Robust Amine-Grafted Porous Organic Polymer for Highly Selective Carbon Dioxide Capture from Air

Direct air capture (DAC) of CO₂ using solid sorbents offers a promising alternative to conventional amine scrubbing due to lower regeneration energy, higher selectivity, and improved stability. In this study, a hydroxyl-rich porous organic polymer (OPTP-8) was synthesized and subsequently functionalized with (3-aminopropyl)trimethoxysilane (APTS) to yield OPTP-8-APTS, a material designed for efficient low-pressure CO₂ capture. Structural characterization confirmed successful grafting of amine functionalities via covalent bonding, while N₂ sorption revealed a significant decrease in surface area postfunctionalization due to partial pore blockage. Despite this reduction, OPTP-8-APTS exhibited enhanced CO₂ uptake at low pressure (0.98 mmol/g at 0.15 bar and 1.58 mmol/g at 1 bar, 298 K), and exceptional CO₂/N₂ selectivity over 900 at 298 K and exceeding 2200 at 273 K under DAC conditions (400 ppm of CO₂). This enhancement is attributed to strong chemisorption interactions with amine groups, as confirmed by high isosteric heat of adsorption (Q_st > 60 kJ/mol). Furthermore, OPTP-8-APTS demonstrated excellent thermal stability, cyclic durability over 32 cycles, and consistent performance under both dry and humid breakthrough tests. These findings underscore the potential of amine-functionalized POPs for high-performance CO₂ capture in DAC systems.