recycled plastic bags illuminate in the dark as sensors
Researchers at Universitas Gadjah Mada in Yogyakarta, Indonesia, have developed a way to use recycled plastic shopping bags as nanomaterials and sensors that can glow and detect toxic metals in drinking water. The process starts with polyethylene, which is the main plastic used in shopping bags. The researchers convert it into very small particles called carbon quantum dots, or CQDs. These particles are smaller than a virus, and to produce them, the team uses a combination of two methods: pyrolysis and hydrothermal treatment. Pyrolysis involves heating the plastic without oxygen, while hydrothermal treatment involves heating the material in water under pressure.
The researchers then add less than seven percent hydrogen peroxide to help break down the polyethylene, and the full process takes about ten hours. The result is a solution containing the carbon quantum dots (CQDs), which light up under UV light and become fluorescent. The light emission happens because of the structure of the carbon atoms and the chemical groups attached to the surface of the CQDs, so when the UV light hits the particles, electrons in the carbon atoms move to a higher energy level. As the electrons return to their normal level, they release energy in the form of visible light, making the recycled plastic bags illuminate in the dark as sensors.
image by Teslariu Mihai via Unsplash | @photosbymihai
intensity of light detects how much iron is in water
The glow from the recycled plastic bags can help find toxic metals in drinking water as sensors. Weaker light means more toxic metals in the water, and if the glow is strong, it means that there are fewer or no metals in the water. The scientists from Universitas Gadjah Mada and Hokkaido University explain that the carbon quantum dots (CQDs) have oxygen groups on their surface that can attach to certain metals. They have tested the CQDs with different metals and saw that they reacted only with ferric ions, or the iron particles with a charge of three. When the CQDs attach to this iron, the glow becomes weaker, meaning there’s a lot of it in the water.
So far, it can detect as little as 9.50 micromolar, which is enough to check if drinking water is polluted. The results, the research team finds in their study, are accurate and repeated the same way each time. The scientists have also checked how well the CQDs glow using a measure called quantum yield, which shows how much light comes out compared to how much light goes in. The CQDs made from plastic bags reached 10.04 percent, which means they glow strongly enough to be used as a sensor. At the present time, the researchers believe that their discovery can be used in portable water testing kits at a low cost, given the use of recycled plastic bags as sensors.
image by Daniele Levis Pelusi via Unsplash | @yogidan2012
image by Naja Bertolt Jensen | @officialnaja
image by Naja Bertolt Jensen
project info:
name: Recycling of plastic bag waste into carbon quantum dots using optimized pyrolysis-hydrothermal methods for selective Fe (III) sensing
researchers: Ratih Lestari, Yuichi Kamiya, Tutik Dwi Wahyuningsih, Indriana Kartini
institutions: Universitas Gadjah Mada, Hokkaido University | @ugm.yogyakarta, @hokkaidounivpr
study: here