Modification of covalent organic framework by hydrolysis for efficient and selective removal of organic dye

The efficient removal of organic dyes from wastewater is still a major challenge, especially for the massive production of dyeing technology. Herein, polyimide-based covalent-organic frameworks (COFs) with a highly ordered conjugated architecture are synthesized through the condensation reaction of pyromellitic dianhydride (PMDA) with tris (4-aminophenyl) amine (TAPA). Due to a repeated cyclic structure, COFs subjected to alkaline hydrolysis can offer a high density of negatively charged carboxylate anions as adsorption sites for cationic methylene blue (MB) dye through electrostatic interactions. The maximum adsorption capacity of MB on hy-drolyzed COFs is measured to be 315.6 mg/g at pH = 10 and room temperature. Significantly, hydrolyzed COFs exhibit superior adsorption selectivity for MB in a mixture solution with methyl orange (MO) and rhodamine B (RhB). Overall, hydrolyzed COFs are good candidates to serve as an efficient adsorbent for the removal of MB with a high selectivity in the posttreatment of the dyeing process. The employment of COFs with a highly active surface in this study provides new insights for the future development of efficient adsorbents for organic dyes.

Automated summary

Polyimide-based covalent-organic frameworks (COFs) with a highly ordered conjugated architecture were synthesized and hydrolyzed to offer a high density of negatively charged carboxylate anions for the adsorption of cationic methylene blue (MB) dye. The hydrolyzed COFs exhibited superior adsorption selectivity for MB and can serve as an efficient adsorbent in the posttreatment of dyeing processes.