Seeded growth of ZIF-8 on the surface of carbon nanotubes towards self-supporting gas separation membranes

Abstract

We report the synthesis of the first continuous, inter-grown ZIF-8 membrane via the secondary growth method. ZIF-8 crystals were seeded and strongly anchored onto porous carbon nanotube bucky-paper supports and hydrothermally grown into a dense and continuous ZIF-8 network. The self-supporting hybrid metal organic framework membranes were characterized by scanning electron microscopy and shown to exhibit both a very homogeneous structure and a very smooth nanotube-metal organic framework interface. Gas adsorption (H₂, CH₄, CO₂, N₂) and permeation (He, CO₂, N₂ and Xe) tests were performed to evaluate the permeance of each gas and to predict the selectivity. The membranes were highly robust and sustained pressures as high as 500 kPa. Furthermore, the high selectivity of N₂ over CO₂ and Xe (33 and 163 respectively), shown by gas adsorption single gas permeation and mixed gas permeation clearly demonstrates the near defect-free nature of the membranes while the high hydrothermal stability of ZIF-8 makes these novel composites highly promising for water vapour saturated gas treatment.