Abstract

The present work follows a study that permitted to enlighten the influence of TiO₂ coating types on the role of water vapor during Methyl Ethyl Ketone photocatalytic oxidation. For catalysts constituted of a film of TiO₂, the formation of a water layer at the catalyst surface was suggested. Consequently, for this kind of catalysts, not only the adsorption of pollutants on TiO₂ but also their dissolution in water may influence their degradation. Further experiments were then performed to further examine this aspect. A photocatalyst composed of a thin film of TiO₂ was used. Three VOCs having different aqueous solubilities were tested at various initial concentrations and a relative humidity of either 0 or 30%. The experimental results were modelled by the Langmuir-Hinshelwood relation at the initial time considering that the surface reaction was the limiting step of the reaction. For sufficiently low initial concentrations (C₀), the adsorption term (K_AC₀) in the denominator could be neglected. The constants k′ = k_sK_A (k_s is the Langmuir-Hinshelwood kinetic constant and K_A is the equilibrium adsorption constant) were determined by linear regressions. The influence of the aqueous solubility was then assessed by the behavior of the ratio k′_humid/k′_dry.