Excellent Antifouling Performance Research Articles

Enhancement of antifouling and separation properties of poly(m-phenylene isophthalamide) hybrid ultrafiltration membrane using highly crystalline poly(heptazine imide) nanosheets

A highly crystalline phase g-C3N4, namely poly (heptazine imide) (PHI) was synthesized using molten salts. A high-performance ultrafiltration membrane was prepared by blending PHI nanosheets with Poly(m-phenylene isophthalamide) (PMIA) to obtain casting solution, and further prepared by phase conversion method. Hybrid PMIA membranes were prepared by incorporating 0.02–0.10 wt% of PHI, which were further characterized by SEM, AFM, XRD, FTIR, XPS, TGA and surface zeta potential. The hydrophilicity, water flux, and rejection of bovine serum albumin (BSA) of the membrane significantly increased. For instance, the water permeability of M4 (264.6 Lm−2h−1bar−1) was about 2.3 times that of bare PMIA membrane (113.6 Lm−2h−1bar−1), while maintaining a BSA rejection of 94.7 % for a 1000 mgL−1 BSA feed solution. Moreover, the M4 membrane showed excellent antifouling performance with a flux recovery rate of up to 88.7 % and lower irreversible fouling of 11.3 %. This study may provide reference for the modulation of highly crystalline g-C3N4 structure and its application in membrane fabrication for water treatment.

Dual defense against membrane fouling for efficient and sustainable oil/water separation on a novel super-hydrophilic/underwater superoleophobic and catalytic nanofibrous membrane

Membrane separation technology is widely recognized as an efficient method for treating organically polluted wastewater in virtue of high performance and straightforward operation. However, the practical application of membranes is inevitably confronted with contamination issues, presenting a major challenge in terms of fouling resistance. To address this issue, a defensive-offensive dual-defense strategy based on wettability and catalytic ability control is proposed. With this concept, a novel nanofibrous membrane with a unique structure was successfully prepared through polyacrylonitrile (PAN) electrospinning, pre-oxidation, CoFe Prussian blue analogue (PBA) and polypyrrole (PPy) modification, and calcination processes. For the passive defense mode, the as-prepared membrane has shown good underwater-superoleophobicity for various types of oils, good separation capability for corresponding oil–water emulsions with retention ratios of above 99 % and fluxes ranging from 231.5 to 1524.2 L·m−2·h−1·bar−1, as well as organic solvent (dimethylformamide, DMF) resistance. For the offensive defense mode, this membrane exhibits well catalytic degradation performance for refractory pollutants with the assistance of peroxymonosulfate (PMS), which is due to the membrane being decorated with catalytic nanoparticles that contain abundant encapsulated ultra-small Fe doped Co3O4 (∼2.28 nm), and that is much smaller than the size of the pristine PBA (∼33.8 nm). Notably, the surfactants present in oil-in-water emulsions are found to be the main cause of membrane fouling, where the cationic surfactants exhibit the most significant fouling effect, while the introduction of photo-Fenton-like catalysis can endow the membrane with excellent antifouling performance and extended service life, and nearly a fully recover of emulsion separation performance was achieved. Overall, this work paves pathways to the design of advanced membranes for sustainable wastewater treatment.

A self-healing polyurethane/imidazole-modified carboxylated graphene oxide composite coating for antifouling and anticorrosion applications

Marine corrosion and biofouling present significant challenges to maintaining maritime vessels and oceanic infrastructure. Developing coatings that integrate anti-fouling, anti-corrosion, and self-healing properties remains a critical issue. This study introduces imidazolium-modified carboxylated graphene (FCGO) into polyurethane coatings (F-PUSS) containing disulfide bonds to address this challenge. The incorporation of FCGO significantly enhances the mechanical properties of the coating, improving tensile stress by 40 % to 20.97 MPa. The barrier properties of FCGO also provide strong corrosion resistance, with |Z|0.01Hz values an order of magnitude higher than the original samples, even after 15 days of immersion in sodium chloride (3.5 wt%). Additionally, F-PUSS retains corrosion resistance after repairs. The synergistic action of imidazole groups and graphene provides excellent antifouling performance with nearly to an alga rate of 100 % and an antimicrobial rate of 96 %. F-PUSS demonstrates remarkable self-healing capabilities, with a healing efficiency of 78 % after 48 h at 60 °C. This study provides valuable insights for designing multifunctional polymer materials with anti-fouling, anti-corrosion, and self-healing functions.

Superamphiphilic aerogels with 2D lamellar structure of gelatin-tuned 3D supramolecular network of collagen fibers for high-performance separation of surfactant-stabilized emulsified oily wastewater

Superwetting aerogel is a promising alternative for the remediation of emulsified oily wastewater for its high porosity combined with extreme wettability enabled high separation performances to emulsion wastewater. However, it remains challenging for superwetting aerogels to accomplish high-performance dual separation to surfactant-stabilized oil-in-water (O/W) and water-in-oil (W/O) emulsions with high stability. Herein, an environmentally benign superamphiphilic composite aerogel was prepared by a green synthesis route that relied on the utilization of natural amphiphilic biomass. Collagen fibers (CFs) were utilized to construct the three-dimensional (3D) supramolecular skeleton of aerogel to provide high storage capacity of water/oil and outstanding capillary effect to boost the mass transfer. The two-dimensional (2D) lamellar structure of gelatin (Gel) was further grown on the skeleton of CFs aerogel to play the role for simultaneously enhanced demulsifying capability and spreading of emulsions. The as-prepared superamphiphilic aerogel enabled the separation of highly stable surfactant-stabilized O/W and W/O emulsions with high separation efficiency and flux. Excellent recycling performances and anti-fouling performance were also confirmed. Our investigations therefore demonstrated that the structural engineering of superamphiphilic aerogel is a promising way to realize high-performance dual separation of surfactant-stabilized O/W and W/O emulsion wastewater.Graphical

Construction of CS-SDAEM long-chain polysaccharide derivative on TA@CNTs coated PVDF membrane with effective oil-water emulsion purification and low contamination rate

Currently, the most effective way to improve the anti-fouling performance of water treatment separation membrane is to enhance the hydrophilicity of the membrane surface, but it can still cause contamination, leading to the occurrence of flux reduction. The construction of a strong hydration layer to resist wastewater contamination is still a challenging task. In this study, a defect-free hydration layer barrier was achieved by grafting chitosan polysaccharide derivatives (CS-SDAEM) on the membrane, which achieved in effective fouling prevention and low flux decline rate. A layer of tannic acid-coated carbon nanotubes (TA@CNTs) has been uniformly deposited on the commercial PVDF membrane so that the surface was rich in -COOH groups, providing sufficient reaction sites. These reactive groups facilitate the grafting of amphiphilic polymers onto the membrane. This modification strategy achieved in enhancing the antifouling performance. The modified membrane achieved low contamination rate with DR of 16.9 % for wastewater filtration, and the flux recovery rate was above 95 % with PWF of 1100 (L·m−2·h−1). The membrane had excellent anti-fouling performance, which provided a new route for the future development of water treatment membrane.

Eco-friendly, highly interpenetrated and slightly swollen pHEMA hydrogel foam for durable underwater superoleophobicity and emulsion separation

Despite the emergence of hydrogels as ideal candidates for preparing the superhydrophilic materials for emulsion separation, their structural stability and swelling still hinder their long-term use, mainly due to structure defects after swelling. Herein, differing from the common modification, the eco-friendly poly 2-hydroxyethyl methacrylate (pHEMA) hydrogel foam was designed and synthesized via a one-step strategy by using the high internal phase emulsion (HIPE) template method, which endowed it with a highly interpenetrated porous structure. Unlike the normal swellable hydrogels such as poly(N-isoproplyacrylamide) (PNIPAM) hydrogel, or modified hydrogel coatings, the pHEMA hydrogel foam displayed stable structure and underwater superoleophobicity after 20 d of immersion in water. The pHEMA hydrogel foam could separate different kinds of highly surfactant-stabilized oil-in-water (O/W) emulsions with a high separation efficiency of 99.3% for liquid paraffin emulsion obtained solely under gravity-driven. Additionally, it exhibited excellent antifouling performance and long-term acid/alkali tolerance over 100 h without decrease in emulsion separation efficiency (98.0%, oil/water ratio of 99:1) and permeation flux (over 2000 L·m−2·h−1) attributed to its stable bulky structure. Moreover, the pHEMA hydrogel foam demonstrated high cell viability of 96.87% and 95.96% after culturing the 3T3 clone A31 cells in the pHEMA hydrogel foam for 24 h and 48 h, respectively, indicating good biocompatibility. Hence, our work provides a new design to develop an eco-friendly bulk hydrogel foam that achieves stable structure and performance for emulsion separation.

An electrospun iron oxychloride/polyacrylonitrile nanofibrous membrane with superhydrophilic and excellent regeneration properties: Achieving superior oil-in-water emulsion separation

Superhydrophilic polymer membranes are widely used in oil-water separation due to their excellent wettability, high efficiency, low cost, and good biocompatibility. However, challenges such as fouling adhesion and inadequate stability persist during the treatment of oily wastewater. Herein, a novel iron oxychloride/polyacrylonitrile (FeOCl/PAN) nanofibrous membrane with superhydrophilicity and remarkable regenerability was successfully fabricated through simple electrospinning technique, which maintained good physicochemical stability under various harsh conditions with the uniform distribution of FeOCl on PAN fibers. The surface morphology and chemical compositions of the optimized FeOCl/PAN membrane were studied by several characterization techniques. The introduced FeOCl nanocrystals through electrospinning endowed the membrane with a rougher surface structure, significantly improving the hydrophilicity of the FeOCl/PAN nanofibrous membrane. In the cross-flow isooctane-in-water emulsion separation experiment, the initial water flux recovery rate (FRR) of the membrane increased from 92 % for the pure PAN membrane to around 99 %. Meanwhile, the optimized FeOCl/PAN nanofibrous membrane achieved an emulsion (isooctane) flux of approximately 632.9 L m−2 h−1, with an oil droplet removal rate surpassing 99.4 %. Furthermore, by cleaning the membrane with H2O2 (60 mM, pH = 3), the FeOCl/PAN membrane exhibited an exceptionally high water flux recovery rate (∼100 %) after high-concentration paraffin-in-water emulsion (4000 mg L−1) separation. In addition, the FeOCl/PAN membrane also demonstrated excellent antifouling performance in bovine serum albumin (BSA) pollution experiment. In summary, this work might provide a unique strategy for preparing advanced functional membranes with superior efficiency and durability for emulsified oily wastewater treatment.

Polyvinylidene fluoride-based loose nanofiltration membrane with graphene oxide intercalation for efficient small organic molecules desalination

Graphene oxide (GO) loose nanofiltration (LNF) membranes show immense potential for the desalination of small organic molecules. However, it remains a significant challenge to compare the performance of GO LNF membranes prepared via different doping methods and study the mechanisms that influence the separation abilities of the membranes. In this study, LNF membranes prepared via three GO doping methods were examined for flux, retention rate, and the separation performance of small organic molecules and inorganic salts. The membranes coated with dopamine (DA) and GO, and subsequently formed polydopamine (PDA)–GO intercalation, showed the best results. A novel LNF membrane material (PVDF/PDA–GO–TFN; PVDF: polyvinylidene fluoride, TFN: thin-film nanocomposite) was developed to enhance the separation performance of small organic molecules and inorganic salts while improving membrane surface stabilization and anti-fouling performance and reducing the “trade-off” effect. The optimal conditions for PDA–GO intercalation and the best combination for interfacial polymerization (IP) were also determined. The intercalation structure was identified via scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, atomic force microscopy, and Fourier-transform infrared spectroscopy. Furthermore, the separation mechanism of the membrane was determined to be based on the Donnan and steric hindrance effects, according to the correlation analysis of the membrane surface electrical properties (zeta potential), hydrophilicity (contact angle), and pore properties. The PVDF/PDA–GO–TFN LNF membrane displayed a maximum water permeance of 10.45 L/(m2·h·bar), with an 88 % rejection of PEG2000 and a 6.83 % rejection of Na2SO4. Moreover, the membrane exhibited excellent anti-fouling performance and long-term stability, with a mean flux recovery rate of 99.06 % after four cycles of filtration and backwashing tests using small organic molecules and inorganic salt solutions. The inorganic salt retention rate was analyzed using SPSS software, and the results indicated excellent membrane stability. In summary, the preparation of PVDF/PDA–GO–TFN membrane materials provides a novel approach for fabricating LNF membranes that can effectively separate small organic molecules and inorganic salts.

Hydrophilic coating of membrane by UV-induced radical and cationic curing of photosensitive resins: Lower shrinkage, smoother surface and better anti-fouling performance

Hydrophilic coating is frequently used to enhance the anti-fouling performance of membrane. However, traditional strategies often suffer from defects of cumbersome steps, high energy consumption, and unstable coating. Herein, radical and cationic photopolymerization are used for hydrophilic coating of membranes. Two photosensitive resins were first synthesized either by direct radical copolymerization of 3-ethyl-3-(methacryloyloxy) methyloxetane and 2-hydroxyethyl acrylate (Poly(HEA-EMO)) or through post-polymerization modification of poly(2-hydroxyethyl acrylate) with vinyl groups (Poly(HEA-MA)). Subsequently, hydrophilic coating was conducted on the membrane surface by UV-induced curing of different photosensitive resins, either through radical photopolymerization of vinyl-functional Poly(HEA-MA) or cationic photopolymerization of Poly(EMO-HEA) with pendent oxetane groups. The modified membranes showed enhanced hydrophilicity and underwater oleophobicity than the original membrane. Moreover, the coating (PAN / HEA(C5)) by cationic photopolymerization exhibited lower shrinkage, smoother surface, and more excellent antifouling performance than that by radical photopolymerization. After bovine albumin fouling-cleaning cycles, the flux recovery rate (FRR) of the original membrane was only 68.6 %, while the FRR of PAN / HEA(C5) was as high as 98.0 %. Furthermore, it showed superior long-term operational stability, proving the stability of the coating formed by cationic photopolymerization.

High antifouling graphene membranes with Fe2O3 nanoparticles in-situ intercalation for selective dye/salt separation

Effective organic dyes selective separation from high salinity textile wastewater consisting of inorganic salts and organic dyes is of great significant for the textile wastewater treatment. Graphene oxide (GO) have been used widely to form ultrathin high-permeance membrane for molecular and ionic sieving. However, swelling and membrane fouling of GO membrane hampered its practical applications. In this work, high stability and antifouling reduced graphene oxide (rGO) membranes were prepared, and Fe2O3 nanoparticles was used as intercalation to turn the membrane interlayer spacing. The rGO/2Fe2O3 nanocomposite blended membrane exhibited high permeance of 24.90 L m−2 h−1 bar−1, excellent organic dyes rejection (98.15 % and 98.69 % for methylene blue and Evans blue, respectively) and low salt retention (6.26 % for NaCl). Meanwhile, this membrane demonstrated a superior selective dye/salt separation factor up to 232 with a high rejection of 99.59 % to Evans blue and a lower salt rejection of 5.03 % to NaCl. Furthermore, nanofiltration experiments towards Evans blue/NaCl mixed solution indicated that the membrane also exhibited excellent antifouling performance with flux recovery rate of >86 % after six fouling/backwash cycles. Therefore, our work may provide a promising idea for the development of two-dimensional nanofiltration membranes for efficient high salinity textile wastewater treatment.

Multi-bionic strategy combined with surface for anti-fouling

More and more bio-inspired methods are used to obtain anti-fouling surfaces, in which the structure plays a pivotal role in bionic coatings. It is a trend to prepare dynamic anti-fouling surfaces to improve the anti-fouling performance of the surface and synthesis the large-scale surface. Therefore, based on the special multilevel structure of Folium Sennae, the Folium Sennae-inspired surface was prepared and modified by the active molecule from Folium Sennae here (GFSF-x, AGFSF-y). Based on the excellent anti-fouling of Folium Sennae-inspired surfaces, a series of arrayed dynamic surfaces with structure-controlling liquid behavior were prepared (VMxFy). Among them, AGFSF-5 shows an excellent anti-fouling performance, whose anti-diatom attachment rate is as high as 97.8 %. The arrayed-structured coatings (MxFy) exhibit an ability to hinder the adhesion of plaque in mussel adhesion experiments. In addition, the inhibition attachment rate of diatoms of AGMPF-4 (MxFy was subjected to optimal concentration assembly) is 83.7 %, while it is 99.5 % of VMxFy. Besides, the liquid grows dynamically along the arrayed structure, and the height of VMNF-4 increased from 15.12 to 206.26 μm. The bio-inspired surfaces based on the two methods here show outstanding anti-fouling ability, in particular, the arrayed-structured surface controlling liquid behavior. This study provides a new idea for the construction of dynamic structural surfaces and shows the practical application potential due to its ability to large-scale surface texture.

Scalable multifunctional MOFs-textiles via diazonium chemistry

Cellulose fiber-based textiles are ubiquitous in daily life for their processability, biodegradability, and outstanding flexibility. Integrating cellulose textiles with functional coating materials can unlock their potential functionalities to engage diverse applications. Metal-organic frameworks (MOFs) are ideal candidate materials for such integration, thanks to their unique merits, such as large specific surface area, tunable pore size, and species diversity. However, achieving scalable fabrication of MOFs-textiles with high mechanical durability remains challenging. Here, we report a facile and scalable strategy for direct MOF growth on cotton fibers grafted via the diazonium chemistry. The as-prepared ZIF-67-Cotton textile (ZIF-67-CT) exhibits excellent ultraviolet (UV) resistance and organic contamination degradation via the peroxymonosulfate activation. The ZIF-67-CT is also used to encapsulate essential oils such as carvacrol to enable antibacterial activity against E. coli and S. aureus. Additionally, by directly tethering a hydrophobic molecular layer onto the MOF-coated surface, superhydrophobic ZIF-67-CT is achieved with excellent self-cleaning, antifouling, and oil-water separation performances. More importantly, the reported strategy is generic and applicable to other MOFs and cellulose fiber-based materials, and various large-scale multi-functional MOFs-textiles can be successfully manufactured, resulting in vast applications in wastewater purification, fragrance industry, and outdoor gears.

In-situ grown ZnO-nanorods of slippery liquid-injected porous surface coating on Mg alloy with hydrophobic, durable, and anti-corrosion properties

In this work, an in-situ self-grown nano-ZnO/epoxy-based slippery lubricant liquid-injected porous surface (SLIPS) coating with a unique bilayer structure is reported to achieve robustness, hydrophobicity, and anti-corrosion properties. Dense epoxy coated ZnO nanoparticles are used as the anti-corrosion barrier layer. Self-grown ZnO nanorods provide a robust micro- and nano-rough porous structure. The lubricant perfluoropolyether (PFPE) is strongly locked into the porous structure via low surface energy material pretreatment and capillary effect. This SLIPS coating has a high water contact angle (WCA) value and has excellent repellency to various liquids. The SLIPS surface maintains a high contact angle of more than 115° even after 20 days of immersion in corrosive solutions and withstand the erosion of corrosive solutions with pH = 3. It also has a very low corrosion current density of 8.97 × 10−12 A/cm2 and the Rct (the charge transfer resistance) of optimum SLIPS remained 1.41 × 108 ohm cm2 after 70 days immersion in 3.5 wt% NaCl solution, which is in the same order of magnitude as the initial value. The SLIPS coating with excellent mechanical stability, super-hydrophobicity, anti-fouling, chemical stability, and long-term corrosion resistance performance possesses tremendous application potential in long-term corrosion protection of Mg alloys.

Ethanol activation of polyester membrane for superior dye/salt separation performance

Dye wastewater poses a severe danger to the environment and human health. The purification of dye wastewater is the focus and hotspot of most researchers. In this work, ethylene glycol (EG) was selected as an aqueous phase monomer to fabricate polyester membranes through an interfacial polymerization reaction. Then the polyester membrane was activated by ethanol aqueous solution. By adjusting the activation time and concentration of the ethanol, the network of the polyester membrane can be reshaped to endow the membrane with excellent performance. The activation mechanism was also explored here. Compared to the membrane without activation (PE-0%), the permeability of the optimized membrane (PE-40%) was increased by 8.3 times, and a high rejection was maintained (CR: 99.2%). Importantly, the PE-40% membrane also presented good acid and alkali resistance, chlorine resistance, and excellent antifouling performance. Our work provides an effective and feasible strategy for the development of high-performance polyester membranes.

Green maltitol-based nanofiltration membranes featuring high permeance and excellent anti-fouling performance for dye desalination

Polyester loose nanofiltration (LNF) membranes are ideal for achieving dye resource recovery. However, the low permeance and insufficient selectivity of dye/salts for polyester membranes remained a significant challenge. This work employed a low reactivity, hydroxyl-rich, non-toxic, inexpensive and renewable, and larger volume green material maltitol (ML) as an aqueous monomer for preparing high-performance polyester membranes. The ML-based membranes had a smooth surface with a considerable negative charge and strong hydrophilicity. The optimized ML-based membranes (ML-1.0/TMC) possessed remarkable water permeance (104.9 L m−2 h−1 bar−1) and excellent dye/salt selectivity (selectivity for CR/NaCl was 340). Additionally, the ML-1.0/TMC membrane demonstrated outstanding stability and excellent anti-fouling performance. The results indicated that the ML-based membranes had excellent performance in dye filtration tests, demonstrating the great potential of ML-based membranes for dye wastewater resource recycling.

Fouling-Free electrochemical strategy based on vertically-aligned peptide layer for cardiac troponin I sensitive detection in human serum

BackgroundCardiac troponin I (CTnI) is demonstrated as one of the most promising disease biomarkers for early diagnosing acute myocardial infarction (AMI). To date, electrochemical immunosensors have been extensively studied in the field of cTnI determination. But highly accurate and sensitive cTnI detection by this method is still a challenge due to non-specific adsorption on electrode interfaces in complex human serum. As a result, it is necessary to develop an antifouling electrochemical immunosensor with high sensitivity for the detection of cTnI. ResultsIn this work, an antifouling electrochemical immunosensor was constructed based on vertically-aligned peptide layer consisting of Au nanoparticles (AuNPs) and amphiphilic CEAK16 peptide (CEAK16@AuNPs) for sensitive and accurate detection of cTnI in human serum. The vertically-aligned CEAK16@AuNPs interface provided a stable hydration layer originated from attraction of water molecules by amino acids on the hydrophilic side of the CEAK16, which effectively reduced non-specific adsorption and enhanced electron transfer rate. The cTnI immunosensor possessed great analytical performance with a wide range from 1 fg mL−1 to 1 μg mL−1 and a low detection limit of 0.28 fg mL−1 (S/N = 3). Additionally, the proposed CEAK16@AuNPs sensing interface showed excellent long-term antifouling performance and electrochemical activity that preserved 80 % of the initial signal after 20-days exposure in human serum samples. Consequently, the cTnI immunosensor displayed excellent detection accuracy compared to clinical methods and owned good selectivity, stability and reproducibility. SignificanceThe development of this strategy provides a versatile tool for accurate quantitative cTnI analysis in real human serum, thus helping to achieve early AMI diagnosis effectively and holding the promising potentials for other immunosensor in disease diagnosis.

Three-dimensional zwitterionic hydrogel-based evaporators with simultaneous ultrahigh evaporation rates and anti-fouling performance

Zwitterionic hydrogels (ZHs) are commonly adopted as evaporators to address the issues of low evaporation rate and poor salt resistance in solar-driven interfacial desalination due to their unique anti-polyelectrolyte (AP) effect. However, the inherent limitations of ZHs, including low water transfer rates compared to their evaporation rates and poor mechanical properties, have restricted their applications to two-dimensional (2D) evaporator configurations. Herein, we proposed a unique design of three-dimensional (3D) composite solar evaporators based on ZHs and polyvinyl alcohol (PVA) sponge to improve the water transfer capacity and mechanical properties of ZHs, and thus achieve ultrahigh evaporation rates and excellent anti-fouling performance. The porous structure and super hydrophilicity of PVA sponge endowed the prepared 5-cm-high ZH-based solar evaporators (ZHSE) with water transfer rates significantly faster than those without PVA sponge. In addition, the elastic PVA sponge component enhanced the mechanical properties of ZHSE, allowing it to easily fabricate 3D structures to obtain higher evaporation rates. Moreover, PVA sponge barely weakened the AP effect of poly(sulfobetaine methacrylate) (PSBMA) hydrogels in the ZHSE. Consequently, the evaporation rate of ZHSE reached 4.66 kg m-2 h-1 at 3.5 wt%, one of the highest among previous reports, attributed to the contributions from the 3D structural design of the evaporator and AP effect of ZHs. Meanwhile, ZHSE showed outstanding anti-fouling properties and excellent shape stability, working in 20 wt% brine ten hours a day for ten consecutive days without noticeable salt deposition and volume shrinkage. This work provides a new route to design high-performance hydrogel-based evaporators with high water transfer rates.

Positively charged nanofiltration membranes with gradient structures for enhancing separation properties

Creating a gradient structure in a separation layer is an effective approach for enhancing separation performance of thin film composite membranes. Here we present the preparation of a positively charged nanofiltration membrane with a gradient structure. An inner layer consisting of a loose polyester separation layer with large pores was formed through the interfacial polymerization (IP) reaction between triethanolamine (TEA) and trimesoyl chloride (TMC). And a dense and thin top layer composed of a polyamide separation layer was obtained by secondary interfacial polymerization (SIP) reaction using polyethyleneimine (PEI) along with unreacted TMC and residual acyl chloride groups of IP reaction. The influences of TEA concentration, PEI concentration and SIP time on the physicochemical properties and separation performances of the membrane were systematically analyzed. Our results show that the presence of the gradient structure optimized mass transfer pathways and reduced mass transfer resistance, resulting in significantly improved permeability of 13.0 ± 0.5 L·m−2·h−1·bar−1 (over 3 times compared with control-PEI), high MgCl2 rejection of 91.7 ± 0.6 %, and an excellent stability and anti-fouling performance. Our work provides valuable insights and guidance for developing high-performance positively charged NF membrane with gradient structures.

Novel highly permeable ultrathin polyamide composite membrane with interfacial polymerization of 4,6-diaminoresorcinol for molecular separation

Developing ultrathin polyamide thin-film composite (PA TFC) membrane with ultrahigh performance to overcome the perm-selectivity upper bound of molecular separation is still the major challenge for practical applications. Herein, we first designed an ultrahigh performance PA TFC membrane fabricated by interfacial polymerization of 4,6-diaminoresorcinol dihydrochloride (DAR) and trimethyl chloride (TMC) on the substrate. The structural morphology of the PA active layer and the separation performance of the resultant membrane were tuned by DAR dosage. This ultrathin PA TFC membrane breaks the trade-off between water permeance and dye (NOM) selectivity. Accordingly, the optimal membrane had a water flux of 212.5 LHM/bar with superior rejection of 98.6 % and 100 % for BBR and CR, respectively, surpassing the upper-bound limit of most reported polymeric membranes thus far. The membranes also exhibited a high salt passage (>95 %), achieving an impressive screening capacity for the dye/salt mixture as well as excellent antifouling and operation stability performance. This work sheds light on the regulation of the PA selective layer via new amine monomer featuring ultrahigh performance.

The preparation of electrically-enhanced and hydrophilic CNTs-PVDF composite hollow fiber membranes for fouling resistance

The anaerobic membrane bioreactor has great potentials to treat the wastewater with high organic matter due to the efficient anaerobic digestion process and high biomass retention. However, the existence of membrane fouling significantly increases the maintenance cost, and always requires frequent and complex cleaning process to recover the membrane performance. Thus, it is significant to fabricate a membrane with excellent anti-fouling performance for the application in membrane bioreactors. Herein, we prepared the CNTs-PVDF hollow fiber membrane with fouling resistance via loading the conductive CNTs coating on the surface of commercial PVDF membrane by a simple cross-linking reaction with hydrophilic polyvinyl alcohol and succinic acid. “Dual defense” was constructed by the combination of the hydrophilic surface and conductive CNTs coating, which lifted the anti-fouling performance of this membrane. In the assistance of electrical effect, the permeance of the membrane with −1.2 V bias could be recovered to 95 % of original state by simple hydraulic cleaning, while that of the membrane without bias was only 58 % after filtrating the sludge of 2000 mg/L. Furthermore, this membrane also exhibited the superior stability and fouling resistance in the operation of anaerobic electrochemical membrane bioreactor, which was promising for the advanced water treatment.