Polyoxometalate-based ionic frameworks for highly selective CO2 capture and separation

Abstract

During the utilization of structural and functional advantages of polyoxometalates (POMs) for enhanced applications, a suitable assembly of these clusters in framework materials to act as binding nodes represents a promising approach. In contrast to well-developed coordination/covalent combinations, we have developed a convenient strategy to build porous structures of POMs with smaller-sized counterions as bridging ligands via ionic interactions to reinforce their capability in gas adsorption in parallel to metal–organic frameworks (MOFs)/covalent organic frameworks (COFs). With this goal, a series of POMs-based ionic frameworks (IFs) were constructed with triol-ligand modified Anderson–Evans-type clusters as building blocks, and their sodium counter-cations were used as linkers. The three-dimensional (3D) open-frameworks obtained displayed unusually selective CO2 capturing capability and efficient separation from their N2, H2, and CH4 mixtures under low pressure at room temperature. Among the synthesized IFs, the cobalt-centered cluster exhibited the best performance for the uptake and selective separation of CO2 over N2 and CH4 in a range of 0–1 bar, while the nickel-centered cluster displayed the highest selectivity over H2 at 1 bar. Breakthrough experiments based on real binary gas mixtures demonstrated that the cobalt-containing framework illustrated high performance in the actual gas separation and sustained stability against a simulated operating environment.