Designing Flexible Carbon Nanofiber Membranes by Electrospinning and Cross-Linking for Proton Exchange Membrane Fuel Cells

Traditional carbon-based materials suffer from fragility, low mechanical strength, and electrical conductivity when they are used as a gas diffusion layer (GDL) in proton exchange membrane fuel cells (PEMFCs), resulting in low power density. In this study, a flexible carbon nanofiber membrane (CFM) was studied for use as a GDL, prepared by polyacrylonitrile (PAN) electrospinning with the incorporation of carboxylated multiwalled carbon nanotubes (MWCNTs), polyethylenimine (PEI) impregnation, glutaraldehyde (GA) cross-linking, and thermal treatment. The concentrations of MWCNTs in the electrospinning solution and PEI in the impregnation solution were investigated. Interestingly, the mechanical strength and electrical conductivity of CFM showed a triangle trend with the MWCNTs or PEI concentration. The optimal sample (CNT1.5/PEI7/GA-CFM) demonstrated good flexibility, with an in-plane resistivity of 18.60 mΩ cm, a tensile strength of 7.94 MPa, and a bending strength of 20.65 MPa. The peak power density and maximum current density were respectively 1169 mW cm-2 and 2720 mA cm-2, exceeding those of commercial Toray and Cetech GDLs under identical testing conditions. These results illustrate the potential of high-performance electrospun CFMs for GDL applications.

Metal-Coordinated Polymer-Inorganic Hybrids: Synthesis, Properties, and Application

This review examines the recent advancements and unique properties of polymer-inorganic hybrid materials formed through coordination bonding (Class II hybrids), which enable enhanced functionality and stability across various applications. Here, we categorize these materials based on properties gained through complexation, focusing on electrical conductivity, thermal stability, photophysical characteristics, catalytic activity, and nanoscale self-assembly. Two major synthetic approaches to making these hybrids include homogeneous and heterogeneous methods, each with distinct tradeoffs: Homogeneous synthesis is straightforward but requires favorable mixing between inorganic and polymer species, which are predominantly water-soluble complexes. In contrast, heterogeneous methods are post-processing techniques that provide high area selectivity for inorganic precursors, allowing precise integration within polymer matrices. Finally, we highlight the role of hybrid linkers, namely metallosupramolecular polymers, in creating structural diversity. These can be organized into three main groups: metal-organic frameworks (MOFs), coordination polymers (CPs), and supramolecular coordination complexes (SCCs). Each of these groups introduces unique structural and functional properties that expand the potential applications of hybrid materials.

Polyelectrolyte and polyelectrolyte complex-incorporated adsorbents in water and wastewater remediation - A review of recent advances

In recent years, polyelectrolyte-incorporated functional materials have emerged as novel adsorbents for effective remediation of pollutants in water and wastewater. Polyelectrolytes (PEs) are a special class of polymers with long chains of repeating charged moieties. Polyelectrolyte complexes (PECs) are obtained by mixing aqueous solutions of oppositely charged PEs. Herewith, this review discusses recent advances with respect to water and wastewater remediation using PE- and PEC-incorporated adsorbents. The review begins by highlighting some water resources, their pollution sources and available treatment techniques. Next, an overview of PEs and PECs is discussed, highlighting the evolving progress in their processing. Consequently, application of these materials in different facets of water and wastewater remediation, including heavy metal removal, precious metal and rare earth element recovery, desalination, dye and emerging micropollutant removal, are critically reviewed. For water and wastewater remediation, PEs and PECs are mostly applied either in their original forms, as composites or as morphologically-tunable complexes. PECs are deemed superior to other materials owing to their tunability for both cationic and anionic pollutants. Generally, natural and semi-synthetic PEs have been largely applied owing to their low cost, ready availability and eco-friendliness. Except dye removal and desalination of saline water, application of synthetic PEs and PECs is scanty, and hence requires more focus in future research.

Synthesis and Characterization of Polyethylenimine-Silica Nanocomposite Microparticles

A novel procedure for the synthesis of polyethylenimine (PEI)-silica nanocomposite particles with high adsorption capacities has been developed based on an emulsion templating concept. The exceptional chelating properties of PEI as the parent polymer for the particle core promote the binding abilities of the resulting composite for charged species. Further, the subsequent introduction of silica via the self-catalyzed hydrolysis of tetraethoxysilane facilitates production of robust composite particles with smooth surfaces, enabling potential use in multiphase environments. To enable tailored application in solid/liquid porous environments, the production of particles with reduced sizes was attempted by modulating the shear rates and surfactant concentrations during emulsification. The use of high-speed homogenization resulted in a substantial decrease in average particle size, while increasing surfactant loading only had a limited effect. All types of nanocomposites produced demonstrated excellent binding capacities for copper ions as a test solute. The maximum binding capacities of the PEI-silica nanocomposites of 210-250 mg/g are comparable to or exceed those of other copper binding materials, opening up great application potential in resources, chemical processing, and remediation industries.

Development and evaluation of a DGT sampler using functionalised cross-linked polyethyleimine for the monitoring of arsenic and selenium in mine impacted wetlands

Arsenic and selenium are both carcinogenic and their presence in fresh water has attracted the development of robust and accurate monitoring techniques. A new diffusive gradients in thin-films (DGT) sampler was developed and evaluated for the in situ measurements of arsenic and selenium. The binding layer was made from a mixture of sulphonated and phosphonated cross-linked polyethylenimine (SCPEI and PCPEI, respectively). The optimum ratio of a SCPEI and PCPEI resin mixture was determined. The DGT sampler was calibrated under laboratory conditions to determine the influence of sample turbulence, concentration and pH. The optimised DGT passive sampler was field deployed in a mine impacted dam for 12 days. Binding layer optimisation shows that the polymers had to be mixed in a specific ratio of 80% sulphonated and 20% phosphonated per 0.8 g of the resin mixture, in the loose polymer form. Embedding the resin mixture in agarose gel reduced the uptake of both arsenic and selenium dramatically. At sample pH 3.0 and 5.0, the DGT sampler did not show significant differences in uptake of the two elements during the 15 day deployment. The passive sampler had limited adsorption capacity and was found better suited for dilute solutions, with concentrations below 0.5 mg L^-1 of the target metals. This effect was more pronounced when exposed to dam water which had competing cations. Cations may have reduced the capacity by binding to the PEI backbone via the large number of amine groups. Nonetheless, these cations did not show linear uptake.

Selenium(VI) and copper(II) adsorption using polyethyleneimine-based resins: Effect of glutaraldehyde crosslinking and storage condition

This study synthesizes polyethyleneimine-glutaraldehyde (PEI-GA) resins using different amounts of GA to crosslink with a certain amount of PEI and compares these adsorbents for the adsorption of Cu(II) (cations) and Se(VI) (anions). Moreover, the stability of adsorption affinity of PEI-GA resins stored in open or sealed conditions is also studied. Results show that the amount of GA for PEI crosslinking does not affect the adsorption performance for Se(VI), especially when PEI/GA mass ratio is less than 2, while for Cu(II), the increase on GA amount decreases Cu(II) adsorption capacity. This difference is directly correlated to the change in the adsorption mechanism from electrostatic attraction to chelation. The primary and secondary amine groups on PEI can easily react with CO₂ in the air to form carbamate, potentially affecting the adsorption performance of PEI. Results also indicate that the adsorption efficiency for Se(VI) is hardly affected by the storage condition, while that for Cu(II) decreases significantly after 20-day storage compared to the freshly prepared ones. In addition, all of the adsorbents can selectively remove Se(VI) from Se(VI)-As(V) system and Cu(II) from Pb(II)-Cu(II) system, indicating that the crosslinking has no significant influence on the selectivity.

High-Affinity Detection and Capture of Heavy Metal Contaminants using Block Polymer Composite Membranes

Adsorptive membranes offer one possible solution to the challenge of removing and recovering heavy metal ion contaminants and resources from water supplies. However, current membrane-based sorbents suffer from low binding affinities, leading to issues when contaminants are present at trace concentrations or when the source waters have a high concentration of background electrolytes that compete for open binding sites. Here, these challenges are addressed in the design of a highly permeable (i.e., permeability of ∼2.8 × 104 L m-2 h-1 bar-1) sorbent platform based on polysulfone and polystyrene-b-poly(acrylic acid) composite membranes. The membranes possess a fully interconnected network of poly(acrylic acid)-lined pores, which enables the surface chemistry to be tailored through sequential attachment of polyethylenimine brushes and metal-binding terpyridine ligands. The polyethylenimine brushes increase the saturation capacity, while the addition of terpyridine enables high-affinity binding to a diversity of transition metal ions (i.e., Pd2+, Cd2+, Hg2+, Pb2+, Zn2+, Co2+, Ni2+, Fe2+, Nd3+, and Sm3+). This platform removes these metal contaminants from solution with a sorbent capacity of 1.2 mmol g-1 [based on Cu2+ uptake]. The metal capture performance of the functionalized membranes persists in spite of high concentrations of competitive ions, with >99% removal of Pb2+ and Cd2+ ions from artificial groundwater and seawater solutions. Breakthrough experiments demonstrate the efficient purification of feed solutions containing multiple heavy metal ions under dynamic flow conditions. Finally, fluorescence quenching of the terpyridine moiety upon metal ion complexation offers an in situ probe to monitor the extent of sorbent saturation with a Stern-Volmer association constant of 2.9 × 104 L mol-1. The permeability, capacity, and affinity of these membranes, with high-density display of a metal-binding ligand, offer a chemically tailored platform to address the challenges that arise in ensuring clean water.

Polymeric micelles stabilized by polyethylenimine–copper (C2H5N–Cu) coordination for sustained drug release

Polymeric micelles stabilized by polyethylenimine–copper (C₂H₅N–Cu) coordination were described to improve the release property of water-insoluble anticancer drug.