Photochemistry of Colloidal Metal Sulfides 6. Kinetics of Interfacial Reactions at ZnS‐Particles

Abstract

Abstract ZnS sols containing alcohol or formate as reactants for positive holes and nitrous oxide or carbon dioxide as reactants for electrons were illuminated and the yields of the various products determined. Alcohols are oxidized via a one‐hole mechanism, the product being an 1‐hydroxyalkyl radical which undergoes reaction in the bulk solution. Carbon dioxide is exclusively reduced to formic acid via a two‐electron mechanism. Formate is mainly (77%) oxidized to CO 2 in a two‐hole process and less frequently via one‐electron transfer, i.e. formation of intermediate CO 2 − which reacts with other radicals in the bulk solution. A possible role of intermediate zinc atoms in the two‐electron reductions is discussed. In the presence of two reactants for one kind of charge carrier, the yields of the products can often be described by conventional competition kinetics. A scavenger for electrons influences the yield of the reaction of the scavenger for positive holes and vice versa. This influence is described for various pairs of scavengers (such as strong h + and weak e − scavenger; strong h + and strong e − scavenger etc.).