(3) red-ox reaction in the adsorbed phase; (4) desorption of products and (5) removal of products from the interface area. The red-ox reaction in this schematic takes place in the presence of UV light through a generation of reactive oxygen species (ROS) (figure ). In the presence of radiation with a wavelength less than 400 nm, electrons (e -) are excited from the valence band (VB) into the conduction band (CB), generating positively charged holes (h + ). In the aquatic environment the photo-generated electron can reduce a dioxygen molecule to form a superoxide radical anion (O - 2 ), while h + can oxidize water molecules and hydroxide ions, generating hydroxyl radicals and H 2 O 2 hydrogen peroxide molecules. In addition, recombination of electron-hole pairs can generate photon emission (radiative recombination), which in turn can excite ground-state oxygen, producing singlet oxygen. The combined effects of photodissociation of H 2 O 2 in the presence of light and on the surface of the photocatalyst, as well as the complex transport of highly reactive hydroxyl radicals OH• in the reactant mixture, may be responsible for the enhanced photodegradation of MB in the presence of zinc oxide and H 2 O 2 . During the conversion of these molecules mineral acids, CO 2 and H 2 O are produced. The following reaction strategies for the photolysis of H 2 O 2 are based on the literature (Figure in the Supplementary Information). Based on our previous studies, the annealing conditions applied in the process of fabricating our nanoporous ZnO films can lead to differences in the optically active defect density in the films . Therefore, in the current study, we wanted to explore this concept and look at how the properties of differently deposited and annealed material would influence the photocatalytic activity of nanostructured ZnO thin films during degradation of pollution in water, and discuss the role of the defects in the photocatalytic process.