Poly(ethylene oxide)-Based Mixed-Matrix Membranes Compromising N,O-Codoped Ultramicroporous Biomass Carbon for Efficient CO₂ Separation

The development of mixed-matrix membranes (MMMs) with concurrently high permeability and selectivity is critical for efficient CO2 separation and capture. Herein, an ultramicroporous biomass-derived carbon molecular sieve (NOPC-600), featuring high nitrogen and oxygen codoping, was synthesized via low-temperature KOH activation. Cross-linked poly(ethylene oxide) (XLPEO)-based MMMs were fabricated using NOPC-600 as a functional filler. The ultramicroporous architecture and abundant polar sites of NOPC-600 significantly enhanced CO2 solubility and facilitated gas transport, while promoting strong interfacial compatibility with the PEO matrix through hydrogen bonding. At a filler loading of 1.5 wt %, the resulting MMM exhibited a CO2 permeability of 821 barrer and a CO2/N2 selectivity of 48.6, representing improvements of 110 and 49.5%, respectively, over pristine XLPEO, surpassing the 2008 Robeson upper bound. Moreover, the membrane demonstrated excellent stability under mixed-gas conditions. This work presents a promising approach for designing high-performance CO2 separation membranes using N/O-codoped ultramicroporous biocarbon fillers.