Covalent Organic Framework (COF-1) under High Pressure.

Area of Science:

• Materials Science
• Chemistry
• Physics

Background:

• Covalent Organic Frameworks (COFs) are crystalline porous polymers.
• COF-1 features rigid 2D layers with benzene and boroxine rings, linked by weak van der Waals forces.
• The as-synthesized COF-1 contains solvent molecules in its pores, which can be removed via vacuum annealing to yield a high surface area empty-pore structure.

Purpose of the Study:

• To investigate the structural stability and mechanical properties of COF-1 under high pressure.
• To evaluate the impact of pore filling (mesitylene) versus empty pores on COF-1's response to compression.
• To determine the bulk modulus and linear incompressibilities of the COF-1 framework.

Main Methods:

• High-pressure X-ray diffraction (XRD) and Raman spectroscopy were employed.
• Experiments were conducted on both mesitylene-filled (COF-1-M) and empty-pore COF-1 samples.
• First-principles calculations were used to cross-check experimental findings.

Main Results:

• Partial amorphization and framework collapse were observed in both COF-1-M and empty-pore COF-1 above 12-15 GPa.
• The original structure of COF-1-M could be reversibly recovered after compression up to 10-15 GPa.
• The empty-pore COF-1 structure demonstrated remarkable stability, remaining intact up to at least 10 GPa.

Conclusions:

• The porous COF-1 structure exhibits significant mechanical robustness, stable up to 10 GPa even in its empty-pore form.
• The material shows reversible structural recovery after high-pressure treatment.
• The evaluated bulk modulus is 11.2(5) GPa, with linear incompressibilities k[100]=111(5) GPa and k[001]=15.0(5) GPa.