PARTICLE-SIZE AND SURFACE-CHEMISTRY IN PHOTOELECTROCHEMICAL REACTIONSAT SEMICONDUCTOR PARTICLES

In the present paper reactions at small and large ZnS particles have b een investigated. It has been shown that ethanol is selectively oxidiz ed at large (micrometer) particles to acetaldehyde without side produc ts by a ''two hole'' process. In the case of nanometer particles the p rimarily formed alpha-hydroxyethyl radicals in a ''one hole'' process undergo a secondary reaction, i.e., the dimerization and disproportion ation of the free radicals. It has been shown that a two hole process on nanometer particles becomes impossible because the time interval be tween two successive photon absorption incidents which lead to a succe ssful hole transfer process in a 1-nm particle is much longer than the maximum lifetime of the alpha-hydroxyethyl radicals formed in the fir st step. The different mechanisms of ethanol oxidation and the influen ce of surface chemistry are discussed in detail.