【作者】 李莉莉；

【导师】 蔡炳新； 詹拥共；

【作者基本信息】 湖南大学 ， 物理化学， 2010， 硕士

【摘要】 本文以不同的铁盐为铁源,尿素为沉淀剂和十六烷基三甲基溴化铵(CTAB)为结构导向剂,在稀水溶液中反应,通过改变实验条件,合成了一系列具有不同形貌和结构的Fe2O3纳米晶。首先,以Fe(NO3)3·9H2O为铁源,添加Mg(NO3)2成功合成出纳米结构a-Fe2O3纺锥状。借助SEM、TEM、XRD、Raman、XPS和N2吸附-脱附等表征手段,研究α-Fe2O3晶体的形貌、结构、比表面和孔径分布。晶体的尺寸和形貌可通过改变实验参数进行控制。随着晶化时间延长,合成出纺锥状、花瓣状a-Fe2O3单晶：Mg(NO3)2浓度对α-Fe2O3纺锥状单晶起着重要作用,随着浓度的降低,晶体形貌从纺锥状向球形转变；当反应物浓度控制在5.6×10-3 mol·L-1时,有利于纺锥状形貌的形成；焙烧过程可以进一步修饰单晶表面。同时测定a-Fe2O3纺锥状对多巴胺的电化学性质。其次,以Fe(NO3)3·9H2O为铁源,合成了粒径约35 nm的球形a-Fe2O3纳米晶和面包圈状的a-Fe203/Si02复合纳米材料。借助一系列表征手段,考察不同实验参数对α-Fe2O3球形形貌和结构的影响。晶化时间、反应物浓度、尿素浓度对α-Fe2O3球形形貌没有直接影响,而焙烧可以促进羟基氧化物完全转化为α-Fe2O3,但焙烧温度过高,会导致晶体形貌坍塌。通过将球形α-Fe2O3和a-Fe203/Si02复合材料的比表面和孔径尺寸进行对比,两者比表面积分别为19.8m2·g-1和140.4 m2·g-1,而孔径分布的粒径反而变小。最后,以FeSO4·7H2O为铁源,成功合成Fe203六角型枝状纳米颗粒。通过改变实验参数对其形貌和结构进行研究。样品在焙烧过程中存在晶相转化,由β-FeOOH向y-Fe2O3转变,当焙烧温度为650℃时转化成最稳定的α-Fe2O3,磁性也经历了从有到无的过程。晶化时间、反应前静置时间和表面活性剂对晶体形貌影响极大。同时也研究了改变外界因素对晶体形貌的影响。更多还原

【Abstract】 In this thesis, a series of Fe2O3 nano-materials with different morphologies and structures have been synthesized by the template-directed process and modified evaporation-induced self-assembly (EISA) method. Based on the self-assembly of cationic surfactants and inorganic precursors, our approach emploied cetyltrimethylammonium bromide (CTAB), different ferric salts, and urea as structure-directing agent, iron source, precipitation agent in the dilute aqueous solution, respectively. At the same time, their morphologies and structures were studied by changing the experimental conditions.Spindle-like morphology a-Fe2O3 crystal have been prepared in the addition of Mg(NO3)2 in the system. The influences of the experimental conditions, such as reaction time, concentration and calcination on the morphologies of the as-prepared a-Fe2O3 crystal, have been studied. The morphologies and structure of the crystals have been characterized by scanning electron microscopy(SEM), transmission electron microscopy(TEM), X-ray diffraction(XRD) and Raman spectrum(RS). X-ray photoelectron spectroscopy (XPS) was used to gain further insight into the chemical composition of the a-Fe2O3 crystal. The formation mechanism has been presented. Significantly, electrochemical properties of a glassy carbon electrode modified with a-Fe2O3 spindle-like were investigated in neutral media. The cyclic voltammogram(CV) showed a cathodic peak at 170 mV and anodic peak at 110 mV. Conversely, both peaks got strong compared with the bare electrode.The spherical a-Fe2O3 with average size of 35 nm and donut-shaped a-Fe2O3/SiO2 composite nanoparticles have been synthesized in the same system. Different parameters on the morphology and structure of spherical a-Fe2O3 were investigated by a series of characterization methods. It is revealed that the influences, such as crystallization time, reactant concentration, and urea concentration have no direct impact on the morphology of spherical a-Fe2O3, while the calcination temperature can completely promote hydroxyl-oxide to a-Fe2O3. If the calcination temperature was too high, it would lead to the collapse of morphology. The surface areas of theα-Fe2O3 andα-Fe203/Si02 nanoparticles were calculated at 19.8 m2·g-1 and 140.4 m2·g-1.We used ferrous sulfate as iron source by calcining at elevating temperature, the as-synthesized iron oxide precursor was transformed into iron oxide. The phase of the final product could be easily controlled among the FeOOH, y-Fe2O3, and a-Fe2O3 by altering the calcinations conditions. Additionally, magnetic investigations showed that theα-Fe2O3 crystals exhibited weakly ferromagnetic property at room temperature. Reaction time, the standing time and structure-directing agent had a great impact on the crystal morphology. The external factors on the impact of crystal morphology were also studied.更多还原