Cationic Covalent Organic Frameworks for the Enhanced Removal of Non-steroidal Anti-inflammatory Drugs from Water

1, 3,5-Trifomlylphloroglueinol ( TFT) and ethyl bromide( EB were used as building blocks to synthesize a two-dimensional 0-ketoenamine-linked cationic covalent organic framework (COE), namely TFP-EB COF, under solvothermal conditions. The obtained TFP-EB COF exhibits good crystallinity, high specific surface area arid abundant ethidium bromide units, thus it can be applied as the adsorbent for the removal of non steroidal anti-inflammatory drugs (NSAIDs) from aqueous solutions. Interestingly, the cationic TFP-EB COF can adsorb anionic NSAIDs such as diclofenac sodium ( DCF-S) and p-aminosalicylate sodium (PAS -S) in water with fast adsorption kinetics and high adsorption capacity. The maximum adsorption capacities of TFP-EB COF for DCF-S and PAS -S are found to be 350.4 and 145.3 mg/g, respectively. In sharp contrast, the neutral TFP-BND COF synthesized by TFP and 4, 4'-diaminobiphenyl( BND) under similar conditions shows poor adsorption ability toward DCF-S and PAS -S with maximum adsorption capacities of only 59.7 and 13.6 mg/g, respectively. The more excellent adsorption performance of TFP-EB COP' than TIT -MD COP' can be ascribed to the presence of strong electrostatic interaction between the EB units anchored in the TFP-EB COF channels and the carboxylate groups in NSAIDs. In addition, the ion competing experiments and cyclic regeneration experiments were also carried out, which demonstrate the great potential application of cationic TFP-EB COF in the removal of NSAIDs.