Poly Vinylidene Fluoride Microporous Membranes Research Articles

Quaternary phase-field simulation of the effect of additives on the structure of polyvinylidene fluoride microporous membranes

This study builds upon the existing phase-field model of the non-solvent-induced phase separation (NIPS) method, simulating factors that influence membrane formation in a ternary system. A polyvinylidene fluoride (PVDF) membrane system is utilized, and a fourth substance, an additive, is introduced based on the original mathematical model of the ternary system. The interaction parameters of the additives within the system are calculated using the Krevelen method. The simulation is configured to set the values of additive mobility and loss coefficients of the concentration gradient, thereby simulating the effect of additives in the quaternary system on the evolution of the micropore membrane structure. Finally, simulated images of different concentrations of additives with various types are compared with experimental results of microporous structure and porosity formation. This comparison serves to validate the model.

Facile preparation of high performance GO/Mn3O4/PVDF composite membranes with intercalation of manganese oxide nanowires.

Polyvinylidene fluoride (PVDF) has been widely studied and applied in separation membranes due to its high thermal and chemical stability and mechanical strength. However, PVDF has strong hydrophobicity, resulting in easy contamination of the membrane surface and fast flux attenuation, so it is necessary to modify the membrane surface to improve its separation selectivity and service life. In this paper, PVDF microporous membrane was used as the matrix material and graphene oxide (GO) as the separation layer material. The GO/Mn3O4/PVDF composite membrane was prepared by layer self-assembly of GO nanosheets, and the functional layer spacing was adjusted by nanometer Mn3O4 intercalation. The prepared composite membrane showed high flux and separation selectivity in the filtration of organic compounds. The results showed that the rejection of methylene blue increased from 34% to 99.5%, and the flux decreased from 3000 L m-2 h-1 to 95 L m-2 h-1 when GO nanosheets covered the PVDF supporting membrane. After the introduction of Mn3O4 nanowires in the GO interlayer, the dye rejection reached 99.9% and the flux reached 612 L m-2 h-1. Compared with the unintercalated composite membranes, the flux of the prepared composite membranes showed good stability in the treatment of methylene blue, and the rejection remained unchanged.

Phase-Field Simulation of the Effect of Coagulation Bath Temperature on the Structure and Properties of Polyvinylidene Fluoride Microporous Membranes Prepared by a Nonsolvent-Induced Phase Separation.

We used the phase-field model of the existing Nonsolvent Induced Phase Separation (NIPS) method to add the variable of temperature in simulating the changes in the process of membrane formation. The polyvinylidene fluoride (PVDF) membrane system was applied to examine the influence of coagulation bath temperature change on the skin-sublayer of the membrane structure, thereby elucidating the development process of membrane structure under different conditions and shedding light on the most suitable coagulation bath temperature ranges. It was found that as coagulation bath temperature increased, the number of interface pores in the outer skin layer decreased, but the size increased. As a result, it changed from the crack shape to round-hole shape, thus making the pore structure looser. In the sublayer, the mesh support structure was increased, which enhanced the mechanical strength of the membrane. Relevant experiments also verify the effectiveness of the model.

Theoretical and experimental investigation of CO2 capture through choline chloride based supported deep eutectic liquid membranes

The supported liquid membranes (SLMs) provide a feasible solution to global warming by combining their high CO2 interaction with stripping in a continuous and single step process. Herein, deep eutectic solvents (DESs), possible substitutes to ionic liquids (ILs), were used as material to synthesize novel SLMs. The DESs were prepared from choline chloride and urea using three different mole ratios 1:2, 1:1, and 2:1 respectively. The prepared DESs were impregnated into the pores of polyvinylidene fluoride microporous membrane support to form novel DES-SLMs. The DESs-SLMs were tested using pure and mixed gas CO2 permeability as well as CO2/N2 and CO2/CH4 separation experiments. Density functional theory calculations were performed to get an insight into the interaction of DES with CO2 over N2/CH4. The complexation energies (Ec) of the DES with CO2, N2, and CH4 were in the order of −29.3, −9.9, and −13.0 kJ/mol, respectively which reflected the high interaction of CO2 with DES over CH4 and N2. The DES with choline chloride to urea molar ratio of 2:1 showed the highest CO2 permeability of 45.6 Barrer and corresponding CO2/CH4 and CO2/N2 selectivity of 61.62 and 78.62, respectively. Finally, a comparison with the supported ionic liquid membranes (SILMs) literature showed that the DESs-SLMs presented comparable CO2 permeability and a significantly high CO2/CH4 selectivity which enabled them to surpass the well-known Robeson’s upper bound proving their commercial potential. This reflects that the DES-SLMs are a green strategy for carbon capture which can replace the SILMs in practical applications.

A Janus facilitated transport membrane with asymmetric surface wettability and dense/porous structure: Enabling high stability and separation efficiency

Facilitated transport membranes have been extensively applied in a myriad of industrial fields, in view of their distinctive capabilities of selective separation of target species (e.g., ions/small molecules). Despite much progress, it remains challenging to tackle the trade-off relationship between the stability and separation efficiency of these membranes. Herein, we propose a Janus facilitated transport membrane with asymmetric surface wettability and dense/porous structure by decorating a hydrophilic and dense polymer inclusion membrane (PIM) skin layer on the surface of a hydrophobic and microporous polyvinylidene fluoride (PVDF) membrane to achieve a notable balance between separation efficiency and leakage-resistance. With the hydrophilic PIM skin layer facing aqueous solutions whilst the hydrophobic PVDF membrane towards organic solution during separation process, the Janus facilitated transport membrane remarkably prevents the leakage of the liquids from 66.7% (using the plain PVDF membrane) to negligible. Through a rapid transformation of the transport mechanism from a short-term hopping in the dense PIM skin layer to an unobstructed motion in the microporous PVDF membrane matrix, the separation efficiency of the Janus facilitated transport membrane has been considerably enhanced from 25% (using the PIM) to about 70%. Investigation of the influencing factors on the structures, properties and separation performance of the Janus facilitated transport membrane suggests that the concentration of the PIM casting solution is of particular importance to the formation of the PIM skin layer and the asymmetric dense/porous structure of the membrane. In addition, the Janus facilitated transport membrane exhibits extraordinary mechanical properties and selectivity. Our work demonstrates that the Janus facilitated transport membrane holds great promise and a wide scope in versatile applications in water treatment, water-oil separation, and recovery of metal ions/small molecules in complex systems (e.g., water-oil-metal ions and water-oil-small molecules).

Effect of Different Pore-Forming Additives on the Formation of PVDF Microporous Membranes for Bucky-Gel Actuator

The microporous polyvinylidene fluoride (PVDF) membranes were prepared by the solvent evaporation method using 50 wt.% of different pore-forming additives: poly(1-ethyl-3-vinylimidazolium tetrafluoroborate) (PIL-BF4), polyethylene glycol 3000 (PEG-3K) and 40000 (PEG-40K), dibutyl phthalate (DBP). The influence of used additive on morphology, porosity, degree of crystallinity, tensile properties, electrolyte uptake and ionic conductivity of the membranes were investigated. The maximum electrolyte uptake of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) was 184 wt.% for the membrane prepared with PEG-40K, however, the membrane was fragile and unsuitable for practical use. The remaining membranes showed approximately the same porosity (45‒48%) and electrolyte uptakes (169‒175%). At the same time, the membranes significantly differed in mechanical properties and ionic conductivity. The membrane prepared with PIL-BF4, unlike others, has a sponge-like structure and demonstrated high mechanical properties, namely tensile strength is 17.7 MPa and fracture strain is 132.5%. Bucky gel actuators were fabricated using membranes prepared with different additives. The blocking force of the actuators based on membranes with different additives decreased in the sequence of PIL-BF4, DBP and PEG. The actuator based on the membrane prepared with PIL-BF4 demonstrates a blocking force of 5.7 mN and a deformation of 1.35 % at 3 V DC.

Facile preparation of superhydrophobic PVDF microporous membranes with excellent anti-fouling ability for vacuum membrane distillation

Superhydrophobic polyvinylidene fluoride (PVDF) microporous membranes with micro-nano hierarchical structure were prepared by combining immersion precipitation with rolling embossing. This method was primarily consisted of semi-gelation process, rolling embossing process and water bath gelation process. The introduction of the semi-gelation process ensured the successful rolling embossing. The membranes were characterized by XRD, SEM, AFM, contact angle, pore size, porosity, N2 flux, and mechanical stability. The results indicated that the water contact angle and the sliding angle of the embossed membrane prepared under the optimal conditions were 151.2° and 5.4°, respectively. The N2 flux of the embossed membrane was higher than that of un-embossed membrane, and the micro-nano hierarchical structure had excellent mechanical stability. The synergy of mechanical properties, porosity, pore sizes and hydrophobicity made embossed membranes suitable for vacuum membrane distillation (VMD) applications. Compared with the un-embossed membrane, the embossed membrane showed better desalination performance and anti-fouling ability. The embossed membrane had a permeation flux of 24.81 kg/m2·h and a 99.9% rejection rate. Fouling was difficult to deposit on the membrane surface and was easy to clean, indicating great potential for applications in VMD. This novel method provides the possibility for the large-scale continuous preparation of superhydrophobic PVDF microporous membranes.

Development of hydrogen selective microporous PVDF membrane

Hydrogen is a sustainable clean and green energy source used to eliminate the problem of greenhouse effect. In the present work, the feasibility of gas permeability in separation of H2 from CO2 and N2 have been examined using polyvinylidene fluoride (PVDF) membranes synthesised in our laboratory by the phase inversion process. Effect of various non-solvent additives, such as lithium chloride (LiCl) and Tetraethoxysilane (TEOS) in the PVDF dope solution, have been studied. The resulted asymmetric flat sheet microporous hydrophobic membrane, shows higher hydrogen permeability and selectivity over other gases (CO2 & N2). It has been observed that the MT5 membrane has shown the highest selectivity for hydrogen in comparison to CO2 and N2. The highest value of selectivity was obtained as 4.8 and 3.7 in case of H2/CO2 and H2/N2 respectively. The permeability of membrane has been obtained in the range of 2.3–4.2 mega barrer. SEM analysis is used for the investigation of membrane surface morphology.

Coupling visible light sono-photocatalysis and sono-enhanced ultrafiltration processes for continuous flow degradation of dyestuff using N-doped titania nanoparticles

Sono-photocatalysis has potential to increase the efficiency of both sonolysis and photocatalysis processes. On the other hand, in the sono-enhanced membrane separation processes the ultrasonic waves are able to clean the membrane surface, inhibit its fouling and enhance the separation efficiency. In this work, visible-light sono-photocatalysis and sono-enhanced membrane separation processes were coupled in a one pot/hybrid reactor for continuous flow removal of a dyestuff from water. First, N-doped titania sono-photocatalyst and microporous polyvinylidene fluoride membrane were prepared and characterized. Then, the hybrid reactor was set for the dyestuff degradation. The effect of operational variables including N-doped titania dosage, pH, retention time, visible-light power, radical scavengers and inorganic oxidants on the degradation efficiency was investigated. An enhancement in the degradation efficiency was observed by adding inorganic oxidants and increasing the retention time and visible light power. However, the degradation efficiency was decreased by increasing pH and adding organic and inorganic radical scavengers. 750 mg/L was the optimum N-doped titania dosage. The efficiency of the hybrid process was higher than other probable processes and the synergistic effect between photocatalysis and sonolysis was 23.51%. Main intermediates of dyestuff degradation were identified and a plausible degradation pathway was proposed using GC-MS analysis.

Preparation and characterisation of new microporous Elvaloy4170 coated PVDF membrane for desalination by air gap membrane distillation

The demand to fabricate membranes much cheaper than usual expensive methods creates an opportunity to find low-cost and more available modifying agents for synthesising an appropriate membrane for membrane distillation (MD) process. In this work, reactive ethylene terpolymer was applied to modify a commercial polyvinylidene fluoride (PVDF) membrane for using in the desalination process. Elvaloy4170 with a hydrophobic structure containing three different functional groups was coated (different contents of 0.5, 1, 1.5 and 2 wt%) on the top surface of the microporous commercial PVDF membrane and the resultant membranes were analysed under air-gap MD process. The fabricated membrane structures were determined by scanning electron microscopy and atomic force microscopy to investigate their elemental and topographical properties. After experiments, the membrane with 1.5 wt% of Elvaloy4170 showed water vapour flux of 1.93 kg/m 2 h and salt rejection of >99.7 which confirmed its suitability to be used in the desalination process. Moreover, to assess the anti-fouling properties of the membranes, real seawater was used as feed solution, and as a result the membrane with 1.5 wt% of Elvaloy4170 presented flux recovery of 87% indicating its enhanced anti-fouling properties compared with the commercial PVDF membrane (flux recovery of 71%).

Effects of modified nano-silica on the microstructure of PVDF and its microporous membranes

In this study, effects of modified silica on the microstructure of polyvinylidene fluoride and its microporous membranes were investigated. The silica was modified by 3-Methacryloxypropyltrimethoxysilane to improve its compatibility with the polyvinylidene fluoride matrix. The relaxation time of polyvinylidene fluoride was markedly improved by modified nano-silica, especially at the loading of 0.1 wt‰. Effects of the modified silica on the nanocomposite microstructure, such as crystallization and orientation behavior, were studied in the manuscript. Furthermore, adding 3-Methacryloxypropyltrimethoxysilane modified silica could effectively handicap the relaxation of orientation structure in polyvinylidene fluoride and facilitate the formation of uniform lamellar structures which could be described by two-dimensional small-angle X-ray scattering testing. Finally, casting films with more uniform lamellar structure was also in favor of fabricating polyvinylidene fluoride microporous membranes by melt-stretching method.

The role of electroencephalography in psychiatry - clinical aspects and correlation of psychopathology in schizophrenia and bipolar disorder

Sono-photocatalysis has potential to increase the efficiency of both sonolysis and photocatalysis processes. On the other hand, in the sono-enhanced membrane separation processes the ultrasonic waves are able to clean the membrane surface, inhibit its fouling and enhance the separation efficiency. In this work, visible-light sono-photocatalysis and sono-enhanced membrane separation processes were coupled in a one pot/hybrid reactor for continuous flow removal of a dyestuff from water. First, N-doped titania sono-photocatalyst and microporous polyvinylidene fluoride membrane were prepared and characterized. Then, the hybrid reactor was set for the dyestuff degradation. The effect of operational variables including N-doped titania dosage, pH, retention time, visible-light power, radical scavengers and inorganic oxidants on the degradation efficiency was investigated. An enhancement in the degradation efficiency was observed by adding inorganic oxidants and increasing the retention time and visible light power. However, the degradation efficiency was decreased by increasing pH and adding organic and inorganic radical scavengers. 750 mg/L was the optimum N-doped titania dosage. The efficiency of the hybrid process was higher than other probable processes and the synergistic effect between photocatalysis and sonolysis was 23.51%. Main intermediates of dyestuff degradation were identified and a plausible degradation pathway was proposed using GC-MS analysis.

A Novel Supported Liquid Membrane Based on Binary Metal Chloride Deep Eutectic Solvents for Ethylene/Ethane Separation

Binary metal chloride deep eutectic solvents (DESs) were first prepared by adding different metal chlorides into 1-butyl-3-methylimidazolium chloride ([BMIM]Cl)/CuCl DESs to improve the activity of the Cu+ carrier for ethylene/ethane separation. The binary metal chloride DESs were impregnated in the polyvinylidene fluoride microporous membrane to prepare the supported liquid membranes (SLMs). The performance of the SLMs based on binary metal chloride DESs was evaluated by ethylene/ethane separation experiments. For the SLM based on 0.5[BMIM]Cl-CuCl-1/15ZnCl2 DES, the selectivity of ethylene/ethane mixture increased from 10.7 to 17.8, and the ethylene permeability decreased slightly from 28.6 barrer to 25.8 barrer, compared to 0.5[BMIM][Cl] SLM without ZnCl2. Furthermore, it exhibited long-term stability for more than 150 h. The beneficial role of ZnCl2 for Cu+ carrier was analyzed by electrospray ionization mass spectrometry, Raman spectroscopy, and quantum mechanical calculation. The Raman spectrum showe...

PVDF modified Pd-SnO2 hydrogen sensor with stable response under high humidity

We deposited polyvinylidene fluoride (PVDF) microporous membrane on the surface of palladium loaded tin dioxide (Pd-SnO2) gas-sensitive film by phase separation to reduce the sensitivity loss of Pd-SnO2 gas-sensitive film at high humidity. The sensitivity loss of the PVDF-Pd-SnO2 gas-sensitive film to 50 ppm H2 at 100 RH% is 22% which is almost one-third of the Pd-SnO2 film (70%). At 100 RH%, the sensitivity loss of Pd-SnO2 film is direct proportional to the H2 concentration, but it become inversely after PVDF microporous membrane deposition. PVDF microporous membrane significantly improved the stability of Pd-SnO2 film under high humidity, and verified the feasibility of non-conductive polymer materials improving the performance of gas-sensitive materials.

A Novel Copper(I)-Based Supported Ionic Liquid Membrane with High Permeability for Ethylene/Ethane Separation

For the separation of an ethylene/ethane mixture, a novel copper(I)-based supported ionic liquid membrane (SILM) with high permeability has been fabricated. This SILM was prepared from a polyvinylidene fluoride microporous membrane impregnating the copper(I) based IL which formed by the cuprous chloride (CuCl) and 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]). Scanning electron microscopy, attenuated total reflection Fourier transform infrared spectroscopy, and time of flight mass spectroscopy were used to characterize the SILM. Pure and mixed gas permeation experiments were carried out to investigate the influences of ILs composition, trans-membrane pressure, temperature, and time upon the separation performance. This SILM showed comparable C2H4 permselectivity but outstanding permeability with a long-term stability beyond the reported polymeric membrane upper bound. At the CuCl/[Bmim][Cl] ratio of 2, the C2H4 permeability and permselectivity reached 2653 barrer and 11.8, respectively. Furthermore, t...

Ammonium persulphate as novel additive for filtration performance improvement of PVDF microporous membrane

Abstract Ammonium persulphate (APS) was used as a novel additive for blending modification of Polyvinylidene Fluoride (PVDF) membrane in this study. The addition of APS changed the macroscopic and micro-structure of membrane, as the small scaly aggregates appeared and hydrophilicity increased slightly. Comparing with blank membrane, the specific surface area of PVDF membrane was reduced from 19.98 m 2 /g to 7.95 m 2 /g, and the total adsorption average pore size of membrane was increased from 89.82 nm to 253.58 nm when 0.7% of APS was added. During the short term filtration, the pure water flux of blank membrane was reduced by 61% and 81% after the first and second testing cycle, respectively. As a comparison, it was only reduced by 39% and 60% for 0.7% APS modified membrane. The effluent turbidity values of those modified membranes were all lower than that of blank membrane. During the long term operation in MBR, the filtration time of 0.7% APS modified membrane lasted for 21 days including 2 operational cycles. Comparing with modified membrane, the filtration time of blank membrane only lasted for 19 days, which included 3 times of membrane cleaning.

Enzyme, β-galactosidase immobilized on membrane surface for galacto-oligosaccharides formation from lactose: Kinetic study with feed flow under recirculation loop

The work focuses on producing galacto-oligosaccharides (GOS) through an enzymatic reaction with lactose under a partial recirculation loop by utilizing membrane-immobilized β-galactosidase. Cross-linking through covalent bonding, using gluteraldehyde, was employed to immobilize enzyme on a microporous polyvinylidene fluoride membrane. GOS synthesis was carried out in a laboratory fabricated reaction cell, whereby three immobilized membranes were housed in series. The reaction was conducted at varying initial lactose concentrations (ILCs) and feed flow rates at pH 6 and 40°C. A maximum GOS of 30% (dry basis) was obtained after 60h of reaction time, 50g/L ILC, 241U of enzyme (specific loading of 600U/g-membrane), and 0.5mL/min of feed flow rate at 56% lactose conversion. The GOS yield increased with increased ILC and decreased feed flow rate. The selectivity of GOS formation increased by increasing both the ILC and the feed flow rate, whereas the reverse was true for mono-saccharides. The immobilized enzyme retained ∼50% of its initial activity after 30 days of storage at 20°C, while the native enzyme lost 100% of its activity within 21 days. Furthermore, a five-step, nine-parameter model was developed, and simulated results showed excellent agreement with the experimental data.

Grafting of hydroxymethylacrylamide and acrylic acid copolymer onto polyvinylidene fluoride membrane by supercritical carbon dioxide and its application in dye separation

We report a thermally induced graft copolymerization of acrylic acid and N‐hydroxymethylacrylamide onto polyvinylidene fluoride microporous membrane by using supercritical carbon dioxide as a solvent and carrier agent. The effects of monomer mole ratio, pressure, reaction temperature, time, and initiator concentration on the degree of grafting were investigated. The morphology of the grafted membrane was studied via scanning electron microscopy. Attenuated total reflectance infrared spectroscopy spectroscopy and X‐ray diffraction proved the existence of grafting monomers. The results of contact angle measurement and water filtration at different pH levels indicated pronounced pH‐sensitive behavior and increased hydrophilicity of the polyvinylidene fluoride grafted membrane. In particular, the grafted membrane was applied to the removal of methylene blue with a relative rejection of 98.1% compared with 30.5% of rejection observed from the pristine polyvinylidene fluoride membrane. Copyright © 2014 John Wiley & Sons, Ltd.

Surface Modification of Poly(Vinylidene Fluoride) Microporous Membrane by Ferric Hydroxide Sol-Gel

Surface modification of poly(vinylidene fluoride) (PVDF) membrane was accomplished by the adsorption of ferric hydroxide sol to impove its hydrophilicity. The adsorption curves of the membranes were analyzed by weight measurements, and the typical results showed a two-platform character in low concentration. The effects of the adsorption time, the ferric hydroxide sol concentration, the test temperature, as well as the water cleaning time on the adsorption amount were observed. Attenuated total reflection-Fourier transform infrared spectroscopy (ATR/ FTIR) analysis showed that the adsorption of ferric hydroxide sol on poly(vinylidene fluoride) microporous membranes (PVDFMM) is effective. The membranes hydrophilic performance was represented by water contact angle measurements. The water contact angles changes from the virgin 128°to the lowest value 81.90° in the range of 0~0.10 mol/L ferric hydroxide aqueous solution. The results indicated that ferric hydroxide sol can be immobilized on the PVDF films by adsorption, and the membrane hydrophilic performence increases with the increase of the adsorption amount of the ferric hydroxide sol onto the PVDF membrane surface.

Dye-sensitized Solar Cells with Higher Jsc by Using Polyvinylidene Fluoride Membrane Counter Electrodes

Abstract A flexible counter electrode (CE) for dye-sensitized solar cells (DSCs) has been fabricated using a micro-porous polyvinylidene fluoride membrane as support media and sputtered Pt as the catalytic material. Non-conventional structure DSCs have been developed by the fabricated CEs. The Pt metal was sputtered onto one surface of the membrane as the catalytic material. DSCs were assembled by attaching the TiO2 electrode to the membrane surface without Pt coating. The membrane was with cylindrical pore geometry. It served not only as a substrate for the CE but also as a spacer for the DSC. The fabricated DSC with the flexible membrane CE showed higher photocurrent density than the conventional sandwich devices based on chemically deposited Pt/FTO glass, achieving a photovoltaic conversion efficiency of 4.43%. The results provides useful information in investigation and development of stable, low-cost, simple-design, flexible and lightweight DSCs.