Photocatalysis

Abstract

Abstract When photons are implicated in a catalytic reaction, the system becomes photocatalytic. The titania catalyst acts (1) by adsorbing the reactants and (2) by absorbing efficient photons which create electrons and holes, responsible for the subsequent redox reactions. Photocatalysis is a complex polyphasic system, involving simultaneously solid, gaseous and liquid phases plus the uv‐irradiation considered as the “electromagnetic” phase. The action of the five basic physico‐chemical parameters which control the kinetics are deeply described and demonstrated. In dry media, photocatalysis can be used as a means for selective mild oxidation reactions. In the presence of water, the generation of OH° radicals gives total oxidation reactions with a total mineralization in CO 2 + H 2 O of pollutants, pesticides, dyes in water as well as total degradation of pollutants in (humid) air. Several examples are given. The actual tendency is the use of fixed beds of titania photocatalysts for air and water purification. Photocatalytic engineering is also developing with pilot plants, especially in the field of solar photocatalysis. Recent results are given about mechanisms, especially addressed to the radical nature of reaction intermediates.