Two researchers from the University of Utah have formulated an environmentally friendly method to manufacture LEDs from food and beverage waste. It is hoped that this method will reduce the need to use toxic elements in LED production.
Michael Free (left) holds a light emitting diode and Prashant Sarswat (right) holds carbon dots in suspension. Photo credit: Prashant Sarswat
LEDs are found in almost all modern illuminated electronics from TVs and flashlights to the lights on Christmas trees. They've become popular as they are an energy efficient alternative to incandescent and fluorescent bulbs.
The Utah method of LED production is beneficial as it means the harmful, toxic waste usually associated with LED production is reduced. Also, its great to see food and beverage waste being used productively instead of leaving it to decompose, occupying space on a landfill.
LEDs work by efficiently converting electricity to light. Around 80% of the energy consumed by LEDs is used to produce light, whereas 80% of the energy consumed by incandescent and fluorescent bulbs is used to produce heat. This is possible as LEDs, unlike incandescent and fluorescent bulbs. do not require a filament to be heated to create light.
Quantum dots (QDs), which are nanoscale crystals that possess luminescent properties, can be used to produce LEDs. QDs can be produced using several methods, some of which use rare and expensive elements to synthesize whilst others result in harmful waste.
In the last decade, researchers have tried to make LEDs using QDs made of carbon which are called carbon dots (CDs). CDs are not as toxic as other types of QDs and possess comparatively good biocompatibility.
For over a year, the University of Utah’s Metallurgical Engineering Research Assistant Professor Prashant Sarswat and Professor Michael Free have managed to create CDs and subsequently LEDs from discarded tortilla pieces.
Sarswat and Free used a solvothermal synthesis method to synthesize CDs from food waste. Their method involved placing the waste into a solvent under extreme conditions (high temperature and pressure) until CDs were formed.
For their experiment, pieces of bread, tortillas and soft drinks were placed separately in their solvent and heated directly and/or indirectly for 30 to 90 minutes.
Once traces of CDs could be identified the two researchers illuminated the CDs to study their color and formation. X-ray photoelectron spectroscopy, AFM imaging, Fourier transform infrared spectroscopy and Raman were also used to establish the different material and optical properties of CDs.
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.
Prof. Prashant Sarswat - University of Utah
The size of the CDs correlates with their color and brightness intensity. Further testing was used to establish which carbon source was ideal for the manufacture of the best CDs. It was observed that the most effective sources were the sugars D-fructose and sucrose which are found in soft drinks.
Finally, to demonstrate that the CDs were appropriate for us in real-world LEDs the CDs were suspended in epoxy resins, and underwent heating and hardening processes.
An environmentally sustainable alternative
As of now, cadmium selenide, a compound that contains two toxic elements, is one of the frequently used sources of QDs. However, with the new research it would be possible to create QDs (in the form of CDs) using food and beverage waste, eliminating the toxicity of the process.
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.
Prof. Michael Free - University of Utah
Apart from the toxicity issues, cadmium selenide is also costly.
With food and beverage waste that is already there, our starting material is much less expensive. In fact, it’s essentially free.
Prof. Prashant Sarswat - University of Utah
The US Department of Agriculture reports that in 2014, about 31% of food produce was wasted. Therefore, it makes sense to utilize this food waste productively for the manufacturing of LEDs.
Going forward, Sarswat and Free are keen on ensuring that the environmentally sustainable production of LEDs provides stability and long-term usage.
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.
Prof. Prashant Sarswat - University of Utah
The research findings were recently published in the Royal Society of Chemistry’s journal Physical Chemistry Chemical Physics.