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A bright idea:

turning food waste into LEDs Light-emitting diodes (LEDs) have been an efficient alternative to fluorescent and incandescent bulbs for several years. Now, University of Utah researchers have found a way to make LEDs even more sustainable than they already are — by creating them from food and beverage waste.

L

EDs can be produced by using quantum dots (QDs),

form infrared spectroscopy, X-ray photoelectron spectroscopy, and

or tiny crystals that have luminescent properties,

Raman and AFM imaging — to determine the CDs’ various optical

to produce light. QDs can be made with numerous

and material properties.

materials, some of which are rare and expensive

“Synthesising and characterising CDs derived from waste is a very

to synthesise — and even potentially harmful to

challenging task,” said Sarswat. “We essentially have to determine the

dispose of.

size of dots which are only 20 nanometres or smaller in diameter,

Research over the past 10 years has focused on using carbon dots

(CDs), QDs made of carbon, to create LEDs instead. CDs have lower

so we have to run multiple tests to be sure CDs are present and to determine what optical properties they possess.”

toxicity and better biocompatibility than other types of QDs, meaning

The various tests first measured the size of the CDs, which cor-

they can be used in a broader variety of applications. But University

relates with the intensity of the dots’ colour and brightness. They then

of Utah Professors Prashant Sarswat and Michael Free have gone one

determined which carbon source produced the best CDs, with sucrose

step further, successfully turning food waste into CDs and, subsequently,

and D-fructose dissolved in soft drinks found to be the most effective

LEDs. Sarswat and Free employed a solvothermal synthesis, in which the

sources. Finally, the CDs were suspended in epoxy resins, heated and

waste was placed into a solvent under pressure and high temperature

hardened to solidify them for practical use in LEDs.

until CDs were formed. In this experiment, the researchers used soft

Not only do the researchers’ LEDs utilise products that would

drinks and pieces of bread and tortilla. The food and beverage waste

otherwise decompose, they will also reduce potentially harmful waste

were each placed in a solvent and heated both directly and indirectly

from the LEDs themselves. One of the most common sources of QDs

for anywhere from 30 to 90 min.

is cadmium selenide, a compound comprising two toxic elements. As

After successfully finding traces of CDs from the synthesis, Sarswat

explained by Free, “QDs derived from food and beverage waste are

and Free proceeded to illuminate the CDs to monitor their formation

not based on common toxic elements such as cadmium and selenium,

and colour. The pair also employed four other tests — Fourier trans-

which makes their processing and disposal more environmentally friendly than it is for most other QDs.” Cadmium selenide is also expensive, with one website listing a price of $529 for 25 mL of the compound. Food and beverage waste, on the other hand, is both readily available — 31% of food produced in 2014 was not available for human consumption, according to the US Department of Agriculture — and essentially free. The results of Sarswat and Free’s study have been published in Physical Chemistry Chemical Physics, a journal of the Royal Society of Chemistry. The researchers hope to continue studying the LEDs produced from food and beverage waste for stability and long-term

Michael Free (left) holds a light-emitting diode and Prashant Sarswat (right) holds carbon dots in suspension. Image credit: Prashant Sarswat.

www.SustainabilityMatters.net.au

performance; the ultimate goal, according to Sarswat, “is to do this on a mass scale and to use these LEDs in everyday devices”.

Feb/Mar 2016 - Sustainability Matters 31

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Sustainability Matters Feb/Mar 2016  

Sustainability Matters is a bi-monthly magazine showcasing the latest products, technology and sustainable solutions for industry, governmen...

Sustainability Matters Feb/Mar 2016  

Sustainability Matters is a bi-monthly magazine showcasing the latest products, technology and sustainable solutions for industry, governmen...