Department of Environmental Science and Engineering, Wuhan University, Wuhan 430079, China.
School of Chemical Engineering and Advanced Materials, The University of Adelaide, Adelaide, SA5005, Australia.
Environ Sci Technol. 2020 May 19;54(10):6438-6447. doi: 10.1021/acs.est.0c01161. Epub 2020 Apr 29.
Persulfates activation by carbon nanotubes (CNT) has been evidenced as nonradical systems for oxidation of organic pollutants. Peroxymonosulfate (PMS) and peroxydisulfate (PDS) possess discrepant atomic structures and redox potentials, while the nature of their distinct behaviors in carbocatalytic activation has not been investigated. Herein, we illustrated that the roles of nitrogen species in CNT-based persulfate systems are intrinsically different. In PMS activation mediated by nitrogen-doped CNT (N-CNT), surface chemical modification (N-doping) can profoundly promote the adsorption quantity of PMS, consequently elevate potential of derived nonradical N-CNT-PMS* complexes, and boost organic oxidation efficiency via an electron-transfer regime. In contrast, PDS adsorption was not enhanced upon incorporating N into CNT due to the limited equilibrium adsorption quantity of PDS, leading to a relatively lower oxidative potential of PDS/N-CNT system and a mediocre degradation rate. However, with equivalent persulfate adsorption on N-CNT at a low quantity, PDS/N-CNT exhibited a stronger oxidizing capacity than PMS/N-CNT because of the intrinsic higher redox potential of PDS than PMS. The oxidation rates of the two systems were in great linearity with the potentials of carbon-persulfate* complexes, suggesting N-CNT activation of PMS and PDS shared the similar electron-transfer oxidation mechanism. Therefore, this study provides new insights into the intrinsic roles of heteroatom doping in nanocarbons for persulfates activation and unveils the principles for a rational design of reaction-oriented carbocatalysts for persulfate-based advanced oxidation processes.
碳纳米管（CNT）活化过一硫酸盐（PMS）和过二硫酸盐（PDS）已被证实为非自由基体系，可用于氧化有机污染物。过一硫酸盐（PMS）和过二硫酸盐（PDS）具有不同的原子结构和氧化还原电位，但其在碳催化活化中表现出不同行为的本质尚未得到研究。本文阐明了氮物种在基于碳纳米管的过硫酸盐体系中的作用本质上是不同的。在氮掺杂碳纳米管（N-CNT）介导的 PMS 活化中，表面化学修饰（N 掺杂）可以显著促进 PMS 的吸附量，从而提高衍生非自由基 N-CNT-PMS复合物的电位，并通过电子转移机制提升有机氧化效率。相比之下，由于 PDS 的平衡吸附量有限，在将 N 掺入 CNT 时，PDS 的吸附并未增强，导致 PDS/N-CNT 体系的氧化电位相对较低，降解速率也较差。然而，在低用量下，PDS/N-CNT 具有更强的氧化能力，因为 PDS 的固有氧化还原电位高于 PMS，尽管在 N-CNT 上具有等效的过硫酸盐吸附量。这两个体系的氧化速率与碳-过硫酸盐复合物的电位呈很好的线性关系，表明 PMS 和 PDS 的 N-CNT 活化均遵循相似的电子转移氧化机制。因此，本研究为深入了解杂原子掺杂纳米碳对过硫酸盐的活化作用提供了新的认识，并揭示了基于过硫酸盐的高级氧化过程中面向反应的碳催化剂的合理设计原则。
