare silvernanoparticle–graphene （Ag–G） composites through sequential reduction of grapheneoxidation and silver ions. The products can readily form a stable aqueous solutionwithout polymeric or surfactant stabilizers, and this makes it possible to producegraphene–silver composites on a large scale using low-cost solution processingtechniques. The paper-like Ag–G film obtained by vacuum filtration is glossy andhas a high reflectivity and good flexibility. Raman signals of graphene for the filmare increased from three-to eightfold with the increase of silver nanoparticle contentin the composites, indicating that the increase can be tuned by changing the densityof silver nanoparticles. The electrochemical properties of the Ag–G film demonstratetheir fast electron-transfer kinetics for the Fe（CN）₆^3-/4-redox system.4. Monodisperse iron oxide nanoparticle-reduced graphene oxide compositeswere prepared by self-assembly in aqueous phase. Pre-synthesized iron oxide nanoparticles were transferred to aqueous phase and then mixed with grapheneoxide dispersion. The iron oxide nanoparticles, with diameter of around10nm, wereself-assembled on the reduced graphene oxide sheets through electrostatic attractionduring the reduction of graphene oxide. X-ray diffraction and selected area electrondiffraction indicated the inverse spinel structure of the iron oxide nanoparticles. Themagnetization curves indicated that all samples exhibited ferromagnetic behavior atroom temperature with small coercivity. The values of specific saturatedmagnetization of composites with different densities of iron oxide nanoparticles are38.3,19.5and7.7emu/g. Permittivity and permeability of composites exhibitobvious fluctuations, which are ascribed to the multiple magnetic resonances. Themultiple resonances involve exchange resonances （the consequence of small sizeeffect, surface effect and spin wave excitations） and natural resonance.5. We describe a simple and green method for preparing silver nanoparticleswith an average diameter in the range from4.0nm to5.0nm and with the standarddeviation as low as0.3nm （polydispersity:5.5%）. The pre-synthesized silver oleateprecursor in oleic acid was thermally reduced to obtain the monodisperse silvernanoparticles without a size selection procedure. This environmentally friendlychemistry approach requires only three reagents （silver nitrate, sodium oleate andoleic acid） which all come from renewable resources. The average diameter of thesenanoparticles can be greatly adjusted by reaction time and finely regulated byreaction temperature at same precursor concentration. The nucleation/diffusionalgrowth model can be used to interpret the size and morphology difference of silvernanoparticles synthesized in different condition. Raman spectra of graphene withand without an active layer of silver nanoparticles were measured to investigate thesurface-enhanced Raman scattering properties of silver nanoparticles. Raman signalof graphene with an active layer increased by fifteen-fold in comparison to thatwithout an active layer. The surface-enhanced Raman scattering activity can beexplained using the interparticle coupling induced Raman enhancement.更多还原