在金属-有机框架上产生环境持久性自由基,Langmuir

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在金属-有机框架上产生环境持久性自由基
Langmuir ( IF 3.7 ) Pub Date : 2022-03-04 , DOI: 10.1021/acs.langmuir.1c03491
Yuqing Ye ₁ , Yuan Li ₁ , Jie Wang ₁ , Shuai Yuan ₁ , Xiaojun Xu ₁ , Xinning Zhang ₁ , Junwen Zhou ₁ , Bo Wang ₁ , Xiaojie Ma ₁

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环境持久性自由基（EPFRs）已被公认为具有生物毒性、环境持久性和全球流动性的重要新兴污染物之一。以前的研究已经确定了表面金属氧化物在 EPFRs 形成中的催化作用，并通过研究各种金属氧化物纳米颗粒和单晶来说明 EPFRs 的金属依赖性。然而，从金属位点的角度对 EPFRs 的形成仍缺乏了解。金属氧化物的各种因素（例如，结晶相和表面物种）被认为有助于产生 EPFR，这给科学家们梳理金属类型的影响带来了巨大的困难。在此，一项实验室研究，就金属阳离子的酸度和氧化强度而言，通过选择金属可变等结构金属有机框架作为材料平台来进行。具体来说，我们在热条件下评估了氯取代苯酚蒸气和邻苯二酚在 MIL-100(M) (M = Al、Cr、Fe) 上产生的 EPFR。发现金属位点的高路易斯酸度对于捕获上述两种酚类前体、激活 O-H 键和促进 EPFRs 形成至关重要。在富含 5 倍配位铝的 MIL-100 上生成半衰期长达 70 天的自由基物种发现金属位点的高路易斯酸度对于捕获上述两种酚类前体、激活 O-H 键和促进 EPFRs 形成至关重要。在富含 5 倍配位铝的 MIL-100 上生成半衰期长达 70 天的自由基物种发现金属位点的高路易斯酸度对于捕获上述两种酚类前体、激活 O-H 键和促进 EPFRs 形成至关重要。在富含 5 倍配位铝的 MIL-100 上生成半衰期长达 70 天的自由基物种^{3 个以上}的网站。通过使用²⁷ Al 固态核磁共振光谱进一步证实了未配对的电子自旋密度捐赠。尽管它们比Al ³⁺具有更高的氧化能力，但暴露的Cr ³⁺和Fe ³⁺位点由于路易斯酸度不足而对EPFRs的形成表现出不可检测的催化活性。我们的结果表明，表面物质而不是路易斯酸位点可能是在 Fe ₂ O ₃等金属氧化物上形成 EPFR 的主要因素。

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Generation of Environmentally Persistent Free Radicals on Metal–Organic Frameworks

Environmentally persistent free radicals (EPFRs) have been recognized as one of the important emerging contaminants with biological toxicity, environmental persistence, and global mobility. Previous studies have identified the catalytic role of surface metal oxides in EPFRs formation and illustrated the metal-dependence of EPFRs by studying on various metal oxide nanoparticles and single crystals. However, there is still lack of an understanding on the formation of EPFRs from the point of view of metal sites. Various factors (e.g., crystalline phases and surface species) of metal oxides are regarded to contribute to the generation of EPFRs, which present profound difficulties for scientists to tease apart the impact of metal type. Herein, a laboratory investigation, in terms of the acidity and oxidation strength of metal cations, was conducted by selecting metal-variable isostructural metal–organic frameworks as material platforms. Specifically, we evaluated EPFRs generation on MIL-100(M) (M = Al, Cr, Fe) from chlorine-substituted phenol vapor and catechol under thermal conditions. It is found that high Lewis acidity of metal sites is crucial for capturing the above two phenolic precursors, activating the O–H bond and promoting EPFRs formation. Radical species with half-life as long as 70 days were generated on MIL-100 rich in 5-fold coordinated Al³⁺ sites. The unpaired electron spin density donation was further confirmed by using ²⁷Al solid-state nuclear magnetic resonance spectroscopy. Despite their higher oxidation power than Al³⁺, the exposed Cr³⁺ and Fe³⁺ sites show undetectable catalytic activity for the formation of EPFRs, because of their insufficient Lewis acidity. Our results suggest that the surface species rather than Lewis acid sites may be a major contributor to the formation of EPFRs on metal oxides like Fe₂O₃.

更新日期：2022-03-04

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