ABSTRACT
This chapter examines redox reactions on colloidal metal and metal oxides in aqueous solution. The examination is restricted to redox reactions with colloidal particles that have been initiated by either electromagnetic radiation (ultraviolet-visible) or ionizing radiation. In the study of catalyzed redox reactions involving free radicals or electronically excited shortlived species, the catalysts must be dispersed within the medium to compete successfully with radical recombination reactions and fast radiative or nonradiative relaxation processes which dissipate the chemical energy of the excited reactants. Almost invariably, colloid stability against coagulation is important in redox catalysis. In many cases, the occurrence of a redox reaction at metal surfaces can destabilize a colloid. Radiolysis of colloidal solutions has long been known to drastically alter the mobility of sols, and to coagulate or peptize them. The accumulation of electrons on the metal oxide particles may lead to polarization of the particle and to the hydrogen evolution reaction.
