Center for Molecular Modeling - D. De Vos

New Tricarboxylate Plasticizers for Use in Polylactic Acid: Synthesis, Thermal Behavior, Mechanical Properties and Durability

jvekeman — Mon, 08 Apr 2024 09:20:34 +0000

A. De Bruyne, K.C. Gómez, G. O'Rourke, M. Denayer, J. Vekeman, F. De Proft, W. Stuyck, J. Leinders, P. Van Puyvelde, D. De Vos

Journal of Polymers and the Environment

32, 4483-4495

2024

Abstract

We report the use of novel biobased plasticizers prepared starting from citric acid (CA) in polylactic acid (PLA). Citric acid based plasticizers are well-known softeners for PLA, with citrate esters as the most commonly used class. However, citrate esters are known to leach out of the plastic material over time. This problem is currently addressed by acetylating the tertiary hydroxyl group of citric acid via complex and environmentally polluting processes. An alternative strategy consists in the reductive removal of the tertiary hydroxyl group, resulting in propane-1,2,3-tricarboxylic acid. Derivatizing this compound leads to novel plasticizers which have not been tested in PLA yet. Here, different esters of propane-1,2,3-tricarboxylic acid were synthesized and blended in PLA. Their influence on the thermal (T_g and T_m) and the mechanical properties (Young’s modulus, stress and strain) of PLA along with their migration out of the material were compared to those of commercially available citric acid based plasticizers. Our results show that similar or better results were obtained with these new PLA plasticizers.

DOI

http://dx.doi.org/10.1007/s10924-024-03254-0

Analysing the potential of the selective dissolution of elastane from mixed fiber textile waste

leen — Tue, 07 Feb 2023 08:23:33 +0000

K.T. Phan, S. Ügdüler, L. Harinck, R. Denolf, M. Roosen, G. O'Rourke, D. De Vos, V. Van Speybroeck, K. De Clerck, S. De Meester

Resources Conservation and Recycling

191, 106903

2023

Abstract

Textile products are composed of various blends of synthetic or natural polymers. Elastane increases the functionality during use phase, but impedes high quality recycling. This study investigates the selective chemical dissolution of elastane from blended textile. Hansen solubility parameters and COSMO-RS were applied for solvent screening. The most recommended biobased solvents were experimentally validated with polyester, polyamide, cotton, wool and elastane for which solubility limits were determined and hence, their selectivity towards elastane dissolution. A TGA-corrected gravimetric method was developed as quantification tool and showed that tetrahydrofurfuryl alcohol and ɣ-valerolactone have comparable elastane dissolution capabilities to classical solvents (5 mg elastane/g solvent). Polyester/elastane and polyamide/elastane blends were subjected to this process as case studies. The LCA study showed that this selective solvent-based dissolution process saves 60% CO₂-eq./kg textile waste compared to incineration. This interdisciplinary work can set the benchmark for further developing and upscaling physical/dissolution recycling processes for blended textiles.

Green Open Access

DOI

https://doi.org/10.1016/j.resconrec.2023.106903

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Correlating MOF-808 parameters with mixed-matrix membrane (MMM) CO2 permeation for a more rational MMM development

aran — Tue, 20 Apr 2021 12:20:40 +0000

R. Thür, D. Van Havere, N. Van Velthoven, S. Smolders, A. Lamaire, J. Wieme, V. Van Speybroeck, D. De Vos, I. Vankelecom

Journal of Materials Chemistry A

9 (21), 12782-12796

2021

Abstract

Consistent structure-performance relationships for the design of MOF (metal-organic framework)-based mixed-matrix membranes (MMMs) for gas separation are currently scarce in MMM literature. An important step in establishing such relationships could be to correlate intrinsic MOF parameters, such as CO₂ uptake and the CO₂ adsorption enthalpy (Q_st), with the separation performance indicators of the MMM (i.e. separation factor and permeability). Such a study presumes the availability of a platform MOF, which allows systematic comparison of the relevant MOF parameters. MOF-808 can take up the role of such platform MOF, owing to its unique cluster coordination and subsequent ease of introducing additional functional molecules. For this purpose, formic acid (FA) modulated MOF-808 (MOF-FA) was post-synthetically functionalized with five different ligands (histidine (His), benzoic acid (BA), glycolic acid (GA), lithium sulfate (Li₂SO₄) and trifluoroacetic acid (TFA)) to create a series of isostructural MOFs with varying affinity/diffusivity properties but as constant as possible remaining properties (e.g. particles size distribution). CO₂ uptake and CO₂ adsorption enthalpy of the MOFs were determined with CO₂ sorption experiments and Clausius-Clapeyron analysis. These MOF properties were subsequently linked to the CO₂/N₂ separation factor and CO₂ permeability of the corresponding MMM. Unlike what is often assumed in literature, MOF-808 CO₂ uptake proved to be a poor indicator for MMM performance. In contrast, a strong correlation was observed between Q_st at high CO₂ loadings on one hand and CO₂ permeability under varying feed conditions on the other hand. Furthermore, correlation coefficients of Q_st,15 and Q_st,30 (Q_st at 15 and 30 cm³ (STP)/g) with the separation factor were significantly better than those calculated for CO₂ uptake. The surprising lack of correlation between membrane performance and CO₂ uptake and the strong correlation with Q_st opens possibilities to rationally design MMMs and stresses the need for more fundamental research focused on finding consistent relationships between filler properties and the final membrane performance.

DOI

http://dx.doi.org/10.1039/D0TA10207E

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Shape-selective C–H activation of aromatics to biarylic compounds using molecular palladium in zeolites

massimo — Mon, 16 Nov 2020 16:24:26 +0000

J. Vercammen, M. Bocus, S. E. Neale, A. Bugaev, P. Tomkins, J. Hajek, S. Van Minnebruggen, A. Soldatov, A. Krajnc, G. Mali, V. Van Speybroeck, D. De Vos

Nature Catalysis

3, 1002-1009

2020

Abstract

The selective activation of inert C–H bonds has emerged as a promising tool for avoiding the use of wasteful traditional coupling reactions. Oxidative coupling of simple aromatics allows for a cost-effective synthesis of biaryls. However, utilization of this technology is severely hampered by poor regioselectivity and by the limited stability of state-of-the-art homogeneous Pd catalysts. Here, we show that confinement of cationic Pd in the pores of a zeolite allows for the shape-selective C–H activation of simple aromatics without a functional handle or electronic bias. For instance, out of six possible isomers, 4,4′-bitolyl is produced with high shape selectivity (80%) in oxidative toluene coupling on Pd-Beta. Not only is a robust, heterogeneous catalytic system obtained, but this concept is also set to control the selectivity in transition-metal-catalysed arene C–H activation through spatial confinement in zeolite pores.

DOI

http://dx.doi.org/10.1038/s41929-020-00533-6

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Paper_final.pdf

Engineering a highly defective stable UiO-66 with tunable Lewis-Brønsted acidity - The role of the hemilabile linker

alexander — Tue, 28 Jan 2020 15:56:11 +0000

X. Feng, J. Hajek, H. S. Jena, G. Wang, S. K. P. Veerapandian, R. Morent, N. De Geyter, K. Leyssens, A.E.J. Hoffman, V. Meynen, C. Marquez, D. De Vos, V. Van Speybroeck, K. Leus, P. Van der Voort

JACS (Journal of the American Chemical Society)

142 (6), 3174-3183

2020

Abstract

The stability of metal-organic frameworks (MOFs) typically decreases with an increasing number of defects, limiting the number of defects that can be created and limiting catalytic and other applications. Herein, we use a hemilabile (Hl) linker to create up to maximum 6 defects per cluster in UiO-66. We have synthesized hemilabile UiO-66 (Hl-UiO-66) using benzene dicarboxylate (BDC) as linker and 4-sulfonatobenzoate (PSBA) as the hemilabile linker. The PSBA acts not only as a modulator to create defects, but also as a co-ligand that enhances the stability of the resulting defective framework. Furthermore, upon a post-synthetic treatment in H2SO4, the average number of defects increases to the optimum of six missing BDC linkers per cluster (3 per formula unit), leaving the Zr-nodes on average 6-fold coordinated. Remarkably, the thermal stability of the materials further increases upon this treatment. Periodic density functional theory calculations confirm that the hemilabile ligands strengthen this highly defective structure by several stabilizing interactions. Finally, the catalytic activity of the obtained materials is evaluated in the acid-catalyzed isomerization of α-pinene oxide. This reaction is particularly sensitive to the Brønsted or Lewis acid sites in the catalyst. In comparison to the pristine UiO-66, which mainly possesses Brønsted acid sites, the Hl-UiO-66 and the post-synthetically treated Hl-UiO-66 structures exhibited a higher Lewis acidity and an enhanced activity and selectivity. This is further explored by CD3CN spectroscopic sorption experiments. We have shown that by tuning the number of defects in UiO-66 using PSBA as the hemilabile linker, one can achieve highly defective and stable MOFs and easily control the Brønsted to Lewis acid ratio in the materials, and thus their catalytic activity and selectivity.

DOI

http://dx.doi.org/10.1021/jacs.9b13070

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Active Role of Methanol in Post-Synthetic Linker Exchange in the Metal-Organic Framework UiO-66

wim — Wed, 14 Nov 2018 08:06:51 +0000

J. Marreiros, C. Caratelli, J. Hajek, A. Krajnc, G. Fleury, B. Bueken, D. De Vos, G. Mali, M. Roeffaers, V. Van Speybroeck, R. Ameloot

Chemistry of Materials

31 (4), 1359-1369

2019

Abstract

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 sol-vents. 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-aminoterephthalic acid 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 metastable states in which dangling linkers are similar to monocarboxylate defects that can be introduced during UiO-66 synthesis, such dangling link-ers undergo fast exchange. The presence of missing linker or missing cluster defects at the start of the ex-change process was shown to have no considerable impact on the equilibrium composition. After the ex-change process, the incoming 2-aminoterephthalate and remaining terephthalate linkers were distributed homogeneously in the framework for the typical small crystal size of UiO-66 (≈500nm).

Open Access version available at UGent repository

Green Open Access

DOI

http://dx.doi.org/10.1021/acs.chemmater.8b04734

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The remarkable amphoteric nature of defective UiO-66 in catalytic reactions

michel — Fri, 23 Dec 2016 15:56:00 +0000

J. Hajek, B. Bueken, M. Waroquier, D. De Vos, V. Van Speybroeck

ChemCatChem

9 (12), 2203-2210

2017

Abstract

One of the major requirements in solid acids and bases catalyzed reactions is that the reactants, intermediates or activated complexes cooperate with several functions of catalyst support. In this work the remarkable bifunctional behavior of the defective UiO-66(Zr) metal organic framework is shown for acid-base pair catalysis. The active site relies on the presence of undercoordinated zirconium sites, which may be tuned by removing framework linkers and by removal of water from the inorganic bricks using a dehydration treatment. To elucidate the amphoteric nature of defective UiO-66, the Oppenauer oxidation of primary alcohols has been theoretically investigated using density functional theory (DFT) and the periodic approach. The presence of acid and basic centers within molecular distances has been shown crucial for determining the catalytic activity of the material. Hydrated and dehydrated bricks have a distinct influence on modulation of the acidity and basicity of the active sites. In any case both functions need to cooperate in a concerted way to enable the chemical transformation.

Open Access version available at UGent repository

Gold Open Access

DOI

http://dx.doi.org/10.1002/cctc.201601689

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Hajek_et_al-2017-ChemCatChem.pdf

Towards metal–organic framework based field effect chemical sensors: UiO-66-NH2 for nerve agent detection

michel — Sat, 09 Jul 2016 19:53:21 +0000

L. Stassen, B. Bueken, H. Reinsch, J.F.M. Oudenhoven, D. Wouters, J. Hajek, V. Van Speybroeck, N. Stock, P.M. Vereecken, R. Van Schajik, D. De Vos, R. Ameloot

Chemical Science

7, 5827-5832

2016

Abstract

We present a highly sensitive gas detection approach for the infamous ‘nerve agent’ group of alkyl phosphonate compounds. Signal transduction is achieved by monitoring the work function shift of metal–organic framework UiO-66-NH2 coated electrodes upon exposure to ppb-level concentrations of a target simulant. Using the Kelvin probe technique, we demonstrate the potential of electrically insulating MOFs for integration in field effect devices such as ChemFETs: a three orders of magnitude improvement over previous work function-based detection of nerve agent simulants. Moreover, the signal is fully reversible both in dry and humid conditions, down to low ppb concentrations. Comprehensive investigation of the interactions that lead towards this high sensitivity points towards a series of confined interactions between the analyte and the pore interior of UiO-66-NH₂.

Open Access version available at UGent repository

DOI

http://dx.doi.org/10.1039/C6SC00987E

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A breathing zirconium metal-organic framework with reversible loss of crystallinity by correlated nanodomain formation

jelle — Tue, 02 Feb 2016 07:37:01 +0000

B. Bueken, F. Vermoortele, M.J. Cliffe, M.T. Wharmby, D. Foucher, J. Wieme, L. Vanduyfhuys, C. Martineau, N. Stock, F. Taulelle, V. Van Speybroeck, A.L. Goodwin, D. De Vos

Chemistry - A European Journal

2016, 22, 1-5

2016

Abstract

The isoreticular analogue of the metal–organic framework UiO-66(Zr), synthesized with the flexible trans-1,4-cyclohexanedicarboxylic acid as linker, shows a peculiar breathing behavior by reversibly losing long-range crystalline order upon evacuation. The underlying flexibility is attributed to a concerted conformational contraction of up to two thirds of the linkers, which breaks the local lattice symmetry. X-ray scattering data are described well by a nanodomain model in which differently oriented tetragonal-type distortions propagate over about 7–10 unit cells.

DOI

http://dx.doi.org/10.1002/chem.201600330

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chem.201600330 Bart Bueken Zrcdc.pdf

A Flexible Photoactive Titanium Metal-Organic Framework Based on a [Ti-3(IV)(mu(3)-O)(O)(2)(COO)(6)] Cluster

michel — Fri, 21 Aug 2015 19:59:38 +0000

B. Bueken, F. Vermoortele, D.E.P. Vanpoucke, H. Reinsch, C. Tsou, P. Valvekens, T. De Baerdemaeker, R. Ameloot, C. Kirschhock, V. Van Speybroeck, J. Mayer, D. De Vos

Angewandte Chemie int. Ed.

127, 14118 –14123

2015

Abstract

The synthesis of titanium-carboxylate metal-organic frameworks (MOFs) is hampered by the high reactivity of the commonly employed alkoxide precursors. Herein, we present an innovative approach to titanium-based MOFs by the use of titanocene dichloride to synthesize COK-69, the first breathing Ti MOF, which is built up from trans-1,4-cyclo-hexanedicarboxylate linkers and an unprecedented [Ti-3(IV)(mu(3)-O)(O)(2)(COO)(6)] cluster. The photoactive properties of COK-69 were investigated in depth by proton-coupled electron-transfer experiments, which revealed that up to one Ti-IV center per cluster can be photoreduced to Ti-III while preserving the structural integrity of the framework. The electronic structure of COK-69 was determined by molecular modeling, and a band gap of 3.77 eV was found.

DOI

http://dx.doi.org/10.1002/anie.201505512

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