Kinetic and mechanism investigation on the gamma irradiation induced degradation of quizalofop-p-ethyl

ABSTRACT

An efficient gamma radiolytic decomposition of one of the extensively used herbicides in the world quizalofo-p-ethyl (QPE) was explored under different experimental conditions. Aqueous solutions of QPE were irradiated by gamma rays emitted by a Cobalt 60 source. QPE aqueous solutions were irradiated at doses of 0.5–3 kGy with 26.31 Gy min⁻¹ dose rate. Obtained results indicated that removal efficiency of 98.5% and 73% of QPE were obtained, respectively, in absence and in presence of dissolved oxygen. Change of absorption spectra, pH effect and Total Organic Carbon (TOC) were carried out and studied. It was found that all absorption bands decreased with increasing irradiation dose and disappear totally after 3 kGy applied dose. Three pH conditions (pH = 10, pH = 6.2 and pH = 3) were applied in radiolytic degradation of QPE showing that the best removal efficiency has been found for neutral pH. Interestingly, the % TOC removal reaches 98% at 3 kGy indicated practically total mineralization. Furthermore, spectrophotometric analyses argued in favour of a pseudo-first-order kinetic of QPE degradation. The resulting apparent rate constant value is approximately k_app = (0.012 ± 0.001) min⁻¹. Finally, several by-products such as 6-chloroquinoxalin -2-ol, 2-(4-hydroxy-phenyoxy) propionate, 1,4-hydroquinone, quinone, 4-chlorobenzene-1,2diol and 1,2,4-benzenetriol were identified by gas chromatography–mass spectrometry (GC/MS) evidencing that radiation process starting with the fragmentation of the molecule involving the hydroxyl radical, which is generated by the radiolysis of water. Based on the identification intermediates, a degradation mechanistic schema of QPE has been proposed.

GRAPHICAL ABSTRACT

KEYWORDS:

• Gamma radiation
• quizalofop-p-ethyl
• hydroxyl radicals
• total organic carbon
• GC–MS

Acknowledgements

The authors thankfully acknowledge the financial support of the Tunisian Ministry of Higher Education and Scientific Research (Tunisia). The authors would also like to thank technical and financial support from the IAEA to carry out the research.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

All data generated or analysed during this study are included in this published article.

Additional information

Funding

The authors thankfully acknowledge the financial support of the Tunisian Ministry of Higher Education and Scientific Research (Tunisia). The authors would also like to thank the technical and financial support from the IAEA to carry out the research.