Performance Of Polyvinylidene Fluoride Membranes Research Articles

Effect of chitosan crosslinking time on the structure and antifouling performance of polyvinylidene fluoride membrane by surface gelation-immersion precipitation phase inversion.

Polyvinylidene fluoride (PVDF) porous membrane was prepared by a two-step method of surface gelation-immersion precipitation phase inversion. Chitosan/acetic acid solution and glutaraldehyde aqueous solution were sequentially sprayed onto the surface of the PVDF solution film, with chitosan crosslinking and gelation occurring simultaneously on the film surface. The solution film was then immersed in a coagulation bath to obtain a modified PVDF porous membrane. The effect of the crosslinking time of chitosan and glutaraldehyde on the structure and properties of the PVDF porous membrane was discussed. The results showed that with the prolongation of crosslinking time, the surface structure of the membrane changed from a dense skin layer to a porous structure; the porosity and the mean pore size of the modified PVDF membranes increased first and then decreased, and the contact angle gradually decreased. When the crosslinking time extended to 15 min, the water flux of modified membrane (M153) reached a maximum value. BSA dynamic cyclic filtration experiment showed that the retention rate (R) of the modified membrane was significantly improved, compared to 68.3% retention rate of the blank membrane (M000), but the crosslinking time had little effect on the retention rates of the four modified membranes. The antifouling data showed that the flux recovery rate of the blank membrane was 73.0%, while the flux recovery rate of the modified membrane can reach as high as 84.40%, and the irreversible pollution rate of the blank membrane was 27.7%, while the irreversible pollution rate of the modified membrane reduced to 15.6%. These results indicated that, after surface chitosan crosslinking, the hydrophilicity and antifouling properties of PVDF membranes were improved. PRACTITIONER POINTS: Modified PVDF membranes with crosslinking CS coating were prepared by a two-step method of surface gelation-immersion precipitation phase inversion. -OH groups and -NH2 groups of CS coating improve the hydrophilicity and the antifouling property of modified PVDF membranes. Modified PVDF membranes had larger mean pore size and higher porosity than unmodified membrane. Flux recovery rates of the modified membranes were higher than that of unmodified membrane. Pollution degree, reversible pollution rate, and irreversible pollution rate of modified membranes were lower than those of unmodified membrane.

Hydrophobic modification of polyvinylidene fluoride membranes in supercritical carbon dioxide fluids

Polyvinylidene fluoride (PVDF) membranes exhibit exceptional chemical stability and find applications in various fields, including building membranes, flexible sensors, blood purification, and seawater desalination. Nevertheless, the hydrophobic performance of PVDF membranes in these applications is subpar and requires enhancement. Supercritical carbon dioxide (scCO2) fluid demonstrates a beneficial expansion effect on PVDF membranes and exhibits good solubility with fluorine reagents. This study employs scCO2 as a medium to introduce a fluorine reagent onto the surface of PVDF membranes, forming a layer of low surface energy substance that significantly improves the membrane's hydrophobicity. The results indicate the feasibility of hydrophobic modification of PVDF membranes using scCO2 as a medium, leading to improved hydrophobic properties. When using a fluorine reagent with a relatively large molecular weight, PVDF membranes in scCO2 fluid at 110 °C and 20–25 MPa for 4 h results in a substantial improvement in the hydrophobicity of the PVDF membrane, with the contact angle reaching 117.2° (compared to the primitive membrane's 80°). Scanning electron microscopy (SEM) analysis confirms the presence of a layer of low surface energy material on the modified PVDF membrane surface. Thermogravimetric (TG) and differential thermogravimetric (DTG) analyses demonstrate that the hydrophobic modification using scCO2 enhances the crystallinity and thermal stability of the PVDF membrane, raising the thermal cracking temperature from 425.3 °C to 450.5 °C. Fourier-transform infrared spectroscopy (FT-IR) reveals clear absorption peaks of the fluorine reagent at 1740 cm−1 and 1211 cm−1. Nuclear magnetic resonance (NMR) confirms the presence of characteristic peaks of hydrogen on the fluorine reagent, confirming the embedding of the hydrophobic reagent onto the PVDF membrane surface. This modification method holds significant potential for guiding the development of hydrophobic surfaces, contributing to carbon neutrality, and meeting environmental sustainability goals.

Improved performance of polyvinylidene fluoride membrane blended with modified multi‐walled carbon nanotubes by electret treatment

AbstractIn this paper, electret treatment was used to enhance the electrostatic repulsion between the membrane and bovine serum albumin, so as to improve the anti‐fouling ability and recycling rate of the membrane. The polarization charge is provided by the dipole orientation of polyvinylidene fluoride (PVDF) materials, and the space charge is composed of the interfacial charge between the filler and the matrix and the bulk charge of the hollow structure of the multi‐walled carbon nanotubes. The results showed that after electret treatment, the surface potential of the membrane increased, the PVDF crystal type changed from α to β, and the crystallinity increased. Grafting of N‐vinylpyrrolidone onto multi‐walled carbon nanotubes (MWCNTs‐g‐PVP), which contain a large number of hydrophilic groups after modification, reduces the contact angle of the composite film from 86.9° to 62.7°. The pure water flux and flux recovery rate of MWCNTs‐g‐PVP/PVDF composite membranes after electret treatment was increased from 189.31 L·m−2·h−1 and 90% to 233.55 L·m−2·h−1 and 94.7%, respectively, and the rejection rate increased about 30%. Through the circulation experiment, it can be seen that the anti‐fouling performance and recycling rate of the membrane is improved, which is caused by electrostatic repulsion.

Improving the hydrophilicity and antifouling performance of PVDF membranes via PEI amination and further poly (methyl vinyl ether-alt-maleic anhydride) modification

Polyvinylidene fluoride (PVDF) is an excellent material for porous membranes due to its outstanding chemical resistance, thermal stability, and film formability. However, the lower surface energy and the hydrophobicity of PVDF, result in poor wettability and organic fouling. In the present work, polyethyleneimine (PEI) was covalently bound on PVDF through the amination reaction in the casting solution. After converting the solution into membranes by phase inversion, the PEI-aminated PVDF membrane was further modified with poly (methyl vinyl ether-alt-maleic anhydride) (PEOSMA). The PEOSMA-modified membranes possess super hydrophilicity and antifouling performance. The protein adsorption capacity of the modified membrane was extremely low, only 5.65 μg/cm2. The pure water recovery rate (FRR) reached 97%, with BSA rejection over 97%. The presented protocol offers an effective in-situ covalent modification method for PDVF membranes with a high potential in large-scale applications.

Aliquots of MIL-140 and Graphene in Smart PNIPAM Mixed Hydrogels: A Nanoenvironment for a More Eco-Friendly Treatment of NaCl and Humic Acid Mixtures by Membrane Distillation.

The problem of water scarcity is already serious and risks becoming dramatic in terms of human health as well as environmental safety. Recovery of freshwater by means of eco-friendly technologies is an urgent matter. Membrane distillation (MD) is an accredited green operation for water purification, but a viable and sustainable solution to the problem needs to be concerned with every step of the process, including managed amounts of materials, membrane fabrication procedures, and cleaning practices. Once it is established that MD technology is sustainable, a good strategy would also be concerned with the choice of managing low amounts of functional materials for membrane manufacturing. These materials are to be rearranged in interfaces so as to generate nanoenvironments wherein local events, conceived to be crucial for the success and sustainability of the separation, can take place without endangering the ecosystem. In this work, discrete and random supramolecular complexes based on smart poly(N-isopropyl acrylamide) (PNIPAM) mixed hydrogels with aliquots of ZrO(O2C-C10H6-CO2) (MIL-140) and graphene have been produced on a polyvinylidene fluoride (PVDF) sublayer and have been proven to enhance the performance of PVDF membranes for MD operations. Two-dimensional materials have been adhered to the membrane surface through combined wet solvent (WS) and layer-by-layer (LbL) spray deposition without requiring further subnanometer-scale size adjustment. The creation of a dual responsive nanoenvironment has enabled the cooperative events needed for water purification. According to the MD's rules, a permanent hydrophobic state of the hydrogels together with a great ability of 2D materials to assist water vapor diffusion through the membranes has been targeted. The chance to switch the density of charge at the membrane-aqueous solution interface has further allowed for the choice of greener and more efficient self-cleaning procedures with a full recovery of the permeation properties of the engineered membranes. The experimental evidence of this work confirms the suitability of the proposed approach to obtain distinct effects on a future production of reusable water from hypersaline streams under somewhat soft working conditions and in full respect to environmental sustainability.

Preparation and characterization of superior hydrophilic PVDF/DA membranes by the self-polymerization approach of dopamine.

Polyvinylidene fluoride (PVDF) membranes are favored for their excellent properties. However, the inherent strong hydrophobicity of PVDF membranes limits their development in the field of water treatment. The objective of this study was to improve the performance of PVDF membranes using the self-polymerization, strong adhesion properties, and biocompatible effects of dopamine (DA). The PVDF/DA membrane modification conditions were simulated and optimized using response surface methodology (RSM), and the experimental design was used to investigate three main parameters. The results showed that the DA solution concentration of 1.65g/L, the coating time of 4.5h, the post-treatment temperature of 25°C, the contact angle decreased from 69° to 33.9°, and the pure water flux on the PVDF/DA membrane was higher than that on the original membrane. The absolute value of the relative error between the actual and predicted values is only 3.36 %. In the MBR parallel comparison test, compared with the PVDF/DA membrane, the total amount of extracellular polymers (EPS) of the PVDF membrane increased by 1.46 times and the polysaccharide increased by 1.56 times, which further showed that the PVDF/DA modified membrane had the excellent anti-pollution ability. Through Alpha diversity analysis, the biodiversity detected on PVDF/DA membranes was higher than that of PVDF membranes, which further proved its good bio-adhesion ability. These findings could offer a reference for the hydrophilicity, antifouling, and stability of PVDF/DA membranes, which would establish the foundation for the comprehensive applications in MBR.

Impact of Nanoclays on Polyvinylidene Fluoride Mixed Matrix Membranes for the Efficient Treatment of Oily Wastewater

Background: Membrane technology demonstrated a sustainable methodology for water reclamation from oily-wastewater, but it is prone to fouling during longer filtration runs. In this study, fouling resistant polyvinylidene fluoride (PVDF) mixed matrix membranes (MMMs) containing nanoclays such as halloysite (HT) and montmorillonite (MMT) were fabricated for the effective treatment of oily wastewater. Methods: Phase inversion technique was followed for the fabrication of HT-PVDF and MMT-PVDF MMMs. Physiochemical characterization and filtration experiments were studied to evaluate the influence of nanoclays on PVDF membrane performance. Results: Fourier transform infrared spectroscopy (FTIR) and morphology analyses indicated that both nanoclays are layered structured with abundant hydrophilic functional groups. The dispersions of HT and MMT were confirmed by surface morphology and topography analysis of PVDF MMMs. The hydrophilicity property was improved in HT-PVDF and MMT-PVDF MMMs, which was evident in the contact angle analysis. Among the membranes, MMT-PVDF MMMs held the higher water permeability of 2.59 x10-8 m/s.kPa. For oil-water filtration, HT-PVDF and MMT-PVDF MMMs displayed higher normalized flux with maximum rejection of more than 95%. Conclusion: Overall, MMT would be cost-effective nanofiller for the development of antifouling PVDF MMMs against oil-water filtration.

Developing a robust photocatalytic and antifouling performance of PVDF membrane using spinel NiFe2O4/GO photocatalyst for efficient industrial dye wastewater treatment

Photocatalytic nanohybrid polyvinylidene fluoride (PVDF) membrane incorporated by nickel ferrite/ graphene oxide (NiFe2O4/GO) photocatalyst is fabricated in this study. To prevent the fast electron/hole recombination rate in NiFe2O4 photocatalyst, GO nanoparticle was added to synthesize the NiFe2O4/GO photocatalyst. The fabricated membranes were tested for industrial dye wastewater treatment, which mainly contained Remazol red RB-133 as the colorant. The modified membranes were synthesized by adapting the non-solvent induced phase separation (NIPS-blending) technique, and their filtration performance were assessed both in the conventional dark filtration condition and under ultraviolet (UV) light exposure. Scanning electron microscopy – Energy dispersive x-ray (SEM-EDX) results reveal that the PVDF/NiFe2O4/GO membrane features a smooth, defect-free surface with a well-built finger-like structure, as well as a well-distributed NiFe2O4/GO distribution on the membrane's surface. Some new hydrophilic groups are recorded on PVDF/NiFe2O4/GO by the Fourier-transform infrared (FTIR) analysis such as -OH, Fe-O, Ni-O, and CO and some crystallite sites of NiFe2O4 and GO, which is helpful to improve the surface hydrophilicity. The permeability, pollutant removal, membrane stability, photodegradation ability, and antifouling activity of the modified membranes in the filtration process under UV light exposure were significantly improved. This membrane removed 83.22% of COD and 92.38% of dye when it was performed under UV light irradiation. The presence of photocatalytic activity on the membranes’ surface also improves the antifouling activity by converting the irreversible fouling into the reversible fouling, hence, the modified membranes have a better performance stability than the other membranes.

Efficient oil-water emulsion treatment via novel composite membranes fabricated by CaCO3-based biomineralization and TA-Ti(IV) coating strategy.

Continuous increasing discharge of industrial oily wastewater and frequent occurrence of oil spill accidents have taken heavy tolls on global environment and human health. Organic-inorganic modifications can fabricate superhydrophilic/submerged superoleophobic membranes for efficient oil-water separation/treatment though they still suffer from complex operation, non-environmental friendliness, expensive cost or uneven distribution. Herein, a new strategy regarding tannic acid (TA)-Ti(IV) coating and CaCO3-based biomineralization through simple inkjet printing processes was proposed to modify polyvinylidene fluoride (PVDF) membrane, endowing the membrane with high hydrophilicity (water contact angle (WCA) decreased from 86.01° to 14.94°) and underwater superoleophobicity (underwater contact angle (UOCA) > 155°). The optimized TA-Ti(IV)-CaCO3 modified membrane possessed perfect water permeation to various oil/water emulsions (e.g., 355.7 L·m-2·h-1 for gasoline emulsion) under gravity with superior separation efficiency (>98.8 %), leading the way in oil/water emulsion separation performance of PVDF membranes modified with polyphenolic surfaces to our knowledge. Moreover, the modified membrane displayed rather high flux recovery after eight cycles of filtration while maintaining the original excellent separation efficiency. The modification process proposed in this study is almost independent of the nature of the substrate, and meets the demand for simple, inexpensive, rapid preparation of highly hydrophilic antifouling membranes, showing abroad application prospect for oil-water emulsion separation/treatment.

Surface free energy, microstructure and performance of polyvinylidene fluoride (PVDF) membrane: the influence of hydrophilic porogens

Polyvinylidene fluoride (PVDF) membrane are widely used in water treatment due to its good physical and chemical properties, and the pores of PVDF membranes determine most of the characteristics of PVDF membrane. The hydrophilic porogens play an important role in the preparation of PVDF membranes and the regulation of membrane pores. In this work, three hydrophilic porogens with different quality components were used to prepare PVDF ultrafiltration membranes by the nonsolvent induced phase separation (NIPS) method. Through the Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), mechanical strength, contact angle and other characterizations, the influence of hydrophilic porogens on the surface free energy, microstructure and performance of PVDF membrane were studied. The results suggest that lithium chloride (LiCl) can inhibit the formation of macropores and improve the mechanical strength of the membrane. Polyvinylpyrrolidone (PVP) can form through-hole through the PVDF membrane. All three hydrophilic porogens can increased the surface free energy of the PVDF membranes, where polyethylene glycol (PEG) had the most impact on the surface free energy.

The potential of polyvinylidene fluoride (PVDF)-kaolin membrane for water treatment

Polyvinylidene fluoride (PVDF)-kaolin membrane has been successfully fabricated. The addition of kaolin is aimed to optimize the performance of PVDF membrane for water treatment. Kaolin was prepared using 0.1 N HCl to activate the material. The fabrication of membranes was using phase inversion with 6 variations on PVDF composition within the membrane. FTIR analysis on kaolin activation shows minor changes on peak intensities and broadness without any addition or loss peak that indicates there is no reaction and only activation is occurred. The addition of kaolin affects the pure water flux. All of modified membranes shows gradually change on porosity and hydrophobicity properties under the contact angle measurement.

The effect of polyvinylpirrolidone on the performance of polyvinylidene fluoride membranes

In this investigation, polyvinylidene fluoride membranes were resulted by a phase inversion technique with polyvinylpyrrolidone (PVP) as an agent to form pores, as well as n-methyl pyrrolidone as a solvent. In addition, the effect of PVP concentration (1-4%) was investigated to prepare membranes with better membrane antifouling performance and characteristics. Furthermore, functional groups, morphological structures, and membrane porosity were analysed by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and membrane porosity calculation. The surface SEM images revealed that the size of the modified membrane pores increased. The increase of the PVP concentration added, resulted in the number of modified membrane pores. FTIR spectra confirmed that PVP functional groups were dispersed in the PVDF membrane matrix. Optimum pure water permeability (PWP) of 60 L/(m2?h?bar) was achieved using 3% PVP, resulting in a humic acid rejection percentage of 80% and a water flux recovery ratio (FRR) of 85%. These findings indicate that the utilization of PVP as a pre-forming agent resulted in higher PWP, lower humic acid rejection, and good antifouling properties.

Investigating the effect of PEG200 and two-dimensional h-BN on PVDF membrane performance for membrane distillation–crystallization

Although water supplies are prominently dependent on desalination technology, desalination plant facing severe issues of discharged brine concentrate. Membrane distillation crystallization is an emerging synergistic technology that resolves the issue of brine concentrate by recovering clean water and value-added minerals simultaneously. In the present study, properties of polyvinylidene fluoride (PVDF) membrane were modified by incorporation of exfoliated fillers of hexagonal boron nitride and polyethylene glycol. The changes in morphology, surface roughness, hydrophobicity, thermal stability, and chemical composition of the prepared membranes were evaluated by scanning electron microscopy, atomic force microscopy, contact angle, thermogravimetric analysis, Fourier-transform infrared spectroscopy, respectively. Membrane distillation crystallization experiments were conducted to observe the effect of modified membranes on the permeate flux and salts recovery at different feed temperatures. The results showed a significant improvement in the permeate flux with modified membranes compared with pure PVDF membrane. It was found that hexagonal boron nitride/polyethylene glycol200 incorporated PVDF membrane gave the higher permeate flux (3.41 kg/m2 h for K2SO4 and 2.62 kg/m2 h for KNO3) at a temperature of 80 °C along with higher salts recovery than pure PVDF membranes. A 100 h long run test was conducted on modified membranes, which showed consistency in permeate flux with a marginal increase in conductivity.

Polyvinylidene Fluoride/Nanoclays (Cloisite 30B and Palygorskite) Mixed Matrix Membranes with Improved Performance and Antifouling Properties

In this study, it was attempted to prove the effectiveness of nanoclays as economical and nontoxic nanofillers through comparison with carbon nanotubes (CNTs). Two hydrophilic nanoclays, namely, Cloisite 30B and palygorskite (PGS), were used as nanofillers to improve the morphology and performance of polyvinylidene fluoride (PVDF) ultrafiltration (UF) membranes. A nonsolvent-induced phase separation (NIPS) method was used to prepare mixed matrix membranes (MMMs). The effects of the nanoclays on morphology, performance, and antifouling properties of the prepared MMMs were investigated. It was found that compared to PVDF membranes, the hydrophilicity, antifouling properties, and morphology of the fabricated MMMs are improved significantly. Compared to PVDF membranes, pure water flux (PWF) values of the MMMs containing the optimum contents of Cloisite 30B (0.5 wt %) and palygorskite (1 wt %) improved by 44.7 and 61.7%, respectively. Acid-treated CNTs were used as a reference additive, and the performance and antifouling properties of the prepared PVDF/nanoclay MMMs were compared with the prepared PVDF/acid-treated CNT MMMs. It was found that the PWF values of the MMM containing optimum contents of PGS and Cloisite 30B nanoclays are 86 and 77%, respectively, compared with that of the MMM containing acid-treated CNTs. The PVDF/Cloisite 30B MMM exhibited lower PWF than the PVDF/PGS MMM, which could be attributed to the plate-like structure of Cloisite 30B. Also, the flux recovery ratio (FRR) values of the mixed matrix membranes containing optimum contents of PGS and Cloisite 30B nanoclays were 95.65 and 92.06%, respectively, compared to that of the MMM containing acid-treated CNTs. Also, the BSA rejections of the prepared MMMs containing optimum contents of Cloisite 30B and palygorskite were comparable with that of the MMM containing acid-treated CNTs. Therefore, nanoclays can be suggested as economical and ecofriendly nanofillers for improving the PVDF membrane performance.

Green approach for the synthesis of ultrafiltration photocatalytic membrane for tannery wastewater: modeling and optimization

A novel polyvinylidene fluoride/titanium dioxide solar active photocatalytic membrane with excellent rejection and reduction ability was prepared by phase inversion technique. The ex situ formed titanium dioxide nanoparticles using extract of Cajanus cajan of average size 10.5 nm were immobilized in the polymer matrix to enhance the performance of polyvinylidene fluoride membrane. This paper explores the innovation of synthesizing a cost-effective bifunctional membrane to eliminate toxic heavy metal: hexavalent chromium from wastewater using a synergistic approach of separation to reject hexavalent chromium and further reducing the toxicity by photocatalytic reduction of concentrated hexavalent chromium. The purpose of this work is to optimize the process condition that governs the process, namely pH, transmembrane pressure (Pa) and chromium concentration (mg/l), to maximize the rejection and reduction percentage using the same material. A quite high value of 97.59% rejection and 91.733% reduction values were suggested by response surface methodology at the predicted value of parameters: pH 5.55, 3.608 × 10⁵ Pa and at 26.652 mg/l. Real industry was also treated and could achieve > 90% rejection and > 85% reduction of Cr.

Improvement of PVDF nanofiltration membrane potential, separation and anti-fouling performance by electret treatment

Electret treatment was a simple method to enhance the charge-electrode properties of polyvinylidene fluoride (PVDF) materials due to the increase of space charge and polarization charge of PVDF materials. The polarization charge was due to the electric dipole orientation change in loose nanofiltration PVDF membrane, which increased the electric dipole moment and improved the polarity of surface potential. Importantly, electret charges were less affected by ambient humidity. Therefore, the electret treatment could improve the surface negative potential of loose nanofiltration PVDF membrane, so as to improve its anti-fouling performance under certain conditions. Based on the above theoretical analysis, the influence and mechanism of the electret treatment on the surface potential, morphology, structure, hydrophilicity and anti-pollution performance of PVDF membrane were studied in this manuscript. When the electret time was 7.5 min and the electret voltage was 30 kV, the surface negative potential was the highest. The content of β phase crystals was 39.1%, which was 12.18% higher than that of untreated membrane. In addition, the surface morphology of PVDF membrane did not change significantly, but the water contact angle decreased slightly, and the pore size increased by 0.36–0.75 nm. Importantly, the flux and the rejection of dye and BSA increased to some extent, and the maximum rejection rate and water flux were increased by 10.34% and 20.25%, respectively. Through the cyclic filtration test and analysis, the anti-fouling performance of membrane was increased due to electrostatic repulsion.

Enhanced photocatalytic performance of polyvinylidene fluoride membrane by doped CuFe2O4 nanocrystals for water treatment

CuFe2O4 nanocrystals with the size about 60 nm were synthesized under hydrothermal conditions, and doped them into polyvinylidene fluoride (PVDF) membranes for enhancing their photocatalytic performance. The morphology, phase, and photoelectric performance of CuFe2O4/PVDF membranes were confirmed by X-ray photoelectron spectroscopic (XPS), scanning transmission microscopy (SEM), and transient photoelectrochemical analysis. As a result, the morphologies of CuFe2O4 nanocrystals could change with the concentration of NaOH solution under hydrothermal conditions. CuFe2O4 nanocrystals showed strong facet-dependent photoelectric and photocatalytic properties. PVDF membrane doped with CuFe2O4 nanocubes showed excellent photocatalytic activity of Congo red degradation (95%), and kept the good self-cleaning performance after five circles. The flux and rejection performance displayed the CuFe2O4 nanocubes/PVDF membrane kept high water flux (40 L/m2 h) and Congo red rejection (99%), and the composite membrane have good potential in water treatment applications.

Effect of Adding Functionalized Graphene on the Performance of PVDF Membrane in Direct Contact Membrane Distillation

In this paper, the effect of adding modified graphene nanoplatelets (MGNPs) as a filler on the characteristics and performance of Polyvinylidene fluoride (PVDF) membrane in a direct contact membrane distillation (DCMD) configuration was investigated. Both pure PVDF and PVDF/MGNPs composite (2%) membranes were fabricated by using electrospinning technique. The fabricated membranes were characterized using different analyses techniques such as SEM imaging, XRD analysis, static water contact angle as well as membrane porosity and liquid enter pressure measurements. Also, the average fiber diameter and the average membrane pore diameter were estimated using ImageJ software. The prepared PVDF/MGNPs composite membrane exhibited lower fiber diameter by about 5.7%, whereas the contact angle increased by 10 and liquid entry pressure increased by 11.7%. The membrane also showed an enhanced flux that reached about 19.8 kg/m2∙h at feed inlet temperature of 65°C, feed flow rate of 30 l/h. and feed inlet concentration of 10000 ppm. This represents about 13.46% improvement over the pure PVDF membrane at the same conditions. The produced membrane presents a viable alternative to commercial MD membranes.

Novel mussel-inspired zwitterionic hydrophilic polymer to boost membrane water-treatment performance

Although the polyvinylidene fluoride (PVDF) membranes have been widely used for commercial water treatment, the fouling problem adversely affects the membrane deploying longevity, which can be alleviated by the facile surface segregation technology. However, the long-term stability of surface segregation modifiers (SSMs) in membrane is still a challenging issue because the inherent hydrophilicity makes SSMs to slowly dissolve in water. To improve the long-term stability of SSMs and boost the PVDF membrane performance for water treatment, a versatile catechol containing poly (ethylene glycol) modifier with zwitterionic characteristics (SZ-PEG) was synthesized and blended with PVDF to construct PVDF/SZ-PEG membranes with excellent fouling-resistance via surface segregation during non-solvent induced phase separation (NIPS). The incorporation of SZ-PEG endows the membrane with a high porosity through the reduced thermodynamic stability of casting solutions, enhancing the pure water flux of novel SSM modified membrane by 423% compared to the pristine PVDF membrane. Interestingly, the hydrophilic catechol groups in the SZ-PEG polymer accumulate on the membrane surface, resulting in both a high flux recovery ratio (FRR) of ∼96.9% and a good bovine serum albumin (BSA) rejection rate of ∼93.8%. The long-term stability of SZ-PEG polymers in the PVDF/SZ-PEG membrane is proven for 30 day incubation. The interesting findings may offer new insight into surface manipulation of PVDF/SZ-PEG membranes which is particularly effective in tuning the surface characteristics for drug delivery because of their excellent biocompatibility.

Reversibility of membrane performance and structure changes caused by extreme cold water temperature and elevated conditioning water temperature

The effects of extreme cold water temperature, elevated cleaning water temperature, cleaning time on membrane performance, and pore size distribution were studied using flat-sheet polyvinylidene fluoride (PVDF) membranes. Extreme cold water temperature led to a decrease in membrane permeability, and membrane pore size shrinkage. The use of periodical warm water (35 °C) membrane conditioning could almost completely recover the membrane permeability and pore size structure loss caused by extreme cold water temperature, while the use of room temperature (23±1 °C) conditioning recovered majority of the membrane permeability and structure loss caused by extreme cold water temperature. Changes in membrane performance correlate well with changes in membrane structure. Membranes periodically conditioned in warmer water temperature showed a higher permeability than that periodically conditioned at room temperature from a long-term operation of three months. The results suggest the change in PVDF membrane performance and structure caused by extreme cold water temperature is almost completely reversible after periodical warm water conditioning, and thus the use of warm water conditioning and/or chemical cleaning will benefit the recovery of membrane performance and structure change caused by extreme cold water temperature in cold regions.