Breaking down microplastics

Australian and Chinese engineers have developed carbon nanosprings that show promise in breaking down microplastics polluting oceans and rivers without harming nearby microorganisms. 

The tiny springs are also designed to become magnetic once they’ve been used, so they can be recollected and used again. 

The development is described in a paper in the journal Matter. The project brought together researchers from the University of Adelaide, Curtin University and Edith Cowan University in Australia, and China’s Guangdong University of Technology.

Although often invisible to the naked eye, microplastics are ubiquitous pollutants. Some, such as the exfoliating beads found in popular cosmetics, are simply too small to be filtered out during industrial water treatment. Others are produced indirectly, when larger debris like soda bottles or tires weather amid sun and sand.

In the latest research, the team generated short-lived chemicals, called reactive oxygen species, which trigger chain reactions that chop the various long molecules that make up microplastics into tiny and harmless segments that dissolve in water.  

The problem is, however, 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.

To get around this, they used carbon nanotubes laced with nitrogen to help boost generation of reactive oxygen species. 

The carbon nanotube catalysts removed a significant fraction of microplastics in just eight hours, the researchers say, while remaining stable themselves in the harsh oxidative conditions needed for microplastics breakdown. 

The coiled shape increases stability and maximises reactive surface area. As a bonus, by including a small amount of manganese, buried far from the surface of the nanotubes to prevent it from leaching into water, the minute springs became magnetic.

“Having magnetic nanotubes is particularly exciting because this makes it easy to collect them from real wastewater streams for repeated use in environmental remediation,” says co-author Xiaoguang Duan, from the University of Adelaide.  

As no two microplastics are chemically quite the same, the next step will be to ensure the nanosprings work on microplastics of different compositions, shapes and origins.

The researchers also intend to continue to confirm the non-toxicity of any chemical compounds occurring as intermediates or by-products during microplastics decomposition.

And they hope these byproducts can 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,” says Adelaide’s Shaobin Wang, the senior author.