Microplastics, pieces of plastic that are smaller than 5 millimeters in size, pollute waterways and oceans all over the world. They end up in the environment after breaking off from clothes and tires. They also come from fertilizer and as a result of trashed plastic bags and bottles disintegrating into smaller pieces.
Cleaning up the tiny plastic pieces is a significant challenge that humanity faces today. Now researchers report tiny microcleaners with dozens of soft, tentacle-like appendages that can actively swim around in water and capture microplastics. Once they have done their work, they bubble up to the surface for collection.
One way to remove microplastics from water bodies is to filter them out using membranes. But these traditional water purification methods “are not practical or cost-effective for removing microplastics from large volumes of water or an open environment,” write chemical and biomolecular engineer Orlin Velev and colleagues from North Carolina State University in Advanced Functional Materials.
As a more unconventional route to trapping microplastics, researchers have been looking at tiny self-propelled motors to capture microplastics. Many of these micromotors rely on chemical reactions that require fuels such as hydrogen peroxide. Plus, they have to be actively collected after use.
The NCSU researchers made microcleaners that are easier to use. The team starts with materials called soft dendritic colloids (SDCs). These are soft, branched particles that can stick to just about any surface even in salty water. They can be made from a variety of polymers. The researchers used chitosan, a biodegradable polymer that is made from chitin, the carbohydrate that forms the hard shells of crustaceans.
The researchers form small pellets of dried SDCs. They infuse one side of the pellet with a plant-based oil. When the pellets are put in water, the oil creates a lower surface tension on one side and pushes the pellet forward. As the pellet moves forward, the SDC articles in the pellets separate and spread out to descend in water and hunt microplastics.
The microcleaners also contain small particles of magnesium that are coated with gelatin. As the SDCs descend and capture microplastics, the gelatin slowly dissolves in water. This exposes the magnesium, which reacts with water, creating bubbles. The bubbles make the SDCs rise to the surface “bringing the captured plastics particles to the surface in a dense, scummy mixture,” says Haeleen Hong, the paper’s first author.
That mixture can be skimmed off the surface to remove the microplastic-laden particles. In the paper, the team shows that the particles can swim and collect microplastics for up to 30 minutes.
Source: Haeleen Hong et al. Designing of Self-Dispersing Soft Dendritic Microcleaners for Microplastics Capture and Recovery. Advanced Functional
