THE INFLUENCE OF SOLUTION MATRIX ON THE PHOTOCATALYTIC DEGRADATION OFTNT IN TIO2 SLURRIES

Previous work had demonstrated that TNT, a widespread hazardous waste, is effectively mineralized in aerated TiO2 slurries using near-UV rad iation. However, prior work failed to evaluate the reaction under cond itions likely to be encountered in field applications. The present stu dy was undertaken to examine the impact of pH and the presence of inor ganic ions and organic acids commonly found in natural waters on rates of TiO2 photocatalyzed TNT transformation and mineralization. Raising the pH slightly increased the rate of TNT transformation, primarily a s a result of an increased rate of TNT photolysis, but significantly r educed rates of mineralization due to increased electrostatic repulsio n between the catalyst surface and anionic TNT intermediates. The pres ence of inorganic anions did not substantially hinder TNT transformati on at alkaline pH, but mineralization rates were diminished when the a nion either adsorbed strongly to the photocatalyst or was an effective hydroxyl radical scavenger. Addition of humic acid to the solution ma trix did not alter the net rate of TNT transformation, but did decreas e the overall decay rate of dissolved organic carbon. The propensity o f humic acid to transform TNT through sensitized photocatalysis, and t he importance of this reaction in overall compound degradation, were a lso assessed. Data indicated that humic acids can serve to sensitize T iO2 photocatalytic degradation of TNT, but under the aerated solution conditions of this work rates of humic sensitized photolysis were high er than rates of sensitized photocatalysis. (C) 1997 Elsevier Science Ltd.