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.

摘要

在不同的实验条件下探索了世界上广泛使用的一种除草剂精喹禾灵 (QPE) 的有效伽马辐射分解。QPE 的水溶液被钴 60 源发射的伽马射线照射。QPE 水溶液以 0.5–3 kGy 的剂量和 26.31 Gy min ^{−1进行辐照}剂量率。获得的结果表明，在不存在和存在溶解氧的情况下，QPE 的去除效率分别为 98.5% 和 73%。对吸收光谱的变化、pH 效应和总有机碳 (TOC) 进行了研究。发现所有吸收带都随着照射剂量的增加而减少，并在 3 kGy 应用剂量后完全消失。将三种 pH 条件（pH = 10、pH = 6.2 和 pH = 3）应用于 QPE 的辐射降解，表明已发现中性 pH 的最佳去除效率。有趣的是，在 3 kGy 下，TOC 去除率达到 98%，表明几乎完全矿化。此外，分光光度分析支持 QPE 降解的伪一级动力学。由此产生的表观速率常数值约为k_app  = (0.012 ± 0.001) min ⁻¹。最后，几种副产物如 6-氯喹喔啉-2-醇、2-(4-羟基-苯氧基)丙酸酯、1,4-氢醌、醌、4-氯苯-1,2-二醇和 1,2,4-苯三醇通过气相色谱 - 质谱法（GC / MS）鉴定，证明辐射过程始于涉及羟基自由基的分子分裂，这是由水的辐射分解产生的。基于识别中间体，提出了 QPE 的降解机制方案。