Role of Photoinduced Charge Carrier Separation Distance in Heterogeneous Photocatalysis: Oxidative Degradation of CH₃OH Vapor in Contact with Pt/TiO₂ and Cofumed TiO₂-Fe₂O₃

Author

M. Sadeghi
W. Liu
T. G. Zhang
Pericles Stavropoulos, Missouri University of Science and TechnologyFollow
Boris Levy

Abstract

As a means of testing the widely held premise of a positive correlation between photoinduced charge carrier separation distance (CCSD) and the photocatalytic activity of particulate photocatalysts, an investigation of the oxidative degradation of CH₃OH vapor in contact with coatings of particulate Pt (0− 8 wt %)/TiO₂ is combined with time-resolved photocharge (TRPC) measurements. Preliminary studies were also performed on several commercially available cofumed Fe₂O₃− TiO₂ (0, 2, and 6− 8 wt % Fe) particulate photocatalysts. TRPC is capable of providing a noncontact electronically derived measure of CCSD. Contrary to common wisdom prevalent at the initiation of this study, Pt/TiO₂ catalysts displaying the largest CCSD values do not correspond with highest photocatalytic efficiency for the oxidative degradation of CH₃OH. Indeed the present investigation supports an extension of a “Russell-like” mechanism for oxidative degradation of organic molecules, where photoelectrons, e^-, and photoholes, h⁺, each initiate the formation of interacting chemical intermediates, i.e. O₂^•- and HOCH₂(OO)^•, in close proximity on the catalyst surface, thereby reducing the need for surface diffusion over large distances for the reaction to proceed toward production of the observed HCOOCH₃ product. This process competes with charge carrier recombination at small CCSD values, which yield the highest rates of CH₃OH consumption and HCOOCH₃ formation attained in this study. It is speculated that this extension of the Russell-like mechanism, as applied to the solid/vapor photocatalytic degradation of methanol, may also provide the basis for the maximum in the rate of degradation of aqueous solutions of dichloroacetic acid, using sol− gel prepared Fe₂O₃− TiO₂ mixed oxide photocatalysts as a function of weight percent Fe.

Recommended Citation

M. Sadeghi et al., "Role of Photoinduced Charge Carrier Separation Distance in Heterogeneous Photocatalysis: Oxidative Degradation of CH₃OH Vapor in Contact with Pt/TiO₂ and Cofumed TiO₂-Fe₂O₃," Journal of Physical Chemistry, vol. 100, no. 50, pp. 19466 - 19474, American Chemical Society (ACS), Dec 1996.

The definitive version is available at https://doi.org/10.1021/jp961335z

Department(s)

Chemistry

International Standard Serial Number (ISSN)

0022-3654

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 1996 American Chemical Society (ACS), All rights reserved.

Publication Date

01 Dec 1996