The formed vacancies are replaced with the dissociated water
molecules, resulting in an increase of the concentration of
OH− ions on the superhydrophilic surface. Consequently,
the adhesion of microorganisms (or of organic compounds)
decreases when TiO2 coating becomes superhydrophilic. The
synergetic effect of the photocatalysis and hydrophilicity creates
a self-cleaning surface. This phenomenon is the main advantage
of an immobilized photocatalyst in comparison to a photocatalyst
suspension. The inactivation of the microorganisms isascribed to the reaction of electrons (ecb
−) with O2 and of holes
(hvb
+) with HO− or H2O, to form reactive oxygen species (H2O2
and O2
•−, HO•, etc.). In most studies, hydroxyl radicals (•OH)
are recognized as responsible for the microbial inactivation.
There are two kinds of hydroxyl radicals, and one group can bind
to the surface,