The mixed oxide photocatalyst, TiO2-SiO2 has been observed to contain trapped conduction band electrons after annealing in vacuum. These electrons are consumed by adsorption of particular electrophilic molecules. It is found that O-2 and an adsorbed organic molecule containing a Cl moiety can remove trapped electrons, whereas a similar organic molecule, not containing Cl, is ineffective in charge removal. The measurement of trapped electronic charge is made by observation of the intensity of the background IR absorption in the 4000 to 1400 cm(-1) region, which originates from trapped electron excitation into a continuum of excited electronic states by IR photons. (C) 2003 Elsevier B.V. All rights reserved.