A Zwitterionic Ligand‐Based Cationic Metal‐Organic Framework for Rapidly Selective Dye Capture and Highly Efficient Cr₂O₇²⁻ Removal

Abstract

A cationic metal-organic framework (MOF), [Cu₂ L(H₂ O)₂ ]⋅(NO₃ )₂ ⋅5.5 H₂ O (1) has been successfully synthesized from a zwitterionic ligand 1,1'-bis(3,5-dicarboxyphenyl)-4,4'-bipyridinium chlorine ([H₄ L]Cl₂ ). The framework of compound 1 contains classical {Cu₂ (O₂ C)₄ } paddlewheels, and possesses typical nbo-type topology and two types of channels with sizes of 5.0 and 15.54 Å. Benefitting from the 3D cationic framework and high pore volume, compound 1 shows interesting selective adsorption ability for anionic dyes. Such material can be successfully employed in a chromatographic column to efficiently separate mixed dyes of Fluorescein Sodium and Methylene Blue. In addition, compound 1 exhibits excellent Cr₂ O₇^2- removal capacity with maximum adsorption amount of 222.5 mg g^-1 , which ranks among the higher Cr₂ O₇^2- adsorption amounts of MOF materials ever reported, based on ion-exchange. The strategy to construct cationic MOFs based on zwitterionic ligands will promote the development of functional porous materials for the capture and removal of anionic pollutant species from contaminated liquid.