Patterning Effect of a Sol-Gel TiO_2 Overlayer on the Photocatalytic Activity of a TiO_2/SnO_2Bilayer-Type Photocatalyst

摘要

TiO_2 films with a thickness of 75 +- 5 nm (anatase) were formed on SnO_2-film (580 +- 80 nm) coated soda-lime glass substrates (SnO_2/SL-glass) by a sol-gel method. Although the photocatalytic activity for CH_3CHO oxidation (#lambda#ex > 300 nm) significantly exceeded that of a standard TiO_2/quartz sample, it decayed with illumination time (t) at t > 0.75 h. Stripes of anatase TiO_2 films of 40 nm in thickness and 1 mm in width were prepared on the SnO_2/SSL-glass substrate in a 1-mm pitch by photolysis of an organically modified sol-gel film. The TiO_2 patterning further increased the photocatalytic activity by a factor of 4.1 as compared to the non-patterned sample, and it was also maintained at 0 < t 2h. The flat band potentials of the TiO_2 and SnO_2 films are determined to be -0.34 and _0.07 V (vs. SHE), respectively, at pH = 7 by the Mott-Schottky plots. On the basis of the results, the outstanding patterning effects could be rationalized in terms of the vectorial charge separation at the interface between TiO_2 and SnO_2.