Excellent hydrophilic and anti-bacterial fouling PVDF membrane based on ag nanoparticle self-assembled PCBMA polymer brush

A silver nanoparticles-poly(carboxybetaine methacrylate)(AgNPs-PCBMA) nanocomposite was prepared on poly(vinylidene fluoride)(PVDF) membrane surface to improve its hydrophilicity and antifouling properties. Firstly, the PVDF membranes were grafted by PCBMA via physisorbed free radical grafting technique. Then Ag+ coordinated to the carbonyl group on PCBMA andsubsequently was reduced to silver nanoparticles. The hydrophilicity of the PVDF-gPCBMA/Ag membrane wasenhanced with the increasing fixed degree(FD) of AgNPs, and the original water contact angle of membrane was reduced to 33.97°. Additionally, water flux recovery ratio(FRR) andbovine serum albumin(BSA) rejection ratio of PVDF-g-PCBMA/AgNPs membrane wereimproved from 52% to 93.32% and 28.12% to 91.12%, respectively. Further, the PVDF-g-PCBMA/AgNPs membranes exhibited the more pronounced inhibition zone. The study demonstrated that compared with pure AgNPs or the PCBMA polymer brush, the synergistic effect of PCBMA and AgNPs made PVDF membranes havebetter hydrophilicity and anti-bacterialperformances.     

Nanostructured polyethersulfone membranes for dye and protein separation: Exploring antifouling role of holmium (III) molybdate nanosheets

Nanostructured polymer membranes are nowadays of crucial importance in achieving antifouling properties. Nanomaterials with tunable composition, size, and morphology, surface modification and functionality offer unprecedented opportunities for efficient wastewater treatment. In this work, the effect of holmium (III) molybdate (Ho₂MoO₆) nanomaterial as a new nanofiller on preparation of nanostructured polyethersulfone (PES) mixed matrix membranes was examined in terms of hydrophilicity, membrane morphology, permeability, dye and protein separation and antifouling property. The Ho₂MoO₆ nanosheets were synthesized and characterized by FTIR, XRD, and FESEM and used in different amounts in PES matrix. The pore size and the membrane porosity increased with Ho₂MoO₆ loading. The nanocomposite membranes showed enhancement in hydrophilicity, antifouling properties, dye rejection and permeability. The remarkably pure water flux (195 L/m²h at 3 bar) and 92.3% flux recovery after bovine serum albumin (BSA) filtration were obtained for the membrane mixed with 2 wt% Ho₂MoO₆ compared to 95 L/m²h and 75.2% obtained for the bare PES, respectively. Moreover, significantly high rejection of Acid Red 125 (95 ± 1%) was achieved. Thus, the experimental results established the potential efficiency of the novel nanocomposite membrane for the separation applications.     

Synthesis and property of a novel sulfonated poly(ether ether ketone) with high selectivity for direct methanol fuel cell applications

A novel membrane material based on random copolymer composed of poly(acrylonitrile-([3-(methacryloylamino)propyl]-dimethyl(3-sulfopropyl) ammonium hydroxide)) (PAN–MPDSAH) was synthesized by the water phase suspension polymerization. The zwitterionic PAN-based membranes were prepared through blending PAN and PAN–MPDSAH copolymer by a phase inversion method. The zwitterionic PAN-based membranes have higher hydrophilicity and wettability, and lower protein adsorption in comparison with the control PAN membrane. Ultrafiltration experiments revealed that membrane fouling, especially irreversible membrane fouling, for the zwitterionic PAN-based membranes is remarkably reduced due to the incorporation of zwitterionic PMPDSAH segments on the membrane surfaces. Moreover, the reversible membrane fouling during ultrafiltration process can be easily washed away by simple water cleaning. The zwitterionic PAN-based membranes can run for a long time and be reused without significant decrease of separation performance.     

Crosslinked poly(ethylene oxide) fouling resistant coating materials for oil/water separation

Potential fouling reducing coating materials were synthesized via free-radical photopolymerization of aqueous solutions of poly(ethylene glycol) diacrylate (PEGDA). Crosslinked PEGDA (XLPEGDA) exhibited high water permeability and good fouling resistance to oil/water mixtures. Water permeability increased strongly with increasing the water content in the prepolymerization water mixture, going from 10 to 150 L μm/(m² h bar) as prepolymerization water content increased from 60 to 80 wt.%. However, molecular weight cutoff decreased as water content increased. These materials were applied to polysulfone (PSF) UF membranes to form coatings on the surface of the PSF membranes. Oil/water crossflow filtration experiments showed that the coated PSF membranes had water flux values 400% higher than that of an uncoated PSF membrane after 24 h of operation, and the coated membranes had higher organic rejection than the uncoated membranes.     

Amino acids functionalized graphene oxide for enhanced hydrophilicity and antifouling property of poly(vinylidene fluoride) membranes

Herein, functionalized graphene oxide (GO) was prepared by the covalent functionalization with amino acids (lysine, glycine, glutamic acid and tyrosine) in this study. Zeta potential results demonstrated that covalent functionalization of GO with amino acids was favourable for their homogeneous dispersion in water and organic solvents. Based on the higher absolute value of zeta potential and the better dipersion stability of GO-lysine, the PVDF/GO-lysine hybrid membranes were then prepared via the phase inversion induced by immersion precipitation technique. SEM images showed a better pore diameter and porosity distribution on the PVDF/GO-lysine membrane surface. The zeta potential absolute value of the PVDF/GO-lysine membrane surface was higher than that of the virgin PVDF membrane. Furthermore, the PVDF/GO-lysine membranes surface exhibited good hydrophilicity. The water flux of PVDF/GO-lysine membranes can reach to two times of that of the virgin PVDF membrane. And the BSA adsorbed amount on PVDF/GO-lysine surface was decreased to 0.82 mg/cm² for PVDF/GO-lysine-8% membrane. Filtration experiment results indicated that the fouling resistance was significantly improved for the PVDF/GO-lysine membranes. As a result, lysine functionalized GO will provide a promising method to fabricate graphene oxide based hybrid membranes with effective antifouling property and hydrophilicity.     

Pervaporation separation of water + isopropanol mixtures using novel nanocomposite membranes of poly(vinyl alcohol) and polyaniline

Novel nanocomposite polymeric membranes containing nanosized (30–100 nm) polyaniline (PANI) particles dispersed in poly(vinyl alcohol) (PVA) were prepared and used in the pervaporation separation of water–isopropanol feed mixtures ranging from 10 to 50 mass% of water at 30 °C. Of the three nanocomposite membranes prepared, the membrane containing 40:60 surface atomic concentration ratio of PANI:PVA produced the highest selectivity of 564 compared to a value of 77 observed for the plain PVA membrane. Flux of the nanocomposite membranes was lower than those observed for the plain PVA membrane, but selectivity improved considerably. Membranes were characterized by differential scanning calorimetry, dynamic mechanical thermal analyzer, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy. The highest selectivity with the lowest flux was observed for 10 mass% water containing feed mixture. Flux increased with increasing amount of water in the feed, but selectivity decreased considerably. These results were attributed to the acid-doped PANI particles in the PVA membrane as a result of change in the micromorphology of the nanocomposite membranes. In addition, molar mass between cross-links and fractional free volume of the membranes are responsible for the varying membrane performance. Temperature effect on permeability was investigated for 10 mass% water containing feed with the membrane containing higher concentration of PANI particles, the presence of which could be responsible for varied effect of water permeation through the membrane. Membranes of this study could remove as much as 98% of water from the feed.     

Poly(N,N-dimethylaminoethyl methacrylate) grafted poly(vinyl chloride)s synthesized via ATRP process and their membranes for dye separation

To functionalize poly(vinyl chloride)(PVC) for various applications, monomers containing tertiary amine group are incorporated into PVC via atom transfer radical polymerization(ATRP) initiated by the labile chlorines in their backbones. The kinetics of synthesis was carefully investigated, and it is proven that the grafting polymerization process can be effectively controlled by regulating the reaction time. The membranes are fabricated using PVC and copolymers by non-solvent induced phase separation(NIPS) process. The hydrophilicity and pore structure of copolymer membranes were enhanced as well, these membranes are endowed with positive charge. When PDMA%(i.e., the PDMA weight percentage in copolymer) is 31.1%, the flux and Victoria blue B rejection are 26.0 L?m?2?h?1(0.5 MPa) and 91.2%, respectively. Thus, the newly synthesized polymer is proven to be a promising material for dye separation with positive charges.     

Structure-property relationships for novel wholly aromatic polyamide-hydrazides containing various proportions of para-phenylene and meta-phenylene units III. Preparation and properties of semi-permeable membranes for water desalination by reverse osmosis separation performance

Flat sheet asymmetric reverse osmosis membranes were successfully prepared from N,N-dimethylacetamide (DMAc) solutions of a series of novel wholly aromatic polyamide-hydrazides that contained different amounts of para- and meta-phenylene rings. These polyamide-hydrazides were synthesized by a low temperature solution polycondensation reactions of either 4-amino-3-hydroxybenzhydrazide or 3-amino-4-hydroxybenzhydrazide with an equimolar amount of either terephthaloyl dichloride [TCl], isophthaloyl dichloride [ICl] or mixtures of various molar ratios of TCl and ICl in anhydrous DMAc as a solvent. All the polymers have the same structural formula except of the way of linking phenylene units inside the polymer chains. The content of para- to meta-phenylene moieties was varied within these polymers so that the changes in the latter were 10 mol% from polymer to polymer, starting from an overall content of 0-100 mol%. All the membranes were characterized for their salt rejection (%) and water permeability (cm³ cm⁻² day⁻¹) of 0.5 N aqueous sodium chloride feed solution at 3924 kPa operating pressure. The effects of polymers structural variations together with several processing parameters to achieve the best combination of high selectivity and permeability were studied. Effects of various processing parameters of the membranes on their transport properties were investigated by varying the temperature and period of the solvent evaporation of the cast membranes, coagulation temperature of the thermally treated membranes, annealing of the coagulated membranes, casting solution composition, membrane thickness and the operating pressure. During the thermal treatment step, the asymmetric structure of the membranes with a thin dense skin surface layer supported on a more porous layer was established. The former layer seems to be responsible for the separation performance. The results obtained showed that membrane performance was very much influenced by all of the examined processing variables and that membranes with considerably different properties could be obtained from the same polymer sample by using different processing parameters. Thus, the use of higher temperatures and longer exposure times in the protomembrane forming thermal treatment step would result in a membrane of lower solvent content and with a thicker skin layer and consequently led to higher salt rejection at lower water permeability. Most significantly, the membrane properties clearly depended on the polymer structure. Under identical processing condition, substitution para-phenylene rings for meta-phenylene ones within the polymer series resulted in an increase in salt rejection capability of the membranes. This may be attributed to an increase in their chain symmetry associated with increased molecular packing and rigidity through enhanced intermolecular hydrogen bonding. This produces a barrier with much smaller pores that would efficiently prevent the solute particles from penetration. Coagulation temperature controls the structure (porosity) of the membrane particularly its supported layer and consequently its water permeability. Moreover, annealing of the prepared membranes in deionized water at 100 °C was found essential for useful properties in the single-stage separation applications, which required optimum membrane selectivity. Upon annealing, the membrane shrinks resulting in reducing its pore size particularly in the skin layer and consequently improving the salt rejection. Addition of lithium chloride to the casting solution produced a membrane with increased porosity and improved water permeability. Salt rejection capability of the membranes is clearly affected by the applied pressure, reaching its maximum at nearly 4000 kPa. Furthermore, the water permeability is inversely proportional to the membrane thickness, while the salt rejection is not substantially influenced.     

CO2/CH4 mixed gas separation using poly(ether-b-amide)-ZnO nanocomposite membranes: Experimental and molecular dynamics study

Poly (ether-b-amide) (PEBA) mixed matrix membranes (MMMs) filled by different amounts of nano ZnO (up to 1 wt %) were synthesized and their gas separation performance was evaluated for CO₂, CH₄ and N₂ pure gas and their binary mixtures. The ZnO-filled PEBA MMMs were characterized using ATR-FTIR, FESEM, AFM, TGA, DMTA, XRD and Mechanical tensile strength analyses. Generally, it was revealed that 0.5 wt % loading of ZnO into the polymer matrix caused a ZnO−PEO interaction; while ZnO–ZnO self-association hindered the interaction for the MMMs with other loadings of ZnO. As a result, PEBA-ZnO 0.5 wt % MMM possessed a higher glass transition temperature (T_g). Therefore, the CO₂ permeability through PEBA-ZnO 0.5 wt % enhanced 27% than simple PEBA membrane. Moreover, all the fabricated MMMs were simulated by molecular simulation. Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) methods were also applied to simulate the structural and gas transport properties of the membranes. The RDF, XRD, T_g, FFV and density analysis were compared with experimental results. Also, a binary mixture of CO₂:CH₄ (10:90) was used to determine CO₂ permeability and CO₂/CH₄ selectivity, which were considerably reduced compared to single gas experiments. Moreover, the solubility of the binary gas mixture, the energy distribution and density distribution of both gases within the simulated cell were calculated by molecular simulation.     

Application of polysulfone (PSf)– and polyether ether ketone (PEEK)–tungstophosphoric acid (TPA) composite membranes for water electrolysis

The ion exchange membrane using polysulfone (PSf) and polyether ether ketone (PEEK) as a basic material was prepared to apply in the polymer electrolyte membrane electrolysis (PEME). The sulfonated block copolymer of PSf and poly(phenylene sulfide sulfone) (SPSf-co-PPSS) and the sulfonated PEEK (SPEEK) were blended with tungstophosphoric acid (TPA) to avoid water swelling at elevated temperatures led to decrease in mechanical strength. These prepared ion exchange membranes showed some interesting characteristics including physicochemical stabilities, mechanical and membrane properties.The prepared ion exchange membrane was utilized to prepare the membrane electrode assembly (MEA). MEA consisted of Pt/PEM/Pt was prepared by equilibrium and non-equilibrium impregnation–reduction (I–R) methods. The prepared MEA by non-equilibrium I–R method was used in the PEME unit cell. The cell voltages of the MEA using SPSf-co-PPSS/TPA and SPEEK/TPA membranes were 1.83 V and 1.90 V at 1 A/cm² and 80 °C, with platinum loadings of 1.12 and 1.01 mg/cm², respectively.     

Controlled sulfonation of poly(arylene ether sulfone)s and poly(arylene ether ketone)s with different molecular structures for polymer electrolyte membranes

Poly(arylene ether sulfone) copolymers derived from 9,9-bis(4-hydroxyphenyl)fluorene, bisphenol S and 4,4′-difluorodiphenylsulfone and poly(arylene ether ketone) copolymers derived from 4-phenoxybiphenyl, diphenyl ether and isophthaloyl chloride were prepared as precursor polymers for sulfonation reaction in which sulfonic groups are introduced quantitatively into specified positions. Sulfonation reaction for these two series of copolymers by concentrated sulfuric acid was successfully carried out to give sulfonated polymers with controlled positions and degree of sulfonation. Thermal stability, moisture absorption and proton conductivity for these two series of copolymers were measured and the results were compared to those of perfluorosulfonic acid polymers.     

Poly(vinyl alcohol)/poly(methyl methacrylate) blend membranes for pervaporation separation of water + isopropanol and water + 1,4-dioxane mixtures

Pervaporation (PV) separation of water + isopropanol and water + 1,4-dioxane mixtures has been attempted using the blend membranes of poly(vinyl alcohol) (PVA) with 5 wt.% of poly(methyl methacrylate) (PMMA). These results have been compared with the plain PVA membrane. Both plain PVA and PVA/PMMA blend membranes have been crosslinked with glutaraldehyde in an acidic medium. The membranes were characterized by differential scanning calorimetry and universal testing machine. Pervaporation separation experiments have been performed at 30 °C for 10, 15, 20, 30 and 40 wt.% of feed water mixtures containing isopropanol as well as 1,4-dioxane. PVA/PMMA blend membrane has shown a selectivity of 400 for 10 wt.% of water in water + isopropanol feed, while for water + 1,4-dioxane feed mixture, membrane selectivity to water was 104 at 30 °C. For both the feed mixtures, selectivity for the blend membrane was higher than that observed for plain PVA membrane, but flux of the blend membrane was lower than that observed for the plain PVA membrane. Membranes of this study are able to remove as much as 98 wt.% of water from the feed mixtures of water + isopropanol, while 92 wt.% of water was removed from water + 1,4-dioxane feed mixtures at 30 °C. Flux of water increased for both the feed mixtures, while the selectivity decreased at higher feed water concentrations. The same trends were observed at 40 and 50 °C for 10, 15 and 20 wt.% of water mixtures containing isopropanol as well as 1,4-dioxane feed mixtures, which also covered their azeotropic composition ranges. Membrane performance was studied by calculating flux (J_p), selectivity (), pervaporation separation index (PSI) and enrichment factor (β). Permeation flux followed the Arrhenius trend over the range of temperatures investigated. It was found that by introducing a hydrophobic PMMA polymer into a hydrophilic PVA, the selectivity increased dramatically, while flux decreased compared to plain PVA, due to a loss in PVA chain relaxation.     

Preparation and characterization of ZIF-8 and ZIF-67 incorporated poly(vinylidene fluoride) membranes for pervaporative separation of methanol/water mixtures

Metal–organic frameworks (MOFs) are made up of metal centers and organic binders with larger surface area and distinct pore structures. Particularly significant advancement in MOF membranes has been achieved in three different directions: preparation of MOF membranes with larger surface area, improving the membrane performance by surface modification, and its usage with added features. However, its significance has not been completely known and concluded yet. MOF membranes are used in a variety of membrane-based separation like gas permeation, nanofiltration, pervaporation, membrane distillation, etc. This research aims to synthesize MOFs (ZIF-8 and ZIF-67) and MOF membranes (ZIF-8/PVDF and ZIF-67/PVDF) and used them in the pervaporative separation of the methanol/water mixture. MOFs and MOF membranes were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and thermogravimetry analysis. Methanol/water mixtures were be used to study the performance of the prepared membranes. A study on the process parameters such as temperature (40, 45, 50, and 55°C), feed pressure (4, 8, 12, and 16 psi), and feed composition (10%, 20%, 30%, and 40% of water) was carried out to examine the effect of each process parameters for pure membrane. In contrast, Taguchi screening design was used to screen the most influential process variable. The optimized conditions based on Taguchi screening method were 55°C, 12 psi, and 40 %vol of water in feed. The obtained total flux of 425 L/m²h was observed for M3 membrane. As feed temperature increased, the total flux of all three membranes was increased.     

Comparison of dye (oxazine and thiazine) materials as a photosensitizer for use in photogalvanic cells based on molecular interaction with sodium dodecyl sulphate by spectral study

The photochemistry of dye is playing a significant role for understanding the mechanism of electron transfer reactions in photoelectrochemical devices such as photogalvanic cells, DSSC, semiconductor photo-catalysis, photoconductors, etc. Oxazines (Brilliant Cresyl Blue and Nile Blue O) and thiazines (Azur A, Azur B, Azur C, Methylene Blue and Toluidine Blue O) dyes have been used widely as a photosensitizer with and without surfactants in the photogalvanic cells for solar power conversion and storage. Since, the stability and solubility of photosensitizers (dyes) are increased in the presence of surfactant and these properties lead to enhance the electrical output of the photogalvanic cells. Therefore, here we have studied the extent of interaction of different dyes with sodium dodecyl sulphate (SDS), find out the order of stability of dye–SDS on the basis of magnitudes of shifting in λ_max of dye monomer and try to correlate order of dye–SDS interaction with already reported electrical output data of photogalvanic cells. Brilliant Cresyl Blue, Nile Blue O, Azur A and TB O have shown red shifting while Azur B, Azur C and MB have shown blue shifting in their λ_max value with SDS, which indicates formation of dye–surfactant complex. But, the extent of formation of complex for different dyes with SDS was different due to change in their alkyl groups. Dyes with red shifting have greater stability in excited state as well as higher electrical output data of the cell than dye with blue shifting. On the basis of both red and blue shifting, order of stability of dyes–SDS complex was found as: Brilliant Cresyl Blue?>?Toluidine Blue O?>?Azur A?>?Nile Blue?>?Azur B?>?Methylene Blue?>?Azur C. The order of electrical output values of these dyes in photogalvanic cells have also been supported by literature data in the presence of SDS. Hence, the dye–surfactant complex which would have greater stability in excited state might be more useful for improvement of conversion efficiency and storage capacity of photogalvanic cells in the future.     

Influence of poly(N‐isopropylacrylamide) and poly(N,N′‐diethyl acrylamide) coatings on polysulfone/polyacrylonitrile‐based membranes for protein separation

Herein we describe the design and the assembly of temperature sensitive polysulfone (PS)/polyacrylonitrile (PAN) blend membranes using supercritical fluid technology. Blended membranes were prepared using the CO₂‐assisted phase inversion method, and their pores were coated with two thermoresponsive hydrogels‐poly(N‐isopropylacrylamide) (PNIPAAm) and poly(N,N′‐diethylacrylamide) (PDEAAm). Permeation experiments of bovine serum albumin (BSA) and lysozyme (LYS) solutions were used to evaluate the performance and temperature‐responsive behavior of coated membranes. While membranes coated with PNIPAAm presented similar protein permeation profiles at temperatures below and above its lower critical solution temperature, PDEAAm coating imparted a temperature‐responsive behavior to PS/PAN (90:10) membranes and selective permeation of proteins with different sizes. Copyright © 2011 John Wiley & Sons, Ltd.     

End-group cross-linked membranes based on highly sulfonated poly(arylene ether sulfone) with vinyl functionalized graphene oxide as a cross-linker and a filler for proton exchange membrane fuel cell application

High-performance end-group cross-linked sulfonated poly(arylene ether sulfone) (SPAES) membranes are developed using thiolate-terminated SPAES with very high degree of sulfonation (DS) such as 90 mol% (SK-SPAES90) and vinyl functionalized graphene oxide (VGO) as a cross-linker and a filler through the thiol-Michael addition reaction. Since free-standing membranes for fuel cell application could not be prepared using the water soluble and highly proton conductive SPAES with high DS of 90 mol%, cross-linked SPAES90 membranes are intentionally prepared. The cross-linked membranes are found to have good physicochemical properties with excellent proton conductivity that can be applied for the proton exchange membrane. In particular, the cross-linked SPAES90 membrane prepared using 1.0 wt% of VGO exhibits better dimensional stability than a SPAES70 membrane from the linear SPAES with DS of 70 mol% and the proton conductivities of this membrane are larger than those of Nafion 211 at 80 °C under different relative humidity conditions (40%-95%).     

A novel solid-phase microextraction using coated fiber based sol-gel technique using poly(ethylene glycol) grafted multi-walled carbon nanotubes for determination of benzene, toluene, ethylbenzene and o-xylene in water samples with gas chromatography-flame ionization detector

In this study, poly(ethylene glycol) (PEG) grafted onto multi-walled carbon nanotubes (PEG-g-MWCNTs) were synthesized by the covalent functionalization of MWCNTs with hydroxyl-terminated PEG chains. For the first time, functionalized product of PEG-g-MWCNTs was used as selective stationary phase to prepare the sol-gel solid-phase microextraction (SPME) fiber in combination with gas chromatography-flame ionization detector (GC-FID) for the determination of ultra-trace levels of benzene, toluene, ethylbenzene and o-xylene (BTEX) in real water samples. The PEG-g-MWCNTs were characterized by Fourier transform infrared spectra and also thermo-gravimetric analysis, which verified that PEG chains were grafted onto the surface of the MWCNTs. The scanning electron micrographs of the fiber surface revealed a highly porous structure which greatly increases the surface area for PEG-g-MWCNTs sol-gel coating. This fiber demonstrated many inherent advantages, the main being the strong anchoring of the coating to the fused silica resulting from chemical bonding with the silanol groups on the fused-silica fiber surface. The new PEG-g-MWCNTs sol-gel fiber is simple to prepare, robust, with high thermal stability and long lifetime, up to 200 extractions. Important parameters influencing the extraction efficiency such as desorption temperature and time, extraction temperature, extraction time, stirring speed and salt effect were investigated and optimized. Under the optimal conditions, the method detection limits (S/N=3) were in the range of 0.6-3 pg mL(-1) and the limits of quantification (S/N=10) between 2 and 10 pg mL(-1). The relative standard deviations (RSDs) for one fiber (repeatability) (n=5) were obtained from 4.40 up to 5.75% and between fibers or batch to batch (n=3) (reproducibility) in the range of 4.31-6.55%. The developed method was successfully applied to real water samples while the relative recovery percentages obtained for the spiked water samples at 20 pg mL(-1) were from 90.21 to 101.90%.