CO₂ Capture by Porous Hyper-Cross-Linked Aromatic Polymers Synthesized Using Tetrahedral Precursors

Low-cost synthesis of porous hyper-cross-linked aromatic polymers (PHAPs) was achieved via the FeCl₃-catalyzed Friedel–Crafts alkylation reaction between tetraphenylsilane or tetraphenylgermanium as a building block and formaldehyde dimethylacetal as a cross-linker. The synthesized polymers were chemically and thermally stable and exhibited high surface areas of up to 1137 m² g^–1 (PHAP-1) and 1059 m² g^–1 (PHAP-2). The adsorption isotherms of the PHAPs revealed a high CO₂ adsorption capacity (104.3–114.4 mg g^–1) with an isosteric heat of adsorption in the range 26.5–27.3 kJ mol^–1 and a moderate CH₄ adsorption capacity (12.6–13.8 mg g^–1) at 273 K and 1 bar. The PHAP networks also exhibited high CO₂/N₂ and CO₂/CH₄ relativities of 29.3–34.2 and 11.3–12.5, respectively, at 273 K.