Hydrogen peroxide-assisted photocatalytic oxidation of phenolic compounds

Abstract

The effect of hydrogen peroxide (H₂O₂) on photocatalytic oxidation of phenol and monochlorophenols (CP) in aqueous suspensions of commercial TiO₂ rutile was investigated. Various concentrations of H₂O₂ were used without and with the presence of TiO₂ under different atmospheres, e.g., N₂ or O₂. Sources of hydroxyl radicals for photocatalytic processes are suggested through the surface hydroxyl group reacting with hole, dissolved oxygen trapping an electron, and photolytic H₂O₂. The combination of TiO₂ and H₂O₂ under UV illumination can greatly enhance the degradation rates of the phenol and chlorophenols. The photocatalytic oxidation with the H₂O₂/UV/TiO₂ system was found to be much more effective than either UV/TiO₂ or UV/H₂O₂ alone. The efficiency of the photocatalytic degradation of phenol was improved from 30 to 97% due to the presence of H₂O₂. As the H₂O₂ concentration increases, more hydroxyl radicals are produced, and the phenol oxidation rate increases. At high H₂O₂ concentration (≥10⁻² M), O₂ or N₂ atmospheres are not important factors for phenol oxidation in the H₂O₂/UV/TiO₂ system.