SiOx Ultrathin Layer Coverage Effect on the (Photo)catalytic Activities of Rutile TiO2

A two-step method consisting of 1,3,5,7-tetramethycyclotetrasiloxane chemisorption and the postheating has formed a uniform and dense silica-like SiOx ultrathin layer (SiOx-UTL) on the surface of rutile TiO2. Diffuse reflectance infrared Fourier transform and solid-state 29Si NMR spectroscopy showed that three-dimensional Si−O−Si networks grow to become rigid by repeating the treatment. The coverage with the SiOx-UTL eliminates the surface acid sites, leading to an almost complete loss of the photocatalytic activity at the thicknesses above 0.36 ± 0.03 nm. On the basis of a tunneling model, the significant restriction of the photocatalytic activity can be accounted for by the excellent barrier effect of the SiOx-UTL for the photogenerated charge carrier transfer from TiO2 to acceptors in solution.