Self-cleaning titania films: an overview of direct, lateral and remote photo-oxidation processes

An overview of the recent investigations into the direct, lateral and remote oxidation of carbon-containing materials is given. The overview begins with the pioneering work of Fujishima and his co-workers involving the remote bleaching of methylene blue by UV-irradiation of titania in the gas phase. The further research of these workers conducted on the remote photocatalytic destruction of various polymers and dyes is then discussed briefly. The notable work of Paz and his co-workers on the lateral, but not remote, oxidation of octadecyltrichlorosilane (OTS) by photoeteched titania films is then examined. The striking observations associated with the lateral oxidation of soot by UV-irradiated thin titania films, reported by Choi and his colleagues, are reported. Finally, the results of our most recent work on soot covered titania films in which the direct, lateral and remote oxidation of soot by UV-irradiated thick titania films could be observed visually is discussed. The most likely agent responsible for these photocatalytic oxidation processes is considered and a suitable candidate, hydroxyl radicals, suggested.