Ionic covalent organic frameworks for Non-Steroidal Anti-Inflammatory drugs (NSAIDs) removal from aqueous Solution: Adsorption performance and mechanism

The presence of non-steroidal anti-inflammatory drugs (NSAIDs) is ubiquitous in ambient waterways due to their excessive consumption, which poses deleterious risks to human health and ecosystems. In this work, two classes of ionic covalent organic frameworks with different pore sizes (iCOFs) [TPA (terephthaldicarboxaldehyde)-TGCl (triaminoguanidinium chloride) and BPDA (4,4′-Biphenyldicarboxaldehyde)-TGCl], which is consisted of guanidine moieties as intrinsic cationic knots and different chain length dialdehydes, were innovatively exploited as adsorbents for the removal of NSAIDs. Studies revealed that the prepared iCOFs had a strong affinity for NSAIDs, particularly for diclofenac sodium (DCF) and ketoprofen (KT). The adsorption isotherms and kinetics data of both these iCOFs were in alignment with the Langmuir model and pseudo-second-order model, respectively. Guanidine-based iCOF knots trigger electrostatic interactions, which are the primarily intrinsic driving force that facilitates the efficient removal of DCF and KT. Furthermore, π-π stacking interactions are proposed based on iCOF skeletons. Additionally, TPA-TGCl was more preponderantly adsorptive toward DCF and KT, with maximum adsorption capacities of 724.64 mg·g−1 for DCF and 240.96 mg·g−1 for KT. Among them, the maximum adsorption capacity of DCF on TPA-TGCl was 27 times higher than that of carbon nanospheres, almost triple that of a magnetic cellulose ionomer/LDH, and two-fold higher than that of UiO-66-SO3H. Finally, the TPA-TGCl effectively achieved five adsorption–desorption cycles. Ultimately, iCOFs simultaneously meet the demands of structural regularity and accessibility to functional sites. Thus, they can be considered as highly efficient and recyclable adsorbents with potential applications for the remediation of the water environment, while providing a scientific basis for functional material design.