Magnetic carboxyl-functionalized covalent organic frameworks for adsorption of quinolones with high capacities, fast kinetics and easy regeneration

Quinolones (QNs) are widely used pharmaceuticals which have been detected in surface water and posed risks to human health. It is important and challenging to develop a novel adsorbent with faster kinetics, higher capacity and easy regeneration. In this work, we creatively designed and synthesized magnetic carboxyl-functionalized covalent organic frameworks (Fe3O4@COF-TpDBd) as a novel adsorbent for QNs. The adsorption performance and mechanism were investigated. The results showed that the electrostatic interactions between Fe3O4@COF-TpDBd and QN molecules varied with pH. Therefore, compared with most reported adsorbents, Fe3O4@COF-TpDBd showed significantly higher adsorption capacities and faster adsorption kinetics under pH-neutral conditions. The kinetics and isotherms experiments proved that the adsorption process was spontaneous and exothermic. The adsorbent can be easily separated from water through magnetism after adsorption. Moreover, the regeneration process can be performed by pH adjustment without any organic solvent or heating, which is more convenient and environmental-friendly than most reported adsorbents. The adsorption capacities remained above 80% after five successive adsorption-desorption cycles. Thus, Fe3O4@COF-TpDBd has the great potential as a novel adsorbent for QNs removal, which has faster kinetics, higher capacity and easy regeneration.