Investigations of HKUST-1 exposed to water vapor, methanol and pyridine atmospheres by near-ambient pressure XPS

  • Metal-organic frameworks (MOFs) are suitable materials for gas storage of small molecules due to their nanoporous, crystalline structure. The extensively studied MOF HKUST-1 consist of Cu(II)-dimers in a paddlewheel structure, with 1,3,5-benzenetricarboxylic acid (BTC) as organic linker. Instability to humidity remains an issue for many types of MOFs, and for HKUST-1, it has been found that exposure to water vapor creates a surface barrier which reduces the gas uptake rate. Near-ambient pressure XPS (NAP-XPS) is a promising method for investigations of the stability and interaction of HKUST-1 with various gas molecules. The oxidation state of copper can be monitored before, during and after exposure to various gases. This does not only provide information on the stability of the MOFs, but also on the interaction with the gas molecules. NAP-XPS measurements of HKUST-1 exposed to methanol, pyridine and water vapor were performed with EnviroESCA, a laboratory NAP-XPS instrumentMetal-organic frameworks (MOFs) are suitable materials for gas storage of small molecules due to their nanoporous, crystalline structure. The extensively studied MOF HKUST-1 consist of Cu(II)-dimers in a paddlewheel structure, with 1,3,5-benzenetricarboxylic acid (BTC) as organic linker. Instability to humidity remains an issue for many types of MOFs, and for HKUST-1, it has been found that exposure to water vapor creates a surface barrier which reduces the gas uptake rate. Near-ambient pressure XPS (NAP-XPS) is a promising method for investigations of the stability and interaction of HKUST-1 with various gas molecules. The oxidation state of copper can be monitored before, during and after exposure to various gases. This does not only provide information on the stability of the MOFs, but also on the interaction with the gas molecules. NAP-XPS measurements of HKUST-1 exposed to methanol, pyridine and water vapor were performed with EnviroESCA, a laboratory NAP-XPS instrument developed by SPECS. Cu 2p, O 1s and C 1s core level spectra and Cu LMM Auger spectra were acquired at pressures ranging from high vacuum to 4 mbar to assess the oxidation state of copper and the stability of the organic linker. Reference measurements in argon atmosphere were conducted in order to have reference spectra with similar full width of half maxima (FHWM) as the spectra measured in reactive atmospheres. Peak fit analysis of the Cu 2p3/2 core level spectra shows that, as expected, the photoelectron signal mainly originates from Cu(II) species. The contribution from Cu(I) is negligible for samples exposed to argon and methanol, but approximately 4% for samples exposed to water vapor and 8% for samples exposed to pyridine. Within the error of the peak fit analysis, there are no changes in relative Cu(II) percentage with increasing water, methanol or pyridine exposure time pointing to saturation reached already at the lowest time of exposure.zeige mehrzeige weniger

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Autor*innen:Marit Kjaervik
Koautor*innen:P. Dietrich, A. Thissen, A. Nefedov, C. Natzeck, C. Wöll, Wolfgang Unger
Dokumenttyp:Vortrag
Veröffentlichungsform:Präsentation
Sprache:Englisch
Jahr der Erstveröffentlichung:2019
Organisationseinheit der BAM:6 Materialchemie
6 Materialchemie / 6.1 Oberflächen- und Dünnschichtanalyse
DDC-Klassifikation:Naturwissenschaften und Mathematik / Chemie / Analytische Chemie
Freie Schlagwörter:HKUST-1; MOF; NAP-XPS; XPS
Themenfelder/Aktivitätsfelder der BAM:Chemie und Prozesstechnik
Veranstaltung:Seminar X-Ray and Electron Spectroscopy at Interfaces group: Chemistry of oxydic and organic interfaces
Veranstaltungsort:Karlsruhe, Germany
Beginndatum der Veranstaltung:11.10.2019
Verfügbarkeit des Dokuments:Datei im Netzwerk der BAM verfügbar ("Closed Access")
Datum der Freischaltung:24.10.2019
Referierte Publikation:Nein
Eingeladener Vortrag:Nein
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