Enhanced photocatalytic ozonation of ciprofloxacin using a novel CaBiO2Cl-doped ZnO nanocomposite: performance, mechanism, and process optimization

In this study, a novel CaBiO 2 Cl-doped ZnO nanocomposite was synthesized and applied for the photocatalytic ozonation of ciprofloxacin (CIP). Comprehensive characterization confirmed the successful formation of the heterojunction structure, improved surface area (from 5.5 to 7.3 m 2 /g), and enhanced light absorption properties. The effects of pH, catalyst dosage, ozone flow rate, and initial CIP concentration were systematically optimized using response surface methodology. Under the optimal conditions (pH 7, CIP 20 mg/L, catalyst 0.3 g/L, and ozone 2 L/h), the ZnO/CaBiO 2 Cl catalyst achieved ≈92 % CIP removal within 30 min, outperforming pure ZnO (≈80–82 %). The combined UV/O 3 /photocatalyst system exhibited a strong synergistic effect with a synergy factor of 2.61. Reactive oxygen species (ROS) analysis revealed that hydroxyl radicals ( • OH) were the dominant oxidizing species, followed by superoxide radicals (O 2 − ), which collectively accelerated CIP degradation. A tentative degradation pathway was proposed, involving hydroxylation, piperazine-ring opening, defluorination, and the formation of low-molecular-weight carboxylic acids. The catalyst also maintained high stability over repeated cycles. Overall, the study demonstrates that the ZnO/CaBiO 2 Cl nanocomposite is an efficient and robust photocatalyst for the advanced oxidation of pharmaceutical contaminants. • The study used a heterogeneous photocatalytic ozonation process with zinc oxide nanoparticles to effectively degrade ciprofloxacin antibiotics. • The optimal operating conditions for achieving maximum degradation efficiency were determined. • The addition of CaBiO 2 Cl as a dopant improved the photocatalyst structure and increased the contact surface between contaminant molecules and photocatalysts. • The Design Expert software was used to model and optimize the process, showing good accordance with experimental data. • The study found that the photocatalytic ozonation technique significantly enhances the degradation of ciprofloxacin compared to other methods.