Spectroscopic monitoring of photocatalytic degradationof the insecticide acetamiprid and its degradationproduct 6-chloronicotinic acid on TiO2 catalyst

Abstract

Two spectroscopicmethods, 1HNMRand FTIR,were developed for themonitoring of the photocatalytic degradation of acetamiprid,a widely used pyridine-based neonicotinoid insecticide, in UV-irradiated aqueous suspensions of O2/TiO2. The 1H NMR methodallowed also the identification of the intermediates such as 6-chloronicotinic and formic acids, as well as separate monitoring ofthe kinetics of degradation of acyclic and aromatic moieties based on the different chemical shifts of the protons belonging to themethyl group of the acyclic and selected proton of the heterocyclic aromatic moiety. The FTIR procedure enabled the monitoring ofthe kinetics of degradation of the cyano group of the compound. The obtained results are in good agreement with the comparativeHPLC-DADandHPLC-MS/MSmeasurements,which also enabled the identification of certain intermediates. To get a deeper insightinto the complex photocatalytic process, the photocatalytic degradation of 6-chloronicotinic acid, a stable degradation intermediateof acetamiprid, was also investigated by 1H NMR and HPLC-DAD methods. Based on the obtained data, a tentative reactionmechanism was proposed for the photocatalytic degradation of acetamiprid.