In Operando Spectroscopic Ellipsometry Investigation of MOF Thin Films for the Selective Capture of Acetic Acid

Abstract

The emission of polar volatile organic compounds (VOCs) is a major worldwide concern of air quality and equally impacts the preservation of cultural heritage (CH). The challenge is to design highly efficient adsorbents able to selectively capture traces of VOCs such as acetic acid (AA) in the presence of relative humidity (RH) normally found at storage in museums (40−80%). Although the selective capture of VOCs over water is still challenging, metal−organic frameworks (MOFs) possess highly tunable features (Lewis, Bronsted, or redox metal sites, functional groups, hydrophobicity, etc.) suitable to selectively capture a large variety of VOCs. In this context, we have explored the adsorption efficiency of a series of MOFs thin films (ZIF-8(Zn), MIL-101(Cr), and UiO-66(Zr)-2CF 3 ) for the selective capture of AA based on a UV/vis and FT-IR spectroscopic ellipsometry in operando study (2−6% of relative pressure of AA under 40% of RH), namely conditions close to the realistic environmental storage conditions of cultural artifacts. For that purpose, optical quality thin films of MOFs were prepared by dip-coating, and their AA adsorption capacity and selectivity were evaluated under humid conditions by measuring the variation of the refractive index as a function of the vapor pressures while the chemical nature of the coadsorbed analytes (water and AA) was identified by FT-IR ellipsometry. While thin films of ZIF-8(Zn) strongly degraded upon exposure to AA/water vapors, films of MIL-101(Cr) and UiO-66(Zr)-2CF 3 present a high chemical stability under those conditions. It was shown that MIL-101(Cr) presents a high AA adsorption capacity due to its high pore volume but exhibits a poor AA adsorption selectivity under humid conditions. In contrast, UiO-66(Zr)-2CF 3 was shown to overpass MIL-101(Cr) in terms of AA/ H 2 O adsorption selectivity and AA adsorption/desorption cycling stability because of its high hydrophobic character, suitable pore size for adequate confinement, and specific interactions.

Effect of Ligand Aromaticity on Cyclohexane and Benzene Sorption in IRMOFs: A Computational Study

“…This research work underlines the significant contribution of palladium to the preferential adsorption of benzene and highlights the potential of Pd-based MOFs for the selective capture of aromatics. Furthermore, as evidenced previously, functionalization of the ligand can also significantly modify the sorption properties of MOFs. − For instance, UiO-66-(CF 3 ) 2 bearing perfluorinated groups on terephthalate ligands exhibits higher hydrophobicity than its isostructural parent (UiO-66­(Zr)) and concomitantly interacts strongly with different VOCs, making this MOF greatly interesting for their selective capture in humid conditions. , Finally, thanks to the fine adjustment of the length of the ligand, one can also precisely control the size of pore aperture inducing either molecular sieving or/and host–guest interactions enhanced by the confinement effect …”

“…25−27 For instance, UiO-66-(CF 3 ) 2 bearing perfluorinated groups on terephthalate ligands exhibits higher hydrophobicity than its isostructural parent (UiO-66(Zr)) and concomitantly interacts strongly with different VOCs, 25 making this MOF greatly interesting for their selective capture in humid conditions. 26,27 Finally, thanks to the fine adjustment of the length of the ligand, one can also precisely control the size of pore aperture inducing either molecular sieving 28 or/and host−guest interactions enhanced by the confinement effect. 26 Compared to these aforementioned widely studied tunable characteristics, the impact of ligand aromaticity is rarely explored parameter in literature for VOC removal by MOFs.…”

Monitoring the Electrochemical Failure of Indium Tin Oxide Electrodes via Operando Ellipsometry Complemented by Electron Microscopy and Spectroscopy

“…Monitoring of electrochemical processes can be obtained by so-called operando approaches. Such methods are established in electrocatalysis, battery, and bioelectrochemistry research, and they describe the spectroscopic or microscopic monitoring of electrochemical processes under operational conditions. − Among them, spectroelectrochemistry relies on the optical transparency of the working electrode, and with the implementation of ITO electrodes, this method was commenced to study redox-active proteins about 60 years ago . Up to now, the operando combination of electrochemistry and spectroscopic ellipsometry is rather rarely applied, possibly due to the challenges of optical modeling and the limitations of continuous and reasonably smooth layers. − Nonetheless, ellipsometry is a powerful tool to obtain both the dielectric optical response function (i.e., complex refractive index) of thin films as well as the electric properties for Drude-like behavior, which apply well to ITO thin films. − Furthermore, ellipsometry is a sensitive probe to monitor the adsorption of ultrathin layers at solid–liquid interfaces such as self-assembled monolayers and biomolecules. − Even specific immobilization of biomolecules and cells at functionalized hybrid interfaces for biosensing purposes can be traced. − More specifically, operando ellipsometry allows to study reversible ion intercalation processes upon electrochemical cycling in battery-related research. − For spatially resolved investigation, operando imaging ellipsometry is an emerging probe for battery electrodes, and it provides insights by monitoring the local change of ellipsometric parameters at selected wavelengths. , …”

In Situ Infrared and UV–Vis Ellipsometries to Probe The Varnish Ageing and Swelling of G. Bellini “Transfiguration”

“…[ 14 ] have set up ellipsometric devices to study the swelling of thin polymer films. In addition, current advances in infrared ellipsometry [ 15 ] open up new possibilities to highlight chemical changes at play.…”

“…[12] Far from the field of cultural heritage, several teams such as Papanu et al [13] or Ogieglo et al [14] have set up ellipsometric devices to study the swelling of thin polymer films. In addition, current advances in infrared ellipsometry [15] open up new possibilities to highlight chemical changes at play.…”