Pollution of water bodies by nitroaromatic compounds, particularly picric acid (PA), represents a significant environmental concern due to its high toxicity, persistence in the environment, and ability to form water-soluble ionized species. In this study, a polyelectrolyte membrane based on a complex of poly(sodium 4-styrenesulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDADMAC) was fabricated using an environmentally friendly aqueous phase separation (APS) method as an extraction matrix for batch-wise adsorptive preconcentration and visual assessment of PA. Membrane morphology and surface properties were characterized by SEM and AFM, and pH-dependent water uptake was evaluated. The results demonstrate that the fabricated polyelectrolyte membrane effectively captures PA from aqueous solutions via π–π stacking and electrostatic interactions, achieving >90% removal efficiency. Furthermore, the color change of the membrane during PA sorption enabled the development of a portable calibration palette for its rapid on-site visual assessment, with an established visual limit of detection of 1·10–5 M. Overall, these findings provide new insights into the interaction mechanisms between nitroaromatic compounds and polyelectrolyte matrices and highlight the potential of PSS–PDADMAC membranes as a sustainable platform for express analytical preconcentration and semi-quantitative monitoring of PA.
Reverse electrodialysis (RED) is a promising technology for harvesting salinity gradient energy from the mixing of seawater and river water. In RED systems, the internal resistance within the flow channels significantly reduces the power density. PF membranes provide an effective approach to reduce the electrical resistance in the flow channels without the use of conventional spacers. In this study, a dashed-line PF membrane was proposed to stabilize the PF structure of ORIGAMI PF proposed in recent years, and the structural and power generation performance were compared among stacks fabricated with flat membranes, dashed-line PF membranes, and solid-line PF membranes. As a result, the dashed-line PF membrane maintained its profile structure for more than two years and exhibited excellent long-term mechanical stability. Although these PF membranes showed a voltage decrease due to concentration polarization, the internal resistance of the stacks was significantly reduced by eliminating the spacer mesh. Consequently, the dashed-line PF membrane exhibited a gross power density of 1.40 W/m², which is approximately twice that of the flat membranes and 20% higher than that of the solid-line PF membranes.
Ceramic microfiltration membranes are widely used in industrial solid–liquid separation processes, yet their permeance is often limited under fouling-prone conditions. In this study, the influence of through-pore density on the permeance and fouling behavior of α-alumina microfiltration membranes was systematically investigated using yeast suspension filtration as a model system. Two membranes with similar pore sizes and comparable separation performance, but distinctly different through-pore densities, were compared. Despite nearly identical pore size distributions, the membrane with higher through-pore density exhibited a more than threefold higher steady-state permeance and significantly lower fouling resistance. Analysis of elemental distribution of a representative cross-sectional line scan revealed that fouling in the high-density membrane was largely confined to the surface, whereas pronounced internal pore blocking occurred in the low-density membrane. Resistance analysis further showed reduced contributions from both pore-blocking and cake layer resistances for the membrane with higher through-pore density. These results demonstrate that through-pore density is a critical structural parameter beyond pore size control and provide an engineering-oriented framework for designing high-performance ceramic microfiltration membranes for fouling-prone applications.
The practical limit of a hollow fiber membrane module is often set by module-level structural constraints rather than by intrinsic membrane properties, but potting design receives little attention in the membrane literature. This limitation is particularly pronounced for modules with a soft, highly swellable selective layer in aggressive feeds using conventional single-epoxy potting. Here we report a composite hot-melt/epoxy potting architecture that enables mechanically stable sealing and extended operation of hollow fiber modules used for liquid-phase separation of cyclic siloxanes from silicone oil. The novel architecture, a compliant thermoplastic hot-melt inner plug surrounded by a high-temperature epoxy, is compared directly with less compatible clear-epoxy and even more durable black-epoxy modules under identical pressurized liquid conditions. Whereas single-epoxy modules show pressure-dependent interfacial leakage and limited lifetime, the composite suppresses polymer–epoxy debonding, and raises the leak-free limit to 900 psia, with stable operation beyond 2000 h at 500 psia. Fluorescence leak-spot visualization confirms that the composite shifts the dominant failure mode away from circumferential debonding at the polydimethylsiloxane (PDMS)–epoxy interfaces. Notably, the thermoplastic component also renders the module thermally reworkable if necessary. A demonstration of this capability is provided wherein reheating in place allows full recovery of the separation factor (105% of the as-fabricated value, within measurement uncertainty) without complete remanufacturing. While leak-free operation remains the ultimate goal, this reworkable option provides a practical safety net as development continues. These results establish potting architecture as a first-order structural design parameter governing the reliability of high-pressure sorp-vection hollow fiber modules.
The disk inhibition zone test is a widely used and visually interpretable method for evaluating the antibacterial properties of membranes. However, the lack of a consistent, standardized methodology for disk inhibition zone testing limits reliable assessment of antibacterial performance in membranes. Herein, we introduce a systematic and reproducible framework for investigating the key experimental parameters, including bacterial concentration (105–109 CFU/mL), nutrient media (i.e., tryptic soy broth (TSB)) concentration (15–60 g/L), incubation time (6–10 h), and various bacterial spreading techniques such as overlayer (OL), glass spreader (GS), and cotton swab (CS) method. Quantitative image analysis in ImageJ, combined with comprehensive statistical evaluation, revealed that bacterial concentration and TSB levels were the most influential factors in determining inhibition zone diameter. In contrast, the choice of spreading technique significantly affected the uniformity and integrity of the inhibition zone. Results showed that utilizing a bacterial concentration of 107 CFU/mL, TSB concentration of ≥ 30 g/L, incubation times of 8-10 h, and the overlayer (OL) method, although less commonly used in the literature, led to the most consistent inhibition zones, as these conditions promote stable bacterial growth kinetics and uniform lawn formation. This framework provides a reliable approach to standardize antibacterial membrane testing and improve cross-study comparability and validation.
Irradiation-driven diffusion plays a central role in a broad range of microstructural phenomena induced by intense ion fluxes. Quantifying radiation-enhanced diffusion coefficients, DRED, in nanometric volumes is therefore essential for identifying materials capable of withstanding continuous irradiation while preserving their structural and functional integrity. Here, we present an analytical framework that uses two experimentally accessible quantities — the membrane thickness, L, and the characteristic saturation time, τ — to quantify radiation-enhanced diffusion coefficients for H/He in nanometric freestanding membranes. Within a Fickian slab model, the dominant diffusion mode gives DRED=L2/(π2τ). Applying this framework to experimental data on saturated H and He uptake in 20–30 nm amorphous Ta2O5 membranes, the analysis yields DRED=10−19–10−20 m2 s−1 at damage rates of 3–6×10−3 dpa s−1. The corresponding diffusion length, DREDτ≈10nm, is commensurate with the membrane thickness, indicating that the approach probes irradiation-driven transport in truly nanometric volumes.
This study investigates the structure–property–performance relationships of advanced membrane materials for crystal violet (CV) dye removal using Principal Component Analysis (PCA). A dataset of electrospun nanocomposite membranes, including pristine, PES/PVDF-blended, and nanofiller-modified variants incorporating ZIF-67, graphene oxide (GO), and graphene nanoplatelets (GNPs) was analysed. PCA reduced dataset complexity and revealed two dominant components explaining 76.50% of the total variance. The first component (PC1, 54.66%) represented a performance axis driven by viscosity, porosity, pore size, flux, and rejection, while the second component (PC2, 21.84%) captured a wettability–processing axis governed by contact angle and flow rate. Based on the dominant PCA loadings, two reduced PCA-derived descriptors were formulated: the Rheology–Structure–Transport Index (RSTI) and the Hydrophilicity–Processing Index (HPI). These descriptors provide compact, physically interpretable summaries of the main PC1 and PC2 tendencies within the analysed dataset, rather than externally validated predictive models. The results show that high membrane performance can be achieved through distinct physicochemical pathways depending on nanofiller type. The proposed PCA-based framework offers a robust and interpretable tool for analysing complex membrane datasets and provides valuable guidance for the rational design and optimisation of advanced membranes for wastewater treatment.
State-of-the-art anion exchange membranes (AEMs) used in alkaline water electrolysis, fuel cells and other devices are often cast from the pre-polymer and later converted to the ion conducting form due to the low solubility of the ion conducting polymer in the casting solvent. In this study, the tradeoffs between solution functionalization of the prepolymer, crosslinking, and high membrane conductivity were addressed through a novel method of membrane fabrication of a vinyl-addition polynorbornene (PNB). Random copolymers of vinyl norbornene (VNB) and bromobutyl norbornene (BBNB) were synthesized and subsequently quaternized in solution by reacting the pendant bromo-alkyl functionality with N,N-dimethyldecylamine through the Menshutkin reaction. The resulting pre-quaternized ionomers were solvent cast and crosslinked by UV-initiated thiol-ene click reaction, which was found to be more efficient than diamine crosslinking through the Menshutkin reaction. The ion exchange capacity, ionic conductivity and mobility, and mechanical properties of the solution processable membranes were investigated at different crosslink density by controlling the mole fraction of the VNB in the prepolymer. The optimal copolymer composition had a hydroxide conductivity of 50 mS cm-1 at 20 degrees C. The solution-quaternized, ion-conducting membranes had 35% higher hydroxide mobility (1.95 & times; 10-4 cm2 V-1 s-1) compared to membranes quaternized after membrane casting due to improved phase segregation as indicated by x-ray scattering. This results in higher ion conductivity at all ion exchange capacity values for the solution quaternized membranes. In a water electrolysis cell, the pre-quaternized membrane with moderate crosslinking achieved 2.14 V at 1.5 A cm-2 and maintained stable operation over 500 h at constant current of 1.5 A cm-2 with minimal degradation of 23 mu V h-1.
Membrane based electrochemical systems for separations and selectivity are a promising method of obtaining valuable chemicals from complex aqueous streams. A critical component of these systems is the cation exchange membrane (CEM). Traditional CEMs are thin layers of hydrocarbon polymers with fixed negative charge groups. The interactions between fixed charges and mobile positive ions are imperative to understand because they correlate to the CEM’s ability to transport cations, yet there is a lack of understanding regarding these interactions. In this work, we use Raman spectroscopy to study changes of the vibrational modes of the fixed sulfonate groups in two commercial CEM’s exchanged with ten different chloride salts. We also report on the differences in vibrational peak shifts between CEMs with low and high water contents. We find that in the low-hydration state there is a linear correlation between fixed charge Raman peak shift and mobile cation’s ionic radius. In the fully hydrated state, Raman peak shifts indicate the electrostatic interactions between fixed and mobile charges are affected by the spatial distance due to an ion’s hydrated radius. These findings are supported by water uptake and conductivity measurements. This study shows we can utilize rapid, non-invasive Raman spectroscopy to improve the state of understanding of transport in CEMs.
Critical materials are vital in energy storage systems, and purification of these compounds will likely require binding of specific ions to selective ligands. Solvent extraction isolates aqueous unbound ions from metal-ion complexes that partition into the organic phase, but this contaminates large volumes of water with organic solvent. As a possible alternative to solvent extraction, this study examines all-aqueous diafiltration to isolate several highly pure polymeric metal-ion complexes in a single, continuous stage. Diafiltration employs addition of water during ultrafiltration (UF) of a solution containing metal ions and polyethyleneimine (PEI). The UF membrane retains polymeric complexes of selectively bound ions while passing non-binding ions to give selectivity. Impurity concentrations decrease exponentially with permeate volume to give 99.99+% pure metal-ion complexes. Using PEI, diafiltration enables Cu2+/Mn2+, Cu2+/Ni2+, Co2+/Mn2+, and Co2+/Li+ separations. Equilibrium calculations identify pH windows for selective complexation of a specific cation. Cu2+/Mn2+ separations achieved 99.99+% Cu(II) purity in the retentate with >92% Cu2+ recovery after filtration of >7 cell volumes. Cu2+/Mn2+, Co2+/Mn2+, Cu2+/Ni2+, and Co2+/Li+ separations yielded 98–99.9% retentate purities within filtration of 2–4 cell volumes. High rejection of the positively charged polymer and unhindered passage of anions generates a Donnan potential that maintains zero current by decreasing anion transport and pulling free cations across the membrane. In some cases, this gives free-cation concentrations in the permeate that are as much as twice those in the feed (negative rejection). This negative rejection accelerates depletion of unbound cations to greatly reduce the filtration volume required for high purity.
Mixed matrix membranes (MMMs) incorporating metal-organic frameworks (MOFs) have emerged as a compelling strategy to overcome the intrinsic permeability-selectivity trade-off that constrains conventional polymeric gas separation membranes. Owing to their crystalline porosity, modular chemistry, and structural diversity, MOFs provide unprecedented opportunities to tailor sorption and diffusion pathways when integrated within polymer matrices. Recent advances in MOF chemistry, including two-dimensional, core–shell, hierarchical, and surface-functionalized frameworks, have significantly expanded the design space for MMMs, enabling separation performances that increasingly exceed established Robeson upper bounds (2008 and 2017).This review critically surveys progress in MOF-based MMMs over the past decade, with a particular focus on the interplay between MOF structure, polymer–filler interfacial morphology, and gas transport behavior. Key parameters governing membrane performance, including MOF particle size, morphology, surface chemistry, dispersion, and loading, are examined in the context of defect formation, pore accessibility, and interfacial compatibility. Strategies to mitigate non-selective voids, pore blockage, and polymer rigidification, such as surface functionalization, polymer grafting, and in situ MOF growth, are discussed and evaluated across representative gas separation systems. This review outlines fundamental design principles and research directions necessary to advance MOF-enabled MMMs toward practical implementation in carbon capture, hydrogen purification, and natural gas upgrading.
The paper demonstrates for the first time the possibility of obtaining PA12/bentonite/kaolinite composite membrane by selective laser sintering to evaluate the possibility of obtaining a polymer-mineral membrane by 3D printing. Diffraction analysis showed that Selective Laser Sintering preserves the crystalline integrity of the mineral and polymer phases without forming new structures. According to low-temperature nitrogen adsorption-desorption data, a sharp decrease in pore volume was observed compared to the ceramic components of the membrane, indicating the blocking of ceramic particles by the polyamide matrix because of sintering. Mapping of electronic images indicates the formation of a surface macroporous architecture with uniform dispersion of all elements. The obtained membrane is characterized by sufficient flexural strength (22-29 MPa) and a small but reproducible water permeability (at the level of 40 cm3/min), which, in our opinion, is due to the presence of a small number of microchannels formed during printing. Successful 3D printing of the powder mixture confirmed its stable fluidity, uniform distribution of powder materials, and absence of defects during laser sintering. The results demonstrate that polyamide and aluminosilicate-based composites are compatible with 3D printing and promising for further development to create a mechanically strong, stable membrane with controllable architecture and structure.
Organic Solvent Nanofiltration has emerged as an energy-efficient alternative to traditional thermal methods; yet its widespread implementation is hindered by its poorly understood transport mechanism. Improving the prediction of membrane flux and retention is therefore essential, which has recently been primarily advanced through data-driven modeling. Prediction and interpretation of organic solvent nanofiltration transport, however, are complicated by the collinearity between solvent size and Hansen solubility, as they are dependent on one another for common organic solvent nanofiltration solvents. Considering both solvent size and solubility are known to correlate strongly with flux, the collinearity of these properties obscures the impact of either of them. We break this collinearity by performing flux measurements on outlier solvents in unmodified and methyl-grafted ceramic membranes at room temperature. Breaking collinearity is achieved using propylene carbonate and glycerol-water mixtures, whose molecular size and solubility (at room temperature) significantly deviate from the trend established by common organic solvent nanofiltration solvents. To quantitatively identify the true driver of flux for each membrane separately, linear models using either solvent kinetic diameter, molar volume, or Hansen solubility as predictors are compared using statistical tests. Our analysis indicates that molecular size (specifically, the squared reciprocal kinetic diameter) is the true predictor of flux for unmodified and methyl-grafted titania membranes separately, while molar volume and Hansen solubility add no further predictive power. This method can be extended to, e.g., investigate membrane and temperature dependence. Decoupling solvent size and Hansen solubility can help improve the understanding of organic solvent nanofiltration transport and, via dimensionality reduction, aid the development of data-driven modeling.
Traditional filtration methods for separating host cell proteins and DNA from adeno-associated viral capsids often result in substantial yield losses. Here, we introduce a new high-yield purification strategy termed Ionic Regulation of Permeation (IROP) for removing impurities in a single unit operation. Rather than relying on static size exclusion or binding interactions, IROP dynamically modulates AAV transport within a nanoporous membrane. At low ionic strength, AAV permeation was negligible, whereas at high ionic strength it was markedly increased, revealing an electrostatic gating mechanism. AAVs retained under low-salt conditions could not be efficiently recovered by a static high-salt wash, indicating steric-electrostatic trapping within membrane pores. In contrast, high-salt filtration enabled high recovery. Leveraging this mechanism, a two-step IROP process, involving low-salt impurity clearance followed by high-salt AAV recovery, achieved greater than 93% AAV recovery with a greater than 90% reduction in HCPs and host cell DNA.
In classical membrane fabrication, water-soluble additives such as polyvinylpyrrolidone (PVP) have been pivotal in generating porosity and tuning surface properties. By contrast, comparable modifiers for membranes produced via all-aqueous processes – such as polyelectrolyte complex (PEC) membranes – remain largely unexplored. Here, we demonstrate that hydroxyethyl cellulose (HEC) and hydroxypropyl cellulose (HPC) act as effective pore formers and structural modifiers in PEC flat-sheet membranes prepared by salt-dilution-induced phase inversion. During fabrication, a fraction of the cellulosic additive is leached from the polymer solution, enhancing membrane porosity and permeability, while the residual fraction reinforces mechanical stability. Crosslinking with sodium trimetaphosphate (STMP) further strengthens the membranes. Membranes using HEC as the cellulosic additive exhibit a tunable increase in pure water permeability (from 43±10 to 123±47 LMH⋅bar−1) and molecular weight cut-off (from 117±64 to 460±360 kDa). In addition, additive pretreatment and crosslinking strategies enable surface charge modulation, shifting it from positive to neutral or negative, and tailoring salt retention profiles. These findings establish cellulosic additives as versatile design elements in the emerging class of aqueous PEC membrane systems.
Carbon molecular sieve (CMS) membranes are very promising for efficient gas separation. In this work, a novel CMS membrane was constructed from the zero-dimension material doped polyimide precursor. The introduction of carbon quantum dots into the polyimide matrix precursor regulated the nanopores structure of the derived CMS membranes precisely for CO2 separation. The PSD (pore size distribution) near 0.35 nm became narrower after the carbon quantum dots incorporation. And, the novel CMS membranes showed attracting enhancement of gas permeability (114.6 Barrer) and selectivity (94.7) for CO2/CH4 separation simultaneously, which broke 2008 upper bound. Furthermore, the zero-dimension materials are the promising fillers to regulate the nanopores structure of the CMS membranes.
This study investigates the critical influence of residual solvent on pore evolution during the non-solvent induced phase separation (NIPS) process. Employing a comprehensive multi-technique approach, including FT-IR spectroscopy, UV absorbance, contact angle, mechanical testing, shrinkage analysis, and confocal fluorescence microscopy, membrane's morphological evolution is elucidated. The findings demonstrate that residual solvent, particularly under elevated cleaning temperatures, significantly promotes pore collapse, leading to a substantial reduction in water flux. To mitigate this issue, we develop a tailored cleaning solution (methanol, water, and calcium chloride) that effectively enhances solvent exchange while maintaining the rejection performance for bovine serum albumin (BSA). Crucially, this research reveals that residual solvent significantly affects membrane performance, influencing pore structure in ways that go beyond the traditional understanding of the initial phase separation process.
This study critically evaluates the effectiveness of Joule-heated membranes (JHMs) in membrane distillation (MD) processes. Using a Nusselt-based mathematical model and experimental validation, we assess whether JHMs can significantly enhance mass transfer and energy efficiency in MD systems. Our results demonstrate that although JHMs do reduce temperature polarization by 2-3 times compared to conventional MD, the overall flux gains remain modest under standard configurations due to limitations in system design, such as uninsulated tanks and insufficient heat localization. The findings suggest that the limitations are not inherent to the JHMs themselves, but rather stem from suboptimal system integration. With targeted improvements in module insulation, flow configuration, and coating materials, JHMs hold promise for scalable and energy-efficient water treatment applications.
