Metal–Organic Frameworks (MOFs) are nanostructured porous materials made up by metal cations and organic linkers forming three-dimensional structures. Since their discovery, the local properties of metal centers in MOFs have often been studied with hard X-ray absorption spectroscopy that is not a surface sensitive technique. Here, we employ the ambient-pressure soft X-ray absorption spectroscopy, using a newly developed experimental setup, to unveil the formation mechanism of surface defective sites in the prototypical Cu(II)- based MOF HKUST-1, as well as the reactivity and selectivity of these sites towards CO2 from the analysis of the Cu L3 -edge near edge X-ray absorption spectroscopy (NEXAFS) data. We observe that, upon thermal heating, Cu(I) defects are formed more abundantly on the surface of the material as compared to the bulk, a process that is almost fully reversed when the MOF is exposed to CO2 , even when mixed with H2 . Additionally, we propose a structure and a formation mechanism for such defective sites, supported by theoretical DFT-based calculations.
Insights into structure and reactivity of MOFs by ambient pressure soft X-ray absorption spectroscopy / Tofoni, Alessandro; Tavani, Francesco; Braglia, Luca; Colombo, Valentina; Torelli, Piero; D’Angelo, Paola. - In: RADIATION PHYSICS AND CHEMISTRY. - ISSN 0969-806X. - 213:(2023), p. 111243. [10.1016/j.radphyschem.2023.111243]
Insights into structure and reactivity of MOFs by ambient pressure soft X-ray absorption spectroscopy
Alessandro Tofoni;Francesco Tavani;Piero Torelli;Paola D’Angelo
2023
Abstract
Metal–Organic Frameworks (MOFs) are nanostructured porous materials made up by metal cations and organic linkers forming three-dimensional structures. Since their discovery, the local properties of metal centers in MOFs have often been studied with hard X-ray absorption spectroscopy that is not a surface sensitive technique. Here, we employ the ambient-pressure soft X-ray absorption spectroscopy, using a newly developed experimental setup, to unveil the formation mechanism of surface defective sites in the prototypical Cu(II)- based MOF HKUST-1, as well as the reactivity and selectivity of these sites towards CO2 from the analysis of the Cu L3 -edge near edge X-ray absorption spectroscopy (NEXAFS) data. We observe that, upon thermal heating, Cu(I) defects are formed more abundantly on the surface of the material as compared to the bulk, a process that is almost fully reversed when the MOF is exposed to CO2 , even when mixed with H2 . Additionally, we propose a structure and a formation mechanism for such defective sites, supported by theoretical DFT-based calculations.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.