Polyvinylidene Fluoride Ultrafiltration Membranes Research Articles

Fouling behavior heterogeneity of typical nanoplastics in widely used polyvinylidene fluoride ultrafiltration membranes

Fouling behavior heterogeneity of typical nanoplastics in widely used polyvinylidene fluoride ultrafiltration membranes

Enhanced removal of fluoride ions using lanthanum-doped coconut shell biochar in PVDF ultrafiltration membranes

Fluoride contamination in surface and ground water poses significant health risks, necessitating a low-energy, cost-effective removal method. Herein, an ultrafiltration (UF) adsorptive membrane doped with lanthanum (La)-based coconut shell biochar was synthesized to effectively remove fluoride ions. Based on the results of adsorption and membrane separation performance, it was found that La-based biochar showed a significantly higher adsorption capacity (126.7 mg F/g) compared to bare biochar (27.41 mg F/g), due to the oxygen-containing functional groups from La2O2CO3 that enhance binding sites and electrostatic attraction for fluoride ions. Furthermore, the addition of La-modified adsorbent to the polyvinylidene fluoride (PVDF) UF membrane markedly altered its structure and surface properties, changing the pore structure to porous, narrowing pore size, increasing active adsorption sites, and improving hydrophilicity. These changes boosted fluoride ion rejection from 9.53 % to 62.07 % with tiny effect on membrane permeability. More important, this UF adsorptive membrane exhibited excellent antifouling ability with the lowest flux decline (J/J0 =0.450) compared to pristine PVDF membrane (J/J0 =0.142), which was owing to the better improved surface properties. In all, this study provides a novel strategy for efficient, economic and selective separation of fluoride ions and further extends the application of UF to the field of ion removal.

Facile and controlled dual-step modification with enhanced anti-fouling performance in polyvinylidene fluoride membranes

Water scarcity and pollution pose significant challenges, necessitating advancements in water treatment technologies. Among various solutions, ultrafiltration membranes, especially those crafted from polyvinylidene fluoride (PVDF), are favored for their mechanical robustness and chemical stability. However, their practical application is often limited by severe membrane fouling due to the inherent hydrophobicity of PVDF. This project introduces a straightforward, controlled method to enhance the anti-fouling properties of PVDF membranes, utilizing a blend of cellulose acetate (CA). The process involves a two-step modification of hydrolysis followed by quaternization, effectively increasing hydroxyl group presence and facilitating subsequent chemical reactions. The optimized membranes achieve a dynamic water contact angle of 0° within 30 s and maintain an electroneutral surface at pH 7.1. With a mean pore size reduction from 28.6 nm to 23.9 nm and an impressive drop in the irreversible fouling ratio from 36.9 % to 0.3 %, these modifications markedly improve the anti-fouling performance. This research demonstrates significant potential for enhancing the functionality of PVDF ultrafiltration membranes through post-fabrication modifications, offering significant benefits for water treatment applications.

Preparation and characterization of oxygen‐functionalized graphene‐doped polyvinylidene fluoride ultrafiltration membranes

AbstractTo separate the oil/water mixtures, polyvinylidene fluoride (PVDF) nanofiber mats were produced using electrospinning. Additionally, PVDF films were made using the solvent evaporation method, and the effectiveness of their separation was evaluated against that of nanofiber mats. By choosing oxygen‐functionalized graphene (with HNO3) as a nano reinforcement, the hydrophobic properties of the PVDF materials made using both techniques were transformed into hydrophilic ones. It has been determined how the characteristics of the solution (viscosity, conductivity, molecular weight, surface tension, and contact angle) relate to the diameter of the nanofiber. Fourier transform infrared spectroscopy‐attenuated total reflection (FT‐IR/ATR), x‐rays diffraction (XRD), scanning electron microscope, thermogravimetric analyses (TGA)/DTG, and differential scanning calorimetric (DSC) have been used to study the chemical and crystal structures, morphology, and thermal behavior of PVDF materials. The addition of oxygen‐functionalized graphene was found to cause a peak in the PVDF composites' FT‐IR/ATR spectrum, roughly in the wavenumber 1400 cm−1, which was identified as the C‐OH bending vibration. Together with the shift in peak strengths, the lack of a discernible shift in the PVDF peak location in the XRD patterns indicates that the addition of oxygen‐functionalized graphene has caused a phase transition in the PVDF in the semi‐crystal structure. Surface hydrophobicity has also been measured using contact angle measurements. The addition of oxygen‐functionalized graphene has been seen to decrease the PVDF's contact angle, resulting in the development of a hydrophilic characteristic. These PVDF‐based materials' oil/water separation capabilities have also been evaluated. PVDF composite films were not as effective as PVDF nanofiber mats with oxygen‐functionalized graphene in the studies to separate the oil/water mixtures. The permeate flux value was determined to be 240 Lm−2 h−1, and the oil/water separation efficiency of nanofibers containing 10% (m/m) PVDF534000 combined with oxygen‐functional graphene was found to be 99%.

Enhanced Removal of Cr (VI) by PEI/nFe3O4 Ultrafiltration Membranes Using Peristaltic Pump-Driven Dynamic Adsorption

In this study, Fe3O4 nanoparticles (nFe3O4) were loaded onto polyvinylidene fluoride ultrafiltration membranes and capped with polyethyleneimine in order to form PEI/nFe3O4 ultrafiltration membranes. We used a peristaltic pump as a driver for dynamic adsorption, and the PEI/nFe3O4 ultrafiltration membrane had a good ability to remove hexavalent chromium (Cr(VI)) from wastewater. The full permeate volume of the PEI/nFe3O4 ultrafiltration membrane was maximized at pH 3. Meanwhile, the removal of Cr(VI) from the wastewater reached 98% and reduced to trivalent chromium (Cr(III)). When the initial concentration of Cr(VI) increased, the active sites on the membrane would be filled and the removal efficiency of Cr(VI) would decrease. Meanwhile, the coexisting ions affect the removal efficiency of Cr(VI), and PO43- has a strong negative effect on the removal efficiency. PEI/nFe3O4 ultrafiltration membrane is an effective combination of multifunctional nanomagnetic materials and membrane materials, which can effectively remove hexavalent chromium from wastewater. The study provides a basis for future applications in the environmental remediation of low-concentration chromium-containing wastewater.

Preparation of hydrophilic and antibacterial bifunctional PVDF ultrafiltration membrane based on pomegranate peel powder

Pomegranate peels are often regarded as waste products, despite its antibacterial properties and hydrophilic functional groups. In this work, varying concentrations (0, 0.05, 0.15, 0.2 and 0.5 wt%) of pomegranate peel powder (PPP) were doped into polyvinylidene fluoride (PVDF) ultrafiltration membranes (UF) as antimicrobial agents and hydrophilic modifiers. With increase in PPP concentration, the water contact angle (from 83° to 66°) and porosity (from 73% to 54%) of the membrane showed a decrease, while the water flux, mechanical strength, and elongation at break had a consistent pattern of first increase followed by subsequent decrease. The morphological characteristics, chemical composition and thermodynamic properties of the membranes were further analyzed by SEM, FTIR, TAG, and DSC respectively. Additionally, in comparison to the PVDF pure membrane, membranes containing PPP demonstrated a more pronounced inhibitory impact on E. coli, and when the concentration was 0.15 wt% (M2), the BSA rejection rate (93.72%) and water flux (734.7 L m−2 h−1) of the membrane reached the peak. In conclusion, this study proposes the consideration of a cost-effective, environmentally friendly UF membrane with hydrophilic and antibacterial dual function, highlighting the promising application of pomegranate peel as agricultural waste in the membrane industry.

Antifouling capability of polyvinylidene fluoride ultrafiltration membranes prepared with poly sulfobetaine methacrylate-modified graphene oxide

To mitigate the decrease in the separation efficiency caused by membrane fouling during the operation of polyvinylidene fluoride (PVDF) ultrafiltration membrane, this experiment employed methylacrylic sulfobetaine (SBMA)-modified graphene oxide (GO) nanoparticles improve the antifouling capability of ultrafiltration membrane. In this study, the hydrophilic material SBMA was grafted onto the surface of GO by free radical polymerization to form PSBMA@GO hydrophilic nanoparticles. PVDF ultrafiltration membranes containing GO nanoparticles or PSBMA@GO nanoparticles were prepared by the phase inversion method for comparative testing. The experimental results showed that after the addition of 0.75 wt% PSBMA@GO nanoparticles, the pure water flux of the PVDF ultrafiltration membrane and the hydrophilicity of the surface were the highest. Based on the scanning electron microscopy (SEM) and atomic force microscopy (AFM) results, the pore structure of the cross section was optimal and the surface roughness was the lowest. Based on the results from the cyclic filtration tests of three typical foulants, the PVDF ultrafiltration membrane with 0.75 wt% PSBMA@GO nanoparticles had the best antifouling capability. Furthermore, the extended DerjaguinLandauVerweyOverbeek (XDLVO) theory was used to explore the interaction energy between foulants and the membrane when in close contact. The results showed that compared to the addition of the GO nanoparticles, the PVDF ultrafiltration membrane with the addition of the PSBMA@GO nanoparticles exhibited a lower attractive interaction energy with foulants. Therefore, the addition of the hydrophilic nanoparticles modified by the hydrophilic material SBMA to ultrafiltration membranes provides a potential new method to improve the antifouling capability of these materials in the future.

Constructing quaternized graphene oxide filtration layer on PVDF membrane by a facile strategy via dopamine crosslinking and its performance

The increasing utilization of polyvinylidene fluoride (PVDF) ultrafiltration membranes in water treatment has necessitated the development of membranes with superior separation, antifouling performance and high pure water permeability. As a hydrophilic and antibacterial modifier, quaternized graphene oxide (QGO) has been successfully applied to improve the antifouling and antibacterial properties of the membranes simultaneously. Herein, we proposed a simple and effective strategy to fabricate a nanocomposite ultrafiltration membrane by coating the PVDF membrane surface with QGO and using polydopamine (PDA) as a “bio-glue”. The filtration followed by cross-linking method was utilized to construct a “brick-mud” structure on the membrane surface. The prepared QGO/PDA-PVDF membrane exhibited favorable separation and antifouling properties (79.5% of BSA rejection rate, 15.7% of irreversible fouling rate when filtering 0.5 g/L BSA solution, 97.2% of E. coli and 96.3% of S. aureus antibacterial rate), while maintaining a high pure water permeability of 1105.4 L.m−2.h−1.bar−1. QGO nanosheets were stably coated on the membrane surface, and the QGO/PDA-PVDF membrane prepared by this novel strategy also demonstrated application potential in the field of seawater desalination pretreatment. Besides, the possible mechanisms during modifications were also discussed. This research could serve as a reference for improving the comprehensive performance of PVDF ultrafiltration membrane through surface coating.

TiO2-PAA-SiO2 pearl chain blend modified polyvinylidene fluoride ultrafiltration membrane with excellent oil-water separation, anti fouling performance and durability

ABSTRACT In this work, a new type of composite nanoparticles, ‘pearl chain’, was developed by linking titanium dioxide and silicon dioxide by polyacrylic acid polymer chains, and the prepared TiO2-PAA-SiO2 composite nanoparticles were analysed by SEM, Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy and thermogravimetric analysis, zeta potential, x-ray diffraction, etc. The success of this work was verified by the successful linking of TiO2-PAA-SiO2 composite nanoparticles.TiO2-PAA-SiO2 composite nanoparticles were analysed to verify the successful attachment of pearl chains. The obtained TiO2-PAA-SiO2 were subsequently blended in different ratios to prepare polyvinylidene fluoride (PVDF) ultrafiltration membranes. The membrane performance was tested by porosity and water contact angle measurements, scanning electron microscopy, as well as experiments using bovine serum proteins and MTBE interception. The results showed that when a certain amount of TiO2-PAA-SiO2 was added, the surface wettability, porosity and permeability of the prepared modified composite membranes were significantly improved, and the BSA adsorption rate was increased from 71.59% to 80.86%, and the retention rate of MTBE was increased by 77%, in addition to showing a better anti-pollution effect (FRR: 91.07%). It was finally concluded that the prepared membranes embedded with 1.0 wt.% TiO2-PAA-SiO2 nanofillers showed good overall filtration performance, better contamination resistance and remarkable durability. The present work successfully demonstrated the feasibility of using polyacrylic acid chemical chains to connect nanoparticles with different functions to prevent particle loss and substantially enhance membrane performance, which is valuable for bridging connection of composite nanoparticles and exploring the development of high-performance ultrafiltration membranes.

Properties and preparation of TiO2‐HAP@PVDF composite ultrafiltration membranes

AbstractThe non‐solvent induced phase separation technology was introduced to formulate titanium dioxide (TiO2)‐hydroxyapatite (HAP) composite modified polyvinylidene fluoride (PVDF) ultrafiltration (UF) membranes, and research was conducted to explore the effect on PVDF UF membrane performance exerted by different addition amounts (0–1.0 wt%) of TiO2‐HAP composite. The results indicated that when 0.3% TiO2‐HAP composite was added, the composite membranes had a through‐channel structure, with a uniform pore structure on the surface, so that they possessed a certainly raised pure water flux. Specifically, in contrast to the pure PVDF membrane, 0.3%‐TiO2‐HAP@PVDF UF membrane exhibited an incremented pure water flux by 59.09%. Besides, TiO2‐HAP@PVDF UF membranes had decreased rejection rate of bovine serum albumin (BSA) together with water contact angle to 58.62% and 70.17°, respectively, compared to the pure PVDF membrane (85.52% & 92.75°), showing good hydrophilicity. Several pure water flux tests on the composite UF membranes revealed that the flux tended to be stable after the 4th test. In summary, the addition of TiO2‐HAP composite is capable of efficiently ameliorating PVDF base membranes from the aspects of microstructure, hydrophilicity, antifouling properties, as well as stability, allowing a good application prospect in actual water treatment.Highlights The HAP can solve the poor adsorption of TiO2. The TiO2 can improves the interfacial adhesion between HAP and polymer. The TiO2‐HAP composite with excellent stability, corrosion resistance and et al. The TiO2‐HAP@PVDF UF membrane with anti‐pollution performance and stability.

Modification of PVDF ultrafiltration membrane for high concentration of nannochloropsis as a raw material for bioethanol: Computations and experiments

Nannochloropsis sp., which is abundant in the ocean and has a high carbohydrate content, has great potential if used as a raw material for bioethanol. However, the low concentration of microalgae in the culture medium (0.5-2 µg/L) and the small size of the microalgae Nannochloropsis sp. (2-8 µm) become problems in the harvesting process. This study aims to increase the concentration of Nannochloropsis sp. during the harvesting process using a LiCl-modified polyvinylidene fluoride (PVDF) membrane. In addition, a computational approach was used to select the best solvent for PVDF and explain the conformational changes of PVDF. The results showed that N-Methyl-2-pyrrolidone is the best solvent for PVDF polymer (the lowest solvation energy is -86.25 Kjmol−1, and the highest binding energy is 1.8 Kjmol−1). The membrane, with the addition of 2% LiCl, had the best performance, increased the microalgae concentration ten times (from 596.4 to 5098 ppm), flux (150 Lm−2h−1bar−1), and rejection (100%). Adding LiCl to the dope solution increased the water flux (from 516 to 614 Lm−2h−1bar−1), changed the PVDF conformation from alpha to beta, and decreased the hydrophobicity of the membrane (from 94.89 to 81.68 °). Layer pore fouling is the fouling that plays a role in reducing microalgae flux during microalgae filtration by Nannochloropsis sp. Meanwhile, the type of washing recommended to overcome layer pore fouling is rinsing by increasing the speed of the filtration flow and immersion in chemical compounds.

Fabrication of PVDF ultrafiltration membrane using modified thermally induced phase separation: The role of amphiphilic and hydrophilic non-solvents

The use of amphiphilic pore formers and hydrophilic non-solvents has demonstrated its effectiveness in improving the surface porosity and permeability of polyvinylidene fluoride (PVDF) ultrafiltration (UF) membranes through the nonsolvent induced phase separation (NIPS) process in literatures. However, in the thermally induced phase separation (TIPS) process, few reports illustrated how the amphiphilic pore-former and water-soluble non-solvent interact with water-insoluble diluents. In this study, water-insoluble dimethyl phthalate (DMP) was used as the main diluent to rule out the effect of diluent outflow. The amphiphilic pore former polyethylene glycol 400 (PEG400) failed to open pores on the outer surface of the membranes because of its amphiphilic nature. On the contrary, UF membranes with a mean pore size of 55 nm could be obtained by adding hydrophilic triethylene glycol (TEG) to the dope with a satisfactory pure water permeability (PWP) of 262.6 L m−2 h−1 bar−1. Moreover, PEG400 can serve as a stabilizer for the TEG droplets during the phase separation if both were added to the polymer dope solution. The addition of both PEG400 and TEG could significantly increase the membrane's PWP to 645.4 L m−2 h−1 bar−1 with moderate enlargement of the mean pore size of the membrane to 84 nm. Additionally, the well-connected membrane structure resulted in the tensile strength of the membranes ranging from 3.07 to 6.65 MPa. This study expands the range of additives used in the TIPS process and demonstrates the different roles of amphiphilic and hydrophilic non-solvents in the TIPS process.

Green synthesis of polyvinylidene fluoride ultrafiltration membrane with upgraded hydrophilicity

The use of Cyrene™ as an alternative non-toxic solvent to produce a PVDF-based ultrafiltration membrane was investigated in this study. Polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) were used as organic additives to explore its ability to improve membrane hydrophilicity. The additives were introduced into the casting solution via phase inversion with a combined non-solvent induced phase separation (NIPS) and evaporation-induced phase separation (EIPS) technique. The prepared membranes were characterized to examine its morphology, mechanical properties, and filtration performance. The results show that the addition of PEG and PVP has proven able to improve the membrane hydrophilicity with the lowest contact angle of 76.81° achieved from the addition of PEG with concentration 3 wt%. However, the nascent membranes were not adequate enough, in terms of its mechanical properties, to undergo performance tests due to its very brittle nature. The overall results from this study demonstrate a great potential as a proposed method of utilizing Cyrene™ as a choice of green solvent to fabricate PVDF-based ultrafiltration membrane with the incorporation of PEG and PVP as organic additives.

PVDF ultrafiltration membranes containing copper oxide-charcoal based graphene oxide nanohybrids with enhanced performance and antifouling properties

Charcoal based graphene oxide-copper oxide (GO-CuO) nanohybrids were successfully synthesized via the co-precipitation method. It was then used to improve polyvinylidene fluoride (PVDF) ultrafiltration (UF) membrane properties and performance. The PVDF/GO-CuO UF nanocomposite membranes containing different contents of the synthesized GO-CuO nanohybrids were prepared via the phase inversion method. It was found that hydrophilicity of PVDF membrane containing 0.2 wt% of the synthesized GO-CuO nanohybrids increases than the neat PVDF membrane, so that its water contact angle (WCA) decreases from 80.68±1.23° for the neat PVDF membrane to 60.53±5.25° for the modified membrane containing 0.2 wt% of the synthesized GO-CuO nanohybrids. On the other hand, compared to the neat PVDF membrane, pure water flux (PWF) of this modified nanocomposite membrane increases by about 77% (from 101.1±1.82 to 178.87±1.47 LMH) and exhibits 94.28±0.93% rejection of bovine serum albumin (BSA). This improvement is due to increased hydrophilicity, porosity, average membrane pore size, and decreased membrane surface roughness. The results of fouling measurements showed 42%, 60%, and 8% reduction in total fouling ratio (Rt), irreversible fouling ratio (Rir), and reversible fouling ratio (Rr), respectively. This indicated that antifouling properties of the modified membrane is significantly improved. It was found that the fabricated PVDF/GO-CuO nanocomposite membrane exhibits better performance than the neat PVDF membrane. Also, the results showed that this membrane also exhibits better properties and performance than the PVDF/GO and PVDF/CuO nanocomposite membranes. Therefore, it can be concluded that the fabricated PVDF/GO-CuO nanocomposite membrane has excellent potential for water and wastewater treatment applications.

Improved water purification by PVDF ultrafiltration membrane modified with GO-PVA-NaAlg hydrogel

This work presents a modified polyvinylidene fluoride (PVDF) ultrafiltration membrane blended with graphene oxide-polyvinyl alcohol-sodium alginate (GO-PVA-NaAlg) hydrogel (HG) and polyvinylpyrrolidone (PVP) prepared by the immersion precipitation induced phase inversion approach. Characteristics of the membranes with different HG and PVP concentrations were analyzed by field emission scanning electron microscopy (FESEM), Atomic force microscopy (AFM), contact angle measurement (CA), and Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The FESEM images showed an asymmetric structure of the fabricated membranes, and possessing a thin dense layer over the top and a layer finger-like. With increasing HG content, membrane surface roughness increases so that highest surface roughness for the membrane containing 1wt% HG is with a Ra value of 281.4 nm. Also, the contact angle of the membrane reaches from 82.5° in bare PVDF membrane to 65.1° in the membrane containing 1wt% HG. The influences of adding HG and PVP to the casting solution on pure water flux (PWF), hydrophilicity, anti-fouling ability, and dye rejection efficiency were evaluated. The highest water flux reached 103.2 L/m2 h at 3 bar for the modified PVDF membranes containing 0.3 wt% HG and 1.0wt% PVP. This membrane exhibited a rejection efficiency of higher than 92%, 95%, and 98% for Methyl Orange (MO), Conge Red (CR), and Bovine Serum Albumin (BSA), respectively. All nanocomposite membranes possessed a flux recovery ratio (FRR) higher than bare PVDF membranes, and the best anti-fouling performance of 90.1% was relevant to the membrane containing 0.3 wt% HG. The improved filtration performance of the HG-modified membranes was due to the enhanced hydrophilicity, porosity, mean pore size, and surface roughness after introducing HG.

Enhanced permeability and antifouling properties of polyvinylidene fluoride ultrafiltration membrane with hydrophilic P(AMPS‐co‐MMA) copolymer

AbstractIn this research, a new amphiphilic random copolymer of 2‐acrylamido‐2‐methylpropane sulfonic acid (AMPS) and methyl methacrylate (MMA) (abbreviated as P(AMPS‐co‐MMA)) was synthesized by solution free radical copolymerization method, and was introduced into hydrophobic polyvinylidene fluoride (PVDF) membrane via nonsolvent induced phase separation (NIPS) process without adding pore‐forming agent to enhance the permeability and antifouling properties of PVDF ultrafiltration membrane. The FT‐NMR spectroscopy confirmed the chemical structure of P(AMPS‐co‐MMA) and copolymerization of AMPS and MMA, the effects of P(AMPS‐co‐MMA) on membrane surface chemical compositions, morphology, roughness, charge, hydrophilicity, permeability and antifouling properties were characterized in‐detail. The results indicate that the PVDF/P(AMPS‐co‐MMA) composite membranes demonstrated excellent permeability, improved antifouling property and long‐term stability due to the optimized membrane microstructure, stronger hydrophilicity and endowed negative charge. The PVDF composite membrane blended with 1.5 wt% P(AMPS‐co‐MMA) showed the best membrane performances, the pure water flux was 286.5 L·m−2·h−1 while the BSA rejection was as high as 98%, and the flux recovery ratio (FRR) and reversible fouling ratio to the total fouling ratio (Rr/Rt) reached 94.8% and 87% respectively, which outpaced ever reported and commercial PVDF membranes. Therefore, P(AMPS‐co‐MMA) copolymer was expected to be a potential excellent pore‐forming material in fabricating high‐performance membranes.

Ultrathin g-C3N4 composite Bi2WO6 embedded in PVDF UF membrane with enhanced permeability, anti-fouling performance and durability for efficient removal of atrazine

A novel Bi2WO6-g-C3N4/polyvinylidene fluoride (PVDF) composite ultrafiltration (UF) membrane (BWO-CN/PVDF) was prepared by microwave hydrothermal and immersion precipitation phase transformation method. The BWO-CN/PVDF-0.10 exhibited an outstanding photocatalytic removal rate of atrazine (ATZ) (97.65 %) under the simulated sunlight and enhanced permeate flux (1356.09 L·m−2·h−1). The multiple optical and electrochemical detection confirmed that combining ultrathin g-C3N4 and Bi2WO6 can increase carrier separation rate and prolong its lifetime. The quenching test revealed that h+ and 1O2 were the prominent reactive species. Additionally, after a 10-cycle photocatalytic process, the BWO-CN/PVDF membrane presented remarkable reusability and durability. And it showed excellent anti-fouling performance by filtering BSA, HA, SA, and Songhua River under simulated solar irradiation. The molecular dynamic (MD) simulation showed that the combination of g-C3N4 and Bi2WO6 can enhance the interaction between BWO-CN and PVDF. This work opens up a new idea for designing and constructing a highly efficient photocatalytic membrane for water treatment.

Demulsifier-Inspired Superhydrophilic/Underwater Superoleophobic Membrane Modified with Polyoxypropylene Polyoxyethylene Block Polymer for Enhanced Oil/Water Separation Properties.

Demulsifiers are considered the key materials for oil/water separation. Various works in recent years have shown that demulsifiers with polyoxypropylen epolyoxyethylene branched structures possess better demulsification effects. In this work, inspired by the chemical structure of demulsifiers, a novel superhydrophilic/underwater superoleophobic membrane modified with a polyoxypropylene polyoxyethylene block polymer was fabricated for enhanced separation of O/W emulsion. First, a typical polyoxypropylene polyoxyethylene triblock polymer (Pluronic F127) was grafted onto the poly styrene-maleic anhydride (SMA). Then, the Pluronic F127-grafted SMA (abbreviated as F127@SMA) was blended with polyvinylidene fluoride (PVDF) for the preparation of the F127@SMA/PVDF ultrafiltration membrane. The obtained F127@SMA/PVDF ultrafiltration membrane displayed superhydrophilic/underwater superoleophobic properties, with a water contact angle of 0° and an underwater oil contact angle (UOCA) higher than 150° for various oils. Moreover, it had excellent separation efficiency for SDS-stabilized emulsions, even when the oil being emulsified was crude oil. The oil removal efficiency was greater than 99.1%, and the flux was up to 272.4 L·m-2·h-1. Most importantly, the proposed F127@SMA/PVDF membrane also exhibited outstanding reusability and long-term stability. Its UOCA remained higher than 150° in harsh acidic, alkaline, and high-salt circumstances. Overall, the present work proposed an environmentally friendly and convenient approach for the development of practical oil/water separation membranes.

Improved oily wastewater rejection and flux of hydrophobic PVDF membrane after polydopamine-polyethyleneimine co-deposition and modification

The surface structure and properties of a membrane largely determine its in-service performance during a filtration process. Polyvinylidene fluoride (PVDF) hydrophobic membrane is widely used in the separation of oily wastewater because of its mechanical strength, but is susceptible to oil fouling, whereas hydrophilic membranes are easily damaged in water due to their wettability but are resistant to oil. The advantages of the two membranes are then combined by modifying the hydrophobic membrane to be hydrophilic to maintain stability, mechanical strength, and antifouling performance. PVDF ultrafiltration membranes were modified with a mixture of different concentrations of polydopamine (PDA) and polyethyleneimine (PEI) using different deposition times (6, 12, and 24 h) and characterized using SEM, FTIR, and contact angle. Membrane performance was tested using a dead-end module for 60 min. The PDA-modified membrane showed a decrease in hydrophilicity from 88.1° to 77.7° after being coated with 0.5 g/L PDA for 6 h, while with the addition of 2 g/L PEI, the hydrophilicity reached 64.6° SEM characterization showed the presence of aggregates formed during the PDA polymerization process and decreased with the addition of PEI. This is in line with the results obtained from the performance test with the dead-end module where the smaller the aggregate, the greater the flux produced. FTIR characterization showed a strong bond between PDA and PDA-PEI with the membrane as the concentration and coating time increased.

In-situ photoreduction strategy for synthesis of silver nanoparticle-loaded PVDF ultrafiltration membrane with high antibacterial performance and stability.

Ultrafiltration (UF) technology using polyvinylidene fluoride (PVDF) membrane has been widely applied to water and wastewater treatment due to its low cost and simple operation process. However, PVDF-based UF membrane always encountered the issue of membrane biofouling that greatly impacted the filtration performance. In this study, we prepare a silver nanoparticle (AgNP)-loaded PVDF (Ag/PVDF) UF membrane by an in-situ photoreduction method to mitigate the membrane biofouling. Different from the previously reported method, AgNPs were synthesized in-situ by a UV photoreduction process, in which Ag+ ions were reduced to zero-valent Ag nanoparticles by the photo-induced reducing radicals. Antibacterial experiments showed that the inhibition efficiency of Ag/PVDF membrane to Escherichia coli reached up to ~ 99% after antibacterial treatment for 24h. In comparison with the pristine PVDF membrane, Ag/PVDF membrane possessed a lower water contact angle (83.7° vs. 38.1°), and its pure water flux increased by 23.7%, and a high bovine serum albumin (BSA) rejection efficiency was maintained. In addition, the high stability of the Ag/PVDF composite membrane was confirmed by the extremely low releasing amount of Ag. This study provides a novel strategy for the preparation of metal nanoparticle-incorporated Ag/PVDF ultrafiltration composite membrane showing favorable antibacterial performance and stability.