The Regular/Persistent Free Radicals and Associated Reaction Mechanism for the Degradation of 1,2,4-Trichlorobenzene over Different MnO2 Polymorphs
The Regular/Persistent Free Radicals and Associated Reaction Mechanism for the Degradation of 1,2,4-Trichlorobenzene over Different MnO2 Polymorphs
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不同 MnO2 多晶型物降解 1,2,4-三氯苯的常规/持久自由基及相关反应机制
DOI：
10.1021/acs.est.8b03789
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发表时间：
2018
影响因子：
11.4
通讯作者：
Wei Da
中科院分区：
文献类型：
--
作者：
Li Qianqian;Huang Xinchen;Su Guijin;Zheng Minghui;Huang Chunhua;Wang Mengjing;Ma Chunyan;Wei Da
到目前为止，人们对K+调节的MnO2隧道结构的催化活性中规则/持久自由基的作用知之甚少。本文合成了三种MnO2晶型(α-，β-和δ-MnO2)，并考察了它们在300℃下对1，2，4-三氯苯(1，2，4-TrCBz)的降解活性。δ-MnO2具有K+可调的二维层状隧道结构，在三种MnO2晶型中活性最高。电子自旋共振光谱结果表明，δ-MnO2具有最丰富的活性氧物种(ROS：O2-·、·OH和1O2)，其次是α-MnO2(O2-·和1O2)和β-MnO2(O2-·)，受计算的势垒支持。有趣的是，人们注意到，在α-和β-MnO2/1，2，4-TrCBz体系中显著地检测到持久性有机自由基，而在更具活性的δ-MnO2/1，2，4-TrCBz体系中没有检测到持久有机自由基。这些因素可能导致了不同的氧化降解过程。在氧化过程中，中间产物，包括苯甲酸和甘油，通过ROS的攻击而形成。在进一步的攻击下，这些中间体裂解成更小的分子，如甲酸、醋酸、丙酸和丁酸。本研究结果对自由基在氯代芳烃催化降解中的作用有了更深入的认识。
The role of regular/persistent free radicals on the catalytic activity of K+-tuned MnO2tunnel structures is poorly understood to date. Herein, three MnO2polymorphs (α-, β-, and δ-MnO2) were synthesized and examined toward the degradation of 1,2,4-trichlorobenzene (1,2,4-TrCBz) at 300 °C. δ-MnO2, with a two-dimensional-layered tunnel structure tuned by K+, exhibited the highest activity among the three MnO2polymorphs. The electron spin resonance spectroscopy results confirmed that δ-MnO2featured the most abundant reactive oxygen species (ROS: O2–•, •OH, and1O2), followed by α-MnO2(O2–•and1O2), and β-MnO2(O2–•), being supported by the calculated energy barrier. It was, intriguingly, noted that persistent organic free radicals, newly recognized as emerging surface-stabilized compound, were remarkably detected in α- and β-MnO2/1,2,4-TrCBz systems but not in more reactive δ-MnO2/1,2,4-TrCBz system. These might contribute to discrepant oxidative degradation process. During the oxidative process, intermediates, including benzoic acid and glycerol, formed via attack by ROS. Upon further attack, these intermediates fragmented into smaller molecules such as formic, acetic, propionic, and butyric acids. The present findings give deeper insights into the role of free radicals on the catalytic degradation of chlorinated aromatics.