Kinetics of Photocatalytic Reactions under Extremely Low-Intensity UV Illumination on Titanium Dioxide Thin Films

Abstract

The photocatalytic decomposition efficiency of gaseous 2-propanol was studied using a titanium dioxide thin film under very weak UV light; the incident UV light intensity was 36 nW−45 μW·cm-2. Under such low-intensity UV illumination, the value of the quantum yield (QY) increased gradually with decreasing number of absorbed photons and finally saturated (28%) for a number of absorbed photons less than 4 × 1011 quanta·cm-2·s-1 for an initial 2-propanol concentration of 1000 ppmv. Thus, purely light-limited conditions were reached. For lower initial concentrations, the QY values decreased, but the same maximum QY value as that for 1000 ppmv was also approached with decreasing light intensity. We discuss these results in terms of the normalized absorbed photon number (I norm/s-1), a parameter that we have defined as the ratio of the number of absorbed photons ([photon]ab) to the number of adsorbed 2-propanol molecules ([M]ad). When all of the experimental QY values were plotted as a function of I norm, all of the points appeared on a single line for a wide range of initial 2-propanol concentrations. On the basis of these results, we conclude that either •OH radicals or 2-propanol molecules must be able to diffuse at least ca. 11 nm on the titanium dioxide surface in order to react with each other. We also conclude that the maximum QY value of 28% represents the intrinsic charge-separation efficiency for this photocatalyst.

Preparation and visible-light photocatalytic activity of Cu-grafted rutile fine powder from selective leaching of BaTiO₃

“…For this study, the illumination intensity at the powder surface was set as 6600 Lux (LX-105; Custom Co., Tokyo, Japan). As described in an earlier report, 30),31) molecules of gaseous IPA are initially decomposed into acetone. They are then finally decomposed to H 2 O and CO 2 .…”

“…30),31) Before evaluation, UV pre-illumination (0.7 mW/cm 2 at 365 nm) onto the sample TiO 2 powder was conducted using a black light bulb for one night (more than 8 h) to remove organic compounds that had been adsorbed onto the surface. Then sample TiO 2 powder (40 mg) was set at the center of a Pyrex glass vessel with a quartz lid (500 ml in volume) in the area of 10.2 cm 2 .…”

Comparative study on visible light photocatalytic activity of Fe-modified TiO₂ powders

“…Such differences are expected to affect the rate difference in IPA decomposition and CO 2 generation because the reported photocatalytic decomposition pathway of gaseous IPA includes several reaction steps. 24), 25) Detailed analysis of the relation between characteristics of Fe-modified TiO 2 and the decomposition performance of various organic compounds will be undertaken in future work.…”

Controlled periodic illumination in semiconductor photocatalysis

“…Previous studies have shown that quantum yields in dilute aqueous suspensions are usually below ~10% while quantum yields of oxidation of organic species in the gas phase exceed 50% under weak UV illumination [7,12,29]. Various methods of improving efficiency have been studied, for example doping of catalysts to enhance efficiency by inhibiting charge carrier recombination or improving light absorption is well reported in the literature [30][31][32][33][34].…”