Following the proof-of-concept work on the chemical vapor deposition of metal-organic frameworks (MOF-CVD) and a demonstration of its potential in microelectronics integration, we now present the fully cleanroom-compatible process for the deposition of large-area MOFs. Led by Alex, the output of this international collaboration was recently published in Chemistry of Materials. In this work, we thoroughly discussed the optimization process and unraveled the mechanism of MOF-CVD which led to a process chart—a guiding paradigm in developing future MOF-CVD formulations.
This marks an important milestone in bringing MOFs a step closer to the industrial-scale microfabrication lines and the production of MOF-based devices.
Although generally stable, ZIFs can undergo post‐synthetic linker exchange (PSLE) in solution under mild conditions. In this work, Joao led an international team of researchers and reported this novel, solvent‐free approach to post‐synthetic linker exchange through exposure to linker vapor. The paper can be accessed here or on the Publications page of our website.
Collaborative work on the role of structural defects in the adsorption and separation of C3 hydrocarbons in Zr-fumarate-MOF (MOF-801) is now published in ACS Chemistry of Materials. Led by Llwellyn's Group in Marseille, this work was made possible by the Marie Skłodowska-Curie Action Innovative Training Network, DEFNET (DEFect NETwork Materials Science and Engineering), a trans-European consortium of 9 academic institutions and 7 partner organizations. We are happy to be part of this collaboration!
Our Cu-MOF-CVD paper, entitled, "Vapour-phase deposition of oriented copper dicarboxylate metal-organic framework thin films", is ChemComm's front cover for September 2019 (68) issue.
Our work on the vapor-deposited zeolitic imidazolate frameworks as gap-filling ultra-low-k dielectrics has now been published in Nature Communications. Here we report a strategy for the integration of metal-organic frameworks (MOFs) as gap-filling low-k dielectrics in advanced on-chip interconnects. The proposed strategy is validated for thin films of the zeolitic imidazolate frameworks ZIF-8 and ZIF-67, formed in 2-methylimidazole vapor from ALD ZnO and native CoOx, respectively. Both materials show a Young’s modulus and dielectric constant comparable to state-of-the-art porous organosilica dielectrics.
The paper is accessible via an open-access platform through this link.
Together with the groups of Prof. Paolo Falcaro and Prof. Roland Resel (TU Graz, Austria), we expanded the scope of materials for MOF-CVD with Cu-MOF thin films. The orientation (crystallinity) was investigated by synchrotron measurements at the European Synchrotron Radiation Facility. Our study was accepted for publication in ChemComm.
Following a typical MOF-CVD protocol thin Cu and CuO precursor layers were deposited from the vapor phase and subsequently reacted with vaporized 1,4-benzenedicarboxylic acid (H2BDC) or trans-1,4-cyclohexanedicarboxylic acid (H2CDC). The resulting CuBDC and CuCDC films have an out-of-plane orientation with pore channels perpendicular to the surface, hence readily accessible for guest molecules as shown by QCM measurements.
UiO-66 is known as one of the most robust metal-organic framework materials. Nevertheless, UiO-66 has also been shown to undergo post-synthetic exchange of structural linkers with surprising ease in some solvents. To date, the exchange mechanism has not yet been fully elucidated. Here, we show how time-resolved monitoring grants insight into the selected case of exchanging 2-minoterephthalate into UiO-66 in methanol. Analysis of both the solid and liquid phase, complemented by computational insights, revealed the active role of methanol in the creation and stabilization of dangling linkers. Similar to monocarboxylate defects that can be introduced during UiO-66 synthesis, such dangling linkers undergo fast exchange. The presence of missing linker or missing cluster defects at the start of the exchange process was shown to have no considerable impact on the equilibrium composition. After the exchange process, the incoming 2-aminoterephthalate and remaining terephthalate linkers were distributed homogeneously in the framework for the typical sub-micron size of UiO-66 crystallites.
We are grateful to the concerted efforts from the excellent researchers of Ghent University and National Institute of Chemistry in Slovenia! Online version of the paper can be accessed here.
Review on Porous Organic and Carbon-based films
Our review paper on Bringing Porous Organic and Carbon‐Based Materials toward Thin‐Film Applications was accepted in Advance Functional Materials. Porous materials have attracted tremendous scientific and industrial interest due to their broad commercial applicability. However, some applications require that these materials are deposited on surfaces to create thin films. In this review, the recent progress of new porous thin‐film material classes is described: porous organic molecular materials, porous organic polymers, covalent organic frameworks, and nanoporous carbon. In each case, the state of the art and current barriers in their thin‐film fabrication, as well as intrinsic material advantages that are suited for different applications are presented. By highlighting the unique structural characteristics and properties of these materials, it is hoped that increased research development and industrial interest will be fostered, which will lead to new methods of thin‐film synthesis and consequently to new applications.
This work was a successful collaboration with several european research groups.
The confinement of anthracene molecules in a metal-organic framework enables reversible yellow to-purple photoswitching of the fluorescence emission. The photoresponse of the host-guest system strongly relies on the unique properties of the MOF host, i.e., the pore geometry, connectivity and volume as well as the structural flexibility. The solid-state photoswitching allows the development of photopatternable, erasable and rewritable paper. Thanks to our international collaborators from KU Leuven, Kiel and Munich!
Stoichiometric proton-coupled electron transfer (PCET) reactions of the metal–organic framework (MOF) MIL-125, Ti8O8(OH)4(bdc)6 (bdc = terephthalate), are described. In the presence of UV light and 2-propanol, MIL-125 was photoreduced to a maximum of 2(e–/H+) per Ti8 node. This stoichiometry was shown by subsequent titration of the photoreduced material with the 2,4,6-tri-tert-butylphenoxyl radical. This reaction occurred by PCET to give the corresponding phenol and the original, oxidized MOF. The high level of charging, and the independence of charging amount with particle size of the MOF samples, shows that the MOF was photocharged throughout the bulk and not only at the surface. NMR studies showed that the product phenol is too large to fit in the pores, so the phenoxyl reaction must have occurred at the surface. Attempts to oxidize photoreduced MIL-125 with pure electron acceptors resulted in multiple products, underscoring the importance of removing e– and H+ together. Our results require that the e– and H+ stored within the MOF architecture must both be mobile to transfer to the surface for reaction. Analogous studies on the soluble cluster Ti8O8(OOCtBu)16 support the notion that reduction occurs at the Ti8 MOF nodes and furthermore that this reduction occurs via e–/H+ (H-atom) equivalents. The soluble cluster also suggests degradation pathways for the MOFs under extended irradiation. The methods described are a facile characterization technique to study redox-active materials and should be broadly applicable to, for example, porous materials like MOFs.