Direct Air Capture of CO2 with Aqueous Peptides and Crystalline Guanidines

Negative emission technologies, including direct air capture (DAC) of carbon dioxide, are now considered essential for mitigating climate change, but existing DAC processes tend to have excessively high energy requirements, mostly associated with sorbent regeneration. Here we demonstrate a new approach to DAC that combines atmospheric CO₂ absorption by an aqueous oligopeptide (i.e., glycylglycine) with bicarbonate crystallization by a simple guanidine compound (i.e., glyoxal-bis-iminoguanidine). In this phase-changing system, the peptide and the guanidine compounds work in synergy, and the cyclic CO₂ capacity can be maximized by matching the pK_a values of the two components. The resulting DAC process has a significantly lower regeneration energy compared to state-of-the-art solvent-based DAC technologies.