Effect of Sn surface states on the photocatalytic activity of anatase TiO₂

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• 作者：Freddy E. Oropeza ; Bastian Mei ; Ilia Sinev ; Ahmet E. Becerikli ; Martin Muhler ; Jennifer Strunk ; ^{jennifer@techem.rub.de}
• 关键词：Photocatalysis ; TiO2 ; SnO2 ; Dye degradation ; Grafting ; Surface doping ; Temperature-programmed reduction ; X-ray absorption spectroscopy ; X-ray photoelectron spectroscopy ; Surface charge trapping
• 刊名：Applied Catalysis B: Environmental
• 出版年：2013
• 出版时间：August-September, 2013
• 年：2013
• 卷：140-141
• 期：Complete
• 页码：51-59
• 全文大小：917 K

文摘

The influence of surface Sn-doping on the photocatalytic properties of anatase TiO₂ has been investigated in samples prepared by a grafting route using Sn(IV) tert-butoxide as Sn precursor. The grafting procedure leads to the formation of isolated Sn(IV) sites on the surface of anatase TiO₂ powders as gauged by structural characterisation based on XRD, Raman spectroscopy and XAS. Studies of the surface reduction based on TPR experiments and XPS provide the conditions for a selective reduction of surface Sn(IV) to the divalent oxidation state. Electronic structure characterisation based on valence band XPS and DRS shows that there is a slight widening of the band gap upon Sn(IV)-grafting, but Sn(II) related states emerge at the top of the main valence band upon reduction at temperatures up to 350 ¡ãC, and this induces visible light absorption. Grafting of TiO₂ with Sn(IV) increases the formation rate of OH radicals on the surface of the material. Reduction of the Sn(IV)-grafted TiO₂ to form surface Sn(II) brings about substantial increase of the photocatalytic efficiency for the methylene blue degradation under irradiation with ¦Ë ¡Ý 320 nm compared with Sn(IV)-grafted and pure anatase TiO₂. This observation is explained based on a surface hole trapping by the Sn(II)-related surface states which lie above the top of the main valence band and can therefore act as trapping sites for holes produced under photoexcitation.