Journal of Membrane Science Letters最新文献

Directly recovering ammonia from waste streams is a sustainable approach for ammonia management since it saves energy from both the Haber-Bosch process, the major industrial method for ammonia synthesis, and wastewater treatment. Membrane distillation (MD), an evaporation-based membrane separation process, has been employed to recover ammonia from ammonia-rich wastewater due to the high volatility of ammonia. In this study, the photothermal effect is incorporated into MD to enhance the ammonia recovery from ammonia-rich wastewater. Carbon black particles are coated on the membrane surface to increase its absorption of solar irradiation at the solution-membrane interface and facilitate the ammonia transport across the membrane. We demonstrate that the system can recover ammonia at a maximum ammonia flux of 4.52 g-N·m⁻²·h⁻¹ with a solar intensity of 1.7 kW·m⁻². The estimated mass transfer coefficient of carbon black coated membrane is 2.67 × 10⁻² m·h⁻¹ with solar irradiation, enhanced by 30.8% when compared to that in a pristine membrane. We also confirm that the improvement of ammonia flux by photothermal effect is equivalent to heating the feed solution by 20–30 °C. Our study demonstrates a promising pathway for utilizing solar energy by photothermal effects to enhance MD for ammonia recovery from ammonia-rich wastewater.

All-silica DD3R zeolite has been recognized as a promising CO₂-selective membrane material owing to its appropriate pore size (0.36 nm × 0.44 nm), strong hydrophobicity, excellent thermal and chemical stabilities. In order to reduce membrane cost, it is meaningful to synthesize thin DD3R zeolite membranes that possess high gas permeance. In this work, high-performance DD3R zeolite membranes were synthesized on TiO₂/α-Al₂O₃ composite hollow fibers by secondary growth method. Sigma-1 zeolite seeds were ball-milled and then fractionated into different-sized seeds by gradient centrifugation. Smaller seed particles were collected after centrifuged at higher rotation speed rate. A very thin and dense DD3R zeolite membrane (thickness: 1.2 µm) was synthesized by using the smallest seeds (ZS4) with average particle size of 163 nm, which were obtained from the supernatant of the third centrifugation at 11,000 rpm. The as-synthesized membranes were employed in separation of equimolar CO₂/CH₄ mixture. Compared with the original ball-milled seeds (ZS1)-induced membrane, the seed ZS4-induced membrane exhibited an improved CO₂ permeance of 1.2 × 10⁻⁷ mol m⁻² Pa⁻¹ s⁻¹ by 62%. All the resultant membranes performed good CO₂/CH₄ separation selectivities between 262 and 364.

Metal-organic frameworks (MOFs) host intrinsically porous structure and rich structural and chemical features. Several MOFs with pore aperture comparable to the size of gas molecules have attracted interest to form the selective layer of membranes. Synthesis of MOFs in nanosheet morphology is highly attractive for this because one can use highly-scalable filter coating to make MOF membranes. However, conventional nanosheet based processing route require several processing steps including centrifugation to prepare a coating dispersion. Herein, we report facile preparation of zeolitic imidazolate frameworks (ZIF) membranes by a straightforward assembly of nanosheets. ZIF-8 nanosheets were obtained by a direct bottom-up synthesis route where crystallization was optimized to obtain large, well-faceted 40-nm-thick nanosheets. Membranes, preferentially oriented along the c-out-of-plane direction, were fabricated by directly filtering the growth solution over a porous polymeric support without any further purification of nanosheets. This also ensures that only a small amount of precursor solution is used minimizing waste. The obtained membranes were compact and free of pinhole defects and yielded H₂/C₃H₈ ideal selectivity over 3000 at 25 °C. We anticipate that this approach can be applied to several MOFs which can be synthesized in nanosheet morphology, advancing the scalability prospects of MOF membranes.

The modification of membranes with polyelectrolytes via the Layer-by-Layer (LBL) method has become state of the art in recent years. It is used to fabricate nanofiltration hollow fiber membranes or to immobilize biomolecules on a membrane surface. However, it still remains a time consuming process. In contrast, this work explores a single-step membrane modification with coating solutions containing both polyanions and polycations. High salt concentration in the coating solution suppresses the complexation of the polyelectrolytes prior to the coating. Then, the controlled reduction of the salt concentration during the coating triggers the formation of a polyelectrolyte complex layer on the membrane. Three coating methods are proposed: (1) In interfacial complexation (IC), the polyelectrolyte solution coats the membrane and is subsequently precipitated by flushing with water. (2) Diffusive desalination (DDS) uses the concentration difference between the coating solution in the lumen and a water stream in the shell side to remove salt ions continuously. (3) In polyelectrolyte concentration (PC), the polyelectrolyte solution is coated at a constant flux. Here, the membrane retains the polyelectrolyte while ions permeate through. First, we evaluate the coating methods regarding their ability to produce nanofiltration membranes, which varies depending on the coating method used. With PC, membranes with up to 79% MgCl₂ rejection and a permeability of 30 LMH/bar are obtained. Moreover, in-situ functionalization of the membranes is investigated by the addition of enzymes. Here, with DDS enzymes are immobilized, mostly achieved through adsorption via electrostatic interactions.

Thin-film nanocomposite (TFN) membranes are promising in improving water treatment due to their high permeability and selectivity. However, little is known about the mechanism by which nanoparticles enhance their performance. In this study, we prepared two series of TFN membranes containing ∼40 nm-sized zeolitic imidazolate framework (ZIF-8) nanoparticles, one with a hydrophobic porous form and the other with a nonporous amorphous form (aZIF-8). The TFN membranes containing 0.15 w/v% ZIF-8 exhibited a 100% increase in water permeance while maintaining a similar NaCl rejection (98.38%) compared to thin-film composite (TFC) membranes used in brackish water reverse osmosis (BWRO). In contrast, adding the same amount of aZIF-8 resulted in almost no water permeance enhancement. By comparing the physicochemical properties of the two materials and the two series of membranes, we found that the only difference was the presence or absence of internal hydrophobic pore structures. We proposed that the hydrophobic internal pores of nanoparticles served as extra water channels while preventing the passage of NaCl during BWRO.

Compared with traditional membrane separation methods such as distillation and chromatography, nanofiltration (NF) affords decreased waste generation and energy consumption. Despite the multiple advantages of NF and materials available for NF membranes, the industrial applicability of this process requires improvement. To address these challenges, we propose four important pillars for the future of membrane materials and process development. These four pillars are digitalization, structure–property analysis, miniaturization, and automation. We fill gaps in the development of NF membranes and processes by fostering the most promising contemporary technologies, e.g., the integration of process analytical technologies and the development of a parallel artificial nanofiltration permeability assay (PANPA) or large online databases. Moreover, we propose the extensive use of density functional theory-aided structure–property relationship methods to understand solute transport process at a molecular level. Realizing an inverse design would allow researchers and industrial scientists to develop custom membranes for specific applications using optimized properties.

Tuning the pore size distribution of hemodialysis membranes is essential for the membrane’s selectivity and significantly affects the quality of the dialysis treatment. Tailoring the membrane’s molecular weight cut-off appropriately balances the removal of middle-molecular-weight uremic toxins while avoiding albumin loss. This undesirable albumin loss is a potential side effect and concern for clinical use when aiming at increased removal of middle molecular weight molecules (middle molecules). It is hypothesized that control of the position of a narrow pore size distribution allows middle molecule removal while simultaneously counteracting the unwanted albumin loss. This study presents a comprehensive ex-vivo methodology and novel data on the balance of the clearance of middle molecules and albumin loss at different blood and dialysate flow rates using novel dialyzers. The outcomes hold significance for dialysis therapy, while the insights acquired have broader implications for the selectivity of ultrafiltration membranes.

The Theranova dialyzer shows the largest clearance for small-middle molecules. Phylther stands out with higher removal of the middle molecule YKL-40 than the other dialyzers but exhibits a significant albumin loss. Theranova demonstrates the best compromise between low albumin loss and good clearances of middle molecules.

Developing silica membranes that are highly selective for CO₂ has always been a challenge due to the small sizes of the pores and less amount of CO₂ philic sites in a typical silica network structure. Herein, we describe the fabrication of silica (tetraethoxysilane) membranes functionalized with 3-aminopropyltriethoxysilyl (APTES) and trifluoroacetic acid (TFA). An interaction generated among primary (NH₂) amines and TFA was identified, which was then also revealed by the reversible nature of CO₂ adsorption/desorption — an opposite trend from observations when using another catalyst (HCl). The resultant TEOS-APTES (TFA) membranes demonstrated CO₂ permeance of 3.8 × 10⁻⁷ mol m ^− 2 s ^− 1 Pa⁻¹ and CO₂/N₂ selectivity of 35 at 50 ⁰C via the effect of surface diffusion. This is attributed to the increased microporosity and structural variations affected by TFA, which enhanced molecular sieving and controls the CO₂-philic sites (-NHCOCF₃) via interaction with amines. This novel approach would be effective for the energy-efficient fabrication of highly CO₂-permeable membranes.

Pressure dependence of gas permeation flux for dual-phase ionic-conducting membranes is critical to the design and operation of separation or reaction processes using these membranes. However, literature on dual-phase membranes has mainly focused on temperature, rather than pressure dependence of gas permeation flux. This paper presents a theoretical approach for the development of the pressure dependence of gas permeation flux for dual-phase membranes, demonstrated with CO₂ permeation for samarium-doped-ceria (SDC)/molten-carbonate (MC) dual-phase membranes. The paper presents a model showing that gas permeation through dual-phase ionic-conducting membranes is controlled not only by the intrinsic ion (or electronic) conductivity of the materials for each phase, but also by the geometric factor defined as the ratio of the volume to tortuosity of each phase. These geometric factors for both phases are determined by the topological structure of each phase. Dual-phase membranes of the same materials can have very different pressure-dependent flux equations depending on the topological structure dictated by synthesis method and conditions. CO₂ permeation through SDC-MC membranes made of SDC with low porosity is controlled by carbonate conduction in the molten carbonate phase, leading to logarithmic CO₂ pressure-dependent flux equation. CO₂ permeation through SDC-MC membrane of SDC with intermediate porosity is controlled by oxygen ionic conduction in the SDC phase, and the CO₂ permeation flux shows power-law dependence on CO₂ pressures. The validity of the model is confirmed by comparison of the modeling results with experimental CO₂ permeation data for SDC-MC membranes. This work provides a direction for developing pressure-dependent gas permeation flux equations for various dual-phase ionic-conducting membranes.

Transforming a vast array of candidate materials into membranes with suitable morphologies and improved molecular separation performance is an arduous and costly endeavor for membrane scientists. With the advancement made in artificial intelligence and machine-learning in recent years, it is timely to ask: can machine learning methods guide gas separation membranes Fabrication? The answer is “YES”, and this article explains the justifications for this answer by systematically reviewing and analyzing the up-to-date research efforts in the field. This work aimed to explore the potential of ML algorithms as an effective and cost-saving tool in guiding the experimental process of developing the next generation polymeric membranes, and in addressing the critical needs in the field. Findings demonstrate that training Heteropolymers instead of Homopolymers, synthesizing novel polymers by an inverse design approach, and using reliable datasets that are created under the same conditions, are the most crucial factors to achieve the design intent. A path from A to Z for anyone who intends to use ML algorithms in the membranes’ synthesis process is offered. The article concludes with a brief discussion on future development prospects and open issues that are yet to be addressed for ML‐driven polymeric‐based membranes design and optimization.