Membrane Permeability Coefficients Research Articles

Power feasibility of single-staged full-scale PRO systems with hypersaline draw solutions

Pressure retarded osmosis (PRO) is a process that allow to generate energy from osmotic gradient. This process uses selective membranes in order to produce electrical energy through a hydraulic turbine. PRO can be used as a renewable energy technology where water resources are inexhaustible. PRO has the advantage of knowing when and how much energy will be produced. Unfortunately at the moment there are certain limiting factors concerning membrane and module characteristics that have prevented PRO to be fully exploited at full-scale. This study aims to assess the impact of hypersaline draw solutions (60–180 g L−1), membrane characteristics such as structural parameter, module membrane surface and permeability coefficients on the net energy generated by single-staged full-scale PRO system with up to 8 spiral wound membrane modules (SWMMs) in series in a pressure vessel. To carry out this study, characteristics of existing PRO membranes at lab-scale were scaled up to 8 inches SWMM. The results showed the change in the optimal operating parameters with the change of membrane characteristics and draw solution concentration. This study concluded that single-staged full-scale PRO process would be viable from an energy point of view if membranes were manufactured on an industrial scale and with the characteristics of existing membranes on a laboratory scale.

Development of Membrane Permeability Coefficient by Means of Novel Molecular Dynamics Methods

The membrane permeability, and its evaluation, is crucial factor in the process of uptake of compounds from outside to inside the cell and in the inhibition of the activity of disease-causing target proteins. Although molecular dynamics (MD) simulations have been shown to be able to reproduce the conformational changes of compounds occurring during membrane permeation, it is still challenging to extract the membrane permeability at an affordable computational workload solely by conventional MD. Indeed, the time scale accessible by MD is far below the one characterizing the actual permeation process. Phenomena occurring in living organisms escaping the reach of standard MD are generally referred to as biological rare events, and the membrane permeation process is one of them. To overcome this time-scale problem, several enhanced sampling methods have been proposed over the years to improve conformational sampling. In this review, a hybrid sampling method that combines the parallel cascade selection MD (PaCS-MD) and the outlier flooding method (OFLOOD), introduced and developed by our group, is proposed as a tool to study the membrane permeation from structural sampling (rare-event sampling). The obtained trajectories are used to estimate the free energy profiles for the membrane permeation and to compute the membrane permeation coefficients. Moreover, we present an example of application of the free energy reaction network method as a versatile way for incorporating explicitly into reaction coordinates the degrees of freedom related to internal motion.

Determination of cell membrane permeability coefficients: Comparison of models in the case of oocytes

Values of cell membranes permeability coefficients for water and molecules of cryoprotective agents (CPAs) are the necessary characteristics for developing physical-mathematical models describing mass transfer processes through cell membranes in order to predict optimal cell cooling rates. We carried out a comparative analysis of the permeability coefficients of mouse oocyte membranes for molecules of water, ethylene glycol (EG), propane-1,2-diol (1,2-PD) and dimethyl sulfoxide (Me2SO), determined by applying the classical Kedem-Katchalsky model, which considers only the penetration of non-electrolyte molecules (water and CPA) through the membrane, and the model developed by us, which takes into account the transmembrane transfer of ions and the associated changes in the transmembrane electric potential. We shown that calculations based on the developed modified model provide lower values of the permeability coefficients of the oocyte membrane for water and CPA molecules. What is important that the obtained by our modified model permeability coefficients for water molecules do not depend on the type of cryoprotectant, while the application of the classical model both in our studies and works of other authors always gave different values of these coefficients in solutions with different cryoprotectants. Our modified model also makes it possible to determine the dynamics of the transmembrane electric potential of the cell under the conditions of transmembrane mass transfer and the duration of the membrane being influenced by the changes in electric potential, that is a parameter that can directly affect the viability of cells.

Utilization of endogenous albumin trafficking pathways in the lungs has potential to modestly increase the lung interstitial access and absorption of drug delivery systems after inhaled administration

ABSTRACT Objectives Drug delivery systems typically show limited access to the lung interstitium and absorption after pulmonary delivery. The aim of this work was to undertake a proof-of-concept investigation into the potential of employing endogenous albumin and albumin absorption mechanisms in the lungs to improve lung interstitial access and absorption of inhaled drug delivery systems that bind albumin. Methods The permeability of human albumin (HSA) through monolayers of primary human alveolar epithelia, small airway epithelia, and microvascular endothelium were investigated. The pulmonary pharmacokinetics of bovine serum albumin (BSA) was also investigated in efferent caudal mediastinal lymph duct-cannulated sheep after inhaled aerosol administration. Results Membrane permeability coefficient values (Papp) of HSA increased in the order alveolar epithelia<small airway epithelia<microvascular endothelium, where the permeability of HSA through small airway and microvascular endothelia were approximately 4- and 28-fold higher than alveolar epithelia, respectively. Only 6.5% of the delivered BSA aerosol dose was absorbed from the lungs of sheep over 5 days, although half of the absorbed dose was absorbed via the lung lymph. Conclusion Drug delivery systems that bind endogenous albumin may show a modest increase in lung permeability and absorption after inhaled delivery compared to systems that do not efficiently bind albumin.

Role of permeability coefficients in salinity gradient energy generation by PRO systems with spiral wound membrane modules

Processes that can transform a salinity gradient into electrical energy have gained attention in recent years. One such process, which uses semipermeable membranes to generate electrical energy through a turbine, is pressure retarded osmosis (PRO). As a potential renewable energy technology, this process could also be integrated in desalination plants to reduce the energy consumption. However, principally because of certain drawbacks concerning membrane and module characteristics, PRO technology has not yet been fully exploited at commercial scale. This study aims to assess the impact of membrane permeability coefficients on the energy generated by full-scale single-stage PRO systems. This allow an evaluation of the performance of PRO modules in series considering variation of the permeability coefficients that may be due to the impact of fouling. An evaluation was made of the HTI OsMem™ 2521 spiral wound membrane module considering a diameter of 8 inches (high up-scaled active area) and different permeability coefficient ranges. The results showed that a 50% water permeability coefficient decrease would produce an approximately 25% decrease in the amount of energy that could be generated, while a 50% increase in the solute permeability coefficient would have virtually no effect when considering optimal operating points. Variation of the water permeability coefficient had more impact on the potential amount of generated energy than variation of the solute permeability coefficient.

Superior diffusion dialysis anion exchange membranes from miscible polyether sulfone – poly(vinyl pyrrolidone-co-styrene) blends

Diffusion dialysis is a promising method for the recovery of titania waste acid due to its low energy consumption and ease of operation. However, the current commercial anion exchange membranes (AEMs) suffer from low acid permeability coefficient and high cost. To address this issue, the development of high-performance AEMs is crucial for the successful recovery of titania waste acid by diffusion dialysis. Previous studies [Journal of Membrane Science, 2022, 662, 120980] have shown that the dense polyether sulfone - poly(vinyl pyrrolidone) (PES-PVP) blend membranes can be converted into AEMs through the protonation reaction of the O atoms in pyrrolidone with H+ in sulfuric acid solution. This process enables the efficient separation of sulfuric acid from ferrous sulfate. The acid permeability coefficient of the blend membrane is influenced by the content and molecular weight of PVP. Higher content and molecular weight of PVP result in a greater acid permeability coefficient of the membranes. It is observed that due to the water solubility of PVP, the amount of PVP added to the blend membranes cannot exceed 60%, however this would restrict further improvement in the acid permeability coefficient of the membranes. Additionally, there is a concern regarding the long-term stability of the membranes as the PVP may get washed out from the membranes. To this, P(VP-co-St) copolymers with a certain hydrophobicity are synthesized through free radical copolymerization of hydrophilic monomer N-vinylpyrrolidone (VP) and hydrophobic monomer styrene (St). PES-P(VP-co-St) dense membranes are then prepared by mixing the P(VP-co-St) copolymers with PES. The objective of this study is to investigate the effects of P(VP-co-St) molecular weight, VP content, and composition of the casting solution on the physicochemical properties, mass transfer properties, and stability of the blend AEMs. The results show that homogeneous dense membranes can be prepared by completely mixing PES with P(VP-co-St) copolymers with 87–90 wt% VP content and 100–150 kDa molecular weight. The permeability coefficients of H2SO4 (PH2SO4) and FeSO4 (PFeSO4) increase with the VP content in the membrane phase. The ion exchange capacity of the PES-P(VP-co-St)-1# AEM varies in the range of 0.32–0.81 mmol/g dry membrane. For the PES-P(VP-co-St) blend membranes, synthesized by blending P(VP-co-St) with 90 wt% VP content with PES at a mass ratio of 7:3 (VP content of 61 wt% in the membranes), the PH2SO4, PFeSO4, and selectivity coefficient of the membranes are 692 × 10−9 m2/h, 5.8 × 10−9 m2/h, and 119, respectively. The PH2SO4 of the PES-P(VP-co-St) AEM is much higher than that of the commercial AEM Tianwei DF-120 while maintaining high selectivity. This study successfully develops AEMs with high performance in diffusion dialysis through a convenient method by blending P(VP-co-St) copolymers with PES.

Dead-end forward osmosis as an alternative for deep sludge dewatering: Evaluation method and characteristics analysis

Sludge deep dewatering technologies that are effective and energy-saving are urgently required. Forward osmosis (FO) technology was recently used for dewatering sludge. However, the final moisture content was too high—above 95.0%—to meet the treatment and disposal requirements. In this study, a novel dead-end forward osmosis (DEFO) technique was proposed and verified for deep dewatering of excess sludge. In DEFO, the feed side is in dead-end mode, while the draw side is in cross-flow mode. Further, when 30.8 g/L excess sludge, 2.0 M NaCl draw solute, 3.0 cm/s cross velocity on the draw side, and 3‰ cationic polyacrylamide dosage was used, the moisture content of the filter cake was as low as 69.2%, equating to 90.0% sludge reduction. A proposed evaluation model for DEFO sludge dewatering behavior includes critical characteristics, such as water flow osmosis resistance and water permeability coefficient of the FO membrane. The sludge dewatering process continued regardless of whether the filter cake broke. In contrast to the conclusions endorsed in traditional dead-end pressure filtration, the DEFO filter cake exhibits an abnormal structure with a dense upper cake and a loose structure for the lower cake, resulting in a permeable filter cake. The photographs, moisture content distribution, and filter cake frozen scan verified this. The solid compressive pressure and hydraulic pressure in the DEFO filter cake were negligible, resulting in low water flow resistance of the filter cake. These findings provide further insights into the use of DEFO technology for deep sludge dewatering.

Chiral gold nanoparticles/graphene oxide membranes with ultrahigh and stable permeance for sieving and enantioseparation

In accurately balancing membrane permeability and separation coefficient, effectively preventing membrane collapse in separation process is the core to improve the efficiency of membrane separation for two-dimensional materials. Here, we used L-cysteine (L-Cys) functionalized gold nanoparticles as scaffolds and spacers and fabricated a multi-effect separation membrane with GO nanosheets. The as-prepared membrane performed the following as a separation membrane: (1) As a robust spacer, the gold nanoparticles, prevented the collapse of the GO sheet and thus the membrane showed stability; (2) The existence of amphiphilic L-cysteine enabled the possibility of regulating the GO sheets layer spacing between 16.9 and 17.8 Å by pH, which achieves controllable ultrahigh permeance for size sieving. The maximum permeation rate of the membrane can reach 216.6 L m−2 h−1 bar−1, which is much greater than that of pure GO membrane; (3) Further, we demonstrate the following properties of the as-prepared membranes embedded with amphiphilic chiral gold nanoparticles for the enantiomer separation. The membrane has high enantioselectivity for Pen racemates, and its chiral separation factor and permeation rate can reach 1.83 and 21.7 L m−2 h−1 bar−1, respectively.

Unexpected permeability enhancement of thermally rearranged (TR) copolybenzoxazole membranes

Gas transport properties of novel thermally rearranged copolybenzoxazole (TR-coPBO) membranes with various copolymerization ratios were investigated. The TR-coPBO membranes were obtained by thermal rearrangement of corresponding copoly(o-hydroxy imide)s with fluorene ring moiety via several rearranged temperatures. The TR-coPBO membranes had larger d-spacing values than corresponding neat TR-PBO membranes without copolymerization and larger specific volumes than those expected from an additive rule, suggesting excessively increased fractional free volumes. Permeability coefficients of the TR-coPBO membranes possessed positive deviations from the values expected by a semilogarithmic additive rule against the copolymerization ratio. The enhanced permeability might be brought by steric repulsion and suppressed molecular chain packing due to the partial introduction of fluorene ring moiety.

Interplay between membrane imperfections and external concentration polarization

Reverse osmosis membranes provide a highly effective and efficient barrier against various kinds of pollutants. Their reliability depends on the integrity of the active layer: in case the active layer is damaged and contains imperfections, unfiltered feed solution can contaminate the permeate. Various types of integrity monitoring techniques have been developed to verify membrane performance, of which the rejection of fluorescent dyes is a well-established technique. Fluorescent dyes are however relatively small solutes for which the membranes can display non-zero diffusive permeability, such that not all dye passage can be attributed to membrane imperfections. Additionally, fluorescent dyes are subject to external concentration polarization (ECP) during filtration, causing a flux-dependent enrichment at the membrane surface, further complicating the analysis of dye rejection data. This study presents a model to discern between membrane permeability, enrichment by ECP and passage through imperfections. The consequences of imperfections on solute passage are explored, showing that imperfections only contribute significantly to the passage of solutes with a low membrane permeability. This leads to underestimates of the external mass transfer coefficient, with the error being increasingly large with decreasing membrane permeability coefficient, relative to the case of an imperfection-free membrane. This error is then related to the proportionality of the Sherwood number, used to calculate external mass transfer coefficients, with solute diffusivity, allowing the quantification of the contribution of imperfections to water flux. The model was experimentally verified using Pyranine rejection in two membrane types, both operated in a lab-scale flat sheet crossflow test system, finding proof of imperfections in one membrane type.

Reverse osmosis membrane and module improvement roadmap for maximum impact

Advancements in Reverse osmosis (RO) membrane modules towards lowering specific cost of pure water can be quantified in terms of two non-dimensional numbers: specific cost of membrane conductance (viz., product of membrane area and permeability) relative to electricity price, and the channel mass-transfer coefficient relative to permeability. Reducing specific cost per unit conductance is more important than simply improving permeability, since high permeability at correspondingly large cost per unit area will not yield cheaper permeate production. The impact of technology improvements is assessed considering RO systems operated at an optimized average flux which minimizes the sum of capital and operating costs. Developing cheaper membrane modules is likely to be more impactful than increasing permeability or mass transfer coefficient. For example, for seawater RO, a 5× increase in permeability or mass transfer coefficient yields 6–8 % reduction in water cost, whereas, a 2× reduction in the amortized specific cost of membrane module yields more savings. Keeping membrane costs unchanged, both permeability and mass transfer coefficient have to be increased simultaneously by 2× to achieve similar savings. Multi-staged (and by extension batch) processes yield larger savings with improved membrane modules, and hence will likely become more prevalent in the future.

Effect of Solubility Improvement via Formation of an Amorphous Composite of Indomethacin and Sulindac on Membrane Permeability.

The importance of permeability as well as solubility of the drug has been recognized in improving the solubility of poorly water-soluble drugs. This study investigated the impact of amorphous composites of indomethacin (IMC) and sulindac (SLD) on the membrane permeability of drugs. The IMC/SLD (1/1) formulation prepared by dry grinding was amorphous with a single glass transition temperature. The Fourier transform IR spectra and Raman spectra revealed formation of hydrogen bonds between the OH group of IMC and the carbonyl group of SLD. These results suggest that an amorphous composite was formed between IMC and SLD through hydrogen bonding. The amount of dissolved IMC and SLD from the amorphous composite of IMC/SLD (1/1) was higher than that of the untreated IMC or SLD in the dissolution test. The permeated amounts and permeation rates of both drugs were enhanced by increasing the solubility of the amorphous composite. Conversely, the apparent membrane permeability coefficients (Papp) were almost same for untreated drugs and amorphous composites. In the case of hydroxypropyl-β-cyclodextrin and sodium dodecyl sulfate, Papp of the drugs decreased with the addition of these compounds, although the drug solubility was enhanced by the solubilization effect. This study revealed that an amorphous composite formed through hydrogen bonding is an attractive pharmaceutical way to enhance the permeated amount and permeation rate without changing the Papp of both the drugs.

Effect of Exogenous Electric Stimulation on the Cardiac Tissue Function In Situ Monitored by Scanning Electrochemical Microscopy.

Cardiac tissue is sensitive to and can be easily damaged by exogenous electric stimulation. However, due to the thermal-electric coeffect and the limitation of in situ and quantitative information on the cardiac tissue function under electric stimulation, the detailed effect and the underlying mechanism of exogenous electric stimulation on the cardiac tissue remain elusive. To address this, in this work, we first constructed an in vitro cardiac tissue model and established a thermal-electric coupled theoretical model for simulating the electric field and temperature distributions around the cardiac tissue, from which we selected the electric field strengths (1.19, 2.37, and 3.39 kV cm-1) and electrical energies (0.001, 0.005, and 0.011 J) for electric stimulations without inducing a thermal effect. Then, we applied electric field stimulations on the cardiac tissue using these parameters and scanning electrochemical microscopy (SECM) to in situ and quantitatively monitor the dynamic changes in the key parameters of the cardiac tissue function, including respiratory activity, membrane permeability, and contraction frequency, after electric field stimulations. The SECM results showed that the oxygen consumption, cell membrane permeability coefficient, and contraction frequency of the cardiac tissue were strongly dependent on electrical energy, especially when the electrical energy was higher than 0.001 J. Our work, for the first time, achieves the in situ and quantitative monitoring of the cardiac tissue function under electric stimulation using SECM, which would provide important references for designing an electric stimulation regime for cardiac tissue engineering and clinical application of electrotherapy.

Transport of Chromium(VI) across a Supported Liquid Membrane Containing Cyanex 921 or Cyanex 923 Dissolved in Solvesso 100 as Carrier Phase: Estimation of Diffusional Parameters.

An investigation of chromium(VI) transport across a supported liquid membrane containing the phosphine oxides Cyanex 921 and Cyanex 923 dissolved in Solvesso 100 as carrier phases was carried out in batch operation mode. Chromium(VI) transport was investigated as a function of different variables: hydrodynamic conditions in the feed (1000-1600 min-1) and stripping (600-1500 min-1) phases, HCl (0.25-2 M) and indium (0.01-0.1 g/L) concentrations in the feed phase, and carrier (0.01 M-0.75 M) concentration in the membrane phase. Indium was recovered in the stripping phase using hydrazine sulphate solutions, and, at the same time, chromium(VI) was reduced to the less harmful Cr(III) oxidation state. Models describing the transport mechanism comprising a diffusion process through the feed aqueous diffusion layer, fast interfacial chemical reaction, and diffusion of the respective chromium(VI)-phosphine oxide complexes across the membrane were developed. The equations describing the rate of transport correlate the membrane permeability coefficient with diffusion and equilibrium parameters, as well as the chemical compositions of the respective metal-carrier phases. The models were used to calculate diffusional parameters for each metal-carrier system, and the minimum thickness of the feed boundary layer was calculated as 1 × 10-3 cm and 6.3 × 10-4 cm for the Cr(VI)-Cyanex 921 and Cr(VI)-Cyanex 923 systems, respectively.

Free-Energy Profiles for Membrane Permeation of Compounds Calculated Using Rare-Event Sampling Methods.

The free-energy profile of a compound is an essential measurement in evaluating the membrane permeation process by means of theoretical methods. Computationally, molecular dynamics (MD) simulation allows the free-energy profile calculation. However, MD simulations frequently fail to sample membrane permeation because they are rare events induced in longer timescales than the accessible timescale of MD, leading to an insufficient conformational search to calculate an incorrect free-energy profile. To achieve a sufficient conformational search, several enhanced sampling methods have been developed and elucidated the membrane permeation process. In addition to these enhanced sampling methods, we proposed a simple yet powerful free-energy calculation of a compound for the membrane permeation process based on originally rare-event sampling methods developed by us. Our methods have a weak dependency on external biases and their optimizations to promote the membrane permeation process. Based on distributed computing, our methods only require the selection of initial structures and their conformational resampling, whereas the enhanced sampling methods may be required to adjust external biases. Furthermore, our methods efficiently search membrane permeation processes with simple scripts without modifying any MD program. As demonstrations, we calculated the free-energy profiles of seven linear compounds for their membrane permeation based on a hybrid conformational search using two rare-event sampling methods, that is, (1) parallel cascade selection MD (PaCS-MD) and (2) outlier flooding method (OFLOOD), combined with a Markov state model (MSM) construction. In the first step, PaCS-MD generated initial membrane permeation paths of a compound. In the second step, OFLOOD expanded the unsearched conformational area around the initial paths, allowing for a broad conformational search. Finally, the trajectories were employed to construct reliable MSMs, enabling correct free-energy profile calculations. Furthermore, we estimated the membrane permeability coefficients of all compounds by constructing the reliable MSMs for their membrane permeation. In conclusion, the calculated coefficients were qualitatively correlated with the experimental measurements (correlation coefficient (R2) = 0.8689), indicating that the hybrid conformational search successfully calculated the free-energy profiles and membrane permeability coefficients of the seven compounds.

The Pseudo-Protic Ionic Liquids TOAH+Cl- and TODAH+Cl- as Carriers for Facilitated Transport of In(III) from HCl Solutions.

A study of indium(III) transport across an immobilized liquid membrane using the pseudo-protic ionic liquids TOAH+Cl- and TODAH+Cl- as carriers has been carried out using batch experiments. Metal transport is investigated as a function of different variables: hydrodynamic conditions in the feed (375-1500 min-1) and receiving (500-750 min-1) phases, HCl (0.5-7 M) and indium (0.01-0.2 g/L) concentrations in the feed phase and carrier (1.25-40% v/v) concentration in the membrane phase. Indium is conveniently recovered in the receiving phase, using a 0.1 M HCl solution. Models are reported describing the transport mechanism, which consists of a diffusion process through the feed aqueous diffusion layer, fast interfacial chemical reaction, and diffusion of the respective indium-pseudo-protic ionic liquid through the membrane. The equations describing the rate of transport are derived by correlating the membrane permeability coefficient to diffusional and equilibrium parameters as well as the chemical composition of the respective indium-pseudo-protic ionic liquid system, i.e., the carrier concentration in the membrane phase. The models allow us to estimate diffusional parameters associated with each of the systems; in addition, the minimum thickness of the feed boundary layer is calculated as 3.3 × 10-3 cm and 4.3 × 10-3 cm for the In-TOAH+Cl- and In-TODAH+Cl- systems, respectively.

Molecular simulation of lignin-related aromatic compound permeation through gram-negative bacterial outer membranes

Lignin, an abundant aromatic heteropolymer in secondary plant cell walls, is the single largest source of renewable aromatics in the biosphere. Leveraging this resource for renewable bioproducts through targeted microbial action depends on lignin fragment uptake by microbial hosts and subsequent enzymatic action to obtain the desired product. Recent computational work has emphasized that bacterial inner membranes are permeable to many aromatic compounds expected from lignin depolymerization processes. In this study, we expand on these findings through simulations for 42 lignin-related compounds across a gram-negative bacterial outer membrane model. Unbiased simulation trajectories indicate that spontaneous crossing for the full outer membrane is relatively rare at molecular simulation timescales, primarily due to preferential membrane partitioning and slow diffusion within the lipopolysaccharide layer within the outer membrane. Membrane partitioning and permeability coefficients were determined through replica exchange umbrella sampling simulations to overcome sampling limitations. We find that the glycosylated lipopolysaccharides found in the outer membrane increase the permeation barrier to many lignin-related compounds, particularly the most hydrophobic compounds. However, the effect is relatively modest; at industrially relevant concentrations, uncharged lignin-related compounds will readily diffuse across the outer membrane without the need for specific porins. Together, our results provide insight into the permeability of the bacterial outer membrane for assessing lignin fragment uptake and the future production of renewable bioproducts.

Effects of water matrix on the rejection of neutral pharmaceutically active compound by thin-film composite nanofiltration and reverse osmosis membranes.

Thin-film composite (TFC) nanofiltration (NF) and reverse osmosis (RO) membranes have been widely used to remove pharmaceutically active compounds (PhACs) from water and wastewater. However, limited information is available to present the rejection of neutral PhACs under complex water matrices. In this study, we used acetaminophen (AAP) as a representative neutral pollutant to study the effects of feedwater matrices on the rejection of neutral PhACs by NF and RO membranes. The results showed that the permeation of solutes and water through NF and RO membranes followed the classical solution-diffusion model. The corresponding permeability coefficients of AAP for the RO membrane showed good consistency, with average values ranging between (6.19-7.56)×10-6μms-1 in fresh and brackish feedwater. Meanwhile, the NF membrane exhibited stable AAP and NaCl fluxes as the applied pressure increased from 4.8 to 7.6bar, suggesting an insignificant influence of convection on solute transport. In addition, a 10-fold increase in NaCl concentration reduced the average AAP permeability coefficient of the NF membrane by 57% (i.e. from 2.8×10-5ms-1 to 1.2×10-5ms-1), highlighting the relevance of co-existing ions to AAP transport. Furthermore, organic fouling resulted in enhanced AAP rejection by both NF and RO membranes at neutral pH level and medium applied pressure (i.e. 5.8bar). Overall, this study provided important insights into the separation mechanism of TFC membranes for neutral PhACs, as well as the complex effects of the water matrix on the solute permeation processes.

Determining small-molecule permeation through lipid membranes.

The passive permeability of cell membranes is of key importance in biology, biomedical research and biotechnology as it determines the extent to which various molecules such as drugs, products of metabolism, and toxins can enter or leave the cell unaided by dedicated transport proteins. The quantification of passive solute permeation is possible with radio-isotope distribution experiments, spectroscopic measurements and molecular dynamics simulations. This protocol describes stopped-flow fluorimetry measurements performed on lipid vesicles and living yeast cells to estimate the osmotic permeability of water and solutes across (bio)membranes. Encapsulation of the fluorescent dye calcein into lipid vesicles allows monitoring of volume changes upon osmotic shifts of the medium via (de)quenching of the fluorophore, which we interpret using a well-defined physical model that takes the dynamics of the vesicles into account to calculate the permeability coefficients of solutes. We also present analogous procedures to probe weak acid and base permeability in vesicles and cells by using the read-out of encapsulated or expressed pH-sensitive probes. We describe the preparation of synthetic vesicles of varying lipid composition and determination of vesicle size distribution by dynamic light scattering. Data on membrane permeation are obtained using either conventional or stopped-flow kinetic fluorescence measurements on instruments available in most research institutes and are analyzed with a suite of user-friendly MATLAB scripts ( https://doi.org/10.5281/zenodo.6511116 ). Collectively, these procedures provide a comprehensive toolbox for determining membrane permeability coefficients in a variety of experimental systems, and typically take 2-3 d.

Swelling-induced morpholine functionalized adamantane-containing poly(aryl ether ketone) membranes for vanadium flow batteries

Swelling-induced morpholine functionalized adamantane-containing poly(aryl ether ketone) (MAPEK) membranes were prepared for vanadium flow batteries. MAPEK membranes were prepared from chloromethylated polymer and morpholine and further swelling-induced with hot phosphoric acid to obtain membranes with enhanced ionic conductivity. The swelling, selectivity, and ionic conductivity of MAPEK membranes were regulated by varying the swelling temperature. Selective swelling-induced microphase separation in MAPEK membranes, forming wider ion transport pathways and resulting in low area resistance. The unique rigid adamantane-containing backbone limited the swelling of membranes. Consequently, MAPEK membranes showed excellent selectivity and conductivity (vanadium ion permeability coefficient of MAPEK membranes was lower than 3.82 × 0−7 cm2min−1) (Nafion212 membrane, 42.5 × 0−7 cm2min−1), and MAPEK-150 membrane exhibited low area resistance (0.17 Ωcm2). The vanadium flow batteries (VFB) with MAPEK-150 membrane exhibited high energy efficiency (91.1% at 80 mAcm−2, 81.4% at 200 mAcm−2). Furthermore, MAPEK membranes showed good stability in VFB and oxidative electrolytes. The swelling-induced method utilized in this work is a versatile and facile method to enhance the conductivity of ion-exchange membranes.