Polyvinylidene Fluoride Substrate Research Articles

Springtail-inspired omniphobic slippery membrane with nano-concave re-entrant structures for membrane distillation

Omniphobic membranes, due to their exceptional properties, have drawn significant attention for overcoming the bottleneck in membrane distillation (MD) technology. This study demonstrates an innovative method for fabricating an omniphobic membrane that is simple and facile compared to other methods such as wet/dry etching and photolithography. The surface morphology of springtails was imitated using electrospraying technique to coat a polyvinylidene fluoride substrate with concave-shaped polystyrene beads that were successfully developed by controlling the electrical traction (voltage) and air resistance (humidity). Then, the lipid coating of springtail surfaces was mimicked by dip-coating the membrane in a low-toxicity short-chain perfluoropolyether lubricant. The concave structure’s tiny air pockets increased membrane hydrophobicity significantly, indicated by the fact that the first round of water bouncing took only 16.3 ms. Finally, in MD treatment of seawater containing 1.0 mM sodium dodecyl sulfate, the optimized omniphobic membrane maintained a stable 99.9% salt rejection rate.

Optimization design and experimental study for flexible fan-shaped interdigital guided wave transducer

To address the challenges of difficult attachment to a rigid substrate and large-area damage scanning on planar and curved panel structures, a novel flexible fan-shaped interdigital guided wave transducer (FFIGWT) is proposed. It consists of a fan-shaped interdigital electrode and a Polyvinylidene Fluoride (PVDF) flexible smart material substrate. The positive interdigital electrode is divided into inner and outer parts, enabling the FFIGWT to simultaneously excite and receive guided waves. Numerical simulations are conducted to investigate the influence of PVDF substrate thickness on wave excitation and reception, as well as the effect of the ratio between the inner and outer radius of the FFIGWT on excitation intensity. The results demonstrate that the reception and excitation of guided waves by the FFIGWT improve with increasing PVDF substrate thickness. The ratio between the inner and outer radius of the transducer's interdigital electrode is positively correlated with excitation intensity. Additionally, the transducer's beam divergence angle approaches the designed angle span of the FFIGWT with an increasing ratio between the inner and outer radius. Experimental validation confirms that the FFIGWT exhibits significantly enhanced wave excitation and reception capabilities in the corresponding FFIGWT region, making it suitable for composite material detection applications.

Antifouling and Antioxidant Properties of PVDF Membrane Modified with Polyethylene Glycol Methacrylate and Propyl Gallate.

In this study, molecules of propyl gallate (PG) and polyethylene glycol methacrylate (PEGMA) were covalently bonded via a transesterification reaction and subsequently grafted onto polyvinylidene fluoride substrates using a homogeneous radiation grafting technique. The enhancement of the membranes' hydrophilicity with the increment of the grafting rate was corroborated by scanning electron microscopy imaging and measurements of the water contact angle. At a grafting degree of 10.1% and after a duration of 4 min, the water contact angle could decrease to as low as 40.1°. Cyclic flux testing demonstrated that the membranes modified in this manner consistently achieved a flux recovery rate exceeding 90% across varying degrees of grafting, indicating robust anti-fouling capabilities. Furthermore, these modified membranes exhibited significant antioxidant ability while maintaining antifouling performance over 30 days. The ability of the modified membranes to scavenge 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS+) free radicals remained nearly unchanged after being stored in pure water for 30 days, and the flux recovery rate remained above 95% after immersion in sodium hypochlorite solution for 30 days. Among the tested membranes, the PVDF-g-PEGMAG modified membrane with a grafting degree of 7.2% showed the best antioxidant effect.

Piezoelectric reverse osmosis (RO) membrane: Fabrication and anti-fouling effect

In this study, a novel piezoelectric RO membrane with vibrating mechanism when exposed to an electric field was developed. The vibration due to the piezoelectric effect can disturb the concentration polarization layer on the membrane surface and minimize membrane fouling. Polyvinylidene fluoride (PVDF) which has piezoelectric properties was selected as the porous substrate for a thin film composite (TFC) polyamide RO membrane in this study. Electrical poling was performed to enhance the piezoelectric properties of the PVDF substrate. RO membranes fabricated via interfacial polymerization using different PVDF substrates (i.e., with and without pre-wetting the PVDF substrate, with and without polyethylene terephthalate (PET) non-woven fabric support (denoted as NWF and no-NWF, respectively), with and without electrical poling) were systematically investigated. The results indicated that RO membrane fabricated on poled PVDF-NWF substrate shows reasonable pure water permeability of ∼2 LMH/bar and sodium chloride (NaCl, 2000 ppm) rejection of ∼98.9 % when tested at 15 bar. In the accelerated fouling study using colloidal silica particles (∼20 nm in diameter, 200 ppm with background of 2000 mg/L NaCl), when the RO membrane fabricated using both unpoled and poled PVDF-NWF substrates were excited with AC signal, membrane fouling was significantly reduced. These findings suggested that electrical poling may not be necessary for such piezoelectric RO membrane.

Constructing nanofiltration membrane on hydrophobic PVDF and PTFE substrates via reverse interfacial polymerization

Polyvinylidene fluoride (PVDF) and polytetrafluoroethylene(PTFE) porous membranes are ideal substrates for preparing thin-film composite (TFC) polyamide (PA) membranes with improved solvent resistance. However, it remains difficult to construct PA skin layers on PVDF and PTFE substrates via conventional interfacial polymerization (IP) due to the hydrophobic nature of these materials. To address this challenge, a reverse IP process was proposed to construct a defect-free PA skin layer on PVDF and PTFE substrates, in which the hydrophobic PVDF and PTFE substrates were soaked with the organic phase to ensure uniform coverage of reacted solution on the substrates. This novel strategy can effectively tackle the issue of uneven wetting of the aqueous phase on hydrophobic substrates in the conventional IP process. The resultant TFC membranes (i.e. Mrev-PVDF and Mrev-PTFE) exhibit excellent nanofiltration (NF) performance in both aqueous and organic solutions. Mrev-PVDF and Mrev-PTFE have MgCl2 rejections of 96.12% and 95.17%, alongside the water permeances of 12.8 LMH/bar and 11.2 LMH/bar, respectively (Mrev-PTFE was activated with DMF). It is further shown that Mrev-PVDF and Mrev-PTFE could also reject 99.4% and 98.5% of Congo red in methanol solution at solvent permeances of over 3.3 LMH/bar, while they also perform excellently in other polar protic solvents. Consequently, this work opens a new window for constructing high-performance TFC PA membranes on hydrophobic substrates and expands the application of the TFC PA NF membrane.

Chiral metal-organic cage modified polyvinylidene fluoride membrane via metal phenolic networks for enantioseparation

High-performance chiral membrane materials hold great promise for the separation of pharmacological enantiomers. The key to achieving high-enantioselective chiral membrane separation is the development of suitable chiral membrane materials. However, traditional chiral separation membranes still face several limitations, including the main problem of the permeability-selectivity trade-off. In this study, a kind of novel chiral metal–organic cage (MOC) modified polyvinylidene fluoride (PVDF) membrane, namely PVDF@TA-Zn@MOC, was fabricated successfully by growing the chiral MOC [Zn3L2] onto the surface of PVDF substrate membranes induced by tannic acid (TA)-Zn2+ (TA-Zn) networks. In brief, ultrathin TA-Zn2+ metal-phenolic network coating was first adhered onto the surface of PVDF substrate membranes, followed with the in-situ growth of chiral MOC [Zn3L2] that was triggered by the coordination-enabled adhesion of Zn2+. A series of chiral PVDF@TA-Zn@MOC membranes were prepared with different hydrophilic properties and MOC loading by adjusting the concentrations of TA and metal/ligand. The transport and separation performances of these membranes were investigated for the mandelic acid (MA) enantiomers, and as a result, when the addition of TA was 1 mg and the metal ion concentration was 3.125 × 10-3 mol·L-1, the chiral membrane PVDF@TA-Zn@MOC-2 exhibited the most extraordinary entrapment ability in both permeability and selectivity for D-MA with an enantiomeric excess value of up to 71 % at a feed solution concentration of 300 ppm for 6 h under the neutral conditions. This method allows for the construction of the chiral hydrophilic MOC nanocoating membranes, which has the potential to broaden the applications of chiral MOC.

Support-free interfacial polymerized polyamide membrane on a macroporous substrate to reduce internal concentration polarization and increase water flux in forward osmosis

Macroporous substrates have great potential in the development of high performance thin film composite forward osmosis (TFC FO) membranes. This paper reports on the preparation of TFC FO membrane via support-free interfacial polymerization (SFIP) technology on a macroporous substrate. SFIP technology can effectively break the bottleneck of conventional interfacial polymerization (IP) technology, which makes it difficult to form a complete polyamide (PA) film on the macroporous substrate. Briefly, the complete PA film is formed at the free water-organic phase interface and then attached to the macroporous substrate by vacuum filtration. The monomer concentration and filtration pressure were adjusted to form the optimal SFIP-PA film. Meanwhile, we chose a macroporous polyvinylidene fluoride (PVDF) microfiltration substrate and screened the pore size to reduce the structural parameters and then the internal concentration polarization, which caused the improvement of water flux. The performance of SFIP-PVDF membranes was investigated and discussed. Under the AL-FS mode with DI water and 1.0 M NaCl solution as the feed solution and draw solution, respectively, the SFIP-PVDF membrane, which used a macroporous PVDF substrate with a pore size of 0.45 μm exhibited a water flux (20 L/m2·h) and a reverse salt flux (2.5 g/m2·h). Besides, the membrane showed good stability in the 72 h test. The specific salt flux (Js/Jw) of SFIP-PVDF membranes was much lower than that of IP-PVDF membranes prepared via IP technology, which were incomplete and defective, suggesting that SFIP technology was superior to IP technology. This work effectively exploits the potential of macroporous substrates for the development of high performance TFC FO membranes and provides an insight into the high performance FO membrane design.

Fabrication of a novel composite nanofiltration membrane with effective treating dye wastewater via integration of phase inversion and interfacial polymerization

In this work, we proposed using the combination of nonsolvent induced phase separation (NIPS) technology and interfacial polymerization (IP) process upon polyvinylidene fluoride (PVDF) substrate as a novel and simple method for preparing high-flux composite nanofiltration membranes. The surface chemical properties, physical structure, hydrophilicity, zeta potential, and permeation experiments of the composite membranes that were prepared with graphene oxide (GO), cyclodextrin (CD), or GO@CD as aqueous monomers were studied. The results indicated that the selective polyester active layer successfully covered the PVDF substrate, and the optimal GO@CD50/PVDF membrane was fabricated using the modification conditions of 1.0 wt% of GO@CD50, 5 min of phase transition time, 0.2 wt% of TMC, and 60 min of IP reaction time, which achieved a high pure water flux (84.8 L m−2 h−1 bar−1) and dye permeation flux (48.7 L m−2 h−1 bar−1 for Rose Bengal); in addition, the dye rejection rate was also high (e.g., 99.6 % for Rose Bengal). Besides, CD nanomaterials can be effectively inserted into the GO lamella to increase the layer spacing of GO sheets and expose more oxygen-containing functional groups; this, in turn, enhances the long-term stability and permeability of the membrane. This study provides practical ways to treat dyes wastewater.

Effects of Porogen PEG and Pore Structure of PVDF Substrates on the Permeability–Selectivity Trade-off of TFC-NF Membranes

Thin-film composite (TFC) nanofiltration (NF) has been widely utilized to separate monovalent ions from multivalent ions in industrial wastewater treatment. In this study, the pore properties of polyvinylidene fluoride (PVDF) substrates were adjusted by varying the content and molecular weights (MWs) of porogen polyethylene glycol (PEG). The TFC membranes fabricated on different substrates showed distinguishable permeance and selectivity. The PVDF membranes with 2 kDa PEG of 0.5–3.0 wt % and 20 kDa PEG of 0.2 wt % were fit for the substrates of the TFC NF membrane. These substrates are usually characterized by evenly distributed surface pores with porosity of 7–12% and tiny finger-like pores of less than 15 μm length. Such pore structures in the substrates are fit for the storage and migration of amine monomers, resulting in a defect-free PA layer. In a 6 h filtration of mining wastewater using an optimized TFC membrane, the permeance remained around 5 LMH/bar and the separation factor of SO42–/Cl– stayed over 13.39 with a maximum value over 30. This study shed light on improving NF membrane performance by simply adjusting the porogen in the substrate casting solution.

SERS performance of silver nanoparticle/reduced graphene oxide-coated filter membranes

Polyvinylidene fluoride (PVDF), polyamide (Nylon) and anodic aluminum oxide (AAO) filter membranes were coated with in-situ synthesized silver nanoparticle/reduced graphene oxide (AgNP/rGO) nanocomposite by vacuum filtration, and surface-enhanced Raman scattering (SERS) performance of the prepared substrates was investigated using Rhodamine 6G (R6G) as a probe molecule. Analyte solutions were applied by drop casting and penetrated into the flexible PVDF and Nylon-based substrates within minutes, enabling very fast SERS measurements; however, this step took up to 2 hrs in the rigid AAO-based substrate. Scanning electron microscopy and Energy-dispersive X-ray spectroscopy mapping results showed that filter membrane surfaces were completely covered with AgNP/rGO nanocomposite at which AgNPs were uniformly distributed on rGO flakes; however, some large, partially reduced or unreduced GO flakes decorated with AgNP agglomerates (AgNP/GO) were also observed. Higher SERS signals were generally obtained from these AgNP/GO flakes compared to the AgNP/rGO coated regions, since they contain higher amount of oxygen-rich functional groups which enabled a higher chemical and electromagnetic enhancement in SERS signals. All the substrates could detect 10−7 M R6G even after being stored in a vacuum desiccator for 3 months, indicating that AgNP/rGO coated filter membranes are promising as stable SERS substrates thanks to their long shelf life.

Hollow fiber membranes comprising of polyvinylamine/polydopamine active layers and a polyvinylidene fluoride substrate for pervaporative concentration of KAc solutions

We report on a thin-film-composite hollow fiber membrane comprising a hydrophilic active layer and a hydrophobic substrate for pervaporative concentration of KAc solutions. A hydrophobic substrate was chosen in order to overcome the potential problems of liquid water crossover through the membrane that typically occurred with a hydrophilic substrate over a prolonged period as a result of capillary condensation and gradual pore wetting even after system shutdown. Attempts were made to co-deposit PVAm/dopamine onto a PVDF hollow fiber substrate to form thin-film-composite hollow fiber membranes. However, it was challenging to deposit hydrophilic macromolecules on a hydrophobic surface. To facilitate the deposition of dopamine/PVAm onto a hydrophobic substrate, where PVAm macromolecules were securely attached to the substrate with the assistance of adhesive dopamine, methanol was used as a co-solvent to improve surface wetting and pre-coating of dopamine was used to form a hydrophilic binding layer that was better prepared for subsequent dopamine/PVAm deposition. It was shown that the use of co-solvent water/methanol (90/10 in vol) in the depositing solution and precoating dopamine for 3 h prior to co-deposition of dopamine/PVAm were appropriate for membrane formation, and the resulting membrane showed stable performance in concentrating KAc solutions at a high feed concentration (70 wt%) over a period of 200 h at an operating temperature of 70℃. A stable water flux of 1.7–1.9 kg/m2h was achieved, with an essentially complete salt retention.

Low-Energy Photons Dual Harvest for Photocatalytic Hydrogen Evolution: Bimodal Surface Plasma Resonance Related Synergism of Upconversion and Pyroelectricity.

Utilization of low-energy photons for efficient photocatalysis remains a challenging pursuit. Herein, a strategy is reported to boost the photocatalytic performance, by promoting low-energy photons dual harvest through bimodal surface plasmon resonance (SPR)-enhanced synergistically upconversion and pyroelectricity. It is achieved by introducing triplet-triplet annihilation upconversion (TTA-UC) materials and plasmonic material (Au nanorods, AuNRs) into composite fibers composed of pyroelectric substrate (poly(vinylidene fluoride)) and photocatalyst Cd0.5 Zn0.5 S. Interestingly, the dual combination of TTA-UC and AuNRs SPR in the presence of polyvinylidene fluoride substrate with pyroelectric property promotes the photocatalytic hydrogen evolution performance by 2.88folds with the highest average apparent quantum yield of 7.0% under the low-energy light (λ > 475nm), which far outweighs the role of separate application of TTA-UC (34%) and AuNRs SPR (76%). The presence of pyroelectricity plays an important role in the built-in electric field as well as the accordingly photogenerated carrier behavior in the composite photocatalytic materials, and the pyroelectricity can be affected by AuNRs with different morphologies, which is proved by the Kelvin probe force microscopy and photocurrent data. This work provides a new avenue for fully utilizing low-energy photons in the solar spectrum for improving photocatalytic performance.

Epoxied SiO2 nanoparticles and polyethyleneimine (PEI) coated polyvinylidene fluoride (PVDF) membrane for improved oil water separation, anti-fouling, dye and heavy metal ions removal capabilities.

Epoxied SiO2 nanoparticles and polyethyleneimine (PEI) was used to coating polyvinylidene fluoride (PVDF) membrane for improved anti-fouling, oil water separation, dye and heavy metal ions removal capabilities. Characterization of the modified membrane revealed that the hydrophilic coating layer was applied onto the PVDF substrate successfully. The modified membrane can exhibit a high degree of superhydrophilicity and underwater superoleophobicity. Consequently over 98% of the oil was retained when this membrane was used in oil water separation. The hydrophilic coating layer enhanced the membrane antifouling performance, and its flux recovery rate reached 96.3% after filtration and washing with bovine serum protein solution (BSA). In addition, the modified membrane presented the ability to adsorb organic dyes and heavy metal ions in water and reject them via filtration. Most importantly, the crosslinking reaction between the epoxied SiO2 nanoparticles and PEI imparts a high degree of stability to the coating layer. Thanks to the simple fabrication method and multifunctional performances of the coating layer described in this report, it may be used to modify other substrates.

Using Cu-TCPP Nanosheets as Interlayers for High-Performance Organic Solvent Nanofiltration Membranes

The development of highly permeable and selective thin-film composite (TFC) membranes is essential for organic solvent nanofiltration (OSN) applications. However, overcoming the permeability–selectivity trade-off in polymer membranes remains highly challenging owing to the difficulty in controlling the thickness and nanostructures of the selective layers. In this study, TFC OSN membranes with sandwich-like structures were developed via interfacial polymerization on Cu-TCPP nanosheet-modified microporous polyvinylidene fluoride (PVDF) substrate surface. The interfacial polymerization was done by using mixed amine (polyethyleneimine and piperazine) in the aqueous phase and the 1,3,5-benzenetricarbonyl trichloride in the hydrophobic ionic liquid phase as monomers. It was found that the Cu-TCPP nanosheets of micrometer lateral dimensions and nanometer thickness (1.5 ± 0.6 nm) can be deposited on the PVDF substrate as an interlayer to facilitate the following interfacial polymerization reaction. The Cu-TCPP interlayer also can be served as a binder between the polyamide selective layer and the microporous PVDF substrate to enhance their mechanical strength. As compared with the PVDF/PA membrane, the PVDF/t-Cu-TCPP/PA membrane exhibited higher elongation (8.0 vs. 4.6%) while ensuring slightly lower tensile strength (36.0 vs. 48.6 MPa). Under optimal synthetic conditions, the TFC membranes could achieve 2.7 L m–2 h–1 bar–1, and 98.9% and 95.0% rejection to Brilliant Blue R (826 Da) and Congo red (697 Da), respectively, in ethanol. Furthermore, the membranes showed steady performance throughout the 36 h nanofiltration of the Rose bengal/ethanol mixture and exhibited good performance in the concentration of lecithin in methanol. Accordingly, this work highlights the potential of using thin metal–organic framework nanosheets as interlayers to develop high-performance TFC membranes for OSN applications.

2D Nano-Mica Sheets Assembled Membranes for High-Efficiency Oil/Water Separation.

Oil-polluted water has become one of the most important environmental concerns nowadays due to the increasing industrial oily wastewater and frequent oil spill accidents. Herein, a novel two-dimensional (2D) nano-mica sheets assembled composite membrane with underwater super-oleophobic properties was developed for effective oil/water separation. A 2D nano-mica sheet was synthesized by a facile solvent-assisted ultrasonic exfoliation and then the obtained 2D nano-mica sheets were co-deposited with dopamine on polyvinylidene fluoride substrate to prepare nano-mica composite membranes (NCM). The NCM is hydrophilic in air and super-oleophobic underwater (the water contact angle in the air is 37.6°, and the oil contact angle in water is 151.4°). Furthermore, the prepared NCM provided outstanding stability in different acid–base environments (pH = 1–11). Noteworthily, the oil removal rate is higher than 99.5% as the sodium dodecyl sulfate SDS-stabilized oil (soya-bean oil, mineral oil and pump oil) -in-water emulsions. Meanwhile, the NCM showed excellent reusability, as the oil removal efficiency kept at 99.0% after ten soya-bean oil-in-water or mineral oil-in-water emulsion filtration cycles. The present work paved a new way for developing a low-cost and environmentally friendly strategy for oily wastewater treatment and developed a high-increment utilization application field for natural minerals.

Effects of polyvinylidene fluoride substrate characteristics on the selectivity of thin‐film composite nanofiltration membrane

AbstractThin‐film composite (TFC) nanofiltration (NF) membranes have been fabricated on polyvinylidene fluoride (PVDF) substrates to separate Cl− and SO42−. With increasing polyvinylpyrrolidone (PVP) content (0–1.00 wt%) in PVDF casting solution, the corresponding substrates have similar surface pore size and hydrophilicity, but have enlarged surface porosity and bulk pore size. Obvious defects were found on TFC membrane surface, which were fabricated on the substrate with large and deep finger‐like pores. On such substrates, piperazine solution is prone to sink to the pore bottom and cannot react with trimesoyl chloride to form a defect‐free polyamide layer. Different from previous reports, the bulk pore size and structure, especially for the finger‐like pore, is found to be a key factor influencing the interfacial polymerization (IP) process. The optimal TFC membrane was prepared on the substrate with 0.15 wt% PVP in casting solution, which had crater‐shaped ridge‐valley structures, relatively high permeability and the largest separation factor of 4.66 for Cl− and SO42−. Although the NF performance needs to be further improved, the results shed lights on the important effects of the substrate bulk pore size and structure on the IP process, which will enlarge the knowledge on the impact of substrate on IP process.

Flexible Soft-Solid Metal-Organic Framework Composite Membranes for H2 /CO2 Separation.

The development of a facile strategy to construct defect-free and flexible metal-organic framework (MOF)-based membranes with high selectivity and good scalability holds great appeal. Here we report the fabrication of soft-solid MOF composite membranes on polyvinylidene fluoride substrates. A representative membrane comprised of quasi-vertically grown lamellar Zn2 (Bim)4 (Bim=benzimidazolate) and lateral ultrathin polyamide film adhering to the MOF side facets. The straight interlayer galleries within unwrapped Zn2 (Bim)4 acted as predominant pathways, while the polyamide served the function of defect elimination, synergistically inducing an unprecedented H2 /CO2 selectivity of 1084 which set a new record for MOF-based membranes. Separation performance was held constant after membrane rolling up into a tube with a diameter of 3 mm or folding and unfolding at 90° for 50 times. ZIF-67 and ZIF-8 composite membranes based on this strategy also realized extremely high H2 /CO2 separation accuracies. These results, which demonstrate the intrinsic molecular sieving capability of MOFs, will promote the development of MOF-based membranes in practical separation applications.

Flexible Soft‐Solid Metal–Organic Framework Composite Membranes for H2/CO2 Separation

AbstractThe development of a facile strategy to construct defect‐free and flexible metal–organic framework (MOF)‐based membranes with high selectivity and good scalability holds great appeal. Here we report the fabrication of soft‐solid MOF composite membranes on polyvinylidene fluoride substrates. A representative membrane comprised of quasi‐vertically grown lamellar Zn2(Bim)4 (Bim=benzimidazolate) and lateral ultrathin polyamide film adhering to the MOF side facets. The straight interlayer galleries within unwrapped Zn2(Bim)4 acted as predominant pathways, while the polyamide served the function of defect elimination, synergistically inducing an unprecedented H2/CO2 selectivity of 1084 which set a new record for MOF‐based membranes. Separation performance was held constant after membrane rolling up into a tube with a diameter of 3 mm or folding and unfolding at 90° for 50 times. ZIF‐67 and ZIF‐8 composite membranes based on this strategy also realized extremely high H2/CO2 separation accuracies. These results, which demonstrate the intrinsic molecular sieving capability of MOFs, will promote the development of MOF‐based membranes in practical separation applications.

Stabilize thin nanoparticle layer of zeolitic imidazole framework-8 (ZIF-8) on different PVDF substrates by contra-diffusion method for high-efficiency ultrafiltration application

In this research, a contra-diffusion cell, which is an effective instrument for growing inorganic layers on porous substrates, was applied to prepare a thin layer of zeolitic imidazole framework-8 (ZIF-8) on polyvinylidene fluoride (PVDF) ultrafiltration membranes. With using of methanol as a solvent, a thin layer of ZIF-8 was fabricated resulted in a flexible inorganic coated organic membrane. The ZIF-8 nanoparticles were formed as a resistant layer on the outer surface and inner pores of PVDF support and its effect on permeability, flux recovery ratio (FRR) and treatment of colored wastewater was investigated. Manufacturing parameters such as the reaction time between Zn2+ ions and imidazole ligands (16, 24 and 36 h) and concentration of PVDF in the casting solution of the support membranes (18, 20 and 22 wt%) were considered. The SEM images showed the well-growing of uniform and a thin layer of ZIF-8. The membrane performance tests revealed that ZIF-8 decorated membranes have higher pure water flux, BSA protein rejection and FRR related to the uncoated PVDF membrane. The fabricated membranes indicated high removal efficiency in three different MW dyes (Rhodamine B, Reactive Green 19 and Direct Black 38), with 75, 85 and 98% rejection, respectively.

Super‐Wetting Porous g‐C3N4 Nanosheets Coated PVDF Membrane for Emulsified Oil/Water Separation and Aqueous Organic Pollutant Elimination

AbstractSuper‐wetting multifunctional membranes are highly attractive in the current decade in the environmental remediation of wastewater containing water‐insoluble emulsified oils and water‐soluble hazardous organic pollutants. Herein, hydroxyl modified porous g‐C3N4 nanosheets (CNNS) coated polyvinylidene fluoride (PVDF) membrane is fabricated by a facile vacuum pumping process. Hydroxyl modified porous g‐C3N4 nanosheets are firmly immobilized on flexible PVDF substrate via sodium alginate (SA) adhesive to create a stable surface micro/nanohierarchical structure. The fabricated CNNS/SA/PVDF membrane achieves the desired surface wettability of superhydrophilicity/underwater superoleophobicity with an anti‐oil‐fouling property. The functionalized membrane exhibits above 99% emulsified oil rejection rate with excellent stability and recyclability when separating oil‐in‐water emulsions. Besides, visible‐light‐response CNNS endow the as‐prepared membrane with excellent photocatalytic activity. The resulted CNNS/SA/PVDF membrane can eliminate organic dye both in static and dynamic water with high flux recovery ratio and renewability, which conducted the procedures of photodegradation of organic dye adsorbed on the membrane surface after filtering the contaminative flowing aqueous solution, and directly the photodegradation of organic dye in stationary aqueous solution, respectively. This facile‐fabrication and high‐performance CNNS/SA/PVDF membrane provides a promising practical application toward oily and organic wastewater treatment. It also promotes the utilization of surface wettability modified g‐C3N4 nanomaterial in the construction of multifunctional interface membrane for environmental purification.