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Photocatalysis with nanostructured zinc oxide thin films: The relationship between morphology and photocatalytic activity under oxygen limited and oxygen rich conditions and evidence for a Mars Van Krevelen mechanism

Paper ID Volume ID Publish Year Pages File Format Full-Text
47292 46466 2010 14 PDF Available
Title
Photocatalysis with nanostructured zinc oxide thin films: The relationship between morphology and photocatalytic activity under oxygen limited and oxygen rich conditions and evidence for a Mars Van Krevelen mechanism
Abstract

The aim of this study was to evaluate the effectiveness of using a range of innovative nanostructured high surface area zinc oxide (ZnO) thin films as photocatalysts, and thereafter to systematically relate initial and reacted surface morphology and irradiated surface area to photocatalytic activity under both limited and rich oxygen conditions.The thin films were produced using an innovative combination of magnetron sputtered surfaces and hydrothermal solution deposition that allows the morphology, porosity and thickness to be controlled by varying the composition and processing conditions. Methylene Blue (MB) was chosen as the model compound and the reaction was performed with ultra violet light (UV) at 254 nm. The thin film morphology and surface area before and after reaction was determined by scanning electron microscopy (SEM). The photocatalytic activity (measured as the rate and extent of MB degradation) was determined for seven different ZnO nanostructured thin films: three different ZnO hydrothermal solution depositions on bare glass slides (S1-CG, S2-CG and S3-CG films), the same three ZnO hydrothermal solution depositions but on glass slides coated with a magnetron sputtered ZnO film (S1-MS, S2-MS and S3-MS films), and glass slides coated with just a magnetron sputtered ZnO film (MS films).A clear relationship between surface morphology (and the related thin film preparation method) and photocatalytic activity was observed for ZnO thin film supported catalysts: the tallest, most aligned structure had the highest photocatalytic activity, whilst the smallest, least aligned structure had the lowest photocatalytic activity. Thus, MB degradation rate was the fastest for the 1 μm thick ZnO thin film with a uniform arrayed structure from the S2-MS deposition technique. The degradation rates of the ZnO thin films were comparable to commercially available ZnO powder on a surface area basis. Photocatalytic degradation of MB under oxygen rich conditions increased for all other films except one film (S1-CG). This was most effective for thin film structure S2-MS, whose reaction rate was increased by 15%. Adding oxygen made the films more stable: in oxygen limited conditions, SEM and atomic absorption spectroscopy indicated zinc leaching had occurred. However, with additional oxygen the zinc leaching was minimised under the same reaction conditions. It is thought that this additional oxygen is either minimising the release of or replacing lost ZnO lattice oxygens, indicating that this ZnO photocatalytic oxidation could be occurring via a Mars Van Krevelen type redox mechanism.

Keywords
Zinc oxide; Nanostructured thin film; Photocatalyst; Methylene Blue; Magnetron sputtered; Mars Van Krevelen
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Photocatalysis with nanostructured zinc oxide thin films: The relationship between morphology and photocatalytic activity under oxygen limited and oxygen rich conditions and evidence for a Mars Van Krevelen mechanism
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis B: Environmental - Volume 97, Issues 1–2, 9 June 2010, Pages 168–181
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