Photocatalytic promoted oxidation of phenolic mixtures: An insight into the operating and mechanistic aspects

The photocatalytic oxidation of a phenolic mixture (gallic acid, tyrosol and syringic acid) has been carried out in the presence of titanium dioxide and a selected inorganic peroxide, namely persulphate, monopersulphate or hydrogen peroxide. The results obtained in UVA irradiated solutions reveal that hydrogen peroxide is the most effective option. The influence of some relevant operating parameters (i.e. initial concentration of phenols, hydrogen peroxide or titanium dioxide) has been investigated. In all cases a saturation-like behaviour has been observed. Thus, an increase in oxidation efficiency is observed when raising, up to a certain value, the initial amounts of reagents/catalyst added to the reactor. Nevertheless, a further increase of any of the previous parameters does not lead to the expected enhancement of the process. From the concave shape of the parent compounds’ depletion profiles, it is suggested that the system proceeds through an autocatalytic route, likely involving the action of organic radicals. A pseudoempirical model has been used to acceptably model the experimental data obtained.