Amino‐Functionalized ZIF‐7 Nanocrystals: Improved Intrinsic Separation Ability and Interfacial Compatibility in Mixed‐Matrix Membranes for CO₂/CH₄ Separation

Abstract

Highly permeable and selective, as well as plasticization-resistant membranes are desired as promising alternatives for cost- and energy-effective CO separation. Here, robust mixed-matrix membranes based on an amino-functionalized zeolitic imidazolate framework ZIF-7 (ZIF-7-NH ) and crosslinked poly(ethylene oxide) rubbery polymer are successfully fabricated with filler loadings up to 36 wt%. The ZIF-7-NH materials synthesized from in situ substitution of 2-aminobenzimidazole into the ZIF-7 structure exhibit enlarged aperture size compared with monoligand ZIF-7. The intrinsic separation ability for CO /CH on ZIF-7-NH is remarkably enhanced as a result of improved CO uptake capacity and diffusion selectivity. The incorporation of ZIF-7-NH fillers simultaneously makes the neat polymer more permeable and more selective, surpassing the state-of-the-art 2008 Robeson upper bound. The chelating effect between metal (zinc) nodes of fillers and ester groups of a polymer provides good bonding, enhancing the mechanical strength and plasticization resistance of the neat polymer membrane. The developed novel ZIF-7 structure with amino-function and the resulting nanocomposite membranes are very attractive for applications like natural-gas sweetening or biogas purification.

Advanced Porous Materials in Mixed Matrix Membranes

“…The incorporation of functional groups, such as NH 2 , SO 3 H, and COOH into MOF structures can facilitate the formation of hydrogen bonding at polymer–MOF interfaces, helping to mitigate the issue of compatibility. For instance, Xiang et al prepared a series of novel ZIF‐7–NH 2 nanocrystals with different ligand ratios by in situ substitution of 2‐aminobenzimidazole into the ZIF‐7 framework, and incorporated them into cross‐linked poly(ethylene oxide) rubbery polymer to prepare MMMs ( Figure a) . The as‐prepared NH 2 ‐functionalized ZIF‐7 nanocrystals are denoted as ZIF‐7–NH 2 ( x ), where x illustrates the percentage of 2‐aminobenzimidazole to the total imidazole ligands in the crystal growth solution.…”

“…c) Schematic illustration of chelating effect in MMMs containing ZIF‐7–NH 2 nanocrystals. Reproduced with permission . Copyright 2017, Wiley‐VCH.…”

Boron Nitride Membranes with a Distinct Nanoconfinement Effect for Efficient Ethylene/Ethane Separation

“…[12a] Until now,the utilization of BN membranes for gas separations has not been reported. [15] TheR ILs consisting of silver salt (carrier) dissolved in an ionic liquid solvent are selected to infuse the nanochannels owing to their great potential for ethylene/ethane separation with long-term stability. [13] Herein, we design aB Nm embrane with distinct nanoconfinement effect for the ethylene/ethane mixed gas separation.…”

Boron Nitride Membranes with a Distinct Nanoconfinement Effect for Efficient Ethylene/Ethane Separation

“…[14] Thei mplementation of BN membrane-based ethylene/ethane separation has the potential to achieve significant energy savings. [15] TheR ILs consisting of silver salt (carrier) dissolved in an ionic liquid solvent are selected to infuse the nanochannels owing to their great potential for ethylene/ethane separation with long-term stability. [16] Compared with the chemical modifications by polymers or crosslinking agents,t he nanoconfinement of RIL within nanochannels is af acile and effective methodology,t he liquid property of RIL and its strong noncovalent interactions with BN nanosheets determined that it can be homogeneously confined within BN nanochannels.T he resulting membrane acquires ac ombined superhigh ethylene permeance of 138 GPU,ahigh ethylene/ethane selectivity of 128, and long-term stability,which is currently the highest performance achieved for ethylene/ethane separation membranes.T othe best of our knowledge,t his is the first report on the utilization of BN membranes in gas separation as well as the in-depth elucidation of nanoconfinement effect within nanochannels.…”