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Composite_Materials_under_visible_lights - J Mater Sci(2010...

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Synthesis and photocatalytic behaviors of Cr 2 O 3 –CNT/TiO 2 composite materials under visible light Ming Liang Chen Kwang Youn Cho Won Chun Oh Received: 13 March 2010 / Accepted: 5 July 2010 / Published online: 17 July 2010 Ó Springer Science+Business Media, LLC 2010 Abstract Cr 2 O 3 –CNT/TiO 2 composites derived from chromium acetylacetonate, multi-walled carbon nanotubes (MWCNT) and titanium n -butoxide (TNB) were prepared, and the photocatalytic activity of the Cr 2 O 3 –CNT and CNT/TiO 2 composites was examined. The Cr 2 O 3 –CNT/ TiO 2 composites were characterized by BET surface area measurement, X-ray diffraction, transmission electron microscopy, and energy dispersive X-ray analysis. The photocatalytic activity was determined from the decom- position of methylene blue (MB) under visible light irra- diation. Methylene blue was photodegraded successfully in the presence of the Cr 2 O 3 –CNT/TiO 2 composite under visible light irradiation. Introduction Metal oxide photocatalysts have attracted increasing attention for their possible applications to the degradation of environmental organic pollutants and solar-energy con- version [ 1 6 ]. TiO 2 is one of the most important semi- conducting oxides owing to its photocatalytic activity, conservative nature, low cost, low toxicity, and stable to light illumination. In addition to these properties, its ability to photocatalytic decompose organic materials has been applied in the environmental industry, i.e., organic pollutant treatment [ 7 , 8 ]. Anatase has higher photocata- lytic activity and has been studied more than the other two forms of TiO 2 [ 9 ]. However, the wide band gap (3.2 eV) and high electron–hole recombination rate of TiO 2 limits its use [ 10 ]. TiO 2 only strongly absorbs UV light ( k \ 380 nm), which accounts for a small fraction of the solar spectrum ( \ 4%). Therefore, the development of modified TiO 2 with high activity under visible light ( k [ 380 nm) is needed take full advantage of the main part of the solar spectrum (mostly 400–600 nm) and even the poor illumination of interior lighting. Therefore, many studies have been carried out to con- vert the TiO 2 absorption from the ultraviolet to visible light region by the ion doping of transition metals [ 11 ]. The presence of metal ion dopants in TiO 2 crystal lattice affects its photoreactivity by altering the charge carrier recombination and interfacial electron-transfer rates by shifting the band gap of the catalysts to the visible region [ 12 ]. A dopant ion may act as an electron trap or hole trap. This would prolong the lifetime of the generated charge carriers, resulting in enhanced photocatalytic activity [ 13 ]. Among these transition metal ions, Cr 3 ? has attracted considerable attention because its introduction can extend the visible light absorption.
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