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Coatings 2014, 4(3), 651-669; doi:10.3390/coatings4030651

Photocatalytic Activity and Stability of Porous Polycrystalline ZnO Thin-Films Grown via a Two-Step Thermal Oxidation Process

1
Department of Chemistry and Physics, Coastal Carolina University, Conway, SC 29528, USA
2
Research & Development Laboratory, Wellman Engineering Resins, Johnsonville, SC 29555, USA
*
Author to whom correspondence should be addressed.
Received: 29 May 2014 / Revised: 8 August 2014 / Accepted: 12 August 2014 / Published: 15 August 2014
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Abstract

The photocatalytic activity and stability of thin, polycrystalline ZnO films was studied. The oxidative degradation of organic compounds at the ZnO surface results from the ultraviolet (UV) photo-induced creation of highly oxidizing holes and reducing electrons, which combine with surface water to form hydroxyl radicals and reactive oxygen species. Therefore, the efficiency of the electron-hole pair formation is of critical importance for self-cleaning and antimicrobial applications with these metal-oxide catalyst systems. In this study, ZnO thin films were fabricated on sapphire substrates via direct current sputter deposition of Zn-metal films followed by thermal oxidation at several annealing temperatures (300–1200 °C). Due to the ease with which they can be recovered, stabilized films are preferable to nanoparticles or colloidal suspensions for some applications. Characterization of the resulting ZnO thin films through atomic force microscopy and photoluminescence indicated that decreasing annealing temperature leads to smaller crystal grain size and increased UV excitonic emission. The photocatalytic activities were characterized by UV-visible absorption measurements of Rhodamine B dye concentrations. The films oxidized at lower annealing temperatures exhibited higher photocatalytic activity, which is attributed to the increased optical quality. Photocatalytic activity was also found to depend on film thickness, with lower activity observed for thinner films. Decreasing activity with use was found to be the result of decreasing film thickness due to surface etching. View Full-Text
Keywords: ZnO; photocatalysis; Rhodamine B; zinc oxide; self-cleaning; antimicrobial ZnO; photocatalysis; Rhodamine B; zinc oxide; self-cleaning; antimicrobial
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MDPI and ACS Style

Moore, J.C.; Louder, R.; Thompson, C.V. Photocatalytic Activity and Stability of Porous Polycrystalline ZnO Thin-Films Grown via a Two-Step Thermal Oxidation Process. Coatings 2014, 4, 651-669.

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