Time-Resolved In Situ Liquid-Phase Atomic Force Microscopy and Infrared Nanospectroscopy during the Formation of Metal–Organic Framework Thin Films

et al. 2018

ChemPhysChem

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Bridging the gap in studying surface reactions, processes, and morphology and measuring at (catalytic) relevant conditions is crucial for our understanding of the working principles of porous crystalline materials. Scanning tunneling microscopy is limited because of the required conductivity of the sample, whereas atomic force microscopy (AFM) is often challenging in use owing to the physical mechanism underlying the technique. Herein, we report a tailor-made autoclave-inserted AFM, able to measure at ∼20 bar and ∼110 °C. First, we show the ability to obtain nanometer resolution on well-defined test samples at before-mentioned conditions. Second, to demonstrate the possibilities of analyzing morphological evolutions at elevated temperatures and pressures, we use this setup to measure the stability of a surface-anchored metal-organic framework (SURMOF) in-situ at pressures of 1-20 bar in the temperature range between 20 and 60 °C. It was found that the showcase HKUST-1 material has a good physical stability, as it is hardly damaged from exposure to pressures up to 20 bar. However, its thermal stability is weaker, as exposure to elevated T damaged the material by influencing the interaction between organic linker and metal cluster. In-situ measurements at elevated T also showed an increased mobility of the material when working at such conditions. Combining the strength of AFM at elevated T and p with ex-situ AFM and spectroscopic measurements on this MOF showcases an example of how porous materials can be studied at (industrially) relevant conditions using the autoclave-inserted AFM.

Section: Resultssupporting

confidence: 88%

Section: Resultsmentioning

confidence: 59%

Behavior of a Metal Organic Framework Thin‐Film at Elevated Temperature and Pressure as Studied with an Autoclave‐Inserted Atomic Force Microscope

Brand

et al. 2018

ChemPhysChem

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“…Thick MOF films are often dense, hence we have synthesized nanowebs at 500, 1000, 2000, 3000 and 5500 rpm with 30 deposition cycles to highlight the change in morphology,F igure 4a.S imilara sf or the thickerc oatings described before,t he nanoweb formed at 550 rpm is showing distinct HKUST-1f eatures, similart oaf ilm made with the DS synthesis approach. [19] The nanowebs show longera nd thinner fibers when the rotations peed is increased, notably ! 3000 rpm as is highlighted in Figure 4b,l eading to higher surfacea reas/volume( Figure S8 a, Supporting Information).…”

Section: Resultsmentioning

confidence: 98%

“…In our earlier work, we have reported the growth mechanism and mode of the HKUST-1 thin-films synthesized by al ayer-bylayer (LbL) andadirect synthesis (DS) approach. [19,20] Although the LbL synthesis is faster (hours to days) than the DS (days to weeks),t he amount of time necessary to grow thickl ayers, suitable for membrane catalysis, is not practical. In this work, we use am ethod according to whicht he precursors are mixed and spin-coated on the SAM-Aus ubstrate (Figure 1).…”

Section: Resultsmentioning

confidence: 99%

“…[22,23] As shown in our earlier work, AFM-IR microscopy can easily identify Cu-BTC bands ande ven provide information on the coordination of the Cu 2 + ions to the linker. [19,20] ToF-SIMS is av ersatile technique used in ab road range of materials. Its ability to detect metal-organic fragments directly, makes it ap owerful tool in SURMOF research.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Nanoweb Surface‐Mounted Metal–Organic Framework Films with Tunable Amounts of Acid Sites as Tailored Catalysts

Rivera‐Torrente

et al. 2019

Chemistry A European J

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Metal-organic frameworks (MOFs) are ap romising class of materials form any applications, due to their high chemical tunability and superb porosity.B yg rowing MOFs as (thin-)films, additional properties and potentiala pplications 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)w as determined that resulted in chemically homogeneous, pure nanowebs. Furthermore, the morphology and (un)coordinated Cu sites in the web were tuned by varyingt he rotation speed of the spin-coating process. X-ray diffraction (XRD) analysis showed that ro-tation speeds ! 2000 rpm (with precursors in aw ater/ethanol solution) generatet he catena-triaqua-m-(1,3,5-benzenetricarboxylate)-copper(II), or Cu(BTC)(H 2 O) 3 coordinationp olymer.X -ray photoelectrons pectroscopy (XPS) highlighted the strongd ecrease in number of (defective) Cu + sites, as the nanowebs mainly consist of coordinated Cu 2 + Lewis acid sites (LAS) and organic linker-linker,f or example, hydrogenbonding, interactions. Finally, the Lewis-acidic character of the Cu sites is illustrated by testing the films as catalysts in the isomerization of a-pineneo xide. The highern umber of LAS (! 3000 rpm), result in higher campholenic aldehyde selectivity reachingu pt o87.7 %. Furthermore, the strength of ac ombined micro-and spectroscopica pproach in understandingt he nature of MOF thin-films in as patially resolved manner is highlighted.[a] L.

The Growth of Metal–Organic Framework Films on Calcium Fluoride and Their Interaction With Reactive Molecules

Jabbour

Nikolopoulos

et al. 2022

Adv Materials Inter

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Within this context, attention is going toward MOF thin films, which are gaining even bigger interest nowadays because they broaden the application window of MOFs, such as in the use of monolithic MOF membranes in gas permeation experiments, electrochemical energy storage or catalytically active coatings. [2][3][4] Being able to control the morphology is very important to fine-tune the material toward specific applications. Some reported work already highlights the great advantage of, for example, monolithic-catalyst membranes over their powder form. [5] Typically, MOF (thin) films are anchored on a supportive substrate to yield a surface-anchored MOF (SURMOF) instead of a self-supportive membrane. The type of substrate has a strong influence on the resulting morphology and defective nature of the SURMOF. [3] Whilst some substrates (e.g., metal oxides) can act as anchor points to grow the MOF material from the solution, other substrates require a pretreatment step with an organic compound to bind the initial nuclei to the surface. These compounds are often applied as self-assembled monolayers (SAMs). By varying the anchoring groups of the SAM, different orientational growth of the same MOF can be observed. [6,7] MOF thin films can be prepared by a wide range of synthesis methods and conceptual approaches. [3,8,9] The most straightforward method involves a direct synthesis (DS) through a solvothermal process, where the substrate is incubated along with the reaction mixture. [10] Spin coating techniques (SCT), [11,12] dip coating and layer-by-layer (LbL), or liquid epitaxy deposition, are indirect synthesis techniques that require multiple repetitive steps, the so-called cycles. [13][14][15] The latter method has been explored to produce SURMOFs with low surface roughness and a low amount of defects. However, every MOF requires a specific set of synthesis parameters to result in homogeneous closed films of crystalline SURMOFs due to the specific chemistry of each ligand-metal-solvent-substrate combination. Some MOFs can grow at room temperature, such as HKUST-1, while Spectroscopy on metal-organic framework (MOF) films and the molecular phenomena associated to them is mostly limited to grazing incidence methods. To allow for transmission-based characterization and highlight the applicability of MOFs on transparent substrates, UiO-67, UU-1, and ZIF-8 MOFs are synthesized on CaF 2 windows. It is revealed that the growth of the UiO-67 MOF follows a Volmer-Weber mechanism using scanning electron microscopy (SEM). This growth is assisted by growing seeds in solution, which anchor on the film and become part of the intergrown film itself. UU-1, a copper-based MOF, is formed after spin coating the Cu-BTC precursors, showing its characteristic fiber-like morphology and resulting inter-fiber macroporosity. ZIF-8 is formed using a "flash"-synthesis, and it is shown that this approach resembles a Volmer-Weber growth mode as well. Last, CO probe molecule adsorption FT-IR spectroscopy is utilized to study the effect of methanol...