Metal–organic
frameworks (MOFs), as porous fillers possessing
molecular sieving properties, have been combined with polymers to
give mixed-matrix membranes (MMMs) with enhanced separation performance.
This field of research has produced a large number of different membranes,
and many MOF/polymer combinations have been tested and reported to
show potential application to industrial gas separation. Although
MOFs have been proposed as novel additives with high porosity and
tunable pore size, which were supposed to outperform other porous
fillers, due to restrictions in separation performance of the filler
and challenges concerning the compatibility of polymer and MOF, only
a small fraction of these works report both improved permeability
and selectivity. In this review these challenges are set into the
context of MOF synthesis and membrane fabrication by the choice of
appropriate polymer/MOF combinations, utilization of the MOF functional
sites, modification of the MOF surface chemistry or pore texture and
size, and also targeted influence of the size and shape of the filler
particles. The effect of the highlighted MOF additives on the gas
separation performance is analyzed and discussed by comparison of
the gas permeability and selectivity. This emphasizes strategies by
which high performing MMMs can be achieved through accessing the full
potential of the porous MOF fillers.