Plasmacatalytic bubbles using CeO2 for organic pollutant degradation

Interactions between effects generated by non-thermal plasma (NTP) and catalysts are increasingly investigated, ranging from energy conversion and material synthesis to pollutant degradation (e.g. volatile organic compounds, VOCs) and water purification. To make the water ecosystem more environmentally and economically sustainable, green and efficient wastewater treatment technologies are urgently required. In this study, a plasmacatalytic bubble column reactor was designed to generate underwater plasma bubbles (PBs) for efficient delivery of plasma-produced gaseous reactive oxidative species to the liquid phase for subsequent applications. This system shows great potential for degrading a stubborn water contaminant azophloxine (AP), which was further enhanced with an addition of CeO2 catalysts, resulting in the catalytic oxidation of the azo dyes. Moreover, the performances and durability of CeO2 were further improved via plasma pre-activation. The plasma-treated CeO2 (CeO2-P) displayed a combination of favourable properties, such as a higher concentration of oxygen vacancies and Ce3+ (observed by XPS), a narrowed energy bandgap, and an increased specific surface area (by 41.39%). Compared with the sole PBs and PBs/CeO2 systems, the highest removal efficiency and kinetic constant up to 99.5% and 0.907 min(-1), respectively, were achieved in the PBs/CeO2-P system. Reactive species trapping corroborated that (OH)-O-center dot and O-center dot(2)- played an integral part in AP degradation. Finally, intermediates in the process of AP degradation were identified and a degradation pathway was proposed. This research would offer a promising remediation methodology for water purification via the integration of underwater plasma bubbles and CeO2 catalysts.

Automated summary

The study developed a Plasma Catalytic Bubble Column Reactor to efficiently treat water by delivering oxidative reactive species produced by plasma to the liquid phase. The addition of CeO2 catalysts enhanced the degradation of water contaminants, with improved performance and durability through plasma pre-activation. The integrated system demonstrated superior removal efficiency and kinetic constant compared to individual components, showing potential for water purification.