Journal of Membrane Science Letters最新文献

Molybdenum disulfide (MoS₂) has been fabricated into thin-film composite (TFC) membranes for dye desalination due to its excellent underwater stability and tunable interlay spacing. However, it remains challenging to synthesize thin layers of MoS₂ with high water permeance and high dye rejection due to the difficulty in fabricating large crystalline sheets or exfoliation. Herein, we report a scalable method coupling bottom-up hydrothermal synthesis and top-down ultrasonic exfoliation to obtain well-dispersed MoS₂ nanosheets and a vacuum filtration method to prepare ultrathin membranes (thickness: 30 – 60 nm) for dye desalination. The MoS₂ nanosheets and membranes are thoroughly characterized for their chemistries and nanostructures. The membrane with 60-nm MoS₂ exhibits water permeance of 32 LMH/bar, Na₂SO₄ rejection of 2.3%, and Direct Red-80 rejection of 99.0%. The MoS₂ membranes exhibit dye desalination performance superior to state-of-the-art commercial polyamide membranes and many leading membranes based on two-dimensional materials.

Polyamide (PA) reverse osmosis membranes are commonly employed in seawater desalination owing to their effective salt rejection and water permeability; however, the elimination of small and neutral boron molecules from seawater remains a significant hurdle in energy-efficient and cost-effective desalination processes. In this work, a seawater reverse osmosis (SWRO) membrane with powerful boron removal competence was designed by adopting an in-situ rapid integration protocol, which utilized aliphatic amines as hydrophobic barriers by bonding the residual chloride groups upon the membrane surface and as molecular plugs by embedding in the PA networks. Consequently, it resulted in a notable improvement in the rejection of neutral boron molecules due to enhanced steric hindrance caused by immobilized amine plugs and synergistically tunned hydrophobic interactions. The permeability coefficient of boron decreased from 4.8 to 0.9 L m⁻² h⁻¹, and the boron rejection increased from 80.7 to 90.5% under the modification conditions with the optimal type and concentration of amines, while displaying a NaCl rejection of 99.8% and an acceptable water permeability of 0.55 L m⁻² h⁻¹ bar⁻¹. Meanwhile, the alteration of membrane chemical compositions and structure properties was kept to a minimum. This study offers intuitive insights into the critical roles played by the aliphatic amines in the selective layer of the membrane for the removal of neutral boron molecules and salts, thereby enabling the fabrication of highly selective SWRO membranes, which may have significant implications for more efficient membrane-based seawater desalination and boron removal.

Viral and non-viral vectors have revolutionised in the last 5 years the approaches to tackling pandemics, cancers and genetic diseases. The intrinsic properties of these vectors present new separation challenges to their manufacture in terms of both the process-related impurities to be removed and the complex labile nature of the target products. These characteristics make them susceptible to heterogeneity and the formation of product-related impurities.

Conventional polyethersulfone membrane filters used for sterile filtration and ultrafiltration of viral vectors and lipid nanoparticles can display limited selectivity and cause product losses. To address these challenges, novel membrane materials and fabrication techniques to overcome the boundary of selectivity-permeability performance have become of interest. Isoporous membranes with well-defined pore size and pore dispersity at the nano-scale show promising separation performance but have only been demonstrated at small scales to date.

This review summarises the decision process for the development of new membrane candidates for vector manufacturing in genomic medicine, including membranes fabricated by lithography, track-etched membranes, anodic aluminium oxide (AAO) membranes and self-assembled block copolymer membranes. By comparing these membranes to existing commercially available products, the possible advantages presented by novel materials and fabrication approaches are identified.

Polyamide membranes made with surfactant-assisted interfacial polymerization (IP) have demonstrated the potential for excellent membrane performance. The presence of surfactants accelerates amine diffusion into the organic phase causing a more complete IP reaction. Even though surfactant-assisted IP has been used in polyamide membranes, the structure-property relationship of the surfactants on amine transport into the organic phase has not been explored in a systematic manner. In this work, MPD diffusion from a membrane support into n-dodecane in the presence of seven different surfactants, which were anionic, cationic, and non-ionic, was evaluated. When the surfactants were used at different concentrations, the MPD concentration was increased in the presence of anionic (48–80%), cationic (32–75%) and non-ionic (26%) surfactants. The MPD concentration was increased in the presence of anionic (by 48–72%), cationic (by 32–75%), and non-ionic surfactants (by 26%) at 15–60 s contact time. For further understanding, the interfacial tension in n-dodecane for the surfactants was measured, however, it did not correlate with our data. This study provides a better understanding of MPD diffusion in the presence of different types of surfactants during RO membrane synthesis, which will help us to engineer membranes with better permeability and selectivity.

Membrane technology offers promise as a breakthrough separation technology in many applications, but is frequently limited by the chemical stability of currently available membrane materials. Recently developed membranes utilizing epoxide-based chemistry have shown great potential as intrinsically stable thin-film composite membranes in water-based applications. However, as these membranes are in their infancy, many synthesis parameters are still to be explored. In this study, the versatility of epoxide chemistry is exploited to demonstrate its potential to serve as a new platform for membrane synthesis, even beyond the field of aqueous applications. It is proven here how the membrane performance can be tailored in a controllable way between 20 – 85% NaCl rejection with a water permeance between 0.5 – 3 L m⁻² h⁻¹ bar⁻¹ by simply selecting epoxide monomers and initiators of different size and functionality. A systematic increase in water permeance and salt passage was observed for epoxide monomers that exhibit a lower functionality and a lower number of aromatic groups, while a threshold nucleophilicity and aliphatic chain length of the initiator are required to obtain a salt-selective layer. This work demonstrates the possibility to easily and predictably tune membrane performance in the tight nanofiltration range, while simultaneously achieving a better understanding of the synthesis-structure-performance relationship of this new class of promising membranes.

Metal-organic frameworks (MOFs) hold great promise as porous materials for pervaporation applications. However, the exploration of MOF membranes in this field is still in its early stages. One of the main challenges is the relatively low mass flux and stability of pure MOF membranes compared to other materials used in pervaporation. In this study, we propose a novel approach to enhance the separation performance of MOF membranes for water and ethanol separation. Our strategy involves incorporating the 2,5-thiophenedicarboxylic acid (TDC) linker into the MOF-303 structure, partially replacing the 3,5-pyrazoledicarboxylic acid (PDC) linker. The goal is to increase the aperture size of the microporous channels in the pristine MOF-303 membrane, thereby improving the mass flux. X-ray diffraction characterization, combined with Rietveld refinement, confirmed that the partial substitution of PDC with TDC resulted in an increased pore-limiting diameter (PLD) of MOF-303. For instance, the pristine MOF-303 exhibited a PLD of 5.78 Å, while MOF-303(70/30) with 70% TDC replacement displayed a PLD of 6.02 Å. To fabricate the mixed-linker MOF-303 membranes, we utilized a seeded growth method, which yielded membranes with dense layers, as confirmed by scanning electron microscopy and air permeation characterization. The prepared membranes were subjected to pervaporation tests to evaluate their performance in separating 90 wt.% ethanol at 60 °C. The pristine MOF-303 membrane exhibited notable separation capabilities, with an average flux of 0.071 kg·m⁻²·hr⁻¹ and a water/ethanol separation factor of 5371. Surpassing the unmodified MOF-303, the mixed-linker MOF-303(50/50) membrane demonstrated improved mass flux and water/ethanol separation factor. Specifically, the MOF-303(50/50) membrane displayed an average flux of 0.092 kg·m⁻²·hr⁻¹ and a water/ethanol separation factor of 8500. Importantly, the unmodified MOF-303 membrane exhibited instability during prolonged pervaporation operation, whereas the mixed-linker MOF-303(50/50) membrane effectively addressed this issue. Further analysis using in situ Fourier transform infrared spectroscopy and water adsorption characterization revealed that MOF-303(50/50) possessed a strong affinity for water, comparable to the pristine MOF-303. Overall, our study highlights the potential of the mixed-linker approach to optimize the separation performance and stability of MOF-based membranes for pervaporation application.

Water channel-based biomimetic membranes (WBMs) are gaining increasing attention due to the effectiveness of water channels in enhancing water permeability and breaking the permselectivity trade-off. However, the ultra-permeable WBMs may suffer from severe membrane fouling issue because a high-water flux tends to result in an accelerated fouling and thus compromises the benefits gained from the usage of water channels. Herein, a novel in-situ modification protocol was proposed to enhance the antifouling performance of ultra-permeable WBMs. The nanovesicles incorporated with aquaporin (AQP) water channels were functionalized with polyethylene glycol brushes (i.e., PEGylation) via a facile self-assembly approach and subsequently encapsulated in the selective layer of thin-film composite membranes through interfacial polymerization. The modification had minimal impact on the function of AQPs, resulting in WBMs with a high water permeance (∼8.2 LMH/bar) and good NaCl rejection (96.4%) comparable to the unmodified WBMs. Moreover, the in-situ modification drastically enhanced the surface hydrophilicity, which endowed the membrane with a superior fouling resistance to organic foulants. The improved fouling resistance ensured a more sustainable operation of ultra-permeable WBMs, particularly in scenarios that favor high water fluxes. This facile modification strategy provides an efficient way to fabricate ultra-permeable and antifouling WBMs for sustainable water purification.

The surface of polyamide reverse osmosis (RO) membranes which regulates interface-dominated phenomena, such as partitioning and fouling, is the one facing the feed during operation. However, the opposite surface of the polyamide selective layer, the one facing the permeate and in contact with the polysulfone porous support, is commonly analyzed in quartz crystal microbalance (QCM) measurements due to limitations of state-of-the-art transfer methodologies. Such measurements on the back surface cannot be generalized because the polyamide layer is chemically and morphologically asymmetric. Herein, we introduce a simple method to coat QCM sensors with polyamide active layers in the correct orientation (i.e., exposing their front surface) and show that interface-dominated phenomena differ significantly between orientations. We start by describing a transfer protocol to coat any surface with a polyamide layer on its front surface orientation. We then systematically analyze the chemical and morphological differences between the two surfaces of the polyamide layer of a commercial RO membrane. Finally, we demonstrate that interface-dominated phenomena depend on the orientation by showing that NaCl partitioning at pH 6 was 1.3 to 2.3-fold higher on the front surface and that organic fouling with humic acid occurred at a lower rate on this surface. The new method presented herein enables measurements on the front surface of polyamide RO membranes, which should be the standard in any future QCM studies.

Although helium is a valuable inert gas available in abundance in the earth's atmosphere, the major source of helium is from natural gas reservoirs. Membrane based separation processes pose many advantages like being cost effective and non-energy intensive. In this current study, we have successfully demonstrated the synthesis of continuous Porous Organic Cage: CC3 membranes to separate equimolar helium methane mixture with permeance of 4.45 × 10⁻⁷ mol/ (m²s Pa) and separation selectivity ($\alpha )$ as high as 8. We also compared the diffusion coefficients of the gases through the membrane to evaluate the dominant mechanism for separation. Lastly, we compared the performance of our membranes to the state-of-the-art membranes with the help of a Robeson plot and found that our membranes outperformed the upper bound.

Sulfur poisoning could result in fast deterioration of Pd-based membranes by the formation of metal sulfides and reduction of hydrogen purity. The introduction of an MoO₂/TS-1 layer could provide an effective protection of the Pd layer. Therefore, in this paper a synthetic method is presented for preparation of sulfur-resistant MoO₂/TS-1 zeolite modified PdCu alloy composite membranes and their application in hydrogen separation under H₂S containing steam. According to the stability test results, the MoO₂/TS-1 zeolite armored layer obviously prolonged the stability of Pd based membrane. After 50 h stability test with 100 ppm H₂S, there were no obvious structural changes and metal sulfide formation detected in the PdCu bulk from SEM images and XRD patterns, indicating that MoO₂/TS-1 armor structure was good enough for protecting the PdCu alloy bulk.