Bare Membrane Research Articles

Different metal-doped ZnS quantum dots photocatalysts for enhancing the permeability and antifouling performances of polysulfone membranes with and without UV irradiation

In this study, the effect of three different transition metal ion dopants (Mn2+, Fe2+, and Co2+) on the characteristics of zinc sulfide (ZnS) quantum dots (QDs) was investigated and the obtained QDs photocatalysts were applied for the modification of polysulfone (PSf) mixed matrix membranes to reduce membrane fouling. The synthesized QDs and fabricated membranes were fully identified with SEM, TEM, AFM, FTIR analyses, and also underwent porosity and contact angle tests. Flux recovery ratios (FRR) significantly increased from 69.8% (bare) to 85.0% (1% Fe-doped ZnS QDs) after modification of membranes with metal-doped QDs. The contact angles of the prepared membranes decreased with doping of dissimilar metals, therefore hydrophilicity increased, and reversible/non-reversible blockages were improved. Besides, the use of UV irradiation during the washing of the membranes increased the FRR of the photocatalytic activated membranes to 91.2%. Compared to the bare PSf membrane in dye solution filtration, 1% Fe-doped ZnS QDs membrane yielded twice as much flux and 15% higher FRR results. Therefore, the results proved that metal-doped QDs can be used in the modification of PSf membranes with high efficiency.

Liquid-Infused Membranes Exhibit Stable Flux and Fouling Resistance.

Antifouling membranes that offer excellent operational lifetimes are critical technologies needed to meet the growing demand for clean water. In this study, we demonstrate antifouling membranes featuring an ultrathin oil layer that stayed immobilized on the surface and in the pore walls of poly(vinylidene fluoride) membranes for multiple cycles of operation at industrially relevant transmembrane pressures. An optimized quantity of a commercial Krytox oil with either a low (K103) or a high viscosity (K107) was infused onto the active surface and into the pores of membranes with a 0.45 μm pore size. The presence of the oil layer was qualitatively confirmed using crystal violet staining and variable pressure scanning electron microscopy. Using a dead-end stirred cell, a consistent pure water permeance value of 3000 L m-2 h-1 bar-1 was achieved for the K103 liquid-infused membranes for at least 10 operation cycles, which was expectedly lower than the permeance of bare control membranes (∼16 000 L m-2 h-1 bar-1), suggesting that a stable oil layer was formed on all membrane-active sites. To quantify if oil was lost during membrane operation, extensive thermogravimetric analysis was conducted on both the as-prepared and used membranes. When challenged with the microorganism, Escherichia coli K12, the liquid-infused membranes statistically reduced microbial attachment by ∼50% versus the control membranes. For the first time, we have demonstrated that by forming an immobilized, robust, and stable oil-coated membrane, we can generate high-performance membranes with stable permeance values that can be operated at relevant transmembrane pressures and provide long-lasting antifouling properties.

Selective Removal of Barium and Hardness Ions from Brackish Water with Chemically Enhanced Electrodialysis

The use of a nonconventional water resource for energy and industrial applications often requires extraction of low-level undesirable ions from matrices of benign dominant ions. In this study, the selective extraction of Ba2+ and Mg2+ from synthetic brine solutions was evaluated using strong acid cation-exchange membranes modified with the surface deposition of macrocyclic molecules including crown ethers and calixarenes. Compared to the bare membrane, vinylbenzo-18-crown-6 (VB18C6) and calix[4]arene-amended membranes showed increased selectivity for Ba2+ and Mg2+ with respect to the dominant ion (Na+) by up to fourfolds, with the calix[4]arene-modified membrane achieving more selective separation than VB18C6. Optimal selectivity was achieved at a moderate-to-high current density (3.1–6.3 mA/cm2), which was attributed to the alleviation of transport limitation in the boundary layer by the surface modification. Amendment of a calix[4]arene derivative with a crown-6 “boot strap” and two carboxylic groups resulted in reduced selectivity due to the formation of strong complexes with divalent ions. These results show that surface deposition of ion sequestrants can be a versatile approach to improve the membrane’s selectivity; however, the performance is sensitive to feed water salinity, current loading, and the macrocycle-ion chemistry, where there is a trade-off between ion affinity and mobility.

Performance improvement of PES membrane decorated by Mil-125(Ti)/chitosan nanocomposite for removal of organic pollutants and heavy metal

The Mil-125(Ti)-CS nanocomposite was successfully synthesized and characterized by using scanning electron microscopy (SEM) images, Fourier-transform infrared (FTIR) analysis and X-ray diffraction (XRD). Then, to improve the membrane performance, the synthesized Mil-125(Ti)-CS nanocomposite was embedded into the polyethersulfone (PES) membrane matrix. The nanofiltration membranes were fabricated via phase inversion method. Presence of chitosan in the structure of Mil-125(Ti) has increased the compatibility of nanoparticles with the polymer and also improved the hydrophilicity of the resulted membranes. The water contact angle of bare membrane (58°) was reduced to 40° by blending of 1 wt% nanocomposite led to increasing the pure water flux. However, the incorporation of more than 1 wt% of the nanocomposite caused the accumulation of nanocomposites and this was reduced the pore radius and permeability. The membrane containing 1 wt% nanocomposite was displayed the highest flux recovery ratio (FRR) ∼ 98% in bovine serum albumin (BSA) filtration. The membranes containing Mil-125(Ti)-CS also showed good performance against fouling. The performance of membranes was evaluated by treatment of six reactive dyes, antibiotic (cefixime), heavy metal, NaCl and Na2SO4 solutions. Addition of Mil-125(Ti)-CS NPs at low concentrations resulted in membranes with high pure water flux, higher separation efficiency, and remarkable anti-fouling behavior.

Synthesis of ZIF‐94 from Recycled Mother Liquors: Study of the Influence of Its Loading on Postcombustion CO2 Capture with Pebax Based Mixed Matrix Membranes

AbstractGlobal energy demand is met in large part, by burning of fossil fuels, which is causing global warming. Mixed matrix membranes (MMMs) with metal organic frameworks (MOFs) as fillers are an interesting alternative for capturing post combustion CO2 which would make the energy sector sustainable. This research is focused on the synthesis of MOF ZIF‐94 from the recycling of its mother liquors and the incorporation of synthesized MOF into a Pebax MH 1657 for MMM fabrication. The pH and the temperature of ZIF‐94 synthesis are modified and monitored and this results in various nanoparticle diameters (average particle size in the range of 41 ± 8–180 ± 73 nm). Incorporation of ZIF‐94 significantly improves the performance of the bare Pebax MH 1657 membrane. The maximum CO2/N2 selectivity and CO2 permeability are obtained for 10 wt% ZIF‐94 loading in 9 wt% (polymer concentration in 70/30 (v/v) ethanol/water solution) Pebax MH 1657 matrix being 36 ± 7 (71% increment compared to bare membrane) and 137 ± 31 Barrer (80% improvement), respectively.

Enhanced water flux and bacterial resistance in cellulose acetate membranes with quaternary ammoniumpropylated polysilsesquioxane

An enhanced water flux and anti-fouling nanocomposite ultrafiltration membrane based on quaternary ammoniumpropylated polysilsesquioxane (QAPS)/cellulose acetate (QAPS@CA) was fabricated by in situ sol-gel processing via phase inversion followed by quaternization with methyl iodide (CH3I). Membrane characterizations were performed based on the contact angle, FTIR, SEM, and TGA properties. Membrane separation performance was assessed in terms of pure water flux, rejection, and fouling resistance. The 7%QAPS@CA nanocomposite membrane showed an increased wettability (46.6° water contact angle), water uptake (113%) and a high pure water permeability of ∼370 L m−2 h−1 bar−1. Furthermore, the 7%QAPS@CA nanocomposite membrane exhibited excellent bactericidal properties (∼97.5% growth inhibition) against Escherichia coli (E. coli) compared to the bare CA membrane (0% growth inhibition). The 7%QAPS@CA nanocomposite membrane can be recommended for water treatment and biomedical applications.

Induced hemocompatibility of polyethersulfone (PES) hemodialysis membrane using polyvinylpyrrolidone: Investigation on human serum fibrinogen adsorption and inflammatory biomarkers released

When blood comes in contact with dialyzer membranes, the interfacial bioactivation reactions occurring at blood/membrane boundaries detect the gross mechanism of thrombogenicity. In the presence of biocompatible polymers, the adhesion and subsequent interactions of platelets, as well as other serum components (e.g., proteins), are altered. It delays thrombus formation. In this study, the hemocompatibility of polyvinylpyrrolidone (PVP) modified polyethersulphone (PES) hemodialysis membrane fabricated using UV-assisted photochemical synthesis was investigated. To obtain varying degrees of PVP modification on each membrane, each coated surface was aged within the viscous polymer suspension for a predetermined duration. The correlation between the membrane induced hemocompatibility with membrane roughness, chemical composition, and surface charge at different aging duration of coating. In our study, we performed a comprehensive investigations on membrane morphology, hydrophilicity and its chemical composition using Atomic Force Microscopy (AFM), Fourier Transform Infra-Red (FTIR) Spectroscopy, Nuclear Magnetic Resonance (NMR), Zeta potential, and Scanning Electron Microscopy (SEM). The coated samples were analyzed using Luminex assays for the inflammatory biomarkers of Serpin/Antithrombin-III, C5a, 1L-1α, 1L-1β, IL6, and C5b-9. Modified membranes showed significant resistance against fibrinogen adsorption compared to their bare membrane counterpart. This inherent antifouling activity against fibrinogen adsorption was observed more on modified membranes that aged longer within the PVP suspension during synthesis. A longer ageing period contributed to the enhanced PVP modification, hence, more stable polymeric hydration layers. In addition, both bare and coated membranes triggered both complement system activation and inflammatory responses, but to a mild degree in the latter case. Coated membranes at longer coating duration, around ∼4 min, had smoother surfaces and lower magnitudes of surface charge and consequently exhibited reduced release of all biomarkers (except IL-1α), indicating enhanced biocompatibility. Higher levels of C5a were observed in membranes coated at 1 and 2 min, promoting modest reduction toward the release of other components.

ZnO@PMMA incorporated PSf substrate for improving thin-film composite membrane performance in forward osmosis process

The performance of the existing forward osmosis membranes is mainly restricted by the internal concentration polarization (ICP) of solutes inside the substrate. In the current work, the poly (methyl methacrylate) (PMMA) grafted ZnO nanoparticle (ZnO@PMMA) was synthesized and introduced as a novel nanofiller to minimize the ICP effect within the polysulfone (PSf) support layer. It was revealed that the ZnO@PMMA nanoparticles could improve the characteristics of the PSf membrane substrate, including the porosity, hydrophilicity, pure water permeability (PWP) and morphology. The optimal support layer has a porosity of 82.4% and PWP of 186.5. The FO performance of modified membranes in terms of water flux (Jw, LMH) and reverse salt flux (Js, gMH) were thoroughly evaluated using a cross-flow system. Also, the water permeability (A, LMH.bar−1) and salt rejection (R, %) were measured by a dead-end RO setup. The obtained TFN-ZP.2 membrane (modified with 0.25 wt% of ZnO@PMMA) showed significantly improved FO water flux (up to 14.6 LMH) and water permeability (2.3 LMH/bar) which was about 2 times that of the bare TFC-FO membrane (5.9 LMH and 1.2 LMH/bar). Additionally, the structure parameter (S) was significantly alleviated (693 ± 85 μm) after the ZnO@PMMA incorporating, indicating reducing the unwanted ICP in TFN-FO membranes.

Leaching of CuO Nanoparticles from PES Ultrafiltration Membranes.

Recent studies have incorporated nanoparticles such as CuO, ZnO, and TiO2 to improve membrane physical and filtration properties. However, one of the major concerns about membrane modification with nanoparticles is the possible leaching of the nanoparticles leading to further contamination of source waters. Therefore, this study investigated the effects of prolonged exposure of polyethersulfone (PES) membranes incorporated with CuO nanoparticles, to different cleaning solutions. The cleaned membranes were extensively characterized for both material properties and separation performance, which enabled a closer look at particle leaching effect through a prolonged exposure. After 840 h of exposure, the presence of CuO in the cleaning solutions was confirmed using dynamic light scattering (DLS), energy-dispersive X-ray spectroscopy (EDS), and inductively coupled plasma mass spectroscopy (ICP-MS) techniques. Nanoparticle leaching resulted in changes in membrane hydrophobicity, surface roughness, pure water permeability, and salt rejection properties. Through comparison with the bare PES membranes, it was shown that cleaning solutions also degraded the membrane polymer. However, the marked effect was less pronounced compared to combined leaching of nanoparticles and degradation of the polymer noted with PES membranes incorporated with CuO nanoparticles. Therefore, when membranes incorporated with nanoparticles are used, a polishing step may be required to remove potentially leached nanoparticles. Leached nanoparticles may result in secondary pollution and pose a health risk concern to nontarget organisms. This work provides insights into the stability of nanocomposite membranes, and the achieved results can be extrapolated to other nanoparticles such as TiO2 and ZnO because they possess similar physicochemical behavior.

Mineral Scaling on Reverse Osmosis Membranes: Role of Mass, Orientation, and Crystallinity on Permeability.

Prior mineral scaling investigations mainly studied the effects of membrane surface properties rather than on the mineral properties and their impact on membrane permeability. In our study, mass, crystal growth orientation, and crystallinity of mineral precipitates on membranes, as well as their effects on membrane permeability have been investigated. Gypsum scaling tests on bare and bovine serum albumin (BSA)-conditioned membranes were conducted under different saturation indices. Results show that a longer scaling period was required for BSA-conditioned membranes to reach the same membrane permeate flux decline as bare membranes. Though the final reduced permeability was the same for both two membranes, the masses of the mineral precipitates on BSA-conditioned membranes were around two times more than those on bare membranes. Further mineral characterizations confirmed that different permeability decay rates of both types of the membrane were attributed to the differences in growth orientations rather than amounts of gypsum precipitates. Moreover, BSA-conditioned layers with high carboxylic density and specific molecular structure could stabilize bassanite and disrupt the oriented growth to inhibit the formation of needle-like gypsum crystals as observed on bare membranes, thus resulting in lower surface coverage with scales on membranes and alleviating the detrimental scaling effect on membrane permeability.

Flux-enhanced reduced graphene oxide (rGO)/PVDF nanofibrous membrane distillation membranes for the removal of boron from geothermal water

• When the rGO concentration was increased, permeate flux was enhanced in AGMD system. • The optimum rGO concentration was described as 0.039 wt% according to membrane characterization such as contact angle, liquid entry pressure (LEP). • Compared to bare PVDF membrane, boron rejection was enhance using modified membrane with 0.039 wt% rGO. • It was obtained that less than 0.5 mg/L boron concentration in permeate water. In this work, fabrication of PVDF nanofiber membrane with reduced graphene oxide (rGO) using electrospinning technique has been carried out to improve AGMD performance. Membrane morphology and different membrane characteristics such as contact angle, thickness, liquid entry pressure (LEP), young module, scanning electron microscopy (SEM) and surface roughness of membrane were analyzed for the characterization of hydrophobic nanofiber membranes. Firstly, rGO/PVDF membranes with different rGO concentrations were produced using the electrospinning method. All fabricated rGO/PVDF membranes were characterized and used in the AGMD system for the treatment of saline water. Secondly, the selected optimum membrane according to characterization and filtration results was used in the AGMD system for the treatment of synthetic and real geothermal water. Results showed that all rGO membranes exhibit higher permeate water flux and salt rejection, lower permeate boron or salt concentration than pure PVDF membrane. In real geothermal water experiments, rGO/PVDF membrane (0.039 wt%) were improved permeate water flux from 19.20 to 30 L/m 2 .h, boron rejection from 96.89% to 98.16%. Also, permeate boron concentration was decreased using rGO/PVDF membrane (0.039 wt%) from 0.305 mg/L to 0.226 mg/L. As a result, fabricated rGO/PVDF membranes were achieved to the enhanced performance of the AGMD system.

Fabrication of visible-light assisted TiO2-WO3-PANI membrane for effective reduction of chromium (VI) in photocatalytic membrane reactor

In this work, TiO 2-WO3(40:1) nanoparticles were hydrothermally prepared and, embedded in Polyaniline (PANI) membrane with varying concentrations (3–7 wt%) and, used in photocatalytic membrane reactor for the removal of Cr(VI) from the aqueous solutions. 4-methyl piperidine (4-MP) was used as a gel inhibiting agent in N-methyl-2-pyrrolidone (NMP) solvent to prepare PANI-based flat-sheet membranes by phase inversion method. Through different characterization technique, it has been found that TiO 2-WO3 incorporated PANI membranes showed enhanced membrane properties like better hydrophilicity, better antifouling properties, higher water uptake, lower contact angle, higher porosity, and better heavy metal removal efficiency compared to bare PANI membranes. PANI membrane with 5 wt% TiO 2-WO3 exhibited a percentage rejection of 98.50% within 60 min at 0.5 MPa transmembrane pressure. Cr(VI) reduction under light and dark conditions was performed in a dead-end filtration cell with a quartz window at the top and the 5 wt% TiO 2-WO3– PANI membrane showed 67.32% reduction under visible light. TiO 2-WO3 incorporated PANI nanofiltration membranes can act as an integrated system consists of a short-circuited photo-anode and cathode under visible light irradiation. Overall, TiO 2-PANI membranes promote Cr(VI) reduction to Cr(III) in the photocatalytic membrane reactor and exhibits a better self-cleaning property.

In situ synchrotron imaging of human serum proteins interactions, molecular docking and inflammatory biomarkers of hemocompatible synthesized zwitterionic polymer coated-polyvinylidene fluoride (PVDF) dialysis membranes

Hemodialysis (HD) treatment leads to biochemical cascades due to protein adsorption and interactions, resulting in life-threatening side effects in many patients. Hemodialysis polyvinylidene fluoride (PVDF) membranes, independent of their structures and geometries, record impeded permeation performance due to their fouling-prone hydrophobic nature. In the present study, a clinical grade PVDF membrane was surface-modified with a new zwitterionic polymer (ZW) synthesized from a ring-opening polymerization between poly (maleic anhydride-alt-1-decene),3-(dimethylamino)-1-propylamine derivative and 1,3-propanesultone. Both coated and untreated PVDF membranes were characterized using appropriate surface analytical techniques before investigating the extent of serum protein fouling and interaction on each membrane surface using Synchrotron Radiation Micro-Computed Tomography (SR-µCT). The adsorption of fibrinogen bounded nanoparticles and their subsequent fouling on the membrane were only intensified within the topmost and mid-sectioned layer for the bare membrane. Surface imaging did not reveal significant presence of adhering protein on the ZW coated membrane surfaces; the results collected from scanning electron microscopy (SEM) and SR-µCT imaging are consistent and in agreement. Reduced episodes of multiprotein could contribute to limited tendencies for biological activations on coated membrane compared to its bare counterpart. This suggests that the bare membrane was a potent complement, coagulation, and inflammation activator; hence, it was bio-incompatible with the uremic blood sample upon contact. This ZW coated membrane also expressed less inflammatory biomarker releases upon incubation in uremic blood samples of chronic kidney disease (CKD) patients undergoing HD therapy. This clinical trial was conducted with a technique consistent with Luminex assays for eight biomarkers. Experimental investigations were also corroborated with in-depth molecular modeling docking in the quest to probe the interactions at active sites of three protein models. Docking of most potent structures into the human serum albumin active sites exhibited two important interactions: a hydrophobic interaction of protein backbones with PVDF model accompanied by polar interactions between CF groups and Arg257. This interaction related to the highest electronegativity from the fluorine atom. The presence of the novel ZW on PVDF significantly reduced protein adhesion due to polymer's positive/negative charged units.

Mechanically robust and highly conductive polymer electrolyte membranes comprising high molecular weight poly[2,2′-(bipyridyl)-bibenzimidazole] and graphene oxide

Promising proton exchange membranes comprising a nitrogen-rich and a high molecular weight poly[2,2′-(bipyridyl)-bibenzimidazole] (BipyPBI) polymer as a substrate and graphene oxide (GO) as a filler were successfully fabricated. The synergism of GO on the membrane physicochemical properties, including the acid doping level, acid retention capability, water uptake, swelling degree, mechanical properties, proton conductivity, oxidative stability, and the hydrogen permeability was studied. The results of the study confirmed the fabrication of mechanically robust and highly conductive proton exchange membranes. Regarding the phosphoric acid (PA) doping level, the BipyPBI/GO membrane reached 17 mol of PA per monomeric unit of BipyPBI (an increase of around 69% in PA-doping level compared to the bare BipyPBI membrane). The proton conductivity at 60 °C under anhydrous conditions increased from 0.002 S cm−1 to 0.019 S cm−1 (around 10-folds increase) when 4 wt% of GO was incorporated into the BipyPBI matrix. In addition, the conductivity reached 0.045 S cm−1 at 140 °C. The activation energy of the proton conduction decreased from 45.6 kJ mol−1 for the bare BiPyPBI to 12 kJ mol−1 for the composite membranes, indicating an improved proton mobility where the GO worked as a carrier-bridge for a smooth proton transfer into the polymer matrix. Furthermore, the H2 permeability reached 1.3 Barrer at 140 °C, indicating the fabrication of tightly-packed membranes. These results provide a very promising membrane for fuel cell applications.

Influence of structurally and morphologically different nanofillers on the performance of polysulfone membranes modified by the assembled PDDA/PAMPS-based hybrid multilayer thin film

A highly efficient nanofiltration membrane should exhibit high separation performance in removing divalent salts and organic solutes, as well as high permeation to meet practical separation and purification applications in aqueous media. Here, we designed a series of hybrid multilayer thin film membranes filled with the structurally and morphologically different nanofillers such as hexagonal boron nitride (HBN) nanosheets and metal-organic framework (MOF) nanoparticles, consisting of 3 and 6 layer pairs of polyelectrolyte through the layer-by-layer self-assembly technique (LBL) and characterized them in terms of dye and salt separation, as well as permeation. The rejection performance and permeability of the designed membranes manifested that HBN nanosheets were more effective than MOF nanoparticles in achieving a high-performance membrane. As compared to the bare multilayer thin film membrane, the addition of HBN nanosheets within the negatively-charged layers of the multilayer thin film membrane consisting of 6 bilayers resulted in good retention of up to 93% and 92% for acid blue (ACB) and bromophenol blue (BPB) dye molecules, respectively. Besides, this membrane exhibited 60% and 45% improvement in the water flux for ACB and BPB solutions, respectively, while the rejection of the sulfate ions maintained an acceptable value around 78%. Furthermore, it was found that this HBN-embedded hybrid multilayer membrane had superior potential for the removal of coherent foulant compared to all samples.

Influence of diazonium‐induced surface grafting on PES NF membrane fouling reduction in algal‐rich water treatment

AbstractThe algae bloom phenomenon incurs a major challenge to conventional drinking water treatment processes due to the discharges of a large amount of intracellular pollutant and odor compounds in the water sources. Membrane processes have been considered as promising technologies to treatment of algal‐rich water due to complete algal cell rejection however, its application has been limited by membrane fouling. In this work, the high‐performance loose antifouling PES NF membranes were fabricated using diazonium‐induced grafting and applied for treating real algal effluent. The modified membranes exhibited complete algal dye removal and turbidity removal throughout the long‐term filtration. Also, the coupling and radically modified membranes can be able to removed COD by up to 90% and 88%, respectively, while a removal efficiency of 24% was observed for bare membrane. It is worth noting that, a relative smooth behavior in permeate flux by loose modified membranes during prolonged algal dye filtration, demonstrating exceptional anti‐fouling property of membranes. In addition, the fouled modified membranes were effectively recovered by water flushing. Both loose modified membranes exhibited excellent resistance in the strongly acidic environment. These high performance antifouling NF membranes affords an innovative methodology toward the treatment of algal‐rich water.

Influence of UV-irradiation intensity and exposure duration on the hemobiocompatibility enhancement of a novel synthesized phosphobetaine zwitterions polyethersulfone clinical hemodialysis membranes.

To improve the biocompatibility of polyethersulfone (PES) membranes utilized for biomedical hemodialysis (HD) applications, surface grafting with hydrophilic polymers has become a reliable modification strategy. Like most photochemical catalyzed reactions, UV-assisted grafting is distinctly advantageous for inducing permanent surface chemistry, enhancing hydrophilicity, improving morphology, and surface charge of membranes. PES membranes may be hydrophilic and chemically stable; however, they also have low protein-binding capacity and very susceptible to fouling and target analyte binding. In this study, novel zwitterionic polymers (PVP-ZW) have been synthesized by UV-assisted grafting PVP to a phosphobetaine monomer in a reaction involving dimethylamino and dioxaphospholane-2-oxide terminal groups in an NVP monomer solution at varying UV exposure conditions. The highlight of the present study is the investigation of the hemocompatibility of coated PES HD membranes at varying UV exposure conditions with respect to membrane chemistry and morphology and its influence on human serum protein adsorption. A clinical investigation of inflammatory biomarker release from incubated coated membranes within uremic blood samples of HD patients reveals they are weak complement and coagulation activators compared to bare PES membrane. The trend of fibrinogen adsorption on coated PES membranes was observed to increase with reducing UV intensity and exposure duration. Fibrinogen adhesion only increased with roughened membrane surfaces, and this also led to the formation of biological activation pathways hindering biocompatibility. Resistance against fibrinogen absorption on zwitterionic modified PES membrane could be linked with the creation of electrostatically induced neutral zwitterionic PVP-phosphobetaine hydration layer with hydrophilic character. Experimental results are accompanied by spectroscopic and morphological imaging evidence. Zwitterion coated PES membranes (PES-PVP-ZW) fabricated from higher UV intensities through longer exposure durations showed significant presence of surface deformations in the forms of inherent exfoliations due to harsh UV reaction conditions. The zeta potential and surface roughness of coated membranes also played significant role in the fibrinogen adsorption on PES membranes during ultrafiltration.

Novel application of ion exchange membranes for preparing effective silver and copper based antibacterial membranes

Ion exchange membranes (IEMs) are widely used in water treatment applications such as electrodialysis. However, the exploration of IEMs as effective antibacterial food contact materials (e.g., food packaging membranes) against pathogenic bacteria to ensure food safety has not been reported. Here, we report a simple but effective method to prepare high performance antibacterial membranes via ion exchange coupled with in-situ reduction. The general membrane properties are characterized using SEM, EDS, FTIR, XPS, XRD, DSC, TGA, water uptake, etc. The distribution of silver and copper in the membranes are generally in line with the distribution of sulfur, indicating that the antibacterial ions are introduced into the membranes via ion exchange and are bonded with the sulfonate groups in the membranes. The antibacterial performance is investigated using zone of inhibition tests and continuous bacteria growth inhibition tests. All of the prepared membranes show obvious antibacterial activities compared to the bare cation exchange membranes. The diameters of inhibition zone against Staphylococcus aureus (S. aureus) are all larger than those of Escherichia coli (E. coli), indicating that the prepared membranes are more efficient in inhibiting S. aureus compared to E. coli. Furthermore, the silver-based membrane shows more sustainable antibacterial activities compared to the copper-based membrane. Especially, the results clearly reveal that the silver-based membrane is capable of killing bacteria instead of just inhibiting the growth of bacteria. We have shown for the first time that membranes derived from IEMs have the potential as food contact materials to inhibit the growth of pathogenic bacteria so as to eliminate the risk of bacterial infections and meanwhile delay food spoilage due to bacteria growth.

Modification of EPVC membranes by incorporating tungsten trioxide (WO3) nanosheets to improve antifouling and dye separation properties

In this research, the modification of emulsion polyvinyl chloride (EPVC) filtration membranes was evaluated by incorporating tungsten trioxide (WO3) nanosheets. The WO3 nanosheets at five different percentages were blended with the polymeric casting solution to prepare flat sheet membranes via the phase separation method. The prepared nanocomposite membranes were characterized by SEM, AFM, ATR, mean pore radius, porosity, and contact angle measurements. The investigated parameters were water flux, rejecting protein and three dyes, antifouling ability, long-term test and reuse ability. The obtained results showed that adding an optimal amount of WO3 (1 wt%) enhanced water flux and dye rejection. The nanocomposite membranes presented a lower contact angle due to the hydrophilicity of inserted WO3 nanosheets. The water permeability increased from 191 L/m2h.bar for the bare membrane to 238.8 L/m2h.bar for 1 wt% WO3 EPVC membrane with 96.6, 95.4 and 57.5% rejection rates for Reactive Green 19, Reactive Red 195 and Reactive Yellow 39 solutions with molecular weights of 1419, 1136.31 and 699.2 g/mole, respectively. The long-term test and reuse ability performance showed that the dye rejection did not change sensibly and good resistance was observed against the flux reduction. In conclusion, WO3 can be applied as a suitable nanosheet to modify PVC membranes.

Membrane cleaning strategy via in situ oscillation driven by piezoelectricity

Despite of the advanced progress made in membrane techniques, cleaning of membrane fouling remains challenging in membrane filtration process, especially during water purification, chemical and food production, etc. Existing techniques for alleviating membrane fouling such as ultrasound treatment can achieve limited improvement. Thus, developing more environmental-friendly, low-cost, and convenient cleaning strategies is highly desired. Here, we propose a self-cleaning concept of self-vibrating membrane with piezoelectric characteristics and demonstrate its feasibility in membrane anti-fouling. A well-designed piezoelectric membrane (ZnO-CNT/PVDF) has been constructed, where the in situ synthesized zinc oxide (ZnO) nanoparticles are served as a nucleation seed promoting the β-phase formation of poly (vinylidene fluoride) (PVDF) and the percolation network structure is formed by carbon nanotubes (CNTs) to achieve piezoelectric vibration. Encouragingly, the piezoelectric membrane resonated to external AC stimulus at 8 kHz and showed the highest vibration amplitude. The resultant ZnO-CNT/PVDF membrane demonstrated strong antifouling properties and excellent permeation recovery efficiency of 98.0% (AC, 12.5 V, 8 kHz), compared to 58.5% of the control ZnO-CNT/PVDF (0 V) and 53.0% of bare PVDF membrane (AC, 12.5 V, 8 kHz). The improved antifouling capacity benefited from that piezoelectric vibration could reduce the filtration resistances caused by concentration polarization (CP) layer and membrane fouling. Moreover, this antifouling mode of piezoelectric vibration is effective toward different charged foulants. This work demonstrates a novel and effective self-cleaning strategy for employing piezoelectric membrane in high-efficiency anti-fouling.