Mini carbon-capturing motors may help lower carbon dioxide levels in the oceans

Researchers have developed carbon-capturing machines much smaller than the width of a human hair, which could one day combat ocean acidification and global warming. According to nanoengineers from the University of California in San Diego, the enzyme-functionalized micromotors can rapidly zoom around in water, remove carbon dioxide and convert it into a usable solid form.

The micromotors, according to a study published in the journal Angewandte Chemie, represent a promising route to mitigate the buildup of carbon dioxide, a major greenhouse gas in the environment. The team, led by nanoengineering professor Joseph Wang, demonstrated that the machines rapidly decarbonated water solutions saturated with carbon dioxide. Within five minutes, they found that the micromotors removed 90 percent of the carbon dioxide from a solution of deionized water. Wang and his colleagues also discovered that the micromotors were just as effective in a sea water solution and removed 88 percent of the carbon dioxide in the same timeframe.

Composed of six-micrometer-long tubes, the micromotors help rapidly convert carbon dioxide into calcium carbonate, which is a solid mineral found in eggshells, shells of various marine organisms, calcium supplements and cement. The machines' outer polymer surface, meanwhile, holds the enzyme carbonic anhydrase, enabling it to speed up the reaction between carbon dioxide and water to form bicarbonate. Calcium chloride, when added to the water solutions, helps convert bicarbonate to calcium carbonate.

According to the researchers, removing carbon dioxide from water is induced by the fast and continuous motion of the micromotors in solution. The team further explains that the micromotors' autonomous movement causes efficient solution mixing, which leads to faster carbon dioxide conversion. They add hydrogen peroxide to generate a stream of oxygen gas bubbles, propelling the micromotors around. When released in water solutions containing as little as two to four percent hydrogen peroxide, the researchers say the machines reached speeds of more than 100 micrometers per second.

The team notes, however, that the use of hydrogen peroxide to fuel the micromotors poses a disadvantage, since it requires the use of expensive platinum materials to build the machines. Following their study, the researchers intend to make carbon-capturing micromotors that can be propelled by water. "If the micromotors can use the environment as fuel, they will be more scalable, environmentally friendly and less expensive," says Kevin Kaufmann, an undergraduate researcher in Wang's lab and a co-author of the study. He adds that in the future, the micromotors can be used as part of a water treatment system, such as a water decarbonation plant.

The study comes on the heels of a research conducted by a team from the Ulsan National Institute of Science and Technology in South Korea, which presented a way to modify used coffee grounds into a carbon capture material to remove prolific and harmful greenhouse gas from the atmosphere.

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