Transformation of Z-thiacloprid by three advanced oxidation processes: Kinetics, intermediates and the role of reactive species

Abstract

Three advanced oxidation processes (AOPs), heterogeneous photocatalysis, vacuum ultraviolet (VUV) photolysis and γ radiolysis were used for the generation of reactive primary free radicals to induce the transformation of Z-thiacloprid in aqueous solution. The effects of dissolved oxygen and the initial concentration (from 10−6 to 10−4molL−1) were investigated. The initial reaction rates increased with the initial concentration of thiacloprid, both in oxygen saturated and oxygen free solutions. Dissolved oxygen had significant effect on the transformation rate only in case of heterogeneous photocatalysis. Three main intermediates and the E-thiachloprid were detected using all three methods. One of these intermediates could be related to the reaction with eaq−, while the other two could be related to the OH-initiated reactions. Heterogeneous photocatalysis showed the highest efficiency regarding the transformation of intermediates in presence of dissolved oxygen, while thiacloprid transformed with the highest initial reaction rate during VUV photolysis. However, according to the Electric energy per order (EEO) data γ radiolysis was found to be the economically most feasible method, requiring several orders of magnitude less energy than VUV photolysis and heterogeneous photocatalysis for reduction of the target compound concentration by one order of magnitude in a unit volume.