Catching the Reversible Formation and Reactivity of Surface Defective Sites in Metal–Organic Frameworks: An Operando Ambient Pressure-NEXAFS Investigation,The Journal of Physical Chemistry Letters

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Catching the Reversible Formation and Reactivity of Surface Defective Sites in Metal–Organic Frameworks: An Operando Ambient Pressure-NEXAFS Investigation
The Journal of Physical Chemistry Letters ( IF 4.8 ) Pub Date : 2021-09-16 , DOI: 10.1021/acs.jpclett.1c02585
Luca Braglia ₁ , Francesco Tavani ₂ , Silvia Mauri ₁ , Raju Edla _{1,

3} , Damjan Krizmancic ₁ , Alessandro Tofoni ₂ , Valentina Colombo ₄ , Paola D'Angelo ₂ , Piero Torelli ₁

Affiliation

In this work, we apply for the first time ambient pressure operando soft X-ray absorption spectroscopy (XAS) to investigate the location, structural properties, and reactivity of the defective sites present in the prototypical metal–organic framework HKUST-1. We obtained direct evidence that Cu⁺ defective sites form upon temperature treatment of the powdered form of HKUST-1 at 160 °C and that they are largely distributed on the material surface. Further, a thorough structural characterization of the Cu⁺/Cu²⁺ dimeric complexes arising from the temperature-induced dehydration/decarboxylation of the pristine Cu²⁺/Cu²⁺ paddlewheel units is reported. In addition to characterizing the surface defects, we demonstrate that CO₂ may be reversibly adsorbed and desorbed from the surface defective Cu⁺/Cu²⁺ sites. These findings show that ambient pressure soft-XAS, combined with state-of-the-art theoretical calculations, allowed us to shed light on the mechanism involving the decarboxylation of the paddlewheel units on the surface to yield Cu⁺/Cu²⁺ complexes and their reversible restoration upon exposure to gaseous CO_2.

中文翻译：

捕捉金属-有机框架中表面缺陷位点的可逆形成和反应性：操作环境压力-NEXAFS 调查

在这项工作中，我们首次应用环境压力操作软 X 射线吸收光谱 (XAS) 来研究原型金属有机框架 HKUST-1 中存在的缺陷位点的位置、结构特性和反应性。我们获得了直接证据，表明在 160 °C 对 HKUST-1 粉末形式进行温度处理后会形成 Cu ⁺缺陷位点，并且它们主要分布在材料表面上。此外，由温度诱导的原始 Cu ²⁺ /Cu ^{2+的脱水/脱羧产生的 Cu}⁺ /Cu ²⁺二聚体配合物的全面结构表征报告了桨轮单元。除了表征表面缺陷外，我们还证明了 CO ₂可以从表面缺陷的 Cu ⁺ /Cu ²⁺位点可逆地吸附和解吸。这些发现表明，环境压力 soft-XAS 与最先进的理论计算相结合，使我们能够阐明涉及表面桨轮单元脱羧生成 Cu ⁺ /Cu ²⁺配合物和它们在暴露于气态 CO _{2 后可逆地恢复。}

更新日期：2021-09-23

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