Unpicking microplastics

Recently the issue of microplastics has been in the news - they’re tiny bits of plastic from a few millimeters in diameter to even nanometers, that can be washed away from everyday objects including cosmetics and clothes, or can be from larger pieces of plastic breaking down over time. Because they’re so small, they aren’t easily filtered out by our current sewage systems, meaning they can end up in the sea, and can cause issues in the marine world. Now, scientists from the University of Adelaide in Australia have announced a new catalyst that they hope can speed up the breakdown of microplastics, in an environmentally friendly way. Ankita Anirban spoke to Ljiljana Fruk from the chemical engineering department at Cambridge, who wasn’t involved in the study, and took a look at this paper for us...

Ljiljana - So in this paper the authors have designed a new catalyst, so they speed up the reaction. So they made a catalyst which is a hybrid between carbon nanotubes and manganese compounds. And manganese is a chemical element which is known as a catalyst in many chemical reactions.

So by designing these catalyst they have shown that they can actually use it to degrade micro plastics. And when we think about the degradation that means not kind of cleaving it into the smaller pieces, but really degrading the chemical structure. This is of course an interesting approach.

Ankita - So you said it was carbon nanotubes - are these just really small tubes of carbon?

Ljiljana - If you imagine a very very very teeny layer of carbon, if you would bind this into the tube then you will get a very small nanotube. In their case it was several hundred nanometres in length, these carbon nanotubes.

Ankita - We can put a catalyst in to speed up a reaction, so does that mean that the reaction was going to happen anyway and we're just speeding it up?

Ljiljana - You know in general there is nothing in nature that stays the same. So eventually the plastics would degrade. It just takes thousands of years. So you would like to speed it up. So what they've shown in paper is exactly how the plastic structure changes over six to eight hours. Eventually they say that you can degrade the plastics into CO2, carbon dioxide, and then this carbon dioxide could be used by marine organisms in the photosynthesis for example if you have a plankton, to produce  bio materials.

So I think the plan with some of these new strategies is basically to use them in sewage water treatment plants. And if you have a combination where you have one reactor within this plant with microorganisms, then the products could be used to create a biomass, so you would have a circular system.

Ankita - So these catalysts are described as springs, why is the shape of that important?

Ljiljana - For catalysis, the surface is important. So if you have a spring-like surface you are introducing different curvature so that the molecules can fit in, but you are also increasing the surface amount that is available for catalysis.

So it's much better to have a curved surface than for example just a planar one.

Ankita - These springs are also magnetic.

Ljiljana - Yes, so having magnetic materials is of course very useful because you can imagine that you throw this catalyst into a mass of water. So how are you going to get it out? One way of getting it out is to use magnetic force. So you basically use a big magnet where you remove your catalyst when the reaction is done. So you first recycle your catalyst, and you ensure that a catalyst is not ending up in the drinking water.

Ankita - So do you think we'll be using these kind of catalysts in sewage treatment plants anytime soon?

Ljiljana - Although this is an interesting concept it will take a while until this is practically usable, because one issue is the production, scale up, of these materials. And the other thing is of course there needs to be a certain time which you invest into studying the bio-compatibility. You would not like anything to leak out into the water what is maybe more toxic than the plastic itself.

Ankita - For now, do you think we should just use less plastic?

Ljiljana - Well you know one of the biggest things is that dealing with plastic would require changes in our lifestyle. This whole hype about microplastics is relatively recent, but I think we first also need to focus on the other plastic waste. Because even if we deal with microplastics there will be new micro plastics produced from the plastic waste we have. So there needs to be changes in policy making but also in the personal relationship to plastics.