Enhanced CO ₂ Transport via Interfacial Engineering in Pebax-Based Mixed-Matrix Membranes Incorporating 2D Ni–Al–Fe Layered Double Hydroxide Nanosheets

Pebax is an attractive material for carbon capture membranes because its polyether-rich segments provide favorable CO 2 -philic pathways. However, pristine Pebax-1657 membranes are still constrained by the conventional permeability–selectivity trade-off, limiting further improvements in separation performance. Incorporating functional nanofillers into Pebax matrices offers a promising strategy to overcome this limitation; however, achieving well-controlled polymer–filler interfaces remains critical for simultaneously enhancing CO 2 permeability and CO 2 /N 2 selectivity. Herein, we report an interfacial engineering strategy using two-dimensional Ni–Al–Fe layered double hydroxide nanosheets containing three metal cations, hereafter referred to as layered triple hydroxide (LTH), as a functional filler in Pebax-1657 membranes. The multimetal LTH nanosheets exhibited a layered platelet morphology, abundant hydroxyl-rich surface chemistry, and a CO 2 adsorption capacity of 0.75 mmol/g, providing favorable interfacial compatibility with the Pebax matrix. Structural, sorption, mechanical, and thermal analyses suggest that well-dispersed LTH nanosheets at low loading preserve the overall Pebax soft-segment transition while partially modifying local chain ordering and polymer–filler interactions, thereby promoting more selective CO 2 transport. At an optimal LTH loading of 0.1 wt %, the MMM achieved a CO 2 permeability of 183 barrer and a CO 2 /N 2 selectivity of 78 at 35 °C and 1 bar, corresponding to improvements of 33% and 42%, respectively, compared with the pristine Pebax-1657 membrane. Under elevated temperature operation at 60 °C, the optimized MMM further achieved a CO 2 permeability of 631.6 barrer and a CO 2 /N 2 selectivity of 99, surpassing both the 2008 and 2019 Robeson upper bounds for CO 2 /N 2 separation. The membrane also maintained stable performance over 120 h of continuous operation. These findings demonstrate that ternary-metal LDH-based interfacial engineering is an effective route to enhance CO 2 /N 2 separation in Pebax-based MMMs while maintaining structural stability at low filler loading.