The mechanism of diclofenac (DIC) degradation by tunnel-structured γ-MnO2, with superior oxidative and catalytic abilities, was determined in terms of solution pH. High-performance liquid chromatography with mass spectroscopy (HPLC–MS) was used to identify intermediates and final products of DIC degradation. DIC can be efficiently oxidized by γ-MnO2 in an acidic medium, and the removal rate decreased significantly under neutral and alkaline conditions. The developed model can successfully fit DIC degradation kinetics and demonstrates electron transfer control under acidic conditions and precursor complex formation control mechanism under neutral to alkaline conditions, in which the pH extent for two mechanisms exactly corresponds to the distribution percentage of ionized species of DIC. We also found surface reactive sites (Srxn), a key parameter in the kinetic model for mechanism determination, to be exactly a function of solution pH and MnO2 dosage. The main products of oxidation with a highly active hydroxylation pathway on the tunnel-structured Mn-oxide are 5-iminoquinone DIC, hydroxyl-DIC, and 2,6-dichloro-N-o-tolylbenzenamine.

中文翻译：

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隧道结构氧化锰对双氯芬酸的 pH 依赖性降解

双氯芬酸 (DIC) 被隧道结构 γ-MnO2 降解的机制，具有优越的氧化和催化能力，是根据溶液 pH 值确定的。使用质谱联用高效液相色谱 (HPLC-MS) 来鉴定 DIC 降解的中间体和最终产物。DIC在酸性介质中可被γ-MnO2高效氧化，在中性和碱性条件下去除率均显着降低。所开发的模型可以成功地拟合 DIC 降解动力学，并证明了酸性条件下的电子转移控制和中性至碱性条件下的前体复合物形成控制机制，其中两种机制的 pH 值范围恰好对应于 DIC 电离物种的分布百分比。我们还发现了表面反应位点 (Srxn)，机理确定动力学模型中的一个关键参数，恰好是溶液 pH 值和 MnO2 剂量的函数。在隧道结构的 Mn 氧化物上具有高活性羟基化途径的主要氧化产物是 5-亚氨基醌 DIC、羟基-DIC 和 2,6-二氯-No-tolylbenzenamine。