| CHAMPAIGN,
Ill. - Using high-intensity ultrasound, researchers
at the University of Illinois at Urbana-Champaign have
created hollow nanospheres and the first hollow nanocrystals.
The nanospheres could be used in microelectronics, drug
delivery and as catalysts for making environmentally
friendly fuels. "We
use high-intensity ultrasound to generate nanoparticles
of molybdenum disulfide or molybdenum oxide, which
bind to the surface of tiny silica spheres that are
much smaller than red blood cells," said Ken
Suslick, the Marvin T. Schmidt Professor of Chemistry
at Illinois and a researcher at the Beckman Institute
for Advanced Science and Technology. "After heating
the spheres to produce uniform coatings, we use hydrofluoric
acid to etch away the silica, leaving hollow shells
of the desired material."
Suslick
and former postdoctoral research associate Arul Dhas
describe their work in a paper that has been accepted
for publication in the Journal of the American Chemical
Society, and posted on its Web site.
Funding was provided by the National Science Foundation.
Hollow
nanospheres crafted from molybdenum disulfide could
serve as a superior catalyst for removing sulfur-containing
compounds from gasoline and other fossil fuels.
"Molybdenum-disulfide
is a layered material, but its catalytic activity
occurs at its edges," Suslick said. "By
distorting and breaking up the layers, hollow nanospheres
offer increased edge-surface area, as well as access
to both inner and outer shell surfaces."
Further
processing of hollow spheres made of molybdenum oxide,
however, results in the unusual formation of hollow
crystals that resemble truncated cubes. Upon heating
a second time - referred to as thermal annealing -
the hollow molybdenum oxide spheres are transformed
into single-crystal boxes with spherical hollow voids.
The
sonochemical procedure could be easily applied to
other material systems to create additional types
of hollow, nanostructured particles, Suslick said.
Sonochemistry
arises from acoustic cavitation - the formation, growth
and implosion of small gas bubbles in a liquid blasted
with sound.
The collapse of these bubbles generates intense local
heating, forming a hot spot in the cold liquid with
a transient temperature of about 9,000 degrees Fahrenheit,
the pressure of about 1,000 atmospheres and the duration
of about 1 billionth of a second.
For
a rough comparison, these values correspond to the
temperature of the surface of the sun, the pressure
at the bottom of the ocean, and the lifetime of a
lightning strike.
Ultrasound
consists of sound waves above 18,000 cycles per second,
to high-pitched to be audible to human ears.
For more news, visit the Illinois News Bureau at http://www.news.uiuc.edu
James
E. Kloeppel, Physical Sciences Editor 217-244-1073;
kloeppel@uiuc.edu
|
