Polymeric Membrane Matrix Research Articles

Joint experimental-computational: Revealing the role of sodium poly(heptazineimide) in the selective separation of CO2 in PEBAX-based mixed matrix membranes

Mixed matrix membranes (MMMs) with the dual properties of porous materials and polymer matrix membranes have become one of the most optimal solutions to the gas separation problem. However, the adapted porous material and the explicit transport mechanism of gases within the mixed matrix membrane hinder its further commercialization. Thanks to their porous nature and tunable gas adsorption properties, heteroatom-doped porous materials, especially nitrogen-doped porous materials, are widely used to design and prepare advanced CO2 separation membranes. Herein, a layered two-dimensional nano-sheet with a nitrogen content of 44.7 % was successfully synthesized via thermal polymerization. And nano-sheets were homogeneously dispersed in a Pebax matrix to make a composite film. Since the CO2 affinity of the nitrogen functional site and the PEO flexible chain, realizing the synergistic improvement of CO2 permeability and selectivity. A comprehensive combined permeation experimental/simulation characterization reveals the CO2 transport pathway within the membrane, indicating the mechanism of action of nitrogen-doped porous packing on CO2 diffusion. Among these, the CO2 permeability of the mixed matrix film containing 5 wt% sodium poly(heptazine imide) (NaPHI) reached 153 Barrer at a feed gas pressure of 9 bar, nearly 149 % compared to the pure Pebax film. The selectivity of CO2/N2 was enhanced to 105, exhibiting a remarkable increase of 159 % and exceeding the 2019 Robeson limit. Importantly, the present work further reveals and demonstrates the gas separation mechanism of nitrogen-doped porous filler/polymer hybrid matrix membranes, which provides new ideas for the design and application of heteroatom-doped porous fillers in the field of gas separation.

Conversion of SOD zeolite into type I porous liquid and preparation of mixed matrix membrane with AO-PIM for efficient gas separation

Low-silica SOD zeolites are among the most promising inorganic materials for mixed matrix membranes (MMMs). However, the gas separation performance is severely hindered by the non-selective voids formed by both the zeolite and polymer membranes, as well as the rigid layer. In this work, SOD-liquid-M2070 PL type I porous liquid was synthesized and subsequently filled into an Amidoxime-functionalized polymer of intrinsic microporosity (AO-PIM) to prepare MMMs. The fillers and MMMs were characterized using FTIR, SEM, TGA, XRD, and gas permeation techniques. SOD-liquid-M2070 PL facilitates the rapid diffusion of CO2 and H2 gas molecules for efficient gas separation. The liquid-like fluidity of SOD-liquid-M2070 PL improves the formation of non-selective pores in the SOD and polymer matrix membranes to enhance gas permeability and selectivity. The CO2, H2 permeability and CO2/N2, H2/N2 selectivity of MMMs composed of 5 wt% SOD-liquid-M2070 PL with optimal filling ratio were increased by 248%, 246%, and 173%, 222%, respectively, compared with pure membranes. It exceeds the 2008 Robeson limit for H2/N2 and approaches much closer to the 2019 Robeson limit for CO2/N2. The field of green environment presents a promising development prospect for low silica SOD zeolite, which exhibits high separation efficiency.

Preparation and characterization of DA@SA catalytic composite membranes strengthened by two-dimensional MXene nanomaterials

Reasonable design of the separation layer structure in the catalytic composite membrane (CCM) is an effective strategy to improve the performance of catalysis and separation. As for the low permeability and obvious non-selective interface defects of the separation layer, a new nanomaterial MXene (Ti3C2TX) was introduced to enhance the permeability of sodium alginate (SA) polymer matrix membrane and dopamine (DA) acted as the binder to improve the non-selectivity between the filler and the polymer, respectively. The porous catalytic layer was proposed by grafting acid ionic liquids (ILs) onto polyvinyl alcohol (PVA). The experimental results showed that the flux of MXene-DA@SA/PAN separation membrane was up to 1640 g∙m−2 h−1, increasing by 70% compared with the pure SA membrane. And the separation factor arrived at 810, increasing by 30.6% compared with the non-dopamine-modified hybrid membrane. Using the developed ILs-g-PVA/MXene-DA@SA/PAN catalytic composite membrane, the conversion rate of acetic acid reached 96.5% within 12 h. This work provides useful enlightenment for improving the efficiency of catalytic reaction by optimizing the separation layer.

Enhancing carbon capture efficiency of zeolite-embedded polyether sulfone mixed-matrix membranes via annealing process

Current work was motivated by rapid advancement in membrane technology for application of gas separation, that resulted in the formation of mixed-matrix membranes (MMMs) with higher selectivity and permeability. MMMs are one way to get above the Robeson upper bound of selectivity against permeability for gaseous separation while retaining the advantages of solution processing. Numerous inorganic materials like zeolites, carbon nanotubes, or metal-organic frameworks can behave as molecular sieves, but they are fragile and difficult to fabricate as standalone membranes. This problem might be solved by embedding them into a more durable polymeric membrane matrix. In this work, symmetric mixed-matrix membranes fabricated through solution casting technique were employed with zeolite A-3 dispersed in a polyether sulfone (PES) matrix. Impacts of zeolite loading and annealing temperatures on thermal stability, morphology and carbon capture performance of prepared membranes were systematically investigated. Carbon capture proficiency of fabricated membranes was assessed in terms of CO2 permeability and CO2/N2 selectivity. In contrast to pristine PES membrane, incorporation of optimal 30 wt% zeolite into polymer matrix enhanced CO2 permeability from 81 to 128 Barrer and CO2/N2 selectivity from 9 to 22. Annealing the composite membranes at 155 °C led to further enhance CO2 permeability at the expense of reduced CO2/N2 selectivity: CO2 permeability of pristine PES membrane enhanced from 81 to 126 Barrer by decreasing its CO2/N2 selectivity from 9 to 6; CO2 permeability improved from 128 to 144 Barrer while CO2/N2 selectivity declined from 22 to 18 for composite membrane imbedded with 30 wt% optimum zeolite loading.

Polymer Electrolyte Membranes Containing Functionalized Organic/Inorganic Composite for Polymer Electrolyte Membrane Fuel Cell Applications.

To mitigate the dependence on fossil fuels and the associated global warming issues, numerous studies have focused on the development of eco-friendly energy conversion devices such as polymer electrolyte membrane fuel cells (PEMFCs) that directly convert chemical energy into electrical energy. As one of the key components in PEMFCs, polymer electrolyte membranes (PEMs) should have high proton conductivity and outstanding physicochemical stability during operation. Although the perfluorinated sulfonic acid (PFSA)-based PEMs and some of the hydrocarbon-based PEMs composed of rationally designed polymer structures are found to meet these criteria, there is an ongoing and pressing need to improve and fine-tune these further, to be useful in practical PEMFC operation. Incorporation of organic/inorganic fillers into the polymer matrix is one of the methods shown to be effective for controlling target PEM properties including thermal stability, mechanical properties, and physical stability, as well as proton conductivity. Functionalization of organic/inorganic fillers is critical to optimize the filler efficiency and dispersion, thus resulting in significant improvements to PEM properties. This review focused on the structural engineering of functionalized carbon and silica-based fillers and comparisons of the resulting PEM properties. Newly constructed composite membranes were compared to composite membrane containing non-functionalized fillers or pure polymer matrix membrane without fillers.

Performance Chitosan Membranes to Filter Humic Acid (HA) Waste from Aquatic Environment

Various pollutants can directly and indirectly threaten the health and safety of our aquatic environment. To overcome this, various methods needed for more efficient wastewater treatment. Wastewater treatment using natural polymer matrix membranes can provide an excellent alternative that is environmentally friendly. For this purpose, a study on filtering humic acid (HA) waste frompolluted water using chitosan membranes has been carried out. The membranes used are chitosan membranes 1%, 2%, 3%, and 4%. The filtration was carried out by using the dead-end filtration method, and the analysis of humic acid was done by using UV-Vis spectrophotometer. The ability of the membrane to screen humic acid waste is indicated by pure water flux (PWF), waste (product) flux (PF), and rejection coefficient (R). The results obtained that the chitosan membrane 2% showed the highest filtration ability 99.87% with pure water flux and product flux of 2938.14 L/m2h and 1678.93 L/m2h, respectively. While the chitosan membranes 3% and 4% gave rejection coefficient of 83.76% and 79.38%, respectively. The chitosan membrane 1%, on the pressure of 100 kPa did not produce flow. So, chitosan membrane 2% can be used as a method to reduce humic acid waste from the aquatic environment, which is environmentally friendly method. So, chitosan membrane 2% can be used as a method to reduce humic acid waste from the aquatic environment, which is environmentally friendly method.

An approach for evaluating gas sorption in polymer matrix membranes based on balancing incoming and outgoing membrane mass fluxes

The transport of gases in polymeric membranes can be described by a solution–diffusion mechanism in which the individual transport parameters are determined from independent measurements of the gas permeability and diffusivity and further measurements of the gas solubility in the polymer of interest. Herein, we propose a new method for determining all three transport parameters from a single permeation experiment performed using a modified classical permeation cell with very small volumes above and below the membrane (1.192 and 0.658 mL, respectively). The new concept is based on the evaluation of gas sorption in the membrane determined from the balance of mass fluxes entering and leaving the membrane. The amount of gas sorbed in the membrane can then be calculated by integrating the area between the fluxes. This arrangement allows for the rapid and complex characterization of the gas transport and separation properties of polymeric materials using a single experiment. The novel approach was tested on a polydimethylsiloxane membrane for three gases having considerably different solubilities in the polymer, and the results were consistent with those obtained using classical procedures.

Influence of mesoporous phosphotungstic acid on the physicochemical properties and performance of sulfonated poly ether ether ketone in proton exchange membrane fuel cell

This study demonstrates the successful development of hybrid mesoporous siliceous phosphotungstic acid (mPTA-Si) and sulfonated poly ether ether ketone (SPEEK) as a proton exchange membrane with a high performance in hydrogen proton exchange membrane fuel cells (PEMFC). SPEEK acts as a polymeric membrane matrix and mPTA-Si acts as the mechanical reinforcer and proton conducting enhancer. Interestingly, incorporating mPTA-Si did not affect the morphological aspect of SPEEK as dense membrane upon loading the amount of mPTA-Si up to 2.5 wt%. The water uptake reduced to 14% from 21.5% when mPTA-Si content increases from 0.5 to 2.5 wt% respectively. Meanwhile, the proton conductivity increased to 0.01 Scm −1 with 1.0 wt% mPTA-Si and maximum power density of 180.87 mWcm −2 which is 200% improvement as compared to pristine SPEEK membrane. The systematic study of hybrid SP-mPTA-Si membrane proved a substantial enhancement in the performance together with further improvement on physicochemical properties of parent SPEEK membrane desirable for the PEMFC application. • Incorporation of porous HPA in SPEEK membrane used as electrolyte layer in PEMFC. • Physical and chemical properties are being characterized to get the best membrane. • The performance analysis concluded the highest performing membrane.

Influence of alumina nanoparticles on the performance of polyacrylonitrile membranes in MBR.

This study aims to investigate the effect of using Al2O3 nanoparticles (NPs) in membrane structure on the operation condition of the membrane bioreactor. To this end, alumina NPs as the high hydrophilic agents with an approximate size of 40nm and a concentration of 0-3 wt.% were placed within the PAN polymeric membrane matrix structure with high hydrophilicity and high mechanical resistance over the others via the phase inversion method. Characterization of synthesized nanocomposite membranes was carried out by SEM analysis. In the presence of the alumina NPs, the porosity of the membranes improved. The water contact angle measurement confirmed the superior hydrophilicity of mixed PAN membranes compared to the pure polymeric membranes. The best nanocomposite membrane with better antifouling properties was selected to evaluate the MBR's performance in wastewater treatment and assessed in terms of the resistance, flux recovery, and COD removal rates. The result of a comparison with pure membrane showed that by increasing the Al2O3 amount up to 2wt.%, irreversible fouling resistance mitigated as much as 50%. Moreover, the flux recovery ratio was increased by 15%, and the COD removal rate was also raised as large as 16%. Our investigation illustrated that the presence of alumina NPs has improved the MBR performance and decreased the irreversible fouling resistance of the membrane.

A review of zeolite materials used in membranes for water purification: history, applications, challenges and future trends

AbstractThis review provides a fundamental assessment of the potential of zeolite particles incorporated into polymeric membranes in view of improving the performance of these membranes. Zeolites are of interest as having extensive potential in separation processes due to their unique frameworks and properties. Significant investigations have been carried out to improve conventional membrane properties by the inclusion of zeolites. Zeolite membranes can be classified into three categories: (i) self‐supported zeolite membranes, (ii) inorganic‐supported zeolite membranes and (iii) zeolites mixed into a polymeric membrane matrix or top layer. The focus of this review is on nanosized zeolite particles incorporated into the polymeric structure of membranes, with specific attention to a polyamide layer used in pressure‐driven membrane processes such as reverse osmosis. The incorporation of inorganic zeolite particles in the polymer matrix enhances the permeability without decreasing the selectivity, and increases the mechanical strength in a harsh environment and fouling and chlorine resistance of the membranes. Agglomeration of nanosized zeolites and defect formation are highlighted as the main obstacles to the fabrication of large‐scale high‐performance zeolite membranes in order to identify strategies to solve these issues. Among the different strategies, adding a crosslinking agent to the interfacial polymerization process might be a promising method for fabricating homogeneous zeolite–polymer composite membranes with excellent performance. This paper provides a better understanding of the knowledge acquired in the development of polymer‐based zeolite nanocomposite membranes and gives perspectives for future research. © 2021 Society of Chemical Industry (SCI).

Synergetic influence of F-MWCNTS on polyvinylpyrrolidone sodium alginate composite membrane for reverse osmosis

In this study, novel composite membrane of functionalized multi-walled carbon nanotubes (F-MWCNTs) polyvinyl pyrrolidine (PVP) and sodium alginate (Na-Alg) with unique characteristics were synthesized for the application of reverse osmosis (RO) desalination. The MWCNTs in different amounts were systematically and uniformly dispersed in PVP/Na-Alg polymer matrix during the synthesis of membranes by dissolution casting method. The effect of F-MWCNTs content in the performance of the composite membrane was investigated for RO desalination process compared to PVP/Na-Alg blended membrane. The spectral studies were carried out by Fourier transform infrared spectroscopy (chemical bonding) and scanning electron microscopy (surface morphology). The thermogravimetric analysis (TGA) of membranes also recommended that composite membrane with the highest content of F-MWCNT has more excellent thermal stability compared to PVP/Na-Alg blended membrane and other modified membrane samples. The most striking experimental results show that the incorporation of F-MWCNTs improved the general RO performance of the composite membranes. The modified composite membrane surface became rough as compared to the PVP/Na-Alg blend membrane surface. The PVP/Na-Alg blended membrane shows a maximum permeation flux of 5.5 L/m2h and high-water content. This experimental analysis also presented that tethered F-MWCNTs/PVP/Na-Alg polymer matrix membrane, with stronger F-MWCNTs/polymer matrix interactions, enhanced the composite membrane's salt rejection performance by 85.4% for the highest content of F-MWCNTs. Therefore, it can be concluded that all the membrane samples presented excellent capacity to resist the growth of gram-negative E. coli bacteria.

Prototyping of a Low-Cost Ion-Selective Electrode Sensor Unit for Determination of Lead Ions in Aqueous Samples

Exposure to lead via drinking water is a substantial health hazard. The current common practice of measuring lead levels in drinking water is to use analytical chemical analysis that involves sophisticated laboratory instruments. As lead contamination in drinking water is often a close-to-home contamination caused by corroded lead service pipes connecting households to main lines or lead-based pluming within the households, a low-cost and portable device that can be conveniently deployed to individual households to monitor lead levels in drinking water would offer consumers the opportunity to obtain first-hand information about the lead levels in their drinking water. The main objective of this study is to develop and prototype a portable low-cost device for detecting lead levels in drinking water. The lead-detecting device consists of two primary components: lead ion-selective electrode (ISE) sensing membrane and a microcontroller-based measuring unit. ISE membrane has proven to show low detection limits, good selectivity, low cost and great potential to be integrated in a miniature device. The ISE membrane in this study utilized polymeric membrane as the matrix with lead-selective ionophores embedded in the matrix. Hydroxyl type Vinyl Chloride-vinyl Acetate Terpolymer was used to create polymeric membrane matrix and allowed for all components to be housed in the membrane. The selected ionophore was Tert-Butylcalix(4)Arene-Tetrakis with its primary function is to differentiate and transport a specific ion (in this case, Pb2+ ions) through a membrane. A limit of detection of 1.0 ´ 10-8 M was achieved along with a linear Nernstian response over a lead concentration range from 1.0 ´ 10-8 M to 1.0 ´ 10-4 M. Durability test of the membrane showed a lifetime close to 30 days. A low-cost printed circuit board (PCB) was custom designed and created as an amplification unit to measure the ISE’s electromotive force (EMF). The custom-built device was able to capture the limit of detection (LOD) of the ISE sensing membrane and showed reasonably good consistency in comparison to measurements from commercial potentiostat.

Adsorption-based strategies for removing uremic toxins from blood

Chronic kidney disease leads to the accumulation of uremic toxins within the blood compartment. Engineered surface that adsorbs toxins from the blood compartment is a promising approach for clearing uremic toxins not easily removed using membrane-based dialysis techniques. A variety of adsorbent materials have been studied with the purpose of targeting a general group of toxins or a specific uremic toxin. Some of these structures have also been incorporated into toxin clearance systems, including column adsorption and membrane adsorption. This review focuses upon, as much as possible, adsorption studies that included the evaluation of uremic toxin removal. We also discuss certain special adsorbent systems like molecularly imprinted polymer and mixed matrix membranes. The clinical application of several adsorbent systems in uremic toxin removal is also reviewed. • Studies using activated carbon, zeolite, mesoporous silica and polymer for uremic toxin removal were reviewed. • The development of molecularly imprinted polymer (MIP) systems and mixed matrix membrane (MMM) in uremic toxin removal was reviewed. • Performance and efficacy of adsorbent systems used in vivo were reviewed and discussed.

Cellulose acetate based Complexation-NF membranes for the removal of Pb(II) from waste water

This study investigates the removal of Pb(II) using polymer matrix membranes, cellulose acetate/vinyl triethoxysilane modified graphene oxide and gum Arabic (GuA) membranes. These complexation-NF membranes were successfully synthesized via dissolution casting method for better transport phenomenon. The varied concentrations of GuA were induced in the polymer matrix membrane. The prepared membranes M-GuA2–M-GuA10 were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, atomic force microscope and bio-fouling studies. Thermal stability of the membranes was determined by thermogravimetric analysis under nitrogen atmosphere. Dead end nanofiltration was carried out to study the perm- selectivity of all the membranes under varied pressure and concentration of Pb(NO3)2. The complexation-NF membrane performances were significantly improved after the addition of GuA in the polymer matrix membrane system. M-GuA8 membrane showed optimum result of permeation flux 8.6 l m−2 h−1. Rejection of Pb(II) ions was observed to be around 97.6% at pH 9 for all the membranes due to electrostatic interaction between CA and Gum Arabic. Moreover, with the passage of time, the rate of adsorption was also increased up to 15.7 mg g−1 until steady state was attained. Gum Arabic modified CA membranes can open up new possibilities in enhancing the permeability, hydrophilicity and anti-fouling properties.

Exploring the Effect of Iron Metal-Organic Framework Particles in Polylactic Acid Membranes for the Azeotropic Separation of Organic/Organic Mixtures by Pervaporation.

A microporous carboxylate metal-organic framework MIL-100 Fe was prepared as submicron particles by microwave-assisted hydrothermal synthesis (Fe-MOF-MW). This product was explored, for the first time, for the preparation of polylactic acid (PLA) mixed matrix membranes. The produced MOF was characterised by powder X-ray diffraction (PXRD), environmental scanning electron microscopy (ESEM) as well as by thermogravimetric analysis (TGA) and nitrogen adsorption/desorption. The effect of different Fe-MOF-MW concentrations (0.1 and 0.5 wt%) on the membrane properties and performance were evaluated. These membranes were used in the pervaporation process for the separation of methanol/methyl tert-butyl-ether mixtures at the azeotropic point. The influence of the feed temperature and vacuum pressure on the membrane performance was evaluated and the results were compared with PLA pristine membranes. Moreover, the produced membranes have been characterised in terms of morphology, MOF dispersion in the polymeric membrane matrix, wettability, thickness, mechanical resistance and swelling propensity. The presence of Fe-MOF-MW was found to have a beneficial effect in improving the selectivity of mixed matrix membranes towards methanol at both concentrations. The highest selectivity was obtained for the PLA membranes embedded with 0.5 wt% of Fe-MOF-MW and tested at the temperature of 25 °C and vacuum pressure of 0.09 mbar.

In vitro study of dual layer mixed matrix hollow fiber membranes for outside-in filtration of human blood plasma

Hemodialysis mainly removes small water-soluble uremic toxins but cannot effectively remove middle molecules and protein-bound uremic toxins. Besides, the therapy is intermittent leading to fluctuating blood values and fluid status which adversely impacts patients’ health. Prolonged hemodialysis (with adequate anticoagulation) could improve the removal of toxins and the development of portable and wearable artificial kidneys could offer more flexibility in the dialysis scheme. This would enhance patients’ overall health, autonomy, mobility and flexibility, allowing patients to participate in social and economic life. However, the time that patients’ blood is exposed to the dialyzer material is longer during prolonged hemodialysis, and blood clots could obstruct the fiber lumen, resulting in a decrease of the effective membrane surface area available for toxin removal. The outside-in filtration (OIF) mode, wherein blood flows through the inter-fiber space instead of through the fiber lumina, has been applied widely in blood oxygenators to prevent fiber clotting, but not in hemodialysis.In this study, we present for the first time the development of a mixed matrix membrane (MMM) for OIF of human blood plasma. This MMM combines diffusion and adsorption and consists of a polymeric membrane matrix with activated carbon (AC) particles on the inside layer, and a polymeric particle-free layer on the outer fiber layer. Our results show that in vitro MMM fibers for OIF demonstrate superior removal of the protein-bound uremic toxins, indoxyl sulfate and hippuric acid, compared to both earlier MMM fibers designed for inside-out filtration mode and commercial high-flux fibers. Statement of significanceCurrent hemodialysis therapy cannot effectively remove protein-bound toxins. Prolonged hemodialysis could improve toxin removal. However, during prolonged hemodialysis, blood clots could obstruct the fiber lumen, resulting in decreased effective membrane surface area available for toxin removal.We have prepared, for the first time, dual layer mixed matrix hollow fiber membranes (MMM) for outside-in filtration (OIF). The OIF mode wherein blood would flow through the inter-fiber space instead of through the fiber lumina could prevent fiber clotting. Moreover, the MMMs combine diffusion and adsorption to improve (protein-bound) toxin removal.We believe that the new design of our MMM fibers is an important contribution concerning the development of artificial kidney systems and the improvement of the health and well-being of patients with renal failure.

Superglassy Polymers to Treat Natural Gas by Hybrid Membrane/Amine Processes: Can Fillers Help?

Superglassy polymers have emerged as potential membrane materials for several gas separation applications, including acid gas removal from natural gas. Despite the superior performance shown at laboratory scale, their use at industrial scale is hampered by their large drop in gas permeability over time due to physical aging. Several strategies are proposed in the literature to prevent loss of performance, the incorporation of fillers being a successful approach. In this work, we provide a comprehensive economic study on the application of superglassy membranes in a hybrid membrane/amine process for natural gas sweetening. The hybrid process is compared with the more traditional stand-alone amine-absorption technique for a range of membrane gas separation properties (CO2 permeance and CO2/CH4 selectivity), and recommendations for long-term membrane performance are made. These recommendations can drive future research on producing mixed matrix membranes (MMMs) of superglassy polymers with anti-aging properties (i.e., target permeance and selectivity is maintained over time), as thin film nanocomposite membranes (TFNs). For the selected natural gas composition of 28% of acid gas content (8% CO2 and 20% H2S), we have found that a CO2 permeance of 200 GPU and a CO2/CH4 selectivity of 16 is an optimal target.

Adsorption-Based Strategies for Removing Uremic Toxins from Blood

Chronic kidney disease leads to the accumulation of uremic toxins within the blood compartment. Engineered surfaces that adsorb toxins from the blood compartment are a promising approach for clearing uremic toxins not easily removed using membrane-based dialysis techniques. A variety of adsorbent materials have been studied with the purpose of targeting a general group of toxins or a specific uremic toxin. Some of these structures have also been incorporated into toxin clearance systems, including column adsorption and membrane adsorption. This review focuses upon, as much as possible, adsorption studies that included the evaluation of uremic toxin removal. We also discuss novel adsorbent systems like molecularly imprinted polymer and mixed matrix membranes. The clinical application of several adsorbent systems in uremic toxin removal is also reviewed.

Dual Layer Mixed Matrix Hollow Fiber Membranes for Outside-In Filtration of Human Blood Plasma

Hemodialysis mainly removes small water-soluble uremic toxins but cannot effectively remove middle molecules and protein-bound uremic toxins. Besides, the therapy is intermittent leading to fluctuating blood values and fluid status which adversely impacts patients’ health. Prolonged hemodialysis could improve the removal of toxins and the development of portable and wearable artificial kidneys could offer more flexibility in the dialysis scheme. This would enhance patients’ overall health, autonomy, mobility and flexibility, allowing patients to participate in social and economic life. However, during prolonged hemodialysis, blood clots could obstruct the fiber lumen, resulting in a decrease of the effective membrane surface area available for toxin removal. The outside-in filtration (OIF) mode, wherein blood flows through the inter-fiber space instead of through the fiber lumina, has been applied widely in blood oxygenators to prevent fiber clotting, but not in hemodialysis. In this study, we present for the first time the development of a mixed matrix membrane (MMM) for OIF of human blood plasma. This MMM combines diffusion and adsorption and consists of a polymeric membrane matrix with activated carbon (AC) particles on the inside layer, and a polymeric particle-free layer on the outer fiber layer. Our results show that in vitro MMM fibers for OIF demonstrate superior removal of the protein-bound uremic toxins, indoxyl sulfate and hippuric acid, compared to both earlier MMM fibers designed for inside-out filtration mode and commercial high-flux fibers.

Property Characterization and Mechanism Analysis of Polyoxometalates-Functionalized PVDF Membranes by Electrochemical Impedance Spectroscopy.

Polyoxometalates (POMs) has proved its advantage in constructing high-performance nanocomposite membranes such as catalytic membranes, adsorptive membranes, and forward osmosis membranes. However, it is challenging or tedious to characterize its distribution and effect on the membrane structures due to the equipment resolution limitation, discrete nano-scaled structures of POMs, and limited doping amount compared to the polymeric membrane matrix. In this paper, POMs-functionalized polyvinylidene fluoride (PVDF) membranes were fabricated by phase inversion combined with the sol-gel method, and electrochemical impedance spectroscopy (EIS) was utilized to analyze the nanocomposite membrane intrinsic properties. Through adjusting the additives in the sol-forming process, a set of membranes with varied intrinsic properties were developed accordingly. The wetting degree of the membranes related to the hydrophilic nature of the membrane surfaces had a crucial influence on the impedance measurements at the early stage. Through EIS analysis, it was demonstrated that the amination of the membrane matrix through (3-aminopropyl)trimethoxysilane (APTMS) treatment and the immobilization of POMs through electrostatic attraction would not generate new pore structures into the membrane and only alter the membrane surface roughness and composition. To my knowledge, it is the first time that EIS was utilized to characterize the hydrophilicity of the membranes and pore structures of the POMs-modified membranes. Our findings indicate that EIS can provide valuable information for probing the structures of other nano-materials-incorporated membranes.