Performance Of Nanofiltration Membranes Research Articles

Improving the performance of loose nanofiltration membranes by poly-dopamine/zwitterionic polymer coating with hydroxyl radical activation

A growing number of sewage treatment plants are utilizing the membrane separation technology for wastewater bleaching and desalination. The surface characteristics of the membrane selective layer have a great impact on the filtration and separation performance. In this study, a facile mussel-inspired method was employed for fabricating loose NF membrane. Hydroxyl radical activation generated by CuSO4/H2O2 was used to realize a rapid polydopamine (PDA) deposition. To obtain an electroneutral, anti-fouling and anti-bacterial surface, a zwitterionic polymer (SBMA) was introduced for PDA/SBMA codeposition and polymerization. XPS, FTIR, SEM, AFM and water contact angle analysis were employed to investigate the characteristics of the selective layer. The RD-1S membrane (2 mg/mL PDA and 2 mg/mL SBMA utilized) shows the optimal surface property. In addition, the filtration and separation performance of multivalent salts (monovalent and divalent ion) and dyes (negatively and positively charged) were investigated in detail. The separation capability of membrane exhibited a high dye rejection and a low salt rejection. The anti-fouling performance of the RD-1S membrane was observed to be excellent, especially from the point of view of fouling resistance reversibility. The elevated surface charge might be the main reason for the significant decrease of irreversible fouling of the RD-1S membrane. Furthermore, the co-existence of chelated copper and SBMA resulted in a reliable anti-bacterial performance. Overall, the separation and anti-bacterial performance of the functional loose NF membrane were comprehensively investigated.

Experimental and statistical investigation on fabrication and performance evaluation of structurally tailored PAN nanofiltration membranes for produced water treatment

The present study aims at investigating the effects of multiple fabrication and design parameters on the performance of nanofiltration (NF) membranes. By employing the Plackett-Burman design method, obtained results demonstrate that citric acid (0–1.5 wt.%), TiO2 (0–1 wt.%), and solvent evaporation time (1–3 min) are the top dominant factors affecting the pure water flux (PWF) of NF membranes. Also, the effects of the dominant factors and their corresponding interactions are statistically assessed through RSM technique by employing a quadratic model. Based on the ANOVA results the proposed models for the PWF and CaSO4 rejection responses are statistically significant. The calculated optimum values for citric acid, TiO2, and solvent evaporation time are 0.87 wt.%, 0.98 wt.%, and 1.34 min respectively. It is shown that by increasing the concentration of TiO2 both PWF and rejection of membrane enhanced from 108.8–131.5 (lit.m−2.h-1) and from 73.5–83 % respectively. Furthermore, an increment in citric acid concentration leads to the promotion of the surface hydrophilicity and salt rejection of membranes. From the morphological point of view, increasing the TiO2 concentration leads to formation of membranes with more porous sublayers while longer solvent evaporation times results in the formation of membranes with smaller macrovoids.

Intercalation of zwitterionic surfactants dramatically enhances the performance of low-pressure nanofiltration membrane

High-performance nanofiltration membrane with excellent perm-selectivity and fouling resistance was fabricated by layer-by-layer deposition of polyelectrolytes, polyethylenimine (PEI) and polystyrene sulfonate (PSS), with the intercalation of self-assemblies of zwitterionic surfactants, 3-(N, N-Dimethylmyristylammonio) propane sulfonate (SB3-14). The integration of SB3-14 to the polyelectrolyte active layer dramatically enhanced the water permeability of the low-pressure nanofiltration (LNF) membrane without compromising the rejection of humic acid (HA). Specifically, the LNF membrane with intercalation of zwitterionic surfactant self-assemblies achieved a water permeability of up to 131 L m−2 h−1 bar−1 and an HA rejection over 99%. In addition, the intercalation of SB3-14 surfactants also made the LNF membrane significantly smoother and less prone to fouling in long-term LNF operation, leading to higher water flux and HA rejection when the LNF process reached a steady state.

MODELLING ION TRANSPORT IN AN AMINE SOLUTION THROUGH A NANOFILTRATION MEMBRANE

Abstract The performance of a flat sheet polyamide nanofiltration membrane in rejection of a binary mixture of heat stable salts (acetate and sulfate) from methyl-diethanolamine (MDEA) solution was investigated. The effects of pressure and concentration of MDEA solution on rejection of acetate and sulfate ions were studied. At MDEA concentration of 20% wt. and pressure of 70 bar, 80% and 98% rejection can be obtained for acetate and sulfate ions, respectively. Membrane performance and transport coefficients were investigated using the Spiegler-Kedem-Katchalsky (SKK) model, film theory and extended Nernst-Planck (FT-ENP) model. The results of the FT-ENP model show accurate agreement with experimental results. This result can be obtained due to considering the charge repulsion of sulfate ions. For sulfate ions, both models show errors less than 1% with >R2=0.98. In the case of acetate, errors less than 3% (>R2=0.75) and 2% (>R2=0.89) were obtained for the SKK and FT-ENP models, respectively.

Dual-functional acyl chloride monomer for interfacial polymerization: Toward enhanced water softening and antifouling performance

Here, a strategy to control surface negative charge, pore size and active layer thickness by manipulating the polyamide (PA) layer structure is proposed to fabricate an advanced water softening nanofiltration (NF) membrane. Based on this strategy, a dual-functional acyl dichloride monomer containing a protected amino group, 5-sulfinyl amino isophthaloyl dichloride (NSO), is designed as organic phase alternative. Because the protected amine group of NSO has higher hydrolytic activity and is prone to de-protect and form free amino group, it has important impact on the interfacial polymerization (IP) process and formed polyamide (PA) structure. To elucidate the role of the protected amino group in regulating PA structure, the desalination performances and structural characteristics of the three PA membranes prepared by NSO monomer and its structurally similar monomers (isophthalyl chloride (IPC) and trimesoyl chloride (TMC)) are systematically investigated. Compared with TMC-based NF membrane, the NSO-based membrane shows a smoother and lower carboxyl group density surface, decreased pore size and a thinner PA rejection layer (~30 nm). As a result, the novel NF membrane exhibits outstanding water softening performance in terms of ultrahigh divalent salts (Na2SO4, MgSO4, MgCl2 and CaCl2) rejections (above 98%) and preferable high water flux (138.25 ± 6.32 LMH), together with superior antifouling property. More importantly, its water softening capability remain stable even under the mixed salt solution including abundant SO42−, which far outperforms the typical poly(piperazine-amide)-based and state-of-the-art commercial NF membranes. This work further establishes the structure-property relationship and enables the rational design of high performance of NF membrane at the molecular level.

PDMS membranes modified by polyelectrolyte multilayer deposition to improve OSN separation of diluted solutes in toluene

New functionalized poly(dimethylsiloxane) (PDMS) membranes were prepared by the surface modification of the commercially available PERVAP4060 membrane (Sulzer™) through cold plasma activation followed by the layer-by-layer assembly method. Four different pairs of polyelectrolytes, i.e., poly(allylamine hydrochloride) (PAH)/poly(acrylic acid) (PAA), PAH/poly(sodium 4-styrene sulfonate) (PSS), poly(diallyldimethylammonium chloride) (PDDA)/PAA, and PDDA/PSS, were used to coat the PDMS layer by the controlled deposition of successive nanolayers (20–50 nm).PERVAP4060 was systematically modified by the deposition of 10 bilayers of polyelectrolyte pairs. These membranes were characterized by contact angle measurements, scanning electron microscopy (SEM), ellipsometry, and atomic force microscopy (AFM). The nanofiltration membrane performance for the rejection of four diluted solutes—two soluble catalysts 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (R-BINAP) and tetraoctylammonium bromide (ToABr) and two linear aliphatic molecules n-Tetratetracontane (C44H90 or C44) and n-Hexadecane (C16H34 or C16)—was studied in the toluene feed solution at up to 40 bar pressure. It was shown that the organic solvent nanofiltration (OSN) mass transfer properties differ clearly depended on the layer-by-layer chemical structure and the characteristics of the solutes. Thus, the intrinsic permeance of toluene in the PEL multilayers were calculated by applying resistance-in-series model. Despite the highly diluted concentrations of the solutes, i.e., <1 wt% for R-BINAP and ToABr, and the high solvent permeate flux, the ToABr, R-BINAP, and C44 solutes were markedly rejected by all the membranes. ToABr had the highest rejection coefficient, up to 97%. As a trend, higher the polarity of the bilayer assembly, lower was the mass transfer of the solvent compared to that of the pristine membrane. The results indicated that a solution–diffusion mechanism is likely to apply. The best rejection of R-BINAP (up to 88%) was obtained when the membrane was coated with 10 bilayers of PAH/PSS. Thus, these prepared polyelectrolyte (PEL)-modified membranes have potential applications in homogeneous catalysis industry, for example in olefin metathesis for expanding the lifetime of soluble catalysts by separating them at mild OSN condition while ensuring the permeation of products.

Negatively charged organic–inorganic hybrid silica nanofiltration membranes for lithium extraction

Abstract Effective extraction of lithium from high Mg2+/Li+ ratio brine lakes is of great challenge. In this work, organic–inorganic hybrid silica nanofiltration (NF) membranes were prepared by dip-coating a 1,2-bis(triethoxysilyl)ethane (BTESE)-derived separation layer on tubular TiO2 support, for efficient separation of LiCl and MgCl2 salt solutions. We found that the membrane calcinated at 400 °C (M1–400) could exhibit a narrow pore size distribution (0.63–1.66 nm) owing to the dehydroxylation and the thermal degradation of the organic bridge groups. All as-prepared membranes exhibited higher rejections to LiCl than to MgCl2, which was attributed to the negative charge of the membrane surfaces. The rejection for LiCl and MgCl2 followed the order: LiCl > MgCl2, revealing that Donnan exclusion effect dominated the salt rejection mechanism. In addition, the triple-coated membrane calcined at 400 °C (M3–400) exhibited a permeability of about 9.5 L ∙ m−2 ∙ h−1 ∙ bar−1 for LiCl or MgCl2 solutions, with rejections of 74.7% and 20.3% to LiCl and MgCl2, respectively, under the transmembrane pressure at 6 bar. Compared with the previous reported performance of NF membranes for Mg2+/Li+ separation, the overall performance of M3–400 is highly competitive. Therefore, this work may provide new insight into designing robust silica-based ceramic NF membranes with negative charge for efficient lithium extraction from salt lakes.

How to understand the effects of heat curing conditions on the morphology and performance of polypiperazine-amide NF membrane

In this study, the impacts of heat curing conditions on the morphology and permeability of polyamide nanofiltration (NF) membranes were comprehensively investigated. The surface chemical composition, morphology, charge property, hydrophilicity and NF performance of the resulting membranes were studied. In order to preserve the instantaneous polyamide layer morphology, freeze drying process was employed after heat curing. Results showed that the surface roughness of the polyamide selective layer increased first and then decreased with curing time. The tunable morphology of polyamide NF membranes can be acquired by adjusting the curing temperature and time. The nascent membrane without heat curing exhibited excellent pure water permeability of 16.7 L m−2 h−1 bar−1 and maintained Na2SO4 rejection of 97.4%. Increasing the curing time, the permeability of the NF membranes was greatly diminished. This work provided novel viewpoint about the effects of heat curing on morphology and permeability for high-performance polyamide NF membrane.

A chitosan-separation-layer nanofiltration membrane prepared through homogeneous hybrid and copper ion enhancement

A novel method of homogeneous hybrid and copper ion (Cu(II)) enhancement was employed to prepare chitosan separation layer over polyacrylonitrile support. Firstly, chitosan nanoparticles (CSPs) and free chitosan molecules in the suspension prepared through adding sodium polyphosphate (SPP) into chitosan solution were simultaneously electrostatically attracted onto the surface of alkali-treated polyacrylonitrile (mPAN) support to obtain chitosan separation layer (CSPM) that was homogeneously hybrided by CSPs. Then, CSPM/mPAN membrane obtained was immersed into CuSO4 solution for chelation cross-linking to obtain CSPM-Cu(II)/mPAN membrane. Results showed the ratio of chitosan to SPP and Cu(II) chelation had markedly affected on the membrane performance. When the ratio of chitosan to SPP was 3.4, CSPM3.4-Cu(II)/mPAN membrane had a Na2SO4 rejection of 93.3% with a pure water flux of 74.8 L/(m2·h), simultaneously increasing by 30.3% rejection and 24.0% flux compared with CSPM3.4/mPAN membrane due to improvement of hydrophilicity and cross-linking degree resulted from Cu(II) enhancement. CSPM3.4-Cu(II)/mPAN membrane showed 3.6 fold flux and almost the same rejection compared with chitosan nanofiltration membrane by interfacial cross-linking reported. Meanwhile, CSPM3.4-Cu(II)/mPAN membrane exhibited 100% anti-bacteria to Escherichia coli, 96.1% flux recovery rate and separation stability. This work provides a new way for nanofiltration membrane preparation and performance improvement.

Thin film nanocomposite nanofiltration hollow fiber membrane fabrication and characterization by electrochemical impedance spectroscopy

Nano-TiO2 nanoparticles were incorporated into thin film nanocomposites (TFN) formed on hollow fiber support membranes composed of a blend of polysulfone and multi-walled carbon nanotubes. Three different TiO2 nanoparticles (0.01%, 0.05% and 0.2% w/v) in the thin film composite were investigated. Formation of the nanocomposite polyamide layer was confirmed by the results of FTIR and scanning electron microscopy. Double-layer capacitance values obtained from electrochemical impedance spectroscopy results showed that effective surface area of the membranes was enhance by the incorporation of nano-TiO2. Nanofiltration membrane performance was examined using solutions of MgSO4 and NaCl under cross-flow system with hollow fiber nanofiltration modules. Fouling of the membrane was evaluated with solutions of humic and tannic acids. The permeate flux of TFN 0.05 composite membranes was improved nearly 12 times with the incorporation of TiO2 with rejections of MgSO4 and NaCl salts of 22% and 5%, respectively. The rejections of the NF membranes for HA and TA were 84% and 74%, respectively, with improved antifouling properties compared to the thin film composite membrane without TiO2, the latter being attributed to increased hydrophilicity of membrane surface.

Controllable Interfacial Polymerization for Nanofiltration Membrane Performance Improvement by the Polyphenol Interlayer.

It is a huge challenge to have a controllable interfacial polymerization in the fabrication process of nanofiltration (NF) membranes. In this work, a polyphenol interlayer consisting of polyethyleneimine (PEI)/tannic acid (TA) was simply assembled on the polysulfone (PSf) substrate to fine-tune the interfacial polymerization process, without additional changes to the typical NF membrane fabrication procedures. In addition, three decisive factors in the interfacial polymerization process were examined, including the diffusion kinetics of fluorescence-labeled piperazine (FITC-PIP), the spreading behavior of the hexane solution containing acyl chloride, and the polyamide layer formation on the porous substrate by in situ Fourier transform infrared (FT-IR) spectroscopy. The experimental results demonstrate that the diffusion kinetics of FITC-PIP is greatly reduced, and the spreading behavior of the hexane solution is also impeded to some extent. Furthermore, in situ FT-IR spectroscopy demonstrates that by the mitigation of this PEI/TA interlayer, the interfacial polymerization process is greatly controlled. Moreover, the as-prepared NF membrane exhibits an increased water permeation flux of 65 L m–2 h–1 (at the operation pressure of 0.6 MPa), high Na2SO4 rejection of >99%, and excellent long-term structural stability.

Manipulating the separation performance of nanofiltration membranes by coating thickness of organic phase during interfacial polymerization

ABSTRACTNanofiltration (NF) membranes have excellent separation capabilities and selective performance, and are widely applied in the field of concentration and separation of salt and inorganic salt mixtures. In this article, NF membranes with a higher comprehensive performance were fabricated using a thinner coated organic phase during interfacial polymerization, which greatly reduced the rejection of sodium chloride and significantly improved the water flux without reducing the rejection of magnesium sulfate. Structure comparison found that thinner polyamide separation layer resulted in the higher crosslinking degree, smaller particle, and relatively rough surface. Based on these analyses, we hypothesized that thermodynamically efficiency in the system varies with the coating thickness. Finally, the mechanism of the influence of the coating thickness of organic phase during heat treatment on the interfacial polymerization process and membrane structure was discussed. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48284.

Thin-film composite membranes with aqueous template-induced surface nanostructures for enhanced nanofiltration

Surface morphology has been proven to significantly affect nanofiltration (NF) membrane performance. However, the morphology control in membrane fabrication remains a great challenge. Herein, based on interfacial manipulation, a new strategy was developed to fabricate NF membranes with tunable 3D surface nanostructures. The manipulation was achieved by forming aqueous template on the substrate surface during the membrane fabrication, which directly influenced the consequent membrane surface morphology. Based on this, a systematic transition of surface morphology from leaf-like shapes to ridges was achieved in a facile way. The representative NF membrane with ridged nanostructures exhibited water permeance of 21.3 Lm-2h-1bar-1 and Na2SO4 rejection of 99.4 % due to increased permeable area, reduced membrane thickness and low-resistance flow channel within the ridged nanostructures. The mechanism and detailed process of forming these 3D surface nanostructures were demonstrated by combining dissipative particle dynamics (DPD) simulations and experiments. In consideration of the simplicity, generality and controllability, this aqueous template-based interfacial manipulation strategy would be of importance to the fabrication of thin-film composite membranes.

Membrane compaction, internal fouling, and membrane preconditioning as major factors affecting performance of solvent resistant nanofiltration membranes in methanol solutions

The viability of using solvent-resistant nanofiltration (SRNF) membranes for concentration of a methanol solution containing a mixture of methyl lactate (ML), glycoaldehyde dimethyl acetal (GLAD), and methylvinylglycolate (MVG) was evaluated in this study. The highest retention was achieved with the GE AG membrane at 60 bars, compared to NF 270, Desal DK, and BW 30 membranes, where the retention was 20–30% lower at the same pressure. All membranes except NF 270 showed a high compaction effect at pressures above 40 bars, which explained the low flux and high retention at high pressures. Preconditioning the membranes with pure ethanol or methanol resulted in no differences in flux compared to the virgin membrane, which was in agreement with the “clustering effect” of the hydrophilic groups, which predicts same hydrophilicity but larger (and fewer) pores on the membrane surface. On the contrary, when the membranes were preconditioned with 50/50 alcohol mixtures of methanol or ethanol and water, a general decrease of flux and retention increase was observed, which was ascribed to the previously reported “pore wetting” effect exerted by water in alcohol mixtures. Increasing pH of the feed solution from 4 to 7 also caused decreases of flux and retention, which was explained by the increased internal fouling due to pore swelling. The results from this study suggest that the balance between compaction of the membrane due to high pressure and the pore size enlargement resulting from swelling and reorganization of the polymer chains of the membrane when subjected to organic solvents determines the size exclusion efficiency and susceptibility of the membrane to internal fouling, which in turn determine the performance of the membrane in terms of retention and flux.

Effect of adding a smart potassium ion-responsive copolymer into polysulfone support membrane on the performance of thin-film composite nanofiltration membrane

Thin-film composite (TFC) nanofiltration (NF) membranes were fabricated via the interfacial polymerization of piperazine (PIP) and 1,3,5-benzenetricarbonyl trichloride on polysulfone (PSf) support membranes blended with K+-responsive poly(N-isopropylacryamideco-acryloylamidobenzo-15-crown-5) (P(NIPAM-co-AAB15C5)). Membranes were characterized by attenuated total reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, atomic force microscope, scanning electron microscope, contact angle, and filtration tests. The results showed that: (1) Under K+-free conditions, the blended P(NIPAM-co-AAB15C5)/PSf supports had porous and hydrophilic surfaces, thereby producing NF membranes with smooth surfaces and low MgSO4 rejections; (2) With K+ in the PIP solution, the surface roughness and water permeability of the resultant NF membrane were increased due to the K+-induced transition of low-content P(NIPAM-co-AAB15C5) from hydrophilic to hydrophobic; (3) After a curing treatment at 95 °C, the improved NF membrane achieved an even higher pure water permeability of 10.97 L⋅m-2⋅h-1⋅bar-1 under 200 psi. Overall, this study provides a novel method to improve the performance of NF membranes and helps understand the influence of supports on TFC membranes.

Supramolecular-Based Regenerable Coating Layer of a Thin-Film Composite Nanofiltration Membrane for Simultaneously Enhanced Desalination and Antifouling Properties.

A high-performance nanofiltration (NF) membrane with simultaneously improved desalination and antifouling properties while maintaining regeneration ability is highly desirable in water treatment. Surface modification is an effective approach to enhance the performance of NF membranes. In the present study, a multifunctional thin-film composite NF membrane (Fe-TFC) was fabricated via coating a regenerable ferric ion-tannic acid (FeIII-TA) layer on the nascent polyamide membrane surface. The Fe-TFC membrane exhibited enhanced hydrophilicity, smaller pore size, and lower negative charge compared with the control membrane. The salt rejections and selectivity of divalent to monovalent ions were greatly improved with only a slight decrease in water permeability due to the presence of the coating layer. Meanwhile, dynamic fouling tests with humic acid demonstrated that the Fe-TFC membrane possessed an enhanced antifouling property and excellent flux recovery rate. After coating, the normalized water flux and flux recovery of the Fe-TFC membrane increased from 0.02 to 0.26 and 32.1 to 76.4% at the end of five cycles of fouling tests, respectively. In addition, the resultant membrane exhibited excellent durability and stability under harsh conditions for ∼10 days. Interestingly, the fouled coating layer can be easily removed by HCl cleaning and regenerated through an in situ strategy. Consequently, the regenerated membranes presented stable antifouling properties and desalination performance after several times of regeneration. It was demonstrated that the unique feature of FeIII-TA networks enables the coating layer to act as a protective layer for the underlying polyamide membrane, leading to the high performance of the composite membrane. This study provides a new insight for surface functionalization and easy regeneration of the TFC nanofiltration membrane in water treatment technology.

Mixed matrix PES-based nanofiltration membrane decorated by (Fe3O4–polyvinylpyrrolidone) composite nanoparticles with intensified antifouling and separation characteristics

In this study, the physico-chemical properties, separation performance and antifouling ability of mixed matrix PES-based nanofiltration membranes decorated by (Fe3O4–polyvinylpyrrolidone) composite nanoparticles were investigated. The morphology of resulted membranes was characterized by scanning electron microscopy)SEM), scanning optical microscopy (SOM) and 3D surface images. The effect of incorporated nanoparticles on membrane properties and performance was determined using water contact angle, water content, membrane pore size and porosity, tensile strength, water flux, salt rejection and BSA solution filtration. The membrane water content was enhanced slightly by embedding Fe3O4/PVP up to 0.1wt.% in membrane body and then reduced again by more NPs ratio. The water contact angle also decreased from 65.18° for neat membrane to 50.5° for the modified ones. All mixed matrix membranes showed higher water flux compared to pristine membrane that measured 3.14(L/m2h) for bare membrane and 9.96 (L/m2h) for the superior ones. Salt rejection measured 82% for the pristine membrane whereas that was between 77%–90% for the nanocomposite membranes. Membrane tensile strength also improved by increase of composite NPs ratio into the polymer matrix. The nanocomposite membranes showed more BSA solution flux and outstanding antifouling properties compared to bare ones. The FRR measured ∼46.2% for bare membrane whereas that was (∼69.9% to ∼89.5%) for the nanocomposite membranes.

Fabrication of pH-sensitive thin-film nanocomposite nanofiltration membranes with enhanced performance by incorporating amine-functionalized graphene oxide

To determine the influence of positively charged graphene-based nanofillers on the nanofiltration (NF) performance as well as strengthen the nanofiller stability in a polypiperazine-amide (PPA) matrix, graphene oxide (GO) was first modified with ethylenediamine (EDA) and polyethylenimine (PEI) to obtain two kinds of aminated graphene oxide (AGO) nanofillers with a positive charge. The characterization results of AGO nanofillers indicated that EDA and PEI were successfully grafted onto GO via amide bonds without destroying the original GO structure. Then, novel thin film nanocomposite (TFN) NF membranes were fabricated by incorporating AGO nanofillers into the PPA skin layer using the interfacial polymerization (IP) method. With the addition of 60 ppm GO-EDA or 40 ppm GO-PEI, the TFN-GO-EDA-60 and TFN-GO-PEI-40 NF membranes showed optimal individual permselectivities ascribed to the formation of thinner, smoother and stronger hydrophilic nanocomposite skin layers. While retaining a rejection level of sodium sulfate >98%, the water fluxes of TFN-GO-EDA-60 and TFN-GO-PEI-40 membranes reached 59.6 and 62.1 L·m−2·h−1, corresponding to 154.4 and 160.9%, respectively, of that of the TFC-blank membrane. Furthermore, both the TFN-GO-EDA-60 and TFN-GO-PEI-40 NF membranes exhibited excellent anti-fouling capabilities, chlorine resistances as well as mechanical stabilities compared with TFC-blank membrane. However, their anti-fouling performance and salt rejection varied with the solution pH due to the positively charged AGO nanofillers. Moreover, GO-PEI demonstrated a greater potential for enhancing the performance of TFN NF membranes compared with that of GO-EDA.

Improved performance of thin-film nanocomposite nanofiltration membranes as induced by embedded polydopamine-coated silica nanoparticles

We modified thin-film nanofiltration membranes by embedding in them silica nanoparticles (SiNPs) coated with polydopamine (PDA), which is well-known to mimic the adhesive characteristics of mussels. The coating process was triggered by the oxidative self-polymerization of dopamine on the surface of SiNPs, and the membranes were fabricated through interfacial polymerization (reaction between piperazine and trimesoyl chloride, TMC). Thin-film nanofiltration membranes embedded with PDA-SiNPs (TFNPDA-SiNPs) were compared with pristine polyamide membrane, as well as with polyamide membrane embedded with uncoated SiNPs. Energy-dispersive X-ray spectroscopy confirmed that TFNPDA-SiNPs contained more nanoparticles than the polyamide membrane with uncoated SiNPs. Accordingly, the hydrophilicity of TFNPDA-SiNPs was higher. TFNPDA-SiNPs fabricated from using a concentration of 0.35 g PDA-SiNPs/g TMC delivered the highest pure water flux of 80.0 ± 4.6 L⋅m−2⋅h−1 at 6 bar; salt rejections were as follows: RNa2SO4 = 97%; RMgSO4 = 94%; RMgCl2 = 68%; RNaCl = 35%. The TFNPDA-SiNPs also demonstrated the greatest antifouling ability, as its flux was the highest at the end of three cycles of antifouling tests, where bovine serum albumin was used as model protein foulant.

Modulating hydrophobicity of composite polyamide membranes to enhance the organic solvent nanofiltration

A kind of thin film composite polyamide nanofiltration (NF) membrane was synthesized via the interfacial polymerization between a new diamine monomer of 4,4′-diaminodiphenylmethane and trimesoyl chloride on the surface of cross-linked polyetherimide, and evaluated in some organic solvents including ACN, MeOH, EtOH, THF, etc. The optimal organic solvent NF membrane was selected to prepare respectively the hydrophilic membrane (Phi-NF) via grafting of Tris and the hydrophobic membrane (Pho-NF) via grafting of 2,2,2-trifluoroethylamine, combining with the characterization of ATR-FTIR, XPS, SEM, 13C NMR, AFM, etc. The permeance values of Phi-NF and Pho-NF membranes change greatly with organic solvents. Pho-NF-2 possesses the highest permeance of 66.4 L m−2 h−1 MPa−1 in THF with the erythrosin B (EB) rejection of 99.5%. Through analyzing the physiochemical properties of the organic solvents and calculating the surface energy, the correlations are deduced for the synthesized membranes, illustrating that the permeances of organic solvents are roughly proportional to the specific solvent properties for Phi-NF-2 and Pho-NF-2. The results suggest one promising method to enhance the separation performance of organic solvent NF membranes.