High-Connectivity 3D Covalent Organic Frameworks with pdp Net for Efficient C₂H₂/CO₂ Separation

Area of Science:

• Materials Science
• Chemistry

Background:

• High-connectivity 3D covalent organic frameworks (COFs) are promising for various applications due to their complex structures and stability.
• Synthesizing 3D COFs using mixed high-nodal building units presents a significant challenge in materials chemistry.

Purpose of the Study:

• To introduce novel 3D COFs, JUC-661 and JUC-662, synthesized from mixed high-nodal building units.
• To investigate the gas separation capabilities of these new COFs, particularly for acetylene/carbon dioxide mixtures.

Main Methods:

• Synthesis of two novel 3D COFs (JUC-661 and JUC-662) using D2h-symmetric 8-nodal and D3h-symmetric 6-nodal building blocks.
• Characterization of the COFs' structure, including unprecedented [8+6]-c pdp nets and mesoporous polyhedral cages.
• Evaluation of gas adsorption and separation performance using dynamic breakthrough experiments under various humidity conditions.
• Computational analysis using Monte Carlo simulations and DFT calculations to understand adsorption mechanisms.

Main Results:

• Successful synthesis of JUC-661 and JUC-662, featuring rare mesoporous polyhedral cages (~3.9 nm).
• Demonstrated outstanding adsorption selectivities for C2H2/CO2 mixtures (4.3 for JUC-661, 5.9 for JUC-662).
• Maintained high separation performance under 100% humidity conditions.
• Computational studies revealed pore cavity structure and fluorination effects enhance C2H2 selectivity.

Conclusions:

• The study expands the structural diversity of 3D covalent organic frameworks.
• JUC-661 and JUC-662 show significant potential for energy-efficient gas separation processes.
• Fluorination of building units can be a strategy to enhance selective adsorption in COFs.