Assessing the Photocatalytic Degradation of Penconazole on TiO2 in Aqueous Suspensions: Mechanistic and Ecotoxicity Studies in Aerated and Degassed Systems

Penconazole (C12H15Cl2N3) is widely used to prevent fungal infection of fruits. Since this toxic fungicide is recalcitrant to biological degradation, it has harmful impacts on aquatic ecosystems. TiO2-based heterogeneous photocatalysis proved to be an efficient method for its mineralization. To monitor the processes occurring under the influence of illumination, the light absorbance, the pH, and the TOC of the samples were measured. The concentration of the model compound and the degradation products were determined by HPLC and IC. Penconazole did not decompose under UV light (λmax = 371 nm) without a catalyst. In the presence of TiO2, mineralization took place. The initial degradation rate in air (7.7 × 10−4 mM s−1) was 5 times higher than under argon. The formation rate of hydrochloric acid (1.04 × 10−3 mM s−1) in the former case significantly contributed to the acidification of the liquid phase. NH4+ also formed, at the rate of 5.9 × 10−4 mM s−1, and very slightly transformed to NO3−. Due to the intermediates identified by HPLC-MS, hydroxylation, H abstraction, and Cl elimination are involved in the degradation mechanism, in which photogenerated HO● radicals, conduction-band electrons, and (under air) superoxide radical anions (O2●−) play considerable roles. The intermediates proved to be much less toxic than penconazole.