New insight to kinetics model for cobalt doped g-C3N4 activated PMS for the efficient removal of ciprofloxacin: A bi-exponential decay model and mechanism

In this work, cobalt-doped graphitic carbon nitride (Co-CN) was synthesized through a high-temperature calcination method and employed to activate peroxymonosulfate (PMS) for ciprofloxacin (CIP) removal. The experimental outcomes demonstrated that under optimized conditions of 0.5 g/L 0.25Co-CN, 2 mM PMS, an initial solution pH of 7, an initial CIP concentration of 5 mg/L, and at a temperature of 30 °C, the removal efficiency of CIP can reach 99.5 % within 45 min. The kinetics of CIP removal by Co-CN activated PMS are accurately modeled by a bi-exponential decay function, indicating a CIP removal process involving both rapid and slower reaction phases. Furthermore, after five cycles of reuse, the catalyst maintained a respectable removal efficiency of 83.3 % for CIP, with pre- and post-reaction characterizations affirming the excellent reusability and stability of 0.25Co-CN. Quenching experiments and Electron Paramagnetic Resonance (EPR) tests confirmed the predominance role of ¹O₂ in the catalytic degradation mechanism. The CoN₄ active sites within 0.25Co-CN were identified as crucial for adsorption and subsequent degradation of CIP. In this study, a novel kinetics model is proposed for fitting the CIP removal process under the synergistic effect of adsorption and catalysis, which provides new insights into the understanding of the dynamic process of organic pollutant removal.