Covalent Organic Framework (COF‐1) under pressure

Covalent Organic Frameworks (COF’s) form a family of polymeric materials composed only by light elements. The absence of metal atoms in their structure makes COF’s distinctly different compared to their relatives, Metal Organic Framework materials (MOF’s). Historically first COF structure (named COF-1) was reported back in 2005 by Cote et al., (Science 310 (2015) 1166).  It consists of benzene rings linked by B₃O₃ into hexagon-shaped 2D sheets which are stacked into a layered structure, resembling in this respect the structure of graphite composed by graphene layers. By analogy with graphene the single layer of COF material could be named as COFene since it represents a true 2D material composed by carbon, hydrogen, boron and oxygen. Unlike graphite, COF-1 is porous material with relatively high surface area which makes it promising for various applications, e.g. for energy storage devices, as a sorbents for gas storage or for membranes.  However, little was known about mechanical properties of COF’s or single layered COFenes except for few theoretical estimations. Unlike graphite or MOF’s, no high pressure studies were available for COFs. The study by A. Talyzin group from Umeå University (Sweden) performed at Elettra at the Xpress beamline and SOLEIL synchrotrons in collaboration with the Technical University of Dresden (Germany) and the Chalmers University (Sweden) is first to evaluate compressibility and pressure limits for stability of COF-1 structure.
 
Synchrotron X-ray diffraction and Raman spectroscopy were used to evaluate what happen with structure of this material at pressures up to 30 GPa. It was found that the ambient pressure structure of COF-1 can be reversibly recovered even after compression up to 10-15 GPa. The COF-1 structure collapses at higher pressures with formation of semi-amorphous phase.  Remarkable stability of highly porous COF-1 structure at high pressures is surprising. For example, porous MOF structures collapse at lower pressures. 
Combination of experimental and theoretical approaches provides insight into stiffness and mechanical properties of unique COF-1 structure which can be considered as typical representative for the whole family of COF materials.
 

Figure 1.    Left: schematics of the high pressure experiments involving diamond anvil cell. Right top: Crystal structure model of COF-1-M with pores filled by disordered mesitylene molecules (balls). Right bottom:  Pressure dependences of unit cell volume of COF-1-M recorded in three separate experiments: red symbols are data corresponding to pressure run in mesitylene.

This research was conducted by the following research team:

Jinhua Sun^1,2, Artem Iakunkov¹, Igor A. Baburin³, Boby Joseph⁴, Vincenzo Palermo², and Alexandr V. Talyzin¹

¹ Department of Physics, Umeå University, Umeå, Sweden
² Department of Industrial and Materials Science, Chalmers Tekniska Högskola, Göteborg, Sweden 
³ Theoretische Chemie, Technische Universitat Dresden, Dresden, Germany
⁴ Gd. R. IISc-ICTP, Elettra-Sincrotrone Trieste, Trieste, Italy 

Contact persons:

Alexandr V. Talyzin, email: