V. Van Speybroeck

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

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
A1

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

An embedded interfacial network stabilizes inorganic CsPbI3 perovskite thin films

J.A. Steele, T. Braeckevelt, V. Prakasam, G. Degutis, H. Yuan, H. Jin, E. Solano, P. Puech, S. Basak, M.I. Pintor-Monroy, H. Van Gorp, G. Fleury, R.X. Yang, Z. Lin, H. Huang, E. Debroye, D. Chernyshov, B. Chen, M. Wei, Y. Hou, R. Gehlhaar, J. Genoe, S. De Feyter, S.M.J. Rogge, A. Walsh, E.H. Sargent, P. Yang, J. Hofkens, V. Van Speybroeck, M.B.J. Roeffaers
Nature Communications
13, 7513
2022
A1

Abstract 

The black perovskite phase of CsPbI3 is promising for optoelectronic applications; however, it is unstable under ambient conditions, transforming within minutes into an optically inactive yellow phase, a fact that has so far prevented its widespread adoption. Here we use coarse photolithography to embed a PbI2-based interfacial microstructure into otherwise-unstable CsPbI3 perovskite thin films and devices. Films fitted with a tessellating microgrid are rendered resistant to moisture-triggered decay and exhibit enhanced long-term stability of the black phase (beyond 2.5 years in a dry environment), due to increasing the phase transition energy barrier and limiting the spread of potential yellow phase formation to structurally isolated domains of the grid. This stabilizing effect is readily achieved at the device level, where unencapsulated CsPbI3 perovskite photodetectors display ambient-stable operation. These findings provide insights into the nature of phase destabilization in emerging CsPbI3 perovskite devices and demonstrate an effective stabilization procedure which is entirely orthogonal to existing approaches.

Confined hot-pressurized water in Brønsted-acidic beta zeolite speeds up the O-demethylation of guaiacol

M. Bocus, E. Van den Broeck, X. Wu, M. Bal, J. Bomon, L. Vanduyfhuys, B. F. Sels, B. U. W. Maes, V. Van Speybroeck
Nature Catalysis
8, 33-45
2025
A1

Abstract 

Biorefinery technologies that convert lignin into platform chemicals are essential to reduce our future dependence on fossil resources. In these technologies, a key process is the acid-catalysed O-demethylation of guaiacol derivatives in hot-pressurized water using Brønsted mineral acids or microporous zeolites. The fundamental understanding of how hydronium ions behave in a confined environment versus bulk is still limited. Here we investigate the O-demethylation of guaiacol in hot-pressurized water with HCl or H-BEA zeolite catalysts to elucidate the impact of zeolite microporosity on reaction mechanisms and rates. Operando molecular simulations combined with experimental kinetic studies reveal that, regardless of the catalyst type, O-demethylation follows a concerted O-activated SN2 mechanism. The reaction rate is higher in the zeolite due to more active, under-coordinated hydronium ions. Additionally, the molecular organization of solvent and reactants around the confined active site plays a crucial role in modulating the association of the reacting species and the reaction kinetics.

Influence of the number of ligands and point group on the electronic structure of Co2+ aqua-complexes

L. De Bruecker, V. Van Speybroeck
Inorganic Chemistry
61, 51, 20743–20756
2022
A1

Abstract 

The nucleation process of zeolitic imidazolate frameworks (ZIFs) is, to date, not yet completely understood, making the search for tailored materials very difficult. Recently, it has been shown that, during the formation process, the symmetry of the precursors is reduced by ligand elimination and substitution reactions. The octahedral precursors with simple ligands, such as water, methanol, and/or NO3, are transformed to five- and finally four-coordinated complexes with imidazole ligands. This reduction of symmetry, caused both by the changing coordination environment and distortions from the perfect symmetry leading to another point group, will have a large influence on the electronic structure and more specifically on the d-orbital splitting. This, in turn, will affect the d–d electronic excitations, which can be followed using UV–vis spectroscopy and which can help to unravel the formation process. In this work, we systematically investigate how the lowering of the number of ligands affects the symmetry and thus the geometry and electronic structure of Co2+ complexes with six, five, and four aqua ligands. Therefore, we first resort to qualitative techniques, such as crystal field theory (CFT) and ligand field theory (LFT), which reveal that the orbital splitting is characteristic for the number of ligands. However, as these techniques are not capable of providing quantitative results without the use of experimental data as input, we perform various computational calculations. Both average of configuration (AOC) and unrestricted density functional theory (UDFT) are thoroughly investigated, and we will determine which technique is the best suited to properly describe the ground state of these systems. To investigate the dependency on the d-orbital occupation, we also investigated V2+, Mn2+, and Ni2+ hexa-aqua-complexes and compared them to the Co systems.

Linker Engineering of 2D Imine Covalent Organic Frameworks for Heterogeneous Palladium-catalyzed Suzuki Coupling Reaction

C. Krishnaraj, H. S. Jena, K. S. Rawat, J. Schmidt, K. Leus, V. Van Speybroeck, P. Van der Voort
ACS Applied Materials & Interfaces
14, 45, 50923-50931
2022
A1

Abstract 

Covalent organic frameworks (COFs) are an emerging class of porous organic polymers that have been utilized as scaffolds for anchoring metal active species to act as heterogeneous catalysts. Though several examples of such COFs exist, a thorough experimental and computational analysis on such catalysts is limited. In this work, a series of two-dimensional (2D) imine COFs (TTA–DFB COF (N), TTA–TBD COF (N∧O), and TTA–DFP COF(N∧N)) were synthesized by using suitable building units to obtain three different coordination sites (N, N∧O, and N∧N). These were post-modified with Pd(II) to catalyze the Suzuki–Miyaura coupling reaction. Pd@TTA–DFB COF, where Pd(II) was coordinated to N sites, showed the fastest reactivity and lower stability. Pd@TTA–DFP COF showed highest stability but slowest reactivity. Pd@TTA–TBD COF was the best among the three with both high stability and fast reactivity. By combining both experimental and computational results, we conclude that the Pd(II) to Pd(0) reduction is a key step in the difference between the catalytic reactivities of the three COFs. This study demonstrates the importance of the building block approach to design COFs for efficient heterogeneous catalysis and to understand the fate of the reaction profile.

Covalent Organic Framework supported Palladium Catalysts

H. Salemi, M. Debruyne, V. Van Speybroeck, P. Van der Voort, M. D'Hooghe, C. Stevens
Journal of Materials Chemistry A
10, 39, 20707-20729
2022
A1

Abstract 

Covalent organic frameworks (COFs), as highly porous crystalline structures, are newly emerging materials designed with tuneable features. They have a high potential to be a host to immobilize metal catalysts. The unique property of these materials, such as their high surface area, oriented channels, and heteroatom enrichment, make them promising materials to improve some disadvantages of heterogeneous metal catalysts. In this review, the fabrication and application of Pd anchored COFs as one of the most critical transition-metal catalysts that play a crucial role in a wide range of reactions is summarized.

Truly combining the advantages of polymeric and zeolite membranes for gas separations

X. Tan, S. Robijns, R. Thür, Q. Ke, N. De Witte, A. Lamaire, Y. Li, I. Aslam, D. Van Havere, T. Donckels, T. Van Assche, V. Van Speybroeck, M. Dusselier, I. Vankelecom
Science
378, 1189-1194
2022
A1

Abstract 

Mixed-matrix membranes (MMMs) have been investigated to render energy-intensive separations more efficiently by combining the selectivity and permeability performance, robustness, and nonaging properties of the filler with the easy processing, handling, and scaling up of the polymer. However, truly combining all in one single material has proven very challenging. In this work, we filled a commercial polyimide with ultrahigh loadings of a high–aspect ratio, CO2-philic Na-SSZ-39 zeolite with a three-dimensional channel system that precisely separates gas molecules. By carefully designing both zeolite and MMM synthesis, we created a gas-percolation highway across a flexible and aging-resistant (more than 1 year) membrane. The combination of a CO2-CH4 mixed-gas selectivity of ~423 and a CO2 permeability of ~8300 Barrer outperformed all existing polymer-based membranes and even most zeolite-only membranes.

Quantum free energy profiles for molecular proton transfers

A. Lamaire, M. Cools-Ceuppens, M. Bocus, T. Verstraelen, V. Van Speybroeck
Journal of Chemical Theory and Computation
19, 1, 18–24
2023
A1

Abstract 

Although many molecular dynamics simulations treat the atomic nuclei as classical particles, an adequate description of nuclear quantum effects (NQEs) is indispensable when studying proton transfer reactions. Herein, quantum free energy profiles are constructed for three typical proton transfers, which properly take NQEs into account using the path integral formalism. The computational cost of the simulations is kept tractable by deriving machine learning potentials. It is shown that the classical and quasi-classical centroid free energy profiles of the proton transfers deviate substantially from the exact quantum free energy profile.

Exploring the phase stability in interpenetrated diamondoid covalent organic frameworks

S. Borgmans, S.M.J. Rogge, J. De Vos, P. Van der Voort, V. Van Speybroeck
Communications Chemistry
6, 1, 5
2023
A1

Abstract 

Soft porous crystals, which are responsive to external stimuli such as temperature, pressure, or gas adsorption, are being extensively investigated for various technological applications. However, while substantial research has been devoted to stimuli-responsive metal-organic frameworks, structural flexibility in 3D covalent organic frameworks (COFs) remains ill-understood, and is almost exclusively found in COFs exhibiting the diamondoid (dia) topology. Herein, we systemically investigate how the structural decoration of these 3D dia COFs—their specific building blocks and degree of interpenetration—as well as external triggers such as temperature and guest adsorption may promote or suppress their phase transformations, as captured by a collection of 2D free energy landscapes. Together, these provide a comprehensive understanding of the necessary conditions to design flexible diamondoid COFs. This study reveals how their flexibility originates from the balance between steric hindrance and dispersive interactions of the structural decoration, thereby providing insight into how new flexible 3D COFs can be designed.

Open Access version available at UGent repository
Gold Open Access

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