Dynamics of models for photocatalysis as studied by time resolved dielectric loss (TRDL) spectrometry

Abstract

The TRDL technique was applied to the problem of elucidating the photophysics of colloidal n-type CdS and Zn(Cd)S powders dispersed in reactive media. The objective of the study was to correlate the internal processes in the powders with their reactivity in half-reactions representative of photocatalytic schemes. Interfacial hole transfer processes and the rates thereof can be observed by this technique. From the pH dependence of the rate of interfacial hole transfer in aqueous media, Langmuir-Hinshelwood kinetics may be inferred, with hydroxide ion as the exclusive reactive species. For photooxidations in both aqueous and organic media, materials specificities are apparent, with the mixed powders, eg Cd(Hg)S or CdS(Se), more reactive than the stoichiometric material. Electron transfer may be observed by TRDL in the mercury substituted powders, and, under some circumstances, it can become limiting to the observable rate of photoconductibity decay in the powders.