Journal of Membrane Science Letters最新文献

MOF/polymer adhesion in Mixed Matrix Membranes (MMMs) has been mainly enhanced so far via MOF and/or polymer functionalization to strengthen the interactions between the two components. This strategy, albeit effective, is generally accompanied by a drop in the permeability and/or selectivity performance of the MMMs. In this contribution, engineering structure defects at the MOF surfaces is proposed as an effective route to create pockets that immobilize part of the polymer chain, which is of crucial importance both to avoid plasticization issues and to enhance the MOF/polymer affinity while overcoming the adhesion/performance trade-off in MMMs. This engineered interfacial interlocking structure also serves as a bridge to accelerate the gas transport from the polymeric region towards the MOF pore entrance. This concept is showcased with a model MMM made of the prototypical UiO-66 MOF and the glassy Polymer of Intrinsic Microporosity-1 (PIM-1) and tested using CO₂, CH₄ and, N₂ as guest species. Our computational findings reveal that a defective UiO-66 MOF surface improves the MOF/PIM-1 adhesion and contributes to accelerate the interfacial gas transport of the slender molecules CO₂ and N₂ and in a lesser extent of the spherical molecule CH₄. This translates into a selective enhancement of the CO₂ transport once combined with CH₄ which paves the ways toward promising perspective for pre-combustion CO₂ capture.

High entropy perovskites bring more space for materials design in many fields. The stability of materials in thermodynamics can be improved by increasing the mixed entropy. In this work, a series of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF) based high entropy perovskite (HEBSCF) were designed to improve the stability of BSCF at intermediate temperatures. The influence of high entropy composition on the lattice parameter, microstructure and stability of HEBSCF were investigated. The results show that HEBSCF can accommodate cations with large size differences. Compared with BSCF, doping elements at A site (HEBSCF-A), B site (HEBSCF-B) or both sites (HEBSCF-AB) can improve the mixed entropy. Among the three doped BSCF, HEBSCF-AB has the highest mixed entropy and shows stable oxygen permeation flux at 750 and 800 °C up to 300 h. No phase transition was observed on HEBSCF-AB after the long-term tests at intermediate temperatures. This research indicates that the high entropy stabilization strategy is feasible to improve the permeation stability of perovskite membranes by inhibiting phase transition.

The toxicity of common solvents used in membrane fabrication threatens the environmental sustainability and questions the claim that membrane technology is a green separation technology. Therefore, there is a need for re-orienting membrane fabrication processes towards greener solutions, making use of less toxic, and possibly environmentally friendly solvents. We employed dimethyl sulfoxide (DMSO), a non-toxic solvent, to prepare casting solutions containing polyvinylidene fluoride and an antifouling random copolymer made of polystyrene and poly(ethylene glycol) methyl ether methacrylate (PS-r-PEGMA). Membranes were formed by vapor-induced phase separation (VIPS). They were shown to be homogeneous in terms of structure and surface chemistry (tested by mapping FT-IR), suggesting compatibility of the polymer/copolymer/solvent system and justifying the choice of DMSO. Membrane hydration was drastically improved after adding PS-r-PEGMA with a water contact angle falling from 140° to 47°. As a result, biofouling by Escherichia coli and whole blood was reduced by > 90% in static conditions. During several filtration cycles of a highly fouling Escherichia coli solution flux recovery ratio could be increased from 16% (pristine membrane) to 29% (PEGylated membrane). All in all, this study reveals that low-biofouling homogeneous porous membranes can be prepared by in-situ modification and the VIPS process using a greener approach than traditionally reported.

Carbonic anhydrase (CA) based membranes with unique biological activities have been widely explored for carbon capture and storage (CCS), owing to their high efficiency, easy operation, low energy requirement, and environmental sustainability. However, limitations of CA enzymes, such as low thermal stabilities, narrow optimum pH ranges, and difficulties in recovery from reaction media, hinder its practical applications. Consequently, combining its enzymatic activity with membrane technologies for industrial uses is an attractive strategy. This current review explores a variety of immobilization approaches and summarizes the mechanistic features of enzymatic membranes in CO₂ capture. Immobilized enzymes can be recycled to reduce process costs and improve the CO₂ permeability and selectivity of the membranes. This makes enzymatic membranes attractive for CCS. The study also summarizes the structure, synthesis, and applications of a variety of CA analogues to demonstrate their advantages compared with natural CA. CA analogues hold promise for industrial and biomimetic applications.

Fouling is a critical consideration for the design of thin-film composite (TFC) nanofiltration membranes. Traditional wisdom believes that fouling propensity is primarily dictated by membrane surface properties while porous substrates play little role (on the basis on the latter have no effect on the foulant-membrane interaction). Nevertheless, porous substrates can regulate the water transport pathways, resulting in uneven water flux distribution over the membrane surface. For the first time, we experimentally investigated the micro-scale water flux distribution for nanofiltration membranes with different substrate porosities and the impact of such flux distribution pattern on fouling. With gold nanoparticles as tracers, we demonstrated more evenly distributed water flux at increasing substrate porosity. This was found to effectively alleviate membrane fouling by eliminating localized hot spots of high flux. Furthermore, higher substrate porosity also effectively enhanced the membrane water permeance due to the optimized water transport pathways. Our study reveals the fundamental relationship between the micro-scale transport behavior and the membrane fouling propensity, which provides a firm basis for the rational design of TFC membranes toward better separation performance.

The CO₂/N₂ separation performances of facilitated transport membranes (FTMs) containing aminoacid salts as mobile carriers were characterized under dilute feed gases with 0.05–20% CO₂. At a reduced CO₂ partial pressure, the carrier saturation in the FTMs was mitigated, which enhanced both the CO₂ permeance and CO₂/N₂ selectivity. The best FTM containing 2-(1-piperazinyl)ethylamine sarcosinate exhibited an uprising CO₂ permeance from 1968 to 3822 GPU and an improved CO₂/N₂ selectivity from 249 to 472 with reducing CO₂ content from 1% to 0.1%. The feasibility of this FTM is exemplified by designing a two-stage enriching membrane cascade to further remove 90% of the CO₂ in a residual coal flue gas containing 1.75% CO₂. Techno-economic analysis indicates a low capture cost of $83.8/tonne. The marginal costs beyond 90% capture are also evaluated for a variety of residual flue gases, indicating that the FTM-based capture from the coal or cement plant residual flue gas is more cost effective than direct air capture.

The production of sub-10 µm cellulose microbeads via membrane emulsification using isoporous membranes is reported here for the first time. Poly(ethylene terephthalate) membranes, with defined interpore distances, pore diameters and straight-through pores were fabricated via photolithography. A dispersed phase of 8 wt% cellulose solution was extruded through the membrane pores, forming, due to shear provided by an overhead stirrer, cellulose solution droplets dispersed in a continuous phase composed of 2 wt% and 5 wt% Span in sunflower oil. Upon phase inversion with ethanol, sub-10 µm microbeads with a coefficient of variation (CV) < 45 % were produced by exploring the Weber number (We_d) - Capillary number (Ca_c) emulsion generation space.

These results show that sub-10 µm cellulose microbeads can be produced using isoporous polymer membranes fabricated via photolithography, for use in a wide range of applications in the personal care, food and drug industries.

The pore constriction (or standard blocking) model is widely used to describe the filtration behavior for a wide range of suspensions/solutions even though the underlying assumption of a uniform reduction in the radius of non-interconnected cylindrical pores is unlikely to be valid in almost any system. This short communication presents an alternative blocking model based on a description of the effective permeability of a fouled membrane accounting for the flow around and under the deposited foulant through the interconnected pore structure of the membrane. The resulting filtration equation gives linear fouling relationships that are very similar to those for the classical pore constriction model, including the slope on a derivative plot, providing a possible justification for the successful use of the pore constriction formalism in describing the flux decline behavior in many membrane systems. In addition, this new blocking model is readily extended to the case where the deposited foulant is permeable to flow. This new composite media blocking model not only provides useful expressions for the rate of flux decline during constant pressure filtration, it also provides insights into the underlying physical mechanisms controlling fouling in membrane systems.

Gas separation membranes based on glassy polymers often show complex responses to feed compositions, membrane morphologies, and operating conditions. The well-known dual mode sorption and transport models are discussed here as tools to assess plasticization and competition effects in asymmetric morphologies. A framework is illustrated based on these models using polyimide asymmetric hollow fibers. This framework can also be applied to emerging polymer families such as thermally rearranged (TR) and polymers of intrinsic microporosity (PIM), to identify opportunities connected to their innate glassy natures.

This study examined membrane fouling and associated microbial taxa in a membrane bioreactor operating at a sub-critical flux condition using next-generation amplicon sequencing. The membrane was operated at a sub-critical flux, thus, fouling was not observed until endogenous decay. The observed fouling could be attributed to endogenous decay which was driven by nutrient deficiency at high sludge age and low food-to-microorganisms ratio (decreasing from 0.15 to 0.09 gBOD/gMLVSS.d). Endogenous decay resulted in a sharp decrease of the number of species and evenness between different species (49.7 and 58.9% compared to the inoculum, respectively). The release of dissolved organic matters and cell debris from endogenous decay as well as the excessive growth of filamentous bacteria, e.g. Thiotrichales were the main contributors to membrane fouling. The relative abundance of Thiotrichales significantly correlated with TMP (Pearson R = 0.996, p-value <0.001), indicating this order's contribution to membrane fouling. Other dominant orders in the mixed liquor after endogenous decay such as Rhizobiales, Burkholderiales, Rhodospirillales and Myxococcales, Flavobacteriales can produce extracellular polymeric substances and aggravating membrane fouling. Fouling layers possess highly similar microbial composition with the mixed liquor, with some filamentous microbial orders, e.g. Corynebacteriales and Oligoflexales showing increased relative abundance by 6.83 and 5.64 folds, respectively.