Comparative Study of Photocatalytic Degradation Mechanisms of Pyrimethanil, Triadimenol, and Resorcinol

The photocatalytic degradation of an endocrine disruptor (resorcinol) and of two fungicides (pyrimethanil and triadimenol) has been studied and compared. The effect of $pH$⁠, oxygen, and $H2O2$ on the photocatalytic degradation of these compounds has been established. The three organics were analyzed by means of high pressure liquid chromatography (HPLC) and their mineralization by total organic concentration (TOC) measurements. The evolution of the toxicity to Lemna minor of the aqueous solutions of the three organics during their photocatalytic treatment has also been studied. The obtained results have been interpreted according to Fourier transform infrared studies on the interaction of the molecules with the catalyst surface and their reaction mechanisms by gas chromatographpy-mass spectrometry (GC-MS) analyses. The toxicity studies have shown that some intermediates acted as nutrients or toxicity antagonists as negative growth rate inhibitions were obtained. After $30min$ of reaction, the resorcinol and pyrimethanil solutions were detoxified, although some amount of the organics still remained. In the case of triadimenol, a 92% detoxification was achieved after $60min$ of reaction. The solar photocatalytic degradations of the pollutants have resulted to be comparable with those obtained with UV lamp. The obtained results suggest that the type of interaction of pyrimethanil and triadimenol with the $TiO2$ surface decides their degradation mechanism by which the effect of $pH$⁠, $H2O2$⁠, and dissolved oxygen is determined. It has also been confirmed that the photocatalytic techniques are very efficient at the detoxification of wastewaters contaminated with these fungicides.