Microstructure Of Membranes Research Articles

Perfluorosulfonic Acid Polymer Membranes: Microstructure and Basic Functional Properties

The development of modern technologies and the requirements that are imposed on the ecology of production require the producing of new polymeric ion-exchange membrane materials with a set of given properties. Such materials are used in systems of separation and purification of liquids and gases, chemical and electrochemical synthesis, in alternative energy. Membranes based on perfluorosulfonic acid (PFSA) polymers have a set of characteristics necessary for their practical application: good transport properties, strength, elasticity and chemical stability. In this review, the microstructure of PFSA membranes, its change upon sorption of water and solvents, the features of ion and gas transport, mechanical properties as well as the dependence of a number of parameters on the chain length and ionic form of the polymer are discussed.

Simultaneous Regulation of Surface Properties and Microstructure of Graphene Oxide Membranes for Enhanced Nanofiltration Performance.

The surface properties and microstructure of graphene oxide (GO)-based membranes are both crucial for enhanced nanofiltration performance. Herein, a GO nanofiltration membrane is fabricated with regulatable surface properties and microstructure via a facile two-step impregnation in KOH and following HCl aqueous solutions. The type and number of oxygen-containing groups in GO membranes change with fewer C-O-C/C-OH and C═O but more COOH groups, and they are readily regulated by alkaline treatment time, which enables enhanced surface hydrophilicity and larger surface ζ potentials. Meanwhile, a few tiny defects are present in the GO sheets, which could increase the number of pores and decrease the length of water nanochannels. Such surface properties and microstructure together determine the excellent nanofiltration performance of the GO membranes with fast and selective water permeation, e.g., ∼99.5% rejection toward CBB G250 and flux of 56.9 ± 1.0 L m-2 h-1. This work provides insights into the design of high-performance two-dimensional laminar membranes.

Highly permeable PA@GO loose nanofiltration membranes enabled by hierarchical transport channels for efficient dye removal

Graphene oxide (GO) membranes exhibit ultrafast water permeation properties, which have been employed in various membrane-based separations including nanofiltration for dye removal from textile wastewater. However, it’s still a great challenge to achieve precise control over the microstructure of GO membranes and obtain ultrathin GO membranes with exceptional separation efficiency and robust membrane structure. Herein, in-situ confined interfacial polymerization (IP) is proposed for fabricating loose polyamide (PA)@GO hybrid membranes with high permeance and dye rejection as well as robust membrane stability. A new diamine of sulfadiazine (SA) with intrinsic hydrophilic and conjugated sulfonamide groups is employed as cross-linker of GO membranes and monomer of PA in IP process, simultaneously. PA is in-situ synthesized in confined GO interlayer via IP process and intercalated into GO interlayer, which enlarges the interlayer spacing of GO membranes gradiently. The combination of hydrophilic PA nanofiltration layer on GO membrane surface and the PA intercalated GO membrane with varying interlayer spacing creates hierarchical transport channels for water molecules, which contributes to the high water permeance. Moreover, the less reactive SA monomer endows PA@GO selective layer with appropriate negative charge and loose transport channels, which contributes to both of high permeance and dye rejection due to Donnon effect and size exclusion effect. The PA@GO hybrid membrane exhibits high permeance of 75.5 L/(m2·h·bar) with TB dye rejection of 99.8 %, and exhibits low NaCl rejection of 11.6 %. Moreover, PA@GO hybrid membrane shows good fouling resistance and long-term stability as well as stable separation performance under harsh conditions. Both of high permeance and dye rejection of PA@GO hybrid membrane suggests that the integration of PA nanofiltration layer and GO membrane via in-situ confined interfacial polymerization can achieve the delicate control over the interlayer channel structure and the physicochemical properties of the membrane surface of GO membranes, which offers a promising method to break through the trade-off effect between permeability and selectivity of GO membranes.

Recent Advances in the Selective Transport and Recovery of Metal Ions using Polymer Inclusion Membranes

AbstractPolymer inclusion membranes (PIMs) have gained significant attention in the field of metal separation and recovery due to their high selectivity, long service life, high stability, flexible design and low cost. Over the past 10 years, interest around PIMs has increased considerably; hence, the number of research papers has grown exponentially. This review provides the preparation methods and composition of PIMs, presents an overview of studies on PIMs reported since 2012, and discusses the relationship between the physicochemical properties of different types of membrane components and the microstructure, selectivity, transport performance and stability of prepared PIMs. This review also elucidates the metal transport mechanism at the interface and interior of PIMs and summarizes the modification and separation intensification methods of PIMs. Additionally, the structure and stability of PIM relative to other liquid membranes are also discussed. Finally, the existing challenges and perspectives of PIMs in the field of metal separation and recovery are proposed and highlighted. Notably, the need for highly selective and low‐cost carriers, a deeper understanding of membrane microstructure and separation mechanisms, and strategies for promoting widespread adoption of polymer inclusion membrane‐electrodialysis technology deserve particular consideration, which are of guiding significance for accelerating the industrialization process of PIMs.

Tailoring the microstructure of silver nanoparticle-intercalated graphene oxide membranes for desalination by pervaporation: Water permeation, membrane fouling, and antibacterial property

Low water flux has limited pervaporation (PV) from being applied in industrial-scale desalination. In this work, membranes embedded with silver nanoparticles (Ag NPs)-intercalated graphene oxide (GO) are proposed and prepared through two methods (self-assembly and blend) to improve membrane water permeation and fouling resistance. The Cs/Ag NP/GO@BM exhibited superior water permeation among the prepared membranes for the following reasons: 1) Water adsorption was improved by both the surface and interlamellar space of the blended matrix; 2) The intercalation effect of Ag NPs and looser stacking structure created more favorable diffusion pathways for water transportation. In the brine fouling test, the water flux of the membrane declined, while the fouling was reversible by NaOH cleaning with a high flux recovery rate (>97 %). Additionally, the Cs/Ag NP/GO@BM exhibited a remarkable antibacterial rate of 99.6 % against E. coli, benefiting from the synergistic inhibiting effect of GO and Ag NPs.

Low-temperature sintering of porous SiC ceramic membrane with industrial-grade sodium meta-aluminate as a sintering additive

Silicon carbide (SiC) ceramic membranes require high sintering temperatures (greater than 1800 °C), which consume substantial energy and increase the production costs. In this study, we report the successful preparation of a low-cost, high-performance SiC ceramic membrane at a low temperature of 800 °C using industrial-grade sodium meta-aluminate (NaAlO2) as a sintering agent. The effects of sintering temperature and NaAlO2 content on the microstructure, porosity, bending strength, pore size, and pure water permeability of the SiC membranes were investigated systematically. The results indicate that the optimal sintering temperature and NaAlO2 content are 800 °C and 10 wt%, respectively. The SiC membrane prepared under these conditions exhibited an average pore size of 2.57 μm, a porosity of 52.07%, a bending strength of 50.2 ± 0.41 MPa, and a very high pure water permeability of 103.3 m3 m−2 h−1 bar−1. Additionally, the SiC membrane prepared in this study also exhibited good chemical stability and could be used in acid and alkali environments for long periods. These results highlight the potential of SiC membranes in various applications, particularly in water treatment and filtration application. The findings of this study are useful to enrich membrane technology knowledge and guide future research and development of related technologies.

Polyvinyl alcohol composite gel membrane modified by natural polysaccharide and waterborne polyurethane

AbstractA new composite gel material was obtained by blending polyvinyl alcohol (PVA) aqueous solution with sodium alginate (SA), sodium carboxymethyl cellulose (CMC‐Na), waterborne polyurethane (WPU), and polyvinylpyrrolidone (PVP). Titanium dioxide nanoparticles (nTiO2) were doped as an antibacterial agent. The liquid composite could to form a transparent protective gel membrane. The microstructure of the gel membrane was observed via scanning electron microscopy, and the intermolecular interaction was investigated by total reflection infrared spectroscopy. The results demonstrated a homogeneous phase and significant hydrogen bonding between chain segments. The best results indicated that the equilibrium swelling rate increased from 147% to 170%, the 3‐h water vapor transmission rate increased from 279.41 g/m2∙day to 374.75 g/m2∙day, and the water contact angle increased from 16.8° to 60.7°, relative to the PVA substrate. The properties of this composite gel material suggest possible biomedical usage, particularly in skin and wound protection scenarios.Highlights A novel gel film‐forming material consisting of a viscous liquid is prepared. Adding polysaccharides modifiers resulted in significant improvements of the performance. The bacteriostatic and antihemorrhagic properties are introduced to the material. Low‐irritating materials were used to prepare the gel material.

The effect of high-temperature proton exchange membranes with microphase separation structure on phosphoric acid loss

Phosphoric acid (PA) leakage of PA-doped high-temperature proton exchange membranes (HT-PEMs) is pivotal for its practical application under working conditions. Here, to enhance the PA retention of HT-PEMs, the concept of microphase separation regulated by flexible long aliphatic side-chain was introduced into poly(isatin-co-p-terphenyl-imidazole) matrix (PITI-CmQ90) via direct superacid-catalyzed copolymerization from N-alkylated isatin monomer. The designed PITI-CmQ90 membranes illustrate obvious microphase separation and larger ionic domain confirmed via Small-angle X-ray scattering (SAXS) analysis suggesting wider proton transport channels. Notably, PA/PITI-C6Q90 membrane exhibits the best PA retention ability under relative humidity (RH) cycle tests at different temperatures, which mainly attributed to the excellent PA interaction through moderate ion aggregation in the microphase-separated PEM matrix verified by solid 31P NMR. As a result, the corresponding MEA displays the most durable single-cell performance under a step-V procedure from 1.0 V to 0.1 V cycle experiments at different temperatures. Therefore, the idea of microphase separation structure on PA retention mentioned in this work helps to study the ionic-pairs interactions from the perspective of membrane microstructure and provide a new strategy to enhance the durability of PEMs.

Effect of cold storage on human milk fat globule membrane: Microstructure and proteomic analysis

We investigated the changes in microstructure and composition of milk fat globule membrane (MFGM) in fresh human milk under different storage temperatures (-18, -3, -0.5, and 4 °C). Freezing at -18 °C resulted in the formation of ice crystals that ruptured the MFGM, leading to aggregation and increased particle size, which could potentially impact lipid digestion and absorption in infants. Conversely, storage at -3, -0.5, or 4 °C were more favorable for maintaining the stability of MFGM structure without ice crystals formation. Notably, -3 °C exhibited the highest preservation of MFGM integrity. Label-free proteomics analysis identified a total of 1525 different MFGM proteins in the initial sample (0 day) and samples preserved at varying temperatures (-18, -3, -0.5, and 4 °C) for a duration of 4 days. Principal component analysis and hierarchical clustering analysis demonstrated two distinct clusters of MFGM proteins across the different storage temperatures. Specifically, MFGM proteomic characteristics at -18 and -3 °C showed more similarities and clustered together with the 0-day samples, while -0.5 and 4 °C formed a separate cluster. Comparative analysis with the control sample (day 0) highlighted significant changes in 202 proteins, most of which played essential roles in binding, catalytic activities, and pathways related to protein, lipid, and fatty acid metabolism. Our findings highlight the superior ability of -3 °C to inhibit bacterial growth compared to 4 and -0.5 °C, and to preserve the microstructure of milk fat globules compared to -18 °C. Thus, for household storage up to 4 days, we recommend a temperature of -3±1 °C, considering temperature fluctuations in domestic refrigerators.

Performance analysis and design for an asymmetric membrane of a hollow fiber hemodiafilter with a two-layer membrane model

A hemodiafilter model including the two-layer membrane model based on the irreversible thermodynamics was first introduced, which considers the convective solute flux besides the diffusive solute one. This model makes it possible to analyze the solute transfer of an asymmetric membrane which is assumed to be equivalent to the two-layer membrane consisting of a skin layer and a porous support layer. Verification was performed with in-vitro data on commercial hemodiafilters for solutes of middle molecular weight, and the results were good in solute clearances. In order to increase the clearance of middle molecular weight solutes in high-performance membranes, it is necessary to increase the solute diffusive permeability in the support layer. Through the model simulation, the author was able to quantitatively grasp the relationship between myoglobin clearance versus membrane microstructure parameters and membrane thickness and to clarify the direction of increase in solute transfer amount. In addition, it made clear that the convective solute transfer is more predominant than the diffusive solute one in ultrafiltration effect of the hemodiafilter with the asymmetric membrane.

Effect of pendant ester groups on gas transport property of 6FDA-BAPP/6FAP copolyimide membrane

Despite the various methods that have been developed, controlling the microstructure of polyimide membranes to achieve excellent separation performance based on target gases remains a challenge. One such method involves rearranging polyimides containing ortho-hydroxyl groups into polybenzoxazoles at temperatures above 400 °C, which can effectively distort the backbones and improve gas diffusion. However, this approach is limited by the extremely high conversion temperatures required and low conversion degrees achieved. The esterification process of the polyimide, which contains ortho-hydroxyl groups to the imide ring, represents a simple and effective approach to enhance the membrane's competitiveness in gas separation without undergoing thermal rearrangement at high temperatures. The polyimide was prepared by the polycondensation of 4,4'-(Hexafluoro isopropylidene) diphthalic anhydride (6FDA), 2,2-double (4,4-amino phenoxy) propane (BAPP), and 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane (6FAP). Microstructures and gas transport coefficients were analyzed when the esterification of 6FDA-BAPP/6FAP was conducted using acetic anhydride and caproic anhydride. In CO2/N2 separation, a-6FDA-BAPP/6FAP exhibits CO2 permeability of 1279.41 ± 66.93 Barrer and perm-selectivity of 40.80 ± 2.27, owing to the significantly improved affinity to CO2. The membrane of c-6FDA-BAPP/6FAP exhibit the further improved CO2 permeability and deteriorated perm-selectivity, due to a leveling effect on the diffusion of CO2 and N2 caused by the pendant caproates with longer alkyl chains. The results confirmed that the gas separation performance of polyimide membrane containing ortho-hydroxyl groups is sensitive to the pendant group.

Effects of graphene oxide membrane thickness reduction on microstructure and crossflow separation performance in kraft black liquor dewatering

Reduced graphene oxide (rGO) membranes are emerging as viable candidates for energy-efficient fractionation of multicomponent biomass streams, such as kraft black liquor (BL). Increased fluxes in rGO membranes under crossflow conditions – while maintaining high solute rejections – are highly desirable for improving the economics of such processes. We have conducted a detailed experimental study of a series of rGO membranes with progressively lower thicknesses (from 130 nm to 40 nm). The influence of the membrane thickness and the membrane microstructure is analyzed in terms of its effects on water permeation flux, divalent salt rejection, and molecular weight cutoff (MWCO) measurements using dye molecules. A selected rGO membrane (70 nm) showing both high fluxes and rejections was scaled up to a 650 cm2 sheet and used for extended crossflow operation under real BL streams for more than 22 days. Techno-economic calculations reveal significant positive effects of membrane thickness reduction on the economics of BL dewatering.

Recent Strategies for Lithium-Ion Conductivity Improvement in Li7La3Zr2O12 Solid Electrolytes.

The development of solid electrolytes with high conductivity is one of the key factors in the creation of new power-generation sources. Lithium-ion solid electrolytes based on Li7La3Zr2O12 (LLZ) with a garnet structure are in great demand for all-solid-state battery production. Li7La3Zr2O12 has two structural modifications: tetragonal (I41/acd) and cubic (Ia3d). A doping strategy is proposed for the stabilization of highly conductive cubic Li7La3Zr2O12. The structure features, density, and microstructure of the ceramic membrane are caused by the doping strategy and synthesis method of the solid electrolyte. The influence of different dopants on the stabilization of the cubic phase and conductivity improvement of solid electrolytes based on Li7La3Zr2O12 is discussed in the presented review. For mono-doping, the highest values of lithium-ion conductivity (~10-3 S/cm at room temperature) are achieved for solid electrolytes with the partial substitution of Li+ by Ga3+, and Zr4+ by Te6+. Moreover, the positive effect of double elements doping on the Zr site in Li7La3Zr2O12 is established. There is an increase in the popularity of dual- and multi-doping on several Li7La3Zr2O12 sublattices. Such a strategy leads not only to lithium-ion conductivity improvement but also to the reduction of annealing temperature and the amount of some high-cost dopant. Al and Ga proved to be effective co-doping elements for the simultaneous substitution in Li/Zr and Li/La sublattices of Li7La3Zr2O12 for improving the lithium-ion conductivity of solid electrolytes.

Metabolism and Microstructure of the Small Intestine Wall in Patients With Colorectal Cancer

RELEVANCE In patients with colorectal cancer (CRC), the normal small intestine, located outside the pathological focus, undergoes changes that may be the cause of digestive dysfunction after radical surgery to remove the tumor.The assessment of metabolic and microstructural changes in the ileum mucosa in patients with colorectal cancer is necessary to correct the algorithms of postoperative therapy and enteral nutrition. Modern means of optical bioimaging are potentially capable of solving this complex diagnostic problem.AIM OF STUDY To study the features of metabolism and morphological structure of the wall of a conditionally normal small intestine in the mucosa in patients with stage 1–3 CRC using macro- FLIM and optical coherence tomography (OCT).MATERIAL AND METHODS The object of the study was the wall of the ileum (66 samples) from the mucosal side of patients with histologically confirmed CRC stages 1–3 with tumor location in the right sections of the colon. Eight samples were obtained from patients with stage 1 CRC, 38 samples were obtained from patients with stage 2 and 20 samples were obtained from patients with stage 3 tumor. The volume of surgical intervention is right-sided hemicolectomy with total mesocolonectomy, CME (D2 lymph node dissection). Fresh tissue samples were examined using fluorescent lifetime macroimaging (macro-FLIM ) and OCT, followed by histological analysis of the material.RESULTS According to a histological study in the small intestine of patients with stage 1 CRC, the mucosa is covered with a normal single-layer prismatic border epithelium. In the intestine samples of patients with stage 2 CRC, mucus hypersecretion with areas of fibrosis and vascular congestion was observed. At the 3rd stage of CRC, the mucous membrane of the small intestine was loose, with local thickenings, areas of fibrosis with severe leukostasis, and foci of atrophy. None of the samples showed histological signs of a malignant tumor.According to OCT data, in the mucous membrane of the small intestine in patients with the 1st and 2nd stages of CRC, the contours of the villi and, partially, the crypts were well visualized. The structure of the villi was smooth, not coarse, and the shape was regular. In patients with stage 3 CRC, the contours of the crypts and villi were indistinct. There were no differences in the OCT picture between histologic preparations in the 1st and 2nd stages of CRC: the structure of the villi of the small intestine was clear, the shape was unchanged. According to FLIM data, statistically significant differences were revealed in the mean fluorescence lifetime values of reduced nicotinamide dinucleotide (phosphate) NAD(P)H (τm) between 2nd and 3rd (p=0.031), 1st and 3rd (p=0.018) by CRC stages. At the 1st stage of CRC τm was 1.61 [1.30; 2.02] ns, at the 2nd stage 1.50 [1.36; 1.73] ns, at the 3rd stage 1.37 [1.22; 1.51] ns. The FLIM results suggest an increase in the role of glycolysis in enterocyte energy metabolism along with progression of the CRC stage.CONCLUSION In patients with cancer of the right colon, lesions of the microstructure of the mucous membrane were revealed in the ileum not affected by the malignancy. At the same time, the severity of microstructural disorders in the wall of the small intestine is associated with the stage of tumor development in the colon. Bioimaging technologies, namely, methods of optical coherence tomography and fluorescence lifetime macroimaging, made it possible to objectively display microstructural and metabolic disorders in the ileum wall. The data of optical colorectal tomography demonstrated differences in the structural picture of the intestinal villi in patients with stages 1–2 and 3 of colorectal cancer. Results of fluorescence lifetime macroimaging of the metabolic cofactor nicotinamide dinucleotide (phosphate) confirmed an increase in the role of glycolysis in the energy metabolism of enterocytes along with an increase in the stage of colorectal cancer. The identified disorders in the state of the small intestine develop in patients with colorectal cancer before surgery and are highly likely to be an important pathogenetic link of malabsorption in the postoperative period. If the hypothesis is confirmed, the developed algorithm for the complex diagnosis of microstructural and metabolic disorders in tissues will expand the possibilities for the rehabilitation of patients with cancer of the right colon.

Effects of the original state of sodium-based additives on microstructure, surface characteristics and filtration performance of SiC membranes

Sodium-contained compounds are promising sintering additives for the low-temperature preparation of reaction bonded SiC membranes. Although sodium-based sintering additives in various original states were attempted, their effects on microstructure and surface properties have rarely been studied. In this work, three types of sodium-based additives, including solid-state NaA zeolite residue (NaA) and liquid-state dodecylbenzene sulfonate (SDBS) and water glass (WG), were separately adopted to prepare SiC membranes, and the microstructure, surface characteristics and filtration performance of these SiC membranes were comparatively studied. Results showed that the SiC membranes prepared with liquid-state SDBS and WG (S-SDBS and S-WG) showed lower open porosity yet higher bending strength compared to those prepared with solid-state NaA (S-NaA). The observed differences in bending strength were further interpreted by analyzing the reaction process of each sintering additive and the composition of the bonding phase in the reaction bonded SiC membranes. Meanwhile, the microstructural differentiation was correlated to the original state of the additives. In addition, their surface characteristics and filtration performance for oil-in-water emulsion were examined and correlated to the membrane microstructure. The S-NaA samples showed higher hydrophilicity, lower surface roughness (1.80 μm) and higher rejection ratio (99.99%) in O/W emulsion separation than those of S-WG and S-SDBS. This can be attributed to the smaller mean pore size and higher open porosity, resulting from the originally solid-state NaA additives. Therefore, this work revealed the comprehensive effects of original state of sintering additives on the prepared SiC membranes, which could be helpful for the application-oriented fabrication by choosing additives in suitable state.

Attenuated thermal-regulated interfacial polymerization towards polyamide nanofiltration membrane with unprecedentedly enhanced performance

The desirable performance of polyamide membranes for seawater/brackish desalination seeks not only high water permeance, but also the pursuit of high salt rejection. However, few techniques have been able to achieve their simultaneous enhancement so far. In this work, we developed a special attenuated thermal-regulated interfacial polymerization (ATRIP) and unraveled the effect of dynamic change temperature on the microstructure of the polyamide membrane. During the ATRIP process, the interfacial temperature experiences a rapid rising and falling, which induces the formation of reaction intermediates of various sizes. The fusion of these reaction intermediates creates a dense polyamide (PA) layer with granular nanostructures on both front and back surface. These convex granular nanostructures create numerous cavities for shortening the water transport path. Therefore, the resulted TFC PA NF membrane from ATRIP exhibits unprecedented increase of permeate flux from 54 to 174 Lm−2h−1 and the increase of MgSO4 rejection from 82.9% to 95.8%. Overall, using attenuated thermal to regulate the IP process provides an effective and simple avenue to break through the “trade-off” relationship between water permeance and salt rejection of TFC PA NF membrane, which can strongly promote the development of desalination technologies.

Low thermal conductivity lanthanum zirconate nanofibrous membranes for thermal insulation

AbstractLanthanum zirconate (LZO) has high‐temperature advantages, including a high melting point, low thermal conductivity, and high structure stability, which has the potential to be used in high‐temperature thermal insulation field. However, low mechanical properties of LZO porous ceramics have limited further applications. In this work, LZO nanofibrous membranes were prepared by electrospinning, and the preparation parameters, including PVP content, spinning voltage, feeding rate, received distance, and the heating process, were investigated to optimize the microstructure of the nanofibrous membranes. The LZO nanofibrous membranes with a grain size of 34.5 nm displayed good morphology after calcining at 1000°C. The LZO fibrous membranes had a very low thermal conductivity of 0.0716 W/m·K at room temperature, showing excellent insulating performance. This work indicates that LZO nanofibrous membranes are promising candidate materials for thermal insulation applications.

Efficient methodology for the preparation and fabrication of cation exchange membranes using trichloroacetic acid and cellulose biopolymer

This article presents a new method for preparing enhanced cation exchange membrane (CEM) for water treatment using cellulose biopolymer. The preparation methodology of CEM membranes was performed in two steps; functionalization followed by fabrication. Firstly, cellulose powder was functionalized with trichloroacetic acid at different reaction times to prepare carboxymethyl tricellulose (CMTC). In the second step, the exchange memberane was fabricated via phase inversion technique using the functionalized cellulosic material and polyethylene glycol as a pore former. The prepared CEM was fully characterized using FTIR, SEM, mechanical properties, and degree of substitution (DS) determination. The morphological microstructure of the CEM membrane was investigated and discussed. The microstructural analysis by FTIR confirmed the functionalization process. The tensile values obtained at different reaction times showed the effectiveness of using trichloroacetic acid in the carboxymethylation and consequently, the stability of the obtained functionalized cellulose. The obtained DS values are higher than that of the commercial CMC and also the published values. It has been observed that the prepared CEM have an average DS value of 1.5 and therefore much higher than the DS value of commercial CMC whose DS ranges between 0.7 and 1.2. The prepared CEM membranes were morphologically investigated by SEM. The SEM photos showed homogeneously distributed small pores on the entire surface of the membrane, and its cross-section is a multilayer with large pores.

Correlation between the Humidity-Dependent Surface Microstructure and Macroconductivity of Anion Exchange Membranes.

Anion exchange membrane (AEM) fuel cells have gained significant interest in recent years due to their promising applications in cost-effective and environmentally friendly energy conversion. Among various factors that affect their performance, water content plays an important role in the conductivity and stability of AEMs. However, the effect of the hydration level on the microstructure of AEMs and the correlation between the microstructure and macroconductivity have not been systematically investigated. In this work, four AEMs, quaternary ammonia polysulfone, quaternary ammonia poly(N-methyl-piperidine-co-p-terphenyl) (QAPPT), and bromoalkyl-tethered poly(biphenyl alkylene)s PBPA and PBPA-co-BPP, have been studied by atomic force microscopy and electrochemical impedance spectroscopy to elucidate the correlation between the humidity-dependent surface microstructure and macroconductivity of the AEMs. We obtained phase images by atomic force microscopy and identified hydrophilic and hydrophobic domains by fitting the distribution curve of phase images, which reasonably distinguishes hydrophilic domains from hydrophobic domains of the membrane surface, and thus, the surface hydrophilic area ratio and average size could be quantitatively analyzed. The conductivities of the membranes were then measured by electrochemical impedance spectroscopy at various humidities. The joint results from atomic force microscopy and electrochemical measurements help clarify the effect of the hydration level on the microphase separation and ionic conduction of the membranes.

Developing a PVDF catalytic membrane with high permeability, fouling resistance and self-cleaning capability for efficient oil/water emulsion separation

To impart PVDF membranes with excellent antifouling performance and catalytic self-cleaning capability, a novel modifier PVDF-g-Py-FePc (PPF) was facilely designed and architecturally constructed through grafting 4-aminopyridine (4-NH2-Py) followed by axial coordinating iron phthalocyanine (FePc) on PVDF backbones. An original PPF@PVDF catalytic membrane has been successfully fabricated though incorporating the Fenton-like modifier PPF into PVDF matrix using the phase inversion method. The influences of the introduction of PPF on membrane micro-structure and separation performance were investigated in detail by XPS, contact angle measurement, SEM, and cross-flow filtration experiment. Owing to the introduction of the modifier PPF, the porosity, mean pore size and surface hydrophilicity of PVDF membrane were enhanced obviously, which results in PVDF membrane with high permeation and excellent fouling resistance. Most importantly, the embedded PPF possesses catalytic active and can more effectively degrade the oil foulants adsorbed on membrane surface or trapped within membrane pores. Thereby, PVDF membrane was endowed a catalytic self-cleaning capability for high-efficient oil/water emulsion separation. As a whole, the PPF@PVDF catalytic membrane as a potential candidate will be applied in the treatment of wastewater containing oil and sewage.