An anionic two dimensional covalent organic framework from tetratopic borate centres pillared by lithium ions

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Nanotechnology

Background:

• Two-dimensional covalent organic frameworks (2D COFs) are typically formed via non-covalent interactions like π-π stacking and hydrogen bonding.
• These interactions govern the layer stacking and properties of 2D COFs.
• Anionic frameworks offer unique properties but are less explored.

Purpose of the Study:

• To introduce a novel 2D anionic covalent organic framework (COF) utilizing ionic interactions for layer connection.
• To investigate the crystallization process and morphological evolution of the borate-based COF.
• To evaluate the impact of ionic interactions and ordered ion arrangement on material conductivity.

Main Methods:

• Synthesis of an amorphous borate-based polymer.
• Solvothermal treatment for crystallization.
• Characterization of crystallite growth and morphology.
• Exfoliation into nanosheets via sonication.
• Conductivity measurements of crystalline vs. amorphous materials.

Main Results:

• A 2D anionic covalent organic framework with tetratopic borate linkages was successfully synthesized.
• Crystallization proceeded from amorphous polymers to hollow crystallite spheres.
• The material could be exfoliated into nanosheets.
• Ordered lithium ion arrangement in the interlayer space significantly enhanced ionic conductivity (tenfold increase).

Conclusions:

• Ionic interactions can effectively connect layers in 2D COFs, complementing traditional non-covalent forces.
• The developed borate-based COF exhibits tunable morphology and can be processed into nanosheets.
• The ordered arrangement of cations within the anionic framework is crucial for achieving high ionic conductivity.