Mechanism of visible light photocatalytic oxidation of methanol in aerated aqueous suspensions of carbon-doped TiO2

作者：Goldstein Sara; Behar David; Rabani Joseph^*

来源：Journal of Physical Chemistry C, 2008, 112(39): 15134-15139.

DOI：10.1021/jp803974a

Visible photolysis of aerated carbon-doped TiO2 (C-TiO2) aqueous suspensions induces methanol oxidation to formaldehyde. The rate of HCHO formation increases with the concentration of CH3OH or C-TiO2 and is nearly doubled in the presence of catalase or excess of H2O2. The mechanism involves oxidation of CH3OH by surface trapped holes, although these holes have lower energy than those formed upon UV photolysis of undoped TiO2. The C-TiO2 electrons reduce O-2 to H2O2. CH3OH oxidation via reduction of H2O2 by the C-TiO2 electrons was observed in the presence of added H2O2, where it competes efficiently with O-2 for the C-TiO2 electrons. At [H2O2] > 0.1 mM, the yield of HCHO is about twice that in the absence of added H2O2. Light absorption measurements in an integrating sphere show that the limiting absorption fraction at high [C-TiO2] is 0.5 at 450 nm, the rest of the light being mostly scattered backward. The HCHO quantum yield depends on the square root of the absorbed light density and is only a few percent at the intensities used in this work. A parallel photocatalytic decomposition of H2O2 has been observed, which is not associated with HCHO formation.

• 出版日期2008-10-2