High Permselectivity Research Articles

Synthesis of high-performance Co-based ZIF-67 membrane for H2 separation by using cobalt ions chelated PIM-1 as interface layer

So far, the reports of ZIF-67 membranes with high permselectivity are rather scarce because ZIF-67 prefers to homogeneous nucleation and growth in the reaction solution rather than heterogeneous nucleation and growth on the substrates. Inspired by the fact that homologous metal ions is helpful to be acted as nucleation centers to promote the preparation of continuous MOF membranes, in this work, we develop a novel and effective synthesis method for in-situ growth of compact ZIF-67 membranes by using Co2+ ions chelated PIM-1 (PIM = polymer of intrinsic microporosity) as interface layer between the ZIF-67 membrane and the α-Al2O3 support. After solvothermal synthesis for 48 h at 120 °C, a well-intergrown ZIF-67 membrane with a thickness of about 12 μm can be formed on the Co2+@cPIM-1 modified α-Al2O3 disk. For single gas permeation at 25 °C and 1 bar, the ZIF-67 membrane shows a high H2 permeance of 6.2 × 10−7 mol m−2 s−1·Pa−1, with H2/CO2, H2/CH4 and H2/C3H8 ideal separation factors of 15.1, 51.7 and 56.4, respectively. Further, other compact and H2 permselective ZIF membranes, such as ZIF-7 and ZIF-8 membranes, can be consistently prepared on the Zn2+@cPIM-1 modified substrates by using the same strategy.

Solvent effects on diffusion channel construction of organosilica membrane with excellent CO2 separation properties

In this work, bis (triethoxysilyl) ethane (BTESE)-derived organosilica membranes were fabricated via the sol-gel method. To obtain organosilica membranes with high perm-selectivity, the network of the membrane was tailored by using different solvents in the preparation of the BTESE-derived sol with different pore sizes and network structures. A solvent with small polarity and a small dielectric constant (εr) can lead to outstanding single gas separation performance on the membrane structure, because the precursors are completely hydrolyzed and effectively stacked into a dense structure, which is beneficial for forming a suitable network for gas separation. The influence of the solvent and membrane thickness on the BTESE-derived membrane were evaluated to determine the mechanism responsible for the separation; this mechanism was found to be controlled not only by molecular sieving but also by selective surface diffusion. The results show that the BTESE-derived membrane prepared using tetrahydrofuran as the solvent exhibited a small network with an optimum thickness (three coating cycles) and led to a high ideal selectivity for CO2/CH4 and CO2/N2, with selectivity values of 33 and 38, respectively; additionally, the permeance of CO2 was 6.32 × 10−8 mol m−2 s−1 Pa−1 at 25 °C.

Water-ion permselectivity of narrow-diameter carbon nanotubes

Carbon nanotube (CNT) pores, which mimic the structure of the aquaporin channels, support extremely high water transport rates that make them strong candidates for building artificial water channels and high-performance membranes. Here, we measure water and ion permeation through 0.8-nm-diameter CNT porins (CNTPs)-short CNT segments embedded in lipid membranes-under optimized experimental conditions. Measured activation energy of water transport through the CNTPs agrees with the barrier values typical for single-file water transport. Well-tempered metadynamics simulations of water transport in CNTPs also report similar activation energy values and provide molecular-scale details of the mechanism for water entry into these channels. CNTPs strongly reject chloride ions and show water-salt permselectivity values comparable to those of commercial desalination membranes.

Growth process and short chain alcohol separation performance of fluoride-containing NaY zeolite membrane

Growth process of the NaY zeolite membranes was investigated by fluoride-containing precursor synthesis gel. Compared with the fluoride-free precursor synthesis gel, the irregular NaY zeolite crystals were dissolved into amorphous by the fluoride-containing precursor synthesis gel initially, the amorphous contained the Y-type zeolite characteristic bands by the IR characterization. The fine square NaY zeolite crystals arose from the amorphous, which were accumulated and gradually grew into a dense NaY zeolite layer on the support surface after 6.5 h. Because the excessive NaY zeolites were dissolved by the strong alkaline and fluoride-containing precursor synthesis gel, there was plenty of amorphous on NaY zeolites layer for prolonging the crystallization time. The as-synthesized NaY zeolite membranes had a good separation performance and repeatability for separation of 10 wt% methanol (MeOH)/methyl methacrylate (MMA) mixture by pervaporation, the flux and separation factor were (1.27 ± 0.07) kg ∙ m−2 ∙ h−1 and (4900 ± 1500) at 323 K, respectively. Besides, the NaY zeolite membranes were applied to separate the other short chain alcohol from the various alcohol/organic ester and alcohol/organic ether mixtures, the NaY zeolite membranes showed high short chain alcohol perm-selectivity.

Recent progress on thin film composite membranes for CO2 separation

• The promising membranes for CO 2 separation are discussed. • The exploration of CO 2 separation membrane in pilot-scale are presented. • The challenges of materials and membrane preparation in large-scale are briefly analyzed. The excess CO 2 emission into the atmosphere is one of the important environmental issues nowadays. It is urgent to develop environmentally friendly and low energy technologies to reduce the CO 2 emission. Membrane technology shows great potential in CO 2 separation because of the inherent merit over other conventional separation techniques. High permselectivity membranes play a vital role in efficient membrane processes. The thin film composite membranes with excellent performance have attracted more and more attentions. In this review, the CO 2 separation membranes are grouped into dense polymer membranes, microporous material membranes and mixed matrix membranes. A number of representative membranes with high performance are highlighted. In addition, the exploration of CO 2 separation membrane in pilot-scale are presented, followed by a brief analysis on the challenges of materials and membrane preparation in large-scale. Finally, the direction for further research is also discussed. It is believed that the review provides potential insights and guidance for the future development of thin film composite membranes for CO 2 separation, and hence promote the development of membrane.

Controlling molten carbonate distribution in dual-phase molten salt-ceramic membranes to increase carbon dioxide permeation rates

Dual-phase molten salt-ceramic membranes show high permselectivity for CO2 when molten carbonate is supported in a porous oxygen-ion and/or electron conductor. In this arrangement, the support likely contributes to permeation. Thus, if one is to understand and ultimately design membranes, it is also important to perform experiments with an inert support where permeation relies upon the molten carbonate properties alone. Here, a nominally inert material (Al2O3) was used in order to restrict permeation to molten carbonate. Model Al2O3 dual-phase membranes were fabricated using laser drilling to provide an order of magnitude difference in molten salt-gas interfacial area between feed and permeate sides. Molten carbonate thickness in the model membranes was also varied, independent of the molten salt-gas interfacial area. For all thicknesses studied, CO2 permeation rates showed a significant temperature dependence from 500 to 750 °C, suggesting an activated process was rate-limiting, likely a permeate-side molten salt-gas interfacial process, i.e. desorption of CO2. We applied these findings in asymmetric hollow-fibre supports, a geometry with inherent modularity and scalability, by developing a new carbonate infiltration method to control molten carbonate distribution within the hollow fibre. Compared to a conventionally prepared dual-phase hollow-fibre membrane with an uncontrolled distribution of carbonates, permeation rates were increased by up to 4 times when the molten salt was confined to the packed-pore network, i.e. without infiltrating the hollow-fibre micro-channels. X-ray micro-CT investigations supported the idea that the resulting increase in interfacial area for desorption of CO2 was the key structural difference contributing to increased permeation rates. For CO2 separation, where large volumes of gas must be processed, such increases in permeation rates will reduce the demand for membrane materials, although one must note the higher permeation rates achievable with oxygen-ion and/or electron conducting supports.

Macrovoid-free high performance polybenzimidazole hollow fiber membranes for elevated temperature H2/CO2 separations

Thermally robust membranes are required for H2 production and carbon capture from hydrocarbon fuel derived synthesis (syn) gas. Polybenzimidaole (PBI) materials have exceptional thermal, chemical and mechanical characteristics and high H2 perm-selectivity for efficient syngas separations at process relevant conditions. The large gas volumes processed mandate the use of a high-throughput, small footprint hollow fiber membrane (HFM) platform. In this work, an industrially attractive spinning protocol is developed to fabricate PBI HFMs with unprecedented H2/CO2 separation performance. A unique dope composition incorporating an acetonitrile diluent is discovered enabling asymmetric macro-void free PBI HFM fabrication using a water coagulant. The influences of dope viscosity, coagulant chemistry, and air gap on HFM morphology are evaluated. Elevated temperature (up to 350 °C) H2 permeances of 400 GPU with H2/CO2 selectivities > 20 are achieved. This unprecedented separation performance is a ground breaking achievement at temperatures traditionally considered out-of-reach for polymeric membranes.

Preparation and characterization of TFC NF membrane with improved acid resistance behavior

In this study, we prepared the novel acid-resistant thin-film composite (TFC) piperazine(PIP)-based nanofiltration (NF) membrane using melamine (Mel), sulfonated-melamine formaldehyde (SMF), and sulfanilamide (SA) through interfacial polymerization on a polysulfone (PSf) support layer. A long-term acid-resistant experiment for divalent salt was carried out with static immersion tests in a 15 wt% sulfuric acid solution. The divalent rejection of the PIP1-SMF0.3-SA0.05 in a 15 wt% sulfuric acid solution was maintained at over 96% after 10 days, and then slightly decreased to 94% for 20 days, and finally was maintained over 90% for 30 days. The flux was maintained at about 20 GFD even after 30 days of immersion in acid. In order to confirm the degree of hydrolysis in amide, the bond dissociation energy (BDE) was calculated using the density functional theory (DFT). BDE values of PIP-TMC, Mel-TMC, and SA-TMC were 79.34, 83.78, and 93.91 kcal/mol. Consequently, PIP1-SMF0.3-SA0.05 having s-triazine and sulfonyl amide group exhibited acid-stable performance because the C–N bond is more stable and the slow hydrolysis reaction in acid. Our research for preparing high perm-selectivity and long-term acid stability membrane can extend NF technology in many industries, particularly in the recovery of rare metals from acidic solutions.

Synthesis and Permselectivity of a Soluble Two-Dimensional Macromolecular Sheet by Solid–Solid Interfacial Polycondensation Followed by Chemical Exfoliation

Two-dimensional (2D) network polymers with nano-sized pores are generally insoluble, and therefore, it is difficult to determine their molecular structures and to fabricate their membranes. Soluble 2D network polymer membranes with angstrom-sized pores and thicknesses have not been reported. Herein, novel soluble 2D macromolecular sheets with angstrom-sized pores (24.6 Å) and thickness (3.4 Å) are synthesized by solid–solid interface polycondensation in laminated membranes of two cis–cisoid poly(imino-containing phenylacetylene)s followed by highly selective photocyclic aromatization (SCAT). First, a two-layered laminated polymer membrane that is self-supporting is prepared, and solid–solid interfacial polycondensation is performed. The insoluble three-dimensional (3D) network polymer layer formed is isolated by removing the soluble unreacted polymer layers. Finally, a SCAT reaction is carried out by irradiation of visible light on the insoluble 3D membrane to produce a soluble 2D macromolecular sheet. The precise 2D molecular structure can be displayed, such as the degree of polymerization, thickness, fraction of rings (pores), and pore size, estimated by GPC, AFM, 1H-NMR, IR, and XRD, because the macromolecule is soluble. Composite membranes containing the 2D macromolecular sheet show good oxygen permselectivity exceeding the Robeson upper line, possibly because the angstrom-sized pores and thicknesses produce high oxygen permselectivity without suppressing the permeability.

Selectivity of Transport Processes in Ion-Exchange Membranes: Relationship with the Structure and Methods for Its Improvement.

Nowadays, ion-exchange membranes have numerous applications in water desalination, electrolysis, chemistry, food, health, energy, environment and other fields. All of these applications require high selectivity of ion transfer, i.e., high membrane permselectivity. The transport properties of ion-exchange membranes are determined by their structure, composition and preparation method. For various applications, the selectivity of transfer processes can be characterized by different parameters, for example, by the transport number of counterions (permselectivity in electrodialysis) or by the ratio of ionic conductivity to the permeability of some gases (crossover in fuel cells). However, in most cases there is a correlation: the higher the flux density of the target component through the membrane, the lower the selectivity of the process. This correlation has two aspects: first, it follows from the membrane material properties, often expressed as the trade-off between membrane permeability and permselectivity; and, second, it is due to the concentration polarization phenomenon, which increases with an increase in the applied driving force. In this review, both aspects are considered. Recent research and progress in the membrane selectivity improvement, mainly including a number of approaches as crosslinking, nanoparticle doping, surface modification, and the use of special synthetic methods (e.g., synthesis of grafted membranes or membranes with a fairly rigid three-dimensional matrix) are summarized. These approaches are promising for the ion-exchange membranes synthesis for electrodialysis, alternative energy, and the valuable component extraction from natural or waste-water. Perspectives on future development in this research field are also discussed.

Low-temperature CO2 hydrogenation overcoming equilibrium limitations with polyimide hollow fiber membrane reactor

Various reactions that employ hydrogen to prepare synthetic fuels generate H2O as a major byproduct. In-situ H2O removal using a membrane can shift the equilibrium and enhance the product yield. However, the selection of a membrane that operates at the elevated reaction temperatures is highly challenging because most inorganic membranes have low H2O permeability at high temperatures. In this study, we synthesized polyimide (PI) hollow fibers with 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and hydroxyl aromatic diamines (2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (APAF) and 3,3′-dihydroxy-4,4′-diamino-biphenyl (HAB)), and integrated them with a fixed-bed reactor for the reverse water-gas shift reaction. The PI membrane showed high H2O permselectivity at elevated temperatures, and its integration into a hollow fiber membrane reactor increases the CO yield by 2–3 times compared to that of a reactor performed without the membrane.

In-Situ Combination of Bipolar Membrane Electrodialysis with Monovalent Selective Anion-Exchange Membrane for the Valorization of Mixed Salts into Relatively High-Purity Monoprotic and Diprotic Acids.

The crystalized mixed salts from the zero liquid discharge process are a hazardous threat to the environment. In this study, we developed a novel electrodialysis (SBMED) method by assembling the monovalent selective anion-exchange membrane (MSAEM) into the bipolar membrane electrodialysis (BMED) stack. By taking the advantages of water splitting in the bipolar membrane and high perm-selectivity of MSAEM for the Cl− ions against the SO42− ions, this combination allows the concurrent separation of Cl−/SO42− and conversion of mixed salts into relatively high-purity monoprotic and diprotic acids. The current density has a significant impact on the acid purity. Both the monoprotic and diprotic acid purities were higher than 80% at a low current density of 10 mA/cm2. The purities of the monoprotic acids decreased with an increase in the current density, indicating that the perm-selectivity of MSAEM decreases with increasing current density. An increase in the ratio of monovalent to divalent anions in the feed was beneficial to increase the purity of monoprotic acids. High-purity monoprotic acids in the range of 93.9–96.1% were obtained using this novel SBMED stack for treating simulated seawater. Therefore, it is feasible for SBMED to valorize the mixed salts into relatively high-purity monoprotic and diprotic acids in one step.

Asymmetric Membrane Capacitive Deionization Using Anion-Exchange Membranes Based on Quaternized Polymer Blends.

Membrane capacitive deionization (MCDI) for water desalination is an innovative technique that could help to solve the global water scarcity problem. However, the development of the MCDI field is hindered by the limited choice of ion-exchange membranes. Desalination by MCDI removes the salt (solute) from the water (solvent); this can drastically reduce energy consumption compared to traditional desalination practices such as distillation. Herein, we outline the fabrication and characterization of quaternized anion-exchange membranes (AEMs) based on polymer blends of polyethylenimine (PEI) and polybenzimidazole (PBI) that provides an efficient membrane for MCDI. Flat sheet polymer membranes were prepared by solution casting, heat treatment, and phase inversion, followed by modification to impart anion-exchange character. Scanning electron microscopy (SEM), atomic force microscopy (AFM), nuclear magnetic resonance (NMR), and Fourier-transform infrared (FTIR) spectroscopy were used to characterize the morphology and chemical composition of the membranes. The as-prepared membranes displayed high ion-exchange capacity (IEC), hydrophilicity, permselectivity and low area resistance. Due to the addition of PEI, the high density of quaternary ammonium groups increased the IEC and permselectivity of the membranes, while reducing the area resistance relative to pristine PBI AEMs. Our PEI/PBI membranes were successfully employed in asymmetric MCDI for brackish water desalination and exhibited an increase in both salt adsorption capacity (>3×) and charge efficiency (>2×) relative to membrane-free CDI. The use of quaternized polymer blend membranes could help to achieve greater realization of industrial scale MCDI.

Multiple-functional molecularly imprinted nanocomposite membranes for high-efficiency selective separation applications: An imitated core-shell TiO2@PDA-based MIMs design

Development of membrane-associated molecularly imprinted materials with fast and high permselectivity has been significant needed in separation engineering field. Herein, for the first time, a subversive synthesis strategy with hierarchical structure was proposed for the preparation of nanocomposite blended molecularly imprinted membranes (NBMIMs). Artemisinin, the high-efficiency antimalarial drug, was chosen as the template molecule. Instead of the direct modification of nanocomposite on membrane surfaces, the double-bonded TiO2@PDA was initially prepared, the blended membrane synthesis procedure was then conducted through a phase conversion process by using the as-prepared TiO2@PDA and PVDF powder as host materials. Importantly, the double-bonded TiO2@PDA-based nanocomposite in blended membranes was first proposed and applied as imprinting-initiated factor during the next artemisinin-imprinted process, leading the formation of imitated core-shell structure on membrane surfaces. It was no surprise that more excellent rebinding capacity (66.9 mg g−1), fast adsorption kinetics and high permselectivity coefficients (more than 17) were successfully achieved. Furthermore, an important conclusion was also obtained that TiO2@PDA-based nanocomposite from NBMIMs would cause significant enhancement of the rebinding capacity, that is to say, more and more artemisinin-imprinted sites would be synthesized by increasing the dosage of TiO2@PDA until 0.5 g. Therefore, a novel direction for the design and manipulation of MIMs materials had been successfully designed and guided for selective separation of artemisinin.

PVA-Based Mixed Matrix Membranes Comprising ZSM-5 for Cations Separation.

The traditional ion-exchange membranes face the trade-off effect between the ion flux and perm-selectivity, which limits their application for selective ion separation. Herein, we amalgamated various amounts of the ZSM-5 with the polyvinyl alcohol as ions transport pathways to improve the permeability of monovalent cations and exclusively reject the divalent cations. The highest contents of ZSM-5 in the mixed matrix membranes (MMMs) can be extended up to 60 wt% while the MMMs with optimized content (50 wt%) achieved high perm-selectivity of 34.4 and 3.7 for H+/Zn2+ and Li+/Mg2+ systems, respectively. The obtained results are high in comparison with the commercial CSO membrane. The presence of cationic exchange sites in the ZSM-5 initiated the fast transport of proton, while the microporous crystalline morphology restricted the active transport of larger hydrated cations from the solutions. Moreover, the participating sites and porosity of ZSM-5 granted continuous channels for ions electromigration in order to give high limiting current density to the MMMs. The SEM analysis further exhibited that using ZSM-5 as conventional fillers, gave a uniform and homogenous formation to the membranes. However, the optimized amount of fillers and the assortment of a proper dispersion phase are two critical aspects and must be considered to avoid defects and agglomeration of these enhancers during the formation of membranes.

Three-dimensional basswood-based membrane with well-designed multilevel/hierarchical imprinting surface: A high-efficiency selective separation system

Three-dimensional (3D) basswood materials were successfully applied to construct molecularly imprinted nanocomposite membranes for the first time. Importantly in this work, the TiO2@PDA-based modification layers were initially achieved on basswood surfaces. And 3D mesoporous wood-based molecularly imprinted membranes (3DW-MIMs) with sandwich-like TC-imprinted layers were finally synthesize through a re-modified surface-initiated sol-gel technique. Interestingly, based on the TiO2-PDA@basswood surfaces, great increasement of TC-imprinted sites could be prepared during the sol-gel imprinting process. So it was no surprise that excellent rebinding capacity (150.5 mg g−1), fast adsorption kinetics and high permselectivity coefficients (more than 9.0) of 3DW-MIMs could be successfully achieved. Furthermore, an important phenomenon had also been found, i.e. the PDA-modified layers caused significant promotions to the rebinding capacities of the as-prepared 3DW-MIMs, that is to say, more and more TC-imprinted sites could be synthesized because of the PDA-modified surfaces. In addition, the as-prepared 3DW-MIMs were synthesized without complicated procedures and polluting the environment. Finally, the experimental results mentioned above, together with the green synthesis processes, strongly demonstrated that our synthesis methodology of 3DW-MIMs had great potential for applications in various fields of selective separation, chemical industry, environment, biological medicine and so on.

Enhanced proton/iron permselectivity of sulfonated poly (ether ether ketone) membrane functionalized with basic pendant groups during electrodialysis

High permselectivity of cation exchange membrane for H+ and divalent metallic ions is essential for waste acid recovery by electrodialysis. Basic tertiary amine and imidazole groups were introduced into sulfonated poly (ether ether ketone) (SPEEK) membrane via a facile and controllable reaction, named as TA-x and IM-x (x was the basic group content), to construct acid-base pairs and reduce the swelling degree of membranes. 1H NMR confirmed the chemical structure of the as-obtained materials and protonation of tertiary amine and imidazole groups. As expected, all TA-x and IM-x membranes showed lower Fe2+ fluxes than pristine SPEEK membrane during electrodialysis because of their lower swelling degree and the electrostatic repulsion of protonated tertiary amine and imidazole groups. Remarkably, their H+ fluxes were kept similar to that of pristine SPEEK membrane. Therefore, the H+/Fe2+ permselectivity of membrane was improved considerably. Among them, IM-30 membrane showed the highest H+/Fe2+ permselectivity of 65.4, which was over three times that of pristine SPEEK membrane (19.1). Therefore, the introduction of basic groups into cation exchange membrane could reduce the swelling degree of membrane and improve the permselectivity between H+ and divalent metallic ions.

Double-layer-based molecularly imprinted membranes for template-dependent recognition and separation: An imitated core-shell-based synergistic integration design

Extensive efforts have been made for research on the development of selective separation membranes, however, the simultaneous promotion of stable selectivity and high permselectivity still faces its challenges. For the first time, a subversive synthesis strategy with hierarchical structure was proposed for the preparation of double-layer-based molecularly imprinted nanocomposite membranes (DLMIMs). Herein, the polydopamine (PDA) based imprinting process was initially performed on the surfaces of SiO2 and activated carbon nanoparticles (ACNPs) to obtain the first PDA-based tetracycline (TC) imprinted layers. After a phase inversion process, a sol-gel polymerization procedure was then conducted for the preparation of second TC-imprinted layers. The TC-imprinted PDA-ACNPs/SiO2-based nanocomposite could be applied as the imprinting-initiated factors during the sol-gel TC-imprinted process, which led to the formation of imitated core-shell structure in the as-prepared blended membranes. Importantly, attributing to the as-synthesized double-layer-based TC-imprinted multilevel domains, abundant TC-recognition sites with high stability could be successfully synthesized in DLMIMs. Therefore, it was no surprise that large rebinding capacity (115.5 mg g−1), fast adsorption kinetics and high permselectivity coefficients (more than 6.5) were successfully achieved. The results of optimization experiments showed that the PDA-based TC-imprinted layer and sol-gel-based TC-imprinted layer would both cause for largely enhancing the rebinding capacity of DLMIMs. In addition, DLMIMs were synthesized without complicated procedures and the whole preparation process was feasible and pollution-free. Finally, we believed that the as-designed synthetic technique of DLMIMs would hold great potential in selective separation field.

Multilevel mineral-coated imprinted nanocomposite membranes for template-dependent recognition and separation: A well-designed strategy with PDA/CaCO3-based loading structure

In spite of the intense efforts in selective separation field, the utilization and preparation of membrane-associated molecularly imprinted membranes with both enhanced rebinding capacities and high permselectivity performance still remain strong challenges. Herein, the bioinspired PDA-modified porous regenerated cellulose membrane (pRCMs) with mineral-coated multilevel structure was first proposed for the preparation of PDA/CaCO3-based imprinted nanocomposite membranes (PCIMs), m-cresol was chosen as the template molecule. Importantly, this bioinspired methodology was redeveloped and optimized to obtain abundant and uniformly distributed CaCO3 nanocomposite on the surfaces of PDA@pRCMs. The as-designed sandwich-like imprinting structure were then constructed on PDA/CaCO3-based surfaces by developing a simple sol-gel imprinting process. Attributing to the design of the uniform CaCO3/PDA@pRCMs surfaces, amount of m-cresol-imprinted sites and permeation selectivity could be both optimized, it was no surprise that more excellent rebinding capacity (97.4 mg g−1), fast adsorption kinetics and high permselectivity coefficients (more than 13) were successfully achieved. Importantly, the whole synthesis process was conducted without complicated procedures and polluting the environment. Finally, the experimental results mentioned above, together with the green synthesis processes strongly demonstrated that our synthesis methodology of PCIMs had great potential for applications in various fields of selective separation, chemical industry, environment, biological medicine and so on.

Novel fluorinated aromatic polymers with ether-bond-free aryl backbones for pure and mixed gas separation

Three novel fluorinated polymers with ether-bond-free aryl backbones were obtained by one-pot, metal-free, room temperature superacid catalyzed non-stoichiometric step polymerization of 1,1,1-trifluoromethyl acetone with carbazole (CBZ), fluorene (FLN) and 9,9-dimethylfluorene (DFL). 1H and 13C NMR analyses of the polymers revealed their linear structure and high regioselectivity of the polymer forming reaction. The polymers also possess high thermostability with decomposition temperature up to 387 °C for CBZ and up to 530 °C for FLN and DFL as well as reasonable mechanical properties. The gas transport properties of six pure gases and binary gas mixture CO2/CH4 (10/90 mol%) are reported. These polymers present a good combination of permeability and selectivity up to 10 bar at 35 °C for CO2/CH4 mixed-gas feed. DFL exhibits the best pure-gas permeability and selectivity (PCO2 = 78.0, PH2 = 151.5, CO2/CH4 = 22.3 and H2/CH4 = 43.3) and mixed-gas permeability and selectivity CO2/CH4 (PCO2 = 71.3, CO2/CH4 = 23.7) at 35 °C and 2 bar with a slight decrease in selectivity at 10 bar. The highest permselectivity is obtained for FLN (CO2/CH4 = 36.7 and H2/CH4 = 88.4) with a separation performance close to the 2008 upper bound trade off.