High Ion-Exchange Capacity Semihomogeneous Cation Exchange Membranes Prepared via a Novel Polymerization and Sulfonation Approach in Porous Polypropylene

Fabrication of pore-filling cation-exchange membrane from waste polystyrene and Spunbond Meltblown Spunbond (SMS) non-woven polypropylene fabric as the substrate

Commercial ion-exchange membranes are typically thick, possessing limited mechanical strength, and have relatively high fabrication costs. In this study, we utilize a three-layer polypropylene fabric known as Spunbond Meltblown Spunbond (SMS) as the substrate. This choice ensures that the resulting membrane exhibits high strength and low thickness. SMS substrates with various area densities, including 14.5, 15, 17, 20, 25, and 30 g/m2, were coated with different concentrations of waste polystyrene solution (ranging from 5 × 104 to 9 × 104 mg/l) before undergoing sulfonation using concentrated sulfuric acid. The physicochemical and mechanical properties of the membrane were characterized and compared with those of commercial Neosepta CMX and Nafion-117 cation-exchange membranes. Remarkably, the fabricated membrane exhibited good performance compared to commercial ones. The cation-exchange capacity (2.76 meq/g) and tensile strength (37.15 MPa) were higher, and the electrical resistance (3.603Ω) and the thickness (130 μm) were lower than the commercial membranes.

Donnan Dialysis for Recovering Ammonium from Fermentation Solutions Rich in Volatile Fatty Acids

For the production of polyhydroxyalkanoates (PHA) using nitrogen-rich feedstocks (e.g., protein-rich resources), the typical strategy of restricting cell growth as a means to enhance overall PHA productivity by nitrogen limitation is not applicable. In this case, a possible alternative to remove the nitrogen excess (NH₄⁺/NH₃) is by applying membrane separation processes. In the present study, the use of Donnan dialysis to separate ammonium ions from volatile fatty acids present in the media for the production of PHA was evaluated. Synthetic and real feed solutions were used, applying NaCl and HCl receiver solutions separated by commercial cation-exchange membranes. For this specific purpose, Fumasep and Ralex membranes showed better performance than Ionsep. Sorption of ammonium ions occurred in the Ralex membrane, thus intensifying the ammonium extraction. The separation performances with NaCl and HCl as receiver solutions were similar, despite sorption occurring in the Ralex membrane more intensely in the presence of NaCl. Higher volumetric flow rates, NaCl receiver concentrations, and volume ratios of feed:receiver solutions enhanced the degree of ammonium recovery. The application of an external electric potential difference to the two-compartment system did not significantly enhance the rate of ammonium appearance in the receiver solution. The results obtained using a real ammonium-containing solution after fermentation of cheese whey showed that Donnan dialysis can be successfully applied for ammonium recovery from such solutions.

Highly effective and sustainable antibacterial membranes synthesized using biodegradable polymers

In order to reduce foodborne diseases caused by bacterial infections, antibacterial membranes have received increasing research interests in recent years. In this study, highly effective antibacterial membranes were prepared using biodegradable polymers, including polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), and carboxymethyl cellulose (CMC). The cation exchange property of CMC was utilized to introduce silver to prepare antibacterial materials. The presence of silver in the membranes was confirmed by EDS mapping, and the reduction of silver ions to metallic silver was confirmed by the Ag3d XPS spectrum which displayed peaks at 374.46 eV and 368.45 eV, revealing that the oxidation state of silver changed to zero. Two common pathogenic bacteria, Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), were used to investigate the antibacterial performance of the prepared membranes. Zone of inhibition and bacteria-killing tests revealed that the antibacterial membranes were efficient in inhibiting the growth of bacteria (diameters of inhibition zone ranged from 16 mm to 19 mm for fresh membranes) and capable of killing 100% of bacteria under suitable conditions. Furthermore, after 6 cycles of continuous zone of inhibition tests, the membranes still showed noticeable antibacterial activities, which disclosed the sustainable antibacterial properties of the membranes.

Novel application of ion exchange membranes for preparing effective silver and copper based antibacterial membranes

Ion exchange membranes (IEMs) are widely used in water treatment applications such as electrodialysis. However, the exploration of IEMs as effective antibacterial food contact materials (e.g., food packaging membranes) against pathogenic bacteria to ensure food safety has not been reported. Here, we report a simple but effective method to prepare high performance antibacterial membranes via ion exchange coupled with in-situ reduction. The general membrane properties are characterized using SEM, EDS, FTIR, XPS, XRD, DSC, TGA, water uptake, etc. The distribution of silver and copper in the membranes are generally in line with the distribution of sulfur, indicating that the antibacterial ions are introduced into the membranes via ion exchange and are bonded with the sulfonate groups in the membranes. The antibacterial performance is investigated using zone of inhibition tests and continuous bacteria growth inhibition tests. All of the prepared membranes show obvious antibacterial activities compared to the bare cation exchange membranes. The diameters of inhibition zone against Staphylococcus aureus (S. aureus) are all larger than those of Escherichia coli (E. coli), indicating that the prepared membranes are more efficient in inhibiting S. aureus compared to E. coli. Furthermore, the silver-based membrane shows more sustainable antibacterial activities compared to the copper-based membrane. Especially, the results clearly reveal that the silver-based membrane is capable of killing bacteria instead of just inhibiting the growth of bacteria. We have shown for the first time that membranes derived from IEMs have the potential as food contact materials to inhibit the growth of pathogenic bacteria so as to eliminate the risk of bacterial infections and meanwhile delay food spoilage due to bacteria growth.

A comprehensive review on the synthesis and applications of ion exchange membranes

Ion exchange membranes (IEMs) are undergoing prosperous development in recent years. More than 30,000 papers which are indexed by Science Citation Index Expanded (SCIE) have been published on IEMs during the past twenty years (2001-2020). Especially, more than 3000 papers are published in the year of 2020, revealing researchers' great interest in this area. This paper firstly reviews the different types (e.g., cation exchange membrane, anion exchange membrane, proton exchange membrane, bipolar membrane) and electrochemical properties (e.g., permselectivity, electrical resistance/ionic conductivity) of IEMs and the corresponding working principles, followed by membrane synthesis methods, including the common solution casting method. Especially, as a promising future direction, green synthesis is critically discussed. IEMs are extensively applied in various applications, which can be generalized into two big categories, where the water-based category mainly includes electrodialysis, diffusion dialysis and membrane capacitive deionization, while the energy-based category mainly includes reverse electrodialysis, fuel cells, redox flow battery and electrolysis for hydrogen production. These applications are comprehensively discussed in this paper. This review may open new possibilities for the future development of IEMs.

A highly hydrophilic cation exchange nonwoven with a further modifiable epoxy group prepared by radiation-induced graft polymerization

Novel cation exchange nonwoven PP-g-SSS/GMA containing epoxy and sulfonic groups was successfully prepared via radiation-induced simultaneous grafting polymerization by attaching GMA and SSS monomers onto PP nonwoven.

Facile functionalization of isotactic polypropylene via click chemistry

Alkynyl functionalized iPP, with 1–4 mol% comonomer incorporation, can be efficiently synthesized and conveniently converted into various functional iPPs and graft copolymers via alkynyl/N₃ reaction.

A scientometric study of the research on ion exchange membranes

A comprehensive scientometric approach was adopted to study the research on ion exchange membranes. The statistical analysis was conducted based on 21 123 publications which were related to the topic of ion exchange membranes. Specifically, from 2001 to 2016, over 18 000 articles were published on ion exchange membranes, indicating researchers' great interest in this topic. Especially, compared to 2001, the number of articles published in 2016 increased approximately six-fold. This trend continued in 2017 since over 2000 articles were published in the year of 2017. Also, these articles were spread across over 1000 different journals, near 100 countries/regions and over 5000 research institutes, revealing the importance of ion exchange membrane as well as the broad research interest in this field. Besides, the properties and applications of ion exchange membranes were also discussed statistically. Furthermore, keywords analysis indicated that fuel cell and proton exchange membrane had the highest cooccurrence frequency. Finally, research areas analysis revealed that ion exchange membranes had a close relation with chemistry, energy and materials.

This paper provides a comprehensive statistical study on the topic of ion exchange membranes and may provide an avenue for future research work in this field.