Antifouling Membranes Research Articles

PVA/TEOS crosslinked membranes incorporating zinc oxide nanoparticles and sodium alginate to improve reverse osmosis performance for desalination

ABSTRACTPure water is becoming less available with increases in world population, so seawater desalination is becoming more important. For efficient seawater desalination, this paper proposes a novel mixed matrix membrane (MMM) based on the deposition of a poly(vinyl alcohol) (PVA) nanofibrous active layer on a 3‐triethoxysilylpropylamine‐functionalized cellulose acetate substrate. The active layer is fabricated by utilizing a tetraethyl orthosilicate–crosslinked PVA incorporating zinc oxide nanoparticles (ZnO‐NPs) and sodium alginate (NaAlg). The overall reverse osmosis performance of the MMMs is enhanced by the infusion of ZnO‐NPs and NaAlg in PVA; we find the optimum concentration for the best performance to be ZnO‐NPs at 0.1 wt % and NaAlg at 0.01 wt %. In terms of permeation flux, salt rejection, salt passage, stability, long‐term rejection, membrane antifouling, reusability, and chlorine resistance, the proposed MMMs are examined using a dead‐end reverse osmosis filtration setup. The results show that the active layer achieves an optimal permeation flux of 34.6 L/m2 h, a natural sea salt rejection of 97%, and a chlorine resistance of 93%, suggesting that the proposed MMMs can be useful for seawater desalination. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47559.

Superhydrophilic and oleophobic membrane functionalized with heterogeneously tailored two-dimensional layered double hydroxide nanosheets for antifouling

Fouling is a common challenge to all membrane-based separation technologies. The current study demonstrated an antifouling membrane with a superhydrophilic but oleophobic (in air) characteristic, which was achieved through covalently tethering heterogeneously tailored two-dimensional layered double hydroxide (LDH) nanosheets to a polyvinylidene fluoride membrane surface. The nanosheets were in situ grafted with alternately arranged sodium 1-dodecanesulfonate (SDS) and 3-aminopropyltriethoxysilane (APTS) chains during preparation. Poly(methacrylic acid) (PMAA) was previously grafted on the membrane via plasma induced graft copolymerization as anchor sites for nanosheet binding. With a simple dip-coating operation, the surface-tailored LDH nanosheets could be bound to the membrane via cross-linking between the amine groups of APTS and carboxyl groups of PMAA. Ultimately, the long hydrophobic SDS and short hydrophilic APTS chains on the nanosheets formed a heterogeneous and infiltration selective (due to steric exclusion) surface on the membrane. As a result, the hydrophilic moieties on the membrane surface were much more accessible to water than to liquids of larger molecular size, thereby bringing about the superhydrophilic but oleophobic characteristic. The functionalization gave rise to both significantly enhanced wettability and hydrophilicity of the membrane, mainly owing to the increase of the electron donor component of surface energy (γAB−). Additionally, the functionalized membrane obtained a greater permeability without compromising its selectivity. Furthermore, as verified in both filtration tests with synthetic and practical foulant solutions, the superhydrophilic and oleophobic characteristic endowed the functionalized membrane with conspicuously greater cleaning efficiency and excellent capability in resisting irreversible fouling, suggesting promising applications in various fields.

Constructing Antifouling Hybrid Membranes with Hierarchical Hybrid Nanoparticles for Oil-in-Water Emulsion Separation.

The development of antifouling membranes plays a vital role in the widespread application of membrane technology, and the hybridization strategy has attracted a significant amount of attention for antifouling applications. In this work, TA/PEI@TiO2 hierarchical hybrid nanoparticles (TPTi HHNs) are first synthesized through a simple strategy combining the multiple catechol chemistries of phenolic tannic acid (TA) with the biomimetic mineralization chemistry of titania. The TPTi HHNs are used as nanofillers to prepare PVDF/TPTi hybrid membranes. The TPTi HHNs endow the membrane with higher porosity, hierarchical roughness, greater hydrophilicity, and underwater superoleophobicity. Upon TPTi HHN loading, the PVDF/TPTi hybrid membranes exhibit enhanced antifouling performance. The flux recovery ratio can reach 92% when utilized to separate oil-in-water emulsion. Even being applied to the three-cycle filtration of oil-in-water emulsion with much higher concentration, the PVDF/TPTi membrane can still maintain a high flux recovery ratio about 85%. This study will provide a facial polyphenol-based platform to fabricate antifouling hybrid nanofillers and antifouling hybrid membranes with promising applications in oil/water separation.

Virus concentration and purification by a microfluidic filtering system with an integrated PEGylated antifouling membrane

We present the integration of a nanoporous membrane functionalized with hydrophilic polymer brushes, poly(ethylene glycol) methacrylate (PEGMA), into a microfluidic device. In order to prevent damage to functional groups on the membrane surfaces, the PEGMA-modified membrane was directly bonded using an intermediate UV-curable adhesive layer by employing the modified “Stamp-and-Stick (SAS)” method and operated at high pressures. We demonstrated that the degree of flux recovery (RFR) of the functionalized membrane during testing with bovine serum albumin, that reached 93% after a cleaning process while unmodified membranes showed only 63% of RFR. The viral particle recovery efficiency and concentration factor were 60.41% and 6.04, respectively.

Tannic acid coating and in situ deposition of silver nanoparticles to improve the antifouling properties of an ultrafiltration membrane

ABSTRACTThe construction of antifouling membranes has been a desirable approach for addressing membrane‐fouling issues in the ultrafiltration (UF) process. Antifouling means antiadhesive and antimicrobial; however, few researchers have achieved both properties in a facile and effective manner. In this article, we report a direct tannic acid (TA) coating method combined with the in situ deposition of silver nanoparticles (Ag NPs); this was used to improve the antifouling properties of a positively charged polymeric UF membrane. The results show that the TA–Ag NP modified membranes showed improved protein resistance (flux recovery rate = 71.2% after modification vs 17.8% before modification) and less attachment of bacteria (Escherichia coli K1) on the membrane surface and reduced cell viability in the resulting bacterial suspension (reduced by ≥90%) because of the combined antimicrobial properties of both the TA and Ag NPs. This indicated that our modification method was promising for UF membrane antifouling applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47314.

Facile preparation of grass-like structured NiCo-LDH/PVDF composite membrane for efficient oil–water emulsion separation

Development of antifouling membrane to separate oil–water emulsions by low energy consumption approach is an urgent demand. Herein, we report for the first time a grass-like structured composite membrane from array growth of nickel cobalt layered double hydroxide (NiCo-LDH) onto the polydopamine modified polyvinylidene fluoride (PVDF) membrane surface via simple hydrothermal strategy. The surface morphology of as-prepared membrane has controlled by hydrothermal time. The obtained NiCo-LDH/PVDF composite membrane exhibits superhydrophilicity/underwater superoleophobicity for separating both surfactant-free and surfactant-stabilized oil–water emulsions by capillary effect under the driving of gravity. Moreover, with the advantages of antifouling performance, the membrane displays outstanding cyclic performance for long-term application, which is promising for practical oily wastewater treatment.

Highly hydrophilic poly(vinylidene fluoride) ultrafiltration membranes modified by poly(N-acryloyl glycinamide) hydrogel based on multi-hydrogen bond self-assembly for reducing protein fouling

Reducing protein fouling in membrane separation and purification process is still a great challenge to the widespread application of ultrafiltration (UF) membranes. In this context, polyvinylidene fluoride (PVDF) UF membranes with enhanced hydrophilicity were modified by grafting hydrophilic poly (N-acryloyl glycinamide) (PNAGA) hydrogel formed through multi-hydrogen bond self-assembly via ultraviolet (UV)-initiated radical graft polymerization. Fourier transform infrared spectra (FTIR) and X-ray photo electron spectroscopy (XPS) reveal that PNAGA gel has been grafted onto the surface of the hydrophobic PVDF membranes. Water contact angle of PNAGA modified membranes reduces from 55.2° ± 1.1 to 0° within 11 s, illustrating a superior hydrophilicity. Ultrasonic 30 min and 7 days pure water filtration tests indicate that the PNAGA hydrogel layer has good stability. The results from anti-fouling test show that, when the pH is 7.0, the flux recovery rate of modified membrane maintains at 99%, the total fouling rate is as low as 30%, and the irreversible fouling rate is only 1.2%. Furthermore, the fouling mechanism investigation shows that fouling layers are not easy to form on the anti-protein-fouling PNAGA hydrogel grafted membranes. This work provides new insights for anti-fouling membrane design and application in protein purification, bio-separation and so on.

Ultrasound-induced settleability and membrane filterability of activated sludge treating milk processing wastewater

In practice, established operation of activated sludge treatment system with high biomass concentration is restricted because of difficulty in settling the sludge in clarifiers. Membrane bioreactor is a modified form of activated sludge, and despite the superior advantages, its widespread application is restricted by the membrane fouling. Therefore, in this research, to improve the sludge sedimentation at high biomass concentration in the activated sludge system, high-frequency ultrasound (1.7 MHz) was exerted in clarifier of activated sludge system and its performance was compared with a bioreactor followed by an antifouling ultrafiltration membrane. The antifouling ability of NH2-functionalized multiwall carbon nanotubes (NH2-MWCNTs)-modified nanocomposite UF membrane during filtration of mixed liquor-activated sludge was investigated. Hydraulic retention time (HRT) (8–44 h) and mixed liquor suspended solids (MLSS) (6000–14,000 mg/L) were chosen as the operating variables to analyze the process. The biological process showed high COD removal efficiency throughout the experiments (> 96%). The membrane and high-frequency ultrasound had no effect on the system performance in terms of COD, TKN, TN, TP removal. However, the HRT and MLSS indicated an increasing impact on flux. The effect of ultrasound on the sludge properties, i.e., sludge volume index, sludge settling velocity and height of sludge at high MLSS concentration (14,000 mg/L), was not considerable. It was concluded at MLSS of below 10,000 mg/L, about 40% water recovery was obtained. As a result, activated sludge equipped with ultrasound showed a promising performance; however, its industrial development needs further examinations to attain the design criteria.Graphical

Hydrophilic and photo-crosslinkable diblock copolymers employed for robust antifouling membrane coatings

Bifunctional copolymers bearing hydrophilic units and photo-crosslinkable units were prepared and employed to coat PVDF membranes and thus improve their antifouling properties and coating stability. A series of methoxy poly(ethylene glycol)-block-poly(2-hydroxyethyl methacrylate) (mPEG-b-PHEMA) diblock copolymers were prepared via the atom transfer radical polymerization (ATRP) of 2-hydroxyethyl methacrylate (HEMA) using different mPEG macroinitiators, and then reacted with cinnamoyl chloride to obtain methoxy poly(ethylene glycol)-block-poly(2-cinnamoyloxyethyl methacrylate) (mPEG-b-PCEMA). Coating PVDF microfilter membranes with mPEG-b-PCEMA and subsequently photo-crosslinking the PCEMA block yielded crosslinked copolymer coatings. The successful preparation of these coatings was confirmed by SEM, TGA, ATR-FTIR and XPS characterization. The hydrophilicity of the membrane increased along with the amount of diblock copolymer coating on the coated PVDF membrane. Based on the results of BSA adsorption and filtration experiments, the antifouling properties of the coated PVDF membrane remarkably improved. Furthermore, the mPEG block chain length and its content in the diblock copolymer had a significant effect on the surface properties of the coated PVDF membrane. More importantly, the copolymer coatings were very stable thanks to the crosslinking of the PCEMA chains of the diblock copolymer.

Antifouling Ultrafiltration Membranes with Retained Pore Size by Controlled Deposition of Zwitterionic Polymers and Poly(ethylene glycol).

We demonstrate antifouling ultrafiltration membranes with retained selectivity and pure water flux through the controlled deposition of zwitterionic polymers and poly(ethylene glycol) (PEG). Molecules for polymerization were immobilized on the membrane's surface yet prevented from attaching to the membrane's pores due to a backflow of nitrogen (N2) gas achieved using an in-house constructed apparatus that we named the polymer prevention apparatus, or "PolyPrev". First, the operating parameters of the PolyPrev were optimized by investigating the polymerization of dopamine, which was selected due to its versatility in enabling further chemical reactions, published metrics for comparison, and its oxidative self-polymerization. Membrane characterization revealed that the polydopamine-modified membranes exhibited enhanced hydrophilicity; moreover, their size selectivity and pure water flux were statistically the same as those of the unmodified membranes. Because it is well documented that polydopamine coatings do not provide a long-lasting antifouling activity, poly(2-methacryloyloxyethyl phosphorylcholine) (polyMPC, Mn = 30 kDa) and succinimidyl-carboxymethyl-ester-terminated PEG ( Mn = 40 kDa) were codeposited while dopamine was polymerizing to generate antifouling membranes. Statistically, the molecular-weight cutoff of the polyMPC- and PEG-functionalized membranes synthesized in the PolyPrev was equivalent to that of the unmodified membranes, and the pure water flux of the PEG membranes was equivalent to that of the unmodified membranes. Notably, membranes prepared in the PolyPrev with polyMPC and PEG decreased bovine serum albumin fouling and Escherichia coli attachment. This study demonstrates that by restricting antifouling chemistries from attaching within the pores of membranes, we can generate high-performance, antifouling membranes appropriate for a wide range of water treatment applications without compromising intrinsic transport properties.

Reactive Photo-Fenton ceramic membranes: Synthesis, characterization and antifouling performance

To develop reactive and antifouling membrane filtration systems, a photo-Fenton ceramic membrane was prepared by coating goethite (α-FeOOH) catalysts on a zirconia/titania alumina membrane via a cross-linking method. Scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD) and Fourier transform infrared spectroscopy (FTIR) were used to characterize α-FeOOH catalysts and the surface coating quality. The cross linker yielded stable covalent binding between catalyst and membrane under room temperature and produced a homogeneous and smooth coating of catalyst on ceramic membranes. Photo-Fenton reactions were initiated with addition of H2O2 under UV irradiation to improve the foulant degradation on membrane surface while filtration. Membrane fouling was simulated by bovine serum albumin (BSA) and humic acid (HA). Our results show that the photo-Fenton reactions on the coated membranes slowed down the fouling kinetics and even reversed the fouling, leading to a stable transmembrane pressure (TMP) over time of filtration, as opposed to a monotonous increase of TMP due to surface fouling. The batch experiments verified that the photo-Fenton reactions achieved the degradation rates of 76% and 86% for HA and BSA respectively within 60 min, with the mineralization rates of over 80% as indicated by the total organic carbon measurement. This study embarks on a novel antifouling membrane filtration process via incorporation of photo-Fenton reactions. The findings are also important for diverse applications of surface fouling mitigation and rationale design of fouling resistant surfaces or materials through photo-Fenton or other catalytic reactions.

Improved Anti-Biofouling Performance of Thin -Film Composite Forward-Osmosis Membranes Containing Passive and Active Moieties.

Forward osmosis (FO) has gained increasing attention in desalination, wastewater treatment, and power generation. However, biofouling remains a major obstacle for the sustainable development of the FO process. Both passive and active strategies have been developed to mitigate membrane biofouling. A comprehensive understanding of different strategies and mechanisms has fundamental significance for the antifouling membrane development. In this study, thin-film composite (TFC) FO membranes were modified with polydopamine (PDA) coating as a passive antibacterial moiety and silver nanoparticles (Ag NPs) as an active antibacterial moiety. Their anti-biofouling performances were investigated both in static and dynamic conditions. In static exposure, the PDA-coated membranes exhibited great passive anti-adhesive property, and the Ag-NP-generated membranes presented both of excellent passive anti-adhesive properties and active antibacterial performance. While in dynamic cross-flow running conditions, Ag NPs effectively mitigated the membrane water flux decline due to their inhibition of biofilm growth, the PDA coating failed because of its inability to inactivate the attached bacteria growth. Moreover, Ag NPs were stable and active on membrane surfaces after 24 h of cross-flow operation. These findings provide new insights into the performances and mechanisms of passive and active moieties in the FO process.

Dual functional membrane with multiple hierarchical structures (MHS) for simultaneous and high-efficiency removal of dye and nano-sized oil droplets in water under high flux

Dual functional membranes with super-wetting and adsorption capacity have drawn great attentions owing to their good application prospect in the treatment of mixed wastewater containing oil and dyes. Despite recent development in such functional membranes, there are still some obstacles need to be resolved. The one is how to further improve the dye adsorption capacity to realize the high-efficiency removal of dye under high permeation flux. The other is to improve the rejection towards nano-sized oil droplets in water. Herein, with porous polypropylene (PP) membrane as substrate, we show that constructing multiple hierarchical structures (MHS) on membrane surface is an effective way to solve the above mentioned problems. The MHS prepared by low-cost tannic acid, 3-Aminopropyltriethoxysilane (APTES), and polyethyleneimine (PEI) are composed of rough layer, nanospheres, and nano nodes with abundant amine groups. On the one hand, the MHS can endow the membrane with high adsorptive capacity (480 mg g−1 toward methyl blue). On the other hand, the MHS can also decrease the pore size of the membrane, making it suitable for separation of nano-sized oil droplets. Moreover, the MHS can also render the membrane superhydrophilicity and excellent anti-oil-adhesion properties. Thanks to these advantages derived from MHS, the obtained dual functional membrane can realize high-efficiency and simultaneous removal of high concentrated dye (10–50 ppm, removal efficiency>95%) and nano-sized oil droplets (about 50–300 nm, oil rejection>99%) from mixed wastewater under high flux (1680 L m−2 h−1). Considering the significantly enhanced performance, as well as the facile and cost-effective process, the as-prepared functional membrane with MHS has good application prospects. Besides, a new insight on the influence of hydrodynamic conditions on membrane fouling during emulsion separation is also proposed, which may guide better design of anti-fouling membranes.

Metal-polyphenol coordination networks: Towards engineering of antifouling hybrid membranes via in situ assembly

Metal-polyphenol coordination networks have been actively explored as a facile, rapid and green platform for developing materials. In this study, novel antifouling hybrid membranes are successfully prepared via in situ assembling metal-polyphenol coordination networks and are proposed for oil/water separation application. Based on the coordination-driven cross-linking and assembling of TiIV and TA within polyvinylidene fluoride (PVDF) membrane matrix, TA-Ti coordination networks are successfully introduced and uniformly distributed in the as-prepared PVDF/TA-Ti membranes. The effects of the embedded TA-Ti coordination networks on both surface morphologies and pore structures of PVDF/TA-Ti membranes are investigated. The surface chemical compositions of PVDF/TA-Ti membranes are analyzed by energy-dispersive X-ray (EDX) and Fourier transform infrared spectroscopy (FTIR). The water contact angle analysis and DSC study on bound water content reveal the outstanding hydration capability of PVDF/TA-Ti membranes, indicating the higher underwater superoleophobicity and antifouling property of PVDF/TA-Ti membranes. The as-prepared PVDF/TA-Ti membranes exhibit remarkably improved antifouling performance with the flux recover ability increased to a maximum level about 100% for the filtration of oil-in-water emulsions. Overall, this study highlights the promising antifouling potential of TA-Ti coordination networks in designing antifouling membranes, and proposes a facile in situ hybridization method for preparing antifouling membranes derived from versatile metal-polyphenol coordination networks.

Advanced Anti-Fouling Membranes for Osmotic Power Generation from Wastewater via Pressure Retarded Osmosis (PRO).

A facile and versatile approach was demonstrated for the fabrication of low-fouling pressure retarded osmosis (PRO) membranes for osmotic power generation from highly polluted wastewater. A water-soluble zwitterionic random copolymer with superior hydrophilicity and unique chemistry was molecularly designed and synthesized via a single-step free-radical polymerization between 2-methacryloyloxyethyl phosphorylcholine (MPC) and 2-aminoethyl methacrylate hydrochloride (AEMA). The P[MPC- co-AEMA] copolymer was then chemically grafted onto the surface of PES/Torlon hollow fibers via amino groups coupling of poly(AEMA) with the polyimide structures of Torlon, leaving the zwitterions of poly(MPC) in the feed solution. Because of the outstanding hydrophilicity, unique cationic and anionic groups, and electrical neutrality of the zwitterionic brush, the newly developed membrane showed great resistances to both inorganic scaling and organic fouling in PRO operations. When using a real wastewater brine comprising multifoulants as the feed, the P[MPC- co-AEMA] modified membrane exhibits a much lower flux decline of 37% at Δ P = 0 bar after 24-h tests and a smaller power density decrease of 28% at Δ P = 15 bar within 12-h tests, compared to 61% and 42% respectively for the unmodified one. In addition to the low fouling tendency, the modified membrane shows outstanding performance stability and fouling reversibility, where the flux is almost fully recovered by physical backwash of water at 15 bar for 0.5 h. This study provides valuable insights and strategies for the design and fabrication of effective antifouling materials and membranes for PRO osmotic power generation.

Dopamine-induced biomimetic mineralization for in situ developing antifouling hybrid membrane

Membrane technology has raised significant interests over the past decade for sustainable water purification. Developing antifouling membranes are always the fundamental strategy to deal with the bottlenecks of ubiquitous membrane fouling. In this work, we provide a novel and facile strategy for developing antifouling hybrid membranes via dopamine-induced biomimetic mineralization of dopamine/TiO2 hybrid nanoparticles (DA/TiO2 HNPs) in situ within polyvinylidene fluoride membrane matrix. During biomimetic mineralization, dopamine, as the cationic inducer, favors the in situ hydrolysis/condensation of the titania precursor to form hybrid nanoparticles within polymer chains. Antifouling hybrid membranes are then obtained via non-solvent induced phase separation. The as-prepared hybrid membranes exhibit homogeneous nanoparticle dispersion, higher surface hydrophilicity, high surface energy, underwater superoleophobicity and higher mechanical strength. The in situ mineralized DA/TiO2 HNPs enhance both the separation performance and antifouling property of hybrid membranes. With the increase of hybrid nanoparticle loading, the water fluxes of the hybrid membranes are increased by three times. Moreover, the antifouling properties of hybrid membranes are effectively improved during the separation of 1 g/L oil-in-water emulsion with flux recovery ratio up to 95%. Especially for the PVDF/DA/TiO2 membrane with highest DA/TiO2 HNPs loading, it can maintains more than 85% flux recovery even challenged with oil-in-water emulsions of 50-fold higher concentration, indicating the reliable and extensive antifouling property of hybrid membranes against oil fouling. This study provides a potential in situ biomimetic mineralization strategy to construct antifouling hybrid membranes, and suggests the promising future of as-prepared antifouling hybrid membranes for water treatment.

Integrated antibacterial and antifouling surfaces via cross-linking chitosan-g-eugenol/zwitterionic copolymer on electrospun membranes.

Integrated antibacterial and antifouling surfaces in favor of avoiding implant-related infections are necessarily required for biomaterials when they contact with the body fluid. In this work, an antibacterial and antifouling membrane was developed via cross-linking chitosan-g-eugenol and the zwitterionic copolymer poly(sulfobetaine methylacrylate-co-2-aminoethyl methacrylate) on the electrospun polycarbonate urethane substrate using genipin as a cross-linker. Antibacterial assays demonstrated that the prepared membranes had efficient antibacterial activity with 92.8 ± 2.5% and 95.2 ± 1.3% growth inhibition rates against Escherichia coli and Staphylococcus aureus, respectively. The investigations on antifouling activity and hemocompatibility of the membranes showed significant resistances to bacterial attachment, non-specific protein adsorption and platelet adhesion, and presented lower hemolytic activity and good anticoagulant activity as well. Moreover, cell culture assays indicated that the prepared membranes exerted no obvious cytotoxicity with more than 80% of relative L929 fibroblast viability. Therefore, the membranes with integrated antibacterial and antifouling properties could be potentially applied in promising indwelling devices.

Enhancing water permeability and fouling resistance of polyvinylidene fluoride membranes with carboxylated nanodiamonds

Polyvinylidene fluoride (PVDF) is a popular membrane material, but it has the drawback of relatively high fouling potential. In this study, we prepared carboxylated nanodiamonds (CNDs) by thermal oxidation, and then incorporated CNDs into PVDF membranes during phase inversion. Transmission electron microscopy (TEM) showed that the CNDs had minimized aggregation and better dispersity compared with the raw nanodiamonds. The prepared membranes were characterized by scanning electron microscope (SEM), atomic force microscopy (AFM) and water contact angle analysis. The bulk porosities and pore sizes of the membranes were evaluated by the gravimetric method and the filtration method, respectively; surface pores were evaluated based SEM images. Compared with the pristine PVDF membrane, CNDs blended membranes had larger porosities and surface pore sizes, higher water permeabilities and hydrophilicities, smoother surfaces, and improved antifouling and cleaning performance due to the incorporation of hydrophilic carboxyl groups. In particular, the irreversible fouling ratio to the total fouling ratio (Rir/Rt) dropped from 85% for the pure PVDF membrane to 21% for the CNDs blended membrane. Our study demonstrates that CNDs are excellent pore-forming fillers in developing antifouling membranes, and they may open up a new avenue to the next generation of high performance membranes.

Fouling-resistant microfiltration membrane modified with magnetite nanoparticles by reversible conjunction

Abstract We developed a stimuli-responsive poly(tetrafluoroethylene) (PTFE) microfiltration (MF) membrane by reversible conjunction of magnetite nanoparticles. We modified the magnetic particles with maleimide functional groups and attached them to a furan-modified PTFE membrane via a Diels–Alder (DA) cycloaddition reaction to prepare an anti-fouling membrane that responds to magnetism and temperature. The combined results of Fourier-transform infrared spectroscopy, X-ray diffractometry, vibrating sample magnetometry, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy investigations clearly showed that the maleimide-modified magnetic nanoparticles were successfully synthesized and coupled with the furan-modified PTFE MF membrane by the DA reaction. The modified membrane produced a micro-vortex under a rotating magnetic field, and showed a high resistance to fouling with a water flux higher than 50% of initial flux even after 30 min in the fouling test, whereas the neat membrane had a water flux falling below 20% of initial flux in 30 min. Moreover, the magnetite nanoparticles were readily and repeatedly regenerated on the MF membrane surface using a thermally driven peel-and-stick process; 75% of the water flux was recovered, even after three fouling cycles.

Pore channel surface modification for enhancing anti-fouling membrane distillation

Membrane surface modification by forming a functional layer is an effective way to improve the anti-fouling properties of membranes; however, the additional layer and the potential blockage of bulk pores may increase the mass transfer resistance and reduce the permeability. In this study, we applied a novel method of preparing anti-fouling membranes for membrane distillation by dispersing graphene oxide (GO) on the channel surface of polyvinylidene fluoride membranes. The surface morphology and properties were characterized by scanning electron microscopy, atomic force microscope, and Fourier transform infrared spectrometry. Compared to the membrane surface modification by nanoparticles (e.g. SiO2), GO was mainly located on the pore surface of the membrane bulk, rather than being formed as an individual layer onto the membrane surface. The performance was evaluated via a direct-contact membrane distillation process with anionic and cationic surfactants as the foulants, separately. Compared to the pristine PVDF membrane, the anti-fouling behavior and distillate flux of the GO-modified membranes were improved, especially when using the anionic surfactant as the foulant. The enhanced anti-fouling performance can be attributed to the oxygen containing functional groups in GO and the healing of the membrane pore defects. This method may provide an effective route to manipulate membrane pore surface properties for anti-fouling separation without increasing mass transfer resistance.