Ozonation of clofibric acid catalyzed by titanium dioxide

The removal of clofibric acid from aqueous solution has been investigated in catalytic and non-catalytic semicontinuous ozonation runs. Kinetic data were analyzed using second order expressions for the reaction between organics and ozone or hydroxyl radicals. Catalytic runs used a commercial titanium dioxide catalyst consisting of fumed colloidal particles. The kinetic constant of the non-catalytic ozonation of clofibric acid at pH 3 was 8.16 x 10(-3) +/- 3.4 x 10(-4) L mmol(-1) s(-1). The extent of mineralization during non-catalytic runs ranged from 50% at pH 7 to 20% at pH 3 in a reaction that essentially took place during the first 10-20 min. The catalyst increased the total extent of mineralization, its effect being more important during the first part of the reaction. The pseudo-homogeneous catalytic rate constant was 2.17 X 10(-2) L mmol(-1) s(-1) at pH 3 and 6.80 x 10(-1) L mmol(-1) s(-1) at pH 5, with up to a threefold increase with respect to non-catalytic constants using catalyst load of 1 g/L. A set of stopped-flow experiments were designed to elucidate the role of catalyst. whose effect was probably due to the adsorption of organics on catalytic sites rather than to the promotion of ozone decomposition. (C) 2009 Elsevier B.V. All rights reserved.