"Nanojars" capture CO2 dissolved in water

 From New Atlas

Carbon dioxide in the atmosphere attracts most of the attention in environmental concerns, but much of that ends up in oceans, making them more acidic. Now scientists have created “nanojars” that can easily capture this and other pollutants from water.

These nanojars are molecules consisting of a copper ion, a pyrazole group and a hydroxide in repeating units, suspended in an organic solvent. When they encounter an ion with a -2 charge – which includes several major pollutants like chromate, arsenate, phosphate and carbonate – these molecules will wrap around the target, neutralizing it.

“We’ve shown that we can extract chromate and arsenate to below US Environmental Protection Agency-permitted levels for drinking water – really, really low levels,” says Gellert Mezei, a scientist on the project.

Afterwards, the nanojars can be removed from the water relatively easily, because the solvent floats on top of the water, forming a layer on the surface. Finally, once the nanojar solvent is removed from the body of water, a weak acid is all it takes to unravel the nanojars and release the trapped ions. These can then be disposed of safely or recycled into useful products.

These nanojars can be customized to target different ions as well. Using one pyrazole makes for nanojars that will go after whatever -2-charged ions are there, but using two bound by a propylene linker targets sulfate more strongly. Using two pyrazoles linked with ethylene binds better to carbonate, which is a particularly important pollutant.

When carbon dioxide in the atmosphere dissolves in water, like the ocean, it can form bicarbonate ions, too many of which can change the water chemistry and make it more acidic. That in turn wreaks havoc on the aquatic environment, messing with a whole range of biological processes and even dissolving some sea creatures. It can even contribute to further atmospheric emissions.

Finding ways to clean up these pollutants is important, but the team cautions that the nanojars are still in the very early stages of development. How they could potentially be scaled up for real-world use will be the subject of further work.

“Whether this process for removing carbon dioxide from water – and indirectly, the atmosphere – would be competitive with other technologies, that I don’t know yet,” says Mezei. “There are many aspects that have to be taken into account, and that’s a tricky business.”

The research was presented at the 2021 fall meeting of the American Chemical Society.

A molecular model of a "nanojar" with a carbonate ion trapped in the center

Gellert Mezei