Oxidation of Catechol and Hydroquinone in Aqueous Media by Heterogeneous Photocatalysis Using Thin Layer of TiO2 P25

Catechol and hydroquinone, two phenolic compounds, have been studied. The oxidation of the two chemicals by heterogeneous photocatalysis TiO2 P25 Degussa based was investigated using a laboratory scale reactor and ultraviolet-A lamp. Thin layers of TiO2 on stainless steel were prepared by electrophoretic deposition. Phenolic compounds were monitored by High- Performance Liquid Chromatography (HPLC) system equipped with a phenyl Xbridge column and Photodiode Array (PDA) detector. The effects of some parameters such as initial concentration of phenolic compounds (50–150 µM), initial pH (2–11) and the degradation kinetics of the two chemicals have been evaluated. The results showed that the degradation rate of catechol and hydroquinone decrease when the initial concentration of pollutants increases whereas the natural pH (5.7 and 4.8 respectively for catechol and hydroquinone) has been found favourable for the degradation of the two chemicals. The first order kinetic fits the oxidation rate of the two chemicals using Langmuir–Hinshelwood model. Two intermediate by-products have been identified: by-product absorbing at the wavelength of 246 nm (1,4-benzoquinone) identified in the case of hydroquinone photodegradation and another intermediate by-product absorbing at the wavelength of 256 nm (probably hydroxybenzoquinone).