The UV/H₂O₂ process is a benchmark advanced oxidation process (AOP) that in situ generates highly reactive and nonselective hydroxyl radical (^•OH) to oxidatively destroy a wide range of organic compounds. Accurately quantifying the concentration of short-lived ^•OH is essential to predict process performance, optimize the operation parameters, and compare with other process options. The ^•OH concentration is typically measured using organic probe molecules that react with ^•OH but not with other oxidants. In the extremely well-characterized UV/H₂O₂ system in which ^•OH is proven to be the dominant oxidant, using photolysis-resistant probes such as benzoic acid and its derivatives is a widely agreed and practiced norm. We herein report that certain ^•OH probe compounds can be degraded in UV/H₂O₂ system by unknown reactive species that has not been reported in the past. Several common organic probes, particularly p-substituted benzoic acid compounds (i.e., p-hydroxybenzoic acid, p-chlorobenzoic acid, and p-phthalic acid), were found to be vulnerable to attack by the unknown reactive species, leading to false quantification of ^•OH concentration under high radical scavenging conditions. Lines of evidence obtained from a series of ^•OH scavenging experiments performed under various conditions (i.e., different concentrations of H₂O₂, ^•OH probe compounds, and dissolved oxygen) point toward excited state H₂O₂. The results from this study suggest the importance of using appropriate ^•OH probe compounds in mechanistic studies and needs for considering the unidentified role of excited state of H₂O₂ on the UV/H₂O₂ process and related AOPs.

UV/H ₂ O ₂工艺是一种基准的高级氧化工艺 (AOP)，它原位生成高反应性和非选择性的羟基自由基 ( ^• OH) 以氧化破坏各种有机化合物。准确量化短寿命^• OH的浓度对于预测工艺性能、优化操作参数以及与其他工艺选项进行比较至关重要。的^• OH浓度是使用与反应的有机探针分子来测量^• OH，但不与其它氧化剂。在特性极好的 UV/H ₂ O ₂系统中，^•OH 被证明是主要的氧化剂，使用抗光解探针如苯甲酸及其衍生物是一种广泛认可和实践的规范。我们在此报告某些^• OH 探针化合物可以在 UV/H ₂ O ₂系统中被过去未报道过的未知活性物质降解。发现几种常见的有机探针，特别是对取代苯甲酸化合物（即对羟基苯甲酸、对氯苯甲酸和对苯二甲酸）容易受到未知活性物质的攻击，导致对^•高自由基清除条件下的 OH 浓度。从一系列在各种条件（即不同浓度的 H ₂ O ₂、^• OH 探针化合物和溶解氧）下进行的^• OH 清除实验中获得的证据指向激发态 H ₂ O ₂。这项研究的结果表明，在机理研究中使用适当的^• OH 探针化合物很重要，并且需要考虑 H ₂ O ₂的激发态对 UV/H ₂ O ₂过程和相关 AOP的未知作用。