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

Abstract

Organic amine (R-NH2) reagents as dominant chemical sorbents for CO2 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 NH3 molecules regulating the interaction between NH3 and CO2 to electrostatic interactions instead of a chemical reaction and achieve CO2 capture under near-ambient conditions. NH3 coordinating with Co(III) significantly reduces its alkalinity and reactivity with CO2 owing to its lone-pair electron donation during coordination. Under a simple protocol, CO2 induces the crystallization of CO2@[Co(NH3)6][HSO4][SO4] clathrate into a hydrogen-bonded granatohedron cage from a cobaltic hexammine sulfate aqueous solution under a CO2 pressure of 56 and 142 kPa at 275 and 298 K, respectively, with a CO2 uptake weight content of 11.7%. We reveal that CO2 interacts with cobaltous hexammine via supramolecular interactions rather than chemical bonding. The clathrate spontaneously separates from the solution as single crystals and readily releases CO2 under ambient conditions in water for cyclic utilization without further treatment. In such a rapid supramolecular capture process, molecular recognition ensures exclusive CO2 selectivity, and soluble clathrate enables the spontaneous CO2 release at a low energy penalty, exhibiting excellent practical potential in carbon capture.