The
copper nanoclusters formed beautiful red crystals.
Courtesy: Journal of the
American Chemical Society.
KAUST
researchers could serve as a roadmap to guide the design of new catalysts and
imaging agents.
A
nanocluster is a type of nanoparticle in which researchers have pinpointed the
precise arrangement of every atom, along with their bond lengths and bond
angles. This detailed information enables researchers to predict the properties
of related clusters, based on their composition and structures. "It
provides a practical model for understanding the intrinsic correlations between
structure and physical-chemical properties through a combination of experiments
and theoretical calculations," says Ren-Wu Huang of the KAUST Catalysis
Center, part of the team behind the new discovery.
Nanoclusters
are typically 1–3 nanometers wide and organized into a core and a shell. The
atomic structure of the core can determine the nanocluster's structure, size
and optical properties, while the shell affects its stability, solubility and
catalytic activity.
Nanoclusters containing copper, silver and gold have potential uses as catalysts, or as nontoxic luminescent imaging agents in living cells. Although silver and gold nanoclusters are well studied, copper nanoclusters have been rather neglected, partly because the metal tends to react with oxygen in air.
The
side (left) and top (right) views of the nanocluster reveal that it is a flat
core of 17 copper atoms (green). The cluster has 64 more copper atoms in its
shell (brown), along with molecules containing sulfur (yellow), nitrogen (blue)
and carbon (grey). Hydrogen atoms are omitted for clarity.
Courtesy: Journal of
the American Chemical Society.
The KAUST
team has now created the largest copper-based nanocluster to date, and they are
studying it with a range of techniques, including X-ray crystallography and
electrospray ionization mass spectrometry. Each 2.8-nanometer-wide cluster
contains 81 copper atoms, 46 benzenethiol molecules, 10tert-butylamine
molecules and 32 hydride ions.
Nanoclusters
generally have polyhedral cores surrounded by symmetrical shells. But the new
copper nanocluster has a flat core of 17 copper atoms, arranged into a repeating
pattern of triangles. "This kind of planar core has never been observed in
previously reported metal nanoclusters," says Osman M. Bakr, who led the
team.
The
nanocluster also has a highly unusual hemispherical shell that is
1.5-nanometers high and covered by benzenethiol molecules. Differences between
the curved and flat surfaces of the hemisphere suggest that the flat face has a
higher reactivity. In addition, computational calculations provided evidence
that the arrangement of these molecules could help to ease the transfer of
electrical charge between different clusters within a crystal, which could
prove crucial in future applications.
"The
development of copper nanoclusters is still in its infancy," says Huang.
"Therefore, the next stage of our research will be the synthesis of copper
nanoclusters with a bigger size and novel structure, and exploring their
potential applications in the field of catalysis."