Particulate and quantum-size heterojunctions are used as a means of promoting charge-carrier separation to specific spatially separated regions on a host titania photoconductor. Quantum yields for the mineralization of a model reactant mixture consisting of trichloroethylene, water, oxygen, and inert carrier gas on titania heterojunction photocatalysts, with the reactants delivered as vapors or gases, are correlated with the charge-carrier separation distances; the charge-carrier separation distance, in turn is a function of the composition and configuration of the heterojunction. Transport properties of optically generated charge carriers in particulate or colloidal catalysts are thought to be important in determining reaction pathways and kinetics. Separation of photoelectrons from photoholes over distances exceeding simple charge transfer to adjacent atoms is frequently suggested as a way to prevent recombination and thusly increase quantum yields; this is the first direct test of such a concept. Time-resolved photocharge (TRPC) measurements, time-resolved microwave photoconductivity (TRMC) determinations, time- resolved absorption and desorption, and diffuse reflectance spectroscopy are used. This work has applications to heterogeneous photocatalysis, photographic imaging, photovoltaic energy conversion, photoelectronic devices, environmental control, and water purification, including the specific system being investigated, namely the photocatalyzed oxidative degradation of organic pollutants on particulate or colloidal semiconductors. //
