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TLDR: Microplastics are pulled out of water using magnets and turned into battery materials
Pop quiz!
Big Takeaways
Microplastics are small pieces of plastic that contaminate water sources
They’re purified by attaching iron particles to them and pulling them out of the water with a magnet
The iron-coated microplastics are heated to 500ºC to degrade the plastic
This leaves carbon-coated iron nanoparticles that are useful as a battery anode
The Problem
Plastic waste is a big environmental problem. We’ve all heard it, but recently it’s been highlighted even more due to the discovery of microplastics.
Over time, plastic pieces break down into smaller bits that are a lot harder to purify. These pieces get into our air, drinking water (looking at you plastic water bottles), and even our rain. When these pieces get small enough they’re called microplastics.
Microplastics are everywhere.
They’re a problem we can’t avoid. So, we have to figure out ways to remove them from the environment and our drinking supply. Ideally, we do this while turning them into something useful.
This is exactly the problem this week’s authors addressed. They separated out microplastics from water using magnetic iron ions and a magnet. Then, they processed the iron-microplastic particles into coated iron nanoparticles to use in a battery.
Electron images (SEM) showing microplastic particles before (a) and after (b) the electrocoagulation treatment process. The treatment attaches iron (Fe) particles to the plastic pieces so that they can be removed (c). Credit: J. Lee et al., Adv. Sci. 2023
The Solution
They used a wastewater treatment process called electrocoagulation to separate the microplastics. In electrocoagulation, electric currents suspend iron ions in a water solution containing microplastics.
These iron ions then attach to the microplastics and cause them to lose their charge. Without a charge keeping them apart, the microplastic pieces all clump together.
Once the charge on the microplastics is gone, they bunch together into larger pieces. These large pieces still have iron particles attached to them, which is convenient since iron is strongly magnetic. With the iron attached, the microplastics can be simply pulled out of the water using a magnet (as shown below).
Iron-covered microplastic particles are removed with a magnet. Credit: J. Lee et al., Adv. Sci. 2023
After they’re pulled out of the water with the magnet, the iron-coated microplastics are processed into useable battery components.
Heating the iron-coated microparticles at 500ºC caused the plastic portions to degrade. Any plastic that doesn’t completely degrade is left behind as carbon, one of the main elements making up most plastics. The left-over plastic forms a carbon shell around the iron nanoparticles, highlighted in red below (“amorphous carbon”).
Iron particle surrounded by a carbon shell. Credit: J. Lee et al., Adv. Sci. 2023
People have tried similar iron-based particles as anodes in batteries before with little success. The biggest two problems were:
The iron particles changed size as the battery charged/discharged leading to a short battery lifetime.
The particles just weren’t that conductive.
Introducing the carbon shell from the microplastics fixed both of these issues.
While plastic isn’t conductive, carbon can be. The type of carbon in the particle shell provides extra conductivity to the iron particles.
The shell serves as a restraint on the particle size. With the shell, the particles couldn’t get very larger. The shell also improves the contact between the iron particles and the other battery components, increasing their conductivity into a useful range.
This paper hits 2 birds with 1 stone: microplastic purification and new battery tech.
They use a common wastewater treatment process to purify microplastics from water. Then they take the resulting particles and turn them into useful battery materials. This way, they’re taking harmful waste and transforming it into a valuable material. They made a nice diagram of their process, included below.
Schematic of this paper’s contents. Credit: J. Lee et al., Adv. Sci. 2023
Hope you enjoyed it! I liked this example of relatively simple science that has the potential for large real-world impact.
See you next week for more science,
Neil
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