Nanotech enables powerful and portable sterilization equipment
For the first time, researchers have created light-emitting diodes (LEDs) on lightweight flexible metal foil.
Engineers at The Ohio State University are developing the foil based LEDs for portable ultraviolet (UV) lights that soldiers and others can use to purify drinking water and sterilize medical equipment.
In the journal Applied Physics Letters, the researchers describe how they designed the LEDs to shine in the high-energy “deep” end of the UV spectrum. The university will license the technology to industry for further development.
Deep UV light is already used by the military, humanitarian organizations and industry for applications ranging from detection of biological agents to curing plastics, explained Roberto Myers, associate professor of materials science and engineering at Ohio State.
The problem is that conventional deep-UV lamps are too heavy to easily carry around.
“Right now, if you want to make deep ultraviolet light, you’ve got to use mercury lamps,” said Myers, who is also an associate professor of electrical and computer engineering. “Mercury is toxic and the lamps are bulky and electrically inefficient. LEDs, on the other hand, are really efficient, so if we could make UV LEDs that are safe and portable and cheap, we could make safe drinking water wherever we need it.”
He noted that other research groups have fabricated deep-UV LEDs at the laboratory scale, but only by using extremely pure, rigid single-crystal semiconductors as substrates—a strategy that imposes an enormous cost barrier for industry.
Foil-based nanotechnology could enable large-scale production of a lighter, cheaper and more environmentally friendly deep-UV LED. But Myers and materials science doctoral student Brelon J. May hope that their technology will do something more: turn a niche research field known as nanophotonics into a viable industry.
“People always said that nanophotonics will never be commercially important, because you can’t scale them up. Well, now we can. We can make a sheet of them if we want,” Myers said. “That means we can consider nanophotonics for large-scale manufacturing.”
In part, this new development relies on a well-established semiconductor growth technique known as molecular beam epitaxy, in which vaporized elemental materials settle on a surface and self-organize into layers or nanostructures. The Ohio State researchers used this technique to grow a carpet of tightly packed aluminum gallium nitride wires on pieces of metal foil such as titanium and tantalum.
The individual wires measure about 200 nanometers tall and about 20-50 nanometers in diameter—thousands of times narrower than a human hair and invisible to the naked eye.
In laboratory tests, the nanowires grown on metal foils lit up nearly as brightly as those manufactured on the more expensive and less flexible single-crystal silicon.
The researchers are working to make the nanowire LEDs even brighter, and will next try to grow the wires on foils made from more common metals, including steel and aluminum.
Dirty to drinkable
Graphene oxide has been hailed as a veritable wonder material; when incorporated into nanocellulose foam, the lab-created substance is light, strong and flexible, conducting heat and electricity quickly and efficiently.
Now, a team of engineers at Washington University in St. Louis has found a way to use graphene oxide sheets to transform dirty water into drinking water, and it could be a global game-changer.
“We hope that for countries where there is ample sunlight, such as India, you’ll be able to take some dirty water, evaporate it using our material, and collect fresh water,” said Srikanth Singamaneni, associate professor of mechanical engineering and materials science at the School of Engineering & Applied Science.
Nanorods’ behavior first theorized 20 years ago, but not seen until now
After their nanorods were accidentally created when an experiment didn’t go as planned, the researchers gave the microscopic, unplanned spawns of science a closer look.
Chemist Satish Nune was inspecting the solid, carbon-rich nanorods with a vapor analysis instrument when he noticed the nanorods mysteriously lost weight as humidity increased. Thinking the instrument had malfunctioned, Nune and his colleagues moved on to another tool, a high-powered microscope.
They jumped as they saw an unknown fluid unexpectedly appear between bunches of the tiny sticks and ooze out. Video recorded under the microscope is shaky at the beginning, as they quickly moved the view finder to capture the surprising event again.
The team at the Department of Energy’s Pacific Northwest National Laboratory would go on to view the same phenomenon more than a dozen times. Immediately after expelling the fluid, the nanorods’ weight decreased by about half, causing the researchers to scratch their heads even harder.
A paper published today in Nature Nanotechnology describes the physical processes behind this spectacle, which turned out to be the first experimental viewing of a phenomenon theorized 20-some years ago. The discovery could lead to a large range of real-world applications, including low-energy water harvesting and purification for the developing world, and fabric that automatically pulls sweat away from the body and releases it as a vapor.
Mixed nanoparticle systems may help purify water and generate hydrogen
Improved photocatalyst microparticles containing gold nanoparticles can be used to purify water. A*STAR researchers have produced a catalyst with gold-nanoparticle antennas that can improve water quality in daylight and also generate hydrogen as a green energy source1. Photocatalytic materials harness sunlight to create electrical charges, which provide the energy needed to drive chemical reactions in molecules attached to the catalyst’s surface.