Journal of Membrane Science最新文献

Polymer with fluorene-based units has garnered significant attention and has been shown an effective way to improve the performance of proton exchange membranes due to its inherent rigidity and multiple sulfonation sites. Nevertheless, fluorene-based sulfonated poly(ether ketone)s exhibited inadequate oxidative stability resulting from the heteroatoms in the main chain. Herein, a series of poly(phenyl ketone)s polymers (PPK-DSF-x) without heteroatoms in the main chain were constructed by Yamamoto coupling and hydrolysis reactions. Since robust poly(phenyl ketone) aromatic backbone ensured commendable chemical and dimensional stability, and sulfonated fluorene-based units promoted the formation of hydrophilic and hydrophobic microscopic phase separation, the PPK-DSF-x membranes exhibited superior stability and proton conductivity. Remarkably, PPK-DSF-45 showed excellent proton conductivity at 80 °C (137.5 mS cm⁻¹). In addition, the oxidative stability of the PPK-DSF-45 membrane was also excellent, maintaining its integrity after immersion in Fenton's reagent for 270 min. Finally, we found that the PPK-DSF-45 membrane achieved a power density of 270 mW cm-² in the fuel cell, surpassing Nafion 212 (245 mW cm⁻²). These results indicated the potential application of fluorene-based poly(phenyl ketone)s PEMs in PEMFCs.

Anion exchange membranes (AEMs) with high selective conductivity and low surface resistance are important for the development of electrodialysis desalination industry. In this work, we design and synthesize a rotaxane of β-cyclodextrin (CD)-alkyldiamine inclusion complex (CDIC) via a host-guest molecular recognition mechanism; the resulting CDIC rotaxane is employed for cross-linking chloromethylated, hydroxy quaternized polysulfone (HQPSf) to make AEMs. β-CD is inherently hydrophilic and its –OH on the outer surface can hydrogen-bond with HQPSf to promote ionic cluster aggregation, leading to enhanced microphase-separated morphology and improved conductivity; the rotaxane-cross-linked structure guarantees good ductility and ion selectivity of the membrane. Therefore, the optimized HQPSf-CDIC membrane gives the most excellent current efficiency discharge current efficiency (92.04 %), the lowest energy consumption (4.68 kWh kg⁻¹), and the maximum Cl⁻ mobility (75.38 mg m⁻² s⁻¹) in the electrodialysis tests, significantly better than the un-crosslinked HQPSf membrane (86.41 %, 5.17 kWh kg⁻¹ and 71.29 mg m⁻² s⁻¹). Our work demonstrates that introducing CDIC rotaxane cross-linked structure can help to enhance microphase separation and improve the performance of AEMs for electrodialysis.

Efforts to utilize biopolymer membranes to diminish the carbon footprint of separation processes are ongoing. Herein, we report the fabrication of isosorbide (ISB)-based poly(arylene ether) biopolymer membranes, including ISB-based poly(arylene ether sulfone) (I-PAES) and ISB-based poly(arylene ether ketone) (I-PAEK) for gas separation. The robust mechanical properties and amorphous nature of ISB-based biopolymers allow for their application to gas separations. Both positron annihilation lifetime spectroscopy (PALS) and free volume analysis using density measurements reveal that replacing bisphenol A (BPA) in polysulfone (PSF) with ISB results in a significant reduction in free volume owing to the absence of bulky dimethyl groups and the presence of polar aliphatic ether groups. Substituting the sulfone group for a ketone group further decreased free volume. Solid-state CP/MAS ¹³C NMR analysis discloses that substituting ISB and replacing sulfonyl moieties with carbonyl groups restricts the rotational motion of internal rings, resulting in inhibited gas diffusion. Consequently, the I-PAEK membrane exhibited H₂/CO₂ and H₂/CH₄ selectivities more than three times and five times higher, respectively, compared to the PSF counterpart. Our present study demonstrates the feasibility of ISB-based poly(arylene ether) biopolymer membranes for gas separation.

A facile method has been developed to fabricate lamellar composite graphene oxide (CGO) membranes by incorporating positively charged surfactants – cetyltrimethylammonium bromide (CTAB). The interlayer spacing of GO nanosheets was regulated by the sum of both vertical and horizontal alignment of CTAB on the GO surface via electrostatic interaction. The CTAB intercalated GO membrane exhibited an internal layer spacing of 16.97 Å compared to 8.26 Å for the GO membrane. The obtained CGO lamellar membrane with well-defined nanochannels showed ultrafast pure water flux of ∼1112 L h⁻¹ m⁻² bar⁻¹ and an excellent separation efficiency of >99 % towards negatively charged organic dye molecules at a high permeation flux of ∼932 L h⁻¹ m⁻² bar⁻¹, which was nearly 2.5-fold enhancement compared with that of the pristine GO membrane (∼400 L h⁻¹ m⁻² bar⁻¹). The electrostatic and π–π interaction forces between the CGO membrane and organic dye molecules played a major role in the overall dye separation mechanism. Furthermore, the CGO membrane demonstrated excellent stability with no loss in separation performance (>96 % organic molecules rejection) after exposure to various pH solutions and deionized water (DI) water. The current work provides a straightforward approach for the formation of highly tunable and stable CTAB-intercalated GO membranes for ultrafast molecular separation.

Efficient magnesium-lithium separation is key to extracting lithium resources from salt lake brines. However, efficient magnesium-lithium separation is constrained by the high magnesium-to-lithium ratios on the nanofiltration separation performance due to the weakened Donnan effect and inherent permeability-selectivity trade-off behaviour. To address this challenge, a dual methylpiperidinium ionic liquid was designed in this work and incorporated into polyamide networks to manipulate the structural properties of polyamide membrane for improved magnesium/lithium separation. We demonstrate that the piperidinium modification of polyamide networks not only modulated and enhanced the morphology, hydrophilicity, free volume and electropositivity, but also synergized the steric hindrance differentiation inside the membrane nanochannels. These structural advantages enabled the modified membrane to achieve high-separation performance with enhanced water permeance of 37.3 L m⁻² h⁻¹ bar⁻¹ and Mg²⁺/Li⁺ selectivity of 30.6 (for Mg/Li mass ratio of 31.2). Molecular dynamics simulations further confirmed that the fast water transport and the difference in the ion separation behaviour are strongly correlated to the enhanced structural properties of membranes. We expect this work to provide insightful guidance for engineering high-performance membranes and make contributions in the application of nanofiltration in lithium mining from high Mg/Li ratio brines.

This research introduces highly efficient nanofiltration (NF) membranes designed for the effective rejection of both divalent cations and anions, a critical feature for advanced water treatment technologies. We have devised a simple yet adaptable approach for fabricating Janus polyamide (PA) thin-films characterized by dual charges, which exhibit pronounced selectivity towards both mono-/divalent anions and cations. Leveraging a straightforward interfacial polymerization (IP) process, we integrated high molecular weight polyethyleneimine (PEI) within the PA matrix. This strategy ensured the preferential formation of a dense, negatively charged upper layer dominated by piperazine (PIP), while cationic macromolecular PEI facilitated the emergence of a loose and positively charged lower layer, thus giving rise to a distinctively charged and structurally heterogeneous PA thin-film. Furthermore, the strategic inclusion of PEI inhibits the diffusion of the PIP, thereby promoting the development of nano-wrinkled structures. This structural innovation not only enhances pure water permeance (16.0 L m⁻² h⁻¹ bar⁻¹) but also optimizes ion selectivity through the coordination of steric hindrance and Donnan effects. Consequently, the Janus charged NF membranes we developed exhibit exceptional selectivity for mono-/divalent ions, particularly demonstrating remarkable ion selectivity for Cl⁻/SO₄²⁻ and Li⁺/Mg²⁺ of 102 and 24, respectively. Our findings introduce a pioneering avenue for fabricating NF membranes that proficiently separate mono-/divalent ions, promising significant advancements in water treatment and purification endeavors.

The challenge of membrane fouling persistently hinders the advancement of membrane technology. The construction of patterned membrane surfaces is anticipated to mitigate the effects of membrane fouling significantly. In this study, ceramic microfiltration membranes with corrugated patterns were fabricated by 3D printing combined with the dip-coating process. To assess the impact of surface patterning on ceramic membrane performance, we initially compared the pore size and pure water flux between straight and corrugated membrane tubes. Both configurations exhibited similar parameters: a support pore size of approximately 1 μm, a membrane layer pore size of about 110 nm, and a pure water permeance of around 950 L m⁻² h⁻¹·bar⁻¹. The corrugated ceramic membranes demonstrated superior anti-fouling properties compared to their straight counterparts during the filtration of nanoparticle suspensions, oil-in-water emulsions, and bacterial suspensions. Specifically, under a nanoparticle suspension concentration of 2000 ppm, a transmembrane pressure of 0.2 MPa, and a flow rate of 1.0 m s⁻¹, the corrugated membrane achieved a stable flux of approximately 1.7 times greater than that of the straight membrane. Furthermore, we explored the effects of surface patterning on fluid dynamics through numerical simulations. The enhanced turbulence dissipation rate in the patterned membrane tubes suggests increased surface turbulence and an improved capacity to remove contaminants. This research offers novel insights into the development of ceramic membranes with enhanced anti-fouling capabilities for water treatment.

Ultra-thin DD3R zeolite membranes exhibit excellent separation properties for CO₂ capture from natural gas, as well as the lower transmembrane resistance. However, the interfacial transport of permeation gas in such systems may dominate the whole separation process. In this work, we employed external force non-equilibrium molecular dynamic (EF-NEMD) simulation to predict the single-component permeabilities of CO₂ and CH₄ through a defect-free DD3R zeolite membrane at different pressured drops. By explicitly including the gas transport from bulk phase to zeolitic channels, the predicted results of EF-NEMD simulation showed good agreements with the reported experimental data. The contribution of interfacial resistance over the total transport resistance (R_inter/R_total) was further evaluated for the membranes with different thicknesses under temperatures between 273 K and 373 K. The results revealed a decrease in R_inter/R_total with increasing membrane thickness, leading to a reduction in CO₂/CH₄ selectivity, and the critical thickness (R_inter/R_total < 0.01) was determined to be approximately 300 nm at pressure of 1.0 MPa and temperature of 298 K. Similarly, the R_inter/R_total decreased with increasing temperature due to the augmentation in molecule kinetic energy. Furthermore, it was confirmed that the gas adsorption effect could expand the effective size of eight membered ring (8-MR) channels in DD3R zeolite membrane, thereby decreasing the CO₂/CH₄ selectivity, despite higher permeation fluxes. The above discoveries essentially benefit the design of the ultra-thin DD3R zeolite membrane through an understanding of CO₂ and CH₄ transport behaviors.

Filtration of biopharmaceutical streams can be complex due to the variety of components in the stream and their interactions among themselves and with the filter pore surfaces. This work used a variety of measurements to study the filtration of model silica nanoparticles through asymmetric hydrophilized polyethersulfone (mPES) membrane in solutions covering a range of pH and ionic strengths. Measurements included particle size, particle concentration, zeta potential, particle-particle and particle-membrane surface intermolecular forces. These measurements were used to rationalize observed particle capture behavior under various filtration conditions. We found that increasing ionic strength and decreasing pH resulted in higher particle aggregation and higher particle retention due to adsorption of model silica nanoparticles to the membrane and sieving of aggregates within the membrane. In addition, captured particles can be eluted from the membrane in some cases, depending on the operating conditions, extent of particle loading, buffer flush pressure, and buffer pH and conductivity conditions. These findings provide insight into methods to improve filtration performance and particle capture or release, including product recovery, in filtration processes.

Overcoming the challenges associated with achieving high uniformity and connectivity of pore channels in ceramic membranes, we designed silicon carbide ceramic membrane derived from the recrystallization process based on the Dinger-Funk equation of the closest-packing model with various grain grading. Furthermore, the effects of particle size distribution on the resulting microstructure and pore architecture of the ceramic membrane was also explored. The findings corroborated the critical importance of raw material particle size distribution in controlling pore size distribution and morphology. After sintering at 1900°C, the silicon carbide ceramic membrane, benefiting from ideal particle packing, exhibited a remarkably uniform pore structure. Notably, the most probable pore size constituted over 70 %, while achieving an open porosity of 51.3 % even without the addition of pore-forming agents. The silicon carbide ceramic membrane also demonstrated exceptional hydrophilicity (water contact angle:∼0°), impressive water permeation (1210 L m⁻² h⁻¹·bar⁻¹), coupled with efficient turbidity removal (∼100 %) in carbon black wastewater treatment applications. Additionally, membrane regeneration proved effective using a dilute NaOH solution backwash, achieving a flux recovery efficiency of 98 %. This strategy had directive significance for designing high-performing silicon carbide ceramic membranes.