UV-assisted degradation of propiconazole in a TiO₂ aqueous suspension: identification of transformation products and the reaction pathway using GC/MS

Abstract

Photocatalytic degradation of propiconazole, a triazole pesticide, in the presence of titanium dioxide (TiO₂) under ultraviolet (UV) illumination was performed in a batch type photocatalytic reactor. A full factorial experimental design technique was used to study the main effects and the interaction effects between operational parameters in the photocatalytic degradation of propiconazole in a batch photo-reactor using the TiO₂ aqueous suspension. The effects of catalyst concentration (0.15–0.4 gL⁻¹), initial pH (3–9), initial concentration (5–35 mg L⁻¹) and light conditions were optimised at a reaction time duration of 90 min by keeping area/volume ratio constant at 0.919 cm² mL⁻¹. Photocatalytic oxidation of propiconazole showed 85% degradation and 76.57% mineralisation under UV light (365 nm/30 Wm⁻²) at pH 6.5, initial concentration 25 mg L⁻¹ and constant temperature (25 ± 1 °C). The Langmuir–Hinshelwood kinetic model has successfully elucidated the effects of the initial concentration on the degradation of propiconazole and the data obtained are consistent with the available kinetic parameters. The photocatalytic transformation products of propiconazole were identified by using gas chromatography–mass spectrometry (GC/MS). The pathway of degradation obtained from mass spectral analysis shows the breakdown of transformation products into smaller hydrocarbons (m/z 28 and 39).

Keywords:

• photocatalytic degradation
• propiconazole (technical)
• TiO₂
• slurry reactor
• UV

Acknowledgements

We would like to acknowledge the following for support: Ms Taranjeet Kaur acknowledges UGC (Govt. of India) for providing the scholarship for research and Central Instrumentation Laboratory (CIL), Panjab University, Chandigarh, for providing instrumental facilities. I am also thankful to Markfed Unit, Mohali (Punjab), for providing the sample of fungicide (propiconazole). Aeroxide (China) for providing free sample of P25-TiO₂.