Selective Bicarbonate Receptors for Direct Ocean Capture of CO₂

Given the alkalinity of the oceans (pH ≈ 8), carbon dioxide exists in surface oceanwater primarily as bicarbonate (HCO₃ ^-) at relatively high concentrations (2.4 mM) but in the presence of many other anions, some of which are in considerable excess, notably chloride and sulfate. Supramolecular receptors for bicarbonate with appropriate affinity and high selectivity over competing ions would enable the development of novel energy-efficient technologies for direct ocean capture (DOC) of carbon dioxide such as facilitated-transport membranes. We report the first lanthanide-based receptors for HCO₃ ^- with uniquely high selectivity and affinity matching oceanic conditions as needed for the development of DOC technologies. Further studies elucidate how the ligand induces high selectivity by predisposing the oxophilic lanthanide complex to bidentate HCO₃ ^- coordination. The ability to release HCO₃ ^- enables the recycling of the receptor and the recovery of pure CO₂.