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Article

Do Gas Nanobubbles Enhance Aqueous Photocatalysis? Experiment and Analysis of Mechanism

1
Department of Chemistry, Faculty of Science, Universitetsparken 5, University of Copenhagen, DK-2100 Copenhagen, Denmark
2
Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA
3
Department of Environmental Engineering and Earth Sciences, Clemson University, Clemson, SC 29634, USA
*
Authors to whom correspondence should be addressed.
These authors contribute equally to this work.
Academic Editors: Gassan Hodaifa and Ewa Kowalska
Catalysts 2021, 11(4), 511; https://doi.org/10.3390/catal11040511
Received: 19 March 2021 / Revised: 11 April 2021 / Accepted: 17 April 2021 / Published: 19 April 2021
The performance of photocatalytic advanced oxidation must be improved in order for the technology to make the jump from academic research to widespread use. Research is needed on the factors that cause photocatalysis to become self-limiting. In this study, we introduced, for the first time, nanobubbles continuously into a running photocatalytic reactor. Synthetic air, O2, and N2 bubbles in the size range of 40 to 700 nm were added to a reaction system comprising P25 TiO2 photocatalyst in stirred aqueous solution excited by UV-A lamps, with methyl orange as a target contaminant. The removal of methyl orange was tested under conditions of changing pH and with the addition of different radical scavengers. Results indicated that the oxygen and air nanobubbles improved the photocatalytic degradation of methyl orange—the removal efficiency of methyl orange increased from 58.2 ± 3.5% (N2 aeration) to 71.9 ± 0.6% (O2 aeration). Dissolved oxygen (DO) of 14.93 ± 0.13 mg/L was achieved using O2 nanobubbles in comparison to 8.43 ± 0.34 mg/L without aeration. The photodegradation of methyl orange decreased from 70.8 ± 0.4% to 53.9 ± 0.5% as pH increased from 2 to 10. Experiments using the scavengers showed that O2 was the main reactive species in photocatalytic degradation under highly dissolved oxygen conditions, which also accounted for the observation that the removal efficiency for methyl orange decreased at higher pH. However, without photocatalyst, nanobubbles alone did not improve the removal of methyl orange, and nanobubbles also did not increase the degradation of methyl orange by only photolysis. These experiments show that oxygen and air nanobubbles can act as environmentally friendly catalysts for boosting the performance of photocatalytic water treatment systems. View Full-Text
Keywords: nanobubbles; photocatalysis; TiO2; methyl orange; dissolved oxygen; scavenger nanobubbles; photocatalysis; TiO2; methyl orange; dissolved oxygen; scavenger
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MDPI and ACS Style

Yu, W.; Chen, J.; Ateia, M.; Cates, E.L.; Johnson, M.S. Do Gas Nanobubbles Enhance Aqueous Photocatalysis? Experiment and Analysis of Mechanism. Catalysts 2021, 11, 511. https://doi.org/10.3390/catal11040511

AMA Style

Yu W, Chen J, Ateia M, Cates EL, Johnson MS. Do Gas Nanobubbles Enhance Aqueous Photocatalysis? Experiment and Analysis of Mechanism. Catalysts. 2021; 11(4):511. https://doi.org/10.3390/catal11040511

Chicago/Turabian Style

Yu, Weijia, Jiaying Chen, Mohamed Ateia, Ezra L. Cates, and Matthew S. Johnson 2021. "Do Gas Nanobubbles Enhance Aqueous Photocatalysis? Experiment and Analysis of Mechanism" Catalysts 11, no. 4: 511. https://doi.org/10.3390/catal11040511

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