From bread to bulb?

Two researchers from the University of Utah have discovered a way to create LEDs from food and beverage waste.

Over the last 18 months, Metallurgical Engineering Research Assistant Professor Prashant Sarswat and Professor Michael Free have successfully turned food waste such as discarded pieces of tortilla into carbon dots (CDs) and subsequently, LEDs.

LEDs can be produced by using quantum dots (QDs), or tiny crystals that have luminescent properties, to produce light. QDs can be made with numerous materials, some of which are rare and expensive to synthesise, and even potentially harmful to dispose of.

Past research has focused on using CDs, or simply QDs made of carbon, to create LEDs instead. Compared to other types of quantum dots, CDs have lower toxicity and better biocompatibility, meaning they can be used in a broader variety of applications.

To synthesise waste into CDs, Sarswat and Free employed a solvothermal synthesis, or one in which the waste was placed into a solvent under pressure and high temperature until CDs were formed. In this experiment, the researchers used soft drinks and pieces of bread and tortilla.

“Synthesising and characterising CDs derived from waste is a very challenging task. We essentially have to determine the size of dots which are only 20 nanometres 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,” said Sarswat.

In comparison, a human hair is around 75,000 nanometres in diameter.

Currently, one of the most common sources of QDs is cadmium selenide, a compound comprised of two toxic elements. The researchers said the ability to create QDs in the form of CDs from food and beverage waste would help eliminate concern over toxic waste.

“QDs derived from food and beverage waste are not based on common toxic elements such as cadmium and selenium, which makes their processing and disposal more environmentally friendly than it is for most other QDs. In addition, the use of food and beverage waste as the starting material for QDs allows for reduced waste and cost to produce a useful material,” said Free.

“With food and beverage waste that are already there, our starting material is much less expensive. In fact, it’s essentially free,” added Sarswat.

Sarswat and Free hope to continue studying the LEDs produced from food and beverage waste for stability and long-term performance.

“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.

The results were recently published in Physical Chemistry Chemical Physics Oct-2015, a journal of the Royal Society of Chemistry.

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