cm502451u_si_001.pdf (7.74 MB)
Formation of Free-Standing Supercrystals from the Assembly of Polyhedral Gold Nanocrystals by Surfactant Diffusion in the Solution
journal contribution
posted on 2014-08-26, 00:00 authored by Chih-Wen Yang, Chun-Ya Chiu, Michael H. HuangGold
supercrystals with polyhedral morphologies can be prepared
from the ordered packing of octahedral and rhombic dodecahedral nanocrystals
in the presence of a sufficient amount of surfactant by slow water
droplet evaporation. The whole supercrystal formation process has
been video-recorded using a specially designed chamber to enclose
a substrate containing the nanocrystal droplet in a moist environment.
Supercrystal growth from the assembly of octahedra is completed within
a shorter time. The presence of cetyltrimethylammonium chloride (CTAC)
within the supercrystals has been confirmed by small-angle X-ray diffraction
analysis. Transmission electron microscopy examination reveals the
tendency of two gold octahedra with face contact to fuse, a process
frequently observed in the formation of octahedron-assembled supercrystals.
Remarkably, we have developed a diffusional surfactant transport approach
to make free-standing supercrystals in bulk aqueous solution by adding
a concentrated CTAC solution to a concentrated particle solution with
a lower CTAC concentration in an Eppendorf tube. Gradual diffusion
of CTAC to the lower nanocrystal solution promotes the growth of polyhedral
supercrystals. A solution with a sufficiently high surfactant concentration
has been shown to be necessary for particle aggregation and supercrystal
formation. This method allows the deposition of dense but evenly distributed
supercrystals on a substrate. Supercrystals were also used to make
a modified electrode for electro-oxidation of glucose. This simple
and organic solvent-free approach to making a large quantity of supercrystals
allows an ample supply of supercrystals for studies of densely assembled
nanocrystal systems and for biomedical applications.
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Keywords
SolutionGold supercrystalsGradual diffusionSupercrystal growthpolyhedral supercrystalspolyhedral morphologiesCTAC concentrationnanocrystal dropletparticle aggregationsupercrystal formation processrhombic dodecahedral nanocrystalsgold octahedraCTAC solutionparticle solutionEppendorf tubenanocrystal solutionSurfactant Diffusionwater droplet evaporationdiffusional surfactant transport approachsurfactant concentrationPolyhedral Gold Nanocrystalsnanocrystal systemssupercrystal formationcetyltrimethylammonium chloridetransmission electron microscopy examinationface contact
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