Bicarbonate anion coordination assisted CO2 capture by using urea–morpholine hybrid receptors in water

Abstract

The development of energy-efficient sorbents for aqueous CO₂ capture remains a significant challenge. This work presents a new design strategy by integrating a tertiary amine (morpholine) with a urea motif into a single molecular receptor. This structure enables autonomous, base-free CO₂ capture in water, where the urea groups provide complementary hydrogen-bonding sites for (bi)carbonate anions, while the morpholine moiety acts as an internal proton acceptor. The resulting receptors demonstrate a rapid uptake of CO₂ from a simulated flue gas (10% CO₂/N₂), achieving a capacity of up to 1.22 mmol g⁻¹. Spectroscopic studies (NMR, MS) and structural analysis of a model complex confirm that the capture proceeds via hydrogen-bond-stabilized bicarbonate formation. Crucially, the captured CO₂ can be completely released under remarkably mild conditions, either by heating at ca. 40 °C or by simple N₂ purging at ambient temperature. The receptors exhibit excellent recyclability over multiple capture–release cycles without capacity loss. This study highlights the potential of fine-tuning supramolecular interactions—particularly hydrogen bonding combined with a built-in base—to create low-energy, water-compatible CO₂ capture systems.