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Conventional versus lattice photocatalysed reactions: Implications of the lattice oxygen participation in the liquid phase photocatalytic oxidation with nanostructured ZnO thin films on reaction products and mechanism at both 254 nm and 340 nm

Paper ID Volume ID Publish Year Pages File Format Full-Text
46908 46453 2011 14 PDF Available
Title
Conventional versus lattice photocatalysed reactions: Implications of the lattice oxygen participation in the liquid phase photocatalytic oxidation with nanostructured ZnO thin films on reaction products and mechanism at both 254 nm and 340 nm
Abstract

This study aimed to investigate the relationship between surface morphologies of nanostructured ZnO thin films, the reaction intermediates and products produced, and the liquid phase and solid phase reaction mechanisms under both oxygen rich and oxygen limited conditions at two different wavelengths (254 nm and 340 nm). Four different ZnO morphologies were prepared by hydrothermal deposition on two different substrates – clean glass (CG) and direct current magnetron sputtered ZnO glass (MS). The two films grown on the MS templates were highly vertically aligned columnar structures and those grown without templates (CG) had little or no structural alignment. Methylene blue (MB) was used as the reactant, since its reaction intermediates and products are well defined and measurable, allowing predictable comparison between these catalysts.Results showed that there was a significant difference in MB degradation rates as well as reaction intermediate formation and destruction rates correlated to the morphologies and crystallinity at both UV wavelengths, with the highest reaction rates at 340 nm. Reaction analysis indicates that there may be a competition between two different photocatalytic mechanisms: conventional photocatalysed radical oxidation and lattice oxygen driven oxidation. The dominant reaction mechanism present depended on the thin film morphology, crystallinity, availability of oxidant and the wavelength of the incident UV. The surface photocatalysed radical formation is thought to be predominant for more highly aligned and more crystalline morphologies, where there was plentiful oxygen and UV irradiation at 340 nm. Lattice oxygen photodegradation is thought to be predominant for less aligned more amorphous morphologies and UV irradiation at 254 nm. Based on these results a new MB ZnO photocatalysed oxidation mechanism is proposed.

Graphical abstract.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Relationship established between surface morphologies of thin film ZnO, reaction intermediates and products, and liquid phase and solid phase reaction mechanisms. ► Highest overall degradation rates occur with 340 nm UV irradiation with highly aligned, more defect free nanostructured morphologies. ► Competition between two different photocatalytic mechanisms: conventional photocatalysed radical oxidation and lattice oxygen driven oxidation. ► Dominant reaction mechanism depends on the thin film morphology, crystallinity, availability of oxidant and the wavelength of the incident UV.

Keywords
Photocatalysis; Zinc oxide; Morphology; Reaction mechanism; Methylene blue; Mars–Van Krevelen
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Conventional versus lattice photocatalysed reactions: Implications of the lattice oxygen participation in the liquid phase photocatalytic oxidation with nanostructured ZnO thin films on reaction products and mechanism at both 254 nm and 340 nm
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis B: Environmental - Volume 106, Issues 3–4, 11 August 2011, Pages 323–336
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us