纳米材料的湿法合成

论文中英文摘要

作者姓名：孙旭平

论文题目：纳米材料的湿化学合成及新颖结构的自组装构建

作者简介：孙旭平，男，1972年08月出生，2000年09月师从于中国科学院长春应用化学研究所汪尔康研究员，于2006年03月获博士学位。

中 文 摘 要

围绕论文题目“纳米材料的湿化学合成及新颖结构的自组装构建”，我们开展了一系列研究工作。通过湿化学途径，在贵金属纳米粒子及其二维纳米结构和导电聚合物纳米带的合成方面进行了深入研究。同时，利用界面自组装及溶液自组装技术，构建了一些新颖结构。本论文研究工作的主要内容和创新点表现在以下几个方面：

(1) 首次提出了一步加热法制备多胺化合物保护的贵金属纳米粒子。我们利用多胺化合物(包

括聚电解质和树枝状化合物)作为还原剂和保护剂，直接加热贵金属盐和多胺化合物的混合水溶液，在不加入其它保护剂和还原剂的情况下，一步制备得到了稳定的贵金属金和银的纳米粒子。我们在实验中发现，树枝状化合物聚丙烯亚胺能对反应生成的金纳米粒子的大小及成核和生长动力学进行有效控制。我们还发现，室温下直接混合浓的阳离子聚电解质分支型聚乙烯亚胺和浓的HAuCl4水溶液可得到高浓度的、稳定的胶体金。这种一步合成法操作简单且方便易行，是一种制备多胺化合物保护的贵金属纳米粒子的通用方法；同时，本方法合成的纳米粒子表面带正电荷，可用作加工纳米粒子功能化薄膜的构建单元。

(2) 首次提出了一种无表面活性剂的、无模板的、大规模制备导电聚合物聚邻苯二胺纳米带的

新方法。我们通过在室温下直接混合邻苯二胺和HAuCl4水溶液，在没有表面活性剂或“硬模板”存在的条件下，获得了长度为数百微米、宽度为数百纳米、厚度为数十纳米的聚邻苯二胺。纳米带的自发形成可归因于反应中生成的金纳米粒子催化的邻苯二胺的一维定向聚合。本方法方便快速，无需加入表面活性剂或使用“硬模板”，且可用于大规模制备。此外，我们通过在室温下直接混合AgNO3和邻苯二胺水溶液，也获得了大量的一维纳米结构，并发现其形貌可通过调节实验参数而改变。我们还发现，当溶液pH降低时，这些一维结构将分解成水溶性的低聚体，而如果再次升高pH，这些低聚体又将自组装形成一

维纳米结构。各种数据表明，这种一维纳米结构是由邻苯二胺被AgNO3氧化后所生成的低聚体在溶液中自组装而形成的。

(3) 发展了一系列可大量制备沿(111)晶面优先生长的单晶金二维结构(包括纳米片及微米盘)

的湿化学合成方法。在室温下直接混合HAuCl4和邻苯二胺水溶液，我们得到了大量的、呈六角形的、纳米厚度的单晶金片，其尺寸达1.5μm，邻苯二胺和HAuCl4间的摩尔比是纳米片形成的关键，这种纳米片不仅能应用于光学领域，还可用于加工具有独特机械性能的新型结构材料。我们通过直接加热浓的HAuCl4和线型聚乙烯亚胺混合水溶液，也获得了大量的金纳米单晶片，其尺寸可达40μm，反应物浓度是获得纳米片的关键因素，这种具有大的(111)晶面的单晶金片有望用做扫描隧道显微镜(STM)的基底。此外，通过加热草酸-HAuCl4混合水溶液，我们还得到了大量的、尺寸达4μm的、呈六角形的金二维结构，但其厚度大于100 nm，为微米盘，其大小和厚度可通过草酸的用量得到控制。

(4) 发展了一种基于溶液中的配位组装的、室温下方便合成有机-无机配位聚合物杂化材料的

单分散亚微米胶体球的新方法。在室温下直接混合H2PtCl6和对苯二胺水溶液，通过对苯二胺和PtCl62-在溶液中的配位自组装，我们得到了亚微米尺寸的、单分散的、配位聚合物球形胶体球。实验表明，粒子大小和多分散度可由反应物间的摩尔比和浓度进行控制，获得单分散胶体球的最佳实验条件是1:1摩尔比和适中的浓度。本研究结果具有比较重要的意义：(1) 它提供了一个温和的、室温条件下获得单分散胶体粒子的合成方法，从而避免了获得单分散的无机材料胶体粒子所必须的高温反应条件；(2) 这种胶体粒子是一种新的杂化材料，它结合了两种组分的优点而具有多种属性，因而可用在许多领域；(3) 这种胶体粒子在强还原剂如NaBH4 存在的情况下，由于其中的 Pt阳离子组分被还原而发生分解，因此可用做易分解的胶体粒子模板加工中空球。此外，我们通过室温下直接混合邻苯二胺的N-甲基吡咯烷酮溶液和AgNO3水溶液，得到了亚微米的球形银胶体粒子(平均粒径达850 nm)。实验结果还表明，升高温度有利于更大尺寸的银粒子的生成，溶剂对纯的银粒子沉淀物的获得起着比较关键的作用。这些亚微米粒子的形成经历了两个阶段：(1) 超饱和溶液中纳米主粒子的成核；(2) 形成的主粒子聚集成更大的均匀的粒子。

(5) 我们发展了一种在表面巯基功能化的电极表面有效固定Ru(bpy)32+的新方法。本方法同时

运用了溶液自组装和固体表面自组装两种技术，即：先将Ru(bpy)32+和柠檬酸根阴离子保护的金纳米粒子的水溶液按照一定比例混合，得到了Ru(bpy)32+-金纳米粒子聚集体，然后把少量聚集体的悬浮液直接滴在表面巯基功能化的电极表面，从而实现Ru(bpy)32+在电极

表面的有效固定。该方法简单易行，制备的电极具有很好的稳定性和电化学发光性能，因而在固态电化学发光检测方面具有很好的应用前景；此外，该方法还可用于在固体表面构建Au纳米粒子多层膜。

(6) 发展了一种通过加热3-噻吩丙二酸(3-thiophenemalonic acid, TA)和H2PtCl6混合水溶液直

接制备小的Pt纳米粒子的新方法，并通过对该胶体溶液用Ru(bpy)32+处理，得到了Ru(bpy)32+-Pt纳米粒子聚集体。通过对在裸电极表面的聚集体进行循环电势扫描，使得聚集体中的TA分子发生电化学聚合而在电极表面形成了稳定的聚合物膜；由于该膜有效地避免了聚集体从电极表面脱落，从而我们得到了非常稳定的、具有极好电化学发光性能的膜。本工作不但提供一种方便制备Pt纳米粒子的新途径，而且还发展了一种在任何表面直接加工电化学发光检测器的新方法，在固态电化学发光检测方面具有重要应用价值。

(7) 通过在室温下直接混合H2PtCl6和Ru(bpy)3Cl2水溶液，我们获得了具有新颖形貌的、含有

Ru(bpy)32+的微结构。实验结果表明，金属价态、金属种类及反应物摩尔比和浓度对微结构的形貌有重要影响，形成的微结构都具有很好的电化学发光性能。这些微结构给我们提供了一种新的功能材料，将在毛细管电泳或毛细管电泳微芯片的固态电化学发光检测方面有着很好的应用前景。

关键词： 纳米材料，湿化学，自组装，电化学发光

Wet-Chemical Routes to the Preparation of Namomaterials and

Self-Assembly-Based Fabrication of Novel Structures

Sun Xuping

ABSTRACT

Both the wet-chemical preparation of nanomaterials and self-assembly-based fabrication of novel structures have been paid considerable attention. We carried out several studies on the preparation of noble metal nanoparticles and its two-dimensional nanostructures and conducting polymers nanobelts via wet-chemical routes. On the other hand, we fabricated some novel structures through self-assembly on planar solid substrates or in solutions. Especially, the application of some structures in the field of solid-state electrochemiluminescence detection is also explored.

We have developed a heat-treatment-based strategy for the one-step preparation of polyamine-protected noble metal nanoparticle. With the use of third-generation poly(propyleneimine) (PPI G3) dendrimer to simultaneously act both as the reducing agent and protective agent, stable noble metal gold nanoparticles have spontaneously formed by heating a solution containing HAuCl4 and PPI G3. As a result, an additional step of introducing a reducing agent as well as a protective agent is no longer needed. It is found that the size, the nucleation and growth kinetics of the gold nanoparticles thus formed can be tuned by changing the initial molar ratio of PPI G3 to gold. Similarly, highly stable Ag nanoclusters with narrow size distribution have been prepared by heating a AgNO3/PPI G3 aqueous solution without the additional step of introducing other reducing agents and protect agents. It is found that as-obtained particle is in coexistence of Ag and Ag2O and increasing temperature results in both the decrease in number of small particles and the increase in size of large particles. In addition, such thermal process has been successfully used to prepare amine-functionalized polyelectrolyte-protected gold nanoparticles by directly heating an aqueous solution containing HAuCl4 and polyelectrolytes. Four polyelectrolytes including N-[3-(trimethoxysilyl)propyl]polyethylenimine (Si-PEI), branched polyethylenmine

(BPEI), linear polyethylenimine (LPEI) and poly(allylamine hydrochloride) (PAH) were used in our study and well-stabilized gold nanoparticles with relatively narrow size distribution were obtained. Because gold nanoparticles thus formed can be combined with the properties of the polyelectrolytes used, they hold promise for use in the biomedical and bioanalytical field and on the other hand, as building blocks for the creation of nanoparticles-containing thin films. This strategy will be general to other polyelectrolytes with the same chemical structure as these four polyelectrolytes used and to the preparation of other nanoparticles such as Ag nanoparticles. Furthermore, we have found that highly concentrated, well-stable gold colloids can be prepared by direct mix of concentrated HAuCl4 and BPEI aqueous solutions at room temperature.

We have developed for the first time a novel but simple surfactantless, templateless method for preparing conducting polymer poly(o-phenylenediamine) nanobelts on a large scale. The mix of HAuCl4 and o-phenylenediamine aqueous solutions at room temperature results in the formation of a large quantity of precipitate. Lower magnification scanning electron microscopy (SEM) image indicates that the precipitate consists of a large quantity of uniform one-dimensional structures. Higher magnification SEM image further reveals these structures are transparent nanobelts with several hundred micrometers in length, several hundred nanometers in width, and several ten nanometers in height. Also observed in these SEM images are a number of nanoparticles. The X-ray diffraction (XRD) analysis of the resulting precipitate reveals the formation of amorphous poly(o-phenylenediamine) polymers with larger crystalline size as well as crystalline gold. Elemental analysis of the resulting precipitate using secondary electrons by SEM indicates the belts are poly(o-phenylenediamine) polymers but the particles are gold particles. The possible formation of the nanobelts can be explained as follows: The reduction of HAuCl4 by o-phenylenediamine leads to the formation of gold nanoparticles with the occurrence of o-phenylenediamine oligomers first, then gold nanoparticles produced serve as active catalysts to catalyze the oriented oxidative polymerization of other o-phenylenediamine monomers by HAuCl4 along the oligomers produced, resulting in the formation of poly(o-phenylenediamine) nanobelts. Furthermore, we have found that mixing of AgNO3 and o-phenylenediamine in aqueous medium results in the formation of uniform one-dimensional structures. However, the formation of such 1D structure involves the following two stages: (1) The oxidation of o-phenylenediamine by AgNO3 leads to the formation of individual

o-phenylenediamine oligomers. (2) The resulting individual oligomers self-assembly to form uniform larger 1D structures. Interestingly, decreasing medium pH can break these 1D structures apart to form individual oligomers, or vice versa. It is also found that both the concentration and molar ratio of reactants have considerable influences on the morphologies of the structures thus formed.

We have developed several wet-chemical approaches for the large-scale preparation of two-dimensional, single-crystalline gold structures including nanoplates and microdisks. The mix of an appropriate volume of an aqueous solution of freshly prepared o-phenylenediamine and HAuCl4 at room temperature with 1:1 molar ratio of o-phenylenediamine to gold gradually leads to a large quantity of precipitate, which is collected by centrifugation, washed several times with THF and water, and then suspended in water. The lower magnification SEM image indicates that the precipitate consists of a large amount of particles, while the higher magnification SEM image clearly reveals that the particles are micrometer-scale plates (about 1.5 µm in size), mainly hexagonal in shape. The distance between two planes of one plate standing against the glass substrate indicates that these plates are nanoplates. The corresponding energy-dispersive X-ray spectrum (EDS) shows these nanoplates are pure metallic gold. Two surface plasmon absorption bands at about 680 and 925 nm which arise from the longitudinal plasmon resonance of gold particles are observed for these gold nanoplates, providing another piece of evidence for the formation of anisotropic gold particles. It suggests that the quantity of o-phenylenediamine in the solution is crucial to yielding gold nanoplates and we may suggest that o-phenylenediamine molecules serve as a soft template and kinetically control the growth rates of various faces of gold particles by selectively adsorbing on to the crystallographic planes, thus resulting in the formation of large single-crystalline gold nanoplates. The importance of the platelet-like gold particles is not restricted to optics; exceptionally interesting materials with unique mechanical properties can be obtained with such colloids. A polyamine process has also been successfully used for the high-yield preparation of single-crystalline gold nanoplates with several 10µm in size, mainly hexagonal in shape, carried out by heating a concentrated aqueous solution of LPEI and HAuCl4 at 100℃. The following experimental facts (1) there are no gold byproducts with other shapes except the nanoplates existing in the resulting products and (2) adding NaBH4 to the colorless supernatant after

the termination of reaction gives no gold particles due to the depletion of HAuCl4 in the mixture by LPEI indicate that this heat-treatment-based polyamine process is a high-yield approach for the preparation of large gold nanoplates. It is found that the concentration of reactants is crucial to the formation of nanoplates. As-prepared gold nanoplates with a large Au(111) face may hold promise for scanning tunneling microscopy (STM) substrates. Furthermore, heating an aqueous oxalic acid/HAuCl4 solution has been proven to be an effective and facile approach for the large-scale production of microsized, single-crystalline, hexagonal gold microplates with a thickness above 100 nm. Both the size and the thickness of these plates can be controlled by the molar ratio of oxalic acid to gold. It is also found that the concentration of reactants strongly influences the formation of the gold plates.

We have demonstrated a novel coordination-based strategy to the fabrication of submicrometer-scale, monodisperse, spherical colloids of organic-inorganic hybrid materials. The mix of p-phenylenediamine and H2PtCl6 aqueous solutions at room temperature results in the formation of a large amount of precipitate. Low magnification SEM image of as-prepared precipitate indicates that the precipitate consists of a large quantity of monodisperse, submicrometer-scale particles about 420 nm in diameter. Higher magnification SEM image reveals that these particles are spherical in shape and well-separated from each other, and a local magnification of a single colloidal sphere by transmission electron microscopy (TEM) indicates that the resulting particles have electron-microscopically perfectly smooth surface. The chemical composition of the resulting colloids was determined by energy-dispersed spectrum (EDS) and the occurrence of the peaks of Pt, Cl, C, and N indicates that the colloids are products of p-phenylenediamine and H2PtCl6. A possible formation process is briefly presented as following: When p-phenylenediamine and PtCl62- are mixed together, the two nitrogen atoms on the para positions of one p-phenylenediamine aromatic ring can coordinate to two different Pt(IV) cations, resulting in p-phenylenediamine-bridged structure, and the Pt species contained in as-formed structure can further capture other p-phenylenediamine molecules by coordination interactions along different directions. This coordination-induced assembly process can proceed repeatedly until the depletion of reactants in the solution, resulting in the formation of large coordination polymers, finally. It is found that the particle size and polydispersity can be controlled by the molar ratio and

concentration of reactants, however, the optimum experimental parameters for the production of monodisperse colloids are 1:1 molar ratio and moderate concentration of the two reactants. Our observations are significant for the following reasons. (1) It provides a mild, room temperature route to fine colloids, avoiding the use of high temperature, which is crucial to the formation of fine colloids of inorganic materials. (2) Such colloids are new hybrid materials with versatile properties provoked by combining the merits of two sources and may find applications in many fields. (3) Such colloids are easily broken up by a strong reducing reagent, such as NaBH4, because of the reduction of the Pt cations contained therein, and therefore, they hold promise as easily decomposable colloidal templates for the fabrication of hollow spheres for a variety of applications. We have also demonstrated the rapid preparation of uniform, large, spherical Ag spheres with relatively low polydispersity through a simple wet-chemical route. The formation of Ag particles with about 750 nm in diameter occurs in a single process, carried out by direct mix of AgNO3 aqueous solution and o-phenylenediamine N-methyl-2-pyrrolidone (NMPD) solution at room temperature. The formation of monodisperse Ag colloids in our previous study can be explained as follows: AgNO3 is reduced by o-phenylenediamine to form metallic Ag atoms. With elapsed time, new Ag atoms are generated in this system and nucleation occurs as the concentration of Ag atoms reaches critical supersaturation, resulting in the formation of nuclei. The nuclei grow to nanoscale primary particles by further addition of Ag atoms, and then the primary particles aggregate to form large Ag spheres with relatively narrow size distribution. It is found that that increasing temperature results in increasing particle size. We have found that the mix of AgNO3 and o-phenylenediamine aqueous solutions, under otherwise identical conditions, yields precipitate consisting of a large quantity of large spherical Ag particles and belt-shaped structures corresponding to the oxidative products of o-phenylenediamine by AgNO3. NMPD is a powerful solvent with low toxicity and broad solubility, completely soluble in water at all temperatures and soluble in most organic solvents. We therefore choose NMPD in our present study as an effective cosolvent to dissolve the oxidative products of o-phenylenediamine in a timely manner, preventing them from precipitating with Ag particles and leading to the formation of pure Ag spheres.

We have developed a novel method based on both solution- and planar solid substrate-based assembly techniques for effective immobilization of Ru(bpy)32+ on sulfhydryl-derivated electrode

surfaces for solid-state electrochemiluminescene detection application. The whole immobilization process involves the following two steps: (1) The addition of Ru(bpy)32+ cations into citrate-capped gold nanoparticles (AuNPs) solution results in the formation of a Ru-AuNPs precipitate due to electrostatic interactions-driven assembly of the positively charged Ru(bpy)32+ cations and the negatively charged citrate ions coating on the AuNPs; (2) The suspension of Ru-AuNPs was placed on the sulfhydryl-derivated ITO electrode surface. The energy-dispersed spectrum (EDS) of the resulting precipitate indicates the precipitate consists of Ru(bpy)32+ and AuNPs. The absence of the peak of S element in the EDS may be attributed to the following two reasons: (1) The content of S element itself is too low to be detected. (2) The sulfhydryl groups are located below the Ru-AuNPs film, and the substrate is nearly completely covered by the Ru-AuNPs film. It is found that the modification of substrate with sulfhydryl group and the resultant strong Au-S interactions between sulfhydryl group and AuNPs are crucial to the effective immobilization of such Ru-AuNPs on the surface and there is no stable film formed on bare ITO surface. The Ru-AuNPs-modified ITO electrode is quite stable, exhibits excellent electrochemiluminescene behavior, and hence holds great promise for solid-state electrochemiluminescene detection in capillary electrophoresis (CE) or a CE microchip. It provides a new methodology for fabrication of stable Ru(bpy)32+-containing structures on a solid electrode surface for solid-state electrochemiluminescene detection and, on the other hand, also provides an interesting method of immobilization of nanoparticles on the surfaces for applications.

We have developed a simple thermal process for the preparation of small Pt nanoparticles, carried out by heating a H2PtCl6/3-thiophenemalonic acid (TA) aqueous solution without the addition of other reducing agents and protective agents. The formation of such Pt nanoparticles can be attributed to the direct redox between TA and PtCl62-. It is found that such Pt nanoparticles were quite stable for several months without any observable aggregation, indicating that TA serves as a very effective protective agent for the formation of Pt nanoparticles, which can be attributed to the fact that the sulfur atom in TA has a very strong nucleophilicity with lone-pair electrons and such a lone-pair electron can form a type of donor-acceptor complex with the Pt atom on the particle surface, yielding TA-protected Pt nanoparticles. The following treatment of such colloidal Pt solution with Ru(bpy)32+ causes the assembly of Pt nanoparticles into aggregates. Given the acidic

reaction condition, the Pt particle surface is mainly covered by protonated carboxylic acid groups and thus the electrostatic interactions between positively charged Ru(bpy)32+ and Pt nanoparticles are only partially responsible for the formation of the aggregates. On the other hand, both TA and Ru(bpy)32+ are rich in π-type bonds and the strong intermolecular π-π interactions between them also contribute to the formation of the aggregates via self-assembly. The most attractive point is that directly placing such aggregates on any bare solid electrode surfaces can produce very stable films exhibiting excellent electrochemiluminescence behaviors. The formation of the stable film of the aggregates on a bare electrode surface can be attributed to the fact that the TA in the aggregates is electrochemically polymerized during the cycling scans to form stable polymer film on electrode surface and the polymer film can effectively protect the aggregates from falling from the electrode surface. Our finding is significant for the following two reasons: (1) It provides a general methodology for the preparation of noble metal nanoparticles for applications; (2) Such assemblies will provide us new kind of materials for solid-state electrochemiluminescence detection in capillary electrophoresis (CE) or a CE microchip.

We have reported on the first preparation of novel, robust Ru(bpy)32+-containing supramolecular microstructures via a solution-based self-assembly strategy, carried out by directly mixing H2PtCl6 and Ru(bpy)3Cl2 aqueous solutions at room temperature. It is found that the microstructures thus formed are robust enough to stand a violent sonication process and their formation is very fast. Given the positive charge of Ru(bpy)32+ and the negative charge of PtCl62-, we may suggest that electrostatic attractions between these two complexes drive the formation of micrometer-scale supramolecular microstructures. The observation that the UV-vis absorption spectra of Ru(bpy)32+ aqueous solution is similar to that of the microstructures suspension in water further indicates that only pure electrostatic interactions are responsible for the formation of the microstructures. The electrochemical behavior of the Ru(bpy)32+ components contained in the solid film of the microstructures formed on the electrode surface is also studied and found to exhibit a diffusion-controlled voltammetric feature. We have found that both the molar ratio and concentration of reactants have a heavy influence on the morphologies of such microstructures. Most importantly, such microstructures exhibit excellent electrochemiluminescence behaviors and therefore hold great promise as new luminescent materials for solid-state electrochemiluminescence

detection in capillary electrophoresis (CE) or CE microchip.

Keywords: nanomaterials, wet-chemical, self-assembly, electrochemiluminescence