Polymer Electrolyte Membranes with Hybrid Cluster Network for Efficient CO₂/CH₄ Separation

Well-connected transport pathways play a critical role in high-performance CO2-facilitated separation membranes. Inspired by the ionic cluster network in polymer electrolyte membranes (PEMs) for fast ion transport, designing a unique CO2-philic cluster network structure is a promising strategy to construct efficient CO2 transport channels in membranes. Herein, a forced induction method is presented to construct a CO2-philic cluster network in membranes. Sulfobutylether-beta-cyclodextrin (sβ-CD) is introduced in a quaternary ammonium polysulfone (QAPSf) matrix. During the membrane formation process, the quaternary ammonium groups on QAPSf are attracted by the sulfonic acid groups on sβ-CD, assembling around and thus forming hybrid clusters. These clusters are swollen and interconnected by water under a humidified state. The hybrid cluster network acts as an effective CO2 transport pathway via clustering quaternary ammonium ion pairs as continuous CO2-facilitated transport sites. Simultaneously, the internal cavity of sβ-CD in hybrid clusters affords additional free volume in membranes, thus enhancing the CO2 permeability. The resultant QAPSf/sβ-CD membrane exhibits an optimal CO2 permeability of 1303 Barrer, a CO2/CH4 selectivity of 39, and good long-term operation stability for 30 days, surpassing the 2008 Robeson upper bound limit. This concept of constructing a hybrid cluster network for facilitated transport is expected to be applicable to explore more advanced PEMs for effective gas separation

Highly Cationized and Porous Hyper-cross-linked Polymer Nanospheres for Composite Anion Exchange Membranes

Hyper-cross-linked polymer (HCP), a category of porous organic materials (POMs), is exploited as an anion conducting membrane via a highly cationized and porous quaternized ammonium triptycene-based HCP in the form of <100 nm nanospheres (QTP-HCP-NS) for the first time. The material possesses a high ion density of 3.65 mmol g–1 as well as a high Brunauer–Emmett–Teller (BET) surface area of 706 m2 g–1. Anion exchange membranes (AEMs) are prepared by mixing different loadings of QTP-HCP-NS with quaternized poly­(phenylene oxide) (QPPO) and compared with a compressed QTP-HCP pellet. Owing to the high ion density and high water sorption, which results in abundant ion conduction channels in QTP-HCP, the ion conductivity of the composite AEMs is enhanced by 79.5% compared with the unfilled QPPO membrane and by 677% compared with a compressed QTP-HCP pellet. In addition, lower dimensional swelling and higher tensile strength are achieved for the composite AEMs. Aggregation and the resulting interfacial defects of QTP-HCP-NS are found in the composite AEM at a high loading and in the comparative compressed pellet, causing a significant reduction in ion conduction and mechanical properties

Deep Eutectic Solvent Membranes Designed by the Same-Anion Strategy for Highly Efficient Ethylene/Ethane Separation

Deep eutectic solvents (DESs) are a new generation of designer and green solvents and offer tremendous opportunities for separation science; however, the construction of high-permeance DES membranes (DESMs) with excellent stability for ethylene/ethane separation is still a challenge. In this study, by the same-anion strategy, a series of DESs with the CF3SO3– anion were designed for the first time and then combined with an ethylene transport carrier (AgCF3SO3) for the construction of DESMs for highly efficient ethylene/ethane separation. DESMs were facilely fabricated by impregnating the as-designed DESs and AgCF3SO3 carrier into the commercial poly­(vinylidene fluoride) membrane, where the DESs not only exhibited good compatibility with AgCF3SO3 but also stimulated high carrier activity and afforded good carrier stability. The resultant DESMs displayed high ethylene permeability, ethylene/ethane selectivity, and excellent stability, especially the maximum permeability and selectivity reached up to 910 barrer and 83, thus being superior to most of the state-of-the-art ethylene/ethane separation membranes. Finally, the separation mechanism was revealed, and the regulation of hydrogen-bond and coordinative interactions within DESMs by the rational structural design accounted for excellent performances. This work extends the DES library and will accelerate the prosperity of DESMs for energy-intensive gas separations

Mixed-Matrix Membranes with Covalent Triazine Framework Fillers in Polymers of Intrinsic Microporosity for CO₂ Separations

Polymers of intrinsic microporosity (PIMs) exhibit high permeability but moderate selectivity, which limits their industrial application in membrane gas separations. Here, a novel CO2-philic perfluorinated covalent triazine framework (FCTF-1) filler in a PIM-1 matrix is utilized to enhance gas selectivity and permeability simultaneously. The predominately organic nature of FCTF-1 improves interfacial compatibility with the polymer matrix. The presence of polar functionality, i.e., triazine rings and fluorine atoms, leads to the preferential sorption of CO2 over CH4, thus increasing solubility selectivity, while the microporosity of FCTF-1 increases diffusion selectivity. PIM-1@FCTF-1 mixed matrix membranes (MMMs) with 2 wt % filler loading exhibited a CO2 permeability of 7300 barrer and a CO2/CH4 selectivity of 16.6. In addition, we report some initial mixed gas propene/propane separation data to determine the applicability of PIM-1@FCTF-1 MMMs to other small molecule separations. This work provides a potential approach to fabricating PIM-1-based MMMs with covalent triazine framework (CTF)-type fillers for gas separation