The absorption of light in TiO2 at the < 390 nm leads to the
promotion of an electron from the valence band to the conduction
band of the semiconductors. The electron–hole pairs that are
generated, migrate toward the surface where they can initiate
the redox reactions with adsorbates. The valence band potential
is positive enough to generate hydroxyl radicals at the surface
and the conduction band potential is negative enough to reduce molecular oxygen