One-Step One-Phase Synthesis of Monodisperse Noble-Metallic Nanoparticles and Their Colloidal Crystals

Abstract

Noble-metallic nanoparticles have attracted increasing research attention during the past decades due to their interesting sizedependent optical, electronic, and catalytic properties. 1,2 Nanoparticles with a narrow size distribution can further function as building blocks for the construction of higher-ordered superlattices that exhibit collective properties of individual nanoparticles. [3][4][5][6][7][8] Although several synthetic routes of noble-metallic nanoparticles have been developed, the challenge remains of obtaining monodisperse nanoparticles with size <10 nm on a large scale. Since the first report in 1994, the syntheses of metallic nanoparticles with size less than 10 nm have been dominated by the Brust method, a twophase protocol that can be easily scaled up to gram scale. However, the nanoparticles prepared by the Brust method and its variations typically have a continuous and broad size distribution in the range of 1-4 nm. 9,10 Similarly, the method based on the solvated metal atom dispersion technique is suitable for preparation of metal nanoparticles on the gram scale, 6,11 but post-heat treatment is generally required for good size dispersivity.Recently, efforts have been made to develop one-phase syntheses in which the reduction of metal takes place homogeneously in a selected organic solvent rather than at the two-phase interface as in the Brust method. 12-15 Even though these one-phase syntheses have been shown to significantly narrow the particle size distribution, to our best knowledge, monodisperse metallic particles with size dispersivity <5% have not yet been reported by using any one-phase synthesis without a subsequent size-selection process.We report here a facile one-step one-phase synthetic route to achieve a variety of metallic nanoparticles by using amine-borane complexes as reducing agents. With the use of different metal sources, both mono-and alloyed metallic nanoparticles with a narrow size distribution can be obtained in a single step on a gram scale. The synthesized nanoparticles are ready to function as building blocks for the formation of large colloidal crystals ( Figure 1) directly from the reaction mixtures.All syntheses were carried out in air by mixing metal source(s) and capping ligand (e.g., thiols) in an organic solvent, such as benzene, toluene, or chloroform. An amine-borane complex was then added to the mixture and stirred until the reduction was complete. As an example, dodecanethiol-capped gold nanoparticles were prepared as follows: 0.25 mmol AuPPh 3 Cl was mixed with 0.125 mL of dodecanethiol in 20 mL of benzene to form a clear solution to which 2.5 mmol of tert-butylamine-borane complex was then added. The color of the mixture darkened gradually and became purple-red after stirring at 55°C for 5 min. TEM samples were prepared by dipping carbon-coated Cu TEM grids directly into the solution and drying in air for at least 2 h. As shown in Figure 1A, long-range close-packed superlattices of 6.2 nm gold nanoparticles ( Figure 1A) can be obtained even without ...

Gold–silica quantum rattles for multimodal imaging and therapy

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Probing atomic ordering and multiple twinning in metal nanocrystals through their vibrations

“…Single-domain gold NCs are synthesized by using a modified Stucky's protocol (4). Briefly, we first dissolve 0.25 mM AuPPh 3Cl in 25 ml of toluene for both samples Au (5.3) and Au(5.1) and 22 ml for sample Au (4.3), and then, dodecanethiol (2 mM) is added to the solution.…”

The van der Waals Interactions of n‐Alkanethiol‐Covered Surfaces: From Planar to Curved Surfaces

“…A detailed experimental analysis of larger NPs is not straightforward. Since small n ‐alkanethiol covered AuNPs are synthetized by a known direct method where NPs were dissolved in an organic solvent (such as dichloromethane or toluene),32 the same procedure fails in the synthesis of larger AT‐covered AuNPs due to precipitation. To overcome this problem, larger NPs were synthetized by an indirect method: first AuNPs of 13, 20 nm and 100 nm were prepared in an aqueous solution (NPs covered by citrates) and then by ligand exchange, the corresponding ATs adsorb on the NPs.…”