A Flexible Microporous Hydrogen-Bonded Organic Framework for Gas Sorption and Separation

Area of Science:

• Materials Science
• Chemistry
• Nanotechnology

Background:

• Hydrogen-bonded organic frameworks (HOFs) are a class of porous materials with tunable properties.
• Developing novel HOFs with enhanced gas adsorption capabilities is crucial for applications in gas storage and separation.

Purpose of the Study:

• To construct and characterize a new three-dimensional HOF (HOF-5) using a novel organic linker.
• To investigate the gas adsorption properties of the activated HOF-5a, particularly for carbon dioxide and acetylene.

Main Methods:

• Synthesis of HOF-5 using 4,4',4″,4‴-tetra(2,4-diamino-1,3,5-triazin-6-yl)tetraphenylethene.
• Powder X-ray diffraction (PXRD) for structural analysis and determination of framework contraction.
• Nitrogen (N2) adsorption-desorption isotherms at 77 K to assess porosity and surface area (BET).
• Powder neutron diffraction and theoretical calculations to elucidate gas encapsulation mechanisms.

Main Results:

• HOF-5 was successfully synthesized and activated to HOF-5a, exhibiting a significant framework contraction of ~21% by volume.
• Activated HOF-5a displayed a Brunauer-Emmett-Teller (BET) surface area of 1101 m²/g.
• HOF-5a showed a stepwise N2 adsorption isotherm, indicating framework flexibility.
• High uptake of acetylene and carbon dioxide under ambient conditions was observed.
• Powder neutron diffraction and theoretical calculations confirmed the encapsulation of CO2 in a pseudo-one-dimensional array within the pores.

Conclusions:

• HOF-5a is a flexible, porous material with potential for gas storage applications.
• The unique pore characteristics of HOF-5a enable efficient capture of CO2 and acetylene.
• The study highlights the structure-property relationship in HOFs for targeted gas adsorption.