Generation of the Reactive Oxygen Species on the surface of nanosized titanium(IV) oxides particles under UV-irradiation and their connection with photocatalytic properties

Abstract

The chemiluminescence spectra of the samples with nanosized titanium(IV) oxide, both commercial – Hombifine N, Hombikat UV100, Degussa P25, «Anatase I» (Sigma Aldrich), «Anatase II» (Russia), and that prepared in present research by hydrothermal and sol-gel methods (anatase, X-ray amorphous titania, η-phase – TiO2-x×mH2O, and peroxide phase – TiOx(O2)2-x×mH2O) in aqueous media in the presence of luminol or lucigenin under UV-irradiation have been studied. The auxiliary program for data processing and calculating of the Reactive Oxygen Species (ROS: O2−, OH radicals, and H2O2) concentration, which correlated with the amount of photoluminescence photons (quantity hν, eV), has been developed. Photocatalytic activity (PCA) of prepared samples has been studied in the reaction of photodegradation of model dyes (methyl orange - MeO and rhodamine 6 G) and harmful organic pollutant (fungicide – difenoconazole, pesticide – thiamethoxam) under UV-irradiation. The connection between the rate constant (k, min-1) of photooxidation of MeO and OH radicals content (in the presence of luminol) and O2−, H2O2 species content (in the presence of lucigenin) has been described by a transition function of an aperiodic link of the 1st order and a polynomial of 2nd degree, respectively. The maximum k value of the reaction of MeO, difenoconazole, and thiamethoxam photodecomposition under UV irradiation has been achieved in the presence of commercial samples with nanosized anatase, characterized by the optimal crystallite size for photocatalysis (Anatase Sigma-Aldrich) and the maximum specific surface area (Hombifine N «Sachtleben Chemie GmbH»). The k value of the reaction of MeO, difenoconazole, and thiamethoxam photodecomposition under UV irradiation was minimal in the presence of samples containing X-ray amorphous titanium(IV) oxide or η-phase. The role of different factors (sample composition and phase modification, the content of reactive oxygen species, the size of nanoparticles at all levels, specific surface area, etc.) in the exhibition of photocatalytic activity has been discussed.