Rapid Transformation from Spherical Nanoparticles, Nanorods, Cubes, or Bipyramids to Triangular Prisms of Silver with PVP, Citrate, and H2O2

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• 作者：Masaharu Tsuji ; Satoshi Gomi ; Yoshinori Maeda ; Mika Matsunaga ; Sachie Hikino ; Keiko Uto ; Takeshi Tsuji ; Hirofumi Kawazumi
• 刊名：Langmuir
• 出版年：2012
• 出版时间：June 19, 2012
• 年：2012
• 卷：28
• 期：24
• 页码：8845-8861
• 全文大小：1110K
• 年卷期：v.28,no.24(June 19, 2012)
• ISSN：1520-5827

文摘

Rapid sphere-to-prism (STP) transformation of silver was studied in aqueous AgNO₃/NaBH₄/polyvinylpyrrolidone (PVP)/trisodium citrate (Na₃CA)/H₂O₂ solutions by monitoring time-dependent surface plasmon resonance (SPR) bands in the UV鈥搗is region, by examining transmission electron microscopic (TEM) images, and by analyzing emitted gases during fast reaction. Roles of PVP, Na₃CA, and H₂O₂ were studied without addition of a reagent, with different timing of each reagent鈥檚 addition, and with addition of H₂O₂ 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 H₂O₂. The covering of Ag nanoparticles with carboxylate groups is necessary to initiate rapid STP transformation by premixing citrate before H₂O₂ addition. Based on our data, rapid prism formation starts from the consumption of spherical Ag particles because of shape-selective oxidative etching by H₂O₂. Oxidative etching of spherical particles by H₂O₂ 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/NaBH₄/PVP/Na₃CA/H₂O₂ 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.