Kim Jongsik, Choe Yun Jeong, Kim Sang Hoon, Choi In-Suk, Jeong Keunhong
Extreme Materials Research Center, Korea Institute of Science and Technology, Seoul 02792, South Korea.
Department of Materials Science and Engineering, Seoul National University, Seoul 08826, South Korea.
JACS Au. 2021 Jun 23;1(8):1158-1177. doi: 10.1021/jacsau.1c00124. eCollection 2021 Aug 23.
NO can compete with omnipotent OH/SO in decomposing aqueous pollutants because of its lengthy lifespan and significant tolerance to background scavengers present in HO matrices, albeit with moderate oxidizing power. The generation of NO , however, is of grand demand due to the need of NO /O, radioactive element, or NaNO/HNO in the presence of highly energized electron/light. This study has pioneered a singular pathway used to radicalize surface NO functionalities anchored on polymorphic α-/γ-MnO surfaces (α-/γ-MnO-N), in which Lewis acidic Mn and NO served to form OH via HO dissection and NO via radical transfer from OH to NO (OH → NO ), respectively. The elementary steps proposed for the OH → NO route could be energetically favorable and marginal except for two stages such as endothermic OH desorption and exothermic OH-mediated NO radicalization, as verified by EPR spectroscopy experiments and DFT calculations. The Lewis acidic strength of the Mn species innate to α-MnO-N was the smallest among those inherent to α-/β-/γ-MnO and α-/γ-MnO-N. Hence, α-MnO-N prompted the rate-determining stage of the OH → NO route (OH desorption) in the most efficient manner, as also evidenced by the analysis on the energy barrier required to proceed with the OH → NO route. Meanwhile, XANES and DRIFT spectroscopy experiments corroborated that α-MnO-N provided a larger concentration of surface NO species with -dentate binding arrays than γ-MnO-N. Hence, α-MnO-N could outperform γ-MnO-N in improving the collision frequency between OH and NO species and in facilitating the exothermic transition of NO functionalities to surface NO analogues per unit time. These were corroborated by a greater efficiency of α-MnO-N in decomposing phenol, in addition to scavenging/filtration control runs and DFT calculations. Importantly, supported NO species provided 5-7-fold greater efficiency in degrading textile wastewater than conventional OH and supported SO analogues we discovered previously.
由于其较长的寿命以及对羟基自由基（HO）基质中存在的背景清除剂具有显著耐受性，尽管其氧化能力适中，但一氧化氮（NO）在分解水中污染物方面无法与全能的羟基自由基（OH）/硫酸根自由基（SO）竞争。然而，由于在高能电子/光存在的情况下需要一氧化氮（NO）/氧气（O）、放射性元素或亚硝酸钠（NaNO）/硝酸（HNO），一氧化氮（NO）的产生具有巨大需求。本研究开创了一条独特的途径，用于使锚定在多晶α-/γ-二氧化锰表面（α-/γ-MnO-N）的表面一氧化氮（NO）官能团自由基化，其中路易斯酸性的锰（Mn）和一氧化氮（NO）分别通过羟基自由基（HO）分解形成羟基自由基（OH）以及通过羟基自由基（OH）向一氧化氮（NO）的自由基转移形成二氧化氮自由基（NO）（OH→NO）。电子顺磁共振（EPR）光谱实验和密度泛函理论（DFT）计算证实，除了吸热的羟基自由基（OH）解吸和放热的羟基自由基（OH）介导的一氧化氮（NO）自由基化这两个阶段外，为OH→NO途径提出的基本步骤在能量上可能是有利的且处于边缘状态。在α-/β-/γ-二氧化锰和α-/γ-二氧化锰-N所固有的锰物种中，α-二氧化锰-N所固有的路易斯酸性强度最小。因此，α-二氧化锰-N以最有效的方式促进了OH→NO途径的速率决定阶段（OH解吸），这也通过对OH→NO途径所需能垒的分析得到了证明。同时，X射线吸收近边结构（XANES）和漫反射红外傅里叶变换光谱（DRIFT）实验证实，与γ-二氧化锰-N相比，α-二氧化锰-N提供了更大浓度的具有双齿结合阵列的表面一氧化氮（NO）物种。因此，在提高羟基自由基（OH）和一氧化氮（NO）物种之间的碰撞频率以及促进单位时间内一氧化氮（NO）官能团向表面二氧化氮（NO）类似物的放热转变方面，α-二氧化锰-N可能优于γ-二氧化锰-N。除了清除/过滤对照实验和DFT计算外，可以分解苯酚的α-二氧化锰-N具有更高的效率，这证实了上述结论。重要的是，负载的一氧化氮（NO）物种在降解纺织废水方面的效率比我们之前发现的传统羟基自由基（OH）和负载的硫酸根自由基（SO）类似物高5 - 7倍。
