Lyu Gengxin, Shi Guosheng, Tang Liang, Fang Haiping, Wu Minghong
School of Environmental and Chemical Engineering, Shanghai University, Shanghai 200444, China.
Division of Interfacial Water and Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China.
Phys Chem Chem Phys. 2017 Apr 5;19(14):9354-9357. doi: 10.1039/c7cp00004a.
Cyanuric acid is a major component of many materials and chemicals, and is the most important intermediate in the degradation processes of sym-triazine compounds in the natural environment, as well as being used for water treatment. However, the degradation mechanism of cyanuric acid is still unclear in various advanced oxidation processes (AOPs), where ˙OH is usually regarded as the dominant radical. Here, using a combination of density functional theory calculations and experimental observations, we unexpectedly show that the sym-triazine ring structure is broken efficiently by reductive free radicals - hydrogen radicals (˙H), rather than traditional ˙OH. The energy barrier of cyanuric acid reacting with ˙H to form the -NH group and break the sym-triazine ring is only 4.96 kcal mol, which is clearly lower than that of cyanuric acid reacting with ˙OH (13.32 kcal mol). Our theoretical predictions are further confirmed by γ photon irradiation experiments, which show that when ˙H is present in the reaction, the nitrogen in cyanuric acid (or other nitrogenous compounds including primidone and bezafibrate) rapidly degrades into NH. In contrast, when ˙H is scavenged, cyanuric acid stops degrading into NH. Our results provide new insight for understanding the decomposition of nitrogenous materials, and we are the first to shed light on the key role of ˙H in organic transformation processes.
氰尿酸是许多材料和化学品的主要成分，是天然环境中对称三嗪化合物降解过程中最重要的中间体，也用于水处理。然而，在各种高级氧化过程（AOPs）中，氰尿酸的降解机制仍不清楚，其中˙OH通常被认为是主要自由基。在此，结合密度泛函理论计算和实验观察，我们意外地发现对称三嗪环结构是由还原性自由基——氢自由基（˙H）有效破坏的，而不是传统的˙OH。氰尿酸与˙H反应形成-NH基团并破坏对称三嗪环的能垒仅为4.96千卡/摩尔，明显低于氰尿酸与˙OH反应的能垒（13.32千卡/摩尔）。我们的理论预测通过γ光子辐照实验得到进一步证实，实验表明当反应中存在˙H时，氰尿酸中的氮（或其他含氮化合物，包括扑米酮和苯扎贝特）会迅速降解为NH。相反，当˙H被清除时，氰尿酸停止降解为NH。我们的结果为理解含氮材料的分解提供了新的见解，并且我们首次揭示了˙H在有机转化过程中的关键作用。
