Spectral dependence of quantum yields in gas-solid heterogeneous photosystems - Influence of anatase/rutile content on the photostimulated adsorption of dioxygen and dihydrogen on titania

In this study we explored the photostimulated adsorption of dioxygen and dihydrogen gases on the surface of Degussa P25 titania particles subsequent to a thermal pre-treatment at 600 and 850 K, which of consequence varied the typical anatase/rutile ratio (83-17%, respectively). The focus was to probe how the anatase/rutile content modified the spectral dependence of the quantum yields of photoadsorption of O-2 and H-2. Dioxygen is photoadsorbed preferentially on the anatase component of the P25 titania specimen, inasmuch as no photoadsorption occurs on an ultrapure rutile particle surface, By contrast, dihydrogen photoadsorbs on both polymorphic structures on the particle surface. A model is proposed wherein the Degussa titania is taken to be composed of rutile domains (surface and bulk) in an otherwise sea of anatase. These represent nothing more than surface defects, which when excited with appropriate radiation generate photoelectrons that spillover onto the anatase phase and photostimulate the adsorption of the acceptor molecules (oxygen). (C) 2002 Elsevier Science B.V. All rights reserved.