Capturing carbon dioxide, e.g., from the flue gas produced by power plants using fossil fuels, is an important part of mitigating emissions and mitigating climate change. One approach to this is the use of aqueous amine solutions, which capture CO₂ either via the formation of an ammonium carbamate under dry conditions or via the formation of an ammonium bicarbonate and/or carbonate under humid conditions. However, the amines used for this can have drawbacks such as toxicity, corrosiveness, and instability under the conditions in CO₂ “scrubbers”.

Tristan H. Lambert, Phillip J. Milner, Cornell University, Ithaca, NY, USA, have found that tertiary amine N-oxides can also be used to remove CO₂ from waste gas streams such as flue gas. The team used 4-methylmorpholine N-oxide (MMNO), which can form a hydrogen-bond-stabilized HCO₃^– species (pictured) with CO₂ under humid conditions.

The researchers found that the inexpensive MMNO shows good stability under the necessary conditions for carbon capture, as well as good CO₂ uptake. In contrast to the amines used for this, the compound is nontoxic and noncorrosive. While the amines require high temperatures for regeneration after capture, MMNO releases CO₂ at about 65 °C in a simulated temperature swing process. Overall, the work demonstrates the promise of trialkylamine N-oxides such as MMNO for use in carbon capture technologies.

• Harnessing Oxidized Amines as Robust Sorbents for Carbon Capture,
  Sijing Meng, Tristan H. Lambert, Phillip J. Milner,
  J. Am. Chem. Soc. 2025.
  https://doi.org/10.1021/jacs.4c16764