Screening Aminated Fibrous Sorbents for Indoor CO2 Removal: Pore-Engineered PEI-Loaded Activated Carbon Fibre Felts

Solid amine adsorbents can capture CO2 at indoor-relevant concentrations (~1000 ppm), but many high-capacity adsorbents rely on granular or powdery supports that are difficult to integrate directly into air purification systems. Here, we applied three amination strategies to commercial fibrous substrates: bridge-grafting on viscose (TEPA-AMVF), direct grafting on polyacrylonitrile (TEPA-PAN), and physical impregnation on pore-engineered activated carbon fibre felt (PEI-ACF). These adsorbents were systematically screened under simulated indoor conditions (1000 ppm CO2, 27 °C, 50% RH). A significant capacity difference was observed: TEPA-AMVF (24.8 mg g−1) < TEPA-PAN (35.8 mg g−1) ≪ PEI-ACF (97.0 mg g−1). The superior performance of PEI-ACF was attributed to KOH activation, which produced a mesopore-rich structure (average pore diameter 26.1 nm at an optimal KOH/carbon ratio of 1.25) and enabled high nominal amine utilisation (0.19 mmol CO2 mmol N−1). PEI-ACF maintained high breakthrough-derived CO2 uptake across realistic indoor conditions (64.2–118.6 mg g−1 over 0%–100% RH; 71.6–124.5 mg g−1 over 400–5000 ppm CO2), exhibited rapid kinetics (pseudo-first-order rate constant k = 1.77 h−1; 81.7% of equilibrium uptake within 1 h), and showed stable but partial regeneration over four adsorption–desorption cycles at 60–70 °C under N2. Compared with granular or resin-based amine sorbents, the self-supporting PEI-ACF felt is expected to offer practical advantages for filter-integrated CO2 removal, including mechanical integrity under airflow, reduced risk of particle leakage, and compatibility with HVAC filter slots. Remaining challenges include direct pressure-drop validation, operation in O2-containing indoor air, long-term cycling, and management of CO2 released during regeneration.