Guanidine-Functionalized Covalent Organic Framework for Efficient Adsorption of Diclofenac Sodium: Synthesis, Performance, and Mechanism
The environmental persistence and ecotoxicity of diclofenac sodium (DCF), a widely used non-steroidal anti-inflammatory drug, necessitate efficient removal strategies. Covalent organic frameworks (COFs) have emerged as promising adsorbents. Here, a novel nanoribbon COF (COF-TFPPy-DGCl) was synthesized via condensation of 1,3,6,8-tetrakis(4-formylphenyl)pyrene and 1,3-diaminoguanidine hydrochloride. The material was characterized by SEM, TGA, FT-IR, and PXRD. Batch adsorption experiments evaluated the effects of pH, contact time, and initial concentration. COF-TFPPy-DGCl exhibited a maximum adsorption capacity of 370 mg·g−1 for DCF, with capacity decreasing as pH increased. Adsorption kinetics followed a pseudo-second-order model, and equilibrium data fitted the Langmuir isotherm. Selectivity tests demonstrated a DCF removal rate of 96.75%, significantly higher than for ciprofloxacin and bisphenol A (<20%). The adsorbent retained 80% of its capacity after five regeneration cycles, indicating high stability. Mechanistic studies revealed that adsorption is driven by a synergistic combination of electrostatic interactions (dominant), π-π stacking, and hydrogen bonding, facilitated by uniformly distributed active sites. Rapid equilibrium was achieved within 30 minutes. These findings establish COF-TFPPy-DGCl as a highly selective, stable, and regenerable adsorbent for DCF removal from water, offering a theoretical basis for designing advanced COF-based water treatment materials.