Construction of a carboxyl-functionalized clover-like covalent organic framework for selective adsorption of organic dyes

Covalent organic frameworks (COFs) with designable structure and well-defined aperture are highly desired as novel adsorbents for elimination of dye pollution. Herein, a new carboxyl-functionalized covalent organic framework (TzDABA COF) with clover-like topology was synthesized by the condensation of 1,3,5-tris(4-formyl-phenyl) triazine (Tz) and 3,5-diaminobenzoic acid (DABA) under solvothermal conditions. The obtained TzDABA COF exhibited rapid adsorption kinetics and excellent adsorption capacities toward multiple cationic organic dyes including methylene blue (MB, 315 mg g-1), crystal violet (CV, 533 mg g-1) and malachite green (MG, 1168 mg g-1) owing to the formation of strong electrostatic interaction and π-π interaction between COF framework and organic dye molecules. Remarkably, with particular ABC stacking mode and an abundant of carboxyl functional groups integrated in the clover-like architecture, the anionic TzDABA COF could effectively separate organic dyes in different modes, representing the first case of carboxyl-functionalized clover-like COF for dye separation based on charge effect and size effect. This study paves a new pathway toward construction of carboxyl-functionalized clover-like COFs and reveals their desiring prospect in field of dyes separation and purification.