High-performance H2/CO2 separation from 4-nm-thick oriented Zn2(benzimidazole)4 film

High-performance membrane-based H2/CO2 separation has the potential to reduce the energy penalty associated with precombustion capture. The state-of-the-art high-performance membranes for this separation are based on two-dimensional (2D) laminates including those based on metal-organic frameworks (MOFs). However, the preparation of these membranes is complex, requiring the use of high-temperature, organic solvents, and a long synthesis time. Yet, they yield a limited H2/CO2 selectivity under pressurized feed conditions indicating the presence of a significant population of defective transport pathways. Herein, we report a facile synthesis of ultrathin, intergrown, and oriented Zn2(benzimidazole)4 or Zn2(bim)4 film with thickness down to 4 nm. They are prepared at room temperature using water as an environmentally-friendly solvent, and with a synthesis time as small as 10 min. This is achieved by screening a crystallization regime involving ultra-dilute precursor solutions where homogeneous nucleation of Zn2(bim)4 is delayed. Rapid in-plane growth of 2D Zn2(bim)4 film is promoted over an atomic-smooth graphene substrate eliminating pinhole defects in the film. Resulting membranes yield a large permselective H2 transport under pressurized H2/CO2 mixture feed. The combination of facile and green synthesis with high-performance separation makes these membranes attractive for precombustion capture.