Hydrazine-Hydrazide-Linked Covalent Organic Frameworks for Water Harvesting.

Area of Science:

• Materials Science
• Chemistry

Background:

• Covalent organic frameworks (COFs) are crystalline porous polymers with tunable properties.
• Developing stable linkages in COFs is crucial for their practical applications.
• Irreversible linkages offer enhanced stability compared to reversible ones.

Purpose of the Study:

• To develop a postsynthetic strategy for creating covalent organic frameworks (COFs) with irreversible hydrazide linkages.
• To investigate the water uptake properties of these novel COFs for potential water harvesting applications.

Main Methods:

• Synthesized 2D and 3D hydrazine-linked frameworks.
• Performed partial oxidation to form irreversible hydrazide linkages.
• Utilized 15N multi-CP-MAS NMR to confirm linkage formation and transformation.
• Analyzed isothermal water uptake profiles of the synthesized COFs.

Main Results:

• Successfully synthesized three hydrazine-linked COFs and converted them to hydrazide-linked COFs.
• Confirmed the formation of hydrazide linkages using 15N multi-CP-MAS NMR.
• Identified a specific COF with excellent water harvesting capabilities from air in arid conditions.
• Observed characteristic S-shaped water sorption profiles with a steep uptake below 18% relative humidity.
• Achieved a total water uptake capacity of 0.45 g g⁻¹.

Conclusions:

• The postsynthetic strategy enables the creation of COFs with stable, irreversible hydrazide linkages.
• The developed COF is highly effective for water harvesting from air, even in arid environments.
• Water sorption analysis is a valuable tool for studying linkage transformations in COFs and understanding their properties.