Center for Molecular Modeling - K. S. Rawat

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

leen — Tue, 25 Feb 2025 09:15:52 +0000

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

Abstract

We developed a robust three-dimensional (3D) covalent organic framework (COF), fully conjugated in both the planar (x, y) 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.

DOI

http://dx.doi.org/10.1021/jacs.4c15825

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2025 - Deng - JACS - 147 - 10219-10230.pdf

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

leen — Tue, 21 Jan 2025 08:23:21 +0000

W. Temmerman, R. Goeminne, K. S. Rawat, V. Van Speybroeck

Advanced Materials

2024

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.

DOI

https://doi.org/10.1002/adma.202412005

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Computational Modeling of Reticular Materials.pdf

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

leen — Tue, 19 Nov 2024 08:12:13 +0000

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

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.

DOI

https://doi.org/10.1002/adma.202413060

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Mesoporous Acridinium‐Based Covalent Organic Framework for Long‐lived Charge‐Separated (1).pdf

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

leen — Mon, 18 Nov 2024 10:21:20 +0000

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

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.

DOI

https://doi.org/10.1016/j.seppur.2024.130368

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

leen — Mon, 17 Jun 2024 08:17:35 +0000

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

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.

DOI

https://doi.org/10.1016/j.xcrp.2024.102057

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

siebe — Wed, 06 Dec 2023 13:17:04 +0000

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

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

DOI

http://dx.doi.org/

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am3c07036_si_001 (2).pdf

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

leen — Tue, 14 Nov 2023 10:13:43 +0000

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

6, 24, 22684-22692

2023

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.

DOI

https://doi.org/10.1021/acsanm.3c03248

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

leen — Tue, 10 Oct 2023 06:45:16 +0000

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

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.

DOI

http://dx.doi.org/10.1002/anie.202313836

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2023 - Chakraborty - Angewandte - 202313836.pdf

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

kuber — Mon, 07 Aug 2023 09:22:44 +0000

A. Chatterjee, J. Sun, K. S. Rawat, V. Van Speybroeck, P. Van der Voort

SMALL

Volume: 19, Issue: 46

2023

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.

DOI

http://dx.doi.org/10.1002/smll.202303189

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Pyrene-Based Covalent Organic Frameworks for Photocatalytic Hydrogen Peroxide Production

leen — Mon, 13 Mar 2023 11:39:30 +0000

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

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

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