Photodegradation in sunlit waters is a major process of contaminant abatement, yet underlying chemical processes in the presence of dissolved organic matter are poorly known. Long-lived photo-oxidants are reactive species formed when the chromophoric dissolved organic matter absorbs sunlight, and they are involved in the degradation of contaminants. Previous works identified long-lived photo-oxidants with phenoxy radicals, which could be formed upon oxidation of natural phenols by the excited triplet states of chromophoric dissolved organic matter. Here, we generated reactive phenoxy radicals by direct ultraviolet-A photolysis of 2-nitrophenol and 4-nitrophenol. We measured the second-order rate constants for reaction of these phenoxy radicals with 2,4,6-trimethylphenol, a model electron-rich phenol. Results show rate constants of 9.39 × 10⁸(M⁻¹s⁻¹) for the 2-nitrophenoxyl radical, and 1.56 × 10⁸(M⁻¹s⁻¹) for the 4-nitrophenoxyl radical. These values are slightly lower than the typical rate constant of the reaction between 2,4,6-trimethylphenol and the excited triplet states of chromophoric dissolved organic matter, of 3 × 10⁹(M⁻¹s⁻¹). This means that 2,4,6-trimethylphenol would not be degraded to comparable extents by the excited triplet states of chromophoric dissolved organic matter and by long-lived photo-oxidants, if long-lived photo-oxidants were generated solely by the triplet states of chromophoric dissolved organic matter. Overall, findings suggest the occurrence of new pathway involving the direct photolysis of organic matter phenols that generates long-lived photo-oxidants.

阳光照射下的水中光降解是污染物减少的主要过程，但在溶解有机物存在下的潜在化学过程知之甚少。长寿命光氧化剂是发色团溶解有机物吸收阳光时形成的反应性物质，它们参与污染物的降解。以前的工作用苯氧基自由基鉴定了长寿命的光氧化剂，苯氧基自由基可能是在发色团溶解有机物的激发三重态氧化天然酚类时形成的。在这里，我们通过 2-硝基苯酚和 4-硝基苯酚的直接紫外 A 光解生成反应性苯氧自由基。我们测量了这些苯氧基与 2,4,6-三甲基苯酚（一种模型富电子苯酚）反应的二阶速率常数。结果显示，2-硝基苯氧基自由基的速率常数为 9.39 × 10⁸（M ⁻¹s⁻¹），4-硝基苯氧基自由基的速率常数为 1.56 × 10⁸（M ⁻¹s ⁻¹）。这些值略低于 2,4,6-三甲基苯酚与发色团溶解有机物的激发三重态反应的典型速率常数 3 × 10⁹（^{M-1 s-1}）。这意味着，如果长寿命光氧化剂仅由发色团溶解有机物的三重态产生，那么 2,4,6-三甲基苯酚不会被发色团溶解有机物的激发三重态和长寿命光氧化剂降解到相当程度。总体而言，研究结果表明出现了涉及有机物酚直接光解的新途径，从而产生长寿命的光氧化剂。