【作者】 王辉；

【导师】 陈乾旺；

【作者基本信息】 中国科学技术大学 ， 无机化学， 2011， 博士

【摘要】 由于磁性纳米材料在磁有序纳米结构、磁响应光子晶体以及磁分离等领域中具有广阔的应用前景,因此,其合成受到了众多研究学者的关注。除此之外,磁性纳米材料在有序化排列以后可以产生许多新颖的性质。因此,它们是制备小型化纳米器件的基础结构单元。本论文旨在探索磁性胶体纳米材料的磁场下合成新方法,研究磁性胶体纳米粒子的一维有序化进程。此外,还着重研究了它们在磁响应光子晶体以及重金属水污染等领域中的实际应用。详细内容归纳如下：1.以二茂铁(0.20 g)和过氧化氢为原料,以丙酮(30 ml)为溶剂,在230。C的反应条件下于反应釜中首先合成了一种由氧化铁纳米晶所组成的团簇粒子(120 nm)结构。在外加磁场诱导的作用之下(0.20 T),这种纳米粒子在丙酮体系中可以组装成单分散的一维有序纳米链结构,链长度可达2岬。实验过程中,我们研究了磁化时间和磁场强度对合成纳米链的影响。结果发现,磁化时间直接决定着合成纳米链的长度,磁场强度也直接决定着合成纳米链的有序程度。此外,我们还研究了过氧化氢的用量对于形成纳米粒子的影响。并发现,改变过氧化氢的用量(1.0 ml和2.0 ml),可以直接改变纳米粒子中磁性材料的组份,并进而影响合成的纳米链的链间距(8 nm和17nm)。实验表明,这种具有一定链间距的纳米链的形成是由粒子之间磁诱导力和静电排斥力共同作用的结果。同时,粒子表面所带的负电荷使其在溶液中具有良好的分散性。2.以二茂铁(1.00 g),过氧化氢(1.00 ml)和聚乙烯吡咯烷酮(PVP)为原料,以乙醇(28 ml)和水(7 ml)为混合溶剂,在230。C的反应条件下于反应釜中直接合成了大量的类项链Fe304和Fe203纳米环。电镜照片表明,这些纳米环都是由不同数量的磁性单粒子氧化铁纳米晶(40nm)所组成。为了阐释纳米环的形成机制,我们研究了纳米粒子的磁性质和组装动力学对于纳米环形成的影响。实验中,我们通过控制反应时间调整纳米粒子的磁性质(结晶),结果发现,在反应时间较短时,具有较差结晶性的纳米粒子依然可以形成纳米环结构。这意味着纳米粒子的磁性质不会影响纳米环的形成。纳米组装动力学对于纳米环的形成的影响通过改变反应温度和反应中PVP的用量来实现。结果发现提高温度和增加PVP的用量有助于纳米环的形成。这表明,纳米环的形成是由磁性纳米粒子的组装动力学所决定。在此基础上,通过控制反应条件,我们初步实现了对于不同尺寸纳米环的可控合成。3.以二茂铁(0.30 g)和过氧化氢(1.50 ml)为原料,以丙酮(30 ml)为溶剂,在240。C的反应条件下于反应釜中合成了一种以碳包覆超顺磁性氧化铁纳米晶体簇(190 nm)为基本粒子的磁响应光子晶体。实验中,我们发现,这种核壳结构的磁响应光子晶体在外加磁场的用下,可以衍射出覆盖整个可见光区域的颜色。磁响应光子晶体的衍射谱数据表明,其衍射波长与磁场强度存在反比关系,即磁场越强,衍射波长越短。反之,亦然。同时,磁核表面的碳层提高了磁响应光子晶体的胶体稳定性,使其在乙醇溶液中密封保存8个月以后,依然可以衍射出与新鲜的粒子一样的颜色以及强度。通过控制反应中过氧化氢(0.50 ml、1.00 ml、1.50 ml、2.00 ml),可以制备出不同尺寸分布(100 nm、150 nm、200 nm、250 nm)的碳包覆超顺磁性氧化铁纳米晶体簇。磁响应现象显示,粒子平均尺寸不同,衍射颜色亦有很大差别。例如：尺寸分布为100 nm的粒子只可衍射出蓝色,而尺寸分布为250 nm的粒子只可衍射出红色。反射谱的数据也证明了粒子的衍射波长与粒子的尺寸存在正比关系。通过分散150 nm的粒子到不同的溶剂(蒸馏水、无水乙醇,DMSO、丙酮)之中,我们研究了磁响应光子晶体的溶剂依赖性。结果显示,溶剂的折射率和极性可以影响磁响应光子晶体的衍射波长和衍射强度。4.以二茂铁(0.30 g)和过氧化氢(1.50 ml)为原料,以丙酮(30 ml)为溶剂,在180。C的反应条件和外加磁场下于反应釜中合成了一种碳包覆的超顺磁性纳米链。通过控制反应温度,我们可以得到具有不同链间距的纳米链,分别为213nm(180。C),186 nm(190。C)和173 nm(200。C)。实验发现,在外加磁场的诱导下,这些纳米链可以衍射出鲜艳的单色可见光,包括红,绿,蓝三种颜色。反射谱结果显示这些纳米链的衍射波长分别为605 nm,526 nm和480 nm。并且这些纳米链的衍射波长与外加磁场的强度没有什么关系,这暗示着它们可以作为磁响应的液体布拉格反射器。除了上述红绿蓝三种颜色的磁响应液体布拉格反射器以外,我们还利用磁场诱导自组装的方法制备了紫色的磁响应布拉格反射器,其是由链间距约为155nm的单分散磁性纳米链所组成。合成方法如下：首先合成粒子尺寸为150 nm的单分散超顺磁性胶体纳米粒子,然后使用外磁场诱导自组装的方法,在室温条件下合成一维纳米链。这种磁性胶体纳米粒子在外磁场下不同时间内的衍射照片从宏观上证实了组装过程的存在。同时,磁性胶体粒子组装后的衍射谱从微观上证实了纳米链的形成,并且它的衍射波长(404 nm)不随磁场强度的变化而变化。这意味着紫色磁响应液体布拉格反射器的形成。5.以表面带有负电荷(-35.18 mV)的碳包覆的超顺磁性胶体纳米粒子(150 nm)作为吸附剂,我们研究了其对于水溶液中重金属离子的吸附过程。以Pb2+为例,定性分析(EDX)实验表明：利用这种纳米材料作为吸附剂,我们可以成功地从水溶液中移除Pb2+。定量分析(ICP)实验表明：在120 min的作用时间、pH值为6以及Pb2+浓度为1 mg/L的条件下,碳包覆的超顺磁性胶体纳米粒子可以从水溶液中移除98%的Pb2+。实验中,我们还研究了作用时间,pH,离子浓度以及离子种类对于粒子吸附效率的影响。结果,发现,在120 min以内,作用时间和吸附效率之间呈正比关系；pH在1至6之间,pH和吸附效率之间呈正比关系；Pb2+浓度在0.1 mg／L到100 mg/L之间,粒子对Pb2+吸附率均在98%以上。离子种类选择三种Pb2+,Hg2+,Cd2+,结果显示,离子水合半径不同,粒子的吸附率存在差异。吸附机理研究表明整个吸附过程存在三个过程：1.静电吸引作用；2。表面羧基的配位作用；3.表面多孔碳层的吸附作用。更多还原

【Abstract】 Due to the widely applications in high-density magnetic data storage media, magnetic responsive photonic crystals, and magnetic separation, an important research effort has been directed towards the study on the synthesis of nanoscale magnetic materials. In addition, magnetic nanomaterials with ordered functional structure have some brand-new properties resulted from the spatial orientation and arrangement of the building blocks and can be viewed as the foundation for the formation of novel miniaturized nanodevices. Therefore, the research about the synthesis, assembly and application of nanoscale magnetic materials is very important from the point of view of science and applications.The main objective of this dissertation is to develop new avenue for the solution-based synthesis of nanoscale magnetic materials, and investigate the relationship between their magnetic parameters and their structure (size and/or shape), and demonstrate some simple and effective technologies for assembling the magnetic block buildings into highly ordered functional structures. Furthermore, the pratical application of functional magnetic nanomaterials will be discussed. The main parts of the as-obtained results are summarized below:1. Magnetite nanoclusters with average size about 120 nm have been prepared and allowed to self-assemble into one-dimensional (1D) nanochain structure with the average length about 2μm by a simple magnetic-field-induced (MFI) assembly approach (0.20 T). The constituent, phase, and morphology of these 1D nanochains have been characterized by X-ray diffraction and Transmission electron microscopy. Magnetic measurement reveals that these 1D nanochains are weakly ferromagnetic at room temperature. In this paper, we discuss the influence of magnetization time and strength of external magnetic field on the formation of 1D nanochains. We also shows that by changing the amount of hydrogen peroxide in starting materials, 1D nanochains with different interparticle spacing can be obtained. This 1D nanochain structure with different interparticle spacing would be an ideal system for the further study of magnetization properties of 1D ordered magnetic nanostructures.2. Necklace-like magnetite and maghemite nanorings, composed of magnetic nanoparticles (NPs) with average size about 40 nm, have been prepared via a solvothermal process in a colloidal solution by a self-assembly process. The composition, phase, and morphology of these nanorings have been characterized by X-ray diffraction, X-ray absorption, and transmission electron microscopy. In this paper, we discuss the influence of reaction conditions on the formation of nanorings structure including the amount of PVP in starting materials, reaction time and temperature. On the basis of experimental observation, we supposed that magnetite NPs may first assemble into chains by magnetic dipole-dipole interactions. These dipolar chains, which are metastable structures relative to necklace-like nanorings, then produced the rings. So, the stability of chains may determine the yield, size, and morphologies of necklace-like nanorings.3. The core/shell structure of magnetite/carbon colloidal nanoparticles (CNPs) with average size about 190 nm has been prepared via a one-step solvothermal process using ferrocene as a single reactant. The composition, phase, and morphology of the nanostructure have been characterized by X-ray diffraction, and transmission electron microscopy. Magnetic measurements reveal the superparamagnetic nature of the material with a magnetization saturation 40.2 emu/g at room temperature. Under the induction of an external magnetic field, strong diffraction in the visible light spectrum can be observed in a suspension of CNPs in ethanol and the diffraction wavelength varies with the strength of the external magnetic field. After being stored for eight months in an ethanol solution, these CNPs can still diffract visible lights when a magnetic field was applied, which is attributed to carbon coating and creating carboxyl groups on the surface of carbon shells introducing both a steric hindrance and electrostatic repulsions between magnetite nanoparticles.Size and solvent-dependent of magnetic responsive photonic crystals were investigated using carbon-encapsulated superparamagnetic magnetite nanoparticles as building blocks. The wavelength dependence of optical diffraction on particle size was demonstrated using colloidal nanoparticles spherical in shape and having an average diameter of 100 nm,150 nm,200 nm,250 nm, respectively. A colloidal suspension with a particle size of 250 nm can only diffract red light, while the suspension with particle size 100 nm can only diffract blue light no matter how the magnetic induction changed in strength. Solvent-dependent diffraction of photonic crystals under an external magnetic field were carried out by dispersing the colloidal nanoparticles in solvents, including acetone, ethanol, DMSO and water. It is shown that the reflection intensity was reduced as the polarity and reflactive index of solvent increased.4. Superparamagnetic colloidal nanochains (CNCs) coated and linked by carbon were prepared by solvothermal decomposition of ferrocene at a temperature of 180-200℃with a 0.20 T magnetic-field applied. It is demonstrated that CNCs with different intra-particle spaces (216 nm,186 nm, and 173 nm) can be obtained by changing the reaction temperature. Under the induction of an external magnetic field (e.g.0.10 T), the ethanol suspension of the three samples can diffract different wavelengths of visible light, displaying red, green and blue color, respectively. The three samples did not show the dependence of the diffraction wavelength on the strength of induction magnetic field, which indicates that the superparamagnetic CNCs can be used for magnetic responsive Bragg Reflector (BR).In addition, we have also prepared magnetic responsive Bragg reflector with purple visible light and the diffraction wavelength of 404 nm. The BR composed of monodisperse magnetic colloidal nanochains keep fixed diffraction wavelength under different strength of magnetic field (0.10 T-0.20 T) because of their immobile inter-particle spacing (155 nm). The synthetic process of monodisperse magnetic colloidal nanochains are carried out at room temperature by inducing the self-assembly of colloidal nanoparticles when a magnetic field is applied. Therefore, the demonstrated method is simple, convenient and harmless for the magnet used in the synthetic process of magnetic responsive Bragg reflector.5. Superparamagnetic magnetite nanoparticles coated with a thick (11 nm) and porous carbon layer have been prepared, which can serve as an efficient adsorbent for removing heavy metal ions (Pb2+) from an acidic aqueous solution. The nanoparticles show high removal capacities at lower pH values such as 3 and treat high pollution of wastewater (100 mg/L), which are aroused from their porous carbon layer with a carboxyl surface. The material demonstrated in this work also allows the possibility to separate other toxic metal ions (Hg2+, Cd2+) from an aqueous solution via tailoring their surface with special functional groups.更多还原