Formation of nanopore arrays on stainless steel surface by anodization for visible-light photocatalytic degradation of o
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There is high scientific and technological interest to develop photocatalytic coatings on stainless steels surface to remove fouling under light radiation. In this study, a novel method is described to prepare photocleanable stainless steel by anodization to form aligned nanopore arrays (NPAs) on the surface in ethylene glycol containing perchloric acid. Perchloric acid concentration, applied voltage and anodization time of anodization process were investigated. The NPAs are mainly composed of iron (III) oxide and chromium (III) oxide. This photocleanable stainless steel has remarkable visible-light photocatalytic activities, which show potential applications particularly for outdoor purpose. Moreover, the stainless steel surface remains highly polished and exhibits good corrosion resistance after anodization.
I. INTRODUCTION
Stainless steels have found their applications in various fields such as aerospace, marine structures, energy-related machinery, construction equipment, and household appliances. However, composite organic, inorganic and biological fouling occurs on stainless steel surface. The surface fouling will lower the corrosion resistance and smear the highly polished surfaces of stainless steels.1–3 Processes relating to protection of stainless steel from corrosion and keeping the surface clean are an area of study commanding considerable attention, given the broad applications of stainless steel. Applications of photocatalytic processes are widely recognized as viable solutions to solve the surface fouling problems, because organic species can be completely mineralized to carbon dioxide or become nontoxic materials by photocatalytic pathway.4,5 Among many candidates for photocatalysts, titanium dioxide (TiO2) is the most intensively studied material for decontamination and disinfection of water,6,7 purification of volatile organic compounds in indoor air,8 carrying out organic synthesis by solar energy,9 and even for producing hydrogen as fuel by water photohydrolysis.10 Construction of TiO2 coatings on stainless steel surface are therefore of interest for photocatalytic purpose. Several methods have been used to fabricate TiO2 thin films on stainless steel surface, including sputtering,11 chemical or physical vapor deposition,12,13 and sol-gel process.14 In these methods, stainless steels with photocatalytic properties were prepared a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.200 J. Mater. Res., Vol. 27, No. 18, Sep 28, 2012
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by tedious processes that resulted in poor homogeneity. Another major disadvantage is that it is difficult to obtain polished surface in stainless steels using surface coating technologies. Moreover, the band gaps for anatase and rutile TiO2 being 3.2 and 3.0 eV require ultraviolet (UV) light for activation.15 But UV light in solar radiation as reaching the earth’s surface constitutes relatively a small fraction (approximately 3–5%).16 Iron (III) oxide (Fe2O3), the most st
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