Detection of adsorbates on emissive MOF surfaces with X-ray photoelectron spectroscopy

Abstract

The luminescence of azobenzene chromophore struts in a metal organic framework is quenched by nitroaromatic guests. X-ray photoelectron spectroscopic methods verify the emission changes are due to the surface adsorption of the guest molecules rather than encapsulation.

An X-ray Photoelectron Spectroscopy Study of Postsynthetic Exchange in UiO-66

“…Instead, ball-milling and argon bombardment were utilized. We did not observe additional peaks due to sample charging, which has been reported for other MOFs, 35 but did observe linearly offset peak positions (typically 0 to +2 eV) that could be adjusted for by setting the C 1s peak position to 284.8 eV, likely due to minor steady-state sample charging. All MOF-related elements in a given spectrum were then shifted accordingly in a linear fashion, allowing for a more consistent relative comparison across spectra.…”

“…While XPS has demonstrated some utility in the analysis of MOFs, it has yet to be used to explicitly study the PSE process. XPS studies of MOFs to date include its use in the identification of surface species, modifications and adsorbates, ,, and the presence of metal particles, , metal SBUs, and their related oxidation states at the surfaces of MOF films and particles. , With the judicious employment of controls, XPS can be a powerful tool for revealing the relative linker distribution from the particle surface to the interior, even for particles on the nanometer scale, and can uncover chemical differences in PSE and direct synthesis products.…”

The surface chemistry of metal–organic frameworks and their applications

“…Application of new characterization techniques is also allowing the influence of surface chemistry on other potential applications to begin to emerge; Burdette et al have used X-ray photoelectron spectroscopy to show that binding of analytes on the surfaces of emissive MOFs is enough to completely quench their fluorescence, casting doubt on the proposed sensing mechanisms, based on bulk analyte intercalation, of a number of MOF materials. 50 It is clear that modifying the surfaces of MOFs is a powerful protocol for exacting control over bulk physical properties, and a large number of potential applications are beginning to be realized as innovative protocols to control and visualize surface chemistry continue to be developed.…”

Identifying chemical and physical changes in wide-gap semiconductors using real-time and near ambient-pressure XPS

“…2,3 With these assumptions, the binding energy can be used quantitatively to infer the surface chemistry of metal surfaces, for example identifying alloy composition, 4 oxidation 5 and adsorbates. 6 The reproducibility of clean, inert metal surfaces has led to their extensive use for the study of surface reactions and for thin film growth. Advances in instrumentation, in particular the efficiency of electron detectors, is now enabling real-time and in-operando measurements of these surface processes.…”