Oxygen nanobubbles enhanced photodegradation of oxytetracycline under visible light: Synergistic effect and mechanism
Résumé
Nanobubbles have gained much attention due to their unusual properties such as large specific surface area, surface energy and internal energy, thereby, increase the surface reaction and improve the mass transfer efficiency. The long term stability of nanobubbles and generation of reactive oxygen species enables them to address various environmental issues for water purification without secondary pollution. However, there are few studies concerning the application of oxygen nanobubbles in the advanced oxidation processes (AOPs). In this study, first time, oxygen nanobubbles were introduced into the photoreaction system under visible light irradiation for enhanced photodegradation of oxytetracycline (OTC). Results indicated that oxygen nanobubbles significantly improved the photodegradation of OTC through high mass transfer and generation of reactive radicals during the nanobubble collapse. The oxygen nanobubble stability was confirmed to be pH dependent. The nanobubbles concentration increased from 0.76 to 3.78×108 particles/mL, while the mean size decreased from 205 nm to 138 nm as the pH value increased (3.2-11.0). The degradation efficiency of OTC was improved from 45% to 98% with the increase of pH (4.0-11.0). Oxygen nanobubbles hold promise to improve the AOPs, such as reducing catalysts and chemicals usage and costs. Quenching experiments demonstrated that •OH was the predominant active species induced the photodegradation of OTC. With the development of nanobubbles technology, it is anticipated to realize totally chemicals free green technology. This study provides a novel nanobubble/AOPs technology, which will be more efficient and environmental friendly and will have broad application in waste water treatment and drinking water purification.
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