Vertical Graphene-Supported High-Hydrogen Permeance ZIF-8 Membranes

The deployment of green hydrogen energy plays a pivotal role in propelling sustainable development and achieving carbon neutrality. Separating H2 and CH4 is a crucial step in industrial hydrogen purification. Metal–organic framework (MOF) membranes offer vast prospects for applications in gas separation. Breaking the "trade-off" between permeance and selectivity has consistently remained a primary challenge in the realm of separation membranes. In this work, highly permeable H2 separation ZIF-8 membranes were fabricated on a vertical graphene (VG)-modified α-Al2O3 support (VG@α-Al2O3), and the VG layer can afford active sites for synthesizing ZIF-8 membranes and provide more gas transport path to reduce the mass transfer resistance. With the aid of O2 plasma in improving the hydrophilicity of the VG layer, nano-ZIF-8 crystals can be synthesized on the VG to act as seeds (ZIF-8@VG@α-Al2O3) for membrane synthesis, and green synthesis membranes were realized in aqueous solution. At 90 °C for 12 h, about 900 nm-thick membrane layers were synthesized, with a high H2 permeance of 1.8 × 10–6 mol·m–2·s–1·Pa–1 and H2/CH4 separation factor of 9.6. After the synthesis period was increased to 24 h, the denser ZIF-8 membrane resulted in a higher H2/CH4 selectivity (17.2). In contrast to the MOF membranes described in previous studies, satisfactory hydrogen permeance of ZIF-8 membranes can be achieved while maintaining high selectivity.