Physicochemical Properties Of Membranes Research Articles

Physicochemical and electrical properties of DPPC bilayer membranes in the presence of oleanolic or asiatic acid

This study aimed to investigate the effect of selected compounds from the group of triterpene sapogenins on model phosphatidylcholine membranes. Two types of biological membrane model systems were used in the work, i.e., liposomes (microelectrophoresis method) and spherical bilayers (interfacial tension method). Each model was modified with the tested sapogenin compounds, and the change in their physicochemical and electrical parameters was analyzed. Parameters characterizing the equilibrium in the membrane of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)-oleanolic acid (OA) and DPPC-asiatic acid (AA) were determined). Based on the Young-Laplace equation, the interfacial tensions of spherical lipid bilayers were measured. The formation of 1:1 complexes was assumed in the DPPC-OA and DPPC-AA membrane systems, and the parameters characterizing the interactions in the formed complexes were calculated. Microelectrophoresis was used to study the surface charge density of lipid membranes. These values were obtained from electrophoretic mobility data using Smoluchowsky’s equation. The influence of pH on the electrolyte solution and the composition of the membranes was investigated. The results indicate that modifying DPPC membranes with selected triterpene sapogenins, both OA and AA, causes changes in the surface charge density and shifts of the isoelectric point. Data presented in this work, obtained through mathematical derivation and confirmed experimentally, are of great importance for interpreting phenomena occurring in lipid membranes. A quantitative description of equilibria between phosphatidylcholine and sapogenins lets us understand the processes on the membrane surface. The equilibria are particularly significant from the standpoint of cell functioning. Phosphatidylcholine-sapogenin interactions modulate a range of physicochemical properties of membranes, and they are important in the course of the multiple processes involving membranes in the living cell (e.g., transport mechanism).

Impact of functionalized titanium oxide on anion exchange membranes derived from chemically modified PET bottles

The accessibility of newly affordable materials has drawn significant attention to the anion exchange membrane (AEM) technology. However, developing a high-performance AEM with excellent hydroxide conductivity and long-term durability is still challenging. The present work aims to improve the overall properties of AEMs synthesized by chemical modification of Polyethylene terephthalate (PET) bottles as the starting material. The modified PET structure was confirmed using IR, NMR, and HPLC-ESIMS analyses. AEMs were developed by incorporating quaternary ammonium (QA) functional groups into the modified PET structure, necessary for transporting anionic species (OH−). In addition, TiO2 nanoparticles grafted with silane coupling agents containing amine functional groups were synthesized via the sol-gel method and embedded in the polymer matrix. Then, the prepared nanocomposite membranes were thoroughly characterized, and the results displayed an overall improvement in the membrane's physicochemical properties. The composite membrane with 3wt% content of nanoparticle (NC3 %/M-PETm) showed remarkable conductivity, reaching 126 mS/cm at 80 °C, doubling the value of pristine membranes (64 mS/cm) while also displaying alkaline stability, retaining up to 92.2 % of conductivity after 20 days in harsh 2 M KOH at 80 °C. These results proved the suitability of these membranes for electrochemical energy applications. This innovative approach offers potential cost savings in preparing the new membranes while aligning with sustainable and circular economy principles.

Exploring pH-Triggered Lamellar to Cubic Phase Transition in 2-Hydroxyoleic Acid/Monoolein Nanodispersions: Insights into Membrane Physicochemical Properties.

Self-assembled lipid nanoparticles (LNPs) are essential nanocarriers for drug delivery. Functionalization of LNPs with ionizable lipids creates pH-responsive nanoparticles that change structures under varying pH conditions, enabling pH-triggered drug release. Typically, bicontinuous cubic phase nanoparticles (Cubosomes) and lamellar structured vesicles (Liposomes) differ in lipid packing statuses, affecting drug release and cellular uptake. However, most research predominantly focuses on elucidating lattice structure changes of these LNPs without a deep investigation of lipid-membrane properties. Addressing this gap, our study delves into the lipid-membrane physicochemical property variations during the lamellar-to-cubic phase transition. Here, we prepared pH-responsive LNPs using 2-hydroxyoleic acid/monoolein (2-OHOA/MO) binary components. Small-angle X-ray scattering (SAXS) revealed a phase transition from lamellar vesicles (Lα) to cubosomes (Im3m/Pn3m) with pH reduction. Laurdan and 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescence probes tracked the lipid-water interfacial polarity and lipid-membrane fluidity variations during the phase transition. Raman spectroscopy provided further insights into lipid-membrane lipid chain packing and chain torsion. We observed that the changes in lipid-membrane properties coincided with the lamellar-to-cubic phase transition, emphasizing the interplay between the phase structure and lipid-membrane behaviors in the 2-OHOA/MO system. This study provides insights into the lipid-membrane properties variation during the pH-triggered phase transition in the 2-OHOA/MO system, guiding future research toward more effective and reliable pH-responsive drug delivery platforms.

Derivatives of Pyrimidine Nucleosides Affect Artificial Membranes Enriched with Mycobacterial Lipids.

The mechanisms of action of pyrimidine nucleoside derivatives on model lipid membranes of various compositions were studied. A systematic analysis of the tested agents' effects on the membrane physicochemical properties was performed. Differential scanning microcalorimetry data indicated that the ability of nucleoside derivatives to disorder membrane lipids depended on the types of nucleoside bases and membrane-forming lipids. The 5'-norcarbocyclic uracil derivatives were found to be ineffective, while N4-alkylcytidines demonstrated the most pronounced effects, significantly decreasing the dipalmitoylphosphocholine melting temperature and cooperativity of phase transition. The elongation of hydrophobic acyl radicals potentiated the disordering action of N4-alkylcytidines, while an increase in hydrophilicity due to replacing deoxyribose with ribose inhibited this effect. The ability of compounds to form transmembrane pores was also tested. It was found that 5-alkyluridines produced single, ion-permeable pores in phosphatidylglycerol membranes, and that methoxy-mycolic acid and trehalose monooleate potentiated the pore-forming activity of alkyloxymethyldeoxyuridines. The results obtained open up perspectives for the development of innovative highly selective anti-tuberculosis agents, which may be characterized by a low risk of developing drug resistance due to the direct action on the membranes of the pathogen.

Resolving the interactions between hydrophilic CdTe quantum dots and positively charged membranes at the nanoscale

The use of quantum dot nanoparticles (QDs) in bio-applications has gained quite some interest and requires a deep understanding of their interactions with model cell membranes. This involves assessing the extent of nanoparticle disruption of the membrane and how it depends on both nanoparticle and membrane physicochemical properties. Surface charge plays an important role in nanoparticle adsorption, which is primarily driven by electrostatic interactions; yet, once adsorbed, most reported works overlook the subsequent spatial nanoparticle insertion and location within the membrane. There is therefore a need for studies to assess the mutual role of membrane and nanoparticle charge into membrane structure and stability at the nanoscale, with a view to better design and control the functionality of these nanomaterials. In this work, we have resolved the extent of the interactions between hydrophilic, negatively charged CdTe QDs and positively charged lipid bilayers. A multiscale combination of surface-sensitive techniques enabled probing how surface charge mediates QD adsorption and membrane reorganization. Increasing membrane surface charge results into a larger adsorption of oppositely charged QDs, concomitantly inducing structural changes. Hydration of the membrane hydrophobic parts by QDs goes deeper into the inner leaflet with increasing membrane charge, resulting in supported lipid bilayers with decreased nanomechanical stability.

Tailoring physicochemical properties of quaternized polystyrene-ethylene/butylene-styrene membrane for enhanced pervaporation desalination

Pervaporation offers unique advantages for desalination of hypersaline water using highly hydrophilic and selective membrane. Positively charged membrane is superior in repelling cations and preventing scaling through electrostatic repulsion. This study investigates the quaternization and crosslinking of block copolymer styrene-ethylene-butylene-styrene (SEBS) membrane and explores the potential of quaternized membrane for pervaporation desalination. A one-step immersion process was proposed to easily adjust the physicochemical properties of membrane using trimethylamine (TMA) and N,N,N′,N′-tetramethyl-1,6-hexanediamine (TMHDA) for ammonium grafting and crosslinking. Compared to the quaternization with TMA or TMHDA alone, the combination of TMA and TMHDA produces a synergistic effect, improving crosslinking efficiency and facilitating the grafting reaction. This results in high ion exchange capacity (IEC) values and a transformation of microphase separation structure with more interconnected hydrophilic domains. An ultrahigh water permeability coefficient of 0.6 × 106–1.2 × 106 Barrer and highly intrinsic salt rejection were obtained in treating 3.5–20 wt% NaCl solution. The thin film composite QEBS/nylon membranes showed a superior water flux of 116.5 kg·m−2·h−1 and salt rejection of >99.99 % in desalinating 5 wt% NaCl solution at 85 °C. Additionally, the membrane exhibited excellent long-term performance stability and resistance to acid and alkali environment, showing great potential for desalination of hypersaline water.

Divalent cations promote huntingtin fibril formation on endoplasmic reticulum derived and model membranes

Huntington's Disease (HD) is caused by an abnormal expansion of the polyglutamine (polyQ) domain within the first exon of the huntingtin protein (htt). This expansion promotes disease-related htt aggregation into amyloid fibrils and the formation of proteinaceous inclusion bodies within neurons. Fibril formation is a complex heterogenous process involving an array of aggregate species such as oligomers, protofibrils, and fibrils. In HD, structural abnormalities of membranes of several organelles develop. In particular, the accumulation of htt fibrils near the endoplasmic reticulum (ER) impinges upon the membrane, resulting in ER damage, altered dynamics, and leakage of Ca2+. Here, the aggregation of htt at a bilayer interface assembled from ER-derived liposomes was investigated, and fibril formation directly on these membranes was enhanced. Based on these observations, simplified model systems were used to investigate mechanisms associated with htt aggregation on ER membranes. As the ER-derived liposome fractions contained residual Ca2+, the role of divalent cations was also investigated. In the absence of lipids, divalent cations had minimal impact on htt structure and aggregation. However, the presence of Ca2+ or Mg2+ played a key role in promoting fibril formation on lipid membranes despite reduced htt insertion into and association with lipid interfaces, suggesting that the ability of divalent cations to promote fibril formation on membranes is mediated by induced changes to the lipid membrane physicochemical properties. With enhanced concentrations of intracellular calcium being a hallmark of HD, the ability of divalent cations to influence htt aggregation at lipid membranes may play a role in aggregation events that lead to organelle abnormalities associated with disease.

Insights on the G protein-coupled receptor helix 8 solution structure and orientation using a neurotensin receptor 1 peptide.

G-protein coupled receptors (GPCRs) are the largest class of membrane proteins encoded in the human genome with high pharmaceutical relevance and implications to human health. These receptors share a prevalent architecture of seven transmembrane helices followed by an intracellular, amphipathic helix 8 (H8) and a disordered C-terminal tail (Ctail). Technological advancements have led to over 1000 receptor structures in the last two decades, yet frequently H8 and the Ctail are conformationally heterogeneous or altogether absent. Here we synthesize a peptide comprising the neurotensin receptor 1 (NTS1) H8 and Ctail (H8-Ctail) to investigate its structural stability, conformational dynamics, and orientation in the presence of detergent and phospholipid micelles, which mimic the membrane. Circular dichroism (CD) and nuclear magnetic resonance (NMR) measurements confirm that zwitterionic 1,2-diheptanoyl-sn-glycero-3-phosphocholine is a potent stabilizer of H8 structure, whereas the commonly-used branched detergent lauryl maltose neopentyl glycol (LMNG) is unable to completely stabilize the helix - even at amounts four orders of magnitude greater than its critical micellar concentration. We then used NMR spectroscopy to assign the backbone chemical shifts. A series of temperature and lipid titrations were used to define the H8 boundaries as F376-R392 from chemical shift perturbations, changes in resonance intensity, and chemical-shift-derived phi/psi angles. Finally, the H8 azimuthal and tilt angles, defining the helix orientation relative of the membrane normal were measured using paramagnetic relaxation enhancement NMR. Taken together, our studies reveal the H8-Ctail region is sensitive to membrane physicochemical properties and is capable of more adaptive behavior than previously suggested by static structural techniques.

Targeted Anthocyanin Enrichment of Cranberry Juice by Electrodialysis with Filtration Membranes: Impact of Filtration Membrane Physicochemical Properties and Predictive Statistical Models.

To optimize cranberry juice enrichment, correlation between physicochemical properties of filtration membranes (FM) and anthocyanin migration was investigated during electrodialysis with filtration membranes (EDFM) using redundancy (RDA) and multivariate regression (MRGA) analyses. Six polyether sulfone (PES) and polyvinylidene fluoride (PVDF) membranes with molecular weight cut-offs between 150 and 500 kDa, commercially available at large scale, were characterized in terms of nine physicochemical characteristics and used for EDFM. The highest migration of total anthocyanin was obtained with PVDF 250 kDa, with a global migration rate of 3.5 ± 0.4 g/m2·h. RDA showed that two FM properties (mesopore porosity and hydrophilic porosity) were significantly negatively correlated to the anthocyanin's migration and explained 67.4% of their total variation in migration. Predictive MRGA models were also developed for each anthocyanin based on these significant FM properties. A combination of intermolecular interactions may lead to binding in a cooperative and synergistic mode and hinder the anthocyanin migration.

Pervaporation Membranes Based on Polyelectrolyte Complex of Sodium Alginate/Polyethyleneimine Modified with Graphene Oxide for Ethanol Dehydration.

Pervaporation is considered the most promising technology for dehydration of bioalcohols, attracting increasing attention as a renewable energy source. In this regard, the development of stable and effective membranes is required. In this study, highly efficient membranes for the enhanced pervaporation dehydration of ethanol were developed by modification of sodium alginate (SA) with a polyethylenimine (PEI) forming polyelectrolyte complex (PEC) and graphene oxide (GO). The effect of modifications with GO or/and PEI on the structure, physicochemical, and transport characteristics of dense membranes was studied. The formation of a PEC by ionic cross-linking and its interaction with GO led to changes in membrane structure, confirmed by spectroscopic and microscopic methods. The physicochemical properties of membranes were investigated by a thermogravimetric analysis, a differential scanning calorimetry, and measurements of contact angles. The theoretical consideration using computational methods showed favorable hydrogen bonding interactions between GO, PEI, and water, which caused improved membrane performance. To increase permeability, supported membranes without treatment and cross-linked were developed by the deposition of a thin dense layer from the optimal PEC/GO (2.5%) composite onto a developed porous substrate from polyacrylonitrile. The cross-linked supported membrane demonstrated more than two times increased permeation flux, higher selectivity (above 99.7 wt.% water in the permeate) and stability for separating diluted mixtures compared to the dense pristine SA membrane.

Bacterial Glycolipid Acting on Protein Transport Across Membranes.

The process of protein transport across membranes involves a variety of factors and has been extensively investigated. Traditionally, proteinaceous translocons and chaperones have been recognized as crucial factors in this process. However, recent studies have highlighted the significant roles played by lipids and a glycolipid present in biological membranes in membrane protein transport. Membrane lipids can influence transport efficiency by altering the physicochemical properties of membranes. Notably, our studies have revealed that diacylglycerol (DAG) attenuates mobility in the membrane core region, leading to a dramatic suppression of membrane protein integration. Conversely, a glycolipid in Escherichia coli inner membranes, named membrane protein integrase (MPIase), enhances integration not only through the alteration of membrane properties but also via direct interactions with membrane proteins. This review explores the mechanisms of membrane protein integration mediated by membrane lipids, specifically DAG, and MPIase. Our results, along with the employed physicochemical analysis methods such as fluorescence measurements, nuclear magnetic resonance, surface plasmon resonance, and docking simulation, are presented to elucidate these mechanisms.

Concentration-Dependent Effects of Curcumin on Membrane Permeability and Structure.

Growing evidence suggests that many bioactive molecules can nonspecifically modulate the physicochemical properties of membranes and influence the action of embedded membrane proteins. This study investigates the interactions of curcumin with protein-free model membranes consisting of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and DOPC with cholesterol (4/1 mol ratio). The focus is on the capability of curcumin to modify membrane barrier properties such as water permeability assayed through the droplet interface bilayer (DIB) model membrane. For pure DOPC, our findings show a concentration-dependent biphasic effect: a reduction in water permeability is observed at low concentrations (up to 2 mol %), whereas at high concentrations of curcumin, water permeability increases. In the presence of cholesterol, we observed an overall reduction in water permeability. A combination of complementary experimental methods, including phase transition parameters studied by differential scanning calorimetry (DSC) and structural properties measured by attenuated total reflectance (ATR)-FTIR, provides a deeper understanding of concentration-dependent interactions of curcumin with DOPC bilayers in the absence and presence of cholesterol. Our experimental findings align with a molecular mechanism of curcumin's interaction with model membranes, wherein its effect is contingent on its concentration. At low concentrations, curcumin binds to the lipid-water interface through hydrogen bonding with the phosphate headgroup, thereby obstructing the transport of water molecules. Conversely, at high concentrations, curcumin permeates the acyl chain region, inducing packing disorders and demonstrating evidence of phase separation. Enhanced knowledge of the impact of curcumin on membranes, which, in turn, can affect protein function, is likely to be beneficial for the successful translation of curcumin into effective medicine.

Porous Zn-TCPP interlayer with active reaction sites modulates membrane physicochemical properties to improve nanofiltration performance

For nanofiltration (NF) membranes, constructing the interlayer between the substrate and polyamide (PA) layer could balance the trade-off effect between the selectivity and permeability. However, the influencing mechanism of the interlayer to the PA layer is mostly indirect, and how to regulate the physicochemical properties of the PA layer to improve the membrane property remains to be investigated. In this study, porous Zn-TCPP nanosheets with active reaction sites were used to construct interlayer and directly participated in interfacial polymerization (IP) reaction through the edge COOH of nanosheets reacting with piperazine (PIP) to further regulate PA layer physicochemical properties. Controlling the amount of nanosheets involved in the reaction, NF membranes with striated Turing structures, higher negatively charged surface and larger effective filtration area were obtained. The NF membrane permeability with Zn-TCPP interlayer was significantly improved by 123 % while the Cl−/SO42− selectivity was greatly enhanced to 72.69, meanwhile it showed excellent performance stability. This study presents a new perspective that the interlayer can modulate the NF membrane physicochemical properties to improve its performance by directly participating in the IP reaction.

Simple and low-cost anion exchange membrane based on PVA and PDC for acid recovery by diffusion dialysis

Anion exchange membranes were prepared by a simple method on the basis of polyvinyl alcohol (PVA) and 1,4-Piperazinedicarboxaldehyde (PDC). A network structure was formed in the membranes by cross-linking between PVA and PDC. The mechanical stability and acid stability the prepared membranes was tested. The TS value was tested as 17.5–37.8 MPa, Eb was 120.4–54.7% and the mass retention in the acid environment was 98.4–97.2%. Meanwhile, the physicochemical properties of membranes, such as thermogravimetric analysis (TGA), water absorption (WR), ion exchange capacity (IEC) and linear expansion rate (LER). WR was 106.9–136.7%, IEC was 1.03–1.55 mmol/g, and LER was 37.93–33.33%. In practical application, diffusion dialysis (DD) performance of membranes were tested. In DD test, the acid dialysis coefficient (UH+) was 17.5–27.9 × 10−3 m/h, and the separation factor (S) was 31.25–23.38. The UH+ and S were all higher than commercial membrane DF-120 (UH+ is 9 × 10−3 m/h and S is 18.00). Results were shown that the comprehensive properties of membranes were good. Therefore, the prepared membranes had broad application prospects for acid recovery by diffusion dialysis.

Evaluation of Lipids for the Study of Photosynthetic Membranes.

The biological role of lipids goes far beyond the formation of a structural membrane bilayer platform for membrane proteins and controlling fluxes across the membranes. For example, in photosynthetic thylakoid membranes, lipids occupy well-defined binding niches within protein complexes and determine the structural organization of membrane proteins and their function by controlling generic physicochemical membrane properties. In this chapter, two-dimensional thin-layer chromatography (2D TLC) and gas chromatography (GC) techniques are presented for quantitative analysis of lipid classes and fatty acids in thylakoid membranes. In addition, lipid extraction methods from isolated thylakoid membranes and leaves are described together with a procedure for the derivatization of fatty acids to fatty acid methyl esters (FAME) that is required for GC analysis.

Dual-functional Polyvinylidene Fluoride Beta Cyclodextrin-Grafted Graphene Oxide Mixed Matrix Membranes for Removal of Anionic Azo Dyes

Mixed matrix PVDF polymeric membranes were incorporated with β–CD grafted graphene oxide (GO) nanocomposites (β–CD-g-GO) via nonsolvent induced phase separation method and used in the adsorption of congo red (CR) and methyl orange (MO) dyes. The incorporation of β–CD-g-GO (6 wt%) was found to improve the membrane physico-chemical properties and performance. The water content was increased by 24.26%, contact angle reduced from 84.17 to 62.97° while flux increased from 12.42 to 275.03 L m−2 h−1 bar−1. The membranes were able to remove 100% of CR at pH 7 and 99.4% of the MO dye at pH 5 within 240 min. The adsorption kinetics and isotherms were well fitted to the pseudo second-order kinetic model and Freundlich isotherm model respectively. These results indicated that the adsorption of both dyes occurred via chemisorption and in a multilayer on a heterogeneous surface of the membranes. According to these findings, it was concluded that the adsorption mechanism was due to hydrogen bonding interactions between nitrogen and hydroxyl groups, inclusion complexation introduced by β–CD molecules and electrostatic interactions, between the negatively charged oxygen-containing groups of the membrane and the positively charged nitrogen and azo-linkages of the dye molecules. PVDF/β–CD-g-GO membranes have shown excellent adsorption efficiency towards azo dyes. This work indicates that the embedding of adsorptive GO-β–CD nanocomposites in PVDF membranes can remove anionic dyes from wastewater treatment.

Transformation of brackish water Reverse Osmosis membranes to nanofiltration & ultrafiltration membranes by NaOCl treatment: Kinetic and characterization studies

Thin Film Composite (TFC) Reverse Osmosis (RO) membranes used in desalination, reach their End-of-Life (EoL) due to fouling and chemical degradation and pose disposal problem. Their lifetime can be increased by converting them into Ultrafiltration (UF) or Nanofiltration (NF) membranes. The present work demonstrates a systematic methodology in terms of ‘ppm-h/ppm∙h exposure’ to chemically convert brackish water RO membranes into NF and subsequently into UF membranes using sodium hypochlorite (NaOCl). Post-performance studies of pure water flux, monovalent and bivalent salt rejection are carried at each treatment level. RO membrane has transformed into NF at 3000–3 ppm-h, 2000–6 ppm-h, 3000–6 ppm-h and in to UF membrane beyond 10000–3 ppm-h. Gradual changes in physicochemical properties of membrane during conversion are ascertained from Scanning Electron Microscope (SEM), Atomic Force Microscopy (AFM), Attenuated Total Reflection – Fourier Transform Infrared Spectroscopy (ATR-FTIR), X-Ray Photoelectron Spectroscopy (XPS), contact angle, zeta potential etc. The rate of chlorination of polyamide is derived using XPS elemental data from initial stages of NaOCl exposure, and rate of hydrolysis from the membrane resistance, and pH. The overall rate equation is combination of both. The membrane thickness calculated from the kinetics match with experimental data. This study gives account of depolymerization of polyamide upon NaOCl exposure (ppm-h) which can be useful in chemical recycling/treatment of EoL membranes on a plant scale.

STRUCTURAL AND FUNCTIONAL ASPECTS OF THE INTERACTIONS BETWEEN MEDICAL POLYMERS AND THE LIPOSOMS AND BACTERIAL CELLS

Polymers are widely applied as drug delivery systems and implant coatings. The review is devoted to the mechanisms of interaction of biomedical polymers with model cell membranes (liposomes) and real biological objects - bacterial cell surfaces. A comparative analysis of the composition, structure and surface charge of different types of biological membranes has been outlined. We consider the main methods and approaches for studying the effect of polymers on the structure and physico-chemical properties of membranes to uncover adsorption, defects in the bilayer, violations of the integrity of the bilayer, changes in cell morphology, etc. The correlation between the observed effects on model and real objects is analyzed. One of the important tasks of the review is to discover the key polymer’s characteristic (structure, size, charge, etc.) for the design of new high-molecular compounds with specified biological properties.

Graphene oxide composited with different size of organic molecules for hydrogen isotopic water separation in membrane distillation

Developing an efficient light water/tritiated water (H2O/HTO) separation process to meet environmental regulations is important in the nuclear energy field. The membrane distillation processes for the separation of H2O/D2O (deuteriated water), which is usually served as the laboratory model process for H2O/HTO separation, showed good separation performance with graphene oxide (GO)-based membranes. Here, the approach to enhance the H2O/D2O separation performance was explored through regulating interlayer spacing and physicochemical properties of membranes, for which two types of GO membranes were prepared and applied in air-gap membrane distillation: (i) small molecules of urea (UR) or ethanediamine (EDA) were cross-linked with GO platelets to obtain GO-framework (GOF) membranes designated as GO-UR or GO-EDA with varied interlayer spacing. The GO-EDA membrane with a permeation flux of 0.95 L·m−2·h−1 gave higher separation performance than the pristine GO membrane; (ii) macromolecules of hydrophilic polyvinyl alcohol (PVA) or hydrophobic polymethyl methacrylate (PMMA) were intercalated into GO laminates to adjust interlayer spacing and physicochemical properties of membranes. The resultant GO-PVA membrane exhibited a higher permeation flux of 0.94 L·m−2·h−1 and similar separation factor compared with the pristine GO membrane. Moreover, long-term process stability of H2O/D2O separation in membrane distillation was demonstrated using GO-EDA membrane for a 28-h process. Therefore, the results demonstrated that regulating interlayer spacing and physicochemical properties of membranes can provide a facile route to improve performance of GO-based membrane distillation processes for the separation of H2O/D2O, which may be applied to H2O/HTO separation process needed for the treatment of tritiated water in the nuclear energy field.

Insight into polydopamine coating on microfiltration membrane with controlled surface pore size for enhanced membrane rejection

Membrane modification with polydopamine (PDA) is a common practice to enhance membrane selectivity and improve membrane compatibility with nanoparticles or thin films. Depending on the membrane surface properties, dopamine can deposit or penetrate into microporous membranes, leading to alteration in the membrane's physicochemical properties and consequently its performance. In this study, microfiltration (MF) polyethersulfone membranes with varying surface pore sizes were fabricated by manipulating the precasting time (solvent evaporation time of 3s, 15s, 30s and 60s) prior to non-solvent induced phase separation (NIPS) process. Notably, the coating of PDA slightly reduced the membrane's surface pore size and membrane's porosity. M60 membrane which possessed the smallest mean surface pores (∼300 nm), exhibited PDA clusters predominantly formed on top of the membrane surface. With an increase in surface pore size, dopamine can penetrate the porous structure of the MF membrane, leading to the polymerization of dopamine into PDA aggregates on both the membrane surface and inner pores. The M30 membrane had the largest surface pore size (∼500 nm), showing the formation of large PDA globules in the finger-like pores. The membrane (M30P) experienced significant narrowing of the inner pores, resulting in reduced water permeability. Overall, all PDA-coated membranes exhibited improved sucrose rejection (85–95%) compared to the uncoated ones (64–83%). These finding provides insight into the polymerization mechanism of dopamine on porous membranes prior to the incorporation of nanomaterials or thin film coating.