期刊
JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA
卷 247, 期 -, 页码 -出版社
ELSEVIER
DOI: 10.1016/j.elspec.2020.147042
关键词
Near-ambient pressure X-ray photoelectron spectroscopy; Metal-organic frameworks; HKUST-1; Interaction with atmospheres; Water; Methanol; Pyridine; Chemical state of copper
类别
资金
- BAM
- Helmholtz Association
Surface-supported metal-organic frameworks HKUST-1 were used to develop a near ambient pressure XPS approach to investigate interaction with water, methanol, and pyridine atmospheres. The peak shapes in the photoelectron spectra were found to depend on charge compensation efficiency, with reduced copper observed when exposed to water vapor and pyridine. Stern support was found for saturation of Cu(II) percentage with increasing exposure time, and ongoing work aims to elucidate the mechanism of Cu(II) reduction to Cu(I) mediated by water and pyridine in HKUST-1.
Surface-supported metal-organic frameworks HKUST-1 (Hong Kong University of Science and Technology) were used as a model system for a development of a near ambient pressure (NAP) XPS based approach to investigate interaction with atmospheres of water, methanol or pyridine at pressures ranging from 1 to 4 mbar. The films were grown on a gold substrate functionalized with a COOH-terminated self-assembled monolayer using liquidphase epitaxy in a step-by-step fashion. Measurement protocols were developed and optimised for different gases in order to obtain spectra of similar quality in terms of signal intensity, noise and shape. Peak shapes were found to depend on the efficiency of charge compensation. Reference measurements in argon proved to be a useful strategy not only for the evaluation of the Cu(II)-fraction in pristine samples, but also to identify the contributions by the respective gas atmosphere to the C 1s and O 1s photoelectron spectra. Reduced copper was found during the exposition of HKUST-1 to water vapour and pyridine, but this effect was not observed in case of methanol. Additionally, it was established that there are no changes in relative Cu(II) percentage with increasing exposure time. This indicates that saturation was reached already at the lowest time of gas exposure. A detailed elucidation of the mechanism of Cu(II) reduction to Cu(I) in HKUST-1 mediated by water and pyridine is part of ongoing work and not in the scope of the present paper.
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