Imidazolium-functionalized poly (arylene ether ketone) cross-linked anion exchange membranes

Recent advancements in the synthesis of anion exchange membranes and their potential applications in wastewater treatment

Water treatment procedures are increasingly utilized for resource recovery and wastewater disinfection, addressing the current challenges of clean water depletion and wastewater management. Various pollutants, including dyes, acids, pharmaceuticals, and toxic heavy metals have been released into the environment through industrial, domestic, and agricultural activities, posing serious environmental and public health risks. Addressing these issues requires the development of more effective waste treatment processes. Membrane-based treatment technologies offer significant advantages, including high efficiency, versatility, and cost-effectiveness, making them a promising solution for mitigating the impact of these pollutants. In view of this, the potential of ion exchange membranes (IEMs) is continuously increasing due to their advanced characteristics compared to conventional techniques. Anion exchange membranes (AEMs), a special class of IEMs, selectively allow anions to pass through their pores due to the positive charge on their surface. This selective passage aids in resource recovery and removing specific types of pollutants. This review covers preparation methods, modification techniques, and classification of AEMs. It offers a practical classification based on the method of synthesis and structural properties of AEMs. The water-based applications of AEMs including, electrodialysis, diffusion dialysis, and electro-electrodialysis for various wastewater treatments such as heavy metal recovery, dye removal, pharmaceutical removal, and acid separation, have been discussed in detail. Additionally, the effect of various operational parameters on the performance and SWOT (strengths, weaknesses, opportunities, and threats) analysis of AEMs in effluent treatment are presented. The review provides detailed insights into the current status, challenges, and future directions of AEM-based technologies, offering suggestions for future advancements.

Poloxamer 407 Combined with Polyvinylpyrrolidone To Prepare a High-Performance Poly(ether sulfone) Ultrafiltration Membrane

At present, the design and fabrication of polymer membranes with high permeability and good retention ability are still huge challenges. In this study, the commercial Poloxamer 407 (Pluronic F127) is selected as a multifunctional additive, and polyvinylpyrrolidone is used as a pore-forming agent to modify the poly(ether sulfone) membrane by liquid-liquid phase conversion technology to prepare an ultrafiltration membrane with excellent performance. The hydrophobic poly(propylene oxide) segment in Poloxamer 407 guarantees that this copolymer can be firmly anchored to the poly(ether sulfone) matrix, and the hydrophilic poly(ethylene oxide) segments in Poloxamer 407 impart a stronger hydrophilic nature to the modified membrane surface. Therefore, the permeability and hydrophilicity of the modified membrane are significantly improved and the modified membrane also has good stability. When the amount of Poloxamer 407 added to the casting solution reached 0.6 g, the water flux of the modified membrane was as high as 368 L m-2 h-1, and the rejection rate of bovine serum albumin was close to 98%. In the test to isolate organic small molecule dyes, the retention rate of the modified membrane to Congo red is 94.27%. In addition, the modified membrane shows an excellent water flux recovery rate and antifouling ability. It performs well in subsequent cycle tests and long-term membrane life tests and can be used repeatedly. Our work has resulted in poly(ether sulfone) membranes with good performance, which show great potential in the treatment of biomedical wastewater and the removal of industrial organic dye wastewater, it provides ideas for the development and application of amphiphilic polymer materials.

Thermo-Sensitive Microgel/Poly(ether sulfone) Composited Ultrafiltration Membranes

Thermo-sensitive microgels known as PMO-MGs were synthesized via surfactant free emulsion polymerization, with poly(ethylene glycol) methacrylate (OEGMA₄₇₅) and 2-(2-methoxyethoxy) ethyl methacrylate (MEO₂MA) used as the monomers and N, N-methylene-bis-acrylamide used as the crosslinker. PMO-MGs are spherical in shape and have an average diameter of 323 ± 12 nm, as determined via transmission electron microscopy. PMO-MGs/poly (ether sulfone) (PES) composited ultrafiltration membranes were then successfully prepared via the non-solvent-induced phase separation (NIPS) method using a PMO-MG and PES mixed solution as the casting solution. The obtained membranes were systematically characterized via combined X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, Fourier transform infrared spectroscopy and contact angle goniometer techniques. It was found that the presence of PMO-MGs significantly improved the surface hydrophilicity and antifouling performance of the obtained membranes and the PMO-MGs mainly located on the channel surface of the membranes. At 20 °C, the pure water flux increased from 217.6 L·m^-2·h^-1 for pure PES membrane (M00) to 369.7 L·m^-2·h^-1 for PMO-MGs/PES composited membrane (M20) fabricated using the casting solution with 20-weight by percentage microgels. The incorporation of PMO-MGs also gave the composited membranes a thermo-sensitive character. When the temperature increased from 20 to 45 °C, the pure water flux of M20 membrane was enhanced from 369.7 to 618.7 L·m^-2·h^-1.

Tuning Alkaline Anion Exchange Membranes through Crosslinking: A Review of Synthetic Strategies and Property Relationships

Alkaline anion exchange membranes (AAEMs) are an enabling component for next-generation electrochemical devices, including alkaline fuel cells, water and CO2 electrolyzers, and flow batteries. While commercial systems, notably fuel cells, have traditionally relied on proton-exchange membranes, hydroxide-ion conducting AAEMs hold promise as a method to reduce cost-per-device by enabling the use of non-platinum group electrodes and cell components. AAEMs have undergone significant material development over the past two decades; however, challenges remain in the areas of durability, water management, high temperature performance, and selectivity. In this review, we survey crosslinking as a tool capable of tuning AAEM properties. While crosslinking implementations vary, they generally result in reduced water uptake and increased transport selectivity and alkaline stability. We survey synthetic methodologies for incorporating crosslinks during AAEM fabrication and highlight necessary precautions for each approach.

Removal of Metal Ions in Phosphoric Acid by Electro-Electrodialysis with Cross-Linked Anion-Exchange Membranes

There are numerous metallic impurities in wet phosphoric acid, which causes striking negative effects on industrial phosphoric acid production. In this study, the purification behavior of metallic impurities (Fe, Mg, Ca) from a wet phosphoric acid solution employing the electro-electrodialysis (EED) technology was investigated. The cross-linked polysulfone anion-exchange membranes (AEMs) for EED were prepared using N,N,N',N'-tetramethyl-1,6-hexanediamine (TMHDA) to achieve simultaneous cross-linking and quaternization without any cross-linkers or catalysts. The performance of the resulting membranes can be determined using quaternization reagents. When the molar ratio of trimethylamine/TMHDA/chloromethylated polysulfone is 3:1:1, the cross-linked membrane CQAPSU-3-1 exhibits lower water swelling and membrane area resistance than the non-cross-linked membrane. The low membrane area resistance of CQAPSU-3-1 with long alkyl chains is obtained due to the hydrophilic-hydrophobic microphase separation structure formed by TMHDA. EED experiments with different initial phosphoric acid concentrations of 0.52 and 1.07 M were conducted to evaluate the phosphoric acid purification of different AEMs. The results show that the EED experiments were more suitable for the purification of wet phosphoric acid solution at low concentrations. It was found that the phosphoric acid concentration in the anode compartment could be increased from 0.52 to 1.04 M. Through optimization, with an initial acid concentration of 0.52 M, CQAPSU-3-1 exhibits an enhanced metallic impurity removal ratio of higher than 72.0%, the current efficiency of more than 90%, and energy consumption of 0.48 kWh/kg. Therefore, CQAPSU-3-1 exhibits much higher purification efficiency than other membranes at a low initial phosphoric acid concentration, suggesting its potential in phosphoric acid purification application.

Densely Quaternized Fluorinated Poly(fluorenyl ether)s with Excellent Conductivity and Stability for Vanadium Redox Flow Batteries

Cationic group distribution and elemental composition are two key factors determining the conductivity and stability of anion exchange membranes (AEMs) for vanadium redox flow batteries (VRFBs). Herein, fluorinated tetra-dimethylaminomethyl-poly(fluorenyl ether)s (TAPFE)s were designed as the polymer precursors, which were reacted with 6-bromo-N,N,N-trimethylhexan-1-aminium bromide to introduce di-quaternary ammonium (DQA) containing side chains. The resultant DQA-TAPFEs with a rigid fluorinated backbone and flexible multi-cationic side chains exhibited distinct micro-phase separation as probed by small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM). DQA-TAPFE-20 with an ion exchange capacity (IEC) of 1.55 mmol g^-1 exhibited a SO₄^2- conductivity of 10.1 mS cm^-1 at room temperature, much higher than that of a control AEM with an identical backbone but spaced out cationic groups, which had a similar IEC of 1.60 mmol g^-1 but a SO₄^2- conductivity of only 3.2 mS cm^-1. Due to the Donnan repulsion effect, the DQA-TAPFEs exhibited significantly lower VO²⁺ permeability than Nafion 212. The VRFB assembled with DQA-TAPFE-20 achieved an energy efficiency of 80.4% at 80 mA cm^-1 and a capacity retention rate of 82.9% after the 50th cycling test, both higher than those of the VRFB assembled with Nafion 212 and other AEMs in the literature. Therefore, the rationally designed DQA-TAPFEs are promising candidates for VRFB applications.