2 resultados para complexation in solution
Resumo:
The initial rate of the photocatalysed oxidation of methylene blue, MB, by dissolved oxygen in solution, ri(MB), is measured for a series of titania on glass samples exhibiting a wide range of activities. The samples used include two different types of commercial self-cleaning glass and a lab-made sol-geltitania film. The activities of these samples are also assessed using a resazurin-based photocatalyst activity indicator ink, i.e. Rz paii, for which the initial rates of the photocatalysed reduction of Rz were measured, ri(Rz). A plot of ri(MB)vs. ri(Rz) reveals a goodstraight line, thereby demonstrating a linear correlation (for TiO2films on glass at least) between the slow (usually hours) photocatalysed oxidation of organic materials, such as MB, and the fast (typically minutes) photocatalysed irreversible reduction of a dye, like Rz, in a paii. The possible use of paii technology for assessing, in a simple, quick and inexpensive manner, photocatalytic films both in the laboratory and in situ is discussed briefly.
Resumo:
The adsorption and photocatalytic degradation of acetate on TiO2 surfaces was investigated in H2O and D2O by ATR-FTIR and EPR Spectroscopy respectively. These studies were carried out in the dark and under UV(A) illumination to gain additional insights into the adsorption behaviour with the identification of paramagnetic species formed during the oxidation of acetate. Isotopic exchange during the adsorption of D2O on TiO2 surface led to different interactions between the adsorbate and OD groups. At different pH levels, several surface complexes of acetate can be formed such as monodentate, or bidentates. Under UV(A) irradiation of TiO2 aqueous suspensions, the formation of hydroxyl and methoxy radicals evidenced as the corresponding spin-adducts, were found to dominate in alkaline and acidic suspensions respectively. Two possible pathways for the oxidation of acetate have been suggested at different pH levels in solution in terms of the source of the spin adduct formed. These proposed pathways were found to be in good agreement with ATR-FTIR and EPR results.
