Journal of Membrane Science Letters最新文献

Due to the global epidemic outbreak in recent years, membrane research and membrane-derived products have been of increasingly wide interest for medical applications. Currently, a new but important development direction of membranes in medicine goes beyond the separation function of the membrane itself to realize multifunctional integration. With the introduction of additional functions such as scaffold, responsiveness, and sensing, membranes have exhibited excellent performance in the areas of tissue engineering, drug delivery and disease diagnosis. From this perspective, we will review the recent progress made by membranes in the medical field and emphasize the principles of function integration and separation. Possible challenges will be proposed, and future development directions for medicine-related membranes will be discussed.

Loose nanofiltration (LNF) membranes have shown promises in achieving efficient separation on molecular level at relatively low pressure. In this study, a zwitterionic PES/AMN/PSBAE LNF membrane was designed by co-depositing the AMN and an in-house made zwitterionic copolymer of poly(sulfobetaine methacrylate-co-2-aminoethyl methacrylate hydrochloride) (PSBAE), in which a bio-inspired molecule aminomalononitrile (AMN) with prebiotic chemistry was used to replace the commonly applied polydopamine for rapid membrane coating, significantly reducing the surface modification time from more than 20 h to less than 1 h. The AMN-based LNF, namely PES/AMN/PSBAE membrane, was demonstrated in the separation of dye/salt from synthetic textile wastewater, exhibiting superior performance with a high water permeance of 62.9 LMH bar⁻¹ and nearly complete dye/salt fractionation, i.e., simultaneously a high rejection of all dyes tested up to 99.9% and almost complete transport of salts. Combining with material and membrane characterization, the separation performance of the membrane was evaluated, demonstrating the advantages of the prebiotic chemistry coating and zwitterionic functionality. This study provides a new and facile strategy based on the AMN chemistry for LNF membrane surface functionalization to achieve efficient molecular separation.

Almost every single experimental study regarding membranes involves the measurement of contact angle (CA) to quantify the membrane wetting property. However, the interpretation of CA can sometimes be tricky. In this study, we investigate an interesting phenomenon about the CA of a surfactant solution on a microporous hydrophobic membrane. Specifically, a surfactant solution with a very low surface tension can have an unexpectedly high CA on a microporous hydrophobic membrane. In contrast, a water/ethanol mixture with the same surface tension completely wicks the membrane (i.e., zero CA). The drastic difference in CA between the two types of liquid of the same surface tension results from the rapid adsorption of surfactants at the wetting frontier which substantially reduces the local surfactant concentration and increases the local surface tension. The same theory can also be applied to explain the striking difference between the two liquids in capillary rise and liquid entry pressure. The results from this study cast significant doubt on the role of surface tension in understanding the wetting behavior of surfactant solutions when they are in contact with solid with large specific area and raise important questions regarding the utility of measuring CA for surfactant solutions on microporous hydrophobic membranes.

The induced crystallinity behavior of the polymer of intrinsic microporosity (PIM-1) matrix in mixed matrix membranes (MMMs) by a novel class of two-dimensional (2D) metal-organic framework nanosheets, i.e., NUS-8-COOH, is demonstrated. The proposed ideal of enhanced crystallinity induced by NUS-8-COOH nanosheets can be extended to other classes of 2D nanosheet-containing MMMs, thus opening up plentiful opportunities for constructing MMMs with superior interfacial compatibility toward enhanced gas separation performance.

This investigation attempts to establish and verify a novel method for quantifying surface porosity of porous polymeric membranes via contact angle measurements. Herein, we fabricate a series of porous membranes via nonsolvent induced phase separation (NIPS) comprising different concentrations of polyvinylidene fluoride (PVDF) and PVDF-poly (methyl methacrylate) block co-polymer (PVDF-PMMA) with different concentrations of water and isopropyl alcohol (IPA) in the coagulation bath. Both sessile drop and captive bubble contact angle measurements are used to determine contact angles (and porosity) for both dry and wet membranes, respectively. The former method is probably applicable for membrane distillation, aeration and de-aeration where liquid water does not saturate the membrane, whereas the latter may be more indicative of pressure-driven aqueous membrane separations where the membrane is saturated through its cross-section. Image analysis of scanning electron microscope (SEM) images quantified dry membrane surface porosity. We propose a simple analytical model to obtain wet and dry membrane surface porosity from contact angle measurements. Our results suggest that the surface porosity calculated from both wet and dry contact angle data correlates strongly with the surface porosity calculated from SEM values. However, wet contact angles of the membranes with high porosities produce significantly higher porosity values, which also establishes the importance of porous membrane swelling in determining membrane porosity for aqueous membrane separations.

Membrane separation is widely used in food, pharmaceutical and water treatment industries but suffers a longstanding challenge of fouling. In this article, acoustically excited microstructures are demonstrated as a new mechanism to mitigate membrane fouling and remove cake layer aggregations formed on a microfluidic membrane-on-chip device. With acoustic streaming induced by oscillating microstructures near the membrane surface, cake layer fouling was effectively broken up and removed on the acoustofluidic membrane separation device within 100 milliseconds. The device is simple to fabricate and offers direct observation of crossflow microfiltration across the device membrane, giving valuable insight to particle fouling events often unobtainable in traditional membrane device configurations. The device bolsters advantages like label-free and reagent-free particle separation and in situ membrane cleaning during separation, providing a new mechanism for membrane separation applications used across industry.

Herein, we report a new class of biosourced nanofiltration membranes based on chemically recyclable aliphatic polyesters (P(4,5-T6GBL)) and the use of green solvents. Given their chemical recyclability and potential biodegradability, these polyester membranes were designed to have a sustainable lifecycle. The effect of membrane thickness and solvent/non-solvent diffusivity on membrane morphology and organic solvent nanofiltration were investigated. Long-term membrane stability was tested in a continuous crow-flow filtration rig over a week, which exhibited stable methanol permeance at 8.6 ± 0.1 L m⁻² h⁻¹ bar⁻¹. The rejection profiles of the pharmaceuticals oleuropein (540 g mol⁻¹) and roxithromycin (837 g mol⁻¹) were also found to be stable at 87% and 100%, respectively.

Reverse osmosis (RO) is the most important membrane technology for the desalination of water. Measured water and salt fluxes are traditionally analyzed in the context of the solution-diffusion (SD) model which leads to a water permeability, A, and a salt permeability, B. However, this parametrization of the salt flux is not correct for water desalination by RO membranes, because these membranes show markedly different retentions for different feed salt concentrations, a classical observation in the literature, and this effect is not captured by the SD model. Thus, the traditional salt permeability B is not an intrinsic property of these membranes. We present a new analysis for desalination of a 1:1 salt, which follows from a transport theory that is based on the assumption that coions are strongly excluded from the membrane, and we demonstrate that it accurately describes a large dataset of salt retention by an RO membrane as function of pressure and feed salt concentration. This analysis leads to unique values of the water and salt permeabilities, A and $B^{″}$, not dependent on salt concentration or permeate water flux. Because we now have an improved parametrization, we can more accurately compare different membranes or study in more detail how membrane performance depends on conditions such as salt type and temperature. The new equation can provide guidance for the design of high-performance desalination membranes and for process modeling of desalination systems.

This work describes a new approach for synthesizing extremely fouling-resistant, zwitterionic membranes with controlled, tunable pore sizes that extend from ion separations (< 1 nm) to the ultrafiltration range (∼2 nm). These membranes are manufactured by the UV treatment of high zwitterion content amphiphilic copolymers with cross-linkable functionality to stabilize the membrane selective layers, preventing excessive swelling and dissolution of copolymers containing as high as 80 wt% zwitterionic repeat units. Zwitterion weight fraction allows the tuning of membrane performance, with effective pore size and permeance both increasing with zwitterion content. The high zwitterion content membranes were remarkably fouling-resistant and demonstrated a salt-responsive behavior not previously observed with self-assembling zwitterionic copolymer membranes.

A novel all-carbon backbone-based membrane is designed by introducing side chains at the non-coplanar site of twisted “ether-free” main chain via Suzuki coupling reaction. The twisted backbone reduces the hindrance effect, providing broader mobile space for the side chains and enhancing the swing ability of the side chains to facilitate the formation of ion channels and the transportation of OH⁻. As a result, the high conductivity is obtained at a relatively low IEC level. The QPS-PB-4 membrane exhibits a superior OH⁻ conductivity of 50.1 to 94.4 mS cm⁻¹ at 30 ℃ to 80 ℃ with an IEC of only 1.48 mmol g⁻¹, and a low swelling ratio of less than 10%. Which show significant advantage among the traditional side-chain-type AEMs reported in recent years. Moreover, the as-prepared membranes have good mechanical and thermal stability, as well as excellent chemical stability because of the all-carbon backbone designed without any sensitive sites that can be attacked by hydroxide. The conductivity of the QPS-PB-4 membrane decrease by only 8% after treatment at 80 ℃ in 1 M NaOH for 1800 h. The fuel cell assembled with the as-prepared membrane has a peak power density of up to 558.8 mW cm⁻², indicating the promising application potential of the membranes.