Hydrogen-bonded organic framework with tailored pores prepared by enlarging the core size for high-performance Xe/Kr separation

Abstract

The efficient separation of xenon (Xe) and krypton (Kr) mixtures is a valuable but challenging process in the gas industry. Hydrogen-bonded organic frameworks (HOFs) have emerged as a promising class of porous materials for gas separation; however, due to the lack of available design methods, accurately adjusting the pore size of HOFs to improve the separation performance remains a major challenge. Herein, we present a pore engineering optimized strategy by enlarging the core size of the rigid monomers to increase the pore size of benzene cyanide-based HOFs. The replacement of the benzene ring in the molecular core of HOF-40 with a larger-sized dipyrrole ring resulted in the assembly of HOF-FJU-8a with a slightly larger pore size of 4.2 × 4.6 Ų, which is demonstrated as the highest performing HOF material for Xe/Kr separation reported to date. The superior Xe/Kr separation was determined by the gas adsorption and dynamic breakthrough experiments, showing a separation factor of 8.5 and a Kr productivity over 72 L kg⁻¹ from the binary Xe/Kr mixture. The tailored pore size of HOF-FJU-8a played a crucial role in enabling the significant differential host–guest interactions and binding affinity, as confirmed by the single crystal structures of Xe-or Kr-loaded HOF-FJU-8a and GCMC calculations.