V. Van Speybroeck

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)
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.

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.

This publication is licensed under the terms of your institutional subscription. Request reuse permissions.

Turning carbon dioxide into dialkyl carbonates through guanidinium-assisted SN2 ion-pair process

J. Delcorps, K. S. Rawat, M. Wells, E. B. Ayed, B. Grignard, C. Detrembleur, B. Blankert, P. Gerbaux, V. Van Speybroeck, O. Coulembier
Cell Reports Physical Science
5, 7, 102057
2024
A1

Abstract 

The synthesis of dialkyl carbonates, versatile compounds with applications in organic synthesis, pharmaceuticals, and polymers, has attracted considerable attention due to their environmentally benign nature. Here, we describe the selective bimolecular nucleophilic substitution (SN2) reaction between primary and secondary alkyl iodides with 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD)-based carbon dioxide-binding organic liquids. We show that TBD is a great candidate for bulk carbon dioxide and alcohol binding at 100C. TBDbased carbonate salts are selective for SN2 processes, allowing them to work with highly reactive alkyl iodide while eliminating unwanted base quaternization either in acetonitrile or in bulk at both 21C and 65C. The high reactivity of these TBD-based carbon dioxide-binding organic liquids toward backside SN2 processes at low temperature is explained by the presence of the TBD.H+ guanidinium, revealing a unique metal-free cation-assisted SN2 ion-pair process.

Reaching quantum accuracy in predicting adsorption properties for ethane/ethene in ZIF-8 at the low pressure regime

S. Ravichandran, M. Najafi, R. Goeminne, J. F. M. Denayer, V. Van Speybroeck, L. Vanduyfhuys
Journal of Chemical Theory and Computation
20, 12, 5225-5240
2024
A1

Abstract 

Nanoporous materials in the form of metal−organicframeworks such as zeolitic imidazolate framework-8 (ZIF-8) arepromising membrane materials for the separation of hydrocarbonmixtures. To compute the adsorption isotherms in suchadsorbents, grand canonical Monte Carlo simulations have provento be very useful. The quality of these isotherms depends on theaccuracy of adsorbate−adsorbent interactions, which are mostlydescribed using force fields owing to their low computational cost.However, force field predictions of adsorption uptake often showdiscrepancies from experiments at low pressures, providing theneed for methods that are more accurate. Hence, in this work, wepropose and validate two novel methodologies for the ZIF-8/ethane and ethene systems; a benchmarking methodology toevaluate the performance of any given force field in describing adsorption in the low-pressure regime and a refinement procedure torescale the parameters of a force field to better describe the host−guest interactions and provide for simulation isotherms with closeagreement to experimental isotherms. Both methodologies were developed based on a reference Henry coefficient, computed withthe PBE-MBD functional using the importance sampling technique. The force field rankings predicted by the benchmarkingmethodology involve the comparison of force field derived Henry coefficients with the reference Henry coefficients and ranking theforce fields based on the disparities between these Henry coefficients. The ranking from this methodology matches the rankingsmade based on uptake disparities by comparing force field derived simulation isotherms to experimental isotherms in the low-pressure regime. The force field rescaling methodology was proven to refine even the worst performing force field in UFF/TraPPE.The uptake disparities of UFF/TraPPE improved from 197% and 194% to 11% and 21% for ethane and ethene, respectively. Theproposed methodology is applicable to predict adsorption across nanoporous materials and allows for rescaled force fields to reachquantum accuracy without the need for experimental input.

Pages

Subscribe to RSS - V. Van Speybroeck