High-performance H 2 /CO 2 separation from 4-nm-thick oriented Zn 2 (benzimidazole) 4 films

High-performance membrane-based H 2 /CO 2 separation offers a promising way to reduce the energy costs of precombustion capture. Current membranes, often made from two-dimensional laminates like metal-organic frameworks, have limitations due to complex fabrication methods requiring high temperatures, organic solvents, and long synthesis time. These processes often result in poor H 2 /CO 2 selectivity under pressurized conditions due to defective transport pathways. Here, we introduce a simple, eco-friendly synthesis of ultrathin, intergrown Zn 2 (benzimidazole) 4 films, as thin as 4 nm. These films are prepared at room temperature using water as the solvent, with a synthesis time of just 10 minutes. By using ultradilute precursor solutions, nucleation is delayed, promoting rapid in-plane growth on a smooth graphene substrate and eliminating defects. These membranes exhibit excellent H 2 permselectivity under pressurized conditions. The combination of rapid, green synthesis and high-performance separation makes these membranes highly attractive for precombustion applications.