Tannic acid/Fe^(3+)interlayer for preparation of high-permeability polyetherimide organic solvent nanofiltration membranes for organic solvent separation

Organic solvent nanofiltration(OSN)membranes have a great application prospect in organic solvent separation,but the development of OSN membranes is mainly restricted by trade-off between permeability and rejection rate.In this work,a TA/Fe^(3+)polymer was introduced into polyetherimide(PEI)ultrafiltration membranes crosslinked with hexamethylene diamine as the intermediate layer,and OSN membranes with high separation performance and solvent permeability were obtained through interfacial polymerization and solvent activation.The interlayer with high surface hydrophilicity and a fixed pore structure controlled the adsorption/diffusion of the amine monomer during interfacial polymerization,forming a smooth(average surface roughness<5.5 nm),ultra-thin(separation layer thickness reduced from 150 to 16 nm)and dense surface structure polyamide(PA)layer.The PA-Fe^(3+)_3-HDA/PEI membrane retained more than 94%of methyl blue(BS)in 0.1 g·L^(-1)BS ethanol solution at 0.6 MPa,and the ethanol permeation reached 28.56 L^(-1)·m^(-2)·h^(-1).The average flux recovery ratio(FRR)of PA-Fe^(3+)_(3)-HDA/PEI membrane was found to be 84%,which has better fouling resistance than PA-HDA/PEI membrane,and it was found to have better stability performance through different solvent immersion experiments and continuous operation in 0.1 g·L^(-1)BS ethanol solution.Compared with thin-film composite nanofiltration membranes,the PA-Fe^(3+)_(3)-HDA/PEI membrane can be manufactured from an economical and environment-friendly method and overcomes the trade-off between permeability and rejection rate,showing great application potential in organic solvent separation systems.

Preparation of pH-sensitive Composite Nanofiltration Membrane

Positively charged composite nanofiltration （NF） membranes were prepared through interfacial polymerization of poly[2-（N,N-dimethyl amino）ethyl methacrylate]（PDMAEMA） on porous polysulfone （PSF） substrate membranes. The effects of pH on swelling ratio （SR） of the pure crosslinked PDMAEMA membrane and on separation performances of the composite NF membrane were investigated. The results show that the quaternized amino groups produced through interfacial polymerization technique are soluble in both phases, which accelerate the crosslinking reaction as self-catalysts. The swelling/contracting behavior of the pure crosslinked PDMAEMA exhibited a well reversible pH sensitive property. Importantly, the rejection and flux of the composite NF membrane show pH-sensitive behavior in NF process. Furthermore, with the help of a relatively novel method to measure membrane conduction, the true zeta potentials calculated on the basis of the streaming potential measurements proved the pH-sensitive behavior of the NF membrane.

Treatment of Textile Dye Effluent Using a Self-made Positively Charged Nanofiltration Membrane

A selfmade 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 flow and membrane cleaning were investigated. With an applied pressure of 1.0 MPa and a feed flow of 40 L/h, this NF membrane has a removal of 93.3% for CODor 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.

Fabrication of anti-fouling polyamide nanofiltration membrane by incorporating streptomycin as a novel co-monomer

Polyamide(PA)thin-film composite(TFC)na nofiltration(NF)membrane has extremely broad application prospects in separation of monovalent/diva lent inorganic salts mixed solutio n.However,membrane fouling is the main obstacle to the application of PA,TFC and NF membrane.Streptomycin(SM)is a hydrophilic antibiotic containing a large number of hydroxyl and amino groups.In this work,the NF membrane was prepared via interfacial polymerization(IP)between trimesoyl chloride(TMC)in the organic phase and SM/piperazine(PIP)mixture in the aqueous phase.The NF membrane structure and performance were characterized in detail.The results showed that SM successfully participated in the IP.The negative charge and hydrophilicity of membrane surface were improved.The prepared membrane exhibited good anti-adhesion and anti-bacterial performance,Additionally,when the SM concentration was 2%,the prepared membrane exhibited the optimal permselectivity.The water permeance was 89.4L·m^(-2)·h^(-1)·MPa^(-1).The rejection of NaCl and Na_(2)SO_(4) were 17,17%and 97.84%,respectively.The NaCl/Na_(3)SO_(4) separation factor of the SM2-PIP/TMC membrane in 1000 mg·L^(-1) NaCl and 1000 mg·L^(-1)Na_(2)SO_(4) mixed solution was 40,which was 3.3 times that of PIP/TMC membrane.It indicated that SM2-PIP/TMC demonstrated excellent monovalent/divalent salts separation performance.This work provided an easy and effective approach to preparing anti-fouling NF membrane while possessing superior monovalent/divalent salts separation performance.

A NOVEL NANOFILTRATION MEMBRANE PREPARED WITH PAMAM AND TMC (Ⅰ)

A series of nanofiltration (NF) membranes were prepared with poly(amido-amine) (PAMAM) and trimesoyl chloride (TMC) via in situ interfacial polymerization.The effects of the generation number and concentration of PAMAM on the properties of NF membranes were discussed.Fourier transform infrared spectroscopy (FTIR-ATR),atomic force micrgscopy (AFM),scanning electron microscopy (SEM) and contact angle measurements were employed to characterize the resulting membranes.The nanofiltration performances were evalua...

Prussian Blue/Cellulose Acetate Thin Film Composite Nanofiltration Membrane for Molecular Sieving and Catalytic Fouling Resistance

Nanofiltration(NF)membranes as high selective separators are appealing for molecular sieving,which still remains a great challenge for the mixed dyes with same charge.In this study,cellulose acetate(CA)membranes were firstly aminated by ethylene imine polymer(PEI),and then the thin film of metal organic frameworks(MOFs)were constructed onto aminated CA membrane through forward-diffusion,slow crystallization and in situ growth of Fe Co-Prussian blue(FeCo-PB)crystallization layers.The designed PB@CA composite NF membrane shows an ideal rejection for Congo red(CR)/methyl orange(MO)mixture solution,with 99.7%±0.2%for CR and 33.5%±2%for MO.In addition,the composite NF membrane demonstrated good efficiency for photocatalytic degradation of organic fouling(permeability recovery ratio was up to 92%)due to the active FeCo-PB micro-cubes.Thus,this work provides a practical strategy to prepare MOFs mediated thin film composite nanofiltration membrane for precise molecular sieving and catalytic antifouling performances.

Tailoring the microstructure and properties of PES/SPSf loose nanofiltration membranes using SPES as a hydrophilic polymer for the effective removal of dyes via steric hindrance and charge effect

Herein,polyethersulfone(PES)and sulfonated polysulfone(SPSf)blend membranes were prepared with addition of sulfonated polyethersulfone(SPES)as a hydrophilic polymer and adipic acid as a porogen via non-solvent induced phase separation method for effective fractionation of dyes based on the influence of steric hindrance and charge effect.Raman spectroscopy and molecular dynamic simulation modeling confirmed that hydrogen bonds between PES,SPSf,SPES,and adipic acid were crucial to membrane formation and spatial arrangement.Further addition of hydrophilic SPES resulted in a membrane with reduced pore size and molecular weight cut-off as well as amplified negative charge and pure water permeance.During separation,the blend membranes exhibited higher rejection rates for nine types of small molecular weight(269.3–800 Da)dyes than for neutral polyethylene glycol molecules(200–1000 Da).This was attributed to the size effect and the synergistic effect between steric hindrance and charge repulsion.Notably,the synergistic impact decreased with dye molecular weight,while greater membrane negative charge enhanced small molecular dye rejection.Ideal operational stability and anti-fouling performance were best observed in M2(PES/SPSf/SPES,3.1 wt%).Summarily,this study demonstrates that SPES with–SO3‒functional groups can be applied to control the microstructure and separation of membranes.

HYDROPHILIC NANOFILTRATION MEMBRANES WITH SELF-POLYMERIZED AND STRONGLY-ADHERED POLYDOPAMINE AS SEPARATING LAYER

Inspired by the self-polymerization and strong adhesion characteristics of dopamine in aqueous conditions, a novel hydrophilic nanofiltration （NF） membrane was fabricated by simply dipping polysulfone （PSf） ultrafiltration （UF） substrate in dopamine solution. The changes in surface chemical composition and morphology of membranes were determined by Fourier transform infrared spectroscopy （FTIR-ATR）, X-ray photoelectron spectroscopy （XPS）, scanning electron microscopy （SEM） and atomic force microscopy （AFM）. The experimental results indicated that the self-polymerized dopamine formed an ultrathin and defect-free barrier layer on the PSf UF membrane. The surface hydrophilicity of membranes was evaluated through water contact angle measurements. It was found that membrane hydrophilicity was significantly improved after coating a polydopamine （pDA） layer, especially after double coating. The dyes filtration experiments showed that the double-coated membranes were able to reject completely the dyes of brilliant blue, congo red and methyl orange with a pure water flux of 83.7 L/（mE.h） under 0.6 MPa. The zeta potential determination revealed the positively-charged characteristics of PSf/pDA composite membrane in NF process. The salt rejection of the membranes was characterized by 0.01 mmol/L of salts filtration experiment. It was demonstrated that the salts rejections followed the sequence： NaC1 〈 NaaSO4 〈 MgSO4 〈 MgC12 〈 CaCl2, and the rejection to CaC12 reached 68.7%. Moreover, the composite NF membranes showed a good stability in water-phase filtration process.

Influence of incorporating beta zeolite nanoparticles on water permeability and ion selectivity of polyamide nanofiltration membranes

A novel polyamide(PA) thin film nanocomposite(TFN) membrane modified with Beta( β) zeolite was prepared by interfacial polymerization on a poly(ether sulfone)(PES) ultrafiltration membrane. Compared with the PA thin film composite(TFC) membrane, the introduction of β zeolite with porous structure notably increased the water flux of TFN membrane. Because the β zeolite with tiny-sized and well-defined inner-porous acted as prior flow channels for water molecules and a barrier for the sulfate ions. The successful introduction of β zeolite into the(PA) selective layer and their dispersion in the corresponding layer were verified by scanning electron microscope(SEM) and atomic force microscopy(AFM). Water contact angle, zeta potential measurements were used to characterize the changes of membrane surface properties before and after incorporating the β zeolite. With the β zeolite introducing, the water contact angle of modified TFN membrane was decreased to 47.8°, which was benefited to improve the water flux. Meanwhile, the negative charges of the modified TFN membrane was increased, resulting in an enhancement of separation effect on SO4^2- and Cl^-. In term of nanofiltration(NF) experiments, the highest pure water flux of the TFN membranes reached up to 81.22 L m^(-2) hr^-1 under operating pressure of 0.2 MPa, which was 2.5 times as much as the pristine TFC membrane.

Modeling of the separation performance of nanofiltration membranes and its role in the applications of nanofiltration technology in product separation processes

Although there is a voluminous literature on the determination of structural parameters(the pore radius,the ratio of membrane porosity to membrane thickness)of a nanofiltration(NF)membrane and its separation perfor-mance(such as the rejection and the permeation flux)by the simplified Teorell-Meyer-Sievers(TMS)model,little of this research comments on other theories and the consequences of linking modeling evaluation to technological application.Theories used to predict the separation performance of an NF membrane usually include:the non-equilibrium thermo-dynamic model,the pore model,the space charge model,the TMS model,the electrostatic and steric-hindrance model,and the semiempirical model.In the article,we briefly trace the origins or the general ideas of the above-mentioned theories.From there,recent researches on the characterization of mem-brane structural parameters and electrical properties(such as the surface charge density qw)are reviewed.We then turn to research on the separation performance of an NF membrane for single-component solutions of inorganic electrolytes,neutral organic solutions,and a mixture solution of electro-lytes or that of an electrolyte and neutral organic solute.Afterwards,we outline the applications of NF technology in the processes of product separation and conclude with a discussion on the role of models in such applications.

Polyamide Nanofiltration Membrane from Surfactant-assembly Regulated Interfacial Polymerization of 2-Methylpiperazine for Divalent Cations Removal

Removal of metal ions from water can not only alleviate the scaling problem of domestic and industrial water,but also solve the water safety problem caused by heavy metal ion pollution.Here,we fabricate a positively charged nanofiltration membrane via surfactant-assembly regulated interfacial polymerization(SARIP)of 2-methylpiperazine(MPIP)and trimesoyl chloride(TMC).Due to the existence of methyl substituent,MPIP has lower reactive activity than piperazine(PIP)but stronger affinity to hexane,resulting in a nanofiltration(NF)membrane with an opposite surface charge and a loose polyamide active layer.Interestingly,with the help of sodium dodecyl sulfate(SDS)assembly at the water/hexane,the reactivity between MPIP and TMC was obviously increased and caused in turn the formation of a positively charged polyamide active layer with a smaller pore size,as well as with a narrower pore size distribution.The resulting membrane shows a highly efficient removal of divalent cations from water,of which the rejections of MgCl_(2),CoCl_(2)and NiCl_(2)are higher than 98.8%,98.0%and 98.0%,respectively,which are better than those of most of other positively charged NF membranes reported in literatures.

Supramolecular fabrication of hyperbranched polyethyleneimine toward nanofiltration membrane for efficient wastewater purification

Nanofiltration technology has opened an efficient pathway to addressing the grand issue of wastewater purification.Polyethyleneimine(PEI),as a hydrophilic polymer,is a promising material to manufacture separation membranes owing to its superiority.Here,we prepared a hyperbranched PEI-based separation mem-brane through the supramolecular hydrogen bond interaction for wastewater purification.The amino groups in the PEI molecule were partially oxidized to the nitro groups with sodium hypochlorite(NaClO).Moreover,the PEI molecu-lar chains can be regulated from the hyperbranched state to the internal nucle-ation state.Molecular dynamics simulation results further indicated the strong hydrogen bonds among the oxidized PEI(O-PEI)molecular chains and the decreased gyration radius of the O-PEI molecule due to the formation of the nitro groups.In addition,the wettability and zeta potential of O-PEI membranes can be controlled by adjusting the molecular weight and oxidation degree of the PEI molecules.Under the collective effect of size screening and charge repulsion,the O-PEI separation membrane displayed a wide range of purification capabilities for contaminations,such as dye molecules and salts.This work may offer a new strategy to fabricate hyperbranched O-PEI membranes for wastewater purifica-tion.

Removal of sulfamethoxazole by nanofiltration membrane

The retention of sulfamethoxazole (SMZ) by nanofiltration (NF) membranes is strongly influenced by the pH value of the solution. The retention of SMZ reaches its peak value when the solution pH rises above its pKa2 value as the compound transforms into a negatively charged species. Charge repulsion is the main mechanism involved in SMZ removal by NF membranes. In this study, the removal of SMZ by NF membranes, as a function of solution chemistry, was examined at pH 8.9 to investigate the effect of solution conditions on charge repulsion. The results show that the retention of negatively charged SMZ is relatively independent of SMZ concentration, and an increase in the ionic strength of the solution causes a relatively small reduction in retention. A small effect of humic acid (HA) on SMZ retention was noticed at pH 8.9, which can be explained by a small but insignificant improvement in the zeta potential of the membrane caused by HA at high pH values. However, it was found that SMZ concentration in the feed decreased significantly in solutions containing tannic acid (TA). The Adams-Bohart model was applied to our experimental data and was found to be suitable for describing the initial part of the breakthrough curves. The adsorptive parameters of the membrane were determined.

Synthesis of polypiperazine-amide thin-film membrane on PPESK hollow fiber UF membrane

A new interfacial polymerization （IP） procedure is developed in order to synthesize polypiperazine-amide thin-film membrane on the inner surface of poly（phthalazinone ether sulfone ketone） （PPESK） hollow fiber ultrafiltration （UF） membrane. A hollow fiber composite membrane with good performance was prepared and studied by PT-IR and scanning electron microscopy.

Fabrication and Performance of a Low Operating Pressure Nanofiltration Poly(vinyl chloride) Hollow Fiber Membrane

A low operating pressure nanofiltration membrane is prepared by interfacial polymerization between m-phenylenediamine （MPDA） and trimesoyl chloride （TMC） using PVC hollow fiber membrane as supporting. A series of PVC nanofiltration membranes with different molecular weight cutoff （MWCO） can be obtained by controlling preparation conditions. Chemical and morphological characterization of the membrane surface was carried out by FTIR-ATR and SEM. MWCO was characterized by filtration experiments. The preparation conditions were investigated in detail. At the optimized conditions （40 min air-dried time, aqueous phase containing 0.5% MPDA, 0.05% SDS and 0.6% acid absorbent, oil phase containing 0.3% TMC, and 1 min reaction time）, under 0.3 MPa, water flux of the gained nanofiltration membrane reaches 17.8 L/m2-h, and the rejection rates of methyl orange and MgSO4 are more than 90% and 60%, respectively.

Ionic strength directed self-assembled polyelectrolyte single-bilayer membrane for low-pressure nanofiltration

Layer-by-layer assembly is a versatile technique for fabricating nanofiltration membranes,where multiple layers of polyelectrolytes are usually required to achieve reasonable separation performance.In this work,an ionic strength directed self-assembly procedure is described for the preparation of nanofiltration membranes consisting of only a single bilayer of poly(diallyldimethylammoniumchloride)and poly(sodium-4-styrenesulfoate).The influence of background ionic strength as well as membrane substrate properties on the formation of singlebilayer membranes are systematically evaluated.Such a simplified polyelectrolyte deposition procedure results in membranes having outstanding separation performance with permeating flux of 14.21.5 L∙m^(–2)∙h^(-1)∙bar^(–1) and Na2SO4 rejection of 97.1%0.8%under a low applied pressure of 1 bar.These results surpass the ones for conventional multilayered polyelectrolyte membranes.This work encompasses an investigation of ionic strength induced coiling of the polyelectrolyte chains and emphasizes the interplay between-polyelectrolyte chain configuration and substrate pore profile.It thus introduces a new concept on the control of membrane fabrication process toward high performance nanofiltration.

Effects of ion concentration and natural organic matter on arsenic(V) removal by nanofiltration under different transmembrane pressures

The removal of As（V） from synthetic water was studied using four different nanofiltration （NF） membranes （ESNA-1-K1, NF270, ESNA-1-LF, and HODRA-CORE）. The influences of ion concentration, transmembrane pressure （TMP）, and the presence of natural organic matter （humic acid, HA） on the arsenic removal efficiency and permeate flux were investigated. The arsenic rejection of ESNA- 1-LF was higher than those of the other membranes in all experiments （〉 94%）, and the HODRA-CORE membrane gave the lowest removal of arsenic （〈 47%）. An increase in the ion concentration in the feed solution and addition of HA decreased the arsenic rejection of the HODRA-CORE membrane. However, both increasing of the ion concentration and addition of HA made the rejection increased for the other membranes （ESNA-1-K1, NF270, and ESNA-1-LF）. With increasing TMP, for all four NF membranes, increases in both arsenic rejection and permeate flux were observed. The permeate fluxes of the four NF membranes decreased to some extent after addition of HA to the solutions for operating time of 6 hr.

Advanced treatment of municipal wastewater by nanofiltration： Operational optimization and membrane fouling analysis

Municipal sewage from an oxidation ditch was treated for reuse by nanofiltration（NF） in this study. The NF performance was optimized, and its fouling characteristics after different operational durations（i.e., 48 and 169 hr） were analyzed to investigate the applicability of nanofiltration for water reuse. The optimum performance was achieved when transmembrane pressure = 12 bar, p H = 4 and flow rate = 8 L/min using a GE membrane. The permeate water quality could satisfy the requirements of water reclamation for different uses and local standards for water reuse in Beijing. Flux decline in the fouling experiments could be divided into a rapid flux decline and a quasi-steady state. The boundary flux theory was used to predict the evolution of permeate flux. The expected operational duration based on the 169-hr experiment was 392.6 hr which is 175% longer than that of the 48-hr one. High molecular weight（MW） protein-like substances were suggested to be the dominant foulants after an extended period based on the MW distribution and the fluorescence characteristics. The analyses of infrared spectra and extracellular polymeric substances revealed that the roles of both humic- and polysaccharide-like substances were diminished, while that of protein-like substances were strengthened in the contribution of membrane fouling with time prolonged. Inorganic salts were found to have marginally influence on membrane fouling. Additionally, alkali washing was more efficient at removing organic foulants in the long term, and a combination of water flushing and alkali washing was appropriate for NF fouling control in municipal sewage treatment.

Superwetting polyethersulfone membrane functionalized with ZrO_(2) nanoparticles for polycyclic aromatic hydrocarbon removal

Polycyclic aromatic hydrocarbons(PAHs)are persistent and widespread in the aquatic environment,causing potential hazards for human health.In this study,a superwetting and robust PES-PAA-ZrO_(2)nanofiltration membrane was proposed through surface modification for PAH removal with high efficiency.A ZrO_(2)coating was formed on polyethersulfone(PES)membrane surface through chemical bonding,thus the PES-PAA-ZrO_(2)membrane exhibited super-hydrophilicity,under-water oleophobicity,and excellent stability.In comparison with the original PES membrane,the water contact angle of the modified membrane was significantly decreased from about 50°to less than 10°,and quickly dropped to 0°within 1s.This provided a much lower energy barrier for water permeation due to its super-high water affinity.The wastewater treatment efficiency was increased by about 4 times after modification with more than 90%of PAH rejection rate.The excellent robustness of PES-PAA-ZrO_(2)membrane was verified under various conditions,which gave the membrane practical potential for long-term operation.

Preparation,characterization and performance of poly(m-phenylene isophthalamide)/organically modified montmorillonite nanocomposite membranes in removal of perfluorooctane sulfonate

Nanocomposite membranes containing poly（m-phenylene isophthalamide）（PMIA） and organically modified montmorillonite（OMMT） were prepared by a combination of solution dispersion and wet-phase inversion methods, and the effects of OMMT addition on the properties and performance of fabricated nanofiltration membranes were investigated. The membranes were characterized by contact angle measurements, scanning electron microscopy（SEM）, atomic force microscopy（AFM）, thermogravimetric analysis, and zeta potential.The performance of the membranes was elucidated by the removal of perfluorooctane sulfonate（PFOS） at neutral p H. Increasing OMMT concentration improved the thermal stability and hydrophilicity of the membranes. The permeation and rejection of PFOS were significantly improved. The performance of fabricated nanofiltration membranes in removal of PFOS varied depending on the solute and membrane properties as well as solution conditions. Finally,a comparison between fabricated membranes and a commercial NF membrane（ESNA1-K1,Hydecanme） proved that the OMMT addition is a convenient procedure for producing nanocomposite membranes with superior properties and performance.