Membrane Surface Hydrophilicity Research Articles

Synergistic effects of matrix-anchoring and surface-segregation behavior of poly(N-vinylpyrrolidone)-grafted-silica filler for PVDF membrane performance improvement

Three dimensional (3D) poly(N-vinylpyrrolidone)-grafted-mesoporous silica (MS-g-PVP) was first synthesized, and explored as a filler for enhancing filtration performance of poly(vinylidene fluoride) (PVDF) composite membrane in this study. Membrane structure, interfacial property and filtration performance of the composite membranes were studied in detail. The relationships of mesoporous silica properties with membrane performance was systemically revealed. The 3D morphology of MS-g-PVP, that stably anchored in PVDF, endowed the membrane with defects-free, uniform and straight finger-like pores structure, and thus greatly enhanced water flux (maximized to 80.7 L m-2h−1, over 5.7 times than that of pristine PVDF membrane), without BSA rejection efficiency changing (98.6%). Three reasons can be accounted for the membrane performance improvement: i. The hydrophilic MS-g-PVP well dispersed in PVDF membrane matrix, and facilitated the formation of the evenly porous structure for the composite membrane; ii. Surface segregation of MS-g-PVP with the amount and diversity of oxygen-/nitrogen-containing groups on membrane surface, thus improving membrane surface hydrophilicity with contact angle decreasing from 89.0° to 70.6°; iii. Numerous mesopores inside of MS-g-PVP provided additional water pathways. In addition, these synergistic effects also enhanced the fouling-resistance of PVDF/MS-g-PVP membrane, whose flux recovery ratio maintained at 85.8% even after three “fouling-cleaning” dynamic BSA solution (0.2 g L-1) filtration cycles.

Functionalization of reverse osmosis membrane with titania nanotube and polyacrylic acid for enhanced antiscaling properties

Membrane surface scaling is a major challenge in reverse osmosis (RO) desalination process that could irreversibly deteriorate the membrane filtration efficiency. In this study, a hydrophilic coating layer was introduced onto the polyamide (PA) layer of self-developed thin film nanocomposite (TFN) membrane via plasma enhanced chemical vapour deposition (PECVD) technique to increase the membrane surface energy barrier and hydrophilicity towards silica heterogeneous nucleation. The results revealed that the acrylic acid-coated TFN membrane (AA-TFN) exhibited excellent resistance against silica scaling after subjected to saturated silica concentration (168 ppm at pH 6.7), with much higher flux recovery rate (FRR) (88%) compared to the uncoated TFN (75.5%) and conventional thin film composite (TFC) (72%) membranes. This is attributed to its enhanced surface hydrophilicity (contact angle of 26°) and better surface charge (zeta potential of −47 mV at pH 6.7) upon the hydrophilic coating layer deposition which retards the scale deposition. The membrane scaling can be further reduced by increasing the feed pH and at the optimized condition (pH 10), the FRR of AA-TFN membrane could reach up to 98.3%, owing to the increased silica solubility at alkaline condition which minimizes the silica aggregation formation on the membrane surface. Our work demonstrated that surface modification of composite membrane using suitable materials and proper feed pH adjustment could offer a great promise in mitigating the scaling for desalination applications. The findings also provide fundamental insights on the importance of membrane surface properties during silica scaling formation.

Polydopamine modification of high-performance PVDF ultrafiltration membranes prepared by the combined crystallisation and diffusion (CCD) method

Polyvinylidene fluoride (PVDF) membranes produced by the recently developed combined crystallisation and diffusion (CCD) method have a magnitude higher in pure water fluxes than those produced via the conventional membrane manufacturing technology. However, in the research so far, most of the PVDF CCD membranes are hydrophobic, easy to be fouled in filtration applications. Herein, we apply the popular polydopamine (PDA) modification technique to improve the hydrophilicity of PVDF CCD membranes to ensure that their high permeation performance is maintained even in foulant-rich environments. Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray (EDX) analysis were used as characterisation techniques to understand the dynamics of the PDA deposition process. The results showed that an increase in modification time does clearly improve the membrane surface hydrophilicity, but suffers in its permeability, as an inevitable consequence of the increased pore blockage by the deposited PDA layer. Because of this, even in the fouling studies, the sample modified for a shorter duration (2 h) and not longer duration (12 h or 24 h) showed the best overall permeation performance. The permeation results from the fouling study present PDA-modified PVDF CCD membranes as promising alternatives to many of the well-established industry-standard membranes.

Eco-friendly surface modification approach to develop thin film nanocomposite membrane with improved desalination and antifouling properties

IntroductionNanomaterials aggregation within polyamide (PA) layer of thin film nanocomposite (TFN) membrane is found to be a common issue and can negatively affect membrane filtration performance. Thus, post-treatment on the surface of TFN membrane is one of the strategies to address the problem. ObjectiveIn this study, an eco-friendly surface modification technique based on plasma enhanced chemical vapour deposition (PECVD) was used to deposit hydrophilic acrylic acid (AA) onto the PA surface of TFN membrane with the aims of simultaneously minimizing the PA surface defects caused by nanomaterials incorporation and improving the membrane surface hydrophilicity for reverse osmosis (RO) application. MethodsThe TFN membrane was first synthesized by incorporating 0.05 wt% of functionalized titania nanotubes (TNTs) into its PA layer. It was then subjected to 15-s plasma deposition of AA monomer to establish extremely thin hydrophilic layer atop PA nanocomposite layer. PECVD is a promising surface modification method as it offers rapid and solvent-free functionalization for the membranes. ResultsThe findings clearly showed that the sodium chloride rejection of the plasma-modified TFN membrane was improved with salt passage reduced from 2.43% to 1.50% without significantly altering pure water flux. The AA-modified TFN membrane also exhibited a remarkable antifouling property with higher flux recovery rate (>95%, 5-h filtration using 1000 mg/L sodium alginate solution) compared to the unmodified TFN membrane (85.8%), which is mainly attributed to its enhanced hydrophilicity and smoother surface. Furthermore, the AA-modified TFN membrane also showed higher performance stability throughout 12-h filtration period. ConclusionThe deposition of hydrophilic material on the TFN membrane surface via eco-friendly method is potential to develop a defect-free TFN membrane with enhanced fouling resistance for improved desalination process.

Imparting Antimicrobial and Antifouling Properties to Anion Exchange Membrane through the Modification with Gentamicin‐Based Polymer

AbstractA series of gentamicin‐modified anion exchange membranes (AEMs) immobilized by mussel‐inspired dopamine coating is prepared in this work. The purpose is to improve antibacterial activity and fouling resistance of the commercial AEMs (AEM Type I, Fujifilm Co.). As a result of the applied modification, the hydrophilicity of membrane surface improved significantly. Thus, the as‐prepared modified AEMs exhibit the good antifouling property, in electrodialysis (ED) experiments by using the sodium dodecylbenzenesulfonate and albumin from bovine serum as model foulants. Furthermore, taking into account the results of the antibacterial test, the resulting modified AEMs exhibit improved antibacterial property for Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). After a brief contact with bacteria, the antibacterial rates of modified AEMs coating with gentamicin‐based polymer are 80.11% for E. coli and 90.66% for S. aureus, which are much higher than pristine AEM (6.28% and 9.07%), respectively. In addition, the modified membrane has good operational stability during ED process and recovery ability after contamination, and also maintains satisfactory electrochemical properties. This investigation highlights a design of simple strategy for the preparation of antimicrobial and antifouling AEM, which can be used for ED.

Polyamide layer sulfonation of a nanofiltration membrane to enhance perm‐selectivity via regulation of pore size and surface charge

AbstractIn this study, sulfonated nanofiltration membranes were synthesized via interfacial polymerization (IP) of aqueous‐phase piperazine (PIP), 3‐amino‐1‐propanesulfonic acid (APA), and organic‐phase trimesoyl chloride (TMC) monomers on porous substrates. Membranes with different APA contents were thoroughly characterized to determine how APA affected the physicochemical characteristics and perm‐selectivity of the membranes. Membrane characterization confirmed the incorporation of APA into the generated polyamide (PA) layer. The optimal membrane performance was obtained at a 0.8 w/v% aqueous‐phase APA content, where the enhanced membrane molecular weight cutoff (MWCO) and surface hydrophilicity resulted in a pure water permeability of 11.9 L m−2 h−1 bar−1, approximately 13.1% higher than that of the blank membrane. Enhanced electrostatic repulsion of the APA‐modified membrane on Na2SO4 resulted in up to a 96.2% Na2SO4 rejection rate. The 24.3% NaCl rejection rate resulted in NaCl/Na2SO4 selectivity for the mixed‐salt solution of the optimized membrane of 19.9, which was a significant increase over that of the blank. The embedding of APA did not affect the long‐term stability of the NF membrane. The combined effects of the hydrophilicity, charge, and roughness of the membrane surface slightly enhanced the antifouling ability of the APA‐modified membrane over that of the blank. This study provides a facile strategy for the fabrication of NF membranes with high perm‐selectivity.

Facile Surface Modification of Polyamide Membranes Using UV-Photooxidation Improves Permeability and Reduces Natural Organic Matter Fouling.

A new optimized ultraviolet (UV) technique induced a photooxidation surface modification on thin-film composite (TFC) polyamide (PA) brackish water reverse osmosis (BWRO) membranes that improved membrane performance (i.e., permeability and organic fouling propensity). Commercial PA membranes were irradiated with UV-B light (285 nm), and the changes in the membrane performance were assessed through dead-end and cross-flow tests. UV-B irradiation at 12 J·cm-2 enhanced the pure water permeability by 34% in the dead-end tests without decreasing the mono- or divalent ion rejections, as compared with the pristine PA membrane, and led to less fouling by natural organic matter in the cross-flow tests. Scanning electron microscopy (SEM), attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) confirmed that UV-B irradiation opened the pore structure and created carboxylic and amine groups on the PA surface, leading to increased membrane surface charge and hydrophilicity. Thus, an optimal UV-B dose appears to modify only a thin layer of the PA membrane surface, which favorably enhances the membrane performance. UV-B did not alter the structure, flux, or salt rejection for cellulose triacetate (CTA)-based membranes. While other membrane surface modifications include oxidants, strong acids, and bases, the UV-B facile treatment is chemical-free, thus reducing chemical wastes, and easy to apply in roll-to-roll fabrication processes of PA membranes. The results also showed that a low UV irradiation dose could be applied to PA or CTA membranes for disinfection or photocatalytic oxidation.

A new anti-fouling polysulphone nanofiltration membrane blended by amine-functionalized MCM-41 for post treating waste stabilization pond's effluent

Developing an effective and stable separation membrane for water treatment is of much interest while challenging because of the restrictions of membrane fouling and water flux reduction. To minimize this problem, in this work, highly porous and hydrophilic nanostructure of NH2-modified MCM-41 (NH2-MCM-41) was embedded successfully into the nanofiltration (NF) membrane body via commonly used phase inversion method. The unmodified and modified nanofiller was analyzed by Fourier Transform Infrared (FTIR) spectroscopy, X-Ray powder diffractometry (XRD), field emission scanning electron microscopy (FE-SEM), thermogravimetric analysis (TGA), and nitrogen adsorption–desorption. Furthermore, the modified membranes were characterized through surface and cross section FE-SEM images, the membrane surface roughness, hydrophilicity, antifouling properties and dye rejection. Benefiting from porous networks and enhanced hydrophilicity, the mixed matrix membranes (MMMs) revealed more prominent hydrophilic property as well as higher pure water flux (PWF) compared with naked membrane. The polysulphone (PSf) membrane modified with NH2-MCM-41-1.0 exhibited the highest pure water flux (PWF) of 65.43 kg/m2.h and superior antifouling characteristics with a flux recovery ratio (FRR) of around 97.0% and an irreversible fouling resistance (Rir) of 3.2%. Furthermore, the optimal membrane possessed high dye rejection (100%) and antifouling capacity (FRR of 97%) while filtering a field sample, effluent from a local stabilization pond treating municipal wastewater. The fabricated membrane in this study is believed to pave pathways for constructing NF membranes with superior effectiveness for other municipal and industrial wastewaters treatment.

Polyacrylic acid-brushes tethered to graphene oxide membrane coating for scaling and biofouling mitigation on reverse osmosis membranes

Reverse osmosis (RO) membranes are prone to fouling, which increases the cost of operation and decreases water recovery. In this study, a commercial membrane (ESPA2) was coated with an antiscaling material, i.e. polyacrylic acid (PAA), and an antimicrobial material, i.e. graphene oxide (GO), to reduce biofouling and scaling. Bare and modified membranes with polydopamine (ESPA2-PD), as a control, GO (ESPA2-GO), GO and PAA (ESPA2-GO-PAA), and PAA (ESPA2-PAA) were tested for their antiscaling and antibiofouling properties. ESPA2-GO and ESPA2-GO-PAA had the best performance. The latter showed ~15% and 10% increase in normalized water flux compared to ESPA2 in mineral scaling and biofouling tests, respectively. This improvement can be attributed to the decrease in surface charge and the increase in hydrophilicity of membrane surface by both GO and PAA coating. Moreover, the antimicrobial characteristic of GO played a crucial role in reducing biofouling and PAA slightly enhanced antiscaling property when coated on ESPA2 but it did not improve the antibiofouling property. These results highlight the importance of antimicrobial property of the coating for biofouling prevention and show antiscaling materials can be effective not only as an additive to the feed but also as a coating on the membrane to reduce scaling.

Novel visible-light responsive NCQDs-TiO2/PAA/PES photocatalytic membrane with enhanced antifouling properties and self-cleaning performance

In this study, a novel multifunctional composite membrane with photocatalytic, antifouling and self-cleaning properties were prepared through the surface immobilization of nitrogen doped carbon quantum dots modified TiO2 (NCQDs-TiO2) photocatalysts using polyacrylic acid (PAA) as a bridging agent. The surface polymerization of PAA has introduced functional groups for the self-assembly of NCQDs-TiO2 functional layer (denoted as NTO) to improve the hydrophilicity of conventional PES membrane. The modified membranes with varying photocatalyst concentration (0.1, 0.3 and 0.5 wt% NTO) were characterized for their surface chemistry and morphology using SEM-EDX, FTIR, XPS and contact angle analysis. Furthermore, the effect of NCQDs-TiO2 nanocomposite on the membrane performance was assessed in terms of rejection ability, fouling mitigation, self-cleaning and photocatalytic capability using methylene blue as a model pollutant. The characterization results evidenced that the NTO nancomposites were firmly attached on the PES-based supporting layer through the chemical bonding between surface-grafted carboxylic group and Ti atom. The surface hydrophilicity of composite membrane was enormously enhanced following a direct proportionality to NTO loading. The novel NTO/PAA/PES membrane also demonstrated high resistance to MB fouling and was able to revive 93.7% of original water fluxes upon 15 min of visible-light irradiation. Moreover, the modified membranes could efficiently retain 90.9% of MB dye pollutant. The outstanding antifouling and self-cleaning performance were reasonably attributed to the intrinsic hydrophilicity and robust photocatalytic activity of NTO layer. This was further confirmed by the photodegradation of MB wherein the NTO-0.5/PAA/PES membrane degraded 94.9% of MB under 1 hr of visible-light irradiation. With its twofold advantages of membrane filtration and photocatalysis, the visible-light responsive photocatalytic membrane demonstrates huge potential in waste water treatment which could minimize membrane fouling and increase reusability of photocatalyst.

Incorporation of Cellulose Nanocrystals into Graphene Oxide Membranes for Efficient Antibiotic Removal at High Nutrient Recovery

Two-dimensional (2D) material-based membranes hold great promise in wastewater treatment. However, it remains challenging to achieve highly efficient and precise small molecule/ion separation with pure 2D material-fabricated lamellar membranes. In this work, laminated graphene oxide (GO)-cellulose nanocrystal (CNC) hybrid membranes (GO/CNC) were fabricated by taking advantages of the unique structures and synergistic effects generated from these two materials. The characterization results in physiochemical properties, and the structure of the as-synthesized hybrid membranes displayed enhanced membrane surface hydrophilicity, enhanced crumpling surface structure, and slightly enlarged interlayer-spacing with the incorporation of CNCs. Water permeability increases by two to four times with the addition of different CNC weight ratios in comparison to a pristine GO membrane. The optimal GO/CNC membrane achieved efficient rejection toward three typical antibiotics at 74.8, 90.9, and 97.2% for sulfamethoxazole (SMX), levofloxacin (Levo), and norfloxacin (Nor), respectively, while allowing a high passage of desirable nutrients such as NO3- and H2PO4-. It was found that SMX removal is primarily governed by electrostatic repulsion, while adsorption plays a crucial role in removing Levo and Nor. Moreover, the density functional theory calculations confirmed the increased antibiotic removal in the presence of an organic foulant, humic acid. Such a 2D material-based hybrid membrane offers a new strategy to develop fit-for purpose membranes for resource recovery and water separation.

Modification of polyethylene terephthalate track etched membranes by planar magnetron sputtered Ti/TiO2 thin films

This study investigates the surface modification of polyethylene terephthalate track-etched membranes by planar magnetron sputtering of titanium and titanium dioxide thin films to improve its hydrophilicity and photocatalytic activity. After cold plasma treatment to enhanced adhesion, Ti thin films were deposited by planar magnetron sputtering and TiO2 thin films by reactive magnetron sputtering in an Ar-O2 gas atmosphere. The morphology of the deposited thin films was characterised using atomic force microscopy and scanning electron microscopy. The pores retained a mostly circular shape. However, the modified track membrane's surface pore diameter reduced from 0.2 µm to 0.15 µm for Ti coated samples and 0.08 µm for Ti-TiO2 coated samples. Structural studies using X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy and Raman spectroscopy of Ti and TiO2 thin films revealed the intricate composition of the sputtered thin films which was a result of the complexity of sputtering on top of the porous polymer support. Additional investigations in surface wettability and bandgap showed a significant change in the track membrane surface's hydrophilicity and photocatalytic properties after depositing TiO2-Ti, adding to the self-cleaning properties of the coated TM. The bandgap of the film was 3.1 eV and of the indirect type. Both Ti and TiO2-Ti sputtering over the TM surface significantly reduced the water contact angle from 72° for untreated PET to 43° and 45° for Ti-TM and TiO2-Ti-TM, respectively. This study shows that planar magnetron sputtering is a viable approach to surface modification of a porous polymeric support, such as track-etched membranes. The sputtered coating enhanced membrane hydrophilicity, thereby reducing the chance of surface fouling by organic substances, which leads to improved self-cleaning properties.

Rapid and eco-friendly technique for surface modification of TFC RO membrane for improved filtration performance

In this work, an environmentally friendly plasma enhanced chemical vapor deposition (PECVD) technique was employed to rapidly alter the surface properties of commercial thin film composite extra-low energy (XLE) reverse osmosis (RO) membrane to improve its fouling resistance and desalination performance. Hereafter, two different hydrophilic precursors, i.e., aniline monomer and oxygen (O2) gas were respectively introduced to the membrane’s polyamide surface at different plasma treatment duration (15 s and 60 s). At 15-s plasma treatment, our results revealed that the O2-modified membrane outperformed the polyaniline (PANI)-modified membrane and unmodified membrane, attributed to the polar functional groups presented on the polyamide surface. Compared to plasma polymerization of aniline, O2 plasma etching can lower polyamide densification degree which potentially reduce membrane resistance. Evidently, the O2-modified membrane exhibited higher pure water permeability (6.64 L/m2.h.bar) compared to the PANI-modified membrane (5.57 L/m2.h.bar). The enhanced surface hydrophilicity of O2-modified membrane could be noticed when its water contact angle was reduced from 88.39⁰ (unmodified) to 79.46⁰ in just 15-s plasma treatment. Furthermore, this O2-modified membrane achieved an outstanding NaCl and Na2SO4 rejection with an increment of 4.2% and 2.6%, respectively compared to the unmodified membrane. However, prolonged gas plasma treatment (60 s) should be avoided as it can damage polyamide selective layer. With respect to fouling resistance, the best O2-modified membrane demonstrated higher flux recovery rate (96%) than that of unmodified membrane (76.5%) after being used to filter 1000-ppm sodium alginate solution. These results highlighted the versatility of O2 plasma treatment to improve RO membrane performance.

MWCNTs-COOK-assisted high positively charged composite membrane: Accelerating Li+ enrichment and Mg2+ removal

In this work, we successfully synthesized a new functional nano-additive called potassium carboxylate functionalized multi-wall carbon nanotubes (MWCNTs-COOK) and introduced it into the interfacial polymerization system to fine-tune the structure and properties of the nanofiltration (NF) membrane. The embedded MWCNTs-COOK (150 ppm) tightened the network-crosslink structure of the selective layer and contributed to a dense hydrophilic membrane surface with high positive chargeability. In addition, MWCNTs-COOK nano-additives in membrane created some intrinsic fast transport channels for water molecules. The MWCNTs-COOK(150 ppm)-assisted NF membrane exhibited a remarkable high flux of 12.23 L/m2hbar, a high separation factor SLi,Mg of 58, and a high difference in Li+ and Mg2+ rejections around 77%, indicating an excellent Li+ enrichment and Mg2+ removal capabilities, and breaking through the trad-off limit of permeate flux. Simultaneously, the comprehensive performance of the NF membrane can be maintained stably even in long-term utilization. This work opens a simple and effective pathway for accelerating Li+ enrichment and Mg2+ removal, which has great potential for lithium extraction application.

Modulating surface interactions for regenerable separation of oil-in-water emulsions

Developing antifouling coatings is of both fundamental and practical significance, but challenging, for membrane separation of oil-in-water (O/W) emulsions with charged surfactants, which has been conventionally achieved through the short-range hydration interaction from hydrophilic membrane surfaces as a physical barrier. Herein, we report a mussel-inspired antifouling coating formed by carboxyl and quaternary ammonium moieties bearing adjustable surface charge property, employing tunable long-range electrostatic interaction to achieve adaptive antifouling performance in response to the varying electrical characteristic of emulsions. The surface force measurement results showed that modulating the surface electrical properties of the coatings through varying the solution pH could effectively alter their electrostatic interactions with emulsions from attraction to repulsion, in combination with hydrodynamic interactions, to enable emulsion repellence of the coatings. Such functional coatings were further applied on a PVDF membrane with an enhanced water permeability and reusability achieved to separate both the positively and negatively charged emulsions. By properly modulating the membrane surface charge, the modified membrane demonstrated its adaptive antifouling performance for efficient and universal water treatment. This work provides useful insights into the antifouling mechanisms of membranes to O/W emulsions, as well as developing functional materials with tunable surface interactions for various engineering applications.

Incorporation of modified cellulose nanocrystals to polyamide nanofiltration membrane for efficient removal of Cr(III) and Pb(II) ions from aqueous solutions

ABSTRACT In this study, thin-film nanocomposite nanofiltration (TFN) membranes were fabricated using interfacial polymerisation by incorporating modified cellulose nanoparticles (mNCs). In the first place, cellulose nanoparticles were modified by AAPTES, and were then dispersed in an organic solvent with the aim of reaction with the polyamide layer of TFC membrane. The resulting membranes were then tested for the removal of Cr(III) and Pb(II) heavy metals ions from wastewater. Modified nanoparticles and nanocomposite membranes were characterised by FTIR, TEM, AFM, SEM, and zeta potential. FTIR results showed the proper mNCs deposition on the surface of membranes. Also, SEM analyses demonstrated that the incorporation of mNCs to TFC membranes led to higher surface roughness. The performance results indicated that the water flux of TFN membranes increased from 42 L·m−2 h−1 to 125 L.m−2 h−1, which might have been due to the higher surface hydrophilicity of TFN membranes, while the rejection rates of Cr(NO3)3 and Pb(NO3)2 were over 99% at and 88%, respectively, showing a competitive and efficient removal of toxic heavy metal ions Pb(II) and Cr(III). Besides, regarding pH of the membranes, rejection performance of the membrane increased with increased pH so that at pH 8.5, the removal rates of Pb(II) and Cr(III) were 93% and 100%, respectively.

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

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

浸漬型膜分離活性汚泥法の膜ファウリングに及ぼすpolytetrafluoroethylene平膜の親水性の影響

浸漬型膜分離活性汚泥法の膜ファウリングに及ぼすpolytetrafluoroethylene平膜の親水性の影響

Development of a highly-permeable thin-film-based nanofiltration membrane by using surface treatment with Air-Ar plasma

Surface modification of thin-film nanofiltration membranes was carried out to produce high water permeable NF membranes by Air-Ar plasma treatment. The effect of composition of used gases on membrane properties was investigated. Results showed that the plasma treatment decreased the water contact angle obviously from 80.4° to 6.5°, which in turn would increase the membrane surface hydrophilicity. The results of FTIR spectra decisively confirmed the formation of hydrophilic nitrogen and oxygen compounds on the membrane surface. The SEM images of membrane surface also showed significant changes after plasma treatment. AFM analysis indicated smoother surface for the modified membranes compared to pristine membrane; the roughness declined from 55.85 nm for virgin membrane to 28.33 nm for modified membranes. The salt rejection was 90% for pristine membrane and 76.35% to 92.45% for the plasma treated membranes. The water flux for modified membrane treated by 50% Air-50% Ar plasma increased ∼1,446.1% compared to the virgin membrane, whereas the selectivity declined only ∼15.1%.

Zwitterionic Triamine Monomer for the Fabrication of Thin-Film Composite Membranes

A new zwitterionic triamine monomer prepared from tris(2-aminoethyl)amine and 1,3-propane sultone is proposed for the interfacial polymerization with trimesoyl chloride to form thin-film composite membranes for nanofiltration with antifouling properties. The positive effects of the zwitterionic monomer fraction on the surface characteristics of the polyamide layer, fouling resistance, and filtration performance are demonstrated. Increasing the zwitterionic monomers in the selective layer significantly improves the water permeance (two-fold) without affecting the rejection for dyes tested with a molecular weight in the range of 637 and 1673 g/mol. The smoother and more hydrophilic membrane surface of the newly developed membrane provides excellent fouling resistance confirmed by the negligible protein adsorption and permeance drop during the filtration.