P. Van der Voort

High-Throughput Screening of Covalent Organic Frameworks for Carbon Capture Using Machine Learning

J. De Vos, S. Ravichandran, S. Borgmans, L. Vanduyfhuys, P. Van der Voort, S.M.J. Rogge, V. Van Speybroeck
Chemistry of Materials
36, 9, 4315-4330
2024
A1

Abstract 

Postcombustion carbon capture provides a high-potential pathway to reduce anthropogenic CO2 emissions in the short term. In this respect, nanoporous materials, such as covalent organic frameworks (COFs), offer a promising platform as adsorbent beds. However, due to the modular nature of COFs, an almost unlimited number of structures can possibly be synthesized. To efficiently identify promising materials and reveal performance trends within the COF material space, we present a computational high-throughput screening of 268,687 COFs for their ability to efficiently and selectively separate CO2 from the flue gas of power plants using a pressure swing adsorption process. Furthermore, we demonstrate that our screening can be significantly accelerated using machine learning to identify a set of promising materials. These are subsequently characterized with high accuracy, taking into account the effects of competitive adsorption and coadsorption. Our screening reveals that imide, (keto)enamine, and (acyl)hydrazone COFs are particularly interesting for carbon capture. Additionally, the best-performing materials are 3D COFs possessing strong CO2 adsorption sites between aromatic rings at opposite sides of pores with a diameter of 1.0 nm. In 2D COFs, a significant influence of the framework chemistry, such as imide linkages or fluoro groups, is observed. Our design rules can guide experimental researchers to construct high-performing COFs for CO2 capture.

Gold Open Access

Computational Protocol for the Spectral Assignment of NMR Resonances in Covalent Organic Frameworks

S. Vanlommel, S. Borgmans, C. V. Chandran, S. Radhakrishnan, P. Van der Voort, E. Breynaert, V. Van Speybroeck
Journal of Chemical Theory and Computation (JCTC)
20, 9, 3823–3838
2024
A1

Abstract 

Solid-state nuclear magnetic resonance spectroscopy is routinely used in the field of covalent organic frameworks to elucidate or confirm the structure of the synthesized samples and to understand dynamic phenomena. Typically this involves the interpretation and simulation of the spectra through the assumption of symmetry elements of the building units, hinging on the correct assignment of each line shape. To avoid misinterpretation resulting from library-based assignment without a theoretical basis incorporating the impact of the framework, this work proposes a first-principles computational protocol for the assignment of experimental spectra, which exploits the symmetry of the underlying building blocks for computational feasibility. In this way, this protocol accommodates the validation of previous experimental assignments and can serve to complement new NMR measurements.

The application of porous organic polymers as metal free photocatalysts in organic synthesis

M. Debruyne, P. Van der Voort, V. Van Speybroeck, C. Stevens
Chemistry - A European Journal
2024
A1

Abstract 

Concerns about increasing greenhouse gas emissions and their effect on our environment highlight the urgent need for new sustainable technologies. Visible light photocatalysis allows the clean and selective generation of reactive intermediates under mild conditions. The more widespread adoption of the current generation of photocatalysts, particularly those using precious metals, is hampered by drawbacks such as their cost, toxicity, difficult separation, and limited recyclability. This is driving the search for alternatives, such as porous organic polymers (POPs). This new class of materials is made entirely from organic building blocks, can possess high surface area and stability, and has a controllable composition and functionality. This review focuses on the application of POPs as photocatalysts in organic synthesis. For each reaction type, a representative material is discussed, with special attention to the mechanism of the reaction. Additionally, an overview is given, comparing POPs with other classes of photocatalysts, and critical conclusions and future perspectives are provided on this important field.

Development of porous organic polymers as metal free photocatalysts for the aromatization of N-heterocycles

M. Debruyne, N. Raeymackers, H. Vrielinck, S. Radhakrishnan, E. Breynaert, M. Delaey, A. Laemont, K. Leus, J. Everaert, H. Rijckaert, D. Poelman, R. Morent, N. De Geyter, P. Van der Voort, V. Van Speybroeck, C. Stevens, T.S.A Heugebaert
ChemCatChem
2023
A1

Abstract 

Porous organic polymers (POPs), and especially covalent triazine frameworks (CTFs), are being developed as the next generation of metal-free heterogeneous photocatalysts. However, many of the current synthetic routes to obtain these photoactive POPs require expensive monomers and rely on precious metal catalysts, thus hindering their widespread implementation. In this work, a range of POPs was synthesized from simple unfunctionalized aromatic building blocks, through Lewis acidcatalyzed polymerization. The obtained materials were applied, for the first time, as heterogeneous photocatalysts for the aromatization of N-heterocycles. With the use of the most active material, denoted as CTF-Pyr, which consists of photoactive pyrene and triazine moieties, a wide range of pyridines, dihydroquinoline-5-ones, tetrahydroacridine-1,8-diones and pyrazoles were obtained in excellent yields (70-99%). Moreover, these reactions were carried out under very mild conditions using air and at room temperature, highlighting the potential of these materials as catalysts for green transformations.

Engineering of Phenylpyridine- and Bipyridine-Based Covalent Organic Frameworks for Photocatalytic Tandem Aerobic Oxidation/Povarov Cyclization

M. Debruyne, S. Borgmans, S. Radhakrishnan, E. Breynaert, H. Vrielinck, K. Leus, A. Laemont, J. De Vos, K. S. Rawat, S. Vanlommel, H. Rijckaert, H. Salemi, J. Everaert, F. Vanden Bussche, D. Poelman, R. Morent, N. De Geyter, P. Van der Voort, V. Van Speybroeck, C.V. Stevens
ACS Applied Materials & Interfaces
15, 29, 35092–35106
2023
A1

Abstract 

Covalent organic frameworks (COFs) are emerging as a new class of photoactive organic semiconductors, which possess crystalline ordered structures and high surface areas. COFs can be tailor-made toward specific (photocatalytic) applications, and the size and position of their band gaps can be tuned by the choice of building blocks and linkages. However, many types of building blocks are still unexplored as photocatalytic moieties and the scope of reactions photocatalyzed by COFs remains quite limited. In this work, we report the synthesis and application of two bipyridine- or phenylpyridine-based COFs: TpBpyCOF and TpPpyCOF. Due to their good photocatalytic properties, both materials were applied as metal-free photocatalysts for the tandem aerobic oxidation/Povarov cyclization and α-oxidation of N-aryl glycine derivatives, with the bipyridine-based TpBpyCOF exhibiting the highest activity. By expanding the range of reactions that can be photocatalyzed by COFs, this work paves the way toward the more widespread application of COFs as metal-free heterogeneous photocatalysts as a convenient alternative for commonly used homogeneous (metal-based) photocatalysts.

Open Access version available at UGent repository

Phosphorous Covalent Triazine Framework based Nanomaterials for the Electrocatalytic Hydrogen Evolution Reaction

H. S. Jena, C. Krishnaraj, B. K. Satpathy, K. S. Rawat, K. Leus, S. Veerapandian, R. Morent, N. De Geyter, V. Van Speybroeck, D. Pradhan, P. Van der Voort
ACS Applied Nano Materials
2023
A1

Abstract 

The production of hydrogen via electrocatalytic reduction of water using metal-free nanomaterials as the catalyst is a promising and ultimate green approach. Graphitic carbon nitride, covalent organic frameworks, and covalent triazine frameworks (CTFs) are some of the nanostructured materials that are investigated for this purpose. Currently, these materials still lack the efficiency to compete with other techniques (electrolysis). This is because the reaction mechanism and active sites are, in many cases, still poorly understood. In this work, we report a set of metal-free nanostructure-based electrocatalysts, phosphorus covalent triazine frameworks (PCTFs), for electrocatalytic hydrogen production. The hydrogen evolution reaction (HER) performance of PCTF-based nanomaterials is ascribed to the synergistic effect of isolated single nitrogen and phosphorus sites on the large surface area. By combining both experimental and theoretical studies, we found that especially the pyridinic-nitrogen species are the most active sites for the HER. The presence of phosphorus next to the pyridinic-N enhances the HERs. The present results provide a better understanding of the importance of different heteroatoms in nanomaterials as active sites in HERs. Theoretical studies confirmed that phosphorus, being electron rich, creates high electron densities on the nearby N atoms of the CTF materials and intensifies the HER process.

Super-Oxidizing Covalent Triazine Framework Electrocatalyst for Two-Electron Water Oxidation to H2O2

R. Khan, J. Chakraborty, K. S. Rawat, R. Morent, N. De Geyter, V. Van Speybroeck, P. Van der Voort
Angewandte Chemie int. Ed.
Volume: 62, Issue: 47
2023
A1

Abstract 

Electrochemical two-electron water oxidation (2e WOR) is gaining surging research traction for sustainable hydrogen peroxide production. However, the strong oxidizing environment and thermodynamically competitive side-reaction (4e WOR) posit as thresholds for the 2e WOR. We herein report a custom-crafted covalent triazine network possessing strong oxidizing properties as a proof-of-concept metal-free functional organic network electrocatalyst for catalyzing 2e WOR. As the first-of-its-kind, the material shows a maximum of 89.9% Faradaic Efficiency and 1428 μmol/h/cm2 H2O2 production rate at 3.0 V bias potential (vs reversible hydrogen electrode, RHE), which are either better or comparable to the stateof-the-art electrocatalysts. We have experimentally confirmed a stepwise 2e WOR mechanism which was further computationally endorsed by density functional theory studies.

Exploring the Charge Storage Dynamics in Donor–Acceptor Covalent Organic Frameworks Based Supercapacitors by Employing Ionic Liquid Electrolyte

A. Chatterjee, J. Sun, K. S. Rawat, V. Van Speybroeck, P. Van der Voort
SMALL
Volume: 19, Issue: 46
2023
A1

Abstract 

Two donor–acceptor type tetrathiafulvalene (TTF)-based covalent organic frameworks (COFs) are investigated as electrodes for symmetric supercapacitors in different electrolytes, to understand the charge storage and dynamics in 2D COFs. Till-date, most COFs are investigated as Faradic redox pseudocapacitors in aqueous electrolytes. For the first time, it is tried to enhance the electrochemical performance and stability of pristine COF-based supercapacitors by operating them in the non-Faradaic electrochemically double layer capacitance region. It is found that the charge storage mechanism of ionic liquid (IL) electrolyte based supercapacitors is dependent on the micropore size and surface charge density of the donor–acceptor COFs. The surface charge density alters due to the different electron acceptor building blocks, which in turn influences the dense packing of the IL near its pore. The micropores induce pore confinement of IL in the COFs by partial breaking of coulomb ordering and rearranging it. The combination of these two factors enhance the charge storage in the highly microporous COFs. The density functional theory calculations support the same. At 1 A g−1, TTF-porphyrin COF provides capacitance of 42, 70, and 130 F g−1 in aqueous, organic, and IL electrolyte respectively. TTF-diamine COF shows a similar trend with 100 F g−1 capacitance in IL.

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

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.

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