It has been well documented that an electron-hole
pair is generated when a TiO2 photocatalyst is excited by UV irradiation,
which requires energy that is equal to or higher than its
band gap energy. The electron-hole pairs react with water, hydroxyl
groups, and molecular oxygen absorbed on the TiO2 surface, generating
reactive oxygen species such as the hydroxyl radical (•OH)
and superoxide anion (•O2
−).