A new technique that uses spring-shaped carbon nanotubes to catalyze the decomposition of microplastic particles has been developed by Australian researchers, who say this approach could be used as a way to clean up plastic contamination in wastewater .
Microplastics have become ubiquitous pollutants in domestic wastewater as well as rivers, lakes and seas, threatening marine life and human health. Some cosmetic products generate large quantities of microbeads, which are difficult to eliminate in wastewater treatment plants.
Shaobin Wang and his colleagues at the University of Adelaide hope that this problem can be solved by using an oxidant that produces free radicals to attack the plastic, eventually breaking it down completely and generating water and carbon dioxide.
The oxidant they were working with was polymonosulfate, a typical persulfate salt with an asymmetric structure (HO-SO4) which generates sulfate and hydroxyl radicals. To activate it, the team designed magnetic nanocarbon structures: carbon nanotubes coiled in a spring-like helix shape with nitrogen dopants and encapsulated manganese carbide nanoparticles.
“We built a nanospring structure to increase mechanical strength and metallic nanoparticles buried under the carbon layer to provide carbonaceous materials with magnetic properties, which can be easily recycled later in the presence of a magnet.” , Explain Xiaoguang Duan, member of the Adelaide team. One of their goals was also to overcome some major drawbacks associated with the use of nanoscale carbon materials, such as poor stability and recycling difficulties.
Their system succeeded in degrading pieces of polyethylene during laboratory tests. After a few hours of treatment, visible cracks appeared on the surface of the microplastic beads and small pieces of plastic debris formed a thin film which then developed holes as it was digested. Toxicity testing has shown that the organic intermediates are environmentally safe for algae, with the potential to serve as food for them in a wastewater treatment system.
âThe challenge for future applications is to further reduce the cost of large-scale manufacturing of carbon catalysts and to find effective strategies to separate the microplastics from the aqueous effluent,â says Wang. His team is now focusing on other types of low-cost, high-performance carbonaceous materials with a porous structure and strong mechanical strength.
Jesus Ojeda Ledo, a chemical engineer at Swansea University in the UK, describes the work as exciting, although he stresses that more testing is needed. âTheir best microplastic removal was achieved after 8 hours at 160 Â° C,â he notes, âand this may not be entirely practical in a true wastewater treatment scenario. Future disposal technologies are expected to be less time consuming and less energy intensive.
He adds that the toxicity was based on the green algae in the reaction filtrate, while “the wastewater ecosystem is much more complex and additional testing may be needed.”
Matthew Davidson, an inorganic chemist at the University of Bath, UK, adds that it is vital to develop better methods of removing and recycling plastics and that catalytic degradation could be a useful approach. âAlthough this requires a separation which can be technically difficult and expensive,â he stresses. “It’s premature to say if it’s too expensive but, in my opinion, it will be difficult to make such an approach cost effective.”