【作者】 欧平；

【导师】 韩高荣； 徐刚；

【作者基本信息】 浙江大学 ， 材料学， 2007， 硕士

【摘要】 铁的氧化物（Fe_xO_y）和羟基氧化物（FeOOH），包括α-Fe₂O₃、Fe₃O₄和α-FeOOH等都是属于氧化物系统的磁性材料。随着尺寸的减小和形貌的变化，其纳米结构由于小尺寸效应、表面效应、量子尺寸效应和宏观量子隧道效应，导致多种电磁特性或物理特性发生变化，从而在颜料、催化剂、磁记录介质、磁性涂料、气体传感器以及在环境保护过程中的气体脱硫、废水处理等工业应用领域表现出比块材更加优异的性能。此外，Fe_xO_y、FeOOH纳米结构在其他尖端的领域如临床诊断、医药传输、磁流体等方面的应用前景也受到人们的瞩目。因此，关于不同形貌和尺寸的Fe_xO_y、FeOOH纳米结构的合成、表征和性能研究具有重要意义。本论文采用水热／溶剂热法来合成铁的氧化物（Fe_xO_y）和羟基氧化物（FeOOH）纳米材料。以Fe（NO₃）₃·9H₂O和KOH（矿化剂）为反应物料，从溶剂、表面修饰剂、反应温度、矿化剂浓度、反应时间等因素出发研究了制备工艺对Fe_xO_y、FeOOH纳米结构形成和特性的影响规律及作用机理。论文研究的主要内容和结果如下：1．以Fe（NO₃）₃·9H₂O和KOH为反应物料，以乙醇为溶剂，聚乙烯醇（PVA）作为稳定剂，溶剂热法合成了直径为20～100nm的α-Fe₂O₃纳米颗粒，它们的粒径分布较均匀、分散性好、结晶性较好。研究表明，适量的高分子修饰可以改善纳米晶粒的分散性和尺寸分布的均匀性，PVA结构中的大量自由的强极性羟基基团可以与金属离子之间形成螯合键，紧密包覆在金属离子周围，形成一个有PVA链限制形状的有限结构，使得合成的纳米粒子大小被限制，不易形成团聚，具有较好的稳定效果。2．利用溶剂热方法，采用Fe（NO₃）₃·9H₂O和KOH为反应物料，乙二醇为溶剂，在220℃下反应24小时，合成了大量尺寸均一的Fe₃O₄纳米颗粒，其直径约为16nm，结晶性较好。研究了温度和矿化剂浓度对产物形貌的影响。结果表明，通过对温度和矿化剂浓度的调节，可以获得粒径可控、均匀的立方相Fe₃O₄纳米粒子。利用该方法制备Fe₃O₄纳米粒子，方法简单，产量大，而且制备的晶体具有明显的小尺寸效应。3．以Fe（NO₃）₃·9H₂O和KOH为反应物料，乙二醇为溶剂，引入适量PEG作为表面修饰剂，利用溶剂热方法制备纳米材料时发现产物形貌中出现了一定量直径约为5nm，长约为30～50nm的Fe₃O₄纳米针。研究了PEG的添加量对形成Fe₃O₄纳米针的影响，并且探讨了PEG促进纳米针生长的机理。4．利用水热法，以Fe（NO₃）₃·9H₂O和KOH反应物料，在100℃下反应6小时，合成了大量具有较大长径比的α-FeOOH纳米线，其直径在80nm，长度为1.5～2μm，单根纳米线为结晶良好的正交相针铁矿结构α-FeOOH，并且纳米线沿针铁矿结构α-FeOOH的[001]轴方向取向生长。研究了反应温度、矿化剂浓度和反应时间对产物形貌的影响。结果表明：当温度低于一定值（40℃）时，无论是在低浓度矿化剂的条件下还是在高浓度矿化剂的条件下都得不到α-FeOOH，产物为无定形相；在100℃时，随着矿化剂浓度的升高，将越来越不利于α-FeOOH纳米线的合成；在高温（200℃）下，α-FeOOH会在极短时间内生成，并且随着时间的延长而迅速相转变为α-Fe₂O₃。5．以本文合成的α-FeOOH纳米线为原料，在不同温度下对其进行热处理，保温0.5小时。结果表明：不同温度下，α-FeOOH在热处理过程中呈现了相同的相变途径，即脱水形成α-Fe₂O₃，相变温度为240～295.1℃且不同温度热处理后得到的α-Fe₂O₃保持了α-FeOOH原来的纳米线状，线表面有孔洞。高氯酸铵（AP）的催化性能实验结果表明：不同温度下热处理得到的α-Fe₂O₃纳米线均使AP的高温分解温度显著下降，其中热处理温度为350℃时，得到的产物使AP高温分解温度的降幅最大，为71.4℃。更多还原

【Abstract】 Iron oxides（Fe_xO_y） and Iron oxide hydroxides（FeOOH） nanomaterials have been prepared by hydrothermal/solvothermal methods that employed Fe（NO₃）₃·9H₂O and KOH（mineralizer） as starting materials. The effects of solvent, surfactant, reaction temperature, mineralizer concentration and holding time on the phase formation, performance, and reaction mechanism of Fe_xO_y and FeOOH nanostructures were studied. The preparation processes have been investigated by means of XRD, TEM, HRTEM, SEM, FI-IR, PPMS and TG-DTA. The main work in this thesis is as follows:1. Based on the effect of eth on the growth of α-Fe₂O₃ nanoparticles, mass α-Fe₂O₃ nanoparticles surface-modified by polyvinyl alcohol （PVA） have been synthesized via solvothermal treatment of Fe（NO₃）₃·9H₂O and KOH. The as-prepared α-Fe₂O₃ nanoparticles showed well crystalline and disperser with the diameter of 20～100nm. It was found PVA is one kind of excellent surfactant to control the size of particles and improve the disperser and stability of nanoparticles in the solution. A lot of free hydroxyls with highly polar in the structure of PVA make it have easy to form chelating-bonds with metal ion by using its hydroxyls as ligands so that metal ion can be surround by it to form limited space for the ligands of PVA restricting, which prevented the growth of nanoparticles and their congregation.2. Large-scale Fe₃O₄ nanoparticles with uniform diameter of 16nm were synthesized using a simple solvothermal route that employed Fe（NO₃）₃·9H₂O and KOH as starting materials, ethylene glycol （eg） as the solvent. The effects of temperature and mineralizer concentration on the morphology of products were studied. The results showed that size of cubic phase Fe₃O₄ nanoparticles could be controlled by the temperature and mineralizer concentration. The present method is simple, large-production and nanocrystals prepared using this method exhibited significantly small size effect.3. When the Fe₃O₄ powers were synthesized by solvothermal treatment ofFe（NO₃）₃·9H₂O and KOH, using PEG as a capping agent, ethylene glycol （eg） as thesolvent, it can be found that some Fe₃O₄ nanopins with the diameter of 5nm and the length of 30～50nm were formed in solutions. The concentration of PEG was supposed to play an important role in the formation of Fe₃O₄ nanopins. The mechanism of PEG accelerating Fe₃O₄ nanopins’ formation was preliminarily discussed.4. Large-scale α-FeOOH nanowires were synthesized by hydrothermal treatment of Fe（NO₃）₃·9H₂O and KOH. X-ray diffraction （XRD） pattern and transmission electron microscopy （TEM） images show that the products are orthorhombic structure α-FeOOH nanowires with diameter of 80nm and length up to 1.5²um. Selected area electron diffraction （SAED） and high resolution TEM （HRTEM） studies indicated the single-crystalline nature of α-FeOOH nanowires with an oriented growth along the [001] axis direction. The effects of temperature, mineralizer concentration and time on the morphology of products were studied. It was found that: No effect on the crystallinity of α-FeOOH when different mineralizer concentration were used at low temperature（40oC）, amorphous phase will be obtained; With the increase of the mineralizer concentration, the crystallinity of α-FeOOH decrease and a few hexagonal α-Fe₂O₃ were gained at 100°C; At high temperature（200oC）, α-FeOOH nanowires obtained by hydrothermal synthesis processing convert to hexagonal α-FejOs rapidly.5. Heat treatment of the as-prepared α-FeOOH nanowires in this dissertation at different temperature for 0.5h. The results showed that phase transformation of α-FeOOH occured between 240°C and 295.1°C, which obeyed the same process described as 2α-FeOOH→α-Fe₂O₃+H₂O at different heat treatment temperature. XRD and TEM showed that the products of heat treatment also remained nanowire morphology with many holes on the surface. The experiment on catalytic performance for ammonium perchlorate （AP） indicated that all the products obtained by heat treatment of α-FeOOH nanowires at different temperature made the temperature of high-temperature exothermic peak of AP decrease. The sample obtained upon heating α-FeOOH nanowires at 350°C made it largest decrease by 71.4°C.更多还原