ZnO can produce electron–hole pairs under light irradiation of
higher energy than its band gap energy (Liu, Morishima, Yatsui,
Kawazoe, & Ohtsu, 2011). Electron–hole pairs (e− h+) are created
to induce the redox reactions at the surface of ZnO. The hole (h+)
reacted with OH− on the surface of ZnO nanoparticles, generating
hydroxyl radicals (OH•), superoxide anion (O2
−), and perhydroxyl