Nitrogen-rich triphenylamine-based porous organic polyaminals for the adsorption/separation of C1–C3 light hydrocarbons and efficient iodine capture

Abstract

Covalent cross-linked porous organic polymers (POPs) have shown great potential in adsorption and separation fields owing to their high surface areas, easy functionalization, and porous design using synthetic strategies. Herein, we report the facile preparation of two triphenylamine-based nitrogen-rich porous organic polyaminals (TPOAs), denoted as TPOA-F and TPOA-OH, from triphenylamine-based triazine-hexamine and commercially available fluorine- and hydroxyl-monoaldehydes, respectively via a amine–aldehyde condensation reaction without any catalyst addition. These two resulting TPOAs possessed large specific surface areas (1179 and 565 m² g⁻¹) and hierarchical pore distribution (0.58 to 5.20 nm). Owing to this, TPOAs exhibited highly promising application potential for natural gas purification (mainly light hydrocarbons and CO₂ separation). Among them, TPOA-F shows the highest C₃H₈ uptake of 225 mg g⁻¹, C₂H₆ uptake of 122 mg g⁻¹, and CO₂ uptake of 155 mg g⁻¹ at 273 K/1 bar and C₃H₈ uptake of 187 mg g⁻¹, C₂H₆ uptake of 93 mg g⁻¹, and CO₂ uptake of 95 mg g⁻¹ at 298 K/1 bar. Then, the C₃H₈/CH₄, C₂H₆/CH₄, C₃H₈/C₂H₆, C₃H₈/CO₂, C₂H₆/CO₂, and CO₂/CH₄ gas mixture adsorption selectivities for TPOAs demonstrated the values of 68.7–78.8, 14.0–15.7, 4.9–5.0, 16.5–17.4, 3.4–3.5, and 4.2–4.5. Meanwhile, TPOAs also displayed considerable iodine capture performance up to 3.43 g g⁻¹. In addition, this has surpassed many reported porous polyaminal materials for their abundant porosity and nitrogen active sites, which offer host–guest interactions due to the high electron density. This study would provide valuable guidance for the development and application of efficient POP-based adsorption and separation materials.