Material could be used to make better filters, more efficient sensors, and faster catalysts
For the first time, scientists have created a material with a gradient of gold nanoparticles on a silica covered silicon surface using a molecular template. The material, which was developed at North Carolina State University (NCSU) and tested at theNational Synchrotron Light Source(NSLS) at the U.S. Department of Energy’s Brookhaven National Laboratory, provides the first evidence that nanoparticles — each about one thousand times smaller than the diameter of a human hair — can form a gradient of decreasing concentration along a surface. A description of the material appears as the cover story in the July 23 issue of Langmuir.
“This material promises to be the first in a series with many applications in electronics, chemistry, and the life sciences,” said Rajendra Bhat, a Ph.D. student from North Carolina State University (NCSU) and the lead author of the study. Bhat worked with Jan Genzer, a chemical engineering professor at NCSU, and Daniel Fischer, a physicist from the U.S. Department of Commerce’s National Institute of Standards and Technology (NIST).
"Top: Images of gold nanoparticles attached to the silica surface at different distances from the most populated end of the substrate. As the distance increases, the number of particles decreases, revealing a particle gradient. Bottom: Simplified representation of the material showing particles in decreasing concentration along the surface. "
To build the material, the scientists first prepared a very thin layer of organosilanes, sticky molecules with a head and a tail, on a rectangular surface of silica. The head glues to the surface, while the tail sticks out, acting like a hook waiting for a gold nanoparticle to attach to it, explained Genzer, leader of the NCSU team. The molecules, emitted vertically in the form of a vapor by a source close to one side of the surface, slowly fell on it with decreasing concentration as the distance from the source increased, thus creating a gradient to serve as a molecular template.
The next step was to dip the material in a solution containing the gold nanoparticles, each of which was coated with a negatively charged chemical. In the solution, the tails of the organosilane molecules took on a positive charge, so the negatively charged gold particles attached to the oppositely charged tails underneath.
To visualize the gradient of gold particles, Bhat and his colleagues used an atomic force microscope, in which a tiny needle moves along the surface, following its bumps and valleys to reveal its topography. To look at the gradient of the organosilane molecules, the scientists used a technique called near-edge x-ray absorption fine structure (NEXAFS). In NEXAFS, extremely intense x-ray light is sent toward the material, and the electrons emitted by the material and collected with a sensitive detector provide information about the concentration of the organosilane molecules on the surface.
“The distinguishing feature of our approach is that the particles follow a pre-designed chemical template provided by the organosilane sticky groups,” said Genzer. “The ability to manipulate the underlying template allows us to prepare gradient structures of nanoparticles with varying characteristics.”
The main advantage of the gradient structure is that large numbers of structures can be combined on a single substrate and used for high-throughput processing. It might, for example, save time for chemists testing clusters of nanoparticles used as catalysts — chemicals actively sought by the chemical industry to create new, less polluting sources of energy. “Clusters made of different numbers of nanoparticles could be put on a single surface, and scientists could test this surface only once in a chemical reaction, instead of having to run each cluster separately through the reaction,” Fischer said. The material could also be used as a sensor to detect species that have specific affinities for nanoparticles, or as a filter to select particles of given sizes.
Bhat and his colleagues are now exploring the properties of similar materials, with different “sticky” substances and nanoparticles. “This research is so new that we are still thinking of potential applications for these materials,” he said.
This research was funded by the U.S. Department of Energy, which supports basic research in a variety of scientific fields, the National Science Foundation, and the Department of Commerce.
The U.S. Department of Energy’s Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies. Brookhaven also builds and operates major facilities available to university, industrial, and government scientists. The Laboratory is managed by Brookhaven Science Associates, a limited liability company founded by Stony Brook University and Battelle, a nonprofit applied science and technology organization.
Patrice Pages | NewsRelease
Methane vanishing on Mars: Danish researchers propose new mechanism as an explanation
08.07.2019 | Aarhus University
Modelling leads to the optimum size for platinum fuel cell catalysts: Activity of fuel cell catalysts doubled
03.07.2019 | Technische Universität München
Soft robots have a distinct advantage over their rigid forebears: they can adapt to complex environments, handle fragile objects and interact safely with humans. Made from silicone, rubber or other stretchable polymers, they are ideal for use in rehabilitation exoskeletons and robotic clothing. Soft bio-inspired robots could one day be deployed to explore remote or dangerous environments.
Most soft robots are actuated by rigid, noisy pumps that push fluids into the machines' moving parts. Because they are connected to these bulky pumps by tubes,...
Researchers at TU Graz are working together with European partners on new possibilities of measuring vehicle emissions.
Today, air pollution is one of the biggest challenges facing European cities. As part of the Horizon 2020 research project CARES (City Air Remote Emission...
Over the next three years, researchers from the Vrije Universiteit Brussel, University of Cambridge, École Supérieure de Physique et de Chimie Industrielles de la ville de Paris (ESPCI-Paris) and Empa will be working together with the Dutch Polymer manufacturer SupraPolix on the next generation of robots: (soft) robots that ‘feel pain’ and heal themselves. The partners can count on 3 million Euro in support from the European Commission.
Soon robots will not only be found in factories and laboratories, but will be assisting us in our immediate environment. They will help us in the household, to...
Scientists at the University of Leeds have created a new form of gold which is just two atoms thick - the thinnest unsupported gold ever created.
The researchers measured the thickness of the gold to be 0.47 nanometres - that is one million times thinner than a human finger nail. The material is regarded...
An international team of scientists involving the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) in Hamburg has unraveled the light-induced electron-localization dynamics in transition metals at the attosecond timescale. The team investigated for the first time the many-body electron dynamics in transition metals before thermalization sets in. Their work has now appeared in Nature Physics.
The researchers from ETH Zurich (Switzerland), the MPSD (Germany), the Center for Computational Sciences of University of Tsukuba (Japan) and the Center for...
16.08.2019 | Event News
14.08.2019 | Event News
12.08.2019 | Event News
19.08.2019 | Information Technology
19.08.2019 | Physics and Astronomy
19.08.2019 | Life Sciences