Secondary interfacial polymerization seals defects to repurpose water treatment thin film composites membranes for CO2 capture

Secondary interfacial polymerization tailors RO/NF TFCs for CO 2 capture. • A PEI secondary layer mitigates nonselective defects and enhances selectivity. • Mixed-gas tests show about 200 GPU CO 2 permeance with CO 2 /N 2 selectivity about 75. • Reversible 50 ppm SO 2 response; performance is retained after cycling. • PIP-based membranes show higher gas-separation performance than MPD-based analogues. Interfacial polymerization (IP), most commonly based on PIP/TMC and MPD/TMC chemistries, is the foundation for polyamide (PA) thin film composite (TFC) membranes used in water treatment. However, the reaction is rapid and diffusion-limited, which restricts control of the selective layer and often produces structural heterogeneity that lowers selectivity in gas separations. Here, we demonstrate that secondary interfacial polymerization (SIP) can be used to retrofit these liquid-separation membranes for CO 2 capture by creating an interfacial polyethyleneimine (PEI) repair layer that seals and reconstructs nonselective defects in situ. Under optimized conditions, the SIP membrane achieves ~200 GPU CO 2 permeance and ~75 CO 2 /N 2 selectivity (>2× the baseline). PEI seals nonselective voids inside the selective layer and forms an amine-rich, CO 2 -philic transport interface, so CO 2 permeance remains nearly unchanged even though the effective selective-layer thickness increases from 236 nm to 319 nm for the SIP-PIP membrane. The PEI overlayer also improves durability: after 50 ppm SO 2 exposure, CO 2 permeance decreased from 196 to 165 GPU and recovered to 185 GPU upon returning to SO 2 -free feed, and membranes retained >90% of initial performance after repeated pressure and temperature cycling. Notably, PIP-based membranes consistently show higher permeance and selectivity than MPD-based membranes, which is opposite to their ranking in aqueous separations, suggesting that solution-diffusion transport dominates under gas-phase operation. Overall, these results provide a scalable defect-repair strategy for low-cost repurposing of mature IP-based water-treatment membranes into CO 2 capture membranes. Download: Download high-res image (224KB) Download: Download full-size image