The technique, which was developed by Vanderbilt University Assistant Professor of Chemical and Biomolecular Engineering Rizia Bardhan, is described in a paper published online Aug. 4 by the journal Nature Materials.
In the last 30 years, there has been a tremendous amount of research studying nanocrystals – tiny crystals sized between one to 100 nanometers in size (a nanometer is to an inch what an inch is to 400 miles) – because of the expectation that they have unique physical and chemical properties that can be used in a broad range of applications.
One class of applications depends on nanocrystals' ability to grab specific molecules and particles out the air, hold on to them and then release them: a process called adsorption and desorption. Progress in this area has been hindered by limitations in existing methods for measuring the physical and chemical changes that take place in individual nanocrystals during the process. As a result, advances have been achieved by trial-and-error and have been limited to engineered samples and specific geometries.
"Our technique is simple, direct and uses off-the shelf instruments so other researchers should have no difficulty using it," said Bardhan. Collaborators in the development were Vanderbilt Assistant Professor of Mechanical Engineering Cary Pint, Ali Javey from the University of California, Berkeley and Lester Hedges, Stephen Whitelam and Jeffrey Urban from the Lawrence Berkeley National Laboratory.
The method is based on a standard procedure called fluorescence spectroscopy. A laser beam is focused on the target nanocrystals, causing them to fluoresce. As the nanocrystals adsorb the gas molecules, the strength of their fluorescent dims and as they release the gas molecules, it recovers.
"The fluorescence effect is very subtle and very sensitive to differences in nanocrystal size," she explained. "To see it you must use nanocrystals that are uniform in size." That is one reason why the effect wasn't observed before: Fabrication techniques such as ball milling and other wet-chemical approaches that have been widely used produce nanocrystals in a range of different sizes. These differences are enough to mask the effect.
To test their technique, the researchers studied hydrogen gas sensing with nanocrystals made out of palladium. They choose palladium because it is very stable and it readily releases adsorbed hydrogen. They used hydrogen because of the interest in using it as a replacement for gasoline. One of the major technical obstacles to this scenario is developing a safe and cost-effective storage method. A nanocrystal-based metal hydride system is one of the promising approaches under development.
The measurements they made revealed that the size of the nanocrystals have a much stronger effect on the rate that the material can adsorb and release hydrogen and the amount of hydrogen that the material can absorb than previously expected – all key properties for a hydrogen storage system. The smaller the particle size, the faster the material can absorb the gas, the more gas it can absorb and faster it can release it.
"In the past, people thought that the size effect was limited to sizes less than 15 to 20 nanometers, but we found that it extends up to 100 nanometers," said Bardhan.
The researchers also determined that the adsorption/desorption rate was determined by just three factors: pressure, temperature and nanocrystal size. They did not find that additional factors such as defects and strain had a significant effect as previously suggested. Based on this new information, they created a simple computer simulation that can predict the adsorption/desorption rates of various types and size ranges of nanocrystals with a variety of different gases.
"This makes it possible to optimize a wide range of nanocrystal applications, including hydrogen storage systems, catalytic converters, batteries, fuel cells and supercapacitors," Bardhan said.
The research was funded by Department of Energy grants KC0202020 and AC02-05CH11231.
Visit Research News @ Vanderbilt for more research news from Vanderbilt. [Media Note: Vanderbilt has a 24/7 TV and radio studio with a dedicated fiber optic line and ISDN line. Use of the TV studio with Vanderbilt experts is free, except for reserving fiber time.]
David F. Salisbury | Vanderbilt University
Melting solid below the freezing point
23.01.2017 | Carnegie Institution for Science
An innovative high-performance material: biofibers made from green lacewing silk
20.01.2017 | Fraunhofer-Institut für Angewandte Polymerforschung IAP
For the first time ever, a cloud of ultra-cold atoms has been successfully created in space on board of a sounding rocket. The MAIUS mission demonstrates that quantum optical sensors can be operated even in harsh environments like space – a prerequi-site for finding answers to the most challenging questions of fundamental physics and an important innovation driver for everyday applications.
According to Albert Einstein's Equivalence Principle, all bodies are accelerated at the same rate by the Earth's gravity, regardless of their properties. This...
An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
19.01.2017 | Event News
10.01.2017 | Event News
09.01.2017 | Event News
23.01.2017 | Health and Medicine
23.01.2017 | Physics and Astronomy
23.01.2017 | Process Engineering