<p>The development of high-performance CO₂ separation membranes is critical for advancing carbon capture technologies. Two-dimensional (2D) material membranes, with tunable interlayer nanochannels functionalized by nanomaterials (e.g., metal ions), are promising for CO₂ capture. However, it remains a challenge to achieve uniform nanomaterial distribution in the membrane without compromising separation performance. Herein, we proposed a multifunctional molecular immobilization strategy to fabricate a metal ion intercalated graphene oxide (GO) membrane with enhanced CO₂ capture performance. The multifunctional molecular (sodium <i>p</i>-aminobenzenesulfonate, SPABS) enabled an <i>in situ</i> and uniform distribution of Na⁺ in the inter-layer channels of the GO membrane. The amino groups of SPABS underwent nucleophilic addition reactions with the epoxy groups on GO sheets, resulting in the stable inter-layer channels. Meanwhile, the hydrophilic sulfonic acid groups of SPABS enhanced the water adsorption capacity in the GO interlayer channels, synergizing with Na⁺ to form active sites that facilitated the fast and selective transport of CO₂ over N₂. The resulting membrane exhibited an enhanced CO₂ capture performance. The large-sized membrane (15 cm × 20 cm) fabricated by the scalable blade-casting method showed reproducible performance. This work provides insights and a tool for tailoring the nanochannels of 2D material membranes for molecular separation.</p>