Nanoweb Surface‐Mounted Metal–Organic Framework Films with Tunable Amounts of Acid Sites as Tailored Catalysts. Issue 3 (13th December 2019)

• Record Type: Journal Article
• Authors: Mandemaker, Laurens D. B.; Rivera‐Torrente, Miguel; Delen, Guusje; Hofmann, Jan P.; Lorenz, Matthias; Belianinov, Alex; Weckhuysen, Bert M.
• Is Part Of: Chemistry. Volume 26:Issue 3(2020)
• Page Start: 691
• Page End: 698
• Publication Date: 2019-12-13
• Subjects: AFM-IR -- metal–organic frameworks -- nanoweb -- thin films -- ToF-SIMS; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201903761
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: Metal–organic frameworks (MOFs) are a promising class of materials for many applications, due to their high chemical tunability and superb porosity. By growing MOFs as (thin‐)films, additional properties and potential applications become available. Here, copper (II) 1, 3, 5‐benzenetricarboxylate (Cu‐BTC) metal–organic framework (MOF) thin‐films are reported, which were synthesized by spin‐coating, resulting in "nanowebs", that is, fiber‐like structures. These surface‐mounted MOFs (SURMOFs) were studied by using photoinduced force microscopy (PiFM) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). The optimal concentration of precursors (10 mm ) was determined that resulted in chemically homogeneous, pure nanowebs. Furthermore, the morphology and (un)coordinated Cu sites in the web were tuned by varying the rotation speed of the spin‐coating process. X‐ray diffraction (XRD) analysis showed that rotation speeds ≥2000 rpm (with precursors in a water/ethanol solution) generate the catena‐triaqua‐μ‐(1, 3, 5‐benzenetricarboxylate)‐copper(II), or Cu(BTC)(H2 O)3 coordination polymer. X‐ray photoelectron spectroscopy (XPS) highlighted the strong decrease in number of (defective) Cu + sites, as the nanowebs mainly consist of coordinated Cu 2+ Lewis acid sites (LAS) and organic linker–linker, for example, hydrogen‐bonding, interactions. Finally, the Lewis‐acidic character of the Cu sites is illustrated by testing the films as catalysts in the isomerization of α‐pinene oxide. The higher number of LAS (≥3000 rpm), result in higher campholenic aldehyde selectivity reaching up to 87.7 %. Furthermore, the strength of a combined micro‐ and spectroscopic approach in understanding the nature of MOF thin‐films in a spatially resolved manner is highlighted. Abstract : Nanoweb coatings : Metal–organic framework (MOF) coatings show great promise in gas sorption or catalytic applications. In this work, nanoweb coatings were shown to form when a spin‐coating approach was used. By using micro‐ and spectroscopic toolboxes, these coatings were shown to have higher surface areas and higher amounts of Lewis acid sites. When used as catalysts in the isomerization of α‐pinene oxide, the webs showed a higher conversion and campholenic aldehyde selectivity.