Fabrication of defect-free MIL-96 membrane via aluminum isopropoxide gel layer towards exceptional H2/CO2 separation

• Continuous and well-intergrown MIL-96 membranes were prepared. • Aluminum isopropoxide coating can provide active Al metal source. • MIL-96 membrane can be optimized by mixed-solvent regulation. • Membrane crystallinity and formation property can be matched. • MIL-96 membrane exhibits excellent separation performance. A novel approach was developed to fabricate defect-free MIL-96 membranes on an α-Al 2 O 3 support by combining aluminum isopropoxide coating with mixed-solvent regulation. The aluminum isopropoxide gel on the support functions as an active Al source, directing MIL-96 crystal nucleation and growth. A subsequent secondary crystallization can produce a well-intergrown MIL-96 membrane. Here, the gel coating inhibits the preferential crystallization of MIL-96 particles in the support pores, optimizing the microstructure and diminishing inter-crystal defects. By accurately adjusting the formic acid to N-methylformamide ratio in synthesis solution, a balance between membrane crystallinity and formation is achieved. Membrane separation property evaluation revealed an outstanding H 2 permeance of 1800 GPU and an H 2 /CO 2 separation factor of over 24.0, outperforming some advanced polycrystalline MOF membranes. This approach provides a potentially cost-efficient method for the large-scale preparation of MIL-96 membranes, holding great potential for practical applications in membrane separation.