Selective CO₂ Adsorption in Ultrahydrophobic Molecular Pyrene Frameworks by Computational Design

The separation of carbon dioxide from industrial flue gas streams using porous materials is often thwarted by humidity. Most porous sorbents adsorb water more effectively than CO₂. Hence, water can out-compete CO₂ for adsorption sites, lowering the working CO₂ sorption capacity and increasing sorbent regeneration costs. Here, two pyrene-based hydrogen bonded organic frameworks (HOFs) are described that can separate CO₂ under humid conditions. The framework building blocks were chosen in a high-throughput density functional theory screen, followed by crystal structure prediction (CSP) to target a hydrophobic two-dimensionally porous framework. Gas sorption experiments showed selective adsorption of CO₂ and exceptionally low water adsorption in these HOFs. Dynamic column breakthrough measurements using mixed gas environments showed that the CO₂ working capacity was totally unaffected by water under simulated flue gas conditions up to 75% relative humidity. One of the CO₂-selective HOFs, diMeTBAP-α, was shown by CSP to be the most thermodynamically stable structure on the crystal energy landscape. This stability prediction was reflected by experiments, where an isostructural, scalable analogue of diMeTBAP-α, MeTBAP-α, retained its porosity and crystallinity after boiling in aqueous acids, which is important for carbon capture from acidic, humid flue gas.