V. Van Speybroeck

Computational Modeling of the Mobility, Stability and Al Positioning Ability of Cyclic Cationic Organic Structure-Directing Agents in AEI Zeolite

P. Ferri, P. Cnudde, M. Moliner, V. Van Speybroeck, M. Boronat
JACS Au (Journal of the American Chemical Society)
2025
A1

Abstract 

The stability and mobility of a set of organic structure-directing agents (OSDAs) with different molecular geometries and chargedistribution confined within the pear-like cavities of neutral and Al-containingmodels of AEI zeolites have been investigated by using static densityfunctional theory calculations and ab initio molecular dynamics simulations.The objective is to identify the role of electrostatic interactions between theOSDAs’ positive charge at N+ atoms and the anionic framework AlO4−centers on the preferential stabilization of Al at specific crystallographicpositions, opening the possibility to modulate the Al distribution in AEIzeolites. We find that several classical piperidinium-based OSDAs withdiverse methyl-substituent patterns in the N-containing ring but asymmetrical charge distribution, as well as bulkier nonclassical azoniabicycle-heptane-based OSDAs with the positive chargeasymmetrically located at one side of the molecule, behave similarly. All of them remain almost immobile at the center of the aeicavity along the simulations and always stabilize Al preferentially at the T1 crystallographic position. In contrast, an azabicyclo-octane-based OSDA with the positive charge located outside a cyclo-octane ring lacking substituents exhibits an enhanced mobilitythat includes full rotation within the aei cage and the ability to reach the regions of the cavity not accessible to the other OSDAsinvestigated. As a result, this highly mobile OSDA preferentially stabilizes Al in the T3 site, which might lead to differences incatalyst activity and stability for zeolite samples synthesized using this OSDA.

Transforming 2D Imine into 3D Thiazole Covalent Organic Frameworks by Conjugated Connectors: Fully Conjugated Photocatalysts

M. Deng, J. Chakraborty, G. Wang, K. S. Rawat, L. Bourda, J. Sun, I. Nath, Y. Ji, P. Geiregat, V. Van Speybroeck, X. Feng, P. Van der Voort
JACS (Journal of the American Chemical Society)
2025
A1

Abstract 

We developed a robust three-dimensional (3D) covalent organic framework (COF), fully conjugated in both the planar (xy) and interlayer (z) directions, using a one-pot sulfurization process. We converted the two-dimensional (2D) imine-linked COF (Py-BDA-COF) to the 3D thiazole-linked COF (3D-Py-BDA-S-COF). In the interlayer direction (z-axis), the alternating covalently bound acetylene and ethylene arrangements serve as conjugated connectors (“pillars”) and create a fully conjugated and very robust COF in all three dimensions. On top of this, the presence of the sulfur lone pair electrons in the thiazole rings considerably enhances the electron delocalization degree of the frameworks. The 3D-Py-BDA-S-COF is successfully evaluated in the photocatalytic reduction of nitrobenzene.

Ab Initio Predictions of Adsorption in Flexible Metal–Organic Frameworks for Water Harvesting Applications

R. Goeminne, V. Van Speybroeck
JACS (Journal of the American Chemical Society)
147, 4, 3615-3630
2025
A1

Abstract 

Metal–organic frameworks such as MOF-303 and MOF-LA2–1 have demonstrated exceptional performance for water harvesting applications. To enable a reticular design of such materials, an accurate prediction of the adsorption properties with chemical accuracy and fully accounting for the flexibility is crucial. The computational prediction of water adsorption properties in MOFs has become standard practice, but current methods lack the predictive power needed to design new materials. Limitations stem from the way the interatomic potential is described and the inadequate consideration of the framework flexibility. Herein, we showcase a methodology to obtain chemically accurate adsorption isotherms that fully account for framework flexibility. The method relies on very accurate and efficiently trained machine learning potentials and transition matrix Monte Carlo simulations to account for framework flexibility. For MOF-303, quantitatively accurate adsorption isotherms are obtained, provided an accurately benchmarked electronic structure method is used to train the machine learning potential, and local and global framework flexibility is accounted for. The broader applicability is shown through the study of MOF-333 and MOF-LA2–1. Analysis of the water density profiles in the MOFs gives insight into the factors governing the shape and origin of the isotherm. An optimal water harvester should have initial seeding sites with intermediate adsorption strength to prevent detrimental low-pressure water uptake. To increase the working capacity, linker extension strategies can be used while maintaining the initial seeding sites, as was done in MOF-LA2–1. The methodology can be applied to other guest molecules and MOFs, enabling the future design of MOFs with specific adsorption properties.

Gold Open Access

Computational Modeling of Reticular Materials: The Past, the Present, and the Future

W. Temmerman, R. Goeminne, K. S. Rawat, V. Van Speybroeck
Advanced Materials
2024
A1

Abstract 

Reticular materials rely on a unique building concept where inorganic and organic building units are stitched together giving access to an almost limitless number of structured ordered porous materials. Given the versatility of chemical elements, underlying nets, and topologies, reticular materials provide a unique platform to design materials for timely technological applications. Reticular materials have now found their way in important societal applications, like carbon capture to address climate change, water harvesting to extract atmospheric moisture in arid environments, and clean energy applications. Combining predictions from computational materials chemistry with advanced experimental characterization and synthesis procedures unlocks a design strategy to synthesize new materials with the desired properties and functions. Within this review, the current status of modeling reticular materials is addressed and supplemented with topical examples highlighting the necessity of advanced molecular modeling to design materials for technological applications. This review is structured as a templated molecular modeling study starting from the molecular structure of a realistic material towards the prediction of properties and functions of the materials. At the end, the authors provide their perspective on the past, present of future in modeling reticular materials and formulate open challenges to inspire future model and method developments.

The Operando Nature of Isobutene Adsorbed in Zeolite H−SSZ−13 Unraveled by Machine Learning Potentials Beyond DFT Accuracy

M. Bocus, S. Vandenhaute, V. Van Speybroeck
Angewandte Chemie int. Ed.
64, 1, e202413637
2025
A1

Abstract 

Unraveling the nature of adsorbed olefins in zeolites is crucial to understand numerous zeolite-catalyzed processes. A well-grounded theoretical description critically depends on both an accurate determination of the potential energy surface (PES) and a reliable account of entropic effects at operating conditions. Herein, we propose a transfer learning approach to perform random phase approximation (RPA) quality enhanced sampling molecular dynamics simulations, thereby approaching chemical accuracy on both the determination and exploration of the PES. The proposed methodology is used to investigate isobutene adsorption in H−SSZ−13 as prototypical system to estimate the relative stability of physisorbed olefins, carbenium ions and surface alkoxide species (SAS) in Brønsted-acidic zeolites. We show that the tert-butyl carbenium ion formation is highly endothermic and no entropic stabilization is observed compared to the physisorbed complex within H−SSZ−13. Hence, its predicted concentration and lifetime are negligible, making a direct experimental observation unlikely. Yet, it remains a shallow minimum on the free energy surface over the whole considered temperature range (273–873 K), being therefore a short-lived reaction intermediate rather than a transition state species.

Gold Open Access

Water motifs in zirconium metal-organic frameworks induced by nanoconfinement and hydrophilic adsorption sites

A. Lamaire, J. Wieme, S. Vandenhaute, R. Goeminne, S.M.J. Rogge, V. Van Speybroeck
Nature Communications
15, 9997
2024
A1

Abstract 

The intricate hydrogen-bonded network of water gives rise to various structures with anomalous properties at different thermodynamic conditions. Nanoconfinement can further modify the water structure and properties, and induce specific water motifs, which are instrumental for technological applications such as atmospheric water harvesting. However, so far, a causal relationship between nanoconfinement and the presence of specific hydrophilic adsorption sites is lacking, hampering the further design of nanostructured materials for water templating. Therefore, this work investigates the organisation of water in zirconium-based metal-organic frameworks (MOFs) with varying topologies, pore sizes, and chemical composition, to extract design rules to shape water. The highly tuneable pores and hydrophilicity of MOFs makes them ideally suited for this purpose. We find that small nanopores favour orderly water clusters that nucleate at hydrophilic adsorption sites. Favourably positioning the secondary adsorption sites, hydrogen-bonded to the primary adsorption sites, allows larger clusters to form at moderate adsorption conditions. To disentangle the importance of nanoconfinement and hydrophilic nucleation sites in this process, we introduce an analytical model with precise control of the adsorption sites. This sheds a new light on design parameters to induce specific water clusters and hydrogen-bonded networks, thus rationalising the application space of water in nanoconfinement.

Gold Open Access

Mesoporous Acridinium-Based Covalent Organic Framework for Long-lived Charge-Separated Exciton Mediated Photocatalytic [4+2] Annulation

I. Nath, J. Chakraborty, K. S. Rawat, Y. Ji, R. Wang, K. Molkens, N. De Geyter, R. Morent, V. Van Speybroeck, P. Geiregat, P. Van der Voort
Advanced Materials
2024
A1

Abstract 

Readily tuneable porosity and redox properties of covalent organic frameworks (COFs) result in highly customizable photocatalysts featuring extended electronic delocalization. However, fast charge recombination in COFs severely limits their photocatalytic activities. Herein a new mode of COF photocatalyst design strategy to introduce systematic trap states is programmed, which aids the formation and stabilization of long-lived charge-separated excitons. Installing cationic acridinium functionality in a pristine electron-rich triphenylamine COF via postsynthetic modification resulted in a semiconducting photocatalytic donor–acceptor dyad network that performed rapid and efficient oxidative Diels-Alder type [4+2] annulation of styrenes and alkynes to fused aromatic compounds under the atmospheric condition in good to excellent yields. Large mesopores of ≈4 nm diameter ensured efficient mass flow within the COF channel. It is confirmed that the catalytic performance of COF originates from the ultra-stable charge-separated excitons of 1.9 nm diameter with no apparent radiative charge-recombination pathway, endorsing almost a million times better photo-response and catalysis than the state-of-the-art.

Totally conjugated and coplanar covalent organic frameworks as photocatalysts for water purification: Reduction of Cr (VI) while oxidizing water borne organic pollutants

L. Wang, J. Chakraborty, K. S. Rawat, M. Deng, J. Sun, Y. Wang, V. Van Speybroeck, P. Van der Voort
Separation and Purification Technology
359, 1, 130368
2025
A1

Abstract 

Covalent organic frameworks (COFs) have emerged as photocatalytic materials with bandgaps in the visible region. Imine-based COFs, which have been extensively explored, often suffer from limited stability and poor conjugation, hindering their photocatalytic activities. The chemical and hydrolytic stability and the photo catalytic performance of COFs is drastically enhanced by constructing 2D COFs that are fully conjugated in the x, y plane, that have alternating donor–acceptor (D-A) units for better charge separation and that have enhanced conjugation in the z-axis by p-orbital overlap by using highly planar building blocks. In this study, we introduce three highly crystalline sp 2 COFs that are able to photocatalyticlly reduce highly toxic Cr (VI) species to much less toxic and easily removable Cr (III) residues, while simultaneously oxidizing water borne organic pollutants. One of them, the TEB-COF, with the integration of the acetylene group, exhibited excellent photocatalytic ac tivity due to its superior planarity and extended conjugation. TEB-COF is able to completely remove the model dye Rhodamine B and Cr (VI) (10 mg/L) in less than 30 min. This research provides valuable insights into the development of recyclable metal-free photocatalysts for wastewater treatment.

In-Depth Thermodynamic and Kinetic Analysis of Ethane Diffusion in ZIF-8

B. Schmidt, P. Cnudde, V. Van Speybroeck, L. Vanduyfhuys
Journal of Physical Chemistry C
128, 43, 18509-18523
2024
A1

Abstract 

Flexible microporous ZIF-8 crystals show excellent separation behavior of small molecules such as ethaneand ethene. As such, hydrocarbon diffusion plays an essential role in the performance of these materials, yet determining accurate diffusion constants is nontrivial. Both ab initio and force-field based molecular dynamics simulations, coupled with umbrella sampling are applied in this work to characterize the diffusion of ethane in ZIF-8. Diffusion constants are extracted from the simulations by a combination of transition state theory and a random-walk hopping model, and are compared against experimentally measured values from literature. Ethane diffusion is a hindered process characterized by a transition state corresponding to an ethane molecule crossing the gate in between two neighboring cages formed by methylimidazole linkers. Free energy profiles of the diffusion process are derived and analyzed revealing the entropic nature of the barrier due to a counteracting of covalent host deformation energy and nonbonding host–guest interaction. A temperature analysis further confirms the entropic nature of the barrier and reveals an increased gate opening at increasing temperature. Finally, the loading dependency of diffusion is investigated revealing that increasing the ethane loading of the cages slightly slows down diffusion as a result of beneficial guest–guest interactions in the cages. Our findings yield essential elementary insight into how different molecular interactions influence the diffusion path of hydrocarbons throughout ZIF-8 crystals.

Investigation of the Octahedral Network Structure in Formamidinium Lead Bromide Nanocrystals by Low-Dose Scanning Transmission Electron Microscopy

N. J. Schrenker, T. Braeckevelt, A. De Backer, N. Livakas, C.-P. Yu, T. Friedrich, M.B.J. Roeffaers, J. Hofkens, J. Verbeeck, L. Manna, V. Van Speybroeck, S. Van Aert, S. Bals
Nano Letters
24, 35, 10936-10942
2024
A1

Abstract 

Metal halide perovskites (MHP) are highly promising semiconductors. In this study, we focus on FAPbBr3 nanocrystals, which are of great interest for green light-emitting diodes. Structural parameters significantly impact the properties of MHPs and are linked to phase instability, which hampers long-term applications. Clearly, there is a need for local and precise characterization techniques at the atomic scale, such as transmission electron microscopy. Because of the high electron beam sensitivity of MHPs, these investigations are extremely challenging. Here, we applied a low-dose method based on four-dimensional scanning transmission electron microscopy. We quantified the observed elongation of the projections of the Br atomic columns, suggesting an alternation in the position of the Br atoms perpendicular to the Pb–Br–Pb bonds. Together with molecular dynamics simulations, these results remarkably reveal local distortions in an on-average cubic structure. Additionally, this study provides an approach to prospectively investigating the fundamental degradation mechanisms of MHPs.

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