Photocatalysis: Active species, mechanism, and characterisation of efficiency
Résumé
Photocatalysis is based on the irradiation of semiconductor particles by photons of energy equal to or greater than their band gap energy, which form electron/ hole pairs initiating the generation of highly reactive oxygen species (ROS), •OH, O2•− and HO2•. The principle of photocatalysis is well described, however, never it is described what really happened in the solid. Here, I propose to visualize the formation of these active species on the solid and their action on the degradation of pollutants. In particular the action of water and oxygen molecules and the impact of adsorption of pollutant will be described.
Another important point will be addressed: the characterization of the photocatalytic efficiency in water and in air. Actually, to develop new active structure it is important to be able to compare their efficiency. What kind of molecule? What concentration? What source of radiation? What reactor? Ageing? What efficiency value taken into account: initial rates? Rate constant? Mineralization? A lot of crucial point which must be taken into account to avoid loss of time and energy in the development of these new structures.
Finally, scientific and technological locks of the photocatalytic process will be discussed and research directions suggested to address them. Particular focus will be on a new concept (luminous fabric fiber optic) and on the photocatalytic materials active under visible light and/or able to improve the quantum efficiency.