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.
Our review paper on 3D printing in chemical engineering and catalytic technology was accepted in Chemical Society Reviews.
In the field of catalytic technology and chemical engineering the impact of 3D printing, is steadily increasing thanks to a rapidly decreasing equipment threshold. Although still in an early stage, the rapid and seamless transition between digital data and physical objects enabled by these fabrication tools will benefit both research and manufacture of reactors and structured catalysts. 3D printing closes the gap between theory and experiment, by enabling accurate fabrication of geometries optimized through computational fluid dynamics and the experimental evaluation of their properties. Our review highlights the research using 3D printing and computational modeling as digital tools for the design and fabrication of reactors and structured catalysts. The goal of this contribution is to stimulate interactions at the crossroads of chemistry and materials science on the one hand and digital fabrication and computational modeling on the other.
Timothée’s ChemSusChem paper tries to demonstrate how the superior adsorptive properties of porous and crystalline metal-organic framework (MOFs) offer novel and sustainable alternatives for the recovery of biobased fermentative products. This paper resulted from a collaboration with the De Vos group, Stock group (CAU, DE) and Bein group (LMU, DE).
The study focuses on biomass-derived lactic acid, an important platform chemical towards the sustainable production of numerous materials such as the biodegradable poly(lactic acid). The current fermentation process is however limited by the difficulty to recover the lactic acid product from the fermentation broth. Further, the recovery process generates stoichiometric amounts of gypsum which needs to be disposed, thereby implying costs as well as sustainability issues. Our study reveals the high affinity of lactic for open metal sites in Zr-based MOFs and how their use as adsorbent could shortcut most of the multi-step separation process in use, and avoid gypsum generation.
Materials processing, and thin-film deposition in particular, is decisive in the implementation of functional materials in industry and real-world applications. Vapor processing of materials plays a central role in manufacturing, especially in electronics. Metal–organic frameworks (MOFs) are a class of nanoporous crystalline materials on the brink of breakthrough in many application areas. Vapor deposition of MOF thin films will facilitate their implementation in micro- and nanofabrication research and industries. In addition, vapor–solid modification can be used for postsynthetic tailoring of MOF properties. In this context, we review the recent progress in vapor processing of MOFs, summarize the underpinning chemistry and principles, and highlight promising directions for future research.
In this Chemistry - A European Journal paper we try to highlight the underlying concepts of vapor phase growth of MOFs and which exciting perspectives this MOF-CVD approach opens.