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Nanofiltration (NF) membranes were prepared from a solution processable polyelectrolyte complex (PEC) between sodium carboxymethyl cellulose (CMCNa) and poly(2-methacryloyloxy ethyl trimethylammonium chloride) (PDMC). Electrostatic complexation structures of the PEC were studied by light transmittance and field emission electron scanning microscopy (FESEM). It is found that the electrostatic complexation structure of the PEC membranes determines their NF performance, which is conveniently tailored via the pH values of casting solutions. For membranes prepared at the optimum solution pH 2.1, their water flux and salt rejection to K2SO4 (1 g L−1) are 18 g m−2 h−1 and 97%, respectively, when the operation pressure and temperature are 0.6 MPa and 25 °C. Both the water permeability and the salt selectivity are substantially improved compared to the pristine CMCNa NF membrane. In addition, antifouling performance of the PEC membrane is improved, coupled with an exceptional stability versus the operation time.

Graphene oxide (GO) spongy materials as environmental pollutant scavengers have drawn great attention owing to their ultralarge surface area, unique spongy structure and hydrogen-bonding interactions. Herein, a novel GO sponge was synthesized by an improved Hummer's method followed by a freeze-drying process and its adsorption capacity of 2,4,6-trichlorophenol (TCP) was investigated. The structural features of GO sheets and GO sponge have been characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM) and scanning electron microscopy (SEM). Specific surface area assessment and pore distribution measurements were analyzed by Micromeritics ASAP 2020. The adsorption mechanism and kinetics study of TCP on GO sheets and GO sponge were studied using a batch equilibration method. The results suggest that the GO sponge presented a higher adsorption capacity than GO sheets due to its large specific surface area and TCP had an optimum adsorption capacity on both GO sheets and GO sponge at pH 2.0–6.0. Adsorption isotherms and kinetics curves of TCP on GO sheets and GO sponge were nonlinear, indicating a homogeneous monolayer chemical adsorption process.

A series of PVC-Li 1.6 Mn 1.6 O 4 precursor membranes were prepared by the solvent exchange method using spinel-type lithium manganese oxide powder (Li 1.6 Mn 1.6 O 4 ) as the precursor, poly(vinyl chloride) (PVC) as the binder, and N,N-dimethyl acetamide (DMAc) as solvent. The Li + of the precursor membrane was extracted by treated with HCl solution to obtain PVC-H 1.6 Mn 1.6 O 4 lithium ion-sieve membrane adsorbent. The preparation conditions were investigated by changing the concentration of PVC and Li 1.6 Mn 1.6 O 4 , and the thickness of liquid film. The structure, morphology and adsorption properties of PVC-H 1.6 Mn 1.6 O 4 lithium ion-sieve membrane were carried out by scanning electron microscope and atomic absorption spectrophotometer. The adsorption capacity depended on the preparation conditions. The membrane prepared with concentration of 10 wt% PVC and 15 wt% Li 1.6 Mn 1.6 O 4 in DMAc and liquid film thickness of 0.30 mm is optimum for the adsorption of Li + from aqueous solution. The thickness of membrane prepared under above conditions is about 0.1 mm. Repeated adsorption–desorption test indicates that the PVC-H 1.6 Mn 1.6 O 4 lithium ion-sieve membrane can be effectively regenerated with HCl solution and reused for Li + adsorption without significant loss in the adsorption capacity. Li + adsorption experiments confirm that the PVC-H 1.6 Mn 1.6 O 4 lithium ion-sieve membrane possesses high selectivity for Li + in the presence of Na + , K + , Ca 2+ and Mg 2+ . According to the coefficients, the isothermal data correlated with the Langmuir model better than the Freundlich model, and the adsorption process follows a pseudo-second-order kinetic model.

Polyamide reverse osmosis membranes incorporating carboxy-functionalized multi-walled carbon nanotubes (MWNTs) were prepared by interfacial polymerization of metaphenylene diamine and trimesoyl chloride. The pristine MWNTs were pre-treated with mixed acids before being modified with diisobutyryl peroxide to enhance their dispersity and chemical activity. The prepared nanocomposite membranes had a 100–300 nm skin layer and the modified MWNTs were embedded within the skin layer, which was confirmed by scanning electron microscopy and transmission electron microscopy. The surface of the nanocomposite membrane was shown to be more negatively charged than bare polyamide membrane. It was shown that with an increase in the carbon nanotube loading in the membrane, the membrane morphology changed distinctly, leading to a significantly improved flux without sacrificing the solute rejection. Meanwhile, the nanocomposite membranes showed better antifouling and antioxidative properties than MWNT-free polyamide membranes, suggesting that the incorporation of modified MWNTs in membranes is effective for improving the membrane performance.

Self-assembly and non-solvent induced phase separation (SNIPS) was extensively used in the fabrication of isoporous membranes for its compatibility with massive production. However, for the well-defined SNIPS, preparation of isoporous membranes from low χ block copolymers is challenging because self-assembly of these polymers is usually hard to induce. In this work, we showed that such a problem could be effectively overcome through the co-assembly strategy by blending with homopolymers that interacted with block copolymers (BCPs). For the polystyrene- block -poly(N-isopropylacrylamide) (PS- b -PNIPAM) which has relatively small Flory-Huggins interaction parameter (χ ≈ 0.05), the formation of the isopores was readily induced when polyacrylic acid (PAA) was added as an additive. Three PS- b -PNIPAM with the PNIPAM mass fractions ranging from 5.9 to 36.5 wt% were used as membrane-forming materials, and three PAA with different molecular weights (MWs) were used to investigate how MWs of homopolymer affected the isopore formation. The selective H-bonding of PAA with PNIPAM was in-situ determined by infrared spectroscopy, which was supported by small angle X-ray scattering that the microphase separation of PS- b -PNIPAM in solution was remarkably enhanced by the PAA. The contribution of PAA on isopore formation was also found for the casting solutions of a wide range of concentrations and different solvent compositions. Finally, membranes prepared from co-assembly with PAA showed obviously improved pore ordering and higher permeability. Our finding showed herein actually provided a facile route to prepare isoporous membranes from low χ BCPs under general conditions.

It is significant to develop anion exchange membranes (AEMs) with efficient ionic transport and desirable stabilities (mechanical and dimensional) for various applications, including electrodialysis (ED). In this paper, three types of composite AEMs based on quaternized polysulfone (QPSU) and polyvinyl alcohol (PVA) blends: QPSU/PVA composite AEM (M0), potassium thioacetate (PT) modified QPSU blending with PVA (M1) and QPSU blending with 4-formylbenzoic acid (FBA) modified PVA (M2-X, X = mass ratio of the FBA with the values of 0.05 and 0.20), have been investigated. Our investigation demonstrates that the swelling ratios of M1 and M2-0.05 were significantly reduced to 10.9% and 4.7% at 20 °C, much lower than M0 (16.9%). This can be due to the formed hydrogen-bonding network via OH from PVA and >C O from PT structure on PSU within M1 or the ionic crosslinking interactions between COO– from FBA and >N+– on QPSU within M2. Though the free volume inside AEM matrix is reduced, the chloride ion conductivities of M1 and M2-0.05 reach 20.5 mS cm−1 and 23.5 mS cm−1 at 20 °C. In ED application, the optimized M2-0.05 has the highest NaCl removal ratio of 74.6% within 120 min (vs. 61.06% of the commercial AEM-Type II), and exhibits better desalination performance with high current efficiency (98.0% vs.92.8%) and lower energy consumption (2.2 kWh kg−1 NaCl vs. 2.4 kWh kg−1). The simple preparation process and good ED performance of M2-0.05 are indicative of its potential ED application.

Oil/water separation membranes with high flux efficiency and robust anti-oil-fouling property have attracted numerous attention, and superwetting carbon nanotube (CNT) membranes are promising candidates. The key challenges focus on the versatile integration of multiple materials/structures and the facile functionalization towards superhydrophilicity/underwater superoleophobicity. In this study, a polyzwitterion/titania functionalized carbon nanotube membrane for antifouling and high-flux oil/water emulsion separation is synthesized by a novel and simple dual-bioinspired strategy. The strategy involves the co-assembly of polyzwitterion and bioinspired-adhesive polydopamine (PDA) modified CNTs and the bioinspired mineralization of titania nanoparticles (TNPs). The as-prepared CNT membrane is evenly decorated with polyzwitterion and TNPs mediated by the comprehensive adhesive capability of PDA. The integration of the hydrophilic advantages of polyzwitterion and titania and the integration of the multiscale structures of CNTs and TNPs endow membranes with superhydrophilicity, underwater superoleophobicity and anti-oil-adhesion property. The nanoscale porous structures of CNT assembled network ensure the high permeability (about 3400 L m−2 h−1) and separation efficiency (over 99.5% for emulsified oils) of membranes. Furthermore, when applied to oil-in-water emulsion separation, the as-prepared CNT membrane exhibits good recycle performance throughout several filtration cycles and maintains high recovery ratio of 95% after several cycles, indicating excellent antifouling property. The dual-bioinspired strategy combining bioinspired adhesion and bioinspired mineralization provides new insights into the design and construction of nano-structured membranes for oil/water separation.

Solvent resistant nanofiltration (SRNF) membranes are highly demanded in processing organic solutions especially those contain large molecules with molecular weight between 200 to 2000 Da, yet they have some drawbacks such as relatively poor solvent resistance and low solvent permeance. The current work presented an innovative class of amino-functionalized graphene quantum dots (aGQDs) embedded thin-film nanocomposites (TFN) for SRNF membranes which were prepared via interfacial polymerization (IP) and subsequent steps (chemical imidization, crosslinking, and solvent activation). The prepared membranes enabled covalent interactions not only between the IP skin layer and the substrate, but also between the IP layer and the embedded aGQDs. The ethanol permeance and surface porosity increased by 44% and 69%, respectively, with the embedment of aGQDs under the optimal conditions, while the Rhodamine B (RDB, 479 Da) rejection maintained essentially stable above 99%. Furthermore, our novel membranes exhibited excellent long-term stability, with a rejection of over 99% for Rose Bengal (RB, 1017 Da) during the continuous filtration of 100 mg L −1 RB/ N , N -dimethyl formamide (DMF) solution at room temperature for more than 768 h. They also exhibited good organic solvent resistance and high-temperature tolerance in both DMF and NMP solvents, with a RDB rejection of over 99% and an ethanol permeance of about 38 L m −2 h −1 MPa −1 after being immersed in DMF at 80 o C for 248 h, and a RDB rejection of over 99% and an ethanol permeance of about 41 L m −2 h −1 MPa −1 after being immersed in NMP at 80 o C for 232 h. The results demonstrated that the aGQDs-embedded TFN OSN membrane has vast potential in SRNF applications.

Smart gating membranes with self-regulating nanopores/nanochannels are highly desirable for water gating and separation of small molecules. Based on the nanochannels in the graphene oxide (GO) membrane, we designed positive thermo- and negative pH-responsive GO/hydrogel composite membranes (GOGMs) through a simple filtration-accumulation of GO sheets and hydrogels. The shape-flabby hydrogels can be perfectly inlaid between two GO sheets by changing their shape, and also act as a bond between GO and substrates. Thermo- and pH-responsive hydrogels embedded between the GO sheets impart adjustable water channels to the GO membrane. The channel tunability of hydrogel-studded GO membrane derives from the size conversion of hydrogel and the constant layer spacing of GO sheets. The hydraulic permeability of GOGMs was explored within the wide pH range of 2–6 and the temperature interval of 20–44 °C. The results revealed that the hydraulic permeability of the GOGMs can be reversibly adjusted with a high thermo- and pH-responsive gating coefficients. The GOGMs with self-regulated channels have various permeability properties for small molecules under different conditions. Moreover, the membrane thickness and the ratio of microgel to GO both have an effect on the water permeation and response performance of the GOGMs. These environmental stimuli-responsive membranes with thermo- and pH-responsive channels has numerous potential for applications in smart gating systems, liquid-based controlled release systems and smart separation systems.

A ternary nanocomposite consisting of N-doped graphene (NGR)/TiO2/activated carbon (NGRT@AC) was prepared, and the components’ synergetic effect on dye degradation was investigated after deposition on the surface of a polysulfone membrane (PSF). As far as we know, this ternary composite catalyst has never previously been used to degrade dyes nor been used as a functional layer for separation membranes. The surface morphology and structure of the as-prepared membranes were analyzed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The NGRT@AC-modified PSF membrane (NGRT@AC-PSF) presents excellent photodegradation efficiency to methyl orange (MO) under both UV (95.2%) and sunlight (78.1%) irradiation, much higher than those values of PSF, TiO2- modified PSF (TiO2-PSF), and N-doped graphene/TiO2 (NGRT)-modified PSF membranes (NGRT-PSF) under the same conditions. The high flux recovery ratio (95.5%) demonstrates that the NGRT@AC-PSF membrane shows improved antifouling performance. The photocatalytic results prove that surface deposition method (95.2%) was better than the blending method (31.1%) for forming high-performance membranes. Therefore, the NGRT@AC-PSF membrane has the potential for broad applications in dye degradation to treat waste water from textile industries.

Pilot-scale tests were carried out on a nanofiltration (NF)–seawater reverse osmosis (SWRO) integrated membrane system (IMS) using a kind of ultra-low pressure and high selectivity NF membrane (ESNA3, Hydranautics). Three different schemes were investigated for the NF seawater softening processes. The effect of increasing NF permeate recovery rate ( R NF ) on the potential of scaling in the NF and RO modules was investigated in term of concentration polarization modulus ( CP ) of scalant ions, Stiff and Davis Stability Index ( S&DSI ), and Supersaturation Index ( SI ) of CaCO 3 and CaSO 4 . The results show that within the test range, high R NF , large permeate flux and low specific energy consumption ( E s) could be achieved simultaneously for the loosen NF membrane. The E s for ESNA3 membrane could be lower than 0.95 kWh · m − 3 . CP SO4 2 − was larger than CP CO3 2 − in the NF module under the NF retentate recycling operating conditions. The SI data indicated that at R NF of higher than 65% and with antiscalant addition and pH adjustment, CaSO 4 would preferentially precipitate on NF membrane surface. However, with pH adjustment, the S&DSI values on the NF and SWRO membrane surface remained negative, which indicated that CaCO 3 scaling could not form in the pilot test operating range.

Positively charged thin-film composite hollow fiber nanofiltration membranes were developed by the dip-coating method using polypropylene hollow fiber microfiltration membrane as support, polyvinyl alcohol (PVA) and polyquaternium-10 (the reaction product of hydroxyethyl cellulose with a trimethylammonium substituted epoxide, PQ-10) as coating materials, and glutaraldehyde as cross-linking agent. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), measurements of streaming potential and contact angle were employed to characterize the obtained membranes. The permeation properties were estimated through pressurized cross-flow permeation tests and the dye removal performance were evaluated through submerged filtration tests using cationic dye aqueous solutions. It was found that the salt rejection order of the membrane was CaCl2 > MgCl2 > NaCl > MgSO4 > Na2SO4 at neutral pH. The desired membrane with a molecular weight cut-off of about 650 Da had a pure water flux of 25.7 l/m2 h and a rejection of 92.8% to 500 mg/l CaCl2 aqueous solution at 3.0 bar. The membrane could effectively remove cationic dyes from aqueous solution with good long-term performance stability through submerged filtration. The observed rejections to Brilliant green, Victoria blue B and Crystal violet were 99.8, 99.8 and 99.2%, respectively, under the trans-membrane pressure of 0.7 bar.

This work reports a novel polysulfone (PSf) membrane blended with a ternary copolymer having capsaicin-mimic moieties as an anti-fouling and anti-bacterial agent. This copolymer, P(H-M-A), was synthesized from N-(4-hydroxy-3-methoxy benzyl) acrylamide (HMBA), methyl methacrylate (MMA) and acrylic acid (AAc) by free radical polymerization. The effects of the P(H-M-A) content in the membrane casting solution on the structure and ultrafiltration performance of the membrane were investigated. It was shown that incorporating a small quantity of P(H-M-A) into the membrane improved the permeate flux and rejection when tested with a model humic acid (HA) solution and actual raw seawater. The P(H-M-A)-containing membranes exhibited excellent anti-bacterial activity, which was attributed to the capsaicin-mimic moieties, and their anti-fouling characteristics were demonstrated with fouling and cleaning experiments. This work suggests that P(H-M-A) is a potential hydrophilic anti-fouling and anti-bacterial agent for use in membranes for water applications.

Surface modifications including physical and chemical treatments are effective approaches to improve the fouling and chlorine resistances of the commercial thin-film composite (TFC) aromatic polyamide reverse osmosis (RO) membranes. However, the major problem facing the modification is the influence on membrane performance. In this study, surface modification of a commercial TFC RO membrane was performed through redox initiated graft polymerization of N-isopropylacrylamide (NIPAm) followed by acrylic acid (AA) and the modified membrane showed improved membrane properties. Membrane characterization was conducted through ATR-FTIR analysis, zeta-potential analysis, contact angle measurement and cross-flow permeation test. Changes in surface characteristics confirmed the graft polymerizations of NIPAm and AA. The surface of the membrane became more hydrophilic and negatively charged after modification. The membrane modified under certain conditions showed both increased water flux and salt rejection. Fouling experiments with bovine serum albumin (BSA) aqueous solution demonstrated that the modification could mitigate the deposition of foulants on the membrane surface through enhancing electrostatic repulsion and lowering hydrophobic interaction between BSA molecules and membrane surface and thereby improving fouling resistance. Furthermore, chlorination tests also showed that surface modification through graft polymerization of NIPAm followed by AA could effectively enhance the chlorine stability of the polyamide membrane.

2-Amino-1-propanol (AMP) is a key intermediate compound in the production of antibiotics, with increasing demand in industry. In this study, we propose a newly designed bipolar membrane electrodialysis (BMED) system with a novel three-compartment configuration for the processing of AMP from the AMP sulphate solution. The operational parameters were investigated for optimizing the performance of this novel BMED stack, compared to the traditional two-compartment BMED stack in the pilot scale experiment. The experimental results indicate that this novel type of BMED stack offers a better performance for AMP processing than the conventional two-compartment BMED stack. The optimum performance was observed at the current density ranging from 40 to 60 mA cm −2 and a spacer thickness of 0.70 mm. The corresponding current efficiency and energy consumption reached up to 53.4% and 3.135 kWh kg −1 , respectively. The two-compartment BMED stack was found to have a low current efficiency (39.8%) and a high energy consumption (3.864 kWh kg −1 ). Pilot-scale experiments for an industrial application of this novel BMED stack have been applied, demonstrating that the BMED process is feasible and economically alternative for AMP purification in the industry.

Using molecular dynamics simulations, we study the transport of Li+ and Mg2+ through membranes formed from armchair type (8,8) to (11,11) single wall carbon nanotubes (SWNTs) under hydrostatic pressure, and investigate the potential of mean force(PMF), conductance and axial density distributions of ions in the carbon nanotubes, the results show that under 100 MPa, (9,9) and (10,10) SWNT are capable of extracting Li+; when adjusting pressure to 200 MPa, (8,8), (9,9) and (10,10) tubes can separate Li+ and Mg2+ with higher ion fluxes which also augment with increasing tube diameters. By calculating the potential mean force for ion translocation, we show that Mg2+ face greater energy barrier than Li+ when passing the carbon nanotube with same diameter, and free energy difference of ∼8 kJ/mol seem to be the threshold to effectively separate Li+ and Mg2+. Membrane incorporating narrow carbon nanotubes is found to be promising in Li+ and Mg2+ separation.

Pilot-scale experiments were carried out on a nanofiltration (NF)–seawater reverse osmosis (SWRO) integrated membrane system (IMS) to evaluate scaling potential on NF and SWRO membrane surface using a kind of loosen NF membrane and costal seawater. The effect of NF permeate recovery ( R NF ) increasing on the occurrence of scaling in the NF and SWRO module was investigated in term of concentration polarization modulus ( CP ) of scalant ions, Stiff and Davis Stability Index ( SD SD and at R NF of higher than 30%, SI of CaSO 4 on NF membrane surface increased gradually higher than 1.0, which indicated that CaSO 4 scale is more apt to form on the NF membrane surface than CaCO 3 at that NF permeate recovery. This scaling sequence in the loose NF module was different from that in traditional SWRO desalination processes.

Cogeneration for power and desalination could not only improve the economic benefit of the power plant, but also afford the high quality water to solve the freshwater shortage. Considering the demand of power and water, a detailed mathematical model of the cogeneration system targeting the minimum total annual cost (TAC), which includes the power plant, multistage flash (MSF) and reverse osmosis (RO), is proposed and described as a mixed integer nonlinear programming (MINLP) problem. The modified genetic algorithm (MGA) with mixed coding is put forward to solve the model developed by us. A case study, which is supposed to supply 250 MW of power and 12,000 m3/h of water for Huangdao District of Qingdao City, is analyzed in order to illustrate the model capabilities. The results show that the operation pattern of the cogeneration system could be varied in terms of the water demand. When the water demand is lower than 8000 m3/h, the combination of power plant associated with MSF is adopted and the condensing-extraction steam turbine is selected. When the water demand of water is higher than 8000 m3/h, the tri-combination of power plant, MSF and RO is the optimal choice, in which back pressure steam turbine is selected.

In this study, poly(vinylidene fluoride)-graft-poly(2-hydroxyethyl methacrylate) (PVDF-g-PHEMA) and poly(vinylidene fluoride)-graft-poly(dimethylamino)ethyl methacrylate) (PVDF-g-PDMAEMA) covalently binding onto the PVDF polymer synthesized by atom transfer radical polymerization (ATRP), were used as additives in the manufacture of novel PVDF ultrafiltration (UF) membranes. The hydroxyl groups on the PVDF-OH polymer by Fenton reaction were used for the immobilization of alkyl halide ATRP initiator. The effects of chemical composition and surface morphology on blend membrane were investigated by X-ray photoelectron spectroscopy, Fourier transform infrared spectrometer, scanning electron microscopy and thermo-gravimetric analysis. Water contact angles and water intake measurements indicated that the introduction of PHEMA graft chains promoted remarkably the surface hydrophilicity of PVDF membranes. It was also found that PVDF/PVDF-g-PHEMA blend membrane provided higher pure water flux of 87.9 l/m2 h...

In this study, several anti-fouling approaches including coagulation conditions (FeCl 3 dosage and feed pH), air-enhanced backwash (AEB) conditions (backwash interval and AEB duration) and chemical cleaning conditions (reagents, soak time and temperature) were evaluated to enhance the feasibility of a commercial ultrafiltration (UF) membrane as a pretreatment of RO seawater desalination. A tubular commercial ceramic UF membrane with a surface layer of zirconium dioxide (ZrO 2 ) and a supporting layer of α-alumina oxide (α-Al 2 O 3 ) was employed in this study. The results showed that ferric coagulation was functional to enhance the performance of ceramic UF for seawater treatment, especially on COD removal. The trial of cleaning demonstrated that the performance of NaClO was much better than that of HNO 3 under various evaluated pH values. The relevant additional experiments showed that the cleaning efficiency increased with NaClO concentration, soak time and soak temperature but decreases when soak temperature was up to 60 °C. An important finding of this study is that the fouled membrane from coagulation-filtration trial can be easily and quickly recovered by acid cleaning regents followed by NaClO solution. Furthermore, short backwash interval performed more efficiently. However, it is certain that both backwash interval and AEB duration enhanced less than other approaches on the permeate quality. This study finally summarized the operating condition of each anti-fouling approach for the further potential application of UF ceramic membrane as a pretreatment of RO seawater desalination.

The possibility and efficiency of submerged nanofiltration (SNF) in the removal of melanoidins from the biologically treated molasses fermentation wastewater were evaluated in this study. Submerged filtration tests were conducted with biologically treated molasses fermentation effluent employing lab-made membrane modules manufactured from lab-fabricated flat-sheet thin-film composite polyamide nanofiltration membranes with a molecular weight cut-off (MWCO) of about 580 Da. Treatment efficiency in terms of color removal, permeate flux as well as COD reduction was investigated under different trans-membrane pressures (TMPs) and various volume concentrating factors (VCFs). The results showed that melanoidins could be effectively removed from the biologically treated molasses fermentation wastewater by submerged nanofiltration and the electrolytes presented in the effluent were nearly not retained by the membrane, so that the nanofiltration membrane module could be operated under a low suction pressure. Both the removal efficiency of melanoidins and the reduction ratio of COD increased with the increase of TMP and/or VCF at the expense of water permeability. Steady flux of 3.90 L/m2 h, color removal ratio of 99.5% and COD reduction ratio of 93.8% could be achieved by the submerged nanofiltration system operated under the TMP of 0.8 bar and VCF of 4.0. Furthermore, under the same VCF, compared with the pressurized nanofiltration system (PNF), the SNF system is more anti-fouling and easily to be physically cleaned.

Cellulose acetate (CA) hollow fiber membrane with improved permselectivity for nanofiltration was developed by hydrolysis and carboxymethylation of an original cellulose triacetate semi-permeable membrane. The effects of these modifications on the structure and surface properties were characterized by ATR-FTIR, XRD, SEM and measurements of streaming potential and contact angle. The permeation attributes of the obtained membrane were evaluated through cross-flow permeation tests and the improved permselectivity was also demonstrated through dye removal tests. The results showed that hydrolysis greatly increased the membrane pore size and surface hydrophilicity, but decreased the membrane surface charge, while carboxymethylation had little effect on the membrane pore size, but increased the membrane surface hydrophilicity and negative charge. CA hollow fiber nanofiltration membrane with a pure water permeability of 5.2 l/m 2 h bar, NaCl rejection of 66.4% and Na 2 SO 4 rejection of 95.4% could be obtained through modification an original CA semi-permeable membrane having a pure water permeability of 2.3 l/m 2 h bar, NaCl rejection of 90.8% and Na 2 SO 4 rejection of 91.5%. Additionally, in treating Congo red and Methyl blue aqueous solutions, the modified CA membrane exhibited improved dye removal rates and higher water fluxes of more than two times compared with the original membrane.

A novel composite nanofiltration membrane was prepared from O-carboxymethyl chitosan (O-CMC) and epoxy chloropropane (ECH) through coating and chemical cross-linking reaction on the polyacrylonitrile (PAN) supporting layer. O-CMC was synthesized from chitosan and monochloroacetic acid. Chemical structures and compositions of O-CMC and NF membranes were characterized by infrared spectroscopy, and morphological structures were characterized by atomic force microscopy and field emission scanning electron microscopy. Permeation performance of NF membranes was examined with a cross-flow flat NF membrane device. Preparing conditions of NF membranes were optimized by studying the change of salt rejection and permeation flux, and the optimum conditions were determined as follows: casting solution concentration 3 wt.%, ECH concentration; 2 wt.%, cross-linking temperature; 50 °C and cross-linking time; 12 h. Furthermore, properties of the optimal NF membrane were tested in different operating conditions. At 0.5 MPa and 25 °C, its salt rejection and permeation flux to 1000 mg·L− 1 Na2SO4 aqueous solution were 94.36% and 16.78 L · m− 2·h− 1, respectively. Rejections of the membrane to different inorganic electrolyte solutions (1000 mg·L− 1) accorded with the following order: Na2SO4 > NaCl > MgSO4 > MgCl2. In addition, the MWCO was about 689 Da, and the zeta potentials were negative in experimental pH range. At last, good durability and stability were exhibited by the means of long-term operation during 2 weeks.

An novel method on preparation of precursor solution for solvent separation of molybdenum (Mo) and tungsten (W) by hydrogen peroxide (H 2 O 2 )-complexation from the ammonium tungstate solution containing high Mo was studied. The precursor solution was obtained via evaporation deamination and H 2 O 2 -complex transformation processes. Then it was extracted with a mixture extractant of tri-alkyl phosphine oxide (TRPO) and tributyl phosphate (TBP) to separate Mo and W. The results indicated that the evaporation deamination complex method reduced the acid consumption by more than 90% in comparison with the traditional directly acid regulation complex method. The transformation rates of W and Mo were higher than 95% and the decomposition rate of H 2 O 2 was less than 15% at a 1.8 - 1.9 times H 2 O 2 dosage, 45-50 °C, initial pH of 1.80-1.90, and transformation volume ratio of 100% for 60 min in the H 2 O 2 -complexation transformation process. The minimum extraction rate of W was 2%, the maximum extraction rate of Mo was 82.6% and the highest separation coefficient was 76.7 in a single-stage extraction.

Color removal and chemical oxygen demand (COD) reduction of biologically treated textile effluent through submerged filtration using nanofiltration membrane were investigated in this study. Submerged filtration tests of biologically treated textile effluent were conducted under different trans-membrane pressures (TMP) and various volume concentrating factors (VCF) employing lab-made hollow fiber membrane modules. It was found that the color and COD presented in the biologically treated textile wastewater could be effectively removed through submerged filtration using hollow fiber nanofiltration membranes with molecular weight cut-off of about 620 Da, while the electrolytes presented in the effluent were retained by the membrane to a very small extent, especially under VCF higher than 2.0, so that the nanofiltration membrane module could be operated under a low suction pressure. The increase of TMP and/or VCF resulted in a decline in water permeability and an increase in both color removal and COD reduction. Under the TMP of 0.8 bar and VCF of 4.0, the submerged nanofiltration system exhibited a steady permeate flux of 5.15 l/m2 h, a color removal rate of 99.3% and a COD reduction rate of 91.5%. Furthermore, the submerged nanofiltration system possessed high water cleaning efficiency of more than 93.0%.

Thin-film composite (TFC) nanofiltration (NF) membranes with improved acid stability were fabricated through the interfacial polymerization of trimesoyl chloride (TMC) naphthalene-1,3,6-trisulfonylchloride (NTSC), and piperazine (PIP) on a porous polysulfone support membrane by varying the NTSC content in TMC-organic solution. The physico-chemical characteristics of the membranes were analyzed by ATR-FTIR, streaming potential measurement and surface contact angle measurement, the permeation properties were evaluated through cross-flow permeation tests, and the acid stability was investigated through both static acid soaking tests and long-term permeation tests under acidic condition. It was found that, as the NTSC content in TMC-organic solution increased, the membrane surface became more hydrophilic and negatively charged, the pure water permeability and molecular weight cut-off of the formed NF membrane increased from 5.5 to 10.6 l/m 2 h bar and about 360 to 660 Da, respectively, while the rejection rate to Na 2 SO 4 firstly increased from 98.2 to 98.7% and then declined to a lower value of 97.8%. After soaking in 8 w/v% H 2 SO 4 for 30 days or filtration with 4.9 w/v% H 2 SO 4 for 60 days, the TFC membranes prepared from TMC and NTSC showed little performance change, while serious performance deterioration occurred with the TFC membrane prepared from TMC.

Nanofiltration (NF) is suitable for softening seawater and providing permeates with excellent quality for oilfield water injection. However, the industrial application of aqueous polymer solution prepared by NF softened seawater for oilfield polymer flooding has not been reported yet. In this work, a pilot-scale ultrafiltration (UF)–NF integrated membrane system (IMS) has been investigated as a method of removing divalent ions from seawater and providing softened water for oilfield polymer flooding. The performance of the selected NF 4040 spiral membrane module was investigated under different operating conditions. In addition, the performance of the NF membrane module at high system recovery was also investigated to simulate the practical situation. Finally, NF permeation waters were used to prepare HPAM polymer solutions to evaluate the possibility of preparing polymer solution with NF permeation water for polymer flooding in offshore oilfield. The results showed that, with the properly selecte...

Age–momentum correlation (AMOC) positron annihilation technology was applied for the first time to composite nanofiltration membranes (NFMs) with zwitterionic terpolymers (TPs) to explain their high permeability and high salt selectivity. The NFMs showed an increase in the water flux from 32.6 to 46.3 L m–2 h–1 without sacrificing the salt selectivity when the zwitterionic monomer 3-dimethyl(methacryloyloxyethyl)ammonium propanesulfonate (DMAPS) content was increased from 0 to 4.35 mol %. The influence of DMAPS content on membrane microstructure, water permeability, and salt selectivity was evaluated by means of AMOC positron annihilation studies. Positron annihilation results showed that the cross-linked TPs selective layer of NFMs was composed of two types of pores: free volume (based on τ3) with radius of about 3.5–3.1 A and nanocavity (based on τ4) with radius of 16.6–46.6 A. The performance of NFMs depends strongly on the free volume and nanocavity size. The effect of the zwitterionic DMAPS content o...

Reverse osmosis (RO) is currently the most important desalination technology and it is experiencing significant growth. However, the developments of membrane permselectivity in the past decade have been relatively slow, and membrane fouling remains a severe problem. The excellent water transport properties of biological membranes with specialized transmembrane proteins aquaporins as water-selective channels exceed those commercial membranes for water desalination. Supported phospholipid bilayers (SPBs) can maintain the biological activity of molecules and inhibit other non-specific adsorption of biological molecules. In this study, the main work is mostly focused on conditions ensuring most efficient coverage of the supporting nanofiltration (NF) membranes with phospholipid bilayers. Four different NF membranes as supports are explored to form phospholipid bilayers. The presence of SPBs on the four different NF membranes surface is verified and quantified by atomic force microscope (AFM), attenua...

A novel zwitterionic amide monomer (N-aminoethyl piperazine propane sulfonate, AEPPS) was synthesized and utilized in conjunction with piperazine (PIP) to perform the interfacial polymerization with trimesoyl chloride (TMC), producing thin-film composite (TFC) nanofiltration membranes (NFMs) with improved separation performance and antifouling property. Chemical structures and compositions of the zwitterionic monomers AEPPS and NFMs were characterized by (attenuated total reflectance) fourier transform infrared spectroscopy, nuclear magnetic resonance spectrometer and X-ray photoelectron spectroscopy. The surface morphology and hydrophilicity of NFMs were examined by field emission scanning electron microscopy, atomic force microscopy, dynamic water contact angle. The water permeability and antifouling property of NFMs are improved via introducing AEPPS into membranes. When tested with 1 g L −1 K 2 SO 4 aqueous solution at 25 °C and 0.6 MPa, the water flux of NFMs increases from 23.4 L m −2 h −1 to 43.1 L m −2 h −1 with increasing AEPPS content from 0 mol% to 3.2 mol%, while K 2 SO 4 rejection maintains around 97%. The NFMs containing zwitterionic moieties can resist bacterial adsorption and protein fouling efficiently, and show a stable and good separation performance during a long-time filtration process of 288 h.

Cellulose triacetate (CTA) forward osmosis membranes were prepared by immersion precipitation. Following a standard recipe for the preparation of reverse osmosis membranes, the concentrations of polymer, additives (lactic acid, methanol), and solvent composition in the casting solution were investigated with respect to membrane permeation and salt rejection. The membrane preparation parameters including the evaporation time and the coagulation bath temperature were investigated as well. A CTA membrane with a quasi double-skinned morphology was obtained. The CTA FO membrane showed a water flux higher than 10 kg/m2 h using 2 M glucose water solution as the draw solution and 0. 5 M NaCl as feed. A NaCl rejection of 95% was obtained.

Quaternized poly(4-vinylpyridine) (QP4VP) with varying side chains tethered to the pyridinium rings was synthesized. An ionic complexation between QP4VP and sodium carboxymethyl cellulose (CMCNa) was performed to prepare their soluble polyelectrolyte complexes (PECs). The structures of QP4VP, QP4VP–CMCNa PECs and PEC membranes (PECMs) were characterized by Fourier transform-infrared spectroscopy (FT-IR), 1H NMR, scanning electron microscope (SEM) and contact angle (CA) measurements. The effects of the side chain length on the surface hydrophilicity, degree of swelling, and sorption selectivity of the PECMs were studied. PECMs were applied to the pervaporation dehydration of aqueous ethanol, isopropanol and n-butanol. It was found that the separation performance could be tailored with the side chain length of the QP4VP, affording a new strategy for the optimization of the separation performance. For example, the flux of PECMs in the dehydration of 10 wt% water–isopropanol at 60 °C increased from 1000 g/m2 h to 1500 g/m2 h, without sacrificing the selectivity, by increasing the side chain length from 0 to 6 carbon atoms.

Dynamic layer-by-layer (LBL) self-assembly technology was used to prepare as few as three to five bilayers of poly(diallyl-dimethylammonium chloride) (PDADMAC) and poly(styrene sulfonate) (PSS) on negatively charged polysulfone (PS) ultrafiltration (UF) membranes of 50 kDa MWCO and compared with those of the static assembly membranes. The prepared dynamic assembly (PDADMAC/PSS)4 nanofiltration (NF) membrane showed a permeation flux of 60 L m−2 h−1 at 1.0 MPa, much higher than that of the commercial DL membrane (GE Osmonics, USA), but with a rejection of about 90% of SO42− which is relatively less than that of the DL membrane. The rejection performance showed that the dynamic–static assembly was more effective than others. Using dynamic–static assembly preparation, the rejection of (PDADMAC/PSS)3 membrane was about 90%, while the flux was about 55 L m−2 h−1 at 1.0 MPa. The surface morphology of the prepared LBL membranes were characterized by SEM and AFM, and no defect was found. The surface morphology of the membrane prepared by dynamic–static assembly was almost the same as the commercial membranes. The analysis of filtration resistance indicated that the deposition of the first and second bilayer was crucial during the whole preparation process.

A new bio-inspired method was applied in this study to simultaneously improve the monovalent anion selectivity and antifouling properties of anion exchange membranes (AEMs). Three-layer architecture was developed by deposition of polydopamine (PDA) and electro-deposition of N-O-sulfonic acid benzyl chitosan (NSBC). The innermost and outermost layers were PDA with different deposition time. The middle layer was prepared by NSBC. Fourier transform infrared spectroscopy and scanning electron microscopy confirmed that PDA and NSBC were successfully modified on the surfaces of AEMs. The contact angle of the membranes indicated an improved hydrophilicity of the modified membranes. A series of electrodialysis experiments in which Cl−/SO42− separation was studied, demonstrating the monovalent anion selectivity of the samples. The Cl−/SO42− permselectivity of the modified membranes can reach up to 2.20, higher than that of the commercial membrane (only 0.78) during 90 minutes in electrodialysis (ED). The increase value of the resistance of the membranes was also measured to evaluate the antifouling properties. Sodium dodecyl benzene sulfonate (SDBS) was used as the fouling material in the ED process and the membrane area resistance of modified membrane increase value of was only 0.08 Ωcm2 30 minutes later.

Acid stable thin-film composite membrane for nanofiltration was fabricated by interfacial polymerization of naphthalene-1,3,6-trisulfonylchloride (NTSC) and piperazine (PIP) on porous polysulfone support membrane. The performance of the membrane was optimized by studying the preparation parameters including monomer content, reaction temperature and additive in organic phase. The separation performance of the resultant membrane was evaluated through permeation experiments, the membrane property was characterized by ATR-FTIR, XPS AFM, SEM and streaming potential measurements, and the acid stability was investigated through both static acid soaking tests and long-term permeation tests under acidic condition. After exposure to 20%(w/v) H2SO4 for 2 months or running with 4.9%(w/v) H2SO4 for 60 day, the PIP-NTSC composite membrane showed minor change in separation performance and no evident chemical change in the active skin layer, indicating that the developed membrane possessed good acid stability. The desired membrane exhibited a pure water permeability of about 5.8 l/m2 h bar, a MWCO of as high as 5000 Da, and an attractive solute rejection of higher than 86.5% for a feed containing 500 mg/l Na2SO4 at 0.5 MPa. Furthermore, the PIP-NTSC composite membrane could be used to treat acidic effluents from metal industries with good perm-selectivity and long-term stability.

A novel process of solvent extraction for separation of molybdenum (Mo) from ammonium tungstate (W) solution containing high content of Mo was developed using a mixture of tri-alkyl phosphine oxide (TRPO) and tributyl phosphate (TBP) as extractant and hydrogen peroxide (H2O2) as complex agent. The extraction process was studied to optimize various parameters such as extractant concentration, contact time, temperature, dosage of H2O2, and initial pH of aqueous solution. The extraction isotherms for Mo were also plotted. The results indicated that the addition of TBP in organic not only improved phase separation both in extraction and stripping, but also increased the extraction of Mo and decreased the extraction of tungsten (W), and hence improved the separation properties of Mo/W. The extraction of Mo was higher than 63% and the separation coefficient βMo/W was larger than 80 under optimal conditions. The loading capacity was determined to be 12.33 g/L Mo and 9.44 g/L Mo at equilibrium pH of 1.58 and 2.05, respectively. The further separation of W and Mo was realized in stripping process. NH4HCO3 was the optimum stripping agent because of its good phase separation, effective stripping of Mo and high Mo/W selectivity. The effects of contact time, temperature, concentration of stripping agent and O/A ratio on the stripping were investigated with NH4HCO3. The stripping of Mo reached 89% in comparison to that of W that is less than 16% after one contact. The concentration of Mo in strip liquor was 70–90 g/L and the mass ratio of Mo/WO3 in strip liquor was larger than 26 at an O/A ratio of 8:1–10:1 using 0.8–1.0 mol/L NH4HCO3. The stripped organic was directly reused to extraction. A principle flowsheet of the recovery of Mo and W was developed.

Novel polyelectrolyte complexes (PECs) based on dual anionic group copolymers were prepared and their homogeneous membranes were subjected to pervaporation dehydration of acidic feed. Dual anionic copolymers containing weakly charged acid groups (COO − ) and strongly charged acid groups (SO 3 − ), poly(sodium acrylate-co-sodium sytyrenesulfonate) (P(AANa-co-SSNa)), with different compositions were synthesized by radical solution polymerization. SPECs (PECs containing SO 3 groups) consisted of negatively charged P(AANa-co-SSNa) and positively charged chitosan (CS) and their homogeneous SPEC membranes (SPECMs) with tunable compositions were prepared. Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) were used to characterize the structure and composition of P(AANa-co-SSNa) and its SPECs. Field emission scanning electron microscopy (FESEM) and contact angle (CA) were used to survey surface properties of SPECMs. Effects of pH values and temperatures of feed mixtures on the swelling behavior and pervaporation dehydration performance of SPECMs were examined. It is found that SPECMs containing SO 3 groups are resistant of acidic feed and display very good pervaporation performance even for the low pH feed. For instance, the water concentration in permeate for SPECM−0.30 reaches as high as 99.4 wt%, which is much higher than 60 wt% for PECM for water–isopropanol mixture with pH 1.2, and also maintains operation stability. The SPECMs could find considerable potential application to pervaporation dehydration of acidic feed.

To improve the pervaporation selectivity of poly(acrylic acid) sodium (PAAS) membranes incorporated with NaA zeolite, the interface compatibility between zeolite nanocrystals and the polymer matrix was improved by modifying NaA zeolite using 3-aminopropyltriethoxysilane (APTES). Both X-ray photoelectron spectra and FTIR confirmed the chemical modification, while the results of zeolite particle size analysis and scanning electron microscopy revealed the improved dispersion of the modified zeolite. Transmission electron microscopy images of these hybrid membranes indicated that the interface between the polymer and modified zeolite phases had improved. The effects of loaded NaA zeolite on the pervaporation performance of hybrid membranes were investigated. The selectivity of hybrid membranes made from APTES-modified zeolite was higher than that using the original zeolite under the same conditions, because fewer voids resulted from the incompatibility between the zeolite and PAAS and the structure was more homogenous. Based on the Arrhenius plots, the activation energies of water and the ethanol ratio were lower for modified zeolite hybrid membranes, because water molecules experienced less restrictive passage through the membranes compared with the original zeolite-based hybrid membrane. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

In this study, an antibacterial ultrafiltration (UF) membrane was developed by depositing polyethyleneimine (PEI) onto a microporous polyacrylonitrile (PAN) membrane surface via the electrostatic self-assembly followed by immobilization of copper (II) ions on the membrane surface. The resulting PAN–PEI–Cu membrane showed an improved separation performance, copper stability and antibacterial properties. The filtration experiments indicated that the resulting membrane exhibited a steady-state flux of 63 L/(m 2 h) and a rejection of 91% for a feed containing 5 mg/L humic acid (HA) at 0.16 MPa. In addition, an atomic absorption spectrophotometer (AAS) was used to monitor the release of copper ions from the membrane driven by various chelating solutions. It was found that copper on the membrane could still act effectively as a biocide for long-tem operation in raw seawater. Furthermore, the membrane exhibited an antibacterial efficiency of 71.5% against Escherichia coli . This modification technique is simple and practical because dilute solutions are used for surface treatment and commercial membrane units can be modified in their original modules. The membrane is considered to be suitable for such applications as ultrafiltration for pretreatment of seawater desalination.

Five different ratios of SiO2-PAMPS nanoparticles were prepared and these nanoparticles were then blended with polysulfone (PSF)/N, N-Dimethylacetamide (DMAC)/Ethanol solution to fabricate hybrid ultrafiltration membranes via wet phase-inversion process. Effects of SiO2-PAMPS nanoparticles on morphologies and properties of the resultant ultrafiltration membranes were investigated and assessed by measuring the surface and cross morphology, the water contact angle, the pure water flux, the porosity and the pore size. These experimental results suggested that the higher concentration of nanoparticles in casting solution induced a macrovoid enlargement of membrane cross section. Furthermore, the higher monomer mol ratio (MSiO2/MAMPS) of the hybrid nanoparticles in casting solution resulted in a sharp increase of water flux of the ultrafiltration membrane. The hybrid ultrafiltration membrane (SiO2-PAMPS4-0.3 wt.%) had the respective highest water fluxes of 190 L/m2 ∙ h and 687 L/m2 ∙ h at 0.1 MPa and 0.5 MPa. The SiO2-PAMPS nanoparticles rather than SiO2 nanoparticles showed excellent stability on membrane surface even after continuously shaking for 15 days.

Modification of polypropylene (PP) hollow fiber microfiltration membranes for nanofiltration through dip-coating sodium carboxymethyl cellulose (CMCNa) skin layer followed by cross-linking with AlCl3 was investigated in this study. Modification parameters were studied to optimize the membrane performance and the obtained modified membranes were characterized in terms of surface and permeation properties. It was found that the surface property and solute separation capability of the PP hollow fiber membrane were significantly improved by coating CMCNa surface layer, and the optimized modified membrane took on a composite structure with a hydrophilic selective skin layer having an isoelectric point of pH 3.7. The composite layer was negatively charged at neutral pH and was relatively looser in acidic pH compared with that in basic or neutral. Permeation tests revealed that the desired modified membrane possessed a molecular weight cut-off (MWCO) of 760 Da and a high pure water permeability of 10.8 l/m2 h bar, and exhibited rejections to salts following the order of MgCl2

An integrated membrane system (IMS) of ultrafiltration–nanofiltration (UF–NF) technology has been investigated extensively as a means of seawater softening for offshore oilfield water and polymer flooding. The results showed that the softened water generated by the selected NF membrane could meet the water flooding standard for offshore oilfield. At appropriate mixing ratio of softened water and formation water, scales may be avoided completely. Furthermore, the reservoir formation sensitivity evaluation proved the compatibility of NF permeation water with the formation core, which indicates that the permeation water of the selected NF membrane module could be safely used for offshore oilfield water flooding. The prepared aqueous polymer solution using NF softened seawater showed relatively high viscosity and stability at formation temperature for long time, which could meet the demand for offshore polymer flooding. Therefore, the UF–NF integrated membrane technology could efficiently resolve the softened water shortage problem in offshore oilfield water flooding and polymer flooding and ensure continuous and stable oil production.

An ultrafiltration–nanofiltration (UF–NF) integrated membrane system (IMS) was operated for 500 h to examine the performance of the NF membrane in seawater desalination pretreatment. The rejection of divalent ions, TDS, TOC and UV254 by the NF membrane as well as the permeation flux decreased gradually with operating time before each chemical cleaning procedure, while the calculated Stiff and Davis Stability Index (S&DSI) increased gradually from negative up to positive. The result indicates that there exists inorganic fouling during the long run. However, the IMS produced excellent effluent with 93.6% removal of total organic carbon (TOC) for long-term operation. The TOC concentration of the NF permeation samples was in the range of 0.06–0.35 mg/L. The chemical cleaning results indicated that inorganic fouling should be preferentially paid attention to, and a combination of citric acid cleaning and NaOH cleaning may achieve an optimal cleaning efficiency. The long-term operation reveals that the membrane is more prone to fouling gradually after chemical cleaning.

A self-made positively charged nanofiltration(NF) membrane was used to treat textile dye effluent to generate water for reuse, and the factors affecting nanofiltration process such as operating pressure, feed fl ow and membrane cleaning were investigated. With an applied pressure of 1.0 MPa and a feed fl ow of 40 L/h, this NF membrane has a removal of 93.3% for CODcr and a reduction of approximately 51.0% in TDS, salinity and conductivity achieving the chroma removal of 100%. The permeate obtained through this membrane is suitable for recycling. Moreover, the membrane could be reused after being cleaned with 1% NaOH solution.

Submerged nanofiltration of anionic dye aqueous solution by laboratory-fabricated sodium carboxymethyl cellulose (CMCNa)/polypropylene (PP) thin-film composite hollow fiber membrane was investigated in this paper. The CMCNa/PP thin-film composite membranes were prepared through dip-coating CMCNa skin layer on the outer surface of polypropylene microporous hollow fibers followed by cross-linking with FeCl 3 . The molecular weight cut-off (MWCO) and surface zeta potential of the tailor fabricated membrane were estimated through permeation tests using different PEG solutions and measurements of surface steaming potential, respectively. Submerged nanofiltration tests were then performed with anionic dye solutions under different conditions. It was found that, at neutral pH, the negatively charged CMCNa/PP composite hollow fiber membrane with a MWCO of about 700 Da could effectively remove anionic dyes (Congo red and Methyl blue) from aqueous solution with good long-term performance stability and anti-fouling property through submerged nanofiltration. The dye retention and water permeability was affected by the trans-membrane pressure, the dye concentration as well as the presence of salt in the solution. The dye retention, water permeability and salt rejection rate to aqueous solution containing 2000 mg/l Congo red and 10,000 mg/l NaCl were 99.8%, 7.0 l/m 2 h bar, and lower than 2.0%, respectively.

The role of thermo-responsive polymer (TRP) in the cleaning of organic-fouled polyamide-based reverse osmosis membranes was systematically investigated in this study. Fouling and cleaning experiments were performed employing a laboratory-scale cross-flow test unit. Following accelerated organic fouling runs with bovine serum albumin (BSA), cleaning experiments were conducted using de-ionized water and de-ionized water containing TRP with low critical solution temperature under various conditions, respectively. The separation performances of the fresh, fouled and cleaned membranes were characterized through permeation tests. It was found that the phase transition of the TRP that had diffused into the fouling layer would facilitate the removal of foulants located on membrane surface, and thereby improve the cleaning efficiency. The efficiency of the intensified cleaning with TRP solution was largely affected by the type and concentration of TRP, as well as the soaking time of TRP solution. The efficiency of the intensified cleaning could be enhanced by increasing the concentration and/or prolonging the soaking time of TRP solution. Moreover, membrane surface characterization via scanning electron microscopy, attenuated total reflectance infrared and surface contact angle measurements also confirmed the beneficial effect of TRP on the removal of the deposited foulants from the membrane surface.

This work describes the covalently binding of 2-hydroxyethyl methacrylate (HEMA) and 2-(dimethylamino)ethyl methacrylate(DMAEMA) brushes onto the poly(vinylidene fluoride) (PVDF) membrane surfaces via surface-initiated atom transfer radical polymerization (ATRP). Prior to ATRP, PVDF was coated with 3,4-dihydroxyphenylalanine (DOPA). The hydroxyl groups on the polyDOPA-coated PVDF membrane surface and pore surface were used for the immobilization of alkyl halide ATRP initiator. The grafting yield of poly(hydroxyethyl methacrylate) (PHEMA) and poly((dimethylamino)ethyl methacrylate) (PDMAEMA) was determined by weight gain which was linearly increased with the polymerization time. Fourier transform infrared spectrometer (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscope (AFM) were used to characterize the chemical composition and surface morphology of PVDF membrane and modified membrane, respectively. Water contact angles and water intake measurements indicated that the introduction of PHEMA graft chains promoted remarkably the surface hydrophilicity of PVDF membranes. It was also found that PHEMA graft chains provided higher pure water flux and better anti-protein absorption ability to PVDF membranes. Water flux decreased with increasing polymerization times, while the BSA rejection curves shifted to lower molecular weight cutoff values. The quaternized PVDF-g-PDMAEMA, PVDF-g-PDMAEMA-b-PHEMA membranes exhibited excellent antibacterial properties against Staphylococcus aureus. This study not only introduces a modification approach to obtain a PVDF membrane grafting hydrophilic PHEMA, but also provides the antibacterial properties for PVDF membrane with PDMAEMA.