A fluorene based covalent triazine framework with high CO2 and H-2 capture and storage capacities

Abstract

Porous organic polymers have come into focus recently for the capture and storage of postcombusted CO2. Covalent triazine frameworks (CTFs) constitute a nitrogen-rich subclass of porous polymers, which offers enhanced tunability and functionality combined with high chemical and thermal stability. In this work a new covalent triazine framework based on fluorene building blocks is presented, along with a comprehensive elucidation of its local structure, porosity, and capacity for CO2 capture and H-2 storage. The framework is synthesized under ionothermal conditions at 300-600 degrees C using ZnCl2 as a Lewis acidic trimerization catalyst and reaction medium. Whereas the materials synthesized at lower temperatures mostly feature ultramicropores and moderate surface areas as probed by CO2 sorption (297 m(2) g(-1) at 300 degrees C), the porosity is significantly increased at higher synthesis temperatures, giving rise to surface areas in excess of 2800 m(2) g(-1). With a high fraction of micropores and a surface area of 1235 m(2) g(-1), the CTF obtained at 350 degrees C shows an excellent CO2 sorption capacity at 273 K (4.28 mmol g(-1)), which is one of the highest observed among all porous organic polymers. Additionally, the materials have CO2/N-2 selectivities of up to 37. The hydrogen adsorption capacity of 4.36 wt% at 77 K and 20 bar is comparable to that of other POPs, yet the highest among all CTFs studied to date.