Nanomaterials (May 2020)

Enhanced Photocatalytic Degradation of the Imidazolinone Herbicide Imazapyr upon UV/Vis Irradiation in the Presence of Ca<i><sub>x</sub></i>MnO<i><sub>y</sub></i>-TiO<sub>2</sub> Hetero-Nanostructures: Degradation Pathways and Reaction Intermediates

  • Salma Bougarrani,
  • Preetam K. Sharma,
  • Jeremy W. J. Hamilton,
  • Anukriti Singh,
  • Moisés Canle,
  • Mohammed El Azzouzi,
  • John Anthony Byrne

DOI
https://doi.org/10.3390/nano10050896
Journal volume & issue
Vol. 10, no. 5
p. 896

Abstract

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The determination of reaction pathways and identification of products of pollutants degradation is central to photocatalytic environmental remediation. This work focuses on the photocatalytic degradation of the herbicide Imazapyr (2-(4-methyl-5-oxo-4-propan-2-yl-1H-imidazol-2-yl) pyridine-3-carboxylic acid) under UV-Vis and visible-only irradiation of aqueous suspensions of CaxMnOy-TiO2, and on the identification of the corresponding degradation pathways and reaction intermediates. CaxMnOy-TiO2 was formed by mixing CaxMnOy and TiO2 by mechanical grinding followed by annealing at 500 °C. A complete structural characterization of CaxMnOy-TiO2 was carried out. The photocatalytic activity of the hetero-nanostructures was determined using phenol and Imazapyr herbicide as model pollutants in a stirred tank reactor under UV-Vis and visible-only irradiation. Using equivalent loadings, CaxMnOy-TiO2 showed a higher rate (10.6 μM·h−1) as compared to unmodified TiO2 (7.4 μM·h−1) for Imazapyr degradation under UV-Vis irradiation. The mineralization rate was 4.07 µM·h−1 for CaxMnOy-TiO2 and 1.21 μM·h−1 for TiO2. In the CaxMnOy-TiO2 system, the concentration of intermediate products reached a maximum at 180 min of irradiation that then decreased to a half in 120 min. For unmodified TiO2, the intermediates continuously increased with irradiation time with no decrease observed in their concentration. The enhanced efficiency of the CaxMnOy-TiO2 for the complete degradation of the Imazapyr and intermediates is attributed to an increased adsorption of polar species on the surface of CaxMnOy. Based on LC-MS, photocatalytic degradation pathways for Imazapyr under UV-Vis irradiation have been proposed. Some photocatalytic degradation was obtained under visible-only irradiation for CaxMnOy-TiO2. Hydroxyl radicals were found to be main reactive oxygen species responsible for the photocatalytic degradation through radical scavenger investigations.

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