Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon 852, Hong Kong, China.
School of Environment, Tsinghua University, Beijing 100084, China.
Environ Sci Technol. 2021 May 18;55(10):7004-7014. doi: 10.1021/acs.est.0c08531. Epub 2021 Apr 29.
Nitrogen-doped graphitic biochar (NBC) has boosted the development of nonradical peroxymonosulfate (PMS) activation in environmental remediation. However, the specific role of nitrogen species played in NBC-based nonradical carbocatalysis remains vaguely interpreted. To pinpoint the critical nitrogen speciation, a sophisticated thermo-mechanochemical manipulation was exploited to prepare a series of NBCs with similar dimensional structures and oxygen levels but different nitrogen species (.., dopants and vacancies). Different from conventional perspectives, nonradical NBC-based carbocatalysis was found to be preferably determined by the nitrogen vacancies more than their parent nitrogen dopants. Raman depth analysis evidenced that a complete transformation of nitrogen dopants into nitrogen vacancies could be achieved at 800 °C, where an excellent nonradical abatement of 4-chlorophenol (4-CH, 90.9% removal) was found for the NBC800 with a low PMS consumption (1.24 mM). According to PMS adsorption experiments, nitrogen vacancies exhibited the highest affinity toward the PMS molecules compared to nitrogen dopants, which accounted for the superior carbocatalysis. Electron paramagnetic resonance and Raman spectroscopic analyses indicated that the original PMS molecules were bound to positively charged nitrogen vacancies, and a robust metastable complex (*HSO) evolved subsequently hydrogen abstraction by adjacent persistent free radicals. Raman techniques could be adopted to estimate the level of nitrogen vacancies associated with the polarization of electron distribution. The flexible feature and practical prospects of nitrogen vacancy-based carbocatalysis were also observed in the remediation of simulated phenolic industrial wastewater. Overall, this study unravels the dilemma in the current NBC-based nonradical carbocatalysis and advances our understanding of nitrogen doping technology for next-generation biochar design.
氮掺杂石墨生物炭 (NBC) 促进了非自由基过一硫酸盐 (PMS) 在环境修复中的发展。然而，氮物种在 NBC 基非自由基碳催化中的具体作用仍难以解释。为了确定关键的氮形态，采用了复杂的热机械化学处理方法，制备了一系列具有相似尺寸结构和氧水平但不同氮形态（掺杂剂和空位）的 NBC。与传统观点不同，发现非自由基 NBC 基碳催化主要受氮空位而不是其母体氮掺杂剂决定。拉曼深度分析表明，在 800°C 下可以将氮掺杂剂完全转化为氮空位，其中 NBC800 对 4-氯苯酚 (4-CH，去除率为 90.9%) 的非自由基去除效果非常好，PMS 消耗量低 (1.24 mM)。根据 PMS 吸附实验，与氮掺杂剂相比，氮空位对 PMS 分子表现出更高的亲和力，这解释了其优越的碳催化性能。电子顺磁共振和拉曼光谱分析表明，原始 PMS 分子与带正电荷的氮空位结合，随后通过相邻的持久自由基发生了强的亚稳配合物 (*HSO) 氢提取。拉曼技术可用于估计与电子分布极化相关的氮空位水平。在模拟酚类工业废水修复中也观察到了基于氮空位的碳催化的灵活特征和实际前景。总体而言，本研究揭示了当前 NBC 基非自由基碳催化中的困境，并推进了我们对下一代生物炭设计中氮掺杂技术的理解。
