Reaction mechanism and kinetics of DEET visible light assisted photocatalytic ozonation with WO3 catalyst

- Synergistic effect of O3 and visible-light irradiated WO3 during DEET removal.
- Key role of hydroxyl radicals during DEET degradation and mineralization.
- Identification of DEET transformation by-products during photocatalytic ozonation.
- Photocatalytic ozonation mechanism of DEET removal.
- Lumped TOC-hydroxyl radicals based kinetic model of DEET mineralization.

This work is focused on the mechanistic investigation of N,N-diethyl-meta-toluamide (DEET) degradation by photocatalytic ozonation, using WO3 in suspension and visible radiation (wavelength ≥ 390 nm). This combined process proved to be an efficient treatment to completely remove the contaminant, HO radicals being the main species involved. Different oxidation products were identified by liquid chromatography time-of-flight mass spectrometry and ion chromatography analyses, and the evolution of their relative abundances with reaction time was established. The efficiency of photocatalytic ozonation treatment was pointed out not only in the DEET depletion rate but also in the evolution of the main intermediate species and mineralization. All the large intermediates initially formed were completely removed within 60 min reaction time and only short-chain organic acids with very low toxicity remained in solution at concentrations in agreement with the mineralization degree achieved (up to 60% in 2 h). A reaction mechanism of photocatalytic ozonation of DEET involving different chemical reaction steps, with the final formation of short-chain organic acids and mineralization to CO2, has been proposed. A lumped kinetic model based on TOC and hydroxyl radical reaction was developed to simulate DEET, intermediates and short-chain organic acids evolution in terms of TOC that provides a simplified approach for this process.

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