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Carboxyl-functionalized porous aromatic framework for rapid, selective and efficient removal of cationic pollutants from water.

The functionalization of porous aromatic frameworks (PAFs) is essential for task-specific application of these materials as advanced adsorbents in water treatment. In this study, a carboxyl-functionalized PAF was prepared by the post-synthesis modification of a HOCH2-tagged PAF, which was synthesized from a precursor-designed method. The synthesized PAFs were comprehensively characterized. The targeted PAF-COOH showed hierarchical porosity with the coexistence of micropores and mesopores. The carboxyl groups were distributed homogeneously across the whole material, and its content was as high as 4.18 meq g-1. An equilibrium adsorption isotherms study demonstrated that the adsorption of cationic dyes fitted well to the Langmuir model and the maximum adsorption capacities of methylene blue (b-MB) and phenosafranine obtained at pH 10 were 775.19 and 588.24 mg g-1, respectively. The adsorption kinetics of cationic dyes followed the pseudo-second order kinetic model. Quick kinetics was demonstrated with the k2 for a 100 mg L-1 b-MB solution as high as 2.83 g mg-1 min-1 and the equilibrium time was just 0.5 min. In addition, the dye-loaded PAF-COOH could be regenerated easily and showed excellent reusability. These significant characters indicated a promising prospect of the PAF-COOH for water treatment.