Hydroxyl radical-dominated oxidation in catalytic ozonation is, in particular, important in water treatment scenarios for removing organic contaminants, but the mechanism about ozone-based radical oxidation processes is still unclear. Here, we prepared a series of transitional metal (Co, Mn, Ni) single-atom catalysts (SACs) anchored on graphitic carbon nitride to accelerate ozone decomposition and produce highly reactive ·OH for oxidative destruction of a water pollutant, oxalic acid (OA). We experimentally observed that, depending on the metal type, OA oxidation occurred dominantly either in the bulk phase, which was the case for the Mn catalyst, or via a combination of the bulk phase and surface reaction, which was the case for the Co catalyst. We further performed density functional theory simulations and in situ X-ray absorption spectroscopy to propose that the ozone activation pathway differs depending on the oxygen binding energy of metal, primarily due to differential adsorption of O₃ onto metal sites and differential coordination configuration of a key intermediate species, *OO, which is collectively responsible for the observed differences in oxidation mechanisms and kinetics.

中文翻译：

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在催化臭氧化中通过单原子催化剂控制羟基自由基生成的选择性：表面或溶液

催化臭氧化中以羟基自由基为主的氧化在去除有机污染物的水处理方案中尤其重要，但基于臭氧的自由基氧化过程的机理仍不清楚。在这里，我们制备了一系列固定在石墨氮化碳上的过渡金属（Co、Mn、Ni）单原子催化剂（SAC），以加速臭氧分解并产生高活性·OH，用于氧化破坏水污染物草酸（OA） ). 我们通过实验观察到，根据金属类型，OA 氧化主要发生在体相中，这是 Mn 催化剂的情况，或者通过体相和表面反应的组合，这是 Co 催化剂的情况.₃到金属位点和关键中间物种 *OO 的差异配位配置，这是观察到的氧化机制和动力学差异的共同原因。