Even though we can’t see them, microplastics are everywhere. The microscopic pollutants are invisible to the naked eye and yet they are wreaking havoc on the planet’s ecosystems and killing wildlife. There seems to be no way of stopping it either because it’s too small to be filtered out during industrial water treatment.
Whether it be the exfoliating beads found in popular cosmetics or particles produced indirectly when larger debris like soda bottles and tires weather amid sun and sand break down, these microplastics find their way into oceans and rivers posing a global environmental threat with damaging health consequences for animals, humans, and ecosystems.
Luckily, a University of Adelaide-led research team has developed a technique to break down the microplastics using tiny coil-shaped carbon-based magnets. Their new approach may be the solution to purging water sources of the microplastics that pollute them without harming nearby microorganisms. The research has been published in the journal Matter.
Senior author Shaobin Wang, Professor of Chemical Engineering at the University of Adelaide, said:
Microplastics adsorb organic and metal contaminants as they travel through water and release these hazardous substances into aquatic organisms when eaten, causing them to accumulate all the way up the food chain. Carbon nanosprings are strong and stable enough to break these microplastics down into compounds that do not pose such a threat to the marine ecosystem.
To decompose the microplastics, the researchers had to generate short-lived chemicals called reactive oxygen species. These chemicals trigger chain reactions that chop the various long molecules that make up microplastics into tiny and harmless segments that dissolve in water.
The challenge lied in the fact that reactive oxygen species are often produced using heavy metals such as iron or cobalt, which are dangerous pollutants in their own right and thus unsuitable in an environmental context. However, the researchers found a greener solution – carbon nanotubes laced with nitrogen to help boost the generation of reactive oxygen species.
They worked so well that over the course of just eight hours the researchers were able to remove a significant fraction of microplastics from water samples in their lab. Project co-leader Dr. Xiaoguang Duan, said:
It turns out that the degradation products of microplastic are completely harmless, and they can also be used as a carbon source for algae growth. The microplastics are completely transformed into carbon dioxide or other harmless substances, and they will not cause any adverse or toxic effects to microorganisms or fish or other animals in water.
These carbon nanotube catalysts are shaped like springs. Their unique shape made it possible for them to remain stable in the harsh oxidative conditions needed for microplastics breakdown because the coiled shape increases stability and maximizes reactive surface area.
To make them work even better, the team made the minute springs magnetic by including a small amount of manganese buried far from the surface of the nanotubes to prevent it from leaching into the water. “Having magnetic nanotubes is particularly exciting because this makes it easy to collect them from real wastewater streams for repeated use in environmental remediation,” said Duan.
The team’s next step is to ensure that the nanosprings work on microplastics of different compositions, shapes, and origins since no two microplastics are quite the same. Meanwhile, they will continue to rigorously confirm the non-toxicity of any chemical compounds occurring as intermediates or by-products during microplastics decomposition.
It’s possible that the intermediates and byproducts could even be harnessed as an energy source for microorganisms that the polluting plastics currently plague. “If plastic contaminants can be repurposed as food for algae growth, it will be a triumph for using biotechnology to solve environmental problems in ways that are both green and cost-efficient,” Professor Wang says.
