Tunable Supramolecular Cavities Molecularly Homogenized in Polymer Membranes for Ultraefficient Precombustion CO₂ Capture

Abstract

Processable molecular‐sieving membranes are important materials for realizing energy‐efficient precombustion CO2 capture during industrial‐scale hydrogen production. However, the promising design of mixed matrix membranes (MMMs) that aims to integrate the molecular‐sieving properties of nanoporous architectures with industrial processable polymers still faces performance and fabrication issues due to the formation of segregated nanofiller domains in their polymer matrices. Here, an unconventional nanocomposite membrane design is proposed using soluble organic macrocyclic cavitands (OMCs) with tunable open cavity sizes that not only mitigate the formation the discrete nanofiller phases but also deliver distinct molecular‐sieving separations. The versatile organic‐solvent solubility coupled with highly interactive functionalities of OMCs allows them to obtain molecularly homogeneous mixing with matrix polymers and form only one integral continuous phase crucial to the robust processability of polymers. A series of polybenzimidazole‐based molecularly mixed composite membranes (MMCMs) are fabricated via the incorporation of a soluble and thermally stable OMC choice, sulfocalixarenes, with various cavity sizes. These membranes achieve outstanding high‐temperature mixed‐gas H2/CO2 separation performances comparable with several state‐of‐the‐art molecular‐sieving membranes owing to effective size‐sieving gas passages through the open or partially‐intruded supramolecular cavities. The broadly tunable structures and functionalities of OMCs would make their MMCMs attractive for other energy‐intensive molecular separations.

Voltage-Gated Membranes Incorporating Cucurbit[n]uril Molecular Containers for Molecular Nanofiltration

“…Supramolecular compounds are considered to be advanced and efficient separation membrane building blocks due to the presence of intrinsic pores in their molecular structure. 27,28 The cucurbit[n]uril (CB[n]) family of molecular containers 29−31 displays powerful host−guest binding abilities toward hydrophobic cations in water, 32−36 which isolates the guests from the external environment. 37,38 Viologens and their derivatives are popular components of CB[n] (n = 7, 8)based complex functional systems like molecular machines, supramolecular polymers, and drug delivery systems.…”

“…Supramolecular compounds are considered to be advanced and efficient separation membrane building blocks due to the presence of intrinsic pores in their molecular structure. , The cucurbit­[ n ]­uril (CB­[ n ]) family of molecular containers − displays powerful host–guest binding abilities toward hydrophobic cations in water, − which isolates the guests from the external environment. , Viologens and their derivatives are popular components of CB­[ n ] ( n = 7, 8)-based complex functional systems like molecular machines, supramolecular polymers, and drug delivery systems. − Accordingly, we envisioned that formation of the CB[7]-BABD rotaxane complex would suppress dimerization of BABD cation radicals and improve the performance of the resultant NF membranes incorporating CBs. , Previously, we have presented the first examples of IP processes featuring CB­[ n ] rotaxanes as monomers. We found that the water permeability was enhanced threefold by reconfiguring the reconstructing membrane surface. , The design of voltage-gated membranes incorporating CB­[ n ] rotaxane monomers and investigations of their stimuli–response behavior remain unknown.…”

Supramolecular Polymer Networks of Ion-Coordinated Polybenzimidazole with Simultaneously Improved H2 Permeability and H2/CO2 Selectivity

“…To address this, porous SPNs were also synthesized using PBI and organic macrocyclic cavitands (OMCs) with cavity sizes of 3.4−9.6 Å to simultaneously enhance H 2 permeability and H 2 /CO 2 selectivity. 31,32 Nevertheless, the dispersion of the OMCs in industrial asymmetric membranes is yet to be demonstrated. SPNs of ion-coordinated PBI have demonstrated superior self-healing and mechanical properties.…”

Polybenzimidazoles (PBIs) and state-of-the-art PBI hollow fiber membranes for water, organic solvent and gas separations: a review

“…The major challenge in fabricating highperformance PBI-based MMMs is how to uniformly disperse nanoparticles in the polymer matrix via adjusting the size and surface chemistry of nanoparticles and optimizing fabrication protocols. [160][161][162][163][164] PBI/carbon nanotubes, PBI/graphene, and PBI/ graphene oxide, PBI/ZIF nanocomposites have motivated extensive research in the elds of supercapacitors, gas separation, strengthened materials, and fuel cells. 12 Since zeolitic imidazolate frameworks (ZIFs), a subfamily of metal-organic frameworks (MOFs), have characteristics of tailorable cavity sizes, high porosity and good affinity with polymers, exceptional thermal stability and outstanding chemical resistance, 161,165 high-performance PBI/ZIF MMMs have been molecularly designed to improve the H 2 separation performance at high temperatures.…”

“…21, the performance of PBI hollow ber membranes for H 2 /CO 2 separation has gradually surpassed the upper bound of 2008 Robeson's curves. 65,238 Other efforts have been made to (1) blend PBI with thermosets in order to improve the thermal stability, 239 (2) embed soluble organic macrocyclic cavitands (sulfocalixarenes, SCA) to form homogeneous PBI nanocomposite membranes with distinctly molecular-sieving nanocavities, 164,240 (3) grow a selective MOF layer on the PBI HFM surface, 241 (4) dope PBI membranes with a polyprotic acid to improve H 2 /CO 2 diffusivity selectivity, 40 (5) apply Pd alloy (PdAg and PdNi) nanowires in PBI mixed matrix membranes to increase hydrogen diffusivity and reduce Pd embrittlement and susceptibility to poisoning, 242 (6) control the degree of N-quaternization on PBI based polymeric ionic liquids (PILs) to improve CO 2 sorption and gas permeation, 243 and ( 7) carbonize PBI as a carbon molecular sieve (CMS) with greatly enhanced H 2 /CO 2 , O 2 /N 2 size-sieving ability. 244,245 These schemes may potentially enhance the separation performance of PBI-based HFMs if one can successfully and economically convert them from at-sheet congurations to hollow bers.…”