Room-temperature synthesis of ZIF-90 nanocrystals and the derived nano-composite membranes for hydrogen separation

Nanocrystals of ZIF-90 have been synthesized at room temperature through a novel procedure and incorporated into PBI-based nano-composite membranes for hydrogen purification. The physical and chemical structures of the ZIF-90 nanoparticles have been examined via multiple advanced instrumental analyses including DLS, XRD, FESEM, NMR and FTIR. The nanocrystals show identical morphology, crystallinity and chemical structure but a significantly reduced particle size (around 100 nm) when compared with the ZIF-90 particles in previous studies. The derived ZIF-90-PBI nano-composite membranes exhibit homogeneous particle dispersion and fine particle-polymer adhesion, as well as excellent hydrogen purification performance at various testing conditions. The 45/55 (w/w) ZIF-90-PBI membrane with the highest ZIF-90 volume loading of up to 50.9 vol% possesses the best ideal H₂-CO₂ separation performance with a moderate H₂ permeability of 24.5 Barrer and a high H₂-CO₂ selectivity of 25.0 in pure gas permeation tests at 35 °C. The membrane also shows promoted gas separation performance during mixed gas tests at 180 °C with an H₂ permeability of 226.9 Barrer and an H₂-CO₂ separation factor of 13.3 that surpasses the latest Robeson upper bound for H₂-CO₂ separation. This work not only expands the field of nano-composite membrane fabrication, but also provides prospects for interdisciplinary research combining nano-science and chemical engineering for clean energy development.