Institute for Materials Chemistry and Engineering, Kyushu University, Kasuga 816-8580, Japan.
Langmuir. 2012 Jun 19;28(24):8845-61. doi: 10.1021/la3001027. Epub 2012 Apr 24.
Rapid sphere-to-prism (STP) transformation of silver was studied in aqueous AgNO(3)/NaBH(4)/polyvinylpyrrolidone (PVP)/trisodium citrate (Na(3)CA)/H(2)O(2) solutions by monitoring time-dependent surface plasmon resonance (SPR) bands in the UV-vis region, by examining transmission electron microscopic (TEM) images, and by analyzing emitted gases during fast reaction. Roles of PVP, Na(3)CA, and H(2)O(2) were studied without addition of a reagent, with different timing of each reagent's addition, and with addition of H(2)O(2) to mixtures of spheres and prisms. Results show that prisms can be prepared without addition of PVP, although it is useful to synthesize smaller monodispersed prisms. A new important role of citrate found in this study, besides a known role as a protecting agent of {111} facets of plates, is an assistive agent for shape-selective oxidative etching of Ag nanoparticles by H(2)O(2). The covering of Ag nanoparticles with carboxylate groups is necessary to initiate rapid STP transformation by premixing citrate before H(2)O(2) addition. Based on our data, rapid prism formation starts from the consumption of spherical Ag particles because of shape-selective oxidative etching by H(2)O(2). Oxidative etching of spherical particles by H(2)O(2) is faster than that of prisms. Therefore, spherical particles are selectively etched and dissolved, leaving only seeds of prisms to grow into triangular prisms. When pentagonal Ag nanorods and a mixture of cubes and bipyramids were used as sources of prisms, rod-to-prism (RTP), cube-to-prism (CTP), and bipyramid-to-prism (BTP) transformations were observed in Ag nanocrystals/NaBH(4)/PVP/Na(3)CA/H(2)O(2) solutions. Shape-selective oxidative etching of rods was confirmed using flag-type Ag nanostructures consisting of a triangular plate and a side rod. These data provide useful information for the size-controlled synthesis of triangular Ag prisms, from various Ag nanostructures and using a chemical reduction method, having surface plasmon resonance (SPR) bands at a desired wavelength.
快速银球到棱镜（STP）转化在水溶液硝酸银/硼氢化钠/聚乙烯吡咯烷酮（PVP）/柠檬酸钠（Na3CA）/过氧化氢（H2O2）中被研究通过监测时间依赖的表面等离子体共振（SPR）带在紫外-可见区域，通过检查透射电子显微镜（TEM）图像，并通过分析快速反应期间发出的气体。研究了 PVP、Na3CA 和 H2O2 的作用，没有添加试剂，每种试剂添加的时间不同，以及将 H2O2 添加到球体和棱镜的混合物中。结果表明，虽然添加 PVP 有助于合成更小的单分散棱镜，但可以在不添加 PVP 的情况下制备棱镜。在这项研究中发现了柠檬酸钠的一个新的重要作用，除了作为板的{111}面保护剂的已知作用外，它还是通过 H2O2 对 Ag 纳米粒子进行选择性氧化刻蚀的辅助剂。Ag 纳米粒子的羧酸盐覆盖物对于通过在添加 H2O2 之前预混合柠檬酸钠来引发快速 STP 转化是必要的。根据我们的数据，快速棱镜的形成始于 H2O2 的选择性氧化刻蚀导致的球形 Ag 粒子的消耗。H2O2 对球形粒子的氧化刻蚀比棱镜快。因此，球形粒子被选择性地刻蚀和溶解，只留下棱镜的种子来生长成三角形棱镜。当五边形 Ag 纳米棒和立方体和双锥体的混合物用作棱镜的源时，在 Ag 纳米晶/硼氢化钠/PVP/柠檬酸钠/H2O2 溶液中观察到棒到棱镜（RTP）、立方体到棱镜（CTP）和双锥体到棱镜（BTP）的转化。使用由三角形板和侧杆组成的旗型 Ag 纳米结构证实了对棒的选择性氧化刻蚀。这些数据为从各种 Ag 纳米结构和使用化学还原法，在所需波长处具有表面等离子体共振（SPR）带，对三角形 Ag 棱镜的尺寸控制合成提供了有用的信息。
