Atomically dispersed vanadium on g-C3N4 for effective ciprofloxacin degradation via peroxymonosulfate activation: Insights on the nonradical pathway and V redox cycles

This work describes the preparation and characterization of atomically-dispersed V on graphitic carbon nitride (g-C3N4, CN) via a facile calcination method. The V atoms were found to coordinate with the -N and -O in the triazine units of g-C3N4. The catalytic activity of the as-prepared materials was evaluated in ciprofloxacin (CIP) degradation via peroxymonosulfate (PMS) activation. It was found that the presence of V (0.10 at%) noticeably enhanced the catalytic activity of CN, and the V-CN catalyst showed substantial tolerance towards pH changes, interfering species, various water sources, and different antibiotics. Chemical scavenging and electrochemical methods illustrated that the V-CN/PMS/CIP system encompassed of a nonradical electron-transfer pathway (50.0%), singlet oxygen (1O2) pathway (30.8%), sulfate radical (SO4 center dot-) generation (11.5%), and other reactive species (7.7%), and the activation process was due to the V-redox cycles. Peculiarly, V(IV)/V(III) redox cycles were responsible for the nonradical electron-transfer pathway while V(V)/V(IV) redox cycles were behind the SO4 center dot- and 1O2 generation. Additionally, comprehensive investigation on the catalytic affinity of V-CN towards different antibiotics elucidated that the electrochemical properties of the organic pollutant play a major role in the electron-transfer direction during nonradical activation. Lastly, the CIP degradation pathway was proposed, and the toxicity of its degradation intermediates was estimated. Overall, this work deepens the understanding on the potential of V-based materials in catalytic PMS activation.