Enhanced mechanisms of electrocatalytic-ozonation of ibuprofen using a TiO2 nanoflower-coated porous titanium gas diffuser anode: Role of TiO2 catalysts and electrochemical action in reactive oxygen species formation

Abstract

This study aims to systematically investigate the enhanced mechanism of our previously proposed novel electro-heterogeneous catalytic ozonation (E-catazone) process. In this process, a unique TiO2 nanoflower (TiO2-NF)-coated porous titanium gas diffuser served as the anode and aerator at same time, and commercial graphite-coated Ti mesh (Graphite @Ti mesh) acted as cathode. For ibuprofen (kibuprofen,O3 of 9.6 M−1 s−1), an ozone-resistant pharmaceutical micro-pollutant, as the model-pollutant, E-catazone with the TiO2-NF anode showed excellent performance and significant synergistic effect for ibuprofen destruction efficiency and rate, and also delivered much higher enhancement ratios of 7.9 and 6.8 for ibuprofen degradation and TOC removal, respectively. The study revealed that OH is the main reactive oxygen species in the degradation of ibuprofen, and that the OH production was largely increased in E-catazone, by approximately two orders of magnitude of that in the ozonation and EO (electrochemical oxidation) processes. Further, TiO2-NF and electrochemical action were found to play crucial roles in promoting O3 conversion for enabling the enhanced formation of OH. Surprisingly, we found that the presence of the anode catalyst, TiO2-NF, can improve the electro-generation of H2O2 by decreasing cathodic potential, while the electrochemical action can also significantly enhance anodic TiO2-NF interface adsorption and conversion of O3. The results of computational studies showed that TiO2-(OH)2 is the main site for O3 adsorption at anodes, and the application of positive overpotential or coating of TiO2-NF at the anode can significantly improve the interfacial adsorption of O3. Therefore, E-catazone has great potential for synchronously and effectively promoting heterogeneous and homogeneous catalytic reactions of ozone under the synergistic action of TiO2-NF and electrochemical action, and shows broad prospects in application for the efficient degradation of pharmaceutical micro-pollutants.