Phthalazinone structure-based covalent triazine frameworks and their gas adsorption and separation properties

Abstract

In this work, new classes of phthalazinone-based covalent triazine frameworks (PHCTFs) were prepared by ionothermal synthesis from two full rigid dicyano building blocks with rigid, thermostable and asymmetric N-heterocycle-containing structures. The surface and internal morphologies of PHCTFs were examined by FE-SEM and TEM. The resultant microporous polymers, PHCTFs, exhibited BET specific surface areas up to 1845 m² g⁻¹ and a moderately narrow pore size distribution. According to the sorption measurements, the CO₂ uptake can be up to 17.1 wt% (273 K/1 bar) and the H₂ uptake can be up to 1.92 wt% (77 K/1 bar). Moreover, the initial slopes of the single component gas adsorption isotherms in the low pressure range were used as the gas separation ratios. The obtained polymer networks possess satisfactory CO₂/N₂ selectivity performance up to 52 and CO₂/CH₄ selectivity up to 12. Combining the relationship of the structure and performance, it can be concluded that a twisted and non-coplanar topology conformation can be used to improve the porosity of microporous organic polymers. At the same time, the nitrogen- and oxygen-rich characteristics of the phthalazinone core endow the networks with a strong affinity for CO₂ and thereby high CO₂ adsorption capacity. So the pore structure and chemical composition may play very important roles on the adsorption properties of small gas molecules.