Beyond Solution-Based Protocols: MOF Membrane Synthesis in Supercritical Environments for an Elegant Sustainability Performance Balance
Liangliang Liu, Yifan Song, Taotao Ji, Yanwei Sun, Demin He, Haoquan Hu, Yi Liu
Abstract
Supercritical fluids (SCFs) represent materials at temperatures and pressures above their critical points where distinct liquid and gas phases do not exist. SCFs possess several unique properties rendering them excellently adapted for the reaction medium of MOF membranes (like ZIF-8) which, although offering an energy-efficient and eco-friendly option for large-scale industrial separation, are still experiencing a dilemma between process sustainability and performance superiority. In this study we addressed this issue through a facile SCF synthetic protocol employing supercritical CO2 (scCO2) as the reaction medium. Relying on the near-zero surface tension, low viscosity, and high diffusivity of scCO2, nanoscale intercrystalline defects could be effectively patched, resulting in the formation of well-intergrown ZIF-8 membranes with commercially attractive olefin/paraffin (C3H6/C3H8) separation performance. Moreover, after the SCF processing, both discharged CO2 and unreacted ligands could be conveniently recovered and reutilized, resulting in zero pollutant discharge due to the controllable phase transition, variable solubility, and chemical inertness of scCO2. This work sheds lights on the promising prospects of SCF processing for sustainable fabrication of high-performing MOF membranes.