Capturing carbon dioxide from the atmosphere can both alleviate the effects of man-made climate change and allow the use of CO₂ as a chemical feedstock. Many of the possible solutions for carbon capture on an industrial scale have drawbacks such as high energy costs, corrosion problems, low selectivity, or problematic desorption. Enzymes that bind CO₂, such as nickel-containing ureases, can act as an inspiration for better capture complexes.

Ulf-Peter Apfel, Ruhr-Universität Bochum, Germany, and colleagues have synthesized azacryptands that contain two nickel centers and studied their CO₂ uptake kinetics and selectivity. The bimetallic complexes captured CO₂ from air, bound as a bicarbonate bridging the two metal centers. This was confirmed by isotopic labelling. The reaction was selective, no uptake of SO₂, CO, or nitrous oxides was observed.

To reverse the strong binding of CO₂ and release it in gaseous form, it was exchanged with N₃^–. The bimetallic cryptand complex could then be regenerated by irradiation with UV light, which led to decomposition of the azide complex. As the team points out, this approach could allow selective and reversible carbon capture and transport.

• Bimetallic nickel complexes for selective CO₂ carbon capture and sequestration,
  F. Möller, K. Merz, C. Herrmann, U.-P. Apfel,
  Dalton Trans. 2016.
  DOI: 10.1039/C5DT04267D