Analytical Methods of Hydroxyl Radical Produced by TiO 2 Photo-catalytic Oxidation

The performance of photo-catalytic oxidation process is significantly dependent on the amount of hydroxyl radicals produced during the process, and it is an essential prerequisite to quantify its production. However, precise and accurate methods for quantification of hydroxyl radicals have not been developed so far. For this reason, this study was initiated to compare existing methods for analysis of hydroxyl radicals produced by photo-catalytic oxidation and to propose a new method to overcome the limitation of established methods. To simulate photo-catalytic oxidation process, Degussa P25 which has been widely used as a standard photo-catalyst was used with the dose of 0.05 g/L. The light source of process was UVC mercury low-pressure lamp (11 W, ). The results indicate that both potassium iodide (KI)/UV-vis spectrometer and terephthalic acid (TPA)/fluorescence spectrometer methods could be applied to qualitatively measure hydroxyl radicals via detection of triiodide ion () and 2-hydroxyterephthalic acid which are produced by reactions of iodine ion () and TPA with hydroxyl radicals, respectively. However, it was possible to quantitatively measure hydroxyl radicals using TPA method coupled with high-performance liquid chromatograph (HPLC). The analytical results using TPA/HPLC method show that hydroxyl radical of 0.013 M was produced after 8 hours operation of photo-catalytic oxidation under specific experimental conditions of this study. The proposed method is expected to contribute to precise the evaluation of the performance of photo-catalytic oxidation process.