Effect of additives concentration on the surface properties and performance of PVDF ultrafiltration membranes for refinery produced wastewater treatment

The aim of this study was to investigate the effect of pore-forming hydrophilic additives on the porous asymmetric polyvinylideneflouride (PVDF) ultrafiltration (UF) membrane morphology and transport properties for refinery produced wastewater treatment. PVDF ultrafiltration membranes were prepared via a phase inversion method by dispersing lithium chloride monohydrate (LiCl·H₂O) and titanium dioxide (TiO₂) nanoparticles in the spinning dope. The morphological and performance tests were conducted on PVDF ultrafiltration membranes prepared from a different additive content. The top surface and cross-sectional area of the membranes were observed using a field emission scanning electron microscope (FESEM) and energy dispersive X-ray (EDX) analysis. The surface wettability of porous membranes was determined by the measurement of a contact angle. The mean pore size and surface porosity were calculated based on the permeate flux. The results indicated that the PVDF/LiCl/TiO₂ membranes with lower TiO₂ nanoparticles loading possessed smaller mean pore size, more apertures inside the membrane with enhanced membrane hydrophilicity. LiCl·H₂O has been employed particularly to reduce the thermodynamic miscibility of dope which resulted in increasing the rate of liquid–liquid demixing process. The maximum flux and rejection of refinery wastewater using PVDF ultrafiltration membrane achieved were 82.50 L/m² h and 98.83% respectively at 1.95 wt.% TiO₂ concentration.     

Structural and performance properties of UV-assisted TiO2 deposited nano-composite PVDF/SPES membranes

In this research, the surface of poly (vinylidene fluoride) (PVDF)/sulfonated polyethersulfone (SPES) blend membrane prepared via immersion precipitation was modified by depositing of TiO₂ nano-particles followed by UV irradiation to activate their photocatalytic property. The membranes were characterized by FTIR, SEM, AFM, contact angle, dead end filtration (pure water flux and BSA solution flux), antifouling analysis and antibacterial activity. The FTIR spectrum confirmed the presence of OH functional groups on the PVDF/SPES membrane structure, which was the key factor for deposition, and self-assembly of TiO₂ nanoparticles on the membrane surface. The SEM and AFM images indicated that the TiO₂ nanoparticles were deposited on the PVDF/SPES membrane. The contact angle measurements showed that the hydrophilicity of PVDF/SPES membrane was strongly improved by TiO₂ deposition and UV irradiation. The filtration results indicated that the initial flux of TiO₂ deposited PVDF/SPES membranes was lower than the initial flux of neat PVDF/SPES membrane. However, the former membranes showed lower flux decline compared to the neat PVDF/SPES membrane. The BSA rejection of modified membranes was improved. The fouling analysis demonstrated that the TiO₂ deposited PVDF/SPES membranes showed the fewer tendencies to fouling. The results of antibacterial study showed that the UV irradiated TiO₂ deposited PVDF/SPES membranes possess high antibacterial property.     

Nano SiO2 and TiO2 embedded polyacrylonitrile/polyvinylidene fluoride ultrafiltration membranes: Improvement in flux and antifouling properties

Polyvinylidene fluoride (PVDF) and polyacrylonitrile (PAN) ultrafiltration (UF) membranes are widely used in drinking water and wastewater applications. These membranes are prone to fouling and membrane efficiency decreases with time under constant operation. Significant improvements/modifications are necessary to apply these polymers as sustainable membrane materials. In this study, PVDF and PAN UF membranes were modified through incorporation of nanoparticles (NPs) namely SiO₂ and TiO₂. PVDF and PAN UF membranes were prepared by phase inversion method from polymer solutions having dispersed SiO₂ and TiO₂ NPs in it. Membrane surface hydrophilicity, charge, roughness, and morphology were studied. Equilibrium water content and molecular weight cut-off of the membranes were also measured. Addition of NPs increased membrane surface hydrophilicity, equilibrium water content, and surface potential. NPs modified membranes exhibited better membrane flux (35–79% higher) and antifouling properties (flux recovery ratio values 28–41% higher) than the virgin membranes.     

Poly(vinylidene fluoride) ultrafiltration membranes containing hybrid silica nanoparticles: Preparation,characterization and performance

Poly(vinylidene fluoride) (PVDF) ultrafiltration membranes were prepared by immersion precipitation method using poly(hydroxyethyl methacrylate)-block-poly(methyl methacrylate) grafted silica (PHEMA-b-PMMA@SiO₂) nanoparticles as additives. The hybrid nanoparticles were synthesized by the surface initiated atom transfer radical polymerization (SI-ATRP), and they were characterized in detail by FT-IR, TEM, DLS and GPC. Results confirm that core–shell structure is formed after grafting PHEMA-b-PMMA brushes on the silica nanoparticles. Their average hydrodynamic diameter also increases with the prolongation of grafting time. After blending PVDF with the hybrid silica nanoparticles, the composite PVDF membranes exhibit high porosity and improved water permeation. Especially, when the molecular weight is 1.73 × 10⁵ g/mol for PHEMA-b-PMMA on the hybrid nanoparticles, the water flux of the PVDF composite membrane is 2.5 times than that of the control PVDF membrane, while the rejection to bovine serum albumin (BSA) remains at a high level (>90%). In addition, all the composite PVDF membranes show lower BSA adsorption and larger water flux recovery ratio than the control PVDF membrane. The improvement of membrane performance is attributed to the good hydrophilicity of PHEMA-b-PMMA@SiO₂ nanoparticles. Our results suggest that PHEMA-b-PMMA@SiO₂ nanoparticles with moderate molecular weight of PHEMA-b-PMMA are suitable for the property optimization of PVDF-based composite membranes.     

Preparation and performance of the novel PVDF ultrafiltration membranes blending with PVA modified SiO2 hydrophilic nanoparticles

In this study, PVA‐SiO₂ was synthesized by modifying silica (SiO₂) with polyvinyl alcohol (PVA), then a novel polyvinylidene fluoride (PVDF) ultrafiltration (UF) membrane was prepared by incorporating the prepared PVA‐SiO₂ into membrane matrix using the non‐solvent induced phase separation (NIPS) method. The effects of PVA‐SiO₂ particle on the properties of the PVDF membrane were systematically studied by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT‐IR), surface pore size, porosity, and water contact angle. The results indicated that with the addition of PVA‐SiO₂ particles in the PVDF UF membranes, membrane mean pore size increased from 80.06 to 126.00 nm, porosity improved from 77.4% to 89.1%, and water contact angle decreased from 75.61° to 63.10°. Furthermore, ultrafiltration experiments were conducted in terms of pure water flux, bovine serum albumin (BSA) rejection, and anti‐fouling performance. It indicated that with the addition of PVA‐SiO₂ particles, pure water flux increased from 70 to 126 L/m² h, BSA rejection increased from 67% to 86%, flux recovery ratio increased from 60% to 96%, total fouling ratio decreased from 50% to 18.7%, and irreversible fouling ratio decreased from 40% to 4%. Membrane anti‐fouling property was improved, and it can be expected that this work may provide some references to the improvement of the anti‐fouling performance of the PVDF ultrafiltration membrane. POLYM. ENG. SCI., 59:E412–E421, 2019. © 2018 Society of Plastics Engineers     

Fabrication of antifouling membranes by blending poly(vinylidene fluoride) with cationic polyionic liquid

Membrane fouling problem is now limiting the rapid development of membrane technology. A newly synthesized cationic polyionic liquid (PIL) [P(PEGMA-co-BVIm-Br)] was blended with poly(vinylidene fluoride) (PVDF) to prepare antifouling PVDF membranes. The PVDF/P(PEGMA-co-BVIm-Br) exhibited an increased surface hydrophilicity, the water contact angle was reduced from 77.8° (pristine PVDF) to 57.9°. More porous membrane structure was obtained by adding PIL into the blending polymers, as high as 478.0 L/m²·h of pure water flux was detected for the blend PVDF membrane in comparison with pristine PVDF (17.2 L/m²·h). Blending of the cationic PIL with PVDF gave a more positive surface charge than pristine PVDF membrane. Blend membranes showed very high rejection rate (99.1%) and flux recovery rate (FRR, 83.0%) to the positive bovine serum albumin (BSA), due to the electrostatic repulsion between the membrane surface and proteins. After three repeated filtration cycles of positive BSA, the blend PVDF membranes demonstrated excellent antifouling performance, the permeation flux of the membranes was recovered very well after a simple deionized water washing, and as high as 70% of FRR was obtained, the water flux was maintained at above 350 L/m²·h. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48878.     

辣素衍生物改性PVDF膜的制备及其抗菌性能

以甲基丙烯酸甲酯（MMA）和天然辣素8-甲基-N-香草基-6-壬烯酰胺（Capsa）为单体,通过自由基聚合合成辣素衍生物PMMA-Capsa。将PMMA-Capsa与聚偏氟乙烯（PVDF）共混,通过非溶剂诱导相转化法制备PVDF/PMMA-Capsa分离膜,系统地研究了PMMA-Capsa含量对所制备的分离膜表面化学组成、形态结构、亲水性能、抗菌性能及渗透性能的影响。结果表明在成膜过程中PMMA-Capsa倾向于分布在分离膜的表面和孔道表面。随着铸膜液中PMMA-Capsa含量的增加,所制备的分离膜断面结构中海绵层结构逐渐消失,分离膜容易形成粗糙的微孔状表面。PMMA-Capsa的引入使分离膜表面水接触角从88.4°降低到73.1°。渗透实验结果表明分离膜的纯水通量随着PMMA-Capsa含量的增加而增加,而对牛血清蛋白（BSA）的截留率逐渐降低,所制备的PVDF/PMMA-Capsa分离膜的通量恢复率高于纯PVDF膜。PVDF/PMMA-Capsa分离膜具有优异的抗菌性能,对金黄色葡萄球菌的抗菌效率最高可达97.2%。     

Preparation and properties of hydrophobic poly(vinylidene fluoride)–SiO2 mixed matrix membranes for dissolved oxygen removal from water

The application of the membrane method for removing dissolved oxygen (DO) from water on the laboratory scale was studied. Flat mixed matrix membranes were composed of poly(vinylidene fluoride) (PVDF) and hydrophobic nanosilica particles, which were used to improve the DO removal process. The SiO₂ particles were modified by a silane coupling agent and examined by Fourier transform infrared spectroscopy. It was shown that the surface of the SiO₂ particles was bonded to hydrophobic long‐chain alkane groups through chemical bonding. The effects of adding SiO₂ particles on the membrane properties and morphology were examined. The results show that the porosity and pore size of the membrane were affected by the introduction of SiO₂ particles, and the cross‐sectional morphology of the PVDF composite membranes changed from fingerlike macrovoids to a spongelike structure. The membrane performance of DO removal was evaluated through the membrane unit by a vacuum degassing process. It was found that the SiO₂/PVDF hybrid membranes effectively improved the oxygen removal efficiency compared with the original PVDF membranes. The maximum permeation flux was obtained when the loading amount was 2.5 wt %. The effect of the downstream vacuum level was also investigated. The experimental results show that the SiO₂/PVDF hybrid membranes had superior performances and could be an alternative membrane for removing DO from water. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40430.     

Facile surface modification of PVDF microfiltration membrane by strong physical adsorption of amphiphilic copolymers

To endow the surface of poly(vinylidene fluoride) (PVDF) microfiltration (MF) membranes with hydrophilicity and antifouling property, physical adsorption of amphiphilic random copolymers of poly(ethylene glycol) methacrylate (PEGMA) and poly(methyl methacrylate) (PMMA) (P(PEGMA‐r‐MMA)) onto the PVDF membrane was performed. Scanning electron microscopy (SEM) images showed that the adsorption process had no influence on the membrane structure. Operation parameters including adsorption time, polymer concentration, and composition were explored in detail through X‐ray photoelectron spectroscopy (XPS), static water contact angle (CA), and water flux measurements. The results demonstrated that P(PEGMA‐r‐MMA) copolymers adsorbed successfully onto the membrane surface, and hydrophilicity of the PVDF MF membrane was greatly enhanced. The antifouling performance and adsorption stability were also characterized, respectively. It was notable that PVDF MF membranes modified by facile physical adsorption of P(PEGMA₅₈‐r‐MMA₃₃) even showed higher water flux and better antifouling property than the commercial hydrophilic PVDF MF membranes. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3112–3121, 2013     

Investigating the effect of zirconium-based and titanium-based metal–organic frameworks nanoparticles on the performance of polysulfone hollow fiber mixed matrix membrane for dialysis application

This study aims to investigate polysulfone (PSF) mixed matrix membranes (MMMs) properties containing zirconium-based and titanium-based metal–organic frameworks (MOFs). for hemodialysis application. The nanoparticles were synthesized, and the membranes were produced by the phase inversion method. Membrane characterization conducted by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), field emission Scanning electron microscope (FE-SEM), energy-dispersive x-ray analysis (EDX), transmission electron microscopy (TEM), x-ray diffraction (XRD), and atomic force microscopy (AFM) confirmed the presence of MOF nanoparticles. Also, the evaluation of the specific surface area of nanoparticles was done by BET. The water contact angle reduced from 64.4° to 51.2°, indicating the hydrophilicity improvement, enhancing the pure water flux from 46.8 L/m²h for the pristine membrane to 76.7 L/m2h for the pristine membrane M₄. The total fouling resistance decreased from 30% to 21%, and the bovine serum albumin (BSA) adsorption of modified membranes was lower than that of the pristine membrane. Urea and creatinine were cleared significantly for modified ones, up to 82.6% and 72.1%, respectively, and all membranes showed BSA retention of more than 93%. A comparison between MMMs that contained UIO-66-NH₂ and MIL-125-NH₂ showed that the former had a better effect on the performance. M₄ had better results, indicating high water flux, the lowest fouling resistance, high porosity, lower BSA adsorption, proper clearance for urea and creatinine, and 94.2% BSA retention.     

Preparation of PVDF/poly(tetrafluoroethylene‐co‐vinyl alcohol) blend membranes with antifouling propensities via nonsolvent induced phase separation method

Poly(vinylidene fluoride) (PVDF) was blended with a new amphiphilic copolymer, poly(tetrafluoroethylene‐co‐vinyl alcohol) [poly(TFE‐VA)], via non‐solvent induced phase separation (NIPS) method to make membranes with superior antifouling properties. The effects of the VA/TFE segment ratio of the copolymer and the copolymer/PVDF blend ratio on the properties of the prepared membranes were studied. Membranes with similar water permeabilities, surface pore sizes, and rejection properties were prepared and used in bovine serum albumin (BSA) filtrations with the same initial water flux and almost the same operating pressure, to evaluate the sole effect of membrane material on fouling propensity. While the VA/TFE segment ratio strongly affected the membrane antifouling properties, the effects of the copolymer/PVDF blending ratio were not so drastic. Membrane surface hydrophilicity increased, and BSA adsorption and fouling decreased upon blending a small amount of amphiphilic copolymer with a high VA/TFE segment ratio with PVDF (copolymer/PVDF blending ratio 1:5). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43780.     

Preparation of blend polyethersulfone/cellulose acetate/polyethylene glycol asymmetric membranes for oil–water separation

Blend PES/CA hydrophilic membranes were prepared via a phase-inversion process for oil–water separation. PEG-400 was introduced into the polymer solution in order to enhance phase-inversion and produce high permeability membranes. A gas permeation test was conducted to estimate mean pore size and surface porosity of the membranes. The membranes were characterized in terms of morphology, overall porosity, water contact angle, water flux and hydraulic resistance. A cross-flow separation system was used to evaluate oil–water separation performance of the membranes. From FESEM examination, the prepared PES/CA membrane presented thinner outer skin layer, higher surface porosity with larger pore sizes. The outer surface water contact angle of the prepared membrane significantly decreased when CA was added into the polymer solution. The higher water flux of the PES/CA membrane was related to the higher hydrophilicity and larger pore sizes of the membrane. From oil–water separation test, the PES/CA membrane showed stable oil rejection of 88 % and water flux of 27 l/m² s after 150 min of the operation. In conclusion, by controlling fabrication parameters a developed membrane structure with high hydrophilicity, high surface porosity and low resistance can be achieved to improve oil rejection and water productivity.     

PVDF/TiO2/graphene oxide composite nanofiber membranes serving as separators in lithium-ion batteries

Improving the electrochemical properties of membranes in lithium-ion batteries (LIBs) is very important. Many attempts have been made to optimize ionic conductivity of membranes. The aim of this study was fabricating composite nanofiber membranes of poly(vinylidene fluoride) (PVDF), containing titanium dioxide (TiO₂) and graphene oxide (GO) nanoparticles to use in LIBs as separators. The morphology, crystallinity, porosity, pore size, electrolyte uptake, ionic conductivity, and electrochemical stability of the membranes were investigated using scanning electron microscopy, wide-angle X-ray diffraction, Fourier transform infrared spectroscopy, electrochemical impedance spectroscopy, and linear sweep voltammetry. The electrolyte uptake and ionic conductivity of the PVDF/TiO₂/GO composite nanofiber membranes containing 2 wt % GO were 494% and 4.87 mS cm⁻¹, respectively, which were higher than those of the other fabricated membranes as well as the commercial Celgard membrane. This could be attributed to the increased porosity, larger surface area, and higher amorphous regions of the PVDF/TiO₂/GO composite nanofiber membranes as a result of the synergistic effects of the nanoparticles. In this work, suitable optimized membranes with greater electrochemical stability compared with the other membranes were presented. Also, it was demonstrated that the incorporation of the TiO₂ and GO nanoparticles into the PVDF nanofiber membranes led to a porous structure where the electrolyte uptake enhanced. These properties made these membranes promising candidates for being used as separators in LIBs. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48775.     

Preparation of high‐flux ultrafiltration membranes by blending strongly charged polymer

Three kinds of high‐flux ultrafiltration membranes were fabricated by blending strongly charged polymer [sulfonated poly(phenylene oxide) (SPPO)] with neutral polymer [cellulose acetate (CA), polyethersulfone (PES), or polyvinylidene fluoride (PVDF)]. After blending with SPPO, the pure water flux of CA‐SPPO, PES‐SPPO, and PVDF‐SPPO membrane increase by 3, 76, and 30 times at a transmembrane pressure of 100 kPa. Compared with the unblended membranes, the pore radius of CA‐SPPO, PES‐SPPO, and PVDF‐SPPO membrane increased from 31.9 to 33.2 nm, 26.1 to 28.6 nm, and 19.8 to 25.7 nm, respectively. The addition of strongly charged polymer decreased the thermodynamic stability of casting solutions, promoting the phase inversion process and resulting in highly porous structure. The charged groups and hydrophilicity of the polymer facilitate the formation of an additive concentration gradient (more additive in the active layer), endowing the blend membrane with better hydrophilicity and greater wettability gradient. The high porosity, good hydrophilicity, and larger wettability gradient enable the high permeation of blend membranes. This work shows how the strongly charged polymer affects the formation and performance of blend membrane, which will be useful for designing high‐performance membrane. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44570.     

Hydrophilic Modification of PVDF Microfiltration Membrane with Poly (Ethylene Glycol) Dimethacrylate through Surface Polymerization

The hydrophilic modification of poly (vinylidene fluoride) (PVDF) membrane with poly (ethylene glycol) dimethacrylate (PEGDMA) through grafting reaction for antifouling was reported. The influence of PEGDMA content, reaction temperature and time, on the structure, morphology, antifouling, and hydrophilicity of PVDF-g-PEGDMA membrane has been investigated. The PEGDMA monomers that were grafted on the surface of PVDF microfiltration membrane were confirmed by Attenuation total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS), and morphology study conducted by SEM revealed the changes before and after modification. The protein adsorption, filtration performance, water content, and dynamic contact angle were used to characterize the antifouling and hydrophilicity of the modified PVDF membranes. Compared with the pristine PVDF membrane, the bovine serum albumin (BSA) adsorption on the PVDF-g-PEGDMA membrane decreased about 80%, and the water contact angle of the membrane dropped to 0°. Besides, the experimental results revealed no significant differences between the membrane samples with respect to pore size.     

Morphological effects of spherical SiO2 and hexagonal mesoporous MCM-41 nanoparticles in polyacrylonitrile mixed matrix membranes on the biofouling mitigation in short-term filtration

In this study, the morphology of the nanostructures is evaluated on the surface characterization and performance of the polyacrylonitrile (PAN) ultrafiltration mixed matrix membranes (MMM). To this end, silica nanoparticles (NPs) such as spherical (SiO₂) and hexagonal mesoporous (MCM-41) with high hydrophilicity were incorporated at 0.5, 1, and 2 wt%. Attenuated total reflectance-Fourier transform infrared analysis illustrated the placement of NP on the surface of the MMM. Atomic force microscopy studies also showed that SiO₂ NP added to PAN exhibited a smoother surface than MCM-41 NP. Field-emission scanning electron microscope analysis of the MMM identified that all membranes are composed of a finger-like porous structure. Contact angle measurements indicate that the morphology of the NPs has no significant effect on MMM hydrophilicity. Moreover, the performance of the MMM was evaluated, and regardless of NP morphology, the MMM showed better permeate flux with increased loading. A higher pure water flux was observed in the PAN-MCM41-1% membrane (237 L/m² h), possibly because of inherent porosity and high hydrophilicity of MCM-41 compared to SiO₂ NP. Further, the PAN-SiO₂-1% membrane exhibited superior antifouling properties due to a lower surface roughness. The present studies reveal that the morphology of the NP greatly influence on the structure, permeation, and antifouling properties of PAN membranes.     

Fabrication and characterization of poly(vinylidene fluoride)–polytetrafluoroethylene composite membrane for CO2 absorption in gas–liquid contacting process

The wetting resistance of poly(vinylidene fluoride) (PVDF) membrane is a critical factor which determines the carbon dioxide (CO₂) absorption performance of the gas–liquid membrane contactors. In this study, the composite PVDF–polytetrafluoroethylene (PTFE) hollow fiber membranes were fabricated through dry-jet wet phase-inversion method by dispersing PTFE nanoparticles into PVDF solution and adopting phosphoric acid as nonsolvent additive. Compared with the PVDF membrane, the composite membranes presented higher CO₂ absorption flux due to their higher effective surface porosity and surface hydrophobicity. The composite membrane with addition of 5 wt % PTFE in the dope gained the optimum CO₂ absorption flux of 9.84 × 10⁻⁴ and 2.02 × 10⁻³ mol m⁻² s⁻¹ at an inlet gas (CO₂/N₂ = 19/81, v/v) flow rate of 100 mL min⁻¹ by using distilled water and aqueous diethanolamine solution, respectively. Moreover, the 5% PTFE membrane showed better long-term stability than the PVDF membrane regardless of different types of absorbent, indicating that polymer blending demonstrates great potential for gas separation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47767.     

Sulfonated polyphenylsulfone asymmetric membranes: Effect of coagulation bath (acetic acid‐NaHCO3/isopropanol) on morphology and antifouling properties

Sulfonated polyphenylsulfone porous asymmetric membranes, S‐PPSU with different sulfonation degrees, 21, 33, 50 wt %, were prepared by phase inversion. Two different coagulation baths were explored for asymmetric membrane preparation: acetone/isopropanol and acetic acid (AA)‐NaHCO₃/isopropanol. The latter bath allows better morphology control for the nucleation and pore formation of the membrane. Scanning electron microscopy of membranes shows that pore interconnectivity is improved, when the mixture of AA‐NaHCO₃/isopropanol was used for asymmetric S‐PPSU ultrafiltration membranes preparation. S‐PPSU asymmetric membranes show an increasing hydrophilicity with increasing sulfonation degree. Asymmetric membrane antifouling properties improve as the concentration of sulfonic groups increases in the membrane showing twice the flux recovery ratio and lower BSA protein absorption in static and dynamic flux tests. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44502.     

Preparation and properties of polyvinyl chloride ultrafiltration membranes blended with functionalized multi‐walled carbon nanotubes and MWCNTs/Fe3O4 hybrids

To investigate the influence of magnetic materials combined with carbon nanotubes (CNTs) as fillers on the membrane properties, multi‐walled carbon nanotubes (MWCNTs) functionalized by mixed acids (V_H2SO4:V_HNO3=3:1) were loaded by Fe₃O₄ through a hydrothermal method. The obtained MWCNTs/Fe₃O₄ hybrids were characterized by X‐ray diffraction (XRD), Infrared spectroscopy (IR) spectrum, and scanning electron microscope (SEM) and then blended with polyvinyl chloride (PVC) to prepare ultrafiltration (UF) membranes through a phase inversion process. Simultaneously, two other UF membranes, PVC blended with acid‐treated MWCNTs and PVC blended with nothing, were also prepared. The results showed that the membrane porosity and mean pore size increased slightly with the addition of fillers. Static contact angle showed that MWCNTs/Fe₃O₄ hybrids improved the hydrophilicity of membrane surface better than the acid‐treated MWCNTs. Pure water flux increased consistently with the hydrophilicity of the membrane surface. SEM and atomic force microscope (AFM) images showed that the MWCNTs/Fe₃O₄ blended membrane formed a relatively complete pore structure throughout the cross‐section and had a rougher top surface. However, the mechanical properties of membranes with fillers were reduced compared with the pristine PVC membrane. The rejections of membranes for Bovine serum albumin (BSA), Bisphenol A (BPA), and Norfloxacin (NOR) showed that MWCNTs/Fe₃O₄ played an important role in trapping pollutants in membrane filtration. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43417.     

Structure and performance of poly(vinylidene fluoride) membrane with temperature‐sensitive poly(n‐isopropylacrylamide) homopolymers in membrane pores

The poly(vinylidene fluoride) (PVDF)/poly(N‐isopropylacrylamide) (PNIPAM) blend membranes with different PNIPAM contents are prepared by phase inversion of PNIPAM and PVDF in aqueous medium. The membranes are characterized by thermal gravimetric analyses, elemental analysis, Fourier transform infrared spectrometer, X‐ray photoelectron spectroscopy, and scanning electron microscope photographs. The results indicate that PNIPAM chains are largely distributed in membrane pore other than membrane surface, and furthermore, with the increase of PNIPAM content, the porous size, porosity, and water flux through the membrane increase, the hydrophilicity and antiprotein fouling are enhanced. The blend membrane exhibits temperature‐sensitive permeability to aqueous solutions, with the most drastic change being observed at the lower critical solution temperature (LCST) of PNIPAM (around 32°C). Below the LCST, the blend membrane shows a high protein rejection and a low water flux; above the LCST, the blend membrane shows a low protein rejection and a high water flux. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers