Seed assisted synthesis of an anionic metal-organic framework membrane for selective and permeable hydrogen separation

Hydrogen selective metal-organic framework (MOF) membranes with excellent performance are still in high demand. Here, we are developing an anionic MOF material of CPM-5 into a membrane for H-2 separation. A well inter-grown CPM-5 membrane is successfully synthesized on a macroporous glass-frit disk by secondary growth assisted with a pre-deposited seed layer. The anionic framework of CPM-5 can interact strongly with CO2, N-2 and CH4 rather than H-2, shown by the isosteric heats of adsorption in a sequence of CO2 (39.4 kJ mol(-1)) > N-2 (28.4 kJ mol(-1)) > CH4 (25.1 kJ mol(-1)) > H-2 (6.1 kJ mol(-1)). The synthesized CPM-5 membrane is investigated for gas separation of H-2/CO2, H-2/N-2 and H-2/CH4. The results from binary gas permeation show separation factors of 39.4, 27.3 and 16.7 for H-2/CO2, H-2/N-2 and H-2/CH4, respectively; and a H-2 permeance of 11.2-12.0 x 10(-7) mol m(-2) s(-1) Pa-1. The selective separation of H-2 from CO2, N-2 and CH4 is governed by charge-induced adsorption, and verified by the gas adsorption results. The product of separation factor and H-2 permeance exceeds the latest upper bound of polymer membranes and surpasses that of most MOF membranes. In addition, the CPM-5 membrane is thermally stable, durable and reproducible, exhibiting great potential for industrial hydrogen recycling.