Porous Polyvinylidene Fluoride Research Articles

Controlling the polymorphs of PVDF membranes: Effects of a salt additive on PVDF polarization during phase separation processes

Polyvinylidene fluoride (PVDF) membranes, acclaimed for their outstanding chemical resistance, thermal stability, and mechanical properties, play a crucial role in diverse industrial purification applications. While various methods have been employed for fabricating PVDF membranes such as thermally induced, evaporation-induced, vapor-induced, and nonsolvent-induced phase separation processes, controlling the polarity of PVDF chains using these techniques remains challenging. Recent studies have shown that the nonpolar α-phase PVDF is susceptible to organic acid fouling owing to hydrophobic interactions, whereas the β-phase PVDF has demonstrated polarity and offers antifouling properties. Herein, porous PVDF membranes predominantly composed of the β-phase were successfully fabricated by incorporating a small amount of LiCl salt into the PVDF dope solution. The addition of LiCl influences ion–dipole moments between ions and PVDF during phase separation, simultaneously affecting the PVDF chain arrangement and membrane morphology. Since the LiCl additive alters both the pore size and structure of PVDF membranes, both freestanding and non-woven supported membranes were prepared and characterized to assess the effects of polarity and pore size on fouling tendency. Characterizations of prepared PVDF membranes revealed considerable changes in the PVDF polymorph, membrane morphology, pore size, and antifouling properties upon introducing the salt additive. Our findings imply that β-phase–dominant PVDF membranes can be effectively utilized in water purification applications.

Multiscale Polyvinylidene Fluoride/Magnesium–Aluminum Layered Double Hydroxide Gel Electrolytes for Lithium Batteries

A multiscale of porous polyvinylidene fluoride–hexafluoropropylene copolymer/magnesium–aluminum layered double hydroxides (MgAl‐LDHs) composite gel polymer electrolyte is prepared by phase separation method. It is discovered that the ionic conductivity of the electrolyte reaches a maximum value of 1.36 × 10−3 S cm−1, the lithium ions’ mobility is 0.66, and the chemical performance is steady within the 4.85 V window along with the concentration of MgAl‐LDHs up to 0.4 wt% at room temperature. The density functional theory calculations show that the adsorption energy of Li+ with MgAl‐LDH is −3.59 eV and the diffusion potential barrier is 0.37 eV, which is favorable for the dissociation and transport of Li+. Moreover, the anode's initial discharge capacity at 0.1 C achieves 144 mAh g−1, keeping 84.7% of the theoretical capacity of 170 mAh g−1, and the capacity retention and the columbic efficiency maintain 92.4% and 95.7% after 100 cycles at 0.2 C, respectively, through assembling into a Li/PVP–MgAl/LiFePO4 battery.

Piezoelectrically-Induced Antibacterial Properties of Porous Polyvinylidene Fluoride (PVDF) Membrane

Piezoelectrically-Induced Antibacterial Properties of Porous Polyvinylidene Fluoride (PVDF) Membrane

Macromolecule crosslinked composite PVA membranes for pervaporation desalination

Pervaporation (PV) has shown great potential in desalination. Polyvinyl alcohol (PVA) is a widely used material for PV membranes. In the present work, hydrophilic composite membranes for PV desalination were prepared by coating mix solutions of PVA and Poly(methyl vinyl ether-alt-maleic anhydride) (PMVE-MA) on porous polyvinylidene fluoride (PVDF) supports. PMVE-MA, which serves as a macromolecular crosslinker, is well-compatible with PVA. The methyl ether groups in PMVE-MA also endow the crosslinked membrane to maintain good hydrophilicity. To achieve better performance, influences of the PVA concentration, the mass ratio of PVA to PMVE-MA, the crosslinking temperature and time, and the PVDF support on the desalination performance of the composite PV membrane were studied. At optimal conditions, a PVA-(PMVE-MA)/PVDF membrane was prepared. The membrane had a water flux of up to 45 kg·m−2·h−1 for the feed of 3.5 wt% NaCl solution at 50 °C (92 kg·m−2·h−1 at 70 °C). The salt passage was at an extremely low level and the conductivity of the permeate was lower than 100 μs/cm. In addition, the membrane showed excellent antifouling performance. After 14 h desalination of a sodium alginate-containing feed, the flux can be fully recovered by flushing the membrane in situ. The PVA-(PMVE-MA)/PVDF composite membrane shows great potential in desalination applications.

Three-Dimensional Porous Structural Polyvinylidene Fluoride-Blending Ethylene Carbonate and MIL-125 (Ti) Composite Membrane-Based Gel Polymer Electrolyte for Lithium Metal Battery

Lithium metal batteries are considered promising contenders for the next generation of high energy density batteries. However, lithium metal anode with inhomogeneous lithium deposition in liquid electrolyte causes the uncontrolled growth of lithium dendrites. Owing to the high dielectric constant, thermal stability and electromechanical stability of polyvinylidene fluoride, we design a novel gel polymer electrolyte consisting of porous polyvinylidene fluoride polymer matrix, liquid electrolyte, ethylene carbonate and MIL-125 (Ti) (Ti8O8(OH)4(BDC)6, BDC = 1,4-benzene dicarboxylate) for facilitating Li+ transfer and alleviating the growth of lithium dendrites. The high dielectric constant environment facilitates the dissociation of Li+, and the porous polymer matrix structure accommodates more Li+ for fast transfer. Ethylene carbonate reduces the crystallinity of the polymer matrix and improves the ionic conductivity. MIL-125 (Ti) nanoparticles with surface area and uniform micropores improve toughness for enhancing mechanical property, and synergistically promote the Li+ transfer for building stable interfacial phase to alleviate the growth of Li dendrites. Therefore, the gel polymer electrolyte has high ionic conductivity of ∼1.50 × 10−3 S cm−1 at 25 °C, and quasi-solid-state Li/LiFePO4 battery has high discharge capacity of 153.5 mAh g−1 after 250 cycles at 25 °C and 0.3 C.

CeO2@LDH decorated 3D porous module with mortise-tenon structure: Activation of peroxymonosulfate for ultrafast removal of tetracycline

Constructing a robust catalytic module with lower energy consumption, fast liquid transport, and simultaneous highly catalytic oxidizability presents an enticing alternative for industrialized water treatment. Herein, a kind of cerium oxide (CeO2) loaded layered double hydroxide (LDH) composites that was fabricated by seeds embedded epitaxial growth based on hydrothermal method anchored on a three-dimensional porous polyvinylidene fluoride (PVDF) framework (denoted as CeO2@LDH-PVDF) and function as an efficient catalytic activator for peroxymonosulfate (PMS) activation. This module features as lamellar LDH nano-flowers not only in situ anchoring onto both sides of the PVDF surface but also along the wall of the pores in an ab-plane vertically interlaced growth pattern. A packed tower device suitable for the catalytic module is also proposed as proof of concept for consecutive pollutants disposal. This module exhibits dual functions of filtration and oxidation, demonstrating a promising removal efficiency for tetracycline (95.8%, 30 mg/L) in conjunction with PMS. Accurate operation parameters are obtained by using the response surface methodology to further reduce the energy consumption (CeO2 containing: 9.03%, PMS concentration: 0.798 mM; pH: 6.513). Encouragingly, the CeO2@LDH-PVDF is not only capable of achieving ultrafast removal in flowing various contaminants, but also reveals wide practical applicability in tap water and reservoir. Moreover, it provides evidence that the binding force between LDH and PVDF is enhanced by virtue of the unique “Mortise-Tenon” structure, which is conducive to maintaining the catalytic activity. Furthermore, the formation of a complex of M−(HO)OSO3− and the succeeding redox cycle of Ni2+/Ni3+, Fe2+/Fe3+, Co2+/Co3+ explain the generation of reactive radicals in PMS activation. Moreover, a new redox cycle of Ce3+/Ce4+ promotes the utilization efficiency of PMS. Three possible tetracycline degradation pathways are proposed and the toxicity of the by-products is reduced. Finally, the module possesses an ideal universality, good cycling stability, favorable antifouling performance, and superior renewability. It is predicted to be integrated with multiple mature technologies to conduct industrial water treatment due to its changeable shape and durability.

A workflow for the development of template-assisted membrane crystallization downstream processing for monoclonal antibody purification.

Monoclonal antibodies (mAbs) are commonly used biologic drugs for the treatment of diseases such as rheumatoid arthritis, multiple sclerosis, COVID-19 and various cancers. They are produced in Chinese hamster ovary cell lines and are purified via a number of complex and expensive chromatography-based steps, operated in batch mode, that rely heavily on protein A resin. The major drawback of conventional procedures is the high cost of the adsorption media and the extensive use of chemicals for the regeneration of the chromatographic columns, with an environmental cost. We have shown that conventional protein A chromatography can be replaced with a single crystallization step and gram-scale production can be achieved in continuous flow using the template-assisted membrane crystallization process. The templates are embedded in a membrane (e.g., porous polyvinylidene fluoride with a layer of polymerized polyvinyl alcohol) and serve as nucleants for crystallization. mAbs are flexible proteins that are difficult to crystallize, so it can be challenging to determine the optimal conditions for crystallization. The objective of this protocol is to establish a systematic and flexible approach for the design of a robust, economic and sustainable mAb purification platform to replace at least the protein A affinity stage in traditional chromatography-based purification platforms. The procedure provides details on how to establish the optimal parameters for separation (crystallization conditions, choice of templates, choice of membrane) and advice on analytical and characterization methods.

Mercapto functionalized–natural zeolites/PVDF mixed matrix membrane for enhanced removal of methylene blue

Azo dye-containing wastewater is one of the most critical contaminants due to modern industrial activities, especially in the textile industry. Membrane technology has been the most prominent separation technique to alleviate these pollutants with less energy input and less raw material utilization. In this sense, zeolite-based mixed matrix membranes have offered increased filtration performance as they combine the favorable properties of polymeric membranes, molecular sieving, and the negative charge properties of zeolites. The crucial challenge is the compatibility of the inorganic filler and the polymer matrix to boost flux and rejection; otherwise, both will be dramatically compensated. Herein, low-cost natural zeolites were functionalized using mercapto silane ((3-mercaptopropyl) trimethoxysilane) agent and incorporated into porous polyvinylidene fluoride (PVDF). The resulting mixed matrix membranes showed significantly higher rejection (97.01%) and flux (37.14 L m−2h−1) compared to those of pristine PVDF membrane (rejection and flux of 82.78% and 24.05 L m−2h−1, respectively). These positive results are due to the compatibility between the mercapto-functionalized natural zeolites and PVDF matrix. In the absence of mercapto groups, the rejection could be enhanced, but the permeability decreased. In addition, the antifouling properties of the mercapto functionalized–natural zeolites/PVDF mixed matrix membrane is desirable, as indicated by the higher flux recovery ratio and lower reversible and irreversible fouling.

Microstructure control in printable porous polymer composites

The microstructure of a porous polymer matrix composite, specifically the organization of polymer, particles, and pores, plays a defining role in the physical properties of the material. Developing materials and processes that allow us to control the microstructure gives us a powerful tool to create materials with designed performance. Here, a series of porous polyvinylidene fluoride (PVDF) and alumina (Al2O3) composites produced through evaporation induced phase separation (EIPS) are demonstrated. This process utilizes solution processable inks and achieves porosity via a simple drying procedure. This enabled the materials to be printed using direct ink writing (DIW) techniques. The effects of particle size and loading on the mechanical properties and microstructures of these materials were studied. It was found that these materials remain significantly more ductile and extensible than what is expected from particle reinforcement. In the most extreme case, the use of 300 nm Al2O3 particles were found to only minimally reduce strain at failure, even at high loadings. We believe this behavior is enabled by how the EIPS process alters the microstructure of the material and appears to preferentially locate particles at the polymer-pore interface.

Study on Design and Preparation of Conductive Polyvinylidene Fluoride Fibrous Membrane with High Conductivity via Electrostatic Spinning.

The novel conductive polyvinylidene fluoride (PVDF) fibrous membrane with high conductivity and sensitivity was successfully prepared via electrostatic spinning and efficient silver reduction technology. Based on the selective dissolution of porogen of polyvinylpyrrolidone (PVP), the porous PVDF fibrous membrane with excellent adsorbability and mechanical strength was obtained, providing a structure base for the preparation of conductive PVDF fibrous membrane with silver nanoparticles (AgNPs-PVDF). The Ag+ in the AgNO3 mixed solution with PVP was absorbed and maintained in the inner parts and surface of the porous structure. After the reducing action of ascorbic acid-mixed solution with PVP, silver nanoparticles were obtained tightly in an original porous PVDF fibrous membrane, realizing the maximum conductivity of 2500 S/m. With combined excellent conductivity and mechanical strength, the AgNPs-PVDF fibrous membrane effectively and sensitively detected strain signals of throat vocalization, elbow, wrist, finger, and knee (gauge factor of 23). The electrospun conductive AgNPs-PVDF combined the characteristics of low resistance, high mechanical strength, and soft breathability, which provided a new and effective preparation method of conductive fibers for practical application in wearable devices.

Soft Template-Induced Porous Polyvinylidene Fluoride Membrane for Vanadium Flow Batteries

Soft Template-Induced Porous Polyvinylidene Fluoride Membrane for Vanadium Flow Batteries

Preparation and performance of “three-layer sandwich” composite loose nanofiltration membrane based on mussel bionic technology

Abstract In this study, a novel “three-layer sandwich” composite loose nanofiltration (NF) membrane structure by mussel bionic technology was constructed on a porous polyvinylidene fluoride (PVDF) substrate membrane, with a mussel bionic coating as the middle layer and the complex network of polyphenols and metal ions as the top layer. The new composite NF membrane had comprehensive properties such as excellent separation performance, good hydrophilicity and strong antifouling ability. The experimental results showed that the combination of tannic acid (TA) and iron ion (Fe3+) could significantly improve the comprehensive performance of the composite NF membrane, with water flux of more than 3000 L/(m2∙h), and the retention rate of dyes and bovine serum protein (BSA) exceeded 90 %, and contact angle was up to 30°. The combination of TA and copper ion (Cu2+) can greatly enhance the antifouling performance and interception ability of methylene blue. The complexation activity of metal ions and polyphenols was related to the oxidation of metal ions. The PVDF/DA-PEI/TA-M+ composite structure scheme of “three-layer sandwich” NF membrane provides a new idea and future development direction for the development of novel NF membranes with excellent comprehensive performance.

Revealing the selective separation of organics from salty solution in novel aqueous-aqueous membrane extraction co-driven by concentration and pressure difference

Aqueous-aqueous membrane extraction (AAME) has great potential to revolutionize industrial wastewater treatment, achieving the value-added organic product recovery with low operation cost. Here, we first reported the feasibility, performance and mechanism of selective separation of three typical organics (phenol, ethanol and sodium dodecyl sulfate (SDS)) from salty solution not only in common concentration-difference driven but also in novel concentration-pressure-difference co-driven AAME using porous polyvinylidene fluoride (PVDF), non-porous polydimethylsiloxane (PDMS) and composite PVDF/PDMS membranes. In concentration-difference driven AAME, phenol and ethanol were separated from NaCl solution through three membranes, while SDS permeation only occurred on wetted porous PVDF membrane. Note that, volatile phenol and ethanol transported across the porous PVDF and composite PVDF/PDMS via volatilization-diffusion and solution-diffusion. In concentration-pressure-difference co-driven AAME, highest phenol (10.7) and ethanol fluxes (34.7 g m2 h−1) were obtained through composite PVDF/PDMS membrane (ΔP = 3 kPa) and PVDF membrane (ΔP = 9 kPa), respectively, with complete NaCl rejection. These data showed suitable membrane and high ΔP were beneficial to promote organics transmembrane transport. However, overload ΔP increased the membrane wetting risk on porous membranes. Once membrane was wetted, organics transmembrane mass transfer was simplified to direct pore-flow filtration. These findings provide a crucial step toward understanding the potential of AAME in resource recovery from industrial wastewater.

One-step preparation of flexible citric acid-doped polyaniline gas sensor for ppb-level ammonia detection at room temperature

In this work, a citric acid-doped polyaniline/polyvinylidene fluoride (CPP) flexible ammonia sensor was prepared by in situ oxidative chemical polymerization on a flexible porous polyvinylidene fluoride membrane. The CPP sensor exhibited excellent performance at room temperature (217% response for 1 ppm NH3), low detection limit (LOD) reaches 3 ppb, and rapid response and recovery times (30 s /195 s for 1 ppm NH3, respectively). Furthermore, the sensor shows outstanding flexibility and excellent stability. After 10,000 bending cycles, the CPP sensor still produces over 99% stable response. The response reached 95% of its initial value after more than 60 days of storage. The CPP sensor exhibits excellent gas-sensing performance for ammonia gas, mainly attributed to the increase in active sites induced by citric acid doping and the synergistic effect of the porous substrate. The above results demonstrated that the CPP flexible film sensor is a high-performance candidate for enhanced ammonia gas sensing properties at room temperature.

Porous PVDF mats with significantly enhanced dielectric properties and novel dipole arrangement for high-performance triboelectric nanogenerators

In the last decade, various materials and nanoscale modifications have been developed to enhance the performance of the triboelectric nanogenerators (TENGs). Electrospinning of polarizable materials, such as polyvinylidene fluoride (PVDF), has improvements in surface area and dielectric properties through the arrangement of dipoles’ orientation. However, the previously developed electrospun mats for TENG devices still suffer from (i) insufficient dielectric properties due to the presence of low-dielectric air, (ii) process complexity, and (iii) the need for nanoparticle additives. These issues are addressed in this study to develop porous electrospun PVDF mats with significantly enhanced dielectric properties and novel dipole arrangement. Smart multi-layer structures are introduced to overcome the dielectric characteristics of the degraded electrospun mats by the presence of the voids. The new material structure exhibited a significantly increased dielectric constant of 10, which was much higher than single-layer electrospun mats, and was even comparable to the pristine PVDF film without any porosity. Such a material with high dielectric constant and high area-to-volume ratio was utilized as a tribonegative layer in the TENG device, and the corresponding triboelectric performance was analyzed. An output voltage of over 130 V and a current of up to 12 μA were obtained, which were noticeably higher than those of pristine PVDF as well as those of single-layer electrospun mats. Such high performance remained unchanged even after 10,000 cycles. The developed electrospun PVDF mats in this study can therefore be used in the next generation of high-performance TENG devices.

Preparation of a positive porous polyvinylidene fluoride membrane and its removal of mercury containing wastewater

Preparation of a positive porous polyvinylidene fluoride membrane and its removal of mercury containing wastewater

Flexible room temperature sensor with modulation of polyaniline interfacial polymerization by CTAB for ppb-level ammonia detection

A highly selective and sensitive flexible room temperature ammonia (NH3) sensor was produced by in situ polymerizations of polyaniline (PANI) with modulation of Hexadecyl trimethyl ammonium Bromide (CTAB) on a porous Polyvinylidene fluoride film (PVDF). CTAB allows the PANI nanoparticles to grow uniformly on the surface and in the internal pores of the PVDF film, which increases the sensor’s response to the NH3. As a result, the sensor’s response values to 5 ppm NH3 and 0.01 ppm NH3 are 81.3 % and 4.6 % at 20 °C, respectively. The sensor also shows excellent selectivity for NH3 and maintains superior stability. Such a highly responsive and sensitive sensor is expected to be applied to detect chronic kidney disease.

Surface modification of porous polyvinylidene fluoride hollow fiber membrane by sulfonated poly(ether ether ketone) coating for membrane distillation of oily wastewater

AbstractHighly porous polyvinylidene fluoride hollow fiber membranes were fabricated by a non‐solvent induced phase separation process. The membranes were modified by coating an ultra‐thin hydrophilic layer of sulfonated poly(ether ether ketone) (sPEEK) onto the inner surface. An industrial oily wastewater treatment was performed through an air gap membrane distillation (AGMD) process. From field emission scanning electron microscopy, the modified membrane showed an open structure with a large finger‐like outer layer and sponge‐like inner layer. The thickness of the coated sPEEK layer on the inner surface was about 0.5 μm. The coated membrane presented mean pore size of 36 nm and overall porosity of 73%. The inner surface water contact angle decreased from about 82° to 57°. Using Langmuir adsorption experiment, minor oil adsorption on the modified membrane surface was confirmed. A stable water flux of about 12 kg m−2 h−1 and oil rejection of 99% were found during 72 h of the AGMD process for treating the oily wastewater of NGL‐900 (Gachsaran, Iran) plant. The high flux recovery ratio of about 98% was related to the improved anti‐oil‐fouling property. The modified membrane can be a potential candidate for oily wastewater treatment through the MD processes.

Significant enhancement of the output voltage of piezoelectric/triboelectric hybrid nanogenerators based on MAPbBr3 single crystals embedded into a porous PVDF matrix

Methylammonium lead tribromide (MAPbBr3) single crystals (SCs)-polyvinylidene fluoride (PVDF) nanocomposites (NCs) are fabricated by using a simple sol-gel method. Uniform MAPbBr3 SCs are successfully embedded in a porous PVDF matrix to effect a synergism between an enhanced piezoelectric effect and enhanced charge accumulation. A piezoelectric/triboelectric hybrid nanogenerator (HNG) is fabricated utilizing the MAPbBr3 SCs-PVDF NCs as a dielectric layer in a triboelectric nanogenerator (TENG), and its performance is compared with that of a piezoelectric nanogenerator (PENG) based on MAPbBr3-PVDF NCs. The HNG based on the MAPbBr3 SCs-PVDF NCs showed the highest output voltage, 256 V, which is 3.87 times higher than that of the PENG based on the same NCs. The power density (16.17 mA/cm2) of the HNG based on MAPbBr3 SCs-PVDF NCs is approximately 200 times larger than that of the PENG based on the same NCs. This enhancement of the performance of HNG based on the MAPbBr3 SCs-PVDF NCs can be attributed to the very large tribo-piezoelectric coupling efficiency due to the existence of the MAPbBr3 SCs uniformly formed in the porous PVDF matrix.

Rollable Ultraviolet Photodetector Based on ZnAl‐Layered Double Hydroxide/Polyvinylidene Fluoride Membrane

AbstractHigh‐performance, reliable, and rollable ultraviolet (UV) photodetectors have attracted considerable attention for wireless sensor network technology. Despite the improved responsivity of UV photodetectors, high‐performance rollable UV photodetectors have not been reported. This paper reports a rollable UV photodetector based on ZnAl‐layered double hydroxide (LDH) nanosheets on a porous polyvinylidene fluoride (PVDF) membrane. Vertically aligned ZnAl‐LDH nanosheets are grown on a porosity‐controlled PVDF membrane. The UV photodetector exhibits an excellent photoresponse at wavelengths below 420 nm, even in curvature with a 0.6 mm radius. The rollable UV photodetector also shows reliable, responsive performance even after 5 000 rolling cycles, indicating the reasonable durability of the ZnAl‐LDH nanosheet. The reliable photodetector performance is attributed to the elasticity of the PVDF and the strong interfacial adhesion force between the porous PVDF and ZnAl‐LDH nanosheets.