A NbO-type copper metal–organic framework decorated with carboxylate groups exhibiting highly selective CO2 adsorption and separation of organic dyes

Abstract

A porous Cu metal–organic framework (1) based on a pentacarboxylate ligand and paddlewheel SBU was synthesized and structurally characterized. Complex 1 possesses a NbO-type framework with uncoordinated –COO⁻ groups, resulting in its good selectivity for CO₂/N₂ (36) and CO₂/CH₄ (12) as well as a large CO₂-uptake capacity of 140 cm³ g⁻¹ at 273 K and 1 bar. Grand Canonical Monte Carlo (GCMC) simulations revealed that strong CO₂ adsorption sites exist near the open Cu^II sites and the uncoordinated –COO⁻ groups. Significantly, complex 1 exhibits water resistance and selective adsorption of cationic methylene blue (MB⁺) in aqueous solution and the adsorbed MB⁺ can be released in saturated NaCl solution, making it also a promising porous material for charge and pore-size dependent large-molecule capture and separation. The existence of coordinatively unsaturated metal sites as well as the exposed –COO⁻ groups in the framework of 1 is responsible for its selective gas adsorption and dye separation.