Green and feasible fabrication of loose nanofiltration membrane with high efficiency for fractionation of dye/NaCl mixture by taking advantage of membrane fouling

Loose nanofiltration membrane emerges as required recently, since it is hard for conventional nanofiltration membrane to fractionate mixture of dyes and salts in textile wastewater treatment. However, the polymeric membranes unavoidably suffer from membrane fouling, which was caused by the adsorption of organic pollutants (like dyes). Normally, the dye fouling layer will shrink membrane pore size, thus resulting in flux decline and rejection increase. It is thought that membrane fouling may be a double-edged sword and can be an advantage if properly utilized. Thereby, loose nanofiltration membranes were constructed here by a green yet effective method to fractionate dyes/salt mixture by taking advantage of membrane fouling without using poisonous ingredients. A commercially available polyacrylonitrile (PAN) ultrafiltration membrane with high permeability was chosen as the substrate, and dyes were used to contaminate PAN substrate and formed a stable barrier layer when adsorption of dyes reached dynamic equilibrium. The resultant PAN-direct red 80 (DR80) composite membranes displayed superior permeability (~128.4 L m⁻² h⁻¹) and high rejection (~99.9%) to DR80 solutions at 0.4 MPa. Moreover, PAN-DR80 membranes allowed fast fractionation of dyes/sodium chloride (NaCl) mixture, which maintained a negligible dye loss and a low NaCl rejection (~12.4%) with high flux of 113.6 L m⁻² h⁻¹ at 0.4 MPa. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47438.     

Green lignin-based polyester nanofiltration membranes with ethanol and chlorine resistance

As the main water treatment material, polymeric membranes inevitably suffer from membrane fouling. In this work, novel lignin-based polyester composite nanofiltration membranes (NFM) with ethanol and chlorine resistance were fabricated via interfacial polymerization. Lignin alkali (LA), a green lignin derivative, typically treated as chemical waste in the paper industry, was employed as the aqueous monomer, trimesoyl chloride (TMC) is served as the organic monomer. The structure and separation properties of the lignin-based NFM were studied, revealing that the dense polyester separation layer may show good performance for dye removal. The rejections of the optimized LA/TMC-3 membrane with an excellent permeation flux of 13.9 kg m^?2?h^?1 for rose Bengal sodium salt, brilliant blue, congo red, rhodamine B, MgSO₄, and NaCl are 97.6%, 97.3%, 97.8%, 71.34%, 51.4%, and 31.8%, respectively. Moreover, the LA/TMC-3 membrane also shows long-term tolerance in ethanol and sodium hypochlorite solution; the rejection of LA/TMC-3 to dye only decreases 8% after 8 days when immersed in alcohol, while the normalized rejection maintains 94% after 4000 ppm-hours of continuous exposure to chlorine. This lignin-based polyester membrane may broaden the sustainable utilization sphere of lignin derivatives, at that provide a referable direction for the development of membrane materials.     

Solvation-amination-synergy that neutralizes interfacially polymerized membranes for ultrahigh selective nanofiltration

Molecular desalination is broadly used in chemical, food, and textile industries, which needs efficient and anti-fouling separation technologies to reach this goal. Interfacial polymerization is one of the most promising routes to construct ultrahigh selective nanofiltration membranes. However, the irreversible hydrolysis of residual acyl chlorides makes Donnan charges of nascent films distribute unevenly which hinders fine molecular desalination and anti-fouling. Here, we propose a pioneering solvation-amination-synergy strategy to synchronously inhibit the hydrolysis of residual acyl chlorides and promote their amination. The electroneutral nanofiltration membrane with high water permeance (13.2 L m⁻² h⁻¹ bar⁻¹) is quantitatively fabricated that has superb anti-fouling abilities and minimizes Donnan impacts on competitive ion penetrations, so it transmits Na₂SO₄ and NaCl while fully obstructs cationic or anionic dyes (< 500 Da). The ultrahigh molecule to ion selectivities outperform state-of-art nanofiltration membranes, which may provide a paradigm shift for scalable membrane fabrication for various industrial product desalination.     

Novel Ag-AgBr decorated composite membrane for dye rejection and photodegradation under visible light

Photocatalytic membranes have received increasing attention due to their excellent separation and photodegradation of organic contaminants in wastewater. Herein, we bound Ag-AgBr nanoparticles onto a synthesized polyacrylonitrile-ethanolamine (PAN-ETA) membrane with the aid of a chitosan (CS)-TiO₂ layer via vacuum filtration and in-situ partial reduction. The introduction of the CS-TiO₂ layer improved surface hydrophilicity and provided attachment sites for the Ag-AgBr nanoparticles. The PAN-ETA/CS-TiO₂/Ag-AgBr photocatalytic membranes showed a relatively high water permeation flux (~ 47 L·m^–2·h^–1·bar^–1) and dyes rejection (methyl orange: 88.22%; congo red: 95%; methyl blue: 97.41%; rose bengal: 99.98%). Additionally, the composite membranes exhibited potential long-term stability for dye/salt separation (dye rejection: ~97%; salt rejection: ~6.5%). Moreover, the methylene blue and rhodamine B solutions (20 mL, 10 mg·L⁻¹) were degraded approximately 90.75% and 96.81% in batch mode via the synthesized photocatalytic membranes under visible light irradiation for 30 min. This study provides a feasible method for the combination of polymeric membranes and inorganic catalytic materials.     

Separating Cyanide from Coke Wastewater by Cross Flow Nanofiltration

Investigations on separation of cyanide from coke wastewater were carried out in a cross flow nanofiltration membrane module following microfiltration of real industrial wastewater. Different composite polyamide nanofiltration membranes were used in the system while studying their effectiveness in cyanide separation under different operating conditions. Transmembrane pressure, pH, and cross flow velocity exhibited strong influence on percentage removal of cyanide. 94% cyanide rejection with a permeate flux of 79 liters per hour at a transmembrane pressure of 13 kg/cm² and at a volumetric cross flow rate of 700 liters per hour was achieved. The membrane module with a composite membrane having high negative charge was successfully operated without any significant loss in flux even after 72 hours operation. These encouraging results show that microfiltration and nanofiltration with properly selected membranes in an appropriate module could lead to a practical solution to a longstanding problem of cyanide removal from industrial wastewater.     

Graphene oxide–TiO2 composite filtration membranes and their potential application for water purification

Graphene oxide-particle composite films with filtration function have been successfully synthesized by a two-step method. First, graphene oxide–TiO₂ composite sheets are prepared, which can form stable dispersion in water. Then, by assembling these composite sheets, graphene oxide–TiO₂ films are obtained. In these as-prepared films, dilated space and channels are desirably formed by introducing nanoparticles between these carbon sheets, making them promising separation membranes. We used these films as filtration membranes to remove dye molecules (methyl orange and rhodamine B) from water. The results show that apart from the adsorption capacities of these dyes, these graphene oxide–TiO₂ films can also capture additional amount of dye molecules, indicating their potential applications in water purification areas.     

Investigation on the enhancement of solvent-resistant nanofiltration membrane performance utilizing PDA-UiO-66@CNT as an interlayer

With the growing complexity of separation systems, the application of thin film composite nanofiltration (TFN) membranes in organic solvent separation faces numerous challenges. To augment its solvent stability, an in-situ constructed dopamine hydrogel doped with UiO-66@CNT was developed as an intermediate layer on a polyetherimide (PEI) ultrafiltration membrane. Subsequent interfacial polymerization on this interlayer led to the formation of a solvent-resistant nanofiltration membrane with a vast covalent bond structure, large specific surface area, and enhanced hydrophilicity. Our findings revealed that when the CNT loading in the UiO-66@CNT composite nanoparticles was 2 wt%, the TFN-U₂C₂ membrane exhibited a maximum pure water flux of 126.32 L/(m²·h) and a methanol flux of 45.45 L/(m²·h). The rejection rates for Congo red aqueous and methanol solutions were 96.88% and 92.14%, respectively. The membrane also demonstrated commendable anti-fouling properties. Remarkably, even after 48 h of immersion in various organic solvents, the membrane retained its morphology and separation efficiency. Compared to the TFN-U₂ membrane without CNT addition, the enhancement in separation performance was considerably significant. Hence, this membrane has significant potential for application in treatment of wastewater containing organic solvents and is promising in related fields.     

Preparation of highly selective nanofiltration composite membranes based on a novel soluble rigidly contorted monomer

Nanofiltration composite membranes with high selectivity are one of the most critical cores in water treatment, and regulating the surface charge and pore structure of active separation layers in thin film composite membranes is one of the most effective means to improve the selectivity of composite membranes. This article synthesized a novel monomer with positive charge and a rigid twisted Tröger's base structure (named TBDA-SO₃), which was manipulated to improve the microporous structure and surface charge of the composite membrane. By interfacial polymerization, TBDA-SO₃, and piperazine were co-reacted with trimesoyl chloride to successfully prepare positively charged, highly selective, and strongly microporous polyamide composite nanofiltration membranes. The best-performing composite nanofiltration membrane in this article has a permeability similar to that of the control group's poly(piperazine amide) (PPA) membrane (pure water flux, 7.8 L m⁻² h⁻¹ bar⁻¹), but has excellent divalent cation selectivity (52.57), which is 4.4 times that of the control group's PPA membrane.     

Synthesis and characterization of PVA/PES thin film composite nanofiltration membrane modified with TiO2 nanoparticles for better performance and surface properties

Novel polyethersulfone (PES)/poly (vinyl alcohol) (PVA)/titanium dioxide (TiO₂) composite nanofiltration membranes were prepared by dip-coating of PES membrane in PVA and TiO₂ nanoparticles aqueous solution. Glutaraldehyde (GA) was used as a cross-linker for the composite polymer membrane in order to enhance the chemical, thermal as well as mechanical stabilities. TiO₂ nanoparticles with different concentrations (0, 0.05, 0.1, 0.5 wt.%) were coated on the surface of PVA/PES composite membrane. The morphological study was investigated by atomic force microscopy (AFM), scanning surface microscopy (SEM) and along with X-ray diffraction (XRD). In addition, the membranes performances, in terms of permeate flux, ion rejection and swelling factor were also investigated. It was found that the increase in TiO₂ solution concentration can highly affect the surface morphology and filtration performance of coated membranes. The contact angle measurement and XRD studies indicated that the TiO₂ nanoparticles successfully were coated on the surface of PVA/PES composite membranes. However, rougher surface was obtained for membranes by TiO₂ coating. The filtration performance data showed that the 0.1 wt.% TiO₂-modified membrane presents higher performance in terms of flux and NaCl salt rejection. Finally, TiO₂ modified membranes demonstrated the lower degree of swelling.     

Treatment of effluents from textile-rinsing operations by thermally stable nanofiltration membranes

Thermally stable nanofiltration membranes were used to recover hot water from rinsing effluents from acid and reactive dyeing operations. Two types of flat-sheet membranes, MPF-34 (MWCO 200) and MPF-36 (MWCO 1000), were tested at 60°C and 10 bar. Experiments carried out with the made-up feeds containing acid dye and acetic acid showed that both membranes were able to retain more than 99% of dye. MPF-36 suffered from substantial flux decline due to the dye and acid in the feeds but still provided higher fluxes than MPF-34. Furthermore, reactive dye rejection of MPF-36 was acceptable, ranging from 97 to 99.5%, while the fluxes, 105-140 1/m².h, were exceptionally high. MPF-36 was then further tested with the wastewater from industrial processes. The membrane could recover hot water by removing more than 98% of acid dye and 90% of reactive dyes. Despite severe fouling by acid dye, the membrane was still able to provide 40-50 1/m².h of permeate fluxes. For the reactive dye rinsing effluents, remarkably high fluxes of 120-1501/m2.h were obtained. Chemical cleaning of the used membrane with 0.2% wt. HNO₃ and subsequently 0.5% wt. NaOH recovered 80-100% of the flux.     

Sodium bicarbonate as novel additive for fabrication of composite nanofiltration membranes with enhanced permeability

Thin film composite nanofiltration membranes are frequently used to remove the residual salts from industrial wastewater. However, these nanofiltration membranes often have relatively low fluxes that limit their practical applications. To solve the problem, sodium bicarbonate was introduced into the composite nanofiltration membranes via interfacial polymerization of piperazine (PIP) and 1,3,5‐benzenetricarbonyl trichloride (TMC). The membrane surfaces were characterized by scanning electronic microscopy, attenuated total reflection Fourier transform infrared spectroscopy, electro kinetic analyzer, and contact angle goniometer. The results showed that the addition of sodium bicarbonate generated more tiny cracks on membrane surface and decreased the zeta potential of the membrane, which improved the permeation properties of the membrane without significantly decreasing the rejection against four kinds of salts (Na₂SO₄, MgSO₄, NaCl, MgCl₂). The addition of sodium bicarbonate provided a new possibility to improve the permeation properties of thin film composite nanofiltration membranes. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46363.     

Influence of dyes, salts and auxiliary chemicals on the nanofiltration of reactive dye baths: experimental observations and model verification

The aim of this study was to investigate the effects of dyes, salts and auxiliary chemicals in reactive dye baths on the separation performance of nanofiltration membranes. A reactive dye bath was simulated for this purpose with auxiliary chemicals. A DS5-type nanofiltration membrane was used in the experimental runs. Performance of the nanofiltration membrane was evaluated by measuring permeate flux, salt and color rejections in five steps. Reactive black 5, reactive orange 16, NaCl, NaOH, Na₂SO₄, acidic acid, mollan and slipper were used to prepare synthetic dye baths. Pressures in the range of 8 to 24 bars were applied, and flow velocity was kept constant at 0.74 m/s. NaCl rejection of 20% and color rejection of more than 95% were achieved throughout the experiments. Permeate quality was satisfactory enough to recycle these effluents in reactive dyeing. Acidification ofthe original synthetic dye bath solution with HCl and H₂S0₄ decreased the membrane fouling and also increased the NaCl recovery and color rejection. Besides, using HCI instead of H₂SO₄ increased these positive effects. The effects of auxiliary chemicals were determined by using salt rejection model parameters of α and k_D in the presence of an organic ion. There was a correlation among the results of experiments and the model. The model parameters (α and k_D were also calculated for all steps.     

Preparation, morphology and performance evaluation of polyvinylalcohol (PVA)/polyethersulfone (PES) composite nanofiltration membranes for pulp and paper wastewater treatment

In this study, thin film composite PVA/PES nanofiltration membranes were fabricated for the treatment of pulp and paper industrial wastewater. Phase separation induced by immersion precipitation was used to prepare the PES support membrane. PVA/PES composite nanofiltration membranes were prepared by dipping the support PES membrane in the PVA and cross-linking solutions at different conditions. Maleic acid (MA) was used as cross-linking agent. PVA and MA have concentrations of 0.5?C2 and 0.05?C1 wt%, respectively. Morphological studies were carried out by means of scanning electron microscopy (SEM) as well as atomic force microscopy (AFM) techniques. In addition, the hydrophilicity of membranes was examined by contact angle measurements. Permeability and ability of PVA/PES composite nanofiltration membranes to reduce COD of the wastewater were evaluated by a cross flow filtration system. SEM images indicated that the PVA layer was uniformly formed on the PES support membrane. AFM images showed that the surface roughness, porosity and pore sizes of PES support membrane were reduced after formation of PVA layer on the support surface. Moreover, the hydrophilicity of the membranes was significantly increased. Experimental results demonstrated that the PVA/PES composite nanofiltration membranes were able to reduce the COD of wastewater. Optimum conditions for preparation of PVA/PES composite membrane are consisted of PVA concentration: 1 wt%, MA concentration: 0.5 wt%, cross-linking time: 3?min and curing time: 3?min.     

Interfacially polymerized thin film nanofiltration membranes on TiO2 coated polysulfone substrate

In this study, a new approach was developed to prepare the novel thin film composite nanofiltration membranes. In this new approach, nanoparticles were coated completely under the polymeric thin film layer. Thin film composite (TFC) membranes were fabricated by interfacial polymerization on polysulfone (PSf) sublayer using m-phenylenediamine (MPD) and trimesoyl chloride (TMC) respectively as amine monomer and acid chloride monomer. Scanning electron microscopy and atomic force microscopy were used to study surface morphology and roughness properties of NF membranes. Energy dispersive X-ray microanalysis (EDX) was used to analyze the elemental change before and after filtration experiment. Chemical structure and thickness of polyamide formed on TFC membranes were observed by Fourier transmission infrared attenuated total reflectance (FTIR-ATR) spectroscopy. Permeability, salt rejection and pepsin macromolecule rejection of prepared membranes were tested using dead end filtration cell. Antifouling behavior of the membranes was studied by filtering pure water before and after pepsin solution filtration. A smoother and thicker surface without any defect appeared as the concentration of nanoparticle was increased. NaCl rejection was increased from 70% for neat nanofiltration membrane to 84% for 0.5 wt% TiO₂ modified nanofiltration membrane. Antifouling and permeability behavior of the prepared membranes were improved in the new approach. Antibacterial property of prepared membranes was improved as a result of photocatalytic characteristic of TiO₂ nanoparticles.     

Preparation and performance of three‐layered structure composite membrane for heavy metal ions and hazardous dyes rejection

A three‐layered structure composite membrane was successfully fabricated by electrospinning cellulose acetate (CA)/poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV) fibrous layers and coating the chitosan (CS) solution on the CA/PHBV substrate as a barrier layer. For obtaining the proper mechanical property and high filtration performance, different content of glycerol was investigated to mix in CS coating solution. The ovalbumin tests showed that this triple‐structure type of filtration media exhibited a high flux rate (up to 730 L/m² h at the feed pressure of 0.15 MPa) and an excellent rejection rate (98%). The permeation flux of the membrane was significantly higher than other reported electrospun fiber membranes with similar rejection ratios. The CA/PHBV‐CS composite membrane was also used to remove disperse dye and metal ion for water purification. These prepared membranes exhibited efficient adsorption separation performance toward disperse yellow dye with the maximum adsorption capacity reaching up to 188.52 mg/g. The equilibrium absorption capacities of the three tested ions (Cu(II), Pb(II), and Cr(III)) were 46.26, 88.31, and 190.14 mg/g, respectively. Consequently, these membranes can be promising materials in wastewater treatment. © 2018 Society of Plastics Engineers POLYM. ENG. SCI., 59:E322–E329, 2019. © 2018 Society of Plastics Engineers     

Effect of the drying temperature on sulfonated polyether sulfone nanofiltration membranes prepared by a coating method

This study reports on the preparation of a novel sulfonated polyether sulfone nanofiltration membrane via a manual coating method. The as-prepared membrane was modified by changing the drying temperature and utilizing additives. As the drying temperature was increased, the rejection performance of the as-prepared nanofiltration membrane increased, while flux decreased. The nanofiltration membrane dried at 40°C had relatively high permeation flux and good rejection performance for divalent ions and dyes; therefore, it is suitable for dye wastewater treatment. The nanofiltration membrane dried at 50°C had relatively low permeation flux and relatively good rejection performance for inorganic salts. The pore size of the skin layer was reduced as the drying temperature was increased. The average diameters of the as-prepared nanofiltration membranes dried at 40 and 50°C were 5.08 and 1.51 nm, respectively. Due to excellent hydrophilicity and relatively low roughness, the as-prepared nanofiltration membranes dried at 40 and 50°C had superior antipollution characteristics.     

Recycling of waste attapulgite to prepare ceramic membranes for efficient oil-in-water emulsion separation

Large-scale application of ceramic membranes is restricted by high cost resulting from raw materials and sintering process. In this study, low-cost ceramic membranes were prepared with waste attapulgite (WAT) and α-Al₂O₃ as starting materials and used for oily wastewater treatment. The optimal membrane sintered at 1100 °C possessed excellent properties, with open porosity of 41.6%, flexural strength of 37.2 MPa and average pore size of 0.40 μm. The membrane also displayed outstanding permeability and chemical stability. The hydrophilicity and underwater oleophobicity were enhanced after surface modification. When used for oil-in-water emulsion filtration, the permeate flux reached 236.8 L m^?2 h^?2 bar^-1 under a low transmembrane pressure of 0.2 bar and the oil rejection exceeded 99%. Membrane cleaning with a simple ultrasonic treatment could easily achieve flux recovery. This study proposed a feasible strategy for both solid waste utilization and oily wastewater treatment.     

氨基化氧化石墨烯界面聚合制备超薄复合纳滤膜

采用氨基化氧化石墨烯（NGO）为界面聚合水相单体,制备了超薄复合纳滤膜。研究采用傅里叶变换红外光谱（FTIR）、X射线光电子能谱（XPS）、透射电子显微镜（TEM）、扫描电子显微镜（SEM）、原子力显微镜（AFM）表征了NGO以及复合纳滤膜的化学组成和形貌。系统考察了水相单体浓度、有机相单体浓度对于制备的超薄复合纳滤膜性能的影响。该超薄复合膜在低压（0.2 MPa）下纯水通量可达27.8 L·m^-2·h^-1,对小分子染料有较高的截留率（甲基橙截留率74.8%,橙黄钠截留率96.0%,刚果红截留率98.5%,甲基蓝截留率99%）,对于无机盐的截留率较低（Na₂SO₄截留率21.4%,MgSO₄截留率10.7%,NaCl截留率5.3%,MgCl₂截留率1.5%）,展现出优异的染料/盐分离性能。同时制备的复合纳滤膜展现了较好的长周期稳定性以及抗污染特性。     

Peroxopolyoxometalate nanoparticles blended PES membrane with improved hydrophilicity,anti-fouling,permeability, and dye separation properties

Poly(ethersulfone) (PES) is one of the polymers most widely used for the fabrication of ultrafiltration or nanofiltration membranes in various applications, but its membrane suffers from fouling. In this study, preparation, characterization, and performance of PES nanocomposite membrane comprising peroxopolyoxometalate nanoparticles was studied to provide improved permeability and anti-fouling properties. The high oxygen ratio of the PW₄ nanoparticles could enhance the hydrophilicity of the membranes. The PW₄ nanoparticles were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and X-ray diffraction analyses. The mixed matrix membranes were fabricated using a non-solvent induced phase-separation method. The fabricated membranes were characterized using atomic force microscopy, attenuated total reflection, SEM, EDX mapping, total average porosity, thermogravimetric analyze, and water contact angle experiments. The dye flux and rejection, pure water permeability and anti-fouling properties of the membranes were investigated. All of the membranes blended by different contents of the PW₄ nanoparticles presented better performance compared to the unmodified membrane. The filtration performance of the membranes in reactive green 19 (RG19) and reactive yellow 160 (RY160) dye separation showed that all of the PW₄ blended membranes possessed dye rejection greater than 86% and 96% for RY160 and RG19, respectively. The reusability test using bovine serum albumin (BSA) protein and RG19 dye solutions in five cycle experiments presented good reproductivity of the PW₄ blended membranes. The PES membrane containing 1 wt% of PW₄ nanoparticles showed the highest flux recovery ratio (75%) as well as reduced irreversible fouling ratio (8%) through BSA protein filtration.     

单宁酸-多巴胺涂覆制备染料分离用纳滤膜

通过单宁酸及聚多巴胺涂覆,制备了单宁酸(TA)-聚偏氟乙烯(PVDF)纳滤膜,同时评价了改性膜对刚果红、伊文思蓝、活性嫩黄等染料的分离性能。结果表明,改性后膜表面粗糙度略微增大,亲水性明显增强。同时,改性膜具有水下超疏油的性质,能够完全抵抗水下油污的污染。2wt% TA-PVDF纳滤膜对多种染料的截留率能达到96.5%以上,且对刚果红、伊文思蓝、活性嫩黄等染料的截留通量都超过65.7 L/(m2?h?bar)。另外,改性膜在染料分离时截留通量基本不变,稳定性较强,在工业染料废水处理方面有一定的应用前景。