Effect of key operational parameters on the photocatalytic oxidation of phenol by nanocrystalline sol–gel TiO2 under UV irradiation

Nanocrystalline TiO2 materials produced by an acid-catalyzed sol–gel method are used as catalysts in the photocatalytic degradation of phenol under ultraviolet light. Materials with different crystalline and morphological properties are obtained by controlling the temperature used in the calcination step. Induced light conversion and adsorption have opposite dependencies on the light intensity. The operational parameters (nature of TiO2 crystal phase, catalyst concentration, pH and initial phenol concentration) have the expected influence in the efficiency of the photocatalytic degradation process. The effect of two different co-oxidants (H2O2 and Na2S2O8) in the photocatalytic process is also described. A modified Langmuir–Hinshelwood kinetic model is used considering a pseudo-steady state approach in order to explain the dependence of both, the kinetic rate and adsorption equilibrium constants, on light intensity. Hydroquinone and catechol are the main intermediates of the photocatalytic reaction, as result from the reaction of phenol with photogenerated hydroxyl radicals. A possible degradation pathway is advanced.

Nanocrystalline sol–gel TiO2 catalysts are synthesized for use in the photocatalytic oxidation of phenol under UV irradiation. Pure anatase nanocrystallites (8.5 nm) are very efficient photocatalysts. However as the rate of oxidation increases with the intensity of incident light, desorption induced by light absorption also increases, limiting the overall efficiency of the process.Figure optionsDownload as PowerPoint slide