随着纳米科学与技术的出现，金属纳米颗粒因其独特的理化性质而受到广泛关注。金属纳米颗粒的有序组装结构不仅呈现了异于其离散颗粒的集合特性，并且还是构造纳米器件的关键部分。目前，关于球形金属纳米颗粒的组装结构，人们已经做了大量的研究工作；而关于非球形金属纳米颗粒的有序组装结构，则鲜有报道并且主要集中在金纳米棒方面。在本研究中，我们通过苯胺在室温下还原氯金酸的盐酸溶液，方便、高产量地制备了单晶金纳米片的层状组装结构（图1）。特别地，上述的层状组装结构的每一层金纳米片都是通过在其表面原位生成的台阶状凸起相互联接（图2），因此该层状组装结构在粉末和液相分散状态下都可以保持稳定，有利于进一步的研究工作。形成机制的研究表明，在我们提出的制备策略中，以下的四个因素：（1）大量的Cl-的存在；（2）Cl-/O2对的氧化刻蚀作用；（3）苯胺的质子化；（4）较低的反应温度协同影响了氯金酸的还原动力学，使得金纳米颗粒的成核和生长处于动力学控制，有利于非球形颗粒的生成。在这个缓慢的反应过程中，原位生成的具有刚性直链分子结构的聚苯胺对金纳米晶的{111}晶面的选择性但又是不充分的吸附导致了垂直于该晶面的台阶状凸起的产生，最终导致了金纳米片的层状组装结构的生成。
Layered Assemblies of Single Crystal Gold Nanoplates: Direct Room Temperature
Synthesis and Mechanistic Study
Since the emergence of nanoscience, metal nanoparticles have gained enormous attention because of their unique properties not seen from the corresponding bulk solid. It is also essential to fabricate assemblies at one, two, or three dimensions by using the shape-controlled metal nanoparticles as building blocks, because such structures not only display novel collective behaviors different from those of individual nanoparticles but also are a crucial approach to constructing nanodevices. To date, 1D, 2D, or 3D assemblies composed of 0D metal nanoparticles have been extensively studied and reviewed, whereas fabricating ordered assemblies of the metal nanoparticles with anisotropic shape has been met with limited success and is mainly concerned with gold nanorods. In this study, Layered assemblies of single crystal gold nanoplates are directly synthesized in large scale by simply adding aniline to HAuCl4-HCl aqueous solution at room temperature, without the need of extra capping agent or surfactant. The large amount of Cl-, the oxidative etching by the O2/Cl- pair, the protonation of aniline, and the mild reaction temperature cocontribute to greatly slow up the reduction process of AuCl4- for facilitating the formation of these anisotropic gold nanostructures. During this slow growth process, the in situ produced polyaniline with rigidly straight chain molecular structure plays a key role in achieving these layered assemblies by selectively but incompletely adsorbing on {111} facets of gold nanocrystals, which facilitates the generation of steps on {111} facets, resulting in the final gold product with layered structure.
Zhirui Guo, Yu Zhang, Aiqun Xu, Meng Wang, Lan Huang, Kang Xu, and Ning Gu. Layered Assemblies of Single Crystal Gold Nanoplates: Direct Room Temperature Synthesis and Mechanistic Study. J. Phys. Chem. C 2008, 112, 12638–12645
Figure 1. TEM images of the layered assemblies of gold nanoplates with (a) hexagonal and (b) triangular outline, respectively. (c) SAED pattern of a single layer in the assembly; the spots marked with a circle and a square are indexed to {220} and 1/3{422} diffraction spots of fcc gold.
Figure 2. SEM images of the as-synthesized layered assemblies of gold nanoplates at (a) low magnification and (b) high magnification. The steps on the gold nanoplates are labeled by arrows. (c) Lateral section of a single layered assembly.
Figure 3. Oxidative Polymerization Process of Aniline Proceeding through the Loss of Electrons
