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Weijia Yu
Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen, Denmark

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Journal article
Published: 25 April 2021 in Sustainability
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Photocatalysts promised to control pollution in an environmentally benign manner, inexpensively, and with a low or cheap energy input. However, the limited chemical activity of photocatalysts has prevented their widespread use. This limitation has two important consequences; in addition to limited removal efficiency for pollution, photocatalysts may also generate unwanted byproducts due to incomplete reaction. This study focuses on the byproducts formed in the photocatalytic degradation of dimethyl sulfide (DMS) on titanium dioxide (TiO2), using a continuous flow reactor and detection via proton transfer reaction mass spectrometry. TiO2, activated carbon (AC), TiO2/AC (1:1) and TiO2/AC (1:5) were tested using either a laser-driven light source or LED lamps at 365 nm. The samples were characterized using a N2-BET surface area and pore size distributions, Scanning Electron Microscopy, X-ray Diffraction, and X-ray Photoelectron Spectroscopy, which confirmed that TiO2 was successfully coated on activated carbon without unexpected phases. TiO2 and activated carbon showed different removal mechanisms for DMS. The maximum yield of formaldehyde, 11.4%, was observed for DMS reacting on a TiO2/AC (1:5) composite operating at a DMS removal efficiency of 31.7% at 50 C. In addition to formaldehdye, significant products included acetone and dimethyl disulfide. In all, observed byproducts accounted for over half of the DMS material removed from the airstream. The TiO2/AC (1:5) and TiO2/AC (1:1) composites have a lower removal efficiency than TiO2, but a higher yield of byproducts. Experiments conducted from 20 C to 70 C showed that as temperature increases, the removal efficiency decreases and the production of byproducts increases even more. This is attributed both to decreased surface activity at high temperatures due to increased recombination of reactive species, and to the decreased residence time of volatile compounds on a hot surface. This study shows that potentially dangerous byproducts are formed by photocatalytic reactors because the reaction is incomplete under the conditions generally employed.

ACS Style

Weijia Yu; Marten In `t Veld; Rossana Bossi; Mohamed Ateia; Dominique Tobler; Anders Feilberg; Nicolas Bovet; Matthew Johnson. Formation of Formaldehyde and Other Byproducts by TiO2 Photocatalyst Materials. Sustainability 2021, 13, 4821 .

AMA Style

Weijia Yu, Marten In `t Veld, Rossana Bossi, Mohamed Ateia, Dominique Tobler, Anders Feilberg, Nicolas Bovet, Matthew Johnson. Formation of Formaldehyde and Other Byproducts by TiO2 Photocatalyst Materials. Sustainability. 2021; 13 (9):4821.

Chicago/Turabian Style

Weijia Yu; Marten In `t Veld; Rossana Bossi; Mohamed Ateia; Dominique Tobler; Anders Feilberg; Nicolas Bovet; Matthew Johnson. 2021. "Formation of Formaldehyde and Other Byproducts by TiO2 Photocatalyst Materials." Sustainability 13, no. 9: 4821.

Journal article
Published: 19 April 2021 in Catalysts
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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.

ACS Style

Weijia Yu; Jiaying Chen; Mohamed Ateia; Ezra Cates; Matthew Johnson. Do Gas Nanobubbles Enhance Aqueous Photocatalysis? Experiment and Analysis of Mechanism. Catalysts 2021, 11, 511 .

AMA Style

Weijia Yu, Jiaying Chen, Mohamed Ateia, Ezra Cates, Matthew Johnson. Do Gas Nanobubbles Enhance Aqueous Photocatalysis? Experiment and Analysis of Mechanism. Catalysts. 2021; 11 (4):511.

Chicago/Turabian Style

Weijia Yu; Jiaying Chen; Mohamed Ateia; Ezra Cates; Matthew Johnson. 2021. "Do Gas Nanobubbles Enhance Aqueous Photocatalysis? Experiment and Analysis of Mechanism." Catalysts 11, no. 4: 511.