In situ bottom–up growth of metal–organic frameworks in a crosslinked poly(ethylene oxide) layer with ultrahigh loading and superior uniform distribution
A mixed-matrix membrane combining an inorganic filler and polymer phase is an essential part of the scheme enabling improvements in gas separation. The bulk of the literature dealing with the construction of mixed-matrix membranes focuses on dispersing pre-synthesized porous materials in a polymer matrix to enhance the gas separation performance. However, this approach suffers from poor compatibility between inorganic fillers and the polymer and results in an irregular morphology and a defective structure. Herein, we demonstrate a new strategy for the preparation of mixed-matrix membranes with improved inorganic loadings and enhanced compatibility and permeability. We have developed an in situ bottom–up growth approach in which metal–organic framework (MOF) precursors are well dispersed in the polymerization mixture used for the preparation of the polymer membrane. MOF precursors were then rearranged and uniformly distributed within a cross-linked hydrophilic PEG-based polymer membrane using thermal treatment at the melting temperature of the polymer. The resulting hybrid membranes contained up to 67.7 wt% MOF nanocrystals in dense and continuously ordered distributions within the polymer support. Compared with all the reported MOF-based membranes, this value is the highest MOF loading ever. An excellent CO2/N2 selectivity of 38.5 and a CO2 permeability of 1083.7 barrer were achieved, exceeding the known upper-bound limits defined for conventional polymer membranes. Our approach offers a new and facile strategy for the preparation of mixed-matrix membranes with a highly uniform and defect-free structure.