The hydroxyl radicals, the primary oxidizing species in the photocatalytic system, initiate chain reactions, leading to the generation of other radicals and subsequently oxidation of organics [7,12]. Even though it is not necessary for the reaction that hydroxyl radicals and organics are adsorbed at the TiO2 sites, the adsorbed forms are much more helpful to increase the overall reactivity, compared to those free from TiO2 sites (Reactions 12-15) [3,9]:
Other radicals and oxidants (HO2, H2O2) are also generated and are involved in redox reactions to decompose organic contaminants in water (Reactions 16-18) [3,9]:
After the photoexcitation process and the generation of reactive species, a series of reactions lead to complete mineralization of the parent compound. These reactions include hydroxyl radical attack, hydroxylation (e.g., *OH addition, reaction with O2, and elimination of HOO*), dihydroxylation, hydration, hydrogen abstraction, deprotonation, decarboxylation, and one-electron transfer reactions .
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