Microporous ZIF-7 membranes prepared by in-situ growth method for hydrogen separation

• The micro-porous ZIF-7 membrane was prepared using in-situ growth synthesis.
• A new upper boundary for inorganic membranes was constructed to demonstrate the current inorganic membrane performance.
• The current trend in ZIFs membrane performance is highlighted in comparison with other inorganic membranes.

The H2/CO2 selectivity across ZIF-7 membrane prepared by in-situ growth method at synthesis temperature and time of 105 °C and 2 h, respectively, was the highest at 15.98, nearly four times higher than H2/CO2 Knudsen separation factor of 4.7. ZIF-7 membranes prepared from in-situ growth method also surprisingly performed better than ZIF-7 membranes prepared by other innovative techniques such as electro-spray deposition and secondary growth methods that achieved selectivity of 9.59 and 4.7, respectively. Despite lower selectivity performance than the numerically predicted results (the latter fall within the commercially attractive region with H2/CO2 selectivity of 200 and permeability of 2000 barrer), the micro-porous ZIF-7 membrane prepared in this work demonstrated higher H2 permeability of 3770 barrer. Performance comparison between various inorganic membranes, including ZIF-7 and ZIF-8 membranes (that are highly potential for commercial application with H2/CO2 selectivity of 20.29 and permeability of 35541 barrer) was made and a new upper boundary for inorganic membranes was also constructed and reported.