【作者】 许艳艳；

【导师】 陈代荣；

【作者基本信息】 山东大学 ， 无机化学， 2008， 博士

【摘要】 本论文主要采用溶液化学法对铜基化合物纳米颗粒、纳米片及多级纳米结构进行控制合成,探讨其控制机制及内在规律。分别从纳米材料制备、形成机理以及性质表征和应用研究几个方面进行论述,内容涉及水溶液体系中小分子结构导向剂的辅助下氧化物多级纳米结构的制备、形成机制和催化性质,水溶液体系中低分子量聚合物辅助下氧化物中空球、中空立方体及碘化物纳米片的控制合成、形成机制、光学性质和电学性质研究等。旨在探索水溶液中纳米颗粒形成的内在调控机制,寻找构建多级纳米结构材料的更加有效的手段和途径。1.水溶液中小分子配位剂存在下CuO多级结构纳米材料的制备与形成机制以CuCl₂·2H₂O、Na₂（C₄H₄O₆）·3H₂O和NaOH为原料,利用简单的水热法在60～180℃下反应一定时间就可以得到微米级CuO刺球（CPMs）。CPMs由一端粗一端细的扁平纳米刺构成,纳米刺的尖端尺寸小于10nm。改变NaOH和Cu²⁺的摩尔比,刺球的尺寸在100-200nm到4-6μm之间可调,原料的浓度也在一定程度上影响产物的尺寸:而C₄H₄O₆^2-和Cu²⁺的摩尔比则对产物的形貌有很大影响,随着两者之间比例的增大产物形貌由纳米片、纳米刺逐渐过渡到微米刺球;反应温度主要决定CPMs的生成速度,对形貌和尺寸影响不大。通过透射电镜及X-射线粉末衍射跟踪反应过程研究了CPMs的形成机制:首先,溶液中Cu²⁺离子、C₄H₄O₆^2-离子和OH^-离子反应形成Cu（C₄H₂O₆）^2-络阴离子,在加热条件下,Cu（C₄H₂O₆）^2-络阴离子通过可逆水解反应控制释放Cu²⁺和OH^-,形成Cu（OH）₂纳米团簇;然后,Cu（OH）₂纳米团簇在加热条件下快速脱水得到CuO纳米颗粒。纳米团簇表面存在配位的或吸附的酒石酸根离子导致其沿着[010]方向定向聚集生长,形成具有单晶结构的CuO“主干纳米刺”。聚集生长使得“主干纳米刺”上存在很多“台阶”状的缺陷,缺陷处具有高的表面能,有可能为后面的晶体生长提供活性点。溶液中通过可逆反应不断提供Cu²⁺离子和氧原子或者氢氧根离子使其在“主干纳米刺”的高活性“台阶”生长点上,进一步生长而得到新的branch纳米刺,透射电镜分析发现branch纳米刺沿着[101]方向生长。整个反应过程中Cu²⁺离子的释放速率比晶体生长速率慢而且晶体成核所需要的过饱和度比晶体生长所需要的过饱和度大,因此成功地实现了晶体成核和生长过程的分离。为了进一步阐明小分子配位剂在氧化物纳米材料结构和形貌控制及形成机制中的作用,我们针对水体系中CuO的形成进行进一步研究。在90-180℃的温和条件下将CuCl₂·2H₂O与氨水的混合溶液进行水热反应,制备了由纳米片构成的尺寸可调的CuO微米花状结构,其中构成微米花的纳米片具有弯曲的边缘,厚度为20-40nm,宽度为500-800nm。我们利用相似的方法跟踪研究了产物的形成机制:首先,具有层状结构的正交晶系的Cu（OH）₂在NH₃分子的辅助下,得到Cu（OH）₂的纳米带;然后,Cu（OH）₂纳米带脱水得到短的CuO纳米带,CuO纳米带自组装聚集形成CuO纺锤形聚集体;最后CuO纳米片的聚集体继续生长得到CuO微米花。实验结果表明高的氨水浓度、氨水(C_NH3)和铜离子(C_Cu2+)高的摩尔浓度比以及高的反应温度是形成微米花的必要条件。红外光谱结果显示产物表面除了吸附水和表面羟基外没有任何杂质,因此对高氯酸铵的分解表现出优异的催化性能,与尺寸为8-15nm的CuO纳米颗粒具有相似的催化效果。这说明我们的产物虽然聚集尺寸在微米尺度,但是仍能够保持纳米结构单元的性质。微米尺寸的纳米结构颗粒能够克服纳米颗粒易团聚、难混匀等缺点,有利于将来的实际应用。2.低分子量聚乙二醇辅助下Cu₂O中空纳米结构的控制合成与性能研究以CuCl₂·2H₂O和NaNO₃为原料,PEG400为辅助剂,通过两步湿化学法制备了具有介孔壳壁的Cu₂O/PEG400复合物纳米中空球。中空球直径在50-80nm之间,壁厚约为15-20nm,由大约为5nm的纳米晶构成。中空球是由无机组分Cu₂O和有机物PEG构成的,其中Cu₂O的含量大约为72%,壳壁具有介孔结构,介孔孔径的平均尺寸为3.8nm,BET比表面积为85.8m²/g。纳米尺寸的复合物中空球的形成过程是:CuCl₂·2H₂O、NaNO₃和PEG400在180℃下反应形成前驱体溶液,然后前驱体溶液水解得到Cu₂O中空球。第一步反应中PEG400分子起还原剂、溶剂和配位剂的作用,而在水解过程中PEG400分子的胶束聚集体起到模板的作用,指导中空球的形成。壳壁上的介孔是在纳米颗粒定向聚集的过程中形成的。纳米尺寸的复合物中空球表现出奇特的光致发光现象,在414nm和436nm处有强的发光峰,在454、570和637nm处有弱峰。另外,中空球对甲基橙分子表现出优异的吸附性能,可能归因于其复合物结构和介孔结构。以CuCl₂·2H₂O和NaOH为原料,PEG200为辅助剂,制备了前驱体溶液,然后利用前驱体溶液水解在室温中性环境下直接得到规则形貌的具有单晶壳壁和纳米尺寸的Cu₂O中空立方体,其边长在50-90nm之间,壳壁厚度约为6-15nm。通过调节前驱体溶液中反应物的浓度及溶剂的种类,可以在60-200nm之间调节中空纳米立方体的尺寸。NaOH对单晶中空纳米立方体的形成起重要作用,然而其具体的作用机制仍需进一步深入研究。3.利用表面活性剂及低分子量聚合物辅助的溶液过程制备单晶CuI纳米片首次在室温下利用PEG辅助的水溶液路线制备了CuI单晶纳米片,基本过程是将KI和十二烷基苯磺酸钠（SDBS）溶解在PEG600中,CuCl₂·2H₂O溶解在PEG600中,得到两份溶液,将两者混合,得到澄清的紫红色溶液前驱溶液,然后将前驱溶液滴加到NaNO₃水溶液中即可水解得到CuI纳米片。拉曼光谱显示前驱体溶液中形成了I-Cu（Ⅰ）-PEG配合物,因此推测在前驱溶液中PEG600的配位作用使Cu（Ⅰ）稳定存在,阻止了CuI沉淀的形成。在水解过程中PEG600和SDBS的共存对纳米片的形成起主要作用。透射电镜和扫描电镜结果显示纳米片的厚度和面内尺寸分别为60-80nm和几个微米。与块体CuI相比纳米片的相转变温度和熔点分别降低了8℃和12℃。利用AFM探针测得单个纳米片的的电阻率为1.996×10^-2Ω·cm,并且发现纳米片具有光导现象。作为一个通用的合成方法,该路线还可以制备Ag和BiOI纳米片。更多还原

【Abstract】 This paper is focused on controlled synthesis of copper-based inorganic nanoparticles, nanosheets,and hierarchical nanostructures through liquid-phase chemical routes. Growth mechanism,self-assembly of nanoparticles and primary property characterizations were also conducted.Investigations are based on several aspects including controlled synthesis,formation mechanism,and properties and applications. The contents mainly include preparation and formation mechanism of hierarchical transition metal oxide microspheres;controlled synthesis,fabrication mechanism,and optical or catalytic properties of composite hollow spheres,hollow naocubes,and CuI nanosheets.The aim is to study the intrinsic controlling mechanism of nanoparticls in solution and construct nanostructured materials with nanoparticles as building blocks.1.Preparation and formation mechanism of CuO hierarchical nanostructures through a chelating agent assisted aqueous solution routeCuO pricky microspheres（CPMs）were fabricated through a simple hydrothermal route at 60-180℃for a setting time using CuCl₂·2H₂O,Na₂（C₄H₄O₆）·3H₂O,and NaOH as reactants.The CPMs were composed of compressed nanothoms exhibiting tapering feature with tip size of less than 10nm.The size of the CPMs can be tuned from 100-200 nm to 4-6μm by simple adjusting the molar ratio of NaOH to Cu²⁺or reagent contentration.The morphology of the CPMs was determined by the molar ratio of tartrate to Cu²⁺cations.Reaction temperature mainly affected the formation rate of the product rather the size and morphology.The formation mechanism of the nanostructures was investigated in detail through time-dependent experiments with TEM and XRD.At first,Cu（C₄H₂O₆）^2-formed through a reversible reaction in the precursor solution that prevents the formation of precipitates.With the temperature increasing,Cu²⁺and OH^- were released and a homogeneous nucleation of Cu（OH）₂ occurred.Subsequently,Cu（OH）₂ nanoclusters dehydrated and aggregated orientedly to form CuO truck nanothorns along[010]direction due to the coordinated or absorbed tartrate anions on the crystal surface.The aggregation-based growth resulted in many defects in the inner parts and surface of the nanothorns that might supply active sites for next crystal growth.So the constant supply of Cu²⁺cations would facilitate further growth of new CuO nanothorn from the surface steps.The nucleation and crystal growth were successfully separated by controlled releasing of Cu²⁺and OH- ions through the reversible reaction of Cu²⁺cations,OH^-,and C₄H₄O₆^2-anions. We conducted further investigation with CuO as target product to clarify the formation mechanism of nanostructured oxides in solution and shed some light on the effect of the coordinated agent on the formation of the oxides.Nanostructured CuO microflowers with tunable size were prepared by heated the solution of CuCl₂·2H₂O and ammonia at 90-180℃.The CuO microflowers were composed of nanosheets with zigzag edges which were 20-40 nm in thickness and 500-800 nm in width.The formation mechanism of CuO microflowers based on the assembly of Cu（OH）₂ nanobelts was elucidated by tracking the hydrothermal process.At first,due to the layered structure of orthorhombic Cu（OH）₂ and assistant of NH₃ molecules,the Cu（OH）₂ grew preferentially to form the belt-like Cu（OH）₂ crystals.Subsequently,the dehydration of Cu（OH）₂ nanobelts occurred,leading to the formation of short CuO nanoribbons.Then the CuO nanoribbons assembled to form CuO aggregates through an oriented-assembly manner.Finally,the aggregates of CuO nanosheets developed into the CuO microflowers.The high ammonia concentration,high ratio of NH₃ to Cu²⁺（Rac）and elevated temperature were necessary for the formation of microflowers,and the ammonia concentration was critical for the morphology evolution of the particles.The effect of the products as catalyst on the decomposition of ammonium perchlorate was enhanced remarkably compared to bulk CuO and was similar with the CuO nanoparticles with size of 8-15 nm derived from the aqueous solution,which means that although enlarging the overall size of the aggregations into micrometer scale the properties of nanobuilding blocks retained excellently.These nanostructured microparticles avoid the limitations of nanoparticles,such as conglomeration and difficult to mix due to high surface energy,while retain the good catalytic property,which may supply potential applications in the future.2.PEG-assisted formation of nanosized Cu₂O Hollow structures and theis optical propertiesThe nanosized Cu₂O/PEG400 composite hollow spheres（HSs,50-80 nm in diameter） with mesoporous shells of～15-20 nm were synthesized by a poly（ethylene glycol） （PEG）-assisted wet-chemical method using CuCl₂·2H₂O and NaNO₃ as reactants.In the hollow nanostructures,the polymer content was ca.18.1 wt%,and the mean size of the component nanocrystals and the pore diameter were ca.5 and 3.8 nm, respectively.The formation of the products included two steps:at first,PEG200, CuCl₂·2H₂O and NaNO₃ reacted at 180℃for 6h to form a precursor solution,then, after cooled to room temperature the precursor solution hydrolyzed in deionized water to obtain the composite hollow spheres.During the first step,Cu（Ⅱ）were reduced to Cu（Ⅰ）by PEG molecular which can be proved UV-vis spectra.So PEG acts as solvent, reducing agent,and complexing agent.And in the second step poly（ethylene glycol 400）（PEG400）molecules self-assemble to form micelles which act as templates for the formation of the hollow structures.The formation of mesoporous structures is due to the oriented-aggregation of composite nanoparticles.The nanosized-composite HSs exhibited peculiar photoluminescence（PL）phenomenon with strong peaks at 414 and 436 nm and weak ones at 454,570,and 637 nm.Furthermore,the HSs showed excellent adsorption ability for methyl orange（MO）because of their composite and mesoporous shell structures.A precursor solution was prepared with CuCl₂·2H₂O and NaOH as reactants,and PEG200 as solvent,complexing agent and reducing agent.Then nanosized Cu₂O hollow nanocubes with single crystalline shells were produced directly through the hydrolysis of the precursor solution under room temperature.The length and the shell thickness of the hollow nanocubes’ sides are ca.50-90 nm and ca.6-15 nm, respectively.The size of the hollow nanocubes can be tuned from 60 nm to 200 nm by simple adjusting the reagent contentration and solvents of the precursor solution. NaOH play an important role in the formation of the products,however,the detailed formation mechanism still needs further investigation.3.PEG-Assisted Fabrication of Single-Crystalline CuI Nanosheets CuI single-crystalline nanosheets have been prepared for the first time via a PEG-assisted aqueous solution route at room temperature.Certain amount of KI and sodium dodecyl benzenesulfonate（SDBS）was dissolved in PEG600 under stirring to give a clear solution and CuCl₂·2H₂O was dissolved in PEG600,too.The two solutions were mixed together to give a clear amaranth solution which was used as the precursor solution.Then the precursor solution was added into NaNO₃ solution drop by drop with a burette under stirring to generate CuI precipitate at room temperature. Raman spectra and TEM observation on the precursor solution confirmed that aⅠ-Cu（Ⅰ）-PEG complex rather than CuⅠnanoparticles formed in the precursor solution. Thus,PEG600 serve as a complex agent to prevent the formation of CuⅠ.The thickness and in-plane size of the nanosheets were ca.60-80 nm and several micrometers,respectively.The two basal surfaces of these nanosheets were（111） planes.The phase transformation temperature and the melting point decreased 8 and 12℃compared with those of the bulk CuⅠ,respectively.The resistance of a single CuⅠnanosheet was measured by a conductive AFM tip method,and a high conductivity of 1.996×10^-2Ω·cm and a photoconduction phenomenon were observed. As a general process this strategy can be used to prepare more 2-D nanostructures including Ag and BiOⅠ.更多还原