Seed-Mediated Synthesis of Branched Gold Nanocrystals Derived from the Side Growth of Pentagonal Bipyramids and the Formation of Gold Nanostars

Abstract

We report the first synthesis of elongated penta-branched gold nanocrystals with a shape resembling that of a star fruit but with sharp ends by a seeding growth approach. Cetyltrimethylammonium bromide (CTAB) capping surfactant was used, and AgNO 3 was added to the last growth solution to promote the formation of the five side branches. Through an investigation of the products collected by adding AgNO 3 into first, second, third, or fourth growth solution, the penta-branched nanocrystals were found to be derived from pentagonal bipyramid-shaped nanocrystals. Side growth over the twin boundaries results in the formation of five elongated branches with the highest point of each branch bisecting the branch into two halves. Smaller penta-branched nanocrystals with sizes of 70-110 nm and more fully developed larger nanocrystals with sizes of 200-350 nm can be readily prepared. The branches possess singlecrystalline {111} faces. The intermediate products obtained at various time points were examined and their UV-vis absorption spectra recorded. By replacing CTAB with cetyltrimethylammonium chloride surfactant, and controlling the concentration of bromide ions in the solution, gold nanostars with five symmetrical branches and monodispersed sizes of 120-130 nm were synthesized for the first time.

Synthesis of Multilayered Star‐Shaped B6O Particles Using the Seed‐Mediated Growth Method

“…16 A transition from cyclic twin nanowires to parallel twinned platelets was observed in case of the B 4 C, B 6 O, and B-C-O crystals if synthesis temperature was changed from 1100°C to 1400°C. In analogy to development of fivefold symmetry structures in noble metals the growth of wire-like or multilayer structures is sensitive to impurities: Br À ions 17 or Na(OH) 18 initiate such growth in case of gold. Therefore, impurities act as nucleus around which growth in the axial direction takes place.…”

Seed‐Mediated Synthesis of Au Nanocages and Their Electrocatalytic Activity towards Glucose Oxidation

“…Synthesis and characterization of AuNCs: The Au seeds were synthesized according to a previously reported method [21] to give an average diameter of (4.5 AE 0.6) nm (see Figure S1 in the Supporting Information). The AuNCs were synthesized by a four-step seed growth protocol as illustrated in Figure 1.…”

“…This observation is consistent with previous reports. [21] Furthermore, when AgNO 3 was replaced by HNO 3 , KNO 3 , or NaNO 3 , no AuNCs were obtained (data not shown). This suggests that Ag + plays a vital role in the cage structure formation.…”

“…[21,32] It is speculated that Ag atoms are likely to be deposited preferentially on certain facets of the AuNPs by the under-potential deposition (UPD) of silver ions, [32c] and then incorporated into the Au lattice to promote the novel Au nanostructure formation. [21] Possible mechanism of formation of AuNCs: The morphologies of the Au nanostructures formed at different reaction times were characterized by TEM (Figure 7) to understand the formation mechanism of AuNCs. As shown in Figure 7 A, after a short reaction time of 5 min, the AuNPs aggregated and connected to each other to form chains.…”

Preparation and microscopic characterization of magnetite–gold mesoparticles with tunable morphology

“…On the other hand, bromide has a tendency to adsorb to gold crystalline planes, promoting anisotropic growth [20,21]. It is well known that bromide ions adsorb preferentially onto (111) planes, which leads to the formation of pyramidal crystalline tips [22]. To test the influence of the amine groups on the formation of pyramidal tips, a preparation of particles was carried out in which CTAB (cetrimonium bromide) was used in place of TOAB.…”