Journal of Membrane Science Letters最新文献

Vanadium acetylacetonate (V(acac)₃) disproportionation electrochemistry promises a crossover-tolerant, high-voltage flow battery, but exhibits low efficiency and short cycle life. We show that membrane fouling, rather than a parasitic side reaction, dominates early performance fade. Crossover rates through porous membranes were estimated from voltage transients with an adaptive observer while cycling flow-through reactors. For $0.1\text{M}$ V(acac)₃ and $0.3\text{M}$ TEABF₄ in acetonitrile flowed countercurrently at $5.0\text{cm}{\text{s}}^{-1}$ parallel to the separator, fresh Daramic 175 and Celgard 4650 afforded active-species mass-transfer coefficients of $3.8\mu \text{m}{\text{s}}^{-1}$ and $7.5\mu \text{m}{\text{s}}^{-1}$, respectively, which decreased and became non-Fickian as cycling progressed. At $\pm 10\text{mA}{\text{cm}}^{-2}$ from 0%–20% state of charge, voltage efficiency with Celgard fell from 96% to 60% over 27 cycles. Separator replacement restored the coulombic and voltage efficiencies, which repeated their first progression. Impedance spectra from series-connected canary cells reveal that separator resistances remain stable during open-circuit exposure to charged single electrolytes, but increase under applied current or open-circuit contact with differently charged electrolytes.

New method of emulsion synthesis of Nafion®-type copolymer composition by using nanodiamond platform has been proposed and implemented. Produced polymeric coagulate saturated with diamonds (4.1 % wt.) possessed increased ionic capacity of the copolymer comparative to the analogue without diamonds. SEM patterns for coagulate membranes showed labyrinthine structures with diamonds integrated into copolymer without any segregation. This structuring provided necessary elastic and strength properties of new type membranes for hydrogen fuel cells. In new membranes synchrotron experiments exhibited a network of ionic channels which ensured a proton conductivity by one order of magnitude higher than that for the analogue produced of premade components.

Controlling the internal concentration polarization in forward osmosis (FO) membranes by minimizing the substrate thickness is critical to enhancing the water flux. This study aimed to achieve the fabrication of an ultra-thin FO membrane by forming the polyamide (PA) active layer on a thin and straight-bore film, a so-called track-etched (TE) membrane. The polycarbonate TE membrane had a uniform pore size of 0.22 µm and a thickness of 25 µm. The PA active layer was successfully formed only by creating a thin m-phenylenediamine solution layer on the smooth TE membrane surface before interfacial polymerization. The TE- FO membrane with low porosity (14 %) provided a water flux of 21 L/m²h and a reverse salt flux of 8.0 g/m²h when evaluated with a 1.0 M NaCl draw solution. Further evaluations showed the potential of increasing water flux by increasing the TE substrate porosity (14 %) and reducing the apparent PA active layer thickness (504 nm). These results suggest the potential of achieving a high-water flux FO membrane using a thin TE substrate and ultimately improving the validity of FO membrane-based water treatment.

Nanofiltration is widely used in various industries to separate solutes from solvents. To foster a circular economy, establishing a closed-loop lifecycle for the membrane materials is highly important. In this study, we fabricated recyclable nanofiltration membranes from chemically recyclable polymers —polyester P(BiL⁼)_ROP and poly(cyclic olefin) P(BiL⁼)_ROMP— using γ-butyrolactone as a green solvent. These two polymers, of two different polymer classes, were obtained from a single monomer, which could be recycled back to the same monomer, exhibiting the unique “one monomer–two polymers–one monomer” closed-loop chemical circularity. The effect of physical treatment, such as annealing, hot-pressing, and air exposure on the morphological characteristics and performance of the nanofiltration membranes was investigated. We revealed the interplay between membrane pore size, thickness, density and the molecular sieving performance of the nanofiltration membranes. Solute rejections were mainly governed by the membrane pore size. However, solvent flux was mainly governed by the membrane density that determines the free volume interconnectivity. The membranes exhibited a tunable molecular weight cutoff between 553 and 777 g mol⁻¹ and methanol permeance between 5.9 and 9.8 L m^–2 h^–1 bar⁻¹. The membranes exhibited excellent long-term nanofiltration stability over 1 week. The combination of the green solvent used for membrane fabrication and the circular life cycle of the polymer membrane brings one step closer to closing the circularity loop of membrane technology.

Membrane distillation (MD) is a separation technology for many industries including desalination, pharmaceuticals, and food processing. However, MD technology readiness has not reached the required level to penetrate the desalination and water treatment market. One of the challenges to commercialization is the limited development and inaccurate assessment of MD-specific membranes. In fact, measuring the performance of MD membranes is challenging because it is dependent on process parameters, making it difficult to separate the individual influences of the process operating conditions and the membranes’ intrinsic properties. These shortcomings drive the need for a standardized methodology to compare and report membrane performance independently of the process parameters. In this work, we propose a standardized methodology for measuring the permeance of MD membranes using a reduced scale direct contact membrane distillation (DCMD) setup. This methodology has the potential to streamline membrane assessment and support ongoing efforts in MD membrane development and process scale-up.

Advanced membranes fabricated from multilayer/laminated graphene oxide (GO) are promising in water treatment applications as they provide very high flux and excellent rejection of various water pollutants. However, these membranes have limited viability, and suffer from instabilities and swelling due to the hydrophilic nature of GO. In this work, the permeability and rejection performance of laminated GO membranes were improved via functionalization with ethylenediamine (EDA) and polyethyleneimine (PEI). The membranes are fabricated via the pressure-assembly stacking technique, and their structure is well characterized. The performance, rejection, and stability of the fabricated functionalized GO membranes were evaluated. Pillaring the GO layers using diamine and polyamine resulted in exceptionally high water permeability of 113 L/m²h (LMH) compared to only 28 LMH for the pristine GO membrane while simultaneously satisfying high rejection of multivalent salts of 79.4, 35.4, and 19.6 % for Na₂SO₄, MgCl₂, and NaCl, respectively. The results obtained indicate that proper functionalization of GO provides a roadmap for the potential commercialization of such advanced membranes in water treatment applications.

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 demand of lithium for electric vehicles and energy storage devices is increasing rapidly, thus new sources of lithium (such as seawater and natural or industrial brines), as well as sustainable methods for its recovery, will need to be explored/developed soon. This work presents a novel electromembrane process, called Lithium Membrane Flow Capacitive Deionization (Li-MFCDI), which was tested to recover lithium from a synthetic geothermal brine containing a much higher mass concentration of sodium than lithium (more than 650 times). Specifically, a ceramic lithium-selective membrane was integrated into a flow capacitive deionization (FCDI) cell, which was specifically designed, and 3D printed, to allow simultaneous charging and regeneration of the employed flow electrodes. Despite the extremely high Na⁺/Li⁺ mass ratio in the feed stream, 99.98% of the sodium was rejected and the process selectivity for lithium over other monovalent cations was 141 ± 5.85 for Li⁺/Na⁺ and 46 ± 1.46 for Li⁺/K⁺. The Li-MFCDI process exhibited a stable behaviour over a 7-day test period, and the estimated energy consumption was 16.70 ± 1.63 kWh/kg of Li⁺ recovered in the draw solution. These results demonstrate promising potential of the Li-MFCDI for the sustainable lithium recovery from saline streams.

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.