PVDF Membrane Surface Research Articles

Fabrication and characterization of nanocomposite membranes for the rejection of textile dye

In current study nanodiamonds (NDs) and LiCl were added into poly (vinylidene fluoride) (PVDF) matrix to prepare PVDF/ND/LiCl nancomposite membranes by using phase inversion method. Fabrication of nanocomposite membranes was then confirmed by XRD, SEM, FTIR and TGA. The results showed that the nanodiamonds were incorporated into the pores and onto the surface of PVDF membranes. The effect of NDs loading (0.1 to 0.7 wt%) on nanocomposite membranes properties was studied. The presence of NDs in PVDF substrate provided it a hydrophilic character thus improved permeability, antifouling performance and decreased shrinkage ratio. PNL-0.5 (adding 0.5% NDs with PVDF membrane) exhibited the best results with fouling recovery ratio of 95%, malachite green dye rejection of 95%, decolorization rate of 89% and and mechanical stability up to 15 cycles. These results showed that the characteristics of PNL-0.5 were best and can be used for the removal of dyes from industrial effluent.

Graphene-Coated PVDF Membranes: Effects of Multi-Scale Rough Structure on Membrane Distillation Performance.

Graphene-coated membranes for membrane distillation have been fabricated by using a wet-filtration approach. Graphene nanoplatelets have been deposited onto PVDF membrane surfaces. Morphology and physicochemical properties have been explored to evaluate the changes in the surface topography and related effects on the membrane performance in water desalination. The membranes have been tested in membrane distillation plants by using mixtures of sodium chloride and humic acid. The multi-scale rough structure of the surface has been envisaged to amplify the wetting and fouling resistance of the graphene-coated membranes so that a better flux and full salt rejection have been achieved in comparison with pristine PVDF. Total salt rejection and an increase of 77% in flux have been observed for coated membrane with optimized graphene content when worked with NaCl 0.6 M (DCMD, ΔT ≈ 24 °C) over a test period of 6 h. The experimental findings suggest these novel graphene-coated membranes as promising materials to develop functional membranes for high-performing water desalination.

A novel method to immobilize zwitterionic copolymers onto PVDF hollow fiber membrane surface to obtain antifouling membranes

Zwitterionic materials are considered to be a promising new-generation non- or low-fouling materials. However, stable, and straightforward introduction of zwitterions into membranes for commercial production remains as a big challenge yet. Herein for the first time we propose a simple approach to immobilize zwitterionic copolymers on poly(vinylidene fluoride) (PVDF) hollow fiber membrane (HFM) surfaces with considerably high stability via surface entrapment and subsequent simple reactions. First, a commercial amphiphilic copolymer, viz. styrene–maleic anhydride (PSMA), was entrapped on the outer surface of PVDF membranes using co-extrusion by a triple orifice spinneret. PSMA exhibited excellent stability on the PVDF membrane, and its reactive anhydride (MA) group was stabilized on the outer membrane surface. Next, the commercially available zwitterionic copolymer poly(2-methacryloyloxyethyl phosphorylcholine-co-2-aminoethyl methacrylate hydrochloride) (P(MPC-AEMA)) was immobilized on the PVDF/PSMA membrane surface by a simple reaction between the MA groups of PSMA and the amine groups of P(MPC-AEMA). The P(MPC-AEMA) reacted membrane exhibited noticeable bovine serum albumin (BSA) antifouling and antibacterial properties during both static adsorption and dynamic filtration. The flux recovery ratio (FRR) of the membrane exceeded 80% after seven cycles of BSA filtration. The modified membrane showed an even higher FRR (∼95%) during bacterial filtration, and such excellent performance was attributed to its super hydrophilicity. Our novel, advanced and straightforward modification method lights on a spotlight for a new pathway to make immobilization of zwitterions on polymeric membrane without needing complicated reactions or procedures.

Engineering green and high-flux poly(vinylidene fluoride) membranes for membrane distillation via a facile co-casting process

A high-flux and stable poly(vinylidene fluoride) (PVDF) membrane that is also produced in a green method is particularly promising for membrane distillation (MD). In this work, a facile co-casting method was employed to fabricate porous PVDF membranes by using green solvent (PolarClean) and green casting fluids, including Acetyl tributyl citrate (ATBC) and polyethylene glycol 400 (PEG 400). During the co-casting process, ATBC or PEG was functioned as isolation layer to avoid rapid solvent/non-solvent exchange rate that could result in a dense membrane surface. The resulting top PVDF membrane surfaces were both highly porous during the phase inversion process after being cast by ATBC or PEG. In addition, the bottom surfaces were highly porous when using non-woven fabrics (NWFs) as casting supports whatever the PVDF concentrations were. It is worth mentioning that when the PVDF concentrations were below 20 wt%, the NWFs combined with PVDF membrane well that also provided a super-high mechanical strength for PVDF membranes. When the PVDF concentrations were above 25 wt%, the NWFs were detached from the PVDF membrane. Therefore, two kinds of PVDF membranes (with and without NWFs) could be produced. The optimized PVDF membranes with contact angle of above 120° showed above 99.99% and 99.9% rejection for saline water and ginseng extract during the MD process with a highest flux of ∼37 kgm−2h−1. This work provides a green and high-flux PVDF membrane for saline water and food extract in chemical industries.

In Ukrainian

PVDF membranes are extensively applied in ultrafiltration processes of aqueous solutions of different chemical substances owing to its outstanding properties, such as high mechanical strength, thermal stability, and chemical resistance. However, hydrophobicity of this polymer largely limits the practical application of PVDF. Therefore, it is very important to develop methods of modifying the surface of PVDF membranes with the aim to improve their properties. Polyethyleneimine, as a modifying agent, has already been investigated for hydrophilization of the surface. However, the modification process leads to reduction of the volumetric flow and changes of the membrane selectivity because polymer is grafted not only to the surface, but also into the pores of the membranes, reducing their effective radius. Taking everything into account, this investigation is devoted to the development of a technique for surface modification of PVDF membranes with PEI (with pre-filling of pores) to improve their transport properties, at the same time preserving the morphology of the membrane and its characteristics. Nonionic surfactant Tetronic® 701 is used as a pore-filling agent. Commercial ultrafiltration PVDF membranes (with cut-off of 150 kDa) were firstly activated with a carbonate buffer, then the pores were filled with Tetronic® 701, further surface modification of membranes with PEI was performed. The modification process was confirmed by IR spectroscopy. The surface properties of the membranes were studied by scanning electron microscopy. The changes in the hydrophilicity of the modified membranes were studied by measuring the wetting angles of the membrane surface with water, glycerol, and diiodomethane. The transport properties of the membrane were experimentally studied in the process of ultrafiltration of aqueous protein solution (in particular, lysozyme, lipase, BSA); water permeability coefficients and protein rejection coefficients were determined. It was found that the usage of Tetronic® 701 during the membrane modification process allowed improving the water permeability coefficient compared to the membrane modified without pre-filling the pores; hydrophilization of the surface reduced the effect of concentration polarization.

Nanobubble-assisted scaling inhibition in membrane distillation for the treatment of high-salinity brine

In this study, we report the use of nanobubbles (NBs) as a simple and facile approach to effectively delay scaling in membrane distillation (MD) during the treatment of highly saline feed (100 g L−1). Unlike conventional gas bubbling in MD for improving the hydrodynamic flow conditions in the feed channel, here we generated air NBs with an average size of 128.81 nm in the feed stream and examined their impact on membrane scaling inhibition during MD operation. Due to their small size, neutral buoyancy, and negative surface charge, NBs remain in suspension for a longer time (14 days), providing homogenous mixing throughout the entire feed water. The MD performance results revealed that severe membrane scaling happened during the DCMD treatment of high salinity brine in the absence of nanobubbles, which dramatically reduced the distillate flux to zero after 13 h. A one-time addition of air NBs in the saline feed significantly reduced salt precipitation and crystal deposition on the PVDF membrane surface, delayed the occurrence of flux decline, prevented membrane wetting, thereby prolonging the effective MD operating time. With similar feed concentration and operating conditions, only 63% flux decline after 98 h operation was recorded in nanobubble-assisted MD. Two key explanations were suggested for the delayed membrane scaling upon addition of air NBs in the MD feed: (1) NB-induced turbulent flow in the feed channel that increases the surface shear forces at the membrane surface, alleviating both temperature and concentration polarization effect, (2) electrostatic attractions of the counterions to the negatively charged NBs, which reduces the availability of these ions in the bulk feed for scale formation.

Hybrid PVDF-P(L-DOPA)-ZnO membranes for dyes and antibiotics removal through simultaneous action of adsorption and photocatalysis processes

PVDF-P(L-DOPA)-ZnO hybrid membranes were prepared with the purpose to eliminate several classes of pollutants from water: cationic dyes and antibiotics. The PVDF membrane with the pores mean size of 1.5 µm was prepared by the phase inversion method. P(L-DOPA), a PDA analogue, was deposited on the polymeric membrane to facilitate the anchor of in-situ grown ZnO nanoparticles. Several characterization methods were deployed to explore the hybrid membranes' structural, morphological, optical, and photocatalytic properties. The firm P(L-DOPA)-ZnO coating on the PVDF membrane surface converted its hydrophobic nature to a hydrophilic one. For an optimal ZnO nanoparticles amount and size, efficient degradation of Rhodamine B (RhB- 80%) and oxytetracycline (OTC-71%) was obtained in 5 h of UV-light irradiation. The generation of P(L-DOPA)-ZnO Z-scheme photocatalyst promotes an efficient separation of photoinduced electron-hole pairs beneficial to photocatalytic activity. The hybrid membrane revealed similar photocatalytic activity after 3 cycles illustrating high stability. The analysis of the generated reactive oxygen species correlated with radical spin trapping experiments suggest that photogenerated h+ play the main role in the photodegradation of both studied pollutants.

Surface modification of PVDF membrane by sulfonated chitosan for enhanced anti-fouling property via PDA coating layer

In this work, the modified poly (vinylidene fluoride) (PVDF) membranes provided an excellent hydrophilicity and the antifouling properties were fabricated via surface modification by 2-N-propyl sulfonated chitosan (PCS). Without sophisticated and environmentally hazardous operation, PCS was synthesized through ring-opening polymerization and immobilized onto the coated PVDF membrane surface in aqueous acetic acid solution and Tris-HCl buffer dopamine solution, respectively, while polydopamine (PDA) serving as a precursor coating layer. The modified membranes showed inferior BSA adsorption resulting from the construction of hydration layer via hydrogen bond between hydrophilic groups in PCS on membrane surface and water molecules. Due to the excellent hydrophilicity (39°) and minimal irreversible fouling (8.2%) of modified membrane, the water flux recovery rate up to 90.4% was easily attached after two cycles, which is 45% increasing of the PVDF membrane without modification. Additionally, the physic structure of PVDF membranes does not cause damage during surface modification.

Hierarchically superhydrophilic poly(vinylidene fluoride) membrane with self-cleaning fabricated by surface mineralization for stable separation of oily wastewater

Long-term separation of highly emulsified oily wastewater is still challenging in advanced membrane technologies. Herein, β-FeOOH nanorods were in-situ inlaid on a hierarchically superhydrophilic poly(vinylidene fluoride) (PVDF) ultrafiltration membrane surface via a facile biomimetic mineralization process. The β-FeOOH-decorated hierarchical PVDF membrane surface with the organic-inorganic hybrids showed excellent hydrophilicity and ultralow underwater oil adhesion force. After in-situ anchoring of β-FeOOH nanorods, the polydopamine/polyethylenimine (PDA/PEI) modified hierarchical PVDF membrane showed improved permeation flux behaviors, higher oil removal, demulsification, and better anti-oil-fouling properties during 1440-min continuous separation of stabilized soybean oil-in-water (o/w) and crude o/w emulsions. In contrast, the unmodified hierarchically superhydrophilic PVDF membrane maintained efficient emulsion separation for a much shorter period (120 min). Most importantly, the surface-immobilized β-FeOOH exhibited excellent photocatalytic activity for cleaning the oil foulants (soybean oil and crude oil) through the photo-Fenton reaction in the presence of peroxide, endowing the membrane with self-cleaning capability. As a result, the unwanted foulants were successfully removed from the membrane surface, restoring separation performance of the superhydrophilic PVDF membrane for reuse. Therefore, the self-cleaning membrane can treat more oily wastewater and produce more clean water before replacement. The mineralized superhydrophilic PVDF membrane with hierarchical composite micro-/nano structures exhibits satisfactory stability under simultaneous separation and photocatalysis cleaning, showing great potential for tricky oily wastewater treatment and oil resource recovery.

Synthesis of hydrophilic SERS-imprinted membrane based on graft polymerization for selective detection of L-tyrosine

The major limitation of polyvinylidene difluoride (PVDF-)-sensor membrane is its high hydrophobicity. In this study, a hydrophilic PVDF sensor membrane is synthesized by graft modification. The engineered polyvinypyrrolidone (PVP) chains are linked with copolymerized N-vinyl-2-pyrrolidone (NVP) and triethoxyvinylsilane (VTES) by hydrolysis condensation. Subsequently, Ag nanoparticles (NPs) are immobilized on the surface of PVDF membrane through the reduction of AgNO3, and the membrane is utilized as the SERS substrate. Meanwhile, to improve the practical detection efficiency, molecular imprinting technique (MIT) is utilized to obtain a SERS-imprinted membrane for selective detection of L-tyrosine. The morphology and property of SERS-imprinted membrane are analyzed through various techniques. The analysis results suggest that the SERS-imprinted membrane is hydrophilic and is useful for the selective detection of L-tyrosine in aqueous medium. Overall, this study establishes a novel technique for the synthesis of hydrophilic sensor membrane and boosts its applications in SERS detection.

Surface-constructing of visible-light Bi2WO6/CeO2 nanophotocatalyst grafted PVDF membrane for degradation of tetracycline and humic acid

The synthesis of Bi2WO6 and CeO2 photocatalytic nanomaterials exhibit a great ability to photodegrade the antibiotics and shown excellent oxidation of various organic pollutants. Heterostructure 1:1 & 2:1 Bi2WO6/CeO2 nanocomposite was successfully synthesized via the facile sono-dispersion method and exquisite photocatalytic activity. The 0.5 wt% of nanocomposites were well-grafted on PVDF membrane surface via an in-situ polymerization method using polyacrylic acid. The fourier transform infrared (FTIR) spectra demonstrated that the network formation in PVDF induced by the -COOH functional group in acrylic acid. The grafted membrane morphology and strong binding ability over the membranes were validated by scanning electron microscope with energy dispersion (SEM-EDS) and X-ray photoelectron spectroscopy (XPS), respectively. The permeate flux of 49.2 L.m−2 h−1 and 41.65 L.m−2 h were observed for tetracycline and the humic acid solution respectively for 1 wt% of PVP and 0.5 wt% of photocatalytic nanomaterials in PVDF membrane. The tetracycline and humic acid photodegradation rate of 82% and 78% and total resistance of 1.43 × 1010 m−1 and 1.64 × 1010 m−1, 83.5% and 77% flux recovery ratio were observed with N5 membrane. The 2:1 Bi2WO6/CeO2 nanocomposite grafted membrane showed a high permeate flux and better photodegradation ability of organic pollutants in the wastewater.

Design and fabrication of flexible strain sensor based on ZnO-decorated PVDF via atomic layer deposition

Introducing patterned sensors onto polymer substrates has been regarded as a promising way to manufacture multifunctional and integrated flexible sensors, because of their huge potential applications in wearable devices. However, the scalable production of these electronic devices is still limited by the complex process required to achieve high quality. Here, we utilized poly(vinylidene fluoride) (PVDF) as the polymer substrate for its good toughness and environmental stability to fabricate flexible strain sensors with designed patterns. Thanks to the effective plasma pretreatment on PVDF with low activity, the piezoresistive ZnO nanolayer was directly deposited onto the surface of PVDF membrane via atomic layer deposition (ALD). Subsequently, the ZnO/PVDF based strain sensor exhibits a high performance to monitor the strain below 6%, and especially towards the very low strain ranging from 0.1% to 0.6%, which was difficult to be precisely detected by other methods. Interestingly, utilizing the low chemical activity of PVDF, the patterned deposition of ZnO could be facilely achieved via a relatively simple selective plasma pretreatment, which leaded to different wearable sensors be designed, and an array-style sensor be fabricated as in-situ sensors to detect the position under loading. Therefore, this work offers a new strategy to design and fabricate novel integrated wearable electronics.

Development of a syringe membrane-based microextraction method based on metal–organic framework mixed-matrix membranes for preconcentration/extraction of polycyclic aromatic hydrocarbons in tea infusion

Inevitably, the residues of polycyclic aromatic hydrocarbons (PAHs) in tea leaves will be transferred to hot tea infusion, constituting a certain drinking risk; consequently, it is imperative to develop rapid, sensitive, and robust approaches for their trace-level detection. Herein, we developed a syringe membrane-based microextraction (SMME) method for preconcentration/extraction of PAHs in tea infusions. This method utilized metal–organic framework-mixed matrix membranes (MOF-MMMs) as adsorbents, which anchored the nanoparticles of MOFs onto the surface of PVDF membrane. The UiO-66 (Zr)-based MMM possessed high Brunauer-Emmett-Teller (BET) surface area (320.5 m2 g−1) and pore volume (0.18 cm3 g−1), thus enhancing extraction/adsorption efficiency. Under optimized conditions, the limits of detection for PAHs reached as low as 0.02–0.08 μg L−1 with extraction recoveries of 85.5–102.1%, and the inter-day and intra-day precision was lower than 8.4% in tea infusions. Consequently, the SMME/HPLC-DAD method shows a great potential in conventional monitoring of PAHs in tea samples.

Co-deposition of pyrogallol/polyethyleneimine on polymer membranes for highly efficient treatment of oil-in-water emulsion

Poly(vinylidene fluoride) (PVDF) has been widely used in the field of water treatment due to its outstanding chemical tolerance and excellent mechanical strength. However, PVDF membrane often suffers from oil fouling and low flux for separating oil/water emulsions because of low surface energy and strong hydrophobicity. In this work, we propose a bio-inspired biomimetic hydrophilic coating design strategy, in which pyrogallol (PG) and polyethyleneimine (PEI) are used as reactants, and NaIO4 (SP) is used as an oxidant to modify PVDF microfiltration membrane. This strategy realized the conversion of PVDF membrane surface wettability from hydrophobic to superhydrophilic. The membrane structures and performances were investigated by SEM, FT-IR/ATR, XPS, PMI, water contact angle, pure water permeability and oil rejection for toluene-in-water emulsion. The experimental results showed that the membranes deposited with a PG/PEI mass ratio of 1:1 exhibited the best hydrophilicity and water permeation flux. PVDF-PG/PEI-0.2/0.2 was used to treat surfactant-stabilized toluene-in-water emulsion with the highest flux of 1053 L·m−2·h−1 at 0.1 bar and the oil rejection of 98.3%. Moreover, the flux could be wholly restored after simple washing, indicating that the modified PVDF membrane possessed good reusability. Due to the robust adhesion of PG/PEI composite coatings, the proposed strategy for preparing hydrophilic coatings holds significant potentials in the hydrophilic modification of polymer membranes.

Novel PVDF membrane with sandwich structure for enhanced membrane distillation

Membrane distillation (MD) holds great potential in the desalination of high concentration brines but need improvement to achieve sustained permeate flux and durable performance in long-term MD operation. In this study, a novel Janus membrane with sandwich structure was fabricated. Detailly, the microporous PVDF membrane was single-side modified with a bio-inspired hydrophilic polydopamine/polyethylenimine (PDA/PEI) coating, then a hydrophobic nanofiber layer was constructed via forcespinning on the other side as an anti-wetting layer. As the PDA/PEI deposition time increases from 0 to 1.5 h, the contact angle of the modified PVDF membrane surface decreases gradually from 124.6° to 31.3° with little change in membrane morphology and pore structures, resulting in an upward trend of permeate flux up to 50.9 LMH at a feed temperature of 70 °C. The rough forcespun nanofiber layer endows the membrane surface with good hydrophobicity, which brings improved LEP (136.4 kPa) and operation durability for the membrane during MD process. Moreover, numerical simulations were conducted to verify and predict the permeate flux variation of MD membranes under different operation conditions, revealing the superiority of the sandwich-structured Janus membrane combined with the experimental results. Finally, the optimized PDA-PVDF-NF membrane was used for the desalination of model inland brine, exhibiting stable MD performance with high permeate flux of 25 LMH, ~100% salt rejection, and excellent water recovery during a continuous operation as long as 96 h.

PEDOT surface modified PVDF filtration membrane for conductive membrane preparation and fouling mitigation

The organic conductive membrane was prepared by polymerization of 3.4-ethylene dioxythiophene (EDOT) on a PVDF membrane surface via chemical vapor deposition. After modification, the sheet resistance of the organic membrane was 14.07 kΩ/□ and the hydrophilicity of the membrane increased slightly. The adsorption ability of the modified membrane for BSA, sodium humate and sodium alginate decreased, obviously because of the pores being blocked by PEDOT. The solid surface ZETA potential of the modified membrane was much more positive than that of the blank one. The modified membrane showed a certain level of chemical stability during alkali cleaning and NaClO corrosion repeated five times. During the six cycles of short-term filtration, the modified membrane with 1 V/cm of electric field showed stable anti-fouling properties because of less filter cake formation on the membrane surface compared to a blank and modified membrane without electric field. No more divalent cation accumulation on the membrane surface was found under the electric field, which might benefit from its electric neutrality surface.

Surface modified by green synthetic of Cu-MOF-74 to improve the anti-biofouling properties of PVDF membranes

Mitigation of membrane fouling is an important problem to be solved in the application of membrane technology. In this research, we synthesised a kind of Cu-MOF-74 by a facile and environmentally friendly method at room temperature. This kind of Cu-MOF-74 was firstly and successfully coated on poly (vinylidene fluoride) (PVDF) membranes for improving their anti-biofouling performance. The experimental results show that Cu-MOF-74 increases the hydrophilicity and roughness of the PVDF membrane surface, and the antibacterial efficiency of the modified membrane was as high as 97.7% at 4 h. Moreover, we found that the Cu-MOF-74 could sustainably release Cu2+ for one week, the maximum Cu2+ release concentration of PVDF membrane coated by 0.025 g Cu-MOF-74 reached 0.42 mg/L, and the generation of Cu2+ played a significant role in suppressing E. coli. In the meantime, this kind of Cu-MOF-74 can release OH, which will lead to the accumulation of reactive oxygen species (ROS) in bacterial cells. The ·OH can oxidise and destroy bacterial cells, which will be in favour of enhancing the anti-biofouling performance. This novel PVDF membrane surface modified by green synthetic Cu-MOF-74 has a strong antibacterial property and high application potential for water treatment.

Engineering multistructure poly(vinylidene fluoride) membranes modified by polydopamine to achieve superhydrophilicity, excellent permeability, and antifouling properties

AbstractPolydopamine (PDA) was coated on poly(vinylidene fluoride) (PVDF) membranes with different structures to select the most suitable structure for achieving outstanding hydrophilicity, permeability, stability, and antifouling properties. PVDF membranes were prepared with different solvents (N‐methyl‐2‐pyrrolidone [NMP], N,N‐dimethylacetamide [DMAc], N,N‐dimethylformamide [DMF], NMP/DMAc, NMP/DMF, DMAc/DMF, and NMP/DMAc/DMF), and the factors that influenced the phase inversion were discussed. Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM) were employed to characterize various membranes. Results indicated that PDA was coated on PVDF membrane surface and formed a smoother PDA layer. Water contact angle measurement confirmed the increased hydrophilicity of PDA modified membranes, but water flux decreased due to the adhesion of PDA on pore walls. The decrease of static adsorption of bovine serum albumin (BSA), the increase of flux recovery ratio (FRR), and the decline of fouling resistance for PDA modified membranes demonstrated that their antifouling properties have been improved significantly. The membrane prepared with NMP/DMAc displayed the highest decay rate of contact angle (16.6 ± 1.27%), the higher water flux (1358.5 ± 33.87 L m−2 h−1), the highest decrease of BSA adsorption (129.3 ± 5.02 μg cm−2), the highest increase rate of BSA rejection (13.6 ± 0.42%), and the highest FRR (92.8 ± 1.42%). This indicated that NMP/DMAc membrane possessed the most suitable structure to improve membrane performances by PDA coating.

Nanoscale zero-valent iron-modified PVDF membrane prepared by a simple filter-press coating method can robustly remove 2-chlorophenol from wastewater

Abstract In recent years, nanoscale zero-valent iron (nZVI) has been considered an appealing alternative for halogenated organic compound removal for its advantages, such as its high activity. However, easy aggregation limits nZVI activity. In this study, functional nZVI-modified PVDF membranes (nZVI@PVDF membranes) were successfully prepared by a simple and easy-to-follow filter-press coating method and was applied in the ultrafiltration process to treat 2-chlorophenol (2-cp) wastewater. Scanning electron microscopy showed that nZVI particles were relatively uniformly distributed on the membrane surface and formed a fluffy and porous space-stacked structure. 2-cp ultrafiltration degradation results illustrated that nZVI@PVDF membranes revealed good 2-cp removal efficiencies ranged from 56.06% to74.62%. These 2-cp removal efficiencies were higher than those for Fe supported on powder materials and were relatively comparable to those for nZVI composite membranes prepared by complex methods (e.g., blend spinning and cross-linking methods). Furthermore, the 2-cp degradation efficiencies by nZVI@PVDF membranes were not affected much in the presence of natural organic matter and different ions, demonstrating a robust anti-interference ability of nZVI@PVDF membrane. The mechanism underlying its robust performance likely resulted from that nZVI was uniformly distributed and loaded layer by layer on the PVDF membrane surface with high loading capacity, which guaranteed high nZVI activity, layer-layer interception of pollutants and complete reaction between nZVI and pollutants. These findings provide key insights into how nZVI@PVDF membranes could be integrated into the treatment of wastewater containing refractory pollutants.

Tailoring the RhB removal rate by modifying the PVDF membrane surface through ZnO particles deposition

In this work, PVDF membranes coated with ZnO particles were prepared to study the influence of the loading concentration on RhB pollutant removal. The PVDF membranes prepared by phase inversion method contain a mixture of α and β phases as identified by correlating the XRD and FT-IR results. The mean pore size evaluated by SEM measurements is about 4 μm and the asymmetric structure of the membrane was highlighted. The presence of ZnO particles on PVDF membrane was evidenced by XRD, SEM and EXD measurements. By coating with ZnO particles the hydrophilic character of the membrane was improved. The RhB removal was realized using a combined process of two competitive methods: adsorption and photocatalysis. By increasing the ZnO loading the removal efficiency was enhanced. Additionally, the electron spin resonance spectroscopy coupled with spin trapping technique was used to evidence the generation of reactive oxygen species during irradiation, the presence of both hydroxyl radical and superoxide radical being proven.