Effects of zinc(II) and iron(III) doping of titania films on their photoreactivity to decompose rhodamine B
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The heterogeneous photocatalytic oxidation of rhodamine B in aqueous solution containing pure or zinc (iron)-doped titania films has been studied. N-deethylation of rhodamine B was accelerated by iron(III) and zinc(II) doping as compared with pure titania film. It is shown that improvement of electron transfer from dye molecules to the film may be responsible for the high N-deethylation rate for iron-doped (0.5 mol%) film, while for zinc-doped (20 mol%) film, high surface roughness may be the main reason. In addition, both iron and zinc doping brought a new shallow trap to the intragap meaning that the surface defects had increased after doping; this is a possible reason doped films present relative low photoreactivity to catalyze the direct degradation of dye molecules.
I. INTRODUCTION
Heterogeneous semiconductor photocatalysis has attracted a growing scientific and technological interest over the last 20 years in part because of the potential for the use of radiation of semiconductors as catalysts and as a means of mineralization and purification of organic pollutants in environmental aqueous media and air.1,2 Due to the powerful oxidation of the valence band holes, TiO2 has been most frequently investigated for the degradation of a variety of environmentally harmful organic molecules.3–5 However, heterogeneous photocatalysis for water treatment is still in the research stage as some inherent important problems remain for efficient application. Fundamental research is still needed to improve the photocatalyst performance, increase the low photo efficiencies, and take advantage of a wider range of the solar spectrum in this sense. Transition metal ion doping has been studied extensively since it has been expected to satisfy the above demands.6–9 Among the various transition metal ions doping system, iron(III) ion doping has been most widely examined and shown to enhance the efficiency of photocatalytic reactions in most cases. In comparison to iron, zinc ion doping has been believed to be detrimental to photocatalytic reactivity of TiO2. It is also shown that the doping effect greatly depends on the experimental conditions and the mechanisms of doped
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Address all correspondence to this author. Present address: Institute of Photographic Chemistry, Chinese Academy of Sciences, Beijing 100101, People’s Republic of China.
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http://journals.cambridge.org
J. Mater. Res., Vol. 16, No. 10, Oct 2001 Downloaded: 19 Jun 2014
TiO2 are still not well understood. In addition, the effects on photoreaction process and products distribution have rarely been reported.10 Rhodamine B is one of the most important xanthene dyes used in a variety of applications such as paper and dye lasers. In our previous studies, rhodamine B was confirmed to undergo N-deethylation and degradation simultaneously on the TiO2 thin-film surface.11,12 So we prepared iron- and zinc-doped TiO2 thin films and studied the photocatalytic reactions of rhodamine B in an aqueous medium to investigate doping effects on the two different photoreactions.
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