Investigation of the Growth Process of Gold Nanoplates Formed by Thermal Aqueous Solution Approach and the Synthesis of Ultra-Small Gold Nanoplates

Abstract

The growth process of gold nanoplates formed by a thermal aqueous solution approach was investigated by withdrawing drops of a heated solution containing HAuCl4, cetyltrimethylammonium bromide (CTAB), and trisodium citrate and examined the intermediate products formed by a transmission electron microscopy analysis. The formation process proceeds extremely rapidly within seconds of reaction to form large aggregated structures, which are composed of wormlike structures just several nanometers in diameter. These tiny nanostructures are fused extensively toward the central region to form a thicker mass. The central core grows in size via incorporating the exterior wormlike nanostructures and eventually evolves into the plate morphology. Appropriate amounts of CTAB and trisodium citrate were also found to be critical to the formation of nanoplates. This synthesis approach has been extended to prepare ultrasmall triangular gold nanoplates with average widths of 40 ± 7 and 58 ± 10 nm. Because of their relatively uniform sizes, these tiny nanoplates can spontaneously self-assemble into some ordered 2-dimensional structures such as the hexagonally arranged pattern. UV−vis absorption spectroscopy showed that these nanoplates exhibit a strong absorption band at 590−602 nm and a weak and broadband centered at ∼775−900 nm.

Real time monitoring of the shape evolution of branched gold nanostructure

“…Surface plasmons (SP), which involve collective oscillations of electrons confined to a metal/dielectric boundary, such as a metal nanoparticle surface, can interact strongly with incident electro- magnetic fields [1][2][3][4][5][6][7][8][9]. Nanostar, tripod and bipyramids exhibit their well-defined peaks in the visible and NIRs.…”

“…In the past decade or so, one of the most important goals of materials science is the design of materials with tailored shape and size [1][2][3][4][5][6][7][8][9]. This goal underpins on the fact that nanoparticles exhibit unique electrical, optical, magnetic, and catalytic properties due to the emergence of collective properties in nanoscale as a result of the interparticle arrangement [5][6][7][8][9].…”

“…Scientists are achieving ever more exquisite control over the composition, size, shape and surface properties of nanocrystals, which is necessary for setting the stage for fully exploiting the potential of these remarkable materials. In spite of the good progress over the past decade in the synthesis of gold nanomaterials of various sizes and shapes, an important challenge nanomaterials are facing in technological applications are due to the fact that (a) synthesis of different shapes of gold nanoparticles involve different synthetic routes and as a result, they have different surface coating [1][2][3][4][5][6][7][8][9], and (b) the mechanisms underpinning these synthetic methods have evolved empirically and there is no accepted mechanism to explain how shape control works, particularly in a material such as gold where the surface free energies and chemistry of the major facets are similar. The detailed understanding of the design and control parameters should have a profound impact on the exploration of gold nanoparticles in a wide range of technological applications.…”

A Novel Photochemical Method for the Synthesis of Au Triangular Nanoplates inside Nanocavity of Mesoporous Silica Shells

“…1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 7 observed, consistent with the typical SPR of Au triangular nanoplates. 16 For Au nanoparticles prepared without the use of Ag + or at a higher ratio of Au:Ag, the UV-vis spectra only show the 537-nm peak, indicating their spherical shape. Elemental analysis of the Au triangular nanoplates reveals both Au and Ag with atomic ratio of Au:Ag = 33:1 ( Figure S1) …”

“…Various applications have been demonstrated for Au nanoplates in sensing, 7 bioimaging, [8][9] photothermal therapy, [10][11] catalysis, [12][13] and biological diagnostics. 1,14 To date, a number of solution-based synthetic methods have been developed for noble metal triangular nanoplates and spherical nanoparticles including seed-mediated growth, 1, 15 thermal method, 16 photocatalytic approach, [17][18][19] and biological 6 method. For example, Mirkin and coworkers used seed-mediated method for the synthesis of Au triangular nanoplates.…”