By Don Willmott
What's not to like about LEDs? The highly efficient and long-lasting light sources are steadily taking over the lighting market, pushing hot, inefficient incandescent light bulbs into the past. There are only two real gripes to be made about LEDs: they're expensive, and they're often made from toxic materials. Now, however, science is poised to address both issues.
University of Utah Metallurgical Engineering Research Assistant Professor Prashant Sarswat and Professor Michael Free have found a way to create luminescent materials from food waste, hinting at future LED light sources that are far cheaper and far less toxic than the ones we are buying today. Can you really make a light bulb out of yesterday's sandwich and a flat soda? They say yes.
Today's LEDs contain quantum dots, microscopic luminescent crystals that are often made from the cadmium selenide, a compound containing two toxic elements. It's expensive too, more than $500 for 25 milliliters of the substance. That's why researchers started looking for alternative substances to work with. One idea that emerged from the inquiry: good old carbon.
UV light shows how carbon dots glow. (Source: University of Utah/Prashant Sarswat)
To create "carbon dots" (CDs) rather than quantum dots, the Utah team used solvothermal synthesis, putting food waste into a solvent under pressure and high temperature for up to 90 minutes until CDs were created. In this experiment, the researchers explained in a University of Utah press release, they actually used soft drinks and pieces of bread and tortilla, discovering along the way that sucrose and D-fructose dissolved in soft drinks were found to be highly effective sources for the creation of CDs. Once created, the CDs were put in a clear resin to create luminescent objects with several different optical properties.
"Synthesizing and characterizing CDs derived from waste is a very challenging task. We essentially have to determine the size of dots, which are only 20 nanometers or smaller in diameter, so we have to run multiple tests to be sure CDs are present and to determine what optical properties they possess," Sarswat said in the release.
"The ultimate goal is to do this on a mass scale and to use these LEDs in everyday devices. To successfully make use of waste that already exists, that's the end goal," said Sarswat.
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XPRIZE contributor Don Willmott is a New York-based journalist who writes about technology, travel, and the environment for a wide variety of publications and websites.