Tight Ultrafiltration Membranes Research Articles

Green polycaprolactone/sulfonated kraft lignin phase inversion membrane for dye/salt separation

Exploring environmentally friendly, renewable, and cost-effective raw materials is essential in sustainable membrane fabrication. This study presents a facile and scalable method for fabricating a green and biodegradable tight ultrafiltration membrane for dye/salt separation. This involves simply blending biodegradable polycaprolactone (PCL) with the low-cost biobased sulfonated kraft lignin (SKL) additive. Additionally, we employed acetic acid as a green alternative solvent to enhance the sustainability of the membrane fabrication process. The incorporation of hydrophilic SKL into the PCL matrix resulted in increased hydrophilicity (water contact angle changed from 72° to 56°), surface roughness (increased from 29 nm to 43.5 nm), and enhanced negative electrostatic charge of the membrane (−40 mV to −45 mV). The optimized PCL/SKL membrane (M3) exhibited excellent water flux (∼45 LMH) under 40 psi hydraulic pressure coupled with ∼98 % and ∼10 % rejection rates for reactive red (RR) dye and NaCl, respectively. Moreover, the M3 membrane maintained its exceptional dye/salt fractionation performance while separating the mixtures at low salt concentrations. However, with increasing salt concentration (1–50 g/L), the membrane's RR dye rejection declined from ∼90 % to ∼50 %, with a significant reduction in NaCl and Na2SO4 salts rejection (from ∼14 % to ∼1 % and ∼22 % to –∼1 %, respectively). The M3 membrane exhibited remarkable antifouling properties during dye and humic acid filtration with a high flux recovery ratio (>98 %) and low flux decline rate (<7 %). The PCL/SKL membrane also showed excellent stability and maintained consistent separation performance over a long period. Overall, the novel biodegradable PCL/SKL membrane prepared in this study presents a promising avenue toward sustainable membrane fabrication for wastewater treatment applications.

RETRACTED: Advanced multi-functional regenerative and self-healing tight ultrafiltration membrane for dye/salt wastewater efficient purification

Membrane fouling and membrane damage during membrane operation significantly reduce the permeate flux and separation efficiency, and the preparation of ultrafiltration membranes with renewable and self-healing properties is particularly critical for the sustainable recycling of water resources. Herein, we report a novel tight ultrafiltration membrane, which achieves self-healing properties by incorporating modified β-cyclodextrin (β-CD) monomers into the membrane, forming hydrogel by utilizing UV-induced graft polymerization and covalently binding to the membrane substrate, and then utilizing modified Azo to self-assemble into the hydrophobic cavities of the β-CD via host–guest interactions to construct host–guest chemistry to achieve regenerative anti-fouling properties. In addition, the chemical damage caused by UV-induced during the regeneration process is somewhat avoided by the modified azobenzene (Azo) and β-CD. Taking the renewing membrane as an example, the regeneration test shows that the membrane still has high flux recovery (FRR = 92.5 %) and stable separation performance after three regenerations. Physical self-healing tests showed that the dye/salt rejection recovery of the renewing membrane was greater than 95 % for all four common dyes and salts. In the case of chemical damage, a new peak appears in the XPS at 165.4 eV, demonstrating of the reliability of the actual self-healing of chemical damage. Meanwhile, the results of the mechanical properties of the renewing membrane before and after damage show that the membrane can still maintain high mechanical properties after physical self-healing has occurred. This novel anti-fouling and self-healing tight ultrafiltration membrane for practical high salinity textile wastewater separation has a broad application prospect.

Antifouling polyphenylene sulfone tight-ultrafiltration membrane by co-depositing dopamine and zwitterionic polymer for efficient dye/salt separation

The exceptional hydrophilicity and charge equilibrium of zwitterionic polymers render them highly desirable as antifouling materials. In this study, a novel zwitterionic copolymer Poly(2-aminoethyl methacrylate-Ethyl acrylatesulfopropyl piperidine salt) [P(AE-EA)] was successfully synthesized. Subsequently, a novel tight-ultrafiltration (t-UF) antifouling membrane employed for dye/salt separation was fabricated by co-depositing dopamine (DA) and P(AE-EA) onto the polyphenylene sulfone (PPSU) membrane substrate. The polydopamine (PDA) and P(AE-EA) are covalently linked through the formation of a covalent bond via Michael addition and Schiff base reactions. By regulating the ratio of PDA and P(AE-EA), the optimized membrane shows a denser and hydrophilic selective layer. The composition and characteristics of the membrane are investigated by serial characterization. The electrostatic adsorption between the membrane surface and the pollutant can be effectively weakened by the incorporation of a zwitterionic polymer P(AE-EA) with neutral charged and hydrophilicity. The modified membrane demonstrates exceptional antifouling performance for BSA, high rejection towards both negatively and positively charged dyes (Congo red, Methylene blue, Methyl orange and Rhodamine B), as well as efficient salt permeance for NaCl, Na2SO4, MgCl2, Mg2SO4 in comparison to that of the pure PPSU membrane. The results presented herein demonstrate the remarkable potential of the novel zwitterionic t-UF membrane for effectively separating dye/salt mixture solutions in the textile industry.

Rapid thermal process for fabricating α-alumina tight ultrafiltration membrane with narrow pore size distribution

The development of tight ceramic ultrafiltration membranes for water purification facilitates is challenging because of high fabrication costs and low permeate flux. In this study, a low-energy rapid thermal process (RTP) was comprehensively investigated for fabricating of high-precision, permeable α-alumina tight ultrafiltration membranes. Compared to the conventional thermal process (CTP), RTP offers an ultra-fast heating rate and shorter holding time, effectively mitigating grain growth and pore aggregation. Moreover, the decomposition of organic matter is delayed during RTP, providing a lower interfacial energy that enables direct formation of α-alumina at a low temperature of 750 °C. During a secondary subsequent RTP, the residual phase is fully converted to α-alumina by the in-situ seeding effect. By utilizing RTP, we successfully prepared α-alumina ultrafiltration membranes within 30 min by calcination, with an average pore size of approximately 6 nm, a narrow pore distribution coefficient of 1.12, and high permeance of 219 L−1·m−2·h−1·bar−1.

Pressure-driven membranes for advanced treatment of textile wastewater: Dye/salt fractionation, concentration, and cleaning strategies

Textile wastewater commonly contains various organic compounds and salt mixtures, potentially raising serious environmental and health concerns. Traditional treatment approaches are hindered by high salinity; consequently, membrane separation technologies have attracted increasing attention over the past few decades. Herein, four commercial pressure-driven membranes with molecular weight cut-off (MWCO) gradients were employed for the advanced treatment of different types of textile wastewater. Specifically, these membranes were initially subjected to a fractionation test toward the dye/salt mixtures, followed by deep concentration of the dye molecules. Using Congo red (CR), methyl blue (MB), NaCl, and Na2SO4 as representative dyes and salts, the results indicated that all membranes could effectively separate dye/salt mixtures and further conduct a deep concentration process toward the separated dye solutions. However, their efficiency and effectiveness largely depend on the membrane pore size and solution characteristics. For instance, membranes with lower MWCOs experience less fouling and shorter operation durations when treating CR-related solutions. All membranes showed improved fractionation efficiency toward MB/salt mixtures, requiring only approximately 10.2–42.9 % of the operation duration compared to CR-related solutions. The loose nanofiltration membrane proved superior to tight ultrafiltration membranes in both fractionation and concentration processes. Further research on cleaning methodologies demonstrated that both alkali and ethanol cleaning were influential in restoring the membrane performance. An appropriate ethanol/water concentration can effectively regenerate severely fouled membranes, achieving a high flux recovery ratio of ∼95 %. This study evaluated state-of-the-art pressure-driven membranes for textile wastewater treatment and guided cleaning strategies for optimal performance recovery.

High-performance antibacterial tight ultrafiltration membrane constructed by co-deposition of dopamine and tobramycin for sustainable high-salinity textile wastewater management

High-salinity textile wastewater is a pressing environmental concern, urgently requiring the appropriate treatment. Sustainable management of high-salinity textile wastewater via fractionation of the existing dyes and inorganic salts (NaCl) using selective separation membranes is a key approach to address this detrimental concern. Herein, tight composite ultrafiltration membranes with impressive antibacterial function were constructed using one-step co-deposition of dopamine and tobramycin on the porous substrate to fractionate the dyes and NaCl. Triggered by ammonia persulfate, the polydopamine/tobramycin coating layer imparts the fabricated composite ultrafiltration membranes with tight surface structure and narrow pore size distribution, enabling effective dyes/salts fractionation. Specifically, the tight composite ultrafiltration membrane with a molecular weight cutoff of 3692 Da experienced a > 98.0 % rejection against various reactive dyes (molecular weight: <1000 Da) with nearly complete salt transmission (<0.8 % NaCl rejection), demonstrating an effective fractionation of dyes and salts. Additionally, the incorporated tobramycin as a broad-spectrum antibiotic endowed the tight composite ultrafiltration membrane with a sufficient inhibition efficiency (i.e., 100 %) against E. coli bacteria in a short-time contact (i.e., 3 min). Thereby, the tight composite ultrafiltration membrane constructed by fast co-deposition of dopamine and tobramycin established an unparalleled platform technology for sustainable resource recovery (dyes or salts) from high-salinity textile wastewater.

Construction of PDA-PEI/ZIF-L@PE tight ultra-filtration (TUF) membranes on porous polyethylene (PE) substrates for efficient dye/salt separation

Tight ultra-filtration (TUF) membranes were constructed by in situ growing zinc imidazole frameworks micro-crystalline leaves (ZIF-L) in polyethylene imine (PEI) and polydopamine (PDA) deposit layers on porous polyethylene (PE) substrates. The effects of preparation conditions on the surface physical and chemical structures as well as on the dye/salt separation performance of the formed TUF membranes were systematically investigated. By inserting selective water permeation channels and increasing contacting surface areas, in situ-grown ZIF-L arrays tightly cross-linked in the coating matrix greatly increased water permeation without trading off dye/salt retention selectivity. The morphology of the included ZIF-L particles could be varied by adjusting the ligand/Zn molar ratio (α) in the preparation processes. Optimized PDA-PEI/ZIF-L@PE TUF membranes containing ZIF-L of cross-cross block morphology showed very high pure water permeability of 180 ± 20 L·m−2·h−1·bar−1 (LMHB) and retention selectivity (SCR/Na2SO4 and SMB/Na2SO4) of 267 and 43, respectively, as well as excellent stability and anti-fouling properties.

RETRACTED: Construction of self-repairing polyethersulfone membrane with high density hydrophilic microregions by two dimensional restricted channels for enhanced dyes/salts selective separation

Based on the dye/salts separation efficiency and membrane injury caused by serious pollution of dye/salts wastewater, this study constructed a 2D tight ultrafiltration membrane that could both solve the membrane injury problem and improve the dye/salts separation efficiency, the compatibility of good self-healing performance and penetration performance by 2D material magnesium-aluminum Layered double hydroxide (MgAl-LDH). The self-repairing of physical injury was achieved through the swelling effect of AMPS-PAN, this property was proved by permeate flux, the retention performance of salts in dye/salts solution, the comparison of scanning electron microscope (SEM), and the mechanical strength after physical injury. The healing of chemical injury occured through the reaction of CC and polyethersulfone chain breakage, which was confirmed by X-ray photoelectron spectroscopy (XPS), permeate flux, the retention performance of salts in dye/salts solution, and mechanical property. The high separation efficiency of dye/salts was achieved through 2D material MgAl-LDH, which was proved by separation selectivity ɑ. The compatibility of good self-healing performance and penetration performance was obtained by 2D material MgAl-LDH, which was proved by the penetration and self-healing performance. Morever, the membrane illustrated excellent both permeability and dye/sals separation efficiency, just like the permeate flux, the retention performance of sodium sulfate in methyl blue/sodium sulfate solution, the retention performance of Na2SO4 in methyl blue/Na2SO4 solution, the retention rate of methyl blue were 99.1 L/m2h, 12.5%, 7.9%, 97.7%, respectively. The results of pollution index and contact angle also proved that the membrane had anti-pollution performance.

Anti-fouling tight ultrafiltration membrane for gastrodin purification

The issues of flux decline and irreversible membrane fouling must be considered in membrane separation. In this paper, the culture medium, bacterial cells, and proteins were removed using a one-step tight ultrafiltration (UF) membrane separation process. Although the membrane resistance of the tight UF membranes increased owing to their smaller pore size, the stable flux of the 6 nm membrane during fermentation broth filtration of gastrodin was 28.0% higher than that of loose UF membranes, and the flux recovery ratio reached 97.3%. During purification, a higher filtration flux was obtained by retaining the operating pressure within the range of 2–3 bar and the operating temperature range of 50–60 °C. The average flux of a 6 nm 19-channel membrane reached 56 L·m−2·h−1, and the total yield of gastrodin reached 96.2%. This study provides a basis for the large-scale application of tight UF membrane in food industry.

Ultrafiltration and Nanofiltration for the Removal of Pharmaceutically Active Compounds from Water: The Effect of Operating Pressure on Electrostatic Solute-Membrane Interactions.

The present work investigates nanofiltration (NF) and ultrafiltration (UF) for the removal of three widely used pharmaceutically active compounds (PhACs), namely atenolol, sulfamethoxazole, and rosuvastatin. Four membranes, two polyamide NF membranes (NF90 and NF270) and two polyethersulfone UF membranes (XT and ST), were evaluated in terms of productivity (permeate flux) and selectivity (rejection of PhACs) at pressures from 2 to 8 bar. Although the UF membranes have a much higher molecular weight cut-off (1000 and 10,000 Da), when compared to the molecular weight of the PhACs (253-482 Da), moderate rejections were observed. For UF, rejections were dependent on the molecular weight and charge of the PhACs, membrane molecular weight cut-off (MWCO), and operating pressure, demonstrating that electrostatic interactions play an important role in the removal of PhACs, especially at low operating pressures. On the other hand, both NF membranes displayed high rejections for all PhACs studied (75-98%). Hence, considering the optimal operating conditions, the NF270 membrane (MWCO = 400 Da) presented the best performance, achieving permeate fluxes of about 100 kg h-1 m-2 and rejections above 80% at a pressure of 8 bar, that is, a productivity of about twice that of the NF90 membrane (MWCO = 200 Da). Therefore, NF270 was the most suitable membrane for this application, although the tight UF membranes under low operating pressures displayed satisfactory results.

Construction of tight ultrafiltration membrane for efficient dye/salt separation with physical and chemical self-healing property

This work developed a novel self-healing tight UF membrane based on damages to membrane during operation and cleaning via blending AMPS-PANI into the membrane matrix, which can not only endow the membrane with physical and chemical self-healing properties, but also enable the membrane to obtain effective separation performance of inorganic salt and dyes. Taking AMPS-PANI membrane (M4) as an example, the self-healing test showed that the dye/salt rejection rates of M4 membrane recovered to near pre-damage levels (more than 98%) for the physical damage. As for chemical damage, the high-resolution XPS spectra of S 2p of M4 membrane after damage displayed a larger S-C-C peak area than that before damage. The above results prove that the membrane has self-healing ability after physical and chemical damage. The observed physical self-healing property is ascribed to the swelling behavior of AMPS hydrogels, the fluidity of hydrogel chains and strong hydrogen bonding, and owing the chemical self-healing property to the Michael addition reaction between carbon–carbon double bonds and free radicals. The pure water flux, dye/salt rejection rate, structure, mechanical properties and porosity of the self-healing tight UF membrane were systematically investigated to evaluate its feasibility as an actual filtration membrane for textile wastewater. The results of the research indicate that membrane including both physical and chemical self-healing is a promising way to improve water filtration membrane with self-healing ability.

Molecular transformation of dissolved organic matter in reverse osmosis concentrated leachate during a tight-ultrafiltration membrane combined with an O3/GAC system

The dissolved organic matter (DOM) composition in reverse osmosis concentrated landfill leachate (ROCL) is very complex and difficult to treat. In this study, tight ultrafiltration (TU) combined with the O3/granular activated carbon (GAC) catalytic oxidation system was used to treat DOM in ROCL. The treatment effect and mechanism of TU combined with the O3/GAC catalytic oxidation system were carefully studied using ESI FT-ICR MS. The results show that DOM in ROCL mainly has Ali and UnPh-like structures, showing the characteristics of reduction and unsaturation. In the membrane treatment link (i.e., TU and deamination system), the DOM with LO-UnPh-like structures can be effectively intercepted and removed, and the DOM in the effluent mainly has Ali and LO-UnPh-like structures, showing the characteristics of reduction and unsaturation. In the process of the O3/GAC system, DOM with HO-UnPh-like structures was further removed through catalytic oxidation, which not only destroys the aromatic structure of DOM but also forms daughter products with a higher degree of saturation, fewer aromatic properties, fewer carbon atoms, and more oxygen-containing functional groups. The action intensity of •OH in the O3/GAC catalytic oxidation system was verified, and the reaction mechanism of GAC catalytic O3 was analyzed according to the surface properties of GAC. Finally, the GAC after use was treated with several regeneration methods; the results showed that the morphology and structure of the deactivated GAC could be restored by the method of washing–microwave irradiation. This study provides a promising method for the proper treatment of ROCL.

Tight ultrafiltration and loose nanofiltration membranes by concentration polarization-driven fast layer-by-layer self-assembly for fractionation of dye/salt

In continuation of previous work on the construction of molecular selective membrane via layer-by-layer (LbL) assembly (J. Membr. Sci. 641, 2022, 119908), herein, we report an extremely fast concentration polarization-driven LbL (CP-LbL) self-assembly of polyelectrolytes (PEs) on a new partially cross-linked support membrane to obtain molecular selective tight ultrafiltration (TUF) and loose nanofiltration (L-NF) membranes. These membranes have been prepared using low concentration of PEs (2 mM) and with only total three and five layers of self-assembly. The pure water permeances by the TUF and L-NF membranes are 38 Lm−2h−1bar−1 and 25 Lm−2h−1bar−1 respectively. The TUF membrane showed 98.9 to >99% rejections of reactive black 5, rose Bengal, Congo red and other dyes (0.2–1 g L−1). The L-NF membrane exhibits >99.5% rejection of these dyes irrespective of ionic salt concentration. The membranes show very good salt to dye separation efficacy. The L-NF membrane intercepts 96–97% of dyes from real textile wastewater containing mixture of dyes and salt. High dye interception by the membranes is beneficial for the efficient fractionation and resource recovery. This work provides an important strategy for the quick LbL self-assembly using low concentration of PEs to obtain molecular selective membranes for the quick fractionation (∼3.5 diavolume) of dye/salt mixture via diafiltration operation and subsequent concentrating the dye solution.

Low temperature preparation of high-flux α-alumina tight ultrafiltration membrane by modified co-sintering process

A high-efficiency α-alumina ultrafiltration membrane was proposed and fabricated by co-sintering a gel layer with a pre-sintered interlayer. A pre-sintered interlayer with rigidity and low roughness was used, which was conducive to the preparation of a defect-free and ultra-thin separation layer. In the process of co-sintering, the crystal phase of the separation layer was completely transformed to α-alumina at 950 °C, and permeation of pre-sintered interlayer increase with calcination temperature. The prepared α-alumina ultrafiltration membrane had an ultrathin thickness of only ∼140 nm, pure water permeability as high as 230 L m−2h−1 bar−1, and average pore size approximately ∼7 nm. In the separation of polyvinyl alcohol (PVA) wastewater, the membrane had a rejection rate of 99 % and permeability of 60 L m−2h−1 bar−1. In the removal of Congo red dye, it showed a high rejection rate of >99 % and permeability of 212 L m−2h−1 bar−1.

Tight UF membranes with ultrahigh water flux prepared by in-situ growing ZIF particles in NIPS process for greatly enhanced dye removal efficiency

Tight ultra-filtration (TUF) membranes with in-situ grown zeolitic imidazole framework (ZIF) particles embedded in and packed under porous polysulfone (PSF) separating layers were prepared using non-solvent induced phase separation (NIPS) processes. Imidazole ligands contained in casting solutions were released and reacted with divalent Zn2+ cations pre-loaded on non-woven fabric supporting layers. The capillary filling pore size and molecular-weight-cut-off (MWCO) Stokes solute rejection pore size of the formed ZIF/PSF TUF were tuned by varying the loading levels of Zn (II), polyvinylpyrrolidone (PVP) and imidazole, as well as the NIPS reaction time. With thinned PSF separating layer (200–500 nm) and embedding water permeating short-cuts from the ZIF particles, ZIF/PSF TUF membranes showed 7 times higher water permeance (up to 250 L/(m2 h bar)) and greatly enhanced dye/salt retention selectivity, bearing high potential for applications in dye and textile waste water treatment processes.

Tailoring Morphology and Properties of Tight Utrafiltration Membranes by Two-Dimensional Molybdenum Disulfide for Performance Improvement.

To enhance the permeation and separation performance of the polyethersulfone (PES) tight ultrafiltration (TUF) membrane, two-dimensional molybdenum disulfide (MoS2) was applied as a modifier in low concentrations. The influence of different concentrations of MoS2 (0, 0.25, 0.50, 1.00, and 1.50 wt%) on TUF membranes was investigated in terms of morphology, mechanical strength properties, permeation, and separation. The results indicate that the blending of MoS2 tailored the microstructure of the membrane and enhanced the mechanical strength property. Moreover, by embedding an appropriate amount of MoS2 into the membrane, the PES/MoS2 membranes showed improvement in permeation and without the sacrifice of the rejection of bovine serum protein (BSA) and humic acid (HA). Compared with the pristine membrane, the modified membrane embedded with 0.5 wt% MoS2 showed a 36.08% increase in the pure water flux, and >99.6% rejections of BSA and HA. This study reveals that two-dimensional MoS2 can be used as an effective additive to improve the performance and properties of TUF membranes for water treatment.

Construction of high-performance Ce-doped TiO2 tight UF membranes for protein separation

The membrane structure and properties have a significant influence on its anti-fouling performance during the separation process. In this study, Ce was introduced to inhibit the phase transformation of TiO2 to obtain a tight ultrafiltration (UF) membrane with a more uniform pore size, a more integrated membrane layer as well as to strengthen the membrane surface charge to provide superior anti-fouling performance for the membrane during protein separation. Single anatase phase of the material proves that the introduction of Ce effectively inhibited the phase transformation of TiO2 and prevented the occurrence of cracks. The prepared Ce-doped TiO2 membrane exhibited excellent performance, with a membrane thickness of 700 nm, water permeance of 175 L·m−2·h−1·bar−1 and molecular weight cut-off of approximately 18 kDa. Additionally, it showed excellent BSA separation performance, as the stable permeance and rejection rate could be maintained at 120 L·m−2·h−1·bar−1 and 100 %, respectively. Meanwhile, Ce-doped TiO2 membrane showed superior anti-fouling performance compared to pure TiO2 membrane due to its strengthened surface charge and uniform pore size, with the J/J0 maintained a value of 0.69. Based on the obtained results, the Ce-doped TiO2 membranes prepared in this study exhibit good potential for protein separation.

Two-dimensional molybdenum disulfide oxide (O-MoS2) enhanced tight ultrafiltration membrane with improved molecular separation performance and antifouling properties

Tight ultrafiltration (TUF) membranes have shown potential for separating small molecules such as dyes and natural organic matters. However, low permeability and membrane fouling are critical challenges for TUF membranes. In this study, we reported a feasible method to fabricate a TUF membrane by blending polyethersulfone (PES) with novel two-dimensional (2D) molybdenum disulfide oxide (O-MoS2) nanosheets via the phase inversion method. The results indicated that the O-MoS2 could tune the properties and morphologies of TUF membranes. It was found that the addition of 2.0 wt% of O-MoS2 into the PES membrane could reduce the molecular weight cut-off (MWCO) of the O-MoS2/PES membrane from 15322 Da to 8404 Da. As a result, the optimized O-MoS2/PES membrane showed excellent rejections to PEG 10 kDa (92.67 ± 0.12%) and Rose bengal (99.9%). Moreover, The optimized O-MoS2/PES membrane exhibited a high pure water flux (75.24 ± 4.29 L m−2h−1bar-1). By using bovine serum albumin (BSA) as the simulated foulants, the antifouling performance of as-prepared membranes was investigated. The result indicated that the optimized O-MoS2/PES membrane had 88.15% water recovery rate after a 420-min continuous filtration test, which was higher than 80.53% of the pristine membrane. This study demonstrated O-MoS2 could be used as a novel additive to prepare a TUF membrane with high filtration performance.

High-flux, antifouling and highly hydrophilic tight ultrafiltration membranes based on crosslinked PEEKWC/PEI containing positively charged water channel for dyes removal

For the removal of textile dyes, an effective alternative to fabricate tight ultrafiltration membrane was adopted. A series of tight ultrafiltration membranes based on PEEKWC/PEI covalent crosslinking structure were prepared by phase inversion method and showed high-flux and good antifouling performance attributed to the enhancement of hydrophilicity by PEI. The top-surface of the UF membranes was with a water contact angle in range of 24.33° and 40.10° indicating the excellent hydrophilicity. These membranes containing PEI-based positively charged water channel showed high permeability for pure water and salt solutions. As the content of PEI in membrane reaching 20 wt%, the pure water permeability and pure water flux at 3 bar could reach 308 L·m−2·h−1·bar−1 and 925 L·m−2·h−1, respectively. The pure water flux could even reach 1526 L·m−2·h−1 at 5 bar. At the operation pressure of 3 bar, all the UF membranes showed good single-component BBR rejection between 94.87 % and 97.73 %. The rejection of membranes for BBR in dye/salt mixtures was substantially higher than 94.0 % even at a high salt concentration of 60 g/L. The UF membranes with high-flux of pure water and dye solution were discussed, which could be a promising alternative for sustainable textile wastewater treatment and natural water recovery.

Lithium extraction from high magnesium salt lake brine with an integrated membrane technology

Lithium extraction is a great challenge from the high magnesium content salt solution. In this work, an integrated polyamide tight ultrafiltration (UF) and nanofiltration (NF) membranes are systematically investigated to separate Li+ from a high magnesium salt solution. Tight ultrafiltration UA001 and nanofiltration NF270 membranes in the integrated-cascade system not only increased Li+ permeation to 82.5 % but also enhanced the high Mg2+ retention to 94.6 % from the ternary salt solution of LiCl and MgCl2. The solution-diffusion transport model was also developed to calculate the real retention of Li+ and Mg2+, under constant pressure mode. The separation efficiency SFLi/Mg for the ternary salt solution of LiCl + MgCl2 + H2O was more than 15 at a constant pressure of 25 bars with an integrated membrane process, which was higher as compared to single-stage UF and NF270 membranes. Moreover, the high Mg2+/Li+ ratio was also reduced from 30 to 1.9 in the integrated-cascade membrane process.