Effect of polymer molecular weight on the physical properties and CO2/N2 separation of pyrrolidinium-based poly(ionic liquid) membranes

Recycling and 3D-Printing Biodegradable Membranes for Gas Separation-toward a Membrane Circular Economy

Polymer membranes employed in gas separation play a pivotal role in advancing environmental sustainability, energy production, and gas purification technologies. Despite their significance, the current design and manufacturing of these membranes lack cradle-to-cradle approaches, contributing to plastic waste pollution. This study explores emerging solutions, including the use of biodegradable biopolymers such as polyhydroxybutyrate (PHB) and membrane recycling, with a focus on the specific impact of mechanical recycling on the performance of biodegradable gas separation membranes. This research represents the first systematic exploration of recycling biodegradable membranes for gas separation. Demonstrating that PHB membranes can be recycled and remanufactured without solvents using hot-melt extrusion and 3D printing, the research highlights PHB's promising performance in developing more sustainable CO2 separations, despite an increase in gas permeability with successive recycling steps due to reduced polymer molecular weight. The study emphasizes the excellent thermal, chemical, and mechanical stability of PHB membranes, albeit with a marginal reduction in gas selectivity upon recycling. However, limitations in PHB's molecular weight affecting extrudability and processability restrict the recycling to three cycles. Anticipating that this study will serve as a foundational exploration, we foresee more sophisticated recycling studies for gas separation membranes, paving the way for a circular economy in future membrane technologies.

The Influence of Polycation and Counter-Anion Nature on the Properties of Poly(ionic liquid)-Based Membranes for CO2 Separation

The current investigation is focused on the development of composite membranes based on polymeric ionic liquids (PILs) containing imidazolium and pyridinium polycations with various counterions, including hexafluorophosphate, tetrafluoroborate, and bis(trifluoromethylsulfonyl)imide. A combination of spectroscopic methods was used to identify the synthesized PILs and characterize their interaction with carbon dioxide. The density and surface free energy of polymers were performed by wettability measurements, and the results are in good agreement with the permeability and selectivity obtained within the gas transport tests. It was shown that the membranes with a selective layer based on PILs exhibit relatively high permeability with CO₂ and high ideal selectivity CO₂/CH₄ and CO₂/N₂. Additionally, it was found that the type of an anion significantly affects the performance of the obtained membranes, with the most pronounced effect from bis-triflimide-based polymers, showing the highest permeability coefficient. These results provide valuable insights into the design and optimization of PIL-based membranes for natural and flue gas treatment.

Ionogels: recent advances in design, material properties and emerging biomedical applications

Ionic liquid (IL)-based gels (ionogels) have received considerable attention due to their unique advantages in ionic conductivity and their biphasic liquid-solid phase property. In ionogels, the negligibly volatile ionic liquid is retained in the interconnected 3D pore structure. On the basis of these physical features as well as the chemical properties of well-chosen ILs, there is emerging interest in the anti-bacterial and biocompatibility aspects. In this review, the recent achievements of ionogels for biomedical applications are summarized and discussed. Following a brief introduction of the various types of ILs and their key physicochemical and biological properties, the design strategies and fabrication methods of ionogels are presented by means of different confining networks. These sophisticated ionogels with diverse functions, aimed at biomedical applications, are further classified into several active domains, including wearable strain sensors, therapeutic delivery systems, wound healing and biochemical detections. Finally, the challenges and possible strategies for the design of future ionogels by integrating materials science with a biological interface are proposed.

Recent Advances in Poly(Ionic Liquid)-Based Membranes for CO2 Separation

Poly(ionic liquid)-based membranes have been the subject of intensive research in the last 15 years due to their potential for the separation of CO₂ from other gases. In this short review, different types of PIL-based membranes for CO₂ separation are described (neat PIL membranes; PIL-IL composite membranes; PIL-polymer blend membranes; PIL-based block copolymer membranes, and PIL-based mixed matrix membranes), and their state-of-the-art separation results for different gas pairs (CO₂/N₂, CO₂/H₂, and CO₂/CH₄) are presented and discussed. This review article is focused on the most relevant research works performed over the last 5 years, that is, since the year 2017 onwards, in the field of poly(ionic liquid)-based membranes for CO₂ separation. The micro- and nano-morphological characterization of the membranes is highlighted as a research topic that requires deeper study and understanding. Nowadays there is an array of advanced structural characterization techniques, such as neutron scattering techniques with contrast variation (using selective deuteration), that can be used to probe the micro- and nanostructure of membranes, in length scales ranging from ~1 nm to ~15 μm. Although some of these techniques have been used to study the morphology of PIL-based membranes for electrochemical applications, their use in the study of PIL-based membranes for CO₂ separation is still unknown.

Synthesis, Structure and Reactivity of a Cyapho(dicyano)methanide Salt

We describe the synthesis of a cyapho(dicyano)methanide salt, [K(18-crown-6)][C(CN)2 (CP)], from reaction of [Na(18-crown-6)][PH2 ] (18-crown-6=1,4,7,10,13,16-hexaoxacyclooctadecane) with 1,1-diethoxy-2,2-dicyanoethylene (EtO)2 C=C(CN)2 . The reaction proceeds through a Michael addition-elimination pathway to afford [Na(18-crown-6)][HP{C(OEt)=C(CN)2 }]. Addition of a strong, non-nucleophilic base (KHMDS) to this intermediate results in the formation of [K(18-crown-6)][C(CN)2 (CP)]. Subsequent reactivity studies reveal that the cyapho(dicyano)methanide ion is susceptible to protonation with strong acids to afford the parent acid HC(CN)2 (CP). The reactivity of the cyaphide moiety in [C(CN)2 (CP)]- was explored through coordination to metal centers and in cycloaddition reactions with azides.

Recent Advances in Mixed-Matrix Membranes for Light Hydrocarbon (C1-C3) Separation

Light hydrocarbons, obtained through the petroleum refining process, are used in numerous applications. The separation of the various light hydrocarbons is challenging and expensive due to their similar melting and boiling points. Alternative methods have been investigated to supplement cryogenic distillation, which is energy intensive. Membrane technology, on the other hand, can be an attractive alternative in light hydrocarbon separation as a phase change that is known to be energy-intensive is not required during the separation. In this regard, this study focuses on recent advances in mixed-matrix membranes (MMMs) for light hydrocarbon (C1-C3) separation based on gas permeability and selectivity. Moreover, the future research and development direction of MMMs in light hydrocarbon separation is discussed, considering the low intrinsic gas permeability of polymeric membranes.

Overview of Membrane Science and Technology in Portugal

Membrane research in Portugal is aligned with global concerns and expectations for sustainable social development, thus progressively focusing on the use of natural resources and renewable energy. This review begins by addressing the pioneer work on membrane science and technology in Portugal by the research groups of Instituto Superior Técnico-Universidade de Lisboa (IST), NOVA School of Science and Technology-Universidade Nova de Lisboa (FCT NOVA) and Faculdade de Engenharia-Universidade do Porto (FEUP) aiming to provide an historical perspective on the topic. Then, an overview of the trends and challenges in membrane processes and materials, mostly in the last five years, involving Portuguese researchers, is presented as a contribution to a more sustainable water-energy-material-food nexus.

Emerging iongel materials towards applications in energy and bioelectronics

In the past two decades, ionic liquids (ILs) have blossomed as versatile task-specific materials with a unique combination of properties, which can be beneficial for a plethora of different applications. The additional need of incorporating ILs into solid devices led to the development of a new class of ionic soft-solid materials, named here iongels. Nowadays, iongels cover a wide range of materials mostly composed of an IL component immobilized within different matrices such as polymers, inorganic networks, biopolymers or inorganic nanoparticles. This review aims at presenting an integrated perspective on the recent progress and advances in this emerging type of material. We provide an analysis of the main families of iongels and highlight the emerging types of these ionic soft materials offering additional properties, such as thermoresponsiveness, self-healing, mixed ionic/electronic properties, and (photo)luminescence, among others. Next, recent trends in additive manufacturing (3D printing) of iongels are presented. Finally, their new applications in the areas of energy, gas separation and (bio)electronics are detailed and discussed in terms of performance, underpinning it to the structural features and processing of iongel materials.

A Review on Ionic Liquid Gas Separation Membranes

Ionic liquids have attracted the attention of the industry and research community as versatile solvents with unique properties, such as ionic conductivity, low volatility, high solubility of gases and vapors, thermal stability, and the possibility to combine anions and cations to yield an almost endless list of different structures. These features open perspectives for numerous applications, such as the reaction medium for chemical synthesis, electrolytes for batteries, solvent for gas sorption processes, and also membranes for gas separation. In the search for better-performing membrane materials and membranes for gas and vapor separation, ionic liquids have been investigated extensively in the last decade and a half. This review gives a complete overview of the main developments in the field of ionic liquid membranes since their first introduction. It covers all different materials, membrane types, their preparation, pure and mixed gas transport properties, and examples of potential gas separation applications. Special systems will also be discussed, including facilitated transport membranes and mixed matrix membranes. The main strengths and weaknesses of the different membrane types will be discussed, subdividing them into supported ionic liquid membranes (SILMs), poly(ionic liquids) or polymerized ionic liquids (PILs), polymer/ionic liquid blends (physically or chemically cross-linked 'ion-gels'), and PIL/IL blends. Since membrane processes are advancing as an energy-efficient alternative to traditional separation processes, having shown promising results for complex new separation challenges like carbon capture as well, they may be the key to developing a more sustainable future society. In this light, this review presents the state-of-the-art of ionic liquid membranes, to analyze their potential in the gas separation processes of the future.

Influence of ionic liquid-like cationic pendants composition in cellulose based polyelectrolytes on membrane-based CO2 separation

Cellulose acetate (CA) is an attractive membrane polymer for CO₂ capture market. However, its low CO₂ permeability hampers its application as part of a membrane for most relevant types of CO₂ containing feeds. This work investigates the enhancement of CA separation performance by incorporating ionic liquid-like pendants (1-methylimidazol, 1-methylpyrrolidine, and 2-hydroxyethyldimethylamine (HEDMA) on the CA backbone. These CA-based polyelectrolytes (PEs), synthesised by covalent grafting of cationic pendants with anion metathesis, were characterised by NMR, FTIR, DSC/TGA, and processed into thin-film composite membranes. The membrane performance in CO₂/N₂ mixed-gas permeation experiments shows a decrease in CO₂ and N₂ permeability and an initial decrease and then gradual increase in CO₂/N₂ selectivity with increasing HEDMA content. The amount of HEDMA attached to the CA backbone determines overall separation process in bifunctional PEs. This indicates that the hydroxy-substituted cationic pendants alter interactions between PEs network and permeating CO₂ molecules, suggesting possibilities for further improvements.

Facilitated Transport Membranes With Ionic Liquids for CO2 Separations

In recent years, significant development milestones have been reached in the areas of facilitated transport membranes and ionic liquids for CO2 separations, making the combination of these materials an incredibly promising technology platform for gas treatment processes, such as post-combustion and direct CO2 capture from air in buildings, submarines, and spacecraft. The developments in facilitated transport membranes involve consistently surpassing the Robeson upper bound for dense polymer membranes, demonstrating a high CO2 flux across the membrane while maintaining very high selectivity. This mini review focuses on the recent developments of facilitated transport membranes, in particular discussing the challenges and opportunities associated with the incorporation of ionic liquids as fixed and mobile carriers for separations of CO2 at low partial pressures (<1 atm).

Water Vapour Promotes CO2 Transport in Poly(ionic liquid)/Ionic Liquid-Based Thin-Film Composite Membranes Containing Zinc Salt for Flue Gas Treatment

A poly(ionic-liquid) (PIL) matrix can be altered by incorporating additives that will disrupt the polymer chain packing, such as an ionic liquid (IL) and inorganic salts to boost their exploitation as materials for membrane production to be used in CO2 capture. Herein, potential of PIL/IL/salt blends is investigated on the example of poly(diallyldimethyl ammonium) bis(trifluoromethylsulfonyl)imide (P[DADMA][Tf2N]) with N-butyl-N-methyl pyrrolidinium bis(trifluoromethylsulfonyl)imide ([Pyrr14][Tf2N]) and zinc di-bis(trifluoromethylsulfonyl)imide (Zn[Tf2N]2). Composite material with IL and a higher amount of Zn2+ showed an increase in the equilibrium CO2 sorption capacity to 2.77 cm3 (STP)cm −3 bar−1. Prepared blends were successfully processed into thick, dense membranes and thin-film composite membranes. Their CO2 separation efficiency was determined using ideal and mixed-gas feed (vol% CO2 = 50 , dry and with 90% relative humidity). The dominant role of solubility in the transport mechanism is confirmed by combining direct gravimetric sorption measurements and indirect estimations from time-lag experiments. The maximum incorporated amount of Zn2+ salts increased equilibrium solubility selectivity by at least 50% in comparison to the parent PIL. All materials showed increased CO2 permeance values by at least 30% in dry conditions, and 60% in humidified conditions when compared to the parent PIL; the performance of pure PIL remained unchanged upon addition of water vapor to the feed stream. Mixed-gas selectivities for all materials rose by 10% in humidified conditions when compared to dry feed experiments. Our results confirm that the addition of IL improves the performance of PIL-based composites due to lower stiffness of the membrane matrix. The addition of Zn2+-based salt had a marginal effect on CO2 separation efficiency, suggesting that the cation participates in the facilitated transport of CO2.

Influence of Anion Structure on Thermal, Mechanical and CO2 Solubility Properties of UV-Cross-Linked Poly(ethylene glycol) Diacrylate Iongels

Iongel-based CO₂ separation membranes were prepared by fast (< 1 min) UV-initiated polymerization of poly(ethylene glycol) diacrylate (PEGDA) in the presence of different ionic liquids (ILs) with the [C₂mim]⁺ cation and anions such as [TFSI]^-, [FSI]^-, [C(CN)₃]^- and [B(CN)₄]^-. The four ILs were completely miscible with the non-ionic PEGDA network. Transparent and free-standing iongels containing between 60 and 90 %wt of IL were obtained and characterized by diverse techniques (FTIR, TGA, DSC, DMTA, SEM, CO₂ solubility and pure gas permeability). The thermal and mechanical stability of the iongels, as well as CO₂ solubility, were found to be strictly dependent on the IL content and the anion's nature. The TGA results indicated that the iongels mostly follow the thermal profile of the respective neat ILs. The DMTA analysis revealed that the iongels based on fluorinated anions have higher storage modulus than those of cyano-functionalized anions. Conversely, the PEGDA-C(CN)₃ iongels presented the highest CO₂ solubility values ranging from 72 to 80 mmol/g. Single CO₂ permeabilities of 583 ± 29 Barrer and ideal CO₂/N₂ selectivities of 66 ± 3 were obtained with the PEGDA-70 C(CN)₃ iongel membrane. This work demonstrates that the combination of PEGDA with high contents of the best performing ILs is a promising and simple strategy, opening up new possibilities in the design of high-performance iongel membranes for CO₂ separation.

Polyvinylamine Membranes Containing Graphene-Based Nanofillers for Carbon Capture Applications

In the present study, the separation performance of new self-standing polyvinylamine (PVAm) membranes loaded with few-layer graphene (G) and graphene oxide (GO) was evaluated, in view of their use in carbon capture applications. PVAm, provided by BASF as commercial product named Lupamin^TM, was purified obtaining PVAm films with two degrees of purification: Low Grade (PVAm-LG) and High Grade (PVAm-HG). These two-grade purified PVAm were loaded with 3 wt% of graphene and graphene oxide to improve mechanical stability: indeed, pristine tested materials proved to be brittle when dry, while highly susceptible to swelling in humid conditions. Purification performances were assessed through FTIR-ATR spectroscopy, DSC and TGA analysis, which were carried out to characterize the pristine polymer and its nanocomposites. In addition, the membranes′ fracture surfaces were observed through SEM analysis to evaluate the degree of dispersion. Water sorption and gas permeation tests were performed at 35 °C at different relative humidity (RH), ranging from 50% to 95%. Overall, composite membranes showed improved mechanical stability at high humidity, and higher glass transition temperature (T_g) with respect to neat PVAm. Ideal CO₂/N₂ selectivity up to 80 was measured, paired with a CO₂ permeability of 70 Barrer. The membranes’ increased mechanical stability against swelling, even at high RH, without the need of any crosslinking, represents an interesting result in view of possible further development of new types of facilitated transport composite membranes.

Improved Physicochemical Stability and High Ion Transportation of Poly(Arylene Ether Sulfone) Blocks Containing a Fluorinated Hydrophobic Part for Anion Exchange Membrane Applications

A series of anion exchange membranes composed of partially fluorinated poly(arylene ether sulfone)s (PAESs) multiblock copolymers bearing quaternary ammonium groups were synthesized with controlled lengths of the hydrophilic precursor and hydrophobic oligomer via direct polycondensation. The chloromethylation and quaternization proceeded well by optimizing the reaction conditions to improve hydroxide conductivity and physical stability, and the fabricated membranes were very flexible and transparent. Atomic force microscope images of quaternized PAES (QN-PAES) membranes showed excellent hydrophilic/hydrophobic phase separation and distinct ion transition channels. An extended architecture of phase separation was observed by increasing the hydrophilic oligomer length, which resulted in significant improvements in the water uptake, ion exchange capacity, and hydroxide conductivity. Furthermore, the open circuit voltage (OCV) of QN-PAES X10Y23 and X10Y13 was found to be above 0.9 V, and the maximum power density of QN-PAES X10Y13 was 131.7 mW cm-2 at 60 °C under 100% RH.

Towards Biohydrogen Separation Using Poly(Ionic Liquid)/Ionic Liquid Composite Membranes

Considering the high potential of hydrogen (H₂) as a clean energy carrier, the implementation of high performance and cost-effective biohydrogen (bioH₂) purification techniques is of vital importance, particularly in fuel cell applications. As membrane technology is a potentially energy-saving solution to obtain high-quality biohydrogen, the most promising poly(ionic liquid) (PIL)–ionic liquid (IL) composite membranes that had previously been studied by our group for CO₂/N₂ separation, containing pyrrolidinium-based PILs with fluorinated or cyano-functionalized anions, were chosen as the starting point to explore the potential of PIL–IL membranes for CO₂/H₂ separation. The CO₂ and H₂ permeation properties at the typical conditions of biohydrogen production (T = 308 K and 100 kPa of feed pressure) were measured and discussed. PIL–IL composites prepared with the [C(CN)₃]⁻ anion showed higher CO₂/H₂ selectivity than those containing the [NTf₂]⁻ anion. All the membranes revealed CO₂/H₂ separation performances above the upper bound for this specific separation, highlighting the composite incorporating 60 wt % of [C₂mim][C(CN)₃] IL.

Functionalized ionic liquid membranes for CO2 separation

It is imperative to develop efficient, reversible and economic technologies for separating CO₂ which mainly comes from flue gas, natural gas and syngas.