V. Van Speybroeck

Quantum tunneling rotor as a sensitive atomistic probe of guests in a metal-organic framework

K. Titov, M.R. Ryder, A. Lamaire, Z. Zeng, A.K. Chaudhari, J. Taylor, E.M. Mahdi, S.M.J. Rogge, S. Mukhopadhyay, S. Rudić, V. Van Speybroeck, F. Fernandez-Alonso, J.-C. Tan
Physical Review Materials
7, 073402
2023
A1

Abstract 

Quantum tunneling rotors in a zeolitic imidazolate framework ZIF-8 can provide insights into local gas adsorption sites and local dynamics of porous structure, which are inaccessible to standard physisorption or x-ray diffraction sensitive primarily to long-range order. Using in situ high-resolution inelastic neutron scattering at 3 K, we follow the evolution of methyl tunneling with respect to the number of dosed gas molecules. While nitrogen adsorption decreases the energy of the tunneling peak, and ultimately hinders it completely (0.33 meV to zero), argon substantially increases the energy to 0.42 meV. Ab initio calculations of the rotational barrier of ZIF-8 show an exception to the reported adsorption sites hierarchy, resulting in anomalous adsorption behavior and linker dynamics at subatmospheric pressure. The findings reveal quantum tunneling rotors in metal-organic frameworks as a sensitive atomistic probe of local physicochemical phenomena.

Gold Open Access

DOI 

http://dx.doi.org/10.1103/PhysRevMaterials.7.073402

Challenges in modelling dynamic processes in realistic nanostructured materials at operating conditions

V. Van Speybroeck
Philosophical Transactions of the Royal Society A
381, 2250 & 20220239
2023
A1

Abstract 

The question is addressed in how far current modelling strategies are capable of modelling dynamic phenomena in realistic nanostructured materials at operating conditions. Nanostructured materials used in applications are far from perfect; they possess a broad range of heterogeneities in space and time extending over several orders of magnitude. Spatial heterogeneities from the subnanometre to the micrometre scale in crystal particles with a finite size and specific morphology, impact the material's dynamics. Furthermore, the material's functional behaviour is largely determined by the operating conditions. Currently, there exists a huge length–time scale gap between attainable theoretical length–time scales and experimentally relevant scales. Within this perspective, three key challenges are highlighted within the molecular modelling chain to bridge this length–time scale gap. Methods are needed that enable (i) building structural models for realistic crystal particles having mesoscale dimensions with isolated defects, correlated nanoregions, mesoporosity, internal and external surfaces; (ii) the evaluation of interatomic forces with quantum mechanical accuracy albeit at much lower computational cost than the currently used density functional theory methods and (iii) derivation of the kinetics of phenomena taking place in a multi-length–time scale window to obtain an overall view of the dynamics of the process.

This article is part of a discussion meeting issue ‘Supercomputing simulations of advanced materials’.

DOI 

https://doi.org/10.1098/rsta.2022.0239

Understanding the phase transition mechanism in the lead halide perovskite CsPbBr₃ via theoretical and experimental GIWAXS and Raman spectroscopy

A.E.J. Hoffman, R.A. Saha, S. Borgmans, P. Puech, T. Braeckevelt, M.B.J. Roeffaers, J.A. Steele, J. Hofkens, V. Van Speybroeck
APL Materials
Volume 11, Issue 4, article number 041124
2023
A1

Abstract 

Metal-halide perovskites (MHPs) exhibit excellent properties for application in optoelectronic devices. The bottleneck for their incorporation is the lack of long-term stability such as degradation due to external conditions (heat, light, oxygen, moisture, and mechanical stress), but the occurrence of phase transitions also affects their performance. Structural phase transitions are often influenced by phonon modes. Hence, an insight into both the structure and lattice dynamics is vital to assess the potential of MHPs. In this study, GIWAXS and Raman spectroscopy are applied, supported by density functional theory calculations, to investigate the apparent manifestation of structural phase transitions in the MHP CsPbBr3. Macroscopically, CsPbBr3 undergoes phase transitions between a cubic (α), tetragonal (β), and orthorhombic (γ) phase with decreasing temperature. However, microscopically, it has been argued that only the γ phase exists, while the other phases exist as averages over length and time scales within distinct temperature ranges. Here, direct proof is provided for this conjecture by analyzing both theoretical diffraction patterns and the evolution of the tilting angle of the PbBr6 octahedra from molecular dynamics simulations. Moreover, sound agreement between experimental and theoretical Raman spectra allowed to identify the Raman active phonon modes and to investigate their frequency as a function of temperature. As such, this work increases the understanding of the structure and lattice dynamics of CsPbBr3 and similar MHPs.

Gold Open Access

DOI 

http://dx.doi.org/10.1063/5.0144344

ReDD-COFFEE: A ready-to-use database of covalent organic framework structures and accurate force fields to enable high-throughput screenings

J. De Vos, S. Borgmans, P. Van der Voort, S.M.J. Rogge, V. Van Speybroeck
J. Mater. Chem. A
11, 14, 7468-7487
2023
A1

Abstract 

Covalent organic frameworks (COFs) are a versatile class of building block materials with outstanding properties thanks to their strong covalent bonds and low density. Given the sheer number of hypothetical COFs envisioned via reticular synthesis, only a fraction of all COFs have been synthesized so far. Computational high-throughput screenings offer a valuable alternative to speed-up such materials discovery. Yet, such screenings vitally depend on the availability of diverse databases and accurate interatomic potentials to efficiently predict each hypothetical COF’s macroscopic behavior, which is currently lacking. Therefore, we herein present ReDD-COFFEE, the Ready-to-use and Diverse Database of Covalent Organic Frameworks with Force field based Energy Evaluation, containing 268 687 COFs and accompanying ab initio derived force fields that are shown to outperform generic ones. Our structure assembly approach results in a huge amount of computer-ready structures with a high diversity in terms of geometric properties, linker cores, and linkage types. Furthermore, the textural properties of the database are analyzed and the most promising COFs for vehicular methane storage are identified. By making the database freely accessible, we hope it may also inspire others to further explore the potential of these intriguing functional materials.

 

Gold Open Access

DOI 

http://dx.doi.org/10.1039/D3TA00470H

Simulations in the era of exascale computing

C. Chang, V. L. Deringer, K. S. Katti, V. Van Speybroeck, C. M. Wolverton
Nature Reviews Materials
Volume: 8, Issue: 5, Pages: 309-313
2023
A1

Abstract 

Exascale computers - supercomputers that can perform 10(18) floating point operations per second - started coming online in 2022: in the United States, Frontier launched as the first public exascale supercomputer and Aurora is due to open soon; OceanLight and Tianhe-3 are operational in China; and JUPITER is due to launch in 2023 in Europe. Supercomputers offer unprecedented opportunities for modelling complex materials. In this Viewpoint, five researchers working on different types of materials discuss the most promising directions in computational materials science.

DOI 

http://dx.doi.org/10.1038/s41578-023-00540-6

Microscopic Linker Distribution in Mixed-Linker Zeolitic Imidazolate Frameworks via Computational Raman Spectroscopy: Implications for Gas Separation

A.E.J. Hoffman, J. Marreiros, S.M.J. Rogge, R. Ameloot, V. Van Speybroeck
ACS Applied Nano Materials
6, 7, 5645–5652
2023
A1

Abstract 

Mixed-linker zeolitic imidazolate frameworks (ZIFs) are important candidate materials for gas separation. By changing the linker content, their pore size can be tuned, offering the potential to regulate diffusion and adsorption. An important factor affecting these properties in mixed-linker ZIFs is the linker distribution, which is difficult to characterize. In this study, the microscopic linker distribution in mixed-linker ZIF-8/ZIF-90, with respectively methyl and carboxaldehyde functionalization, is elucidated via computational Raman spectroscopy. It is shown that the typical Raman band associated with the carboxaldehyde linker is shifted due to a change in hydrogen-bonding behavior. This insight allows one to explain the microscopic linker distribution in experimental mixed-linker structures.

DOI 

http://dx.doi.org/10.1021/acsanm.3c00106

Absorbing stress via molecular crumple zones: Strain engineering flexibility into the rigid UiO-66 material

S.M.J. Rogge, S. Borgmans, V. Van Speybroeck
Matter
6, 5, 1435-1462
2023
A1

Abstract 

Nanostructured materials such as metal-organic frameworks and perovskites can be tuned toward applications ranging from sensors to photovoltaic devices. Such design requires causal relations between a material’s atomic structure and macroscopic function, which remain elusive. Therefore, we herein introduce strain engineering as a general approach to rationalizing and designing how atomic-level structural modifications induce dynamically interacting strain fields that dictate a material’s macroscopic mechanical behavior. We first demonstrate the potential of strain engineering by designing shear instabilities in UiO-66, leading to counterintuitive behavior. The strain-engineered structures exhibit time- and space-dependent crumple zones that instill flexibility in the rigid material and locally focus the strain, partially preserving the material’s porosity under compression. Secondly, our strain fields help explain stimulus-induced phase coexistence in the flexible CoBDP, DMOF-1(Zn), and MIL-53(Al)-F materials. These examples demonstrate how strain engineering can be adopted to design state-of-the-art materials for challenging applications from the atomic level onward.

 

Gold Open Access

DOI 

http://dx.doi.org/10.1016/j.matt.2023.02.009

Pyrene-Based Covalent Organic Frameworks for Photocatalytic Hydrogen Peroxide Production

J. Sun, H. S. Jena, C. Krishnaraj, K. S. Rawat, S. Abednatanzi, J. Chakraborty, A. Laemont, W. Liu, H. Chen, Y.-Y. Liu, K. Leus, H. Vrielinck, V. Van Speybroeck, P. Van der Voort
Angewandte Chemie int. Ed.
Volume: 62; Issue: 19
2023
A1

Abstract 

Four highly porous covalent organic frameworks (COFs) containing pyrene units were prepared and explored for photocatalytic H2O2 production. The experimental studies are complemented by density functional theory calculations, proving that the pyrene unit is more active for H2O2 production than the bipyridine and (diarylamino)benzene units reported previously. H2O2 decomposition experiments verified that the distribution of pyrene units over a large surface area of COFs plays an important role in catalytic performance. The Py-Py-COF, though contains more pyrene units than other COFs, induces a high H2O2 decomposition due to a dense concentration of pyrene in small proximity over a limited surface area. Therefore, a two-phase reaction system (water-benzyl alcohol) was employed to inhibit H2O2 decomposition. This is the first report on applying pyrene-based COFs in a two-phase system for photocatalytic H2O2 generation.

DOI 

http://dx.doi.org/10.1002/anie.202216719

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

DOI 

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

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