A Metal Chelating Porous Polymeric Support: The Missing Link for a Defect‐Free Metal–Organic Framework Composite Membrane

Abstract

Since the discovery of size-selective metal-organic frameworks (MOFs), researchers have tried to incorporate these materials into gas separation membranes. Impressive gas selectivities were found, but these MOF membranes were mostly made on inorganic supports, which are generally too bulky and expensive for industrial gas separation. Forming MOF layers on porous polymer supports is industrially attractive but technically challenging. Two features to overcome these problems are described: 1) a metal chelating support polymer to bind the MOF layer, and 2) control of MOF crystal growth by contra-diffusion, aiming at a very thin nanocrystalline MOF layer. Using a metal chelating poly-thiosemicarbazide (PTSC) support and adjusting the metal and organic ligand concentrations carefully, a very compact ZIF-8 (ZIF=zeolitic imidazolate framework) layer was produced that displayed interference colors because of its smooth surface and extreme thinness-within the range of visible light. High performances were measured in terms of hydrogen/propane (8350) and propylene/propane (150) selectivity.

Rational Tuning of Zirconium Metal–Organic Framework Membranes for Hydrogen Purification

“…[11] Furthermore,p hysical and chemical modifications of MOF particles and microporous supports is vital to improve the adhesion of the MOF selective layer and prevent the formation of nonselective voids. [12] Tu ning of MOFs in terms of pore size and shape is apractical approach to increase the selectivity of membranes through the sieving effect. Fore xample,C aro et al [13] reported that adecrease in pore size of ZIF-8 to 3.4 could enhance the H 2 /CH 4 and H 2 /N 2 to 12 while the H 2 permeance was not significantly changed compared with the original ZIF-8.…”

Metal–Organic Framework (MOF) Nanorods, Nanotubes, and Nanowires

“…[25][26][27] As aresult, ZIF-8 has been the prototypical material for constructing MOF nano-and superstructures. [31][32][33] On the other hand, 1D nanostructures with controllable morphologies and architectures are in general more difficult to achieve than their 0D counterparts, [34,35] and examples of 1D ZIF-8 structures are thus relatively scarce,w hich are mainly obtained through bottom-up solution synthesis templated by polymer [36,37] or inorganic [38][39][40] 1D nanostructures,as well as through top-down strategies including self-assembly of ZIF-8 nanocrystals under an external electric field [41] and electrospinning from polymer mixture solutions. [31][32][33] On the other hand, 1D nanostructures with controllable morphologies and architectures are in general more difficult to achieve than their 0D counterparts, [34,35] and examples of 1D ZIF-8 structures are thus relatively scarce,w hich are mainly obtained through bottom-up solution synthesis templated by polymer [36,37] or inorganic [38][39][40] 1D nanostructures,as well as through top-down strategies including self-assembly of ZIF-8 nanocrystals under an external electric field [41] and electrospinning from polymer mixture solutions.…”

Electrophoretic Nuclei Assembly for Crystallization of High‐Performance Membranes on Unmodified Supports

“…Recently, ZIF‐8 membranes have been intensively investigated for H 2 /CO 2 , H 2 /CH 4 , H 2 /C 3 H 8 , and C 3 H 8 /C 3 H 6 separations (refer to Section II, Supporting Information). Most of the studies have achieved successful synthesis of high‐performance ZIF‐8 membranes only after modifying the functionality or topography of the underlying porous support.…”

“…Most of the studies have achieved successful synthesis of high‐performance ZIF‐8 membranes only after modifying the functionality or topography of the underlying porous support. Peinemann and co‐workers fabricated an ultrathin ZIF‐8 membrane on a metal chelating polythiosemicarbazide (PTSC) support . The chelating ability of the PTSC rendered a high density of zinc ions at the support surface, which facilitated a uniform heterogeneous nucleation of ZIF‐8 on the polymeric support.…”