Clathrating CO₂ in a Supramolecular Granatohedron Cage with Noncovalent CO₂–NH₃ Interactions and High CO₂ Capture Efficiency under Ambient Conditions

Abstract

Organic amine (R−NH 2 ) reagents as dominant chemical sorbents for CO 2 capture in industrial processes suffer from high energy compensation for regeneration. Herein, we, for the first time, report the finding of Co(III) coordinating with NH 3 molecules regulating the interaction between NH 3 and CO 2 to electrostatic interactions instead of a chemical reaction and achieve CO 2 capture under nearambient conditions. NH 3 coordinating with Co(III) significantly reduces its alkalinity and reactivity with CO 2 owing to its lone-pair electron donation during coordination. Under a simple protocol, CO 2 induces the crystallization of CO 2 @[Co(NH 3 ) 6 ]-[HSO 4 ][SO 4 ] clathrate into a hydrogen-bonded granatohedron cage from a cobaltic hexammine sulfate aqueous solution under a CO 2 pressure of 56 and 142 kPa at 275 and 298 K, respectively, with a CO 2 uptake weight content of 11.7%. We reveal that CO 2 interacts with cobaltous hexammine via supramolecular interactions rather than chemical bonding. The clathrate spontaneously separates from the solution as single crystals and readily releases CO 2 under ambient conditions in water for cyclic utilization without further treatment. In such a rapid supramolecular capture process, molecular recognition ensures exclusive CO 2 selectivity, and soluble clathrate enables the spontaneous CO 2 release at a low energy penalty, exhibiting excellent practical potential in carbon capture.