An official website of the United States government
Abstract Woven covalent organic frameworks (COF) possess entangled 3D frameworks. The metallated version of these structures contains spatially isolated Cu(I) centers and promising optoelectronic properties because of metal‐to‐ligand charge transfer (MLCT). However, despite their potential, woven COFs have not yet been investigated as photocatalysts. In this study, a new woven COF, Cu‐PhenBDA‐COF, functionalized with diacetylene bonds is developed. Cu‐PhenBDA‐COF is fully characterized, and the optoelectronic and photocatalytic properties are compared to previously reported Cu‐COF‐505. The diacetylene bonds of the linker positively impact the optoelectronic properties of Cu‐PhenBDA‐COF and result in a narrower bandgap and better charge separation efficiency. When the Cu(I) center is removed from both woven COFs, the absorption edge is blueshifted, resulting in a wider bandgap, and there is a considerable decrease in the charge separation efficiency, underscoring the pivotal role of MLCT. This trend is reflected in the photocatalytic activity of the woven COFs toward the degradation of sulfamethoxazole in water, where the highest reaction rate constant (kapp) is recorded for the metallated diacetylene functionalized woven COF, Cu‐PhenBDA‐COF.
more »
« less
Microkinetic insights into the role of catalyst and water activity on the nucleation, growth, and dissolution during COF-5 synthesis
The chemical pathway for synthesizing covalent organic frameworks (COFs) involves a complex medley of reaction sequences over a rippling energy landscape that cannot be adequately described using existing theories. Even with the development of state-of-the-art experimental and computational tools, identifying primary mechanisms of nucleation and growth of COFs remains elusive. Other than empirically, little is known about how the catalyst composition and water activity affect the kinetics of the reaction pathway. Here, for the first time, we employ time-resolved in situ Fourier transform infrared spectroscopy (FT-IR) coupled with a six-parameter microkinetic model consisting of ∼10 million reactions and over 20 000 species. The integrated approach elucidates previously unrecognized roles of catalyst p K a on COF yield and water on growth rate and size distribution. COF crystalline yield increases with decreasing p K a of the catalysts, whereas the effect of water is to reduce the growth rate of COF and broaden the size distribution. The microkinetic model reproduces the experimental data and quantitatively predicts the role of synthesis conditions such as temperature, catalyst, and precursor concentration on the nucleation and growth rates. Furthermore, the model also validates the second-order reaction mechanism of COF-5 and predicts the activation barriers for classical and non-classical growth of COF-5 crystals. The microkinetic model developed here is generalizable to different COFs and other multicomponent systems.
more »
« less
- Award ID(s):
- 2132022
- PAR ID:
- 10447624
- Date Published:
- Journal Name:
- Nanoscale
- Volume:
- 15
- Issue:
- 21
- ISSN:
- 2040-3364
- Page Range / eLocation ID:
- 9329 to 9338
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Modern syntheses of colloidal nanocrystals yield extraordinarily narrow size distributions that are believed to result from a rapid “burst of nucleation” (La Mer, JACS , 1950, 72 (11), 4847–4854) followed by diffusion limited growth and size distribution focusing (Reiss, J. Chem. Phys. , 1951, 19 , 482). Using a combination of in situ X-ray scattering, optical absorption, and 13 C nuclear magnetic resonance (NMR) spectroscopy, we monitor the kinetics of PbS solute generation, nucleation, and crystal growth from three thiourea precursors whose conversion reactivity spans a 2-fold range. In all three cases, nucleation is found to be slow and continues during >50% of the precipitation. A population balance model based on a size dependent growth law (1/ r ) fits the data with a single growth rate constant ( k G ) across all three precursors. However, the magnitude of the k G and the lack of solvent viscosity dependence indicates that the rate limiting step is not diffusion from solution to the nanoparticle surface. Several surface reaction limited mechanisms and a ligand penetration model that fits data our experiments using a single fit parameter are proposed to explain the results.more » « less
-
Covalent organic framework (COF)-supported palladium catalysts have garnered enormous attention for cross-coupling reactions. However, the limited linkage types in COF hosts and their suboptimal catalytic performance have hindered their widespread implementation. Herein, we present the first study immobilizing palladium acetate onto a dioxin-linked COF (Pd/COF-318) through a facile solution impregnation approach. By virtue of its permanent porosity, accessible Pd sites arranged in periodic skeletons, and framework robustness, the resultant Pd/COF-318 exhibits exceptionally high activity and broad substrate scope for the Suzuki–Miyaura coupling reaction between aryl bromides and arylboronic acids at room temperature within an hour, rendering it among the most effective Pd/COF catalysts for Suzuki–Miyaura coupling reactions to date. Moreover, Pd/COF-318 demonstrates excellent recyclability, retaining high activity over five cycles without significant deactivation. The leaching test confirms the heterogeneity of the catalyst. This work uncovers the vast potential of dioxin-linked COFs as catalyst supports for highly active, selective, and durable organometallic catalysis.more » « less
-
Abstract The rapid and environmentally benign synthesis of metal‐immobilized covalent organic frameworks (metal/COFs) for heterogeneous catalysis is a pervasive challenge, as the mainstream synthesis is exceedingly time‐consuming (up to four days) and demands the use of hazardous solvents. Herein, we describe a sustainable and efficient one‐step sonochemical strategy for constructing diverse palladium (II)‐immobilized COFs (Pd(II)/COFs). By merging the sonochemistry‐assisted COF synthesis and in situ Pd (II) immobilization into a single step, this strategy enables the rapid formation of Pd(II)/COF hybrids within an hour under ambient conditions using water as the solvent. Notably, gram‐scale synthesis of Pd(II)/COFs is achievable. The resulting Pd(II)/COFs exhibit superb crystallinity and high surface area, leading to remarkable activity, excellent functionality tolerance, and high recyclability for the Suzuki–Miyaura cross‐coupling reaction of aryl bromides and arylboronic acids at room temperature. This one‐step sonochemical strategy effectively addresses the long‐lasting limitations of traditional multistep synthesis, paving a fast and sustainable avenue to diversified metal/COF hybrids for heterogeneous catalysis and potentially other applications.more » « less
-
Abstract Covalent organic frameworks (COFs) are promising for catalysis, sensing, gas storage, adsorption, optoelectricity, etc. owning to the unprecedented combination of large surface area, high crystallinity, tunable pore size, and unique molecular architecture. Although COFs are in their initial research stage, progress has been made in the design and synthesis of COF‐based electrocatalysis for the oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, and CO2reduction in energy conversion and fuel generation. Design principles are also established for some of the COF materials toward rational design and rapid screening of the best electrocatalysts for a specific application. Herein, the recent advances in the design and synthesis of COF‐based catalysts for clean energy conversion and storage are presented. Future research directions and perspectives are also being discussed for the development of efficient COF‐based electrocatalysts.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d2nr06685h
