Manipulation of Covalent Organic Frameworks by Side-Chain Functionalization: Toward Few Layer Nanosheets

Abstract

Recent developments in the field of covalent organic frameworks (COFs) describe the issue of processability. The precise tunability of delamination of such structures to obtain few layered nanosheets by synthetic control has been ventured in this study. Covalent anchoring of a series of linear and branched alkoxy side chains to the backbone of layered covalent organic frameworks was used to achieve this. To support the hypothesis, powder X-ray diffraction studies accompanied by computational modeling revealed that the elongation of side chains increases the interlayer distances of the COFs. This led to a successful study of the solvent-assisted exfoliation by atomic force microscopy techniques to obtain nanosheets with heights less than 2 nm, representing stacks of 4–5 layers. Dispersions of the functionalized COF nanosheets are stable for several hours. Furthermore, the surface properties are drastically changed, rendering the materials hydrophobic, with contact angles reaching up to 142° and complete blockage of the pore space toward water vapor. As a proof of concept, the sheets are processable and could be integrated into separators for lithium-ion batteries.

An Investigation of Conjugated Sulfonamide Materials as Binders for Organic Lithium-Ion Batteries

“…Moreover, a weaker high-angle diffraction peak is observed at 20.5° (0.45 nm; Figure b, inset), and corresponds to interlayer distances resulting from the sulfonamide side chains. This diffraction behavior has been observed previously with side-chain-functionalized two-dimensional frameworks. , The 1D oligomer demonstrated similar diffraction patterns with diffraction peaks at 2.3 and 4.3° representing a d spacing of 3.8 and 2.0 nm. A similar interlayer pattern is also observed at 21° (0.4 nm), which likely results from the sulfonamide side chains.…”

Covalent Organic Framework‐based Solid‐State Electrolytes, Electrode Materials, and Separators for Lithium‐ion Batteries

“…The incorporation of the side-chain modified COFs into separators for LIBs is considered to be an effective strategy to obtain novel separators with good electrolyte wettability and processability. [131] Recently, Bian et al designed a thin COFÀ C16/ PE composite membrane (~9 μm thick) used as separator in LIBs through a vacuum-assisted self-assembly method. [132] In [125] Reproduced with permission from ref.…”

Covalent Organic Frameworks as Model Materials for Fundamental and Mechanistic Understanding of Organic Battery Design Principles

“…Covalent organic frameworks (COFs) are an emerging class of ordered polymers and are among the most designable members of the family of porous organic materials, constructed by using modular chemistry, wherein the molecular building blocks can be decorated with a variety of redox-active groups connected via covalent bonds. , Depending on the geometry and connectivity of the monomeric modules, the network of the COFs can propagate in two or three dimensions with adjustable pore sizes and tunable topologies, which enables easy percolation of guest ion pathways during electrochemical investigations to understand the applicability in charge storage devices, particularly in batteries. , In many 2D COFs, being regarded as a new type of layered materials and resembling the stacked structure of graphite, the strong interlayer π–π interaction generates one-dimensional nanoporous channels (Figure A,B) , These nanochannels can be decorated with functional groups containing heteroatoms, allowing facile interaction with guest ions from the electrolyte under applied potential, and are suitable candidates for rechargeable battery systems, constructed by a counter metal electrode and the COF as a working electrode (Figure A, Figure A) . Additionally, weakening of the π–π stacking interactions enables the exfoliation of the multilayer COFs to a few atom-thick layers, called covalent organic nanosheets (CONs), − where the constituting redox-functionalities are more exposed than in typical COF-derived electrodes, for improved interactions with the guest ions (Figure B). , The COFs with substantial structural rigidity and planarity, propelled by a highly conjugative vinylene linkage , and/or fused aromatic ring, show facile electron transfer to its redox functionalities. Hence, designing electroactive COFs with reasonable electronic conductivity and ample redox centers delivers promising electrode performance.…”