Nonsolvent Induced Phase Inversion Process Research Articles

Stabilizing high-nickel cathodes via interfacial hydrogen bonding effects using a hydrofluoric acid-scavenging separator

Nickel-rich layered Li transition metal oxides are the most promising cathode materials for high-energy-density Li-ion batteries. However, they exhibit rapid capacity degradation induced by transition metal dissolution and structural reconstruction, which are associated with hydrofluoric acid (HF) generation from lithium hexafluorophosphate decomposition. The potential for thermal runaway during the working process poses another challenge. Separators are promising components to alleviate the aforementioned obstacles. Herein, an ultrathin double-layered separator with a 10 μm polyimide (PI) basement and a 2 μm polyvinylidene difluoride (PVDF) coating layer is designed and fabricated by combining a non-solvent induced phase inversion process and coating method. The PI skeleton provides good stability against potential thermal shrinkage, and the strong PI-PVDF bonding endows the composite separator with robust structural integrity; these characteristics jointly contribute to the extraordinary mechanical tolerance of the separator at elevated temperatures. Additionally, unique HF-scavenging effects are achieved with the formation of -CO···H-F hydrogen bonds for the abundant HF coordination sites provided by the imide ring; hence, the layered Ni-rich cathodes are protected from HF attack, which ultimately reduces transition metal dissolution and facilitates long-term cyclability of the Ni-rich cathodes. Li || NCM811 batteries (where “NCM” indicates LiNixCoyMn1-x-yO2) with the proposed composite separator exhibit a 90.6% capacity retention after 400 cycles at room temperature and remain sustainable at 60 °C with a 91.4% capacity retention after 200 cycles. By adopting a new perspective on separators, this study presents a feasible and promising strategy for suppressing capacity degradation and enabling the safe operation of Ni-rich cathode materials.

Novel hexa-fluorinated intrinsically porous polyimide membranes for the desalination of high saline water by air-gap membrane distillation

Hexa-fluorinated porous membranes were prepared from 4,4′-(hexafluoroisopropylidene) diphtalic anhydride (6FDA)- 2,3,5,6- tetramethyl-p-phenylenediamine (TMPD) (6FDA-TMPD), which prepared by a polycondensation reaction between the dianhydride 6FDA and the diamine TMPD at 200 °C, by nonsolvent induced phase inversion process for the desalination of highly saline water (70,000 mg L−1) via membrane distillation (MD) technology. Here, for the first time, we demonstrate the significance of the intrinsic porosity of 6FDA-TMPD polyimide membranes, that not only result in an excellent performance in MD without the addition of porogen chemicals but also outperform other membranes including commercially available membranes. The membrane characteristics were optimized by varying the coagulation bath, dope solution concentration, and thickness. Notably, the developed membranes possess high porosity which can be attributed to the high BET surface area (550 m2 g−1) of 6FDA-TMPD. Membranes developed from an ethanol-based coagulation bath resulted in spongy-like morphology and demonstrated excellent desalination performance with a high flux (∼ 18.20 kg m−2 h−1) and stable salt rejection (> 99.96 %). The reported fabrication approach can be used to delineate the key design parameters for the fabrication of highly efficient intrinsically porous polyimide-based membranes which may pave the way for the practical application of MD for the desalination of highly saline water.Graphical abstract.

Preparation of defect-free hollow fiber membranes derived from PMDA-ODA polyimide for gas separation

Since PMDA-ODA polyimide is insoluble, its soluble precursor PMDA-ODA poly (amic acid) (PAA) is used to prepare hollow fiber membranes (HFMs). Due to the existence of –CO–NH– and –COOH groups, PAA is subject to form hydrogen bonds with water and consequently leads to a very slow phase inversion rate during the non-solvent induced phase inversion process. Therefore, the hollow fiber spinning has to be carried out with a low take-up speed that limits the productivity. In this paper, we increased the take-up speed of PAA hollow fiber to 60 m/min by simply adding LiCl into polymer dope. Moreover, an integrally skinned defect-free PMDA-ODA hollow fiber membrane was obtained at the high take-up speed where the gas permeances were 6.8 ± 0.7, 2.2 ± 0.2, 0.4 ± 0.04 and 0.07 ± 0.01 GPU for H2, CO2, O2 and N2, respectively, with an ideal selectivity of 3.1 ± 0.3, 31 ± 3.0 and 5.7 ± 0.6 for H2/CO2, CO2/N2 and O2/N2, respectively. These results indicated a dense PMDA-ODA layer of 1 μm. To our best knowledge, this is the first time that a defect-free hollow fiber membrane for gas separation is prepared based on PMDA-ODA.

Nanoporous polyethersulfone membranes prepared by mixed solvent phase separation method for protein separation

Nanoporous polyethersulfone (PES) membranes with high surface porosity and uniform pore size distribution were prepared by combining the phase separation in NMP/nonane mixed solvent system with the traditional nonsolvent induced phase inversion process. The effects of PES concentration, nonane concentration, evaporation time, casting solution temperature, and varied mixed solvent systems on the porous PES membrane surface morphology were thoroughly investigated and optimized. The optimized nanoporous PES membrane showed a high surface porosity with a uniform pore size of 20 nm, rendering an exceptional molecular weight cut-off of as low as 100 k Dalton. In addition, the membrane exhibited a significant molecular size exclusion with water permeance of 121 LMH bar−1, bovine serum albumin (BSA) protein rejection of 60.1%, and γ-globulin protein rejection of 99.5% at 0.5 bar, respectively, demonstrating the potential of the as-prepared nanoporous PES membrane for application in protein separation.

In-situ construction of superhydrophobic PVDF membrane via NaCl-H2O induced polymer incipient gelation for membrane distillation

In-situ construction of superhydrophobic polyvinylidene fluoride (PVDF) membrane was prepared through nonsolvent induced phase inversion process for direct contact membrane distillation (DCMD). Saturated sodium chloride aqueous solution (NaCl-H2O) was added to the casting solution as a green phase inversion inducing agent. The variation of polymer crystal and the formation mechanism of micro-nano structure on membrane surface were studied. The results showed that NaCl crystals could act as nucleus for the pre-gelation and crystallization of PVDF chains. The “harsh” nonsolvent, water, accelerated the gelation process. When the optimum amount of NaCl-H2O was added, superhydrophobic membrane with lotus leaf like micro-nano spherical structure and interconnected channels was obtained. The pure water contact angle reached 155.3° with DCMD flux of 54.5 L/m2∙h, which was about 1.6 times for the membrane without NaCl-H2O addition. The stability was also improved owing to the superhydrophobic structure.

Templated preparation of hierarchically porous nitrogen-doped carbon electrode material via a mild phase inversion route for high-performance supercapacitor

• Hierarchically porous nitrogen-doped carbon was prepared through a modified phase–inversion method. • Water vapor treatment induced the formation of mesopores in the whole carbon matrix. • Well-distributed macropores with uniform sizes were formed by using PVDF-HFP template. • The hierarchically porous structure and proper doping level endow the product with high and stable capacitive performances. By using poly (vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) as the template, a kind of nitrogen-doped carbon monolith with well-distributed hierarchical pores was prepared through a modified phase–inversion method. Due to the hierarchically porous structure and proper doping level, the synthesized electrode material delivered superior specific capacitances (312.2 F g −1 at 0.5 A g −1 and 217.6 F g −1 at 20 A g −1 ), as well as remarkable specific energy and power (7.1 Wh kg −1 at 250 W kg −1 ). More significantly, its high chemical and structural stability allow it to reach 109.7% of the original capacitance after 10,000 charge-discharge cycles at the current density of 20 A g −1 . The simple yet efficient synthetic strategy, unique porous structure, and thus the enhanced electrochemical capacitive performances of the prepared nitrogen-doped carbon not only make it a promising electrode material for energy storage devices, but also bring new ideas for the controllable preparation of polymer-derived hierarchically porous carbon materials. By using PVDF-HFP as the macropore template, nitrogen-doped carbon electrode material with hierarchically porous structure was prepared through non-solvent induced phase inversion process for high performance supercapacitors.

Antibacterial and antifouling properties of Ag3PO4/GO nanocomposite blended polyethersulfone membrane applied in dye separation

In this paper, the effect of Ag3PO4/GO nanocomposite upon the antibiofouling and permeation properties of polyethersulfone (PES) mixed matrix membranes were explored. Through the nonsolvent induced phase inversion process, the PES nanofiltration (NF) membrane, including Ag3PO4/GO nanomaterials was prepared. A reduction reaction used to the functionalization of Ag3PO4 on GO nanosheets. Energy-dispersive X-ray (EDX), atomic force microscopy (AFM), water contact angle (WCA), scanning electron microscopy (SEM), zeta potential, and ATR-FTIR analysis were applied for the membrane characterization. All the membranes embedded through the nanocomposites presented a better performance in comparison with the neat PES membrane. The PES membrane containing 0.5 wt% of Ag3PO4/GO exhibited (83 %) flux recovery ratio besides (13 %) irreversible resistance during filtration of BSA protein. Membrane antibacterial properties were studied through the colony-counting process by the photocatalytic activity of Ag3PO4. The PES membrane prepared with 0.5 wt% Ag3PO4/GO reduced 72 % of viable Escherichia coli and 84 % of Staphylococcus aureus in the bacterial suspensions. The nanofiltration performance of the membranes in Lanasol Blue 3R dye separation was investigated. All of the nanocomposite membranes had dye rejection higher than 85 %.

Two-dimensional superstructures filled into polysulfone membranes for highly improved ultrafiltration: The case of cuprous iodide nanosheets

Mixed-matrix membranes blended with nanosized inorganic fillers have been widely used in ultrafiltration (UF) for large molecule separation. In this work, we provide a feasible route to construct mixed-matrix polysulfone (PSf) UF membranes via the nonsolvent-induced phase inversion process, utilizing sheet-like copper iodide superstructures (s-CuI) as fillers. The size of s-CuI in lateral dimension reaches micrometer scale, but the nanosheets can be well embedded in the polymer matrix with their 2D basal planes parallel to the membrane surface. On account of the stacking straight-through channel structure of s-CuI and its large dimension spanning across multiple membrane pores within the layer, the PSf membrane blended with 0.8 wt% content of s-CuI displays optimal UF performance with a pure water permeation (PWP) of 1473 L/(m2 h bar) and a bovine serum albumin (BSA) rejection of 92%. In contrast, the pure PSf membrane only presents a PWP of 556 L/(m2 h bar) and a BSA rejection of 58.2%. Besides, the enhancement of mechanical stability for the PSf/s-CuI 0.8% membrane is significant and the leakage of the s-CuI filler is negligible. Though the antifouling performance of the PSf/s-CuI 0.8% membrane against the protein BSA is limited, its flux is always 2–3 times higher than that of the pure PSf membrane in each step during a sequential test of fouling behavior. This study indicates that it is highly promising to employ designable superstructures as functional fillers to construct novel mixed-matrix membranes with good interfacial compatibility and superior performance.

A novel antibacterial mixed matrixed PES membrane fabricated from embedding aminated Ag3PO4/g-C3N4 nanocomposite for use in the membrane bioreactor

Herein we represent the effects of the presence of Ag3PO4/g-C3N4 nanoparticles in the PES membranes matrix on the permeation properties and anti-biofouling performance by using two different solvents including DMAc and DMSO. The Ag3PO4/g-C3N4 nanocomposites were synthesized via co-precipitation and thermal pyrolysis methods A new polyethersulfone (PES) microfiltration membrane containing g-C3N4 nanosheets/Ag3PO4 nanoparticles was prepared via the nonsolvent induced phase inversion process. High hydrophilicity and the antibacterial properties of Ag3PO4-NH2 nanoparticles made them a superior choice to be combined with g-C3N4 nanosheets to modify the membrane characteristics as a nanofiller additive. Field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), mean pore size measurement, water contact angle, and energy dispersive X-ray (EDS) were applied for the membrane characterization. Also, the permeation performance and antibacterial properties of the membranes were studied. All the membranes incorporated with nanoparticles presented better membrane properties in comparison with the pristine PES membrane. The water permeation was improved from 262.3Lm2−h to 360.0Lm2−h for membrane containing 0.5wt% of the functionalized Ag3PO4/g-C3N4 nanocomposite in the PES/DMSO matrix. To some extent, the excellent antimicrobial ability of these nanohybrid membranes could turn them in to a desirable candidate to overcome biofouling issues in applications such as the membrane bioreactor (MBR) systems. The MBR results also revealed that the pure water flux and the critical flux were enhanced.

From ultrafiltration to nanofiltration: Nanofiltration membrane fabricated by a combined process of chemical crosslinking and thermal annealing

An integrally skinned dense ultrafiltration (UF) membrane was prepared using partially di-quaternized poly(sulfone-co-ethernitrile) random copolymer (PSF-co-DQAPEN) via classical nonsolvent induced phase inversion process (NIPS). Then the original UF membrane was molecularly restructured through a combined process of chemical quaternization-crosslinking reaction and thermal annealing for the preparation of a crosslinked nanofiltration (NF) membrane, in which p-xylylene dichloride (PXDC) and isopropanol were employed as crosslinking agent and nonsolvent treating medium, respectively. The influence of reaction time and crosslinker concentration on membrane performance were investigated. X-ray photoelectron spectroscopy (XPS) of membrane surface and solubility test of membrane were employed to study the chemical composition and crosslinking properties of membranes, and those results revealed that the original membrane had been successfully crosslinked after this post treatment process. The separation performance of membrane was ultimately changed from UF-level to NF-level after the quaternization-crosslinking reaction and thermal annealing treatment process. The optimum crosslinked NF membrane possessed MgCl2 rejection of 98.2% and water permeate flux of 4.12 L m−2 h−1 bar−1. Moreover, owning to the excellent chemical stability of membrane material, the crosslinked membrane had outstanding resistance to chlorine, acid and base, thus it can be used for water softening and removing of positive dyes. Given the convenience and feasibility of this modification method, integrally skinned NF membrane could be easily fabricated via the post chemical crosslinking and thermal annealing process of UF membrane using proper treating approaches.

High molecular weight poly(vinyl pyrrolidone) induces hierarchical surface morphology in poly(vinylidene fluoride) membrane and facilitates separation of oil-water emulsions

Preparation of membranes with hierarchical surface morphology without delaying phase inversion process or increasing time lag between casting and contacting to non-solvent bath is reported. Poly(vinylpyrrolidone) (PVP) acts as a pore forming polymer in membrane preparation via the non-solvent induced phase inversion process. Herein, we report that molecular weight (Mn) of PVP greatly influences the surface morphology of poly(vinylidene fluoride) (PVDF) membrane. PVP of Mn ≥ 360 kDa induces hierarchical globular morphology on PVDF/poly[(methyl methacrylate)-co-(vinylbenzyl chloride)] copolymer membrane, without delaying phase inversion process or increasing time lag between casting of polymer solution and contacting to non-solvent. PVP (Mn ≥360 kDa) exhibited sole effect on the morphology, which did not depend on presence or absence of copolymer nor on the Mn of PVDF. Post modification of the blend membrane with polyethyleneimine gave superhydrophilic and underwater oleophobic membrane. The membrane could separate surfactant-free and surfactant-stabilized oil-water emulsions under applied pressure of 0.35 bar without need of frequent cleaning. A permeate water flux of about 250 L m−2 h−1 with > 99% rejection of oil and flux recovery ratio as high as > 99% was achieved. The membrane modules also showed similar antifouling property during oil-water separation to that of membrane coupons. PVDF/copolymer undergoes nano-phase separation in the casting solution in presence of PVP (Mn ≥360 kDa), formed nano-clusters which remained on the membrane surface. Novel effect of PVP on the surface morphology in continuous-mode membrane preparation, easy post modification, and low flux reduction (15–25%) during separation of oil-water emulsions highlight the potential of the membrane in practical applications.

Preparation, characterisation and critical flux determination of graphene oxide blended polysulfone (PSf) membranes in an MBR system

Microfiltration membranes having different blends of graphene-oxide (GO) (0–1 wt%) and Polysulfone (PSf) (15–20 wt%) were prepared using the classical non-solvent induced phase inversion process. The prepared membranes were characterised for their structural morphology, surface properties, mechanical strength, porosity and pure water flux. Based on the initial characterisation results, four membranes (15 wt% PSf, 15 wt% PSf + 0.25 wt% GO, 15 wt% PSf + 1 wt% GO and 20 wt% PSf + 1 wt% GO) were chosen for critical flux study, that was conducted using flux-step method in a lab scale MBR system. In order to study the application potential of GO blended membranes, the critical flux of each membrane was evaluated in two operational modes i.e., continuous and intermittent modes with backwash. The membranes with maximal GO concentration (15 wt% PSf + 1 wt% GO and 20 wt% PSf + 1 wt% GO) showed higher critical flux (16.5, 12.8 L/m2h and 19, 15 L/m2h for continuous and intermittent mode, respectively). It was observed that the operational modes did not have a significant effect on the critical flux of the membranes with low GO concentration (15 wt% PSf and 15 wt% PSf + 0.25 wt% GO), indicating a minimal of 1 wt% GO was required for an observable effect that favoured intermittent mode of operation. Through these results, ideal operating condition was arrived (i.e., flux maintained at 6.4 L/m2h operated under intermittent mode) and the membranes 15 wt% PSf and 15 wt% PSf + 1 wt% GO were studied for their long-term operation. The positive effect of GO on filtration time, cleaning frequency and against fouling was demonstrated through long term TMP profile of the membranes, indicating the suitability of GO blended membrane for real time wastewater treatment.

A novel ionically cross-linked sulfonated polyphenylsulfone (sPPSU) membrane for organic solvent nanofiltration (OSN)

This paper describes the formation of a new generation of organic solvent nanofiltration (OSN) membranes via one-step in-situ crosslinking method by casting a solution mixture of sulfonated polyphenylsulfone (sPPSU) and hyperbranched polyethylenimine (HPEI) through a non-solvent induced phase inversion process. Ionically cross-linking reactions took place between sPPSU and HPEI, and were confirmed by FTIR and XPS. The as-fabricated membranes showed good chemical stability in ethanol and isopropanol, and were evaluated in terms of pure ethanol permeability and rejection ability of different dyes with molecular weights ranging from 320 to 1017g/mole in ethanol. The effects of HPEI concentration in dope solutions on OSN performance were firstly investigated, it was found that 0.3wt% HPEI gave the highest permeance (7.96Lm−2h−1bar−1) and a rejection of 51% to Rose Bengal (Mw = 1017). To further improve the OSN performance, several post treatments including dip coating and pressure assisted coating were conducted using a 1.0wt% HPEI solution in either water or ethanol. The coating under pressure showed the most effectiveness to enhance the crosslinking reaction and narrow the molecular weight cut off (MWCO). The resultant membrane had a MWCO of ≈ 600g/mole, a rejection of 99.9% to Rose Bengal and an ethanol permeance of 1.47Lm−2h−1bar−1. Compared to the un-modified sPPSU, all ionically cross-linked membranes possess much more stable rejections and permeance over a period of two weeks, especially for the membrane with the pressure assisted coating. These ionically cross-linked membranes may open up new strategies to design high performance OSN membranes due to the facile in-situ cross-linking method.

Superhydrophobic PVDF membrane induced by hydrophobic SiO 2 nanoparticles and its use for CO 2 absorption

Abstract In this study, we reported a simple and facile methodology to prepare superhydrophobic poly(vinylidene fluoride) (PVDF) membrane via nonsolvent induced phase inversion process. The addition of hydrophobic modified SiO2 nanoparticles (HMSNs) in ethanol bath resulted in PVDF precipitation dominantly by solid-liquid demixing, and the obtained membrane was uniformly skinless and composed of spherical microparticles. The deposition of HMSNs on the microspheres formed micro- and nanoscale structure, which was crucial for superhydrophobicity. When HMSNs concentration in bath was 2 g·L−1, the water contact angle of the modified PVDF membrane was higher than 160° and the surface free energy decreased to 0.9 mN·m−1. Since the proposed modification allowed HMSNs migration into the membrane interior during the exchange between solvent and non-solvent, the hydrophobicity of internal surface of membrane pores and channels was also enhanced. This feature successfully inhibited the liquid intrusion into membrane pores, and promised a stable anti-wettability in long-term performance. The modified PVDF membrane was used in membrane contactor for CO2 absorption. The wetting problem was markedly alleviated in an intense 20-day test even with a 12 wt% 2-aminoethanol solution as absorption solution. Our results demonstrated that the incorporation of hydrophobic nanoparticles in coagulation bath is a promising approach to obtain superhydrophobic PVDF membrane for membrane gas absorption.

Investigation of the relation between viscoelastic properties of polysulfone solutions, phase inversion process and membrane morphology: The effect of solvent power

This study displays that the lacy structure could be effectively formed and retained in polysulfone (PSf) membrane morphology, prepared by non-solvent induced phase inversion process, by the adoption of poorer solvent as an additive. With 2-pyrrolidone (2P) as a solvent, the PSf membrane comprised a porous skin layer, lacy structure and fewer macrovoids, while with N-methyl pyrrolidone (NMP) a dense skin layer, finger-like macrovoids and cellular structure were dominant. The addition of 2P and water to PSf/NMP solution increased the viscoelasticity of the polymer solution. When water added to the PSf/NMP solution, the fully cellular structure formed in the PSf membranes due to the enhanced viscosity of the solution and occurring the delayed liquid-liquid demixing process. The enhanced viscoelasticity of the PSf/NMP solution with the utilization of 2P at various ratio slowed down the growth rate of demixed domains during the liquid-liquid demixing process due to the formation of hydrogen bonding between PSf chains and 2P molecules in the solution. The gelation of polymer-rich phase inhibited the coarsening of the phase-separated domains, and consequently, the lacy structure formed and locked in the nascent PSf membrane. The lacy structure formation, as well as the size and shape of the macrovoids in the PSf membranes, were controlled by the amounts of 2P presented in the systems. Also, the performance results showed that the flux is enhanced and salt rejection is declined with 2P content in the dope solution. While, the addition of water yielded reverse results, which they are in good agreement with the membrane morphology.

Tight ultrafiltration membrane: Preparation and characterization of thermally resistant carboxylated cardo poly (arylene ether ketone)s (PAEK-COOH) tight ultrafiltration membrane for dye removal

Cardo poly (arylene ether ketone)s bearing hydrophilic carboxylic acid groups (PAEK-COOH) was successfully synthesized by condensation polymerization of 2-[bis(4-hydroxyphenyl)methyl] benzoic acid and 4,4′-bisfluorodiphenylketone. TGA and DSC analyses demonstrated that the material has an initial decomposition temperature and glass transition temperature of 360°C and 220°C respectively, which revealed the excellent thermal stability of PAEK-COOH. Then PAEK-COOH was employed to fabricate tight ultrafiltration membrane by the nonsolvent induced phase inversion process (NIPS). The water contact angle of the prepared membrane is 61.5°, indicating its good hydrophilicity. The PAEK-COOH tight ultrafiltration membrane possesses a pure water flux of 119.6±2.6Lm−2h−1, dye permeation flux of 100.9±4.3Lm−2h−1 and rejection of 99.8±0.33% for Congo red at dye concentration of 100ppm and operation pressure of 0.4MPa. Membrane has a molecular weight cut off of 9260Da and gives complete penetration of monovalent inorganic salt NaCl but a slight rejection of divalent inorganic salt Na2SO4 (less than 10%). Thus, the membrane could be used in the decolorization of wastewater or fractionation of dye and salt mixture for dye purification. The membrane also exhibits excellent antifouling performance and anti-dye adsorption properties with a flux recovery ratio of 91.5% for BSA and dye adsorption rate below 5.0% for four kinds of studied dyes, respectively.

Ultrafiltration membranes with tunable morphology and performance prepared by blending quaternized cardo poly(arylene ether sulfone)s ionomers with polysulfone

Abstract The original quaternized cardo poly(arylene ether sulfone)s (QPES-I) ionomers was employed as the virgin polyelectrolyte and its counterions (I−) were exchanged with F− and PF6− to prepare QPES with different anions(QPES-X, X = F, PF6), then QPES-X/PSF blended ultrafiltration membranes was prepared by the nonsolvent induced phase inversion process. Scanning electron microscopy (SEM) was used to characterize the cross section morphology and surface morphology of blended membranes, and atom force microscopy (AFM) was employed for obtaining the three-dimensional images of QPES-X/PSF blended membranes, respectively. The surface chemical composition of the asymmetric membrane was investigated by X-ray photoelectron spectroscopy (XPS). Under similar preparation conditions, the water contact angle on membrane surface increased in the order of QPES-F

Surface modification of polyacrylonitrile ultrafiltration membranes using amphiphilic Pluronic F127/CaCO3 nanoparticles for oil/water emulsion separation

In this work, flat sheet polyacrylonitrile (PAN) based ultrafiltration (UF) membranes were fabricated by blending with amphiphilic copolymer Pluronic F127 (PF127) and inorganic calcium carbonate (CaCO3) nanoparticles by nonsolvent induced phase inversion process which was employed as fouling resistant membranes for the separation of oil-water emulsion mixture. CaCO3 nanoparticle was synthesized by controlled precipitation of saturated carbonate and calcium nitrate aqueous solution and was then confirmed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction spectroscopy (XRD) and high-resolution transmission electron microscopy (HR-TEM). The fabricated membranes were characterized by attenuated total reflectance infrared spectroscopy (ATR-FTIR), thermal gravimetric analysis (TGA), mechanical analysis, scanning electron microscopy (SEM), atomic force microscopy (AFM) analysis to study the effect on the addition of PF127 together with varying amount of CaCO3 nanoparticle dosage on the membrane property. The filtration performances of the membranes were evaluated by measuring pure water flux, molecular weight cut off (MWCO), porosity and water content. The membrane hydrophilicity/hydrophobicity was examined through water contact angle measurement and separation efficacy was measured through ultrafiltration of oily feed solution. Membrane properties such as wettability, pure water permeability, mechanical strength, thermal stability, oil removal efficiency of the modified membrane was found to increase high upon addition of 0.75wt% of CaCO3 nanoparticle. Flux recovery was found to elevate from around 63% to 90% after a simple hydraulic wash indicating that the modified hybrid membranes were less susceptible to fouling. The increase in water permeability and antifouling property is ascribed the presence of large number of hydroxyl functional groups coupled with large number of small pores on the modified membrane surface.

Preparation and characterization of PES-cobalt nanocomposite membranes with enhanced anti-fouling properties and performances

Fouling and biofouling are still the challenging issues of membrane application in water industry. One of the practical approaches to control these limits is to develop anti-biofouling membranes. For this reason, novel polymeric membranes loaded with cobalt nanoparticles were produced for evaluating their properties against biofouling. Cobalt nanoparticles (CoNP) were synthesized by the reduction of Co+2 in aqueous solution using 4-aminophenol as reducing agent and cetyltrimethylammonium bromide CTAB as capping agent. The nanocomposite membranes of polyethersulfone-cobalt nanoparticles (PES-CoNP) were prepared by non-solvent induced phase inversion process (NIPS) using N-methyl-pyrrolidone (NMP) as solvent, PVP in different concentration, as pore forming and dispersing agent (of the cobalt nanoparticles) and pure water as non-solvent. The effect of nanoparticles concentration in membrane formation as well as the changes in the morphological and physical chemical properties of the produced membranes was studied, too. The nanocomposite membranes were systematically characterized using, Fourier Transform infrared spectrophotometer (FTIR) X-ray diffraction (XRD), Thermal gravity analysis (TGA), contact angle, zeta potential, porosity, pore size distribution, Atomic Force microscopy (AFM), Field emission scanning electron microscope (FESEM), water permeability, membrane performances in seawater and urban wastewater, antibacterial activity and mechanical properties. The PES-cobalt nanocomposite membranes exhibited good antibacterial activity as well as improved anti-biofouling properties. Overall, the results suggest, the functionalization of PES membranes by loading CoNP could be a viable solution to be applied in water treatment without compromise the performances of the pristine PES membranes.

Study on the fabrication, characterization and performance of PVDF/calcium stearate composite nanofiltration membranes

In this study, hydrophobic nanofiltration membranes were fabricated by blending polyvinylidene fluoride (PVDF) and calcium stearate through nonsolvent induced phase inversion process. The prepared membranes were characterized by attenuated total reflectance infrared spectroscopy (FTIR-ATR), X-ray diffractometry (XRD), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), field emission microscopy with energy dispersive X-ray spectroscopy (FESEM with EDX), scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle measurement, work of adhesion and mechanical strength analysis. The modified composite membranes were thermally and mechanically stable. The filtration performances of the membranes were examined by determining molecular weight cut off (MWCO), porosity, and water uptake rate. The highly hydrophobic character was confirmed by contact angle measurement, work of adhesion analysis and thickness parameters of the membranes. Low surface roughness was evident in AFM topography. The inorganic salts were highly rejected by these membranes in the following sequence Na2SO4>MgSO4>MgNO3>LiCl>NaCl. Humic acid was used as the model foulant to testify the antifouling property. The flux recovery ratio (FRR) was high, ensuring excellent irreversible fouling. Membrane irreversible fouling was enhanced for its dominant charge effects, highly hydrophobic character and low surface roughness; diminishing the organic foulants to get deposited on the membrane surface and also acted with its self cleaning capacity. The modified membranes were good enough to withstand its stability and durability.