Development of a novel photocatalytic reaction system for oxidative decomposition of volatile organic compounds in water with enhanced aeration

Abstract

A novel photocatalytic reaction system, composed of solution and gas spaces that are divided by a thin Teflon film and titanium(IV) oxide (TiO 2)-coated mesh or cloth, for the treatment of contaminated aqueous solutions was developed to be operated with enhanced aeration without bubbling of air in the solution. First, the photocatalytic activities of TiO 2 particles immobilized on two kinds of support material, stainless steel mesh (SSM) and fiberglass cloth (FGC), were investigated for photocatalytic oxidation of 2-propanol, as a model volatile organic compound, dissolved in aerated aqueous solution. The TiO 2 particles immobilized on both support materials exhibited photocatalytic activity to oxidize 2-propanol into acetone and carbon dioxide (CO 2), and the activity levels of the TiO 2 particles immobilized on the two kinds of support materials were comparable. Presumably due to the presence of a small amount of metal species originating in SSM that might work as reduction catalysts, molecular hydrogen (H 2) was also liberated on the TiO 2-immobilized SSM. Results of analysis of weight loss after photoirradiation suggested that the stability of the TiO 2-immobilized FGC was better than that of the TiO 2-immobilized SSM. On the basis of these results, FGC was employed in construction of a photocatalytic reactor equipped with an oxygen (O 2)-permeable Teflon membrane in order to make oxygen pass from a gas space to a solution space and to keep the surface of the immobilized TiO 2 photocatalyst, facing an aqueous solution containing volatile organic compounds, saturated with dissolved O 2. From the results of photocatalytic oxidative decomposition of 2-propanol, it was clarified that the surfaces of TiO 2 particles could be sufficiently supplied with O 2 from the gas space through the membrane to accelerate the oxidation.