Antifouling Membranes Research Articles

"Button and Buttonhole" Supramolecular Structure Enables the Self-Healing Behaviors of Functionalized Poly(ether sulfone) Membranes for Osmotic Power Generation.

Osmotic power generation has emerged as an advanced technology toward water-energy nexus to tackle global water pollution. It provides a sustainable use of salinity gradient from water resources yet encounters major obstacles caused by pressure-retarded osmosis (PRO) membrane fouling. Although membranes with good antifouling properties are widely studied, their antifouling functions are readily lost when scratches or detachments occur through physical damage during operation and chemical degradation by water and corrosive foulants. Consequently, it is important to develop antifouling membranes with autonomous self-healing capabilities. Herein, self-healable functionalized poly(ether sulfone) (PES) antifouling membranes have been fabricated via the sequential conjugation of the zwitterionic random copolymer [poly(1-(1-(1-adamantylcarbonyloxy)methyl)-3-vinylimidazolium bromide-co-1-(3-sulfopropyl)-3-vinylimidazolium-co-vinylamine)] (P(ADVI-co-SBVI-co-VA), abbreviated as PASV copolymer) and linear cyclodextrin polymer (LPCD) on polydopamine-preactivated PES supports. The self-healing behaviors rely on the judiciously designed "button-and-buttonhole" supramolecular network. Specifically, β-cyclodextrins in LPCD and adamantines in PASV act as "buttonholes" and "buttons", respectively. Under physical and chemical damages, the β-cyclodextrin "buttonhole" may sacrificially detach from the adamantine "button" of PASV but then recap another adamantine to restore the protective function. The antifouling and self-healing traits of as-functionalized PES-g-PASV-LPCD membranes were demonstrated by the superior antiprotein behaviors and improved antimicrobial performances on both nonaged and aged samples. In the PRO process, the modified membranes were effective in mitigating organic fouling and exhibited higher power density (79% of the initial value) than the nonmodified ones (47% of the initial value) in municipal wastewater testing. The strategy for engineering inherently healable and antifouling membranes paves a new pathway for the development of sustainable membranes for osmotic power production.

The efficient mixed matrix antifouling membrane for surfactant stabilized oil-in-water nanoemulsion separation

Membrane technology has raised considerable interest in sustainable water purification over the past decade. The development of antifouling membranes is always the basic approach to address the omnipresent bottlenecks of the membrane fouling. In this study, AlSi2O6 nanoparticles were synthesized using a coprecipitation technique and their influence was investigated on the permeation and antifouling properties of ultrafiltration (UF) membranes of polysulfone (PSF). A series of membranes were fabricated with various concentrations (such as 0.0, 2.5, 5 and 7.5 wt%) of AlSi2O6 nanoparticles through diffusion induced phase separation method. The prepared composite membranes demonstrate homogeneous nanoparticles dispersion, greater surface hydrophilicity, elevated surface roughness, and greater mechanical strength. The membrane's separation efficiency and antifouling property rises with increased concentration of AlSi2O6. Results suggest that with higher concentration of AlSi2O6, the water fluxes as well as separation efficiency of oil in water nanoemulsion increase up to 95%. Furthermore, the antifouling characteristics of composite membranes are efficiently enhanced by separating 100 mg / L of oil-in-water nanoemulsion (200 nm size) with a flux recovery ratio of up to 97% even though 52 percent of total fouling. Therefore, these membranes can be expected to become a competitive candidate for the separation of oil-water emulsions separation in the scope of environmental protection.

Photo-Fenton self-cleaning PVDF/NH2-MIL-88B(Fe) membranes towards highly-efficient oil/water emulsion separation

Membrane fouling is one of the major blockages toward the further sustained development of membrane technology. In this work, PVDF/NH2-MIL-88B(Fe) (PVDF/NM88B) membranes were prepared for the first time via one-step simple non-solvent induced phase conversion method. The PVDF/NM88B membrane shows an excellent separation performance (above 99.4%) and permeation flux (340–1970 L m−2 h−1 bar−1) towards different oil/water emulsions. Moreover, PVDF/NM88B membrane exhibits excellent antifouling performance with flux recovery ratio of almost 100% attributing to hydrophilicity and high photo-Fenton activity of NM88B. In addition, the membrane with good mechanical properties and recyclability shows great application potential in wastewater treatment. This work may shine a new light on the promising photo-Fenton self-cleaning prospect of Fe-based MOFs in constructing antifouling membranes for wastewater remediation and potential applications.

Incorporating dual-defense mechanism with functionalized graphene oxide and perfluorosulfonic acid for anti-fouling membranes

Surface segregation method based on the collaborative self-assembly principle was proposed to construct anti-fouling membranes with fouling-resistant and fouling-release mechanisms (dual-defense mechanism). Graphene oxides (GO) functionalized with polyethyleneimine (PEI) and perfluorosulfonic acid (PFSA) were added simultaneously into the casting solution to prepare PVDF/PFSA/PEI-GO hybrid membranes through surface segregation along with phase inversion process. The PEI-GO of hydrophilicity and the PFSA of low surface energy were utilized as additives to incorporate dual-defense mechanism for anti-fouling membranes. Furthermore, the synergistic effect of PEI immobilized on GO and sulfonic acid groups on PFSA generated electrostatic interaction, improving the long-term stability of membranes in aqueous environment. In the oil/water separation performance experiments, PVDF/PFSA/PEI-GO-1% membranes exhibited the highest pure water permeability of 406.7 ± 15.6 L m−2 h−1 bar−1, with flux decay rate (DRt) of 8.6%, and flux recovery rate (FRR) of 98.6%.

Assembly of self-cleaning perfluoroalkyl coating on separation membrane surface

Most membrane-based separation technologies for water treatment are severely limited by fouling-induced flux decline. Herein, a self-cleaning coating with weak chargeability was achieved by assembly of perfluorooctane sulfonate (PFOS) and polyethyleneimine (PEI) on hydrolyzed polyacrylonitrile (HPAN) membrane. The -NH3+ endowed the membrane with hydrophilicity, thus introducing fouling-resistance property. The -CFX in the coating endowed the ultrafiltration membrane with low surface energy (23.3 mJ/m2), thus introducing fouling-release property. Besides, a weakly-charged surface (8.4 mV) was obtained by the charge counteract between -SO3− on PFOS and -NH3+ on PEI, which further intensified the fouling-release property. The resultant membrane with such a self-cleaning coating exhibited superior antifouling property during oil/water emulsion and bovine serum albumin solution filtration. This facile assembly method may open up a new avenue towards engineering antifouling membrane surface for efficient water treatment.

ANOVA Design for the Optimization of TiO2 Coating on Polyether Sulfone Membranes.

There have been developments in the optimization of polyethersulfone (PES) membranes, to provide antifouling and mechanically stable surfaces which are vital to water purification applications. There is a variety of approaches to prepare nanocomposite PES membranes. However, an optimized condition for making such membranes is in high demand. Using experimental design and statistical analysis (one-half fractional factorial design), this study investigates the effect of different parameters featured in the fabrication of membranes, as well as on the performance of a nanocomposite PES/TiO2 membrane. The optimized parameters obtained in this study are: exposure time of 60 s, immersion time above 10 h, glycerol time of 4 h, and a nonsolvent volumetric ratio (isopropanol/water) of 30/70 for PES and dimethylacetamide (PES-DMAc) membrane and 70/30 for PES and N-methyl-2-pyrrolidone (PES-NMP) membrane. A comparison of the contributory factors for different templating agents along with a nanocomposite membrane control revealed that F127 triblock copolymer resulted in an excellent antifouling membrane with a higher bovine serum albumin rejection and flux recovery of 83.33%.

Enhanced MPBR with polyvinylpyrrolidone-graphene oxide/PVDF hollow fiber membrane for efficient ammonia nitrogen wastewater treatment and high-density Chlorella cultivation

Membrane fouling always as the main obstacle hinders wide application of membrane bioreactor (MBR). Development of antifouling membranes is a promising strategy to overcome this issue. In this study, novel polyvinylpyrrolidone (PVP)-graphene oxide (GO)/PVDF hollow fiber membrane with enhanced hydrophilicity and antifouling property was synthesized by assembling PVP-GO nanocomposites via chemical grafting method. The PVP-GO/PVDF membrane was successfully applied into algae-membrane photo-bioreactor (MPBR) with solids retention times (SRTs) of 30 d for high ammonia-nitrogen wastewater treatment at hydraulic retention times (HRTs) of 24 h. The permeability, removal performance and influence on extracellular polymeric substance (EPS) of algae-MPBR with modified PVDF membrane were compared to a control traditional system operated in parallel. Compared with pristine PVDF membrane, PVP-GO/PVDF membrane exhibited improved hydrophilicity (contact angle decreased from 97 to 62°), better permeability (1.7 times) and attractive flux recover rate (96%) in MPBR filtration, which was attributed to uniformly dispersed PVP-GO nanocomposites as spatial brushes for mitigating foulants on membrane surface. In terms of contaminants degradation, COD, NH4-N+ and NO3-N removal efficiency of algae-MPBR with modified membranes were kept above 97.8, 93.1 and 68.7%, much higher than traditional MBR. Moreover, remarkable reduction in hydrophobic proteins amount of EPS on fouling layer was observed for PVP-GO/PVDF membrane. The biomass concentration was maintained around 780 mg/L after 16 days and average biomass production rate reached as high as 45 mg/L d. These results indicated that PVP-GO/PVDF membrane exhibited superior antifouling performance for high-density microbes harvesting and efficient treatment for high ammonia-nitrogen wastewater.

Facile fabrication of omniphobic PVDF composite membrane via a waterborne coating for anti-wetting and anti-fouling membrane distillation

Omniphobic membranes have been brought to great attention recently regarding the ability to resist both water and low surface tension liquids, thus can be utilized for desalination of saline wastewater containing low surface tension contaminants in membrane distillation (MD). In this study, a facile, environment-friendly, and one-step strategy is developed for fabricating an omniphobic membrane with re-entrant structure and low surface energy by spraying a waterborne coating solution comprising of fluorocarbon surfactant (FS, Zonyl@8867L), fluorinated alkyl silane (FAS), and silicon dioxide nano-particles (SiO2 NPs) onto amino functionalized polyvinylidene difluoride (PVDF) membrane via electrostatic adsorption. As a result, the prepared omniphobic FS/FAS/Si membrane possesses high liquid repellency to water, diiodomethane, mineral oil-in-water emulsion (0.10 % v/v), mineral oil, and SDS solution (0.40 mM) with the contact angle of 164.40 ± 0.95°, 159.12 ± 3.12°, 154.31 ± 3.71°, 153.31 ± 2.09°, and 157.14 ± 3.29°, respectively. Compared to the original PVDF membrane, the omniphobic FS/FAS/Si membrane displays higher rejection (about 99.99%) and superior anti-wetting and anti-fouling characteristics even to the saline feed solution with surfactants, oil pollutants, or hydrophilic organic pollutants in MD process. The results mentioned above verify that the obtained omniphobic FS/FAS/Si membrane has potential application for the desalination of the high saline wastewater containing low surface tension contaminants.

Tuning the molecular design of random copolymers for enhancing the biofouling mitigation of membrane materials

Although a lot has been done on the making of antifouling membranes using PEGylated materials, numerous molecular design improvements can still be made on fine-tuning of both composition and chain length. Here, an antifouling copolymer made of styrene and ethylene glycol methacrylate units (PS-co-PEGMA) was used and the results demonstrate that by altering the molar ratio and chain length PS/PEGMA, it can turn the membrane from low-biofouling to almost entirely fouling resistant. At first, a set of 7 copolymers with a molecular weight in a same range but different compositions was prepared, characterized and was used to modify poly(vinylidene fluoride) (PVDF) membranes by vapor-induced phase separation (VIPS) process. Membranes were fully characterized, and antifouling tests carried out with Escherichia coli, Stenotrophomonas maltophilia and fibrinogen all showed that a 30 mol% polystyrene content in the copolymer (PS30P70) led to the best antifouling properties. Increasing or decreasing the styrene amount resulted in increasing the hydrophobicity of the material or decreasing the stability of the modification, respectively, which outcome in both cases was a higher biofouling. Then, 5 copolymers with a fixed composition but different Mws were prepared, and antifouling tests indicated that the longer the chain, the better the antifouling properties. The chain length is essential to the strength of the hydration layer as supported by both mapping FT-IR and DSC measurements.

Low band-gap energy photocatalytic membrane based on SrTiO3–Cr and PVDF substrate: BSA protein degradation and separation application

A series of ultrafiltration (UF) membranes based on mixed matrix of chromium-doped strontium titanate (SrTiO3–Cr) photocatalyst and polyvinylidene difluoride (PVDF) were systematically prepared by non-solvent induced phase inversion technique. Porous PVDF membrane and mixed matrix membranes (MMMs) incorporated with 3–10 wt% SrTiO3–Cr were produced in the UF range using polyethylene glycol as a porogen additive. The crystal morphology and electronic property of as-synthesized Cr-doped SrTiO3 nanoparticles were characterized by XRD and UV–Vis DRS. We found that the SrTiO3–Cr nanoparticles are cubic perovskite structure of approximately 30–40 nm in size with a low band gap energy of 2.05 eV. The morphology, surface roughness, hydrophilicity and textural properties of SrTiO3–Cr/PVDF MMMs were comprehensively characterized using field emission-scanning electron microscope with energy-dispersive X-ray spectroscopy, atomic force microscope, sessile drop technique, and capillary flow porometer. The SrTiO3–Cr was observed to be homogeneously dispersed in all the MMMs and provided additional anti-fouling properties from Bovine Serum Albumin (BSA) protein. The membrane UF property and tri-cycling performance were evaluated under three distinct protocols in (1) Dark, (2) constant UVA exposure, and (3) UVA during post-treatment clean only. By increasing the SrTiO3–Cr concentration, the MMMs displayed an improved homogeneity and macropore distribution with enhanced water permeability given by 51–110 LMH bar−1 pure water flux and 37 to 45 LMH bar−1 BSA water flux in the Dark. A consistently high BSA rejection of 95% and an improved anti-fouling property under constant UVA irradiation were achieved due to a combination of photo-induced hydrophilic and photocatalytic effect. Also, a significant improvement in UF performance in terms of membrane flux recovery was observed in the 3rd protocol signifying that the effect of protein fouling on membrane filtration was further reduced due to a lower degree of BSA fragment deposition in the membrane pores. The findings in this study dramatically lower the operational constraints (transmembrane pressure, membrane cleaning, use of UVA) in the protein filtration process and offer an innovative membrane material for the research of photo-induced, anti-fouling membranes for protein separation applications.

Comparison of NLDH and g-C3N4 nanoplates and formative Ag3PO4 nanoparticles in PES microfiltration membrane fouling: Applications in MBR

Development of antifouling membranes for wastewater treatment technology can serve as an economic and efficient approach urgently demanded. Attempts have been made to develop cost-effective blended microfiltration membranes containing ZnAlCu nanolayered double hydroxide (NLDH) or g-C3N4 nanosheets, and Ag3PO4 and NH2-Ag3PO4 nanoparticles with the view of finding the effect of their chemical and structural properties on the membranes performance. The obtained ZnAlCu-NLDH/polyethersulfone (PES) and g-C3N4/PES nanocomposite membranes exhibited the significant flux recovery ratio (FRR), as an antifouling index, of 75.8 and 70.7%, respectively, as compared with the pristine PES membrane having 50.9% of FRR. Inclusion of Ag3PO4 and NH2–Ag3PO4 nanoparticles remarkably increased the permeate flux of the membranes, so that the pure water flux of nanoparticles blended membranes at the pressure of 0.5bar was found to be 292.6 and 319.5Lm−2h-1, respectively, as compared with 229.2Lm−2h-1 for the pristine PES microfiltration membrane. Moreover, the fabricated membrane containing Ag3PO4/NLDH and NH2–Ag3PO4/g–C3N4 nanofillers showed a high flux, wettability and antifouling properties, with regard to the prevention of the interaction of the organic foulant and the hydrophilic membranes. Consequently, the self-cleaning property of nanocomposite blended membranes and the low leaching of nanocomposites could lead to the fabrication of a promising mixed matrix membrane for practical wastewater treatment in membrane bioreactors (MBRs). The increase in the critical flux (CF) also showed the desirable application of the nanocomposite microfiltration (MF) in MBR.

New Insights in the Natural Organic Matter Fouling Mechanism of Polyamide and Nanocomposite Multiwalled Carbon Nanotubes-Polyamide Membranes.

Polyamide (PA) membranes comprise most of the reverse osmosis membranes currently used for desalination and water purification. However, their fouling mechanisms with natural organic matter (NOM) is still not completely understood. In this work, we studied three different types of PA membranes: a laboratory made PA, a commercial PA, and a multiwalled carbon nanotube (CNT-PA nanocomposite membrane during cross-flow measurements by NaCl solutions including NOM, humic acid (HA), or alginate, respectively). Molecular dynamic simulations were also used to understand the fouling process of NOM down to its molecular scale. Low molecular weight humic acid binds to the surface cavities on the PA structures that leads to irreversible adsorption induced by the high surface roughness. In addition, the larger alginate molecules show a different mechanism, due to their larger size and their ability to change shape from the globule type to the uncoiled state. Specifically, alginate molecules either bind through Ca2+ bridges or they uncoil and spread on the surface. This work shows that carbon nanotubes can help to decrease roughness and polymer mobility on the surfaces of the membranes at the molecular scale, which represents a novel method to design antifouling membranes.

Development of antimicrobial and antifouling nanocomposite membranes by a phase inversion technique

Abstract Membrane separation technology is preferred over conventional techniques because of its simple operation and high efficiency. The major drawback of using a pristine polymer for membrane application includes its rapid fouling tendency, which affects the separation efficiency of membranes; hence, they need to be modified using physical or chemical techniques. Recent developments involve the incorporation of nanoparticles within the polymer to achieve high efficiency along with stability. The hydrophobic membranes of polyvinylidene fluoride (PVDF) blended with titanium dioxide (TiO2) nanoparticles were synthesized using a phase inversion technique to develop an antifouling membrane. The effects of TiO2 loading on the permeation flux and antimicrobial behavior of the membranes were systematically investigated, and the experimental results were also justified using the theoretical model. Extended Derjaguin–Landau–Verwey–Overbeek, high-resolution scanning electron microscopy, and atomic force microscopy were used to study the membrane morphology. It was observed that the antimicrobial properties of different PVDF/TiO2 ratios against Gram-negative Escherichia coli (E. coli) showed excellent results compared with PVDF membrane. The antimicrobial activity was also evaluated to study the exponential growth phases’ retardation of E. coli over the membrane surface. The experimental result for bovine serum albumin filtration was also studied and high protein rejection was achieved for PVDF/TiO2 (1.5 wt%) membrane.

Zwitterion-Ag Complexes That Simultaneously Enhance Biofouling Resistance and Silver Binding Capability of Thin Film Composite Membranes.

Biofouling can be overcome with zwitterion grafts and antimicrobial, metallic nanoparticles. However, the mechanism underpinning this effective approach remains unclear. To elucidate the role of each component in this system while maximizing membrane antifouling and antimicrobial properties, here we performed a comparative study to investigate the impact of zwitterion type and their interactions with Ag of various states. Two different zwitterions (SO3--based and COO--based) were employed to modify polyamide (PA) thin film composite (TFC) membranes, and the metallized and mineralized membranes were developed via in situ formation of silver (Ag) nanoparticles and deposition of silver chloride (AgCl) particles on the zwitterion-modified TFC membranes. The presence of zwitterions was key to enhance Ag content, resulting in significantly improved antimicrobial and antifouling properties without compromising the nanofiltration separation performance. COO--based zwitterions were found more favorable toward Ag metallization and mineralization compared to SO3--based zwitterions. The underlying mechanisms underpinning this discovery were further revealed using density functional theory (DFT) to reveal Gibbs free energy of the binding between zwitterions and Ag+ ions. This fundamental knowledge is crucial for designing next-generation antibiofouling strategies.

Multifunctional graphene oxide loaded nanofibrous membrane for removal of dyes and coliform from water

In this study, we fabricated a trifunctional polyurethane (PU)/graphene oxide (GO) electrospun membrane for adsorption of organic dyes such as methylene blue (MB) and rhodamine B (RB). Moreover, the prepared membrane showed antifouling property and inhibition against bacteria. The GO modified PU nanofiber shows a maximum adsorption capacity of 109.88 mg/g and 77.15 mg/g towards MB and RB respectively. Theoretical studies confirmed that the dye adsorption is followed pseudo-second-order kinetics and the Langmuir adsorption isotherm. The superhydrophilic PU/10GO membrane exhibits high water flux of 17,706 lm−2hr−1. This membrane also exhibits good antifouling property for separating oil-in-water emulsions with 99.99% separation efficiency. The Mechanism of antifouling was investigated using Hermia model. The results showed that PU/GO membranes also have antibacterial activity against Gram-negative and Gram-positive bacterias. Thus a superhydrophilic nanofibrous antifouling membrane that can reject both organic dye molecule and bacteria from contaminated water is developed using simple electrospinning technique.

Control of Membrane Fouling in Organics Filtration Using Ce-Doped Zirconia and Visible Light.

Membrane fouling has been a major issue in the development of more efficient water treatment processes. Specifically in surface waters filtration, organic matter, such as humic-like substances, can cause irreversible fouling. Therefore, this study evaluates the activity of a photocatalytic layer composed of Ce-doped zirconia nanoparticles in improving the fouling resistance during filtration of an aqueous solution of humic acid (HA). These nanoparticles were prepared by hydrothermal and sol–gel processes and then characterized. Before the filtration experiments, the photodegradation of HA catalyzed by Ce-doped zirconia nanoparticles in dispersion was studied. It was observed that the sol–gel prepared Ce-ZrO2 exhibited higher HA removal in practically neutral pH, achieving 93% efficiency in 180 min of adsorption in the dark followed by 180 min under visible-light irradiation using light-emitting diodes (LEDs). Changes in spectral properties and in total organic carbon confirmed HA degradation and contributed to the proposal of a mechanism for HA photodegradation. Finally, in HA filtration tests, Ce-ZrO2 photocatalytic membranes were able to recover the flux in a fouled membrane using visible-light by degrading HA. The present findings point to the further development of anti-fouling membranes, in which solar light can be used to degrade fouling compounds and possibly contaminants of emerging concern, which will have important environmental implications.

Understanding the Antifouling Mechanism of Zwitterionic Monomer-Grafted Polyvinylidene Difluoride Membranes: A Comparative Experimental and Molecular Dynamics Simulation Study.

The antifouling process of the membrane is very vital for the highly efficient treatment of industrial wastewater, especially high salinity wastewater containing oil and other pollutants. In the present work, the dynamical antifouling mechanism is explored via molecular dynamics simulations, while the corresponding experiments about surface properties of the zwitterionic monomer-grafted polyvinylidene difluoride membrane are designed to verify the simulated mechanism. Water can form a stable hydration layer at the grafted membrane surface, where all the simulated radial distribution function of water/membrane, hydrogen bond number, water diffusivity, and experimental oil contact angles are stable. However, the water flux across the membrane will increase first and then decrease as the grafting ratio increases, which not only depends on the reduced pore size of the zwitterionicmonomer-grafted membrane but also results from water diffusion. Furthermore, the dynamical fouling processes of pollutants (taking sodium alginate as an example) on the grafted membrane in water and brine solution are investigated, where both the high grafting ratio and electrolyte CaCl2 can enhance the fouling energy barrier of the pollutant. The results show that both the enhanced hydrophilic property and the electrostatic repulsion can affect the antifouling capability of the grafted membrane. Finally, the ternary synergistic antifouling mechanisms among the zwitterionic membrane, electrolyte, and pollutant sodium alginates are discussed, which could be helpful for the rational design and preparation of new and highly efficient zwitterionic antifouling membranes.

Sustaining fouling resistant membranes: Membrane fabrication, characterization and mechanism understanding of demulsification and fouling-resistance

Antifouling performance of membranes is the key obstacle limiting their practical applications for oil/water separation. In this study, a sustaining antifouling membrane was fabricated by constructing polydopamine (PDA) micro-/nano-spheres on a polyacrylonitrile (PAN) nanofibrous membrane. The secondary PDA nano-spheres not only strengthened the bonding of primary micro-spheres with the substrate, but also diversified the hierarchical structure and chemistry. The composite showed enhanced superhydrophilicity and underwater superoleophobicity. Permeability of PAN-PDAc membrane was maintained as high as 11666 ± 978 Lm−2h−1bar−1 with separation efficiency of higher than 99.9% over a 2-h continuous filtration. This permeability was about 2.7 times of pristine PAN membrane (4260 ± 430 Lm−2h−1bar−1). The extrusion and cutting demulsification on the confined space of PAN-PDA surface was proposed. Antifouling mechanism of the superhydrophilic membrane was first theoretically elucidated based on hydration ability and adhesion free energy with recourse to thermal analysis and Derjaguin-Landau-Verwey-Overbeek theory respectively. It was found that PDA micro-/nano-spheres mediated membrane showed strong hydration ability (higher fraction of non-freezable water) and weak adhesion towards toluene (low free energy of adhesion) compared to pristine PAN membrane. These findings would lead to a better understanding of antifouling demulsification mechanism and improved design of sustaining antifouling membranes for oil/water separation.

Fabrication and characterization of a high-flux and antifouling polyethersulfone membrane for dye removal by embedding Fe3O4-MDA nanoparticles

Iron oxide (Fe3O4) magnetic nanoparticles were successfully synthesized and functionalized with (3-aminopropyl) triethoxysilane (APTES) and melamine-based dendrimer amine (MDA) groups. The resulted nanocomposites and unmodified Fe3O4 were characterized using scanning electron microscopy (SEM), Fourier transform infrared (FTIR), X-ray diffraction (XRD), and vibrating sample magnetometer (VSM) and then, added to the polyethersulfone (PES) membrane casting solution, during the phase inversion technique in order to improve its hydrophilicity, permeability, and antifouling properties. Surface and cross-sectional morphology of the resulted bare and nanocomposite membranes were characterized by SEM images. The effect of blended nanoparticles on membrane hydrophilicity and performance were determined using water contact angle, pure water flux, BSA solution filtration, and Reactive Green 19 dye solution rejection. The water contact angle for the bare PES, PES-Fe3O4 (0.5 wt%), PES-Fe3O4-APTES (0.5 wt%), and PES-Fe3O4-MDA (0.5 wt%) were measured to be 60.31°, 51.08°, 44.86°, and 37.18°, respectively. The pure water flux of the blended PES membranes was enhanced significantly compared to the bare PES due to the higher hydrophilicity. The results of fouling resistance factors including reversible, irreversible, and total fouling showed PES-Fe3O4-MDA (0.5 wt%) as the best antifouling membrane. Compared to the all fabricated membranes, PES-Fe3O4-MDA (0.5 wt%) showed the highest hydrophilicity, permeability, rejection, and antifouling properties.

Impacts of applied voltage on EMBR treating phenol wastewater: Performance and membrane antifouling mechanism

The impacts of electric field applied in MBR (EMBR) for treating phenol wastewater and membrane antifouling mechanism were systematically investigated. Phenol degradation rate increased from 0 to 0.8 V/cm, while decreased from 0.8 to 1.75 V/cm, which significantly positively correlated with key enzymes. The membrane fouling rate of EMBR gradually slowed down with voltage increasing. The applied voltage significantly reduced EPS contents, and altered its compositions probably due to H2O2 oxidation, which were the major reasons for membrane antifouling. Red shift in UV–Vis spectrum at 210–220 nm and reduction of fluorescence emission intensity from tryptophan protein-like substances in EPS reduced the energy requirement for electrons transition of electron-donating groups with voltage increasing. Positively charged bond NH2 decreased and negatively charged bond COO increased in EPS with voltage increasing, which led to the increase of absolute value of zeta potential and then remarkable augmented of electrostatic repulsion between sludge and membrane.