Climate change has a huge impact on the health of the world's oceans. In an attempt to find a solution for carbon dioxide pollution in the oceans, nanoengineers at the University of California, San Diego have developed micromotors that autonomously move through water, removing CO2 and converting it into usable material.

The nano machines are smaller than the width of a human hair and have an external polymer surface to hold the enzyme carbonic anhydrase, which acts to speed up the reaction between carbon dioxide and water to form bicarbonate. Calcium chloride is added to the water solutions to help convert bicarbonate to calcium carbonate. The autonomous and continuous movement of the micromotors through the water is also said to aid the mixing process, which leads to faster carbon dioxide conversion.

That movement is facilitated by the addition of a small amount of hydrogen peroxide to the solution, which reacts with the inner platinum surface of the micromotors and generates a stream of oxygen bubbles that propel them through the water at speeds exceeding 100 micrometers per second.

The researchers report that in the lab, the micromotors managed to remove 90 percent of the carbon dioxide from a solution of deionized water within five minutes. Similar efficiency was observed in a seawater solution, where the tiny machines removed 88 percent of the carbon dioxide. Once their job is done, the micromotors can be recovered from the water solution and reused for further carbon dioxide sequestration.

Though the water solutions in the proof-of-concept experiments contained only two to four percent hydrogen peroxide, the researchers acknowledge its use as fuel for the micromotors is less than ideal. This need for an additional additive, together with the expense of using platinum in the micromotors themselves, has prompted the nanoengineers to look into developing carbon-capturing micromotors that can use the water itself as fuel.

"If the micromotors can use the environment as fuel, they will be more scalable, environmentally-friendly and less expensive," said said Kevin Kaufman, co-author of the study and an undergraduate in the team led by nanoengineering professor and chair Joseph Wang. "In the future, we could potentially use these micromotors as part of a water treatment system, like a water decarbonation plant."

The research has been published in the journal Angewandte Chemie.