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 H2 storage. The framework is synthesized under ionothermal conditions at 300–600 °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 m2 g−1 at 300 °C), the porosity is significantly increased at higher synthesis temperatures, giving rise to surface areas in excess of 2800 m2 g−1. With a high fraction of micropores and a surface area of 1235 m2 g−1, the CTF obtained at 350 °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/N2 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.
Highlights
Whereas the materials synthesized at lower temperatures mostly feature ultramicropores and moderate surface areas as probed by CO2 sorption (297 m2 gÀ1 at 300 C), the porosity is significantly increased at higher synthesis temperatures, giving rise to surface areas in excess of 2800 m2 gÀ1
With a high fraction of micropores and a surface area of 1235 m2 gÀ1, the Covalent triazine frameworks (CTFs) obtained at 350 C shows an excellent CO2 sorption capacity at 273 K (4.28 mmol gÀ1), which is one of the highest observed among all porous organic polymers
CTFs synthesized at low temperatures (300–400 C) may show little crystallinity, yet at the same time may have well-de ned local structures.[1,5,9,32]
Summary
The development of covalent triazine frameworks (CTFs), a subclass of porous organic polymers (POPs), garnered significant attention owing to their high surface areas combined with a highly robust nature, that is, high thermal (>300 C) and chemical stabilities towards concentrated acids and bases.[1,2,3,4,5] CTFs are considered ideal scaffolds for applications such as heterogeneous catalysis,[6,7,8,9] gas storage and separation.[9,10,11,12,13,14,15,16] Recently, low temperature syntheses of CTFs have setThe development of potent gas storage systems has been fueled by the need for highly selective gas capture materials apt to selectively lter out or enrich relevant gases such as methane or carbon dioxide. Ue gas of a coal- red power plant consists of approximately 15% CO2, 5% H2O, 5% O2 and 75% N2 and is emitted at 40–80 C and 1 bar.[20,21] materials suitable for CCS require a high preference for adsorption of CO2 under these conditions. Amine scrubbing and cryogenic cooling are the only established technologies for CO2 capture up to date, which, have the disadvantage of increasing the energy requirements of a power plant by 25– 40%.20,22. The use of solid physical adsorbents for CO2 capture, such as metal– organic frameworks (MOFs) and POPs, was part of several reviews.[20,21,24,25,26,27] Main advantages of solid adsorbents are their
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