Membrane Rejection Research Articles

Molecular simulation study of 2D MXene membranes for organic solvent nanofiltration

MXene membranes has emerged as promising membrane materials due to their rigid lamellar structure and easily functionalized terminal groups. Understanding the mechanism of solvent transportation through MXene membrane at the microscopic level is significant for the development of new MXene based membranes. In this study, MXene membranes with different interlayer d-spacings (e.g., 0.9 nm, 1.45 nm, 2.0 nm, and 2.5 nm) are investigated for organic solvent nanofiltration (OSN) of four solvents (e.g., acetone, acetonitrile, methanol, and ethanol) and a model solute (Nile red). In membrane with the d-spacing of 0.9 nm, the solvent fluxes are regulated by the arrangements of solvents in the membrane. An ordered orientation and arrangement of solvent would result in a high flux. At this time, the solvent arrangement is dominated by the interaction energies between the solvent and membrane surface. When the d-spacing is larger than 1.45 nm, the solvent property (e.g., viscosity) plays the dominant role in flux determination. Compared with reported membranes, a substantially higher solvent flux can be achieved through the 2D MXene lamellar membranes. The solute rejections are controlled by a size-sieving mechanism, and 100% rejection of Nile red could be obtained in MXene membranes with 0.9 and 1.45 nm d-spacings. From the bottom-up, this work reveals the key governing factors that dominate the solvent permeation and solute rejection of 2D MXene lamellar membranes, and would also promote the development of new OSN membranes.

Effect of urea-based chemical cleaning on TrOCs rejection by nanofiltration membranes

Nanofiltration (NF) is an effective method for removing trace organic compounds (TrOCs) from drinking and reused water. However, chemical cleaning of NF membranes may impact their properties, leading to a decrease in TrOCs rejection. To better understand the mechanisms behind changes in membrane rejection after chemical cleaning, we investigated the changes in surface properties and TrOCs rejection of two commercial membranes (NF270 and NF90) after urea/ hydrochloric acid (HCl) cleaning, and compared them to conventional sodium hydroxide (NaOH)/HCl cleaning. The findings indicated that urea cleaning increased the membrane pore size and hydrophilicity while marginally affecting membrane crosslinking and zeta potential. Possibly due to the thicker and denser active layer of NF90, neither urea-based nor NaOH-based cleaning had a significant impact on its TrOCs rejection and permeability. In contrast, NF270 was more susceptible to chemical cleaning, and urea-based cleaning had less impact on its TrOCs rejection than NaOH-based cleaning. Although urea cleaning increased the pore size of the NF270 membrane, its pore size recovered well after HCl cleaning, resulting in good recovery of the rejection of hydrophilic neutral TrOCs. Moreover, urea cleaning had limited effects on the electrical properties of the NF270 and might enhance the hydrophilicity of the membrane, resulting in full recovery of the rejection of hydrophobic and negatively charged TrOCs after urea/HCl cleaning.

Facile dual-functionalization of NF membranes with excellent chlorine resistance and good antifouling property by in-situ grafting of zwitterions

During water treatment, the chlorination degradation by active chlorine and membrane fouling seriously threaten the service life of nanofiltration (NF) membranes. In this work, dual-functionalized NF membranes were facilely fabricated by in-situ grafting of zwitterions, which were generated by in-situ grafting 2,4,6-Triaminopyrimidine (TAP) onto the separation layer and the subsequential quaternization. The introduction of zwitterions was confirmed by ATR-FTIR and XPS. Under constant chlorine exposure (24000 ppm·h), chlorine with high concentration proved to be more corrosive. After harsh 24000 ppm·h chlorination in different environments (pH = 4.0, 7.0, and 10.0, respectively), all the salt rejections of the zwitterion-grafted NF membranes (the QTAP NF membranes) were higher than 98.0% and barely decreased. The flux of the QTAP NF membranes was 23.5% higher than that of the pristine NF membranes in acid chlorine environment after chlorination. The SEM and ATR-FTIR results indicated that no obvious change occurred to the surface morphologies and chemical structures for the QTAP NF membranes after chlorination. Flux recovery ratio (Bovine serum albumin) of the QTAP NF membranes was 91.2%, which indicated good antifouling property. The quaternization process slightly increased the rejection for inorganic salts. The zwitterions endowed the membranes with excellent chlorine resistance and good antifouling property. This study could provide a facile and effective strategy for constructing dual-functional NF membranes with chlorine-resistance and antifouling property.

Methylene blue rejection and antifouling properties of different carbonaceous additives-based polyvinylidene fluoride membrane

In the present study, various polyvinylidene fluoride (PVDF)-based membranes were successfully fabricated via non-solvent induced phase separation (NIPS) method utilising different carbon-based materials as additive. The incorporation of reduced graphene oxide (rGO), multi-walled carbon nanotubes (MWCNTs) and GO-MWCNTs hybrid along with titanium dioxide (TiO2) definitely affect the fabricated membrane’s morphology, hydrophilicity, porosity, filtration performance and antifouling properties. Based on dead-end filtration measurement, rGO-based PVDF/TiO2 membrane presented excellent pure water flux (2446.887 L/m2h) with membrane permeability of 1143.850 L/m2hMPa compared to other membranes. Furthermore, the inclusion of rGO and TiO2 also resulted in the highest methylene blue (MB) dye rejection rate (∼92%) compared to MWCNTs (62.22%) and GO-MWCNTs (86.69%). It was believed that steric hindrance effect played a major role in enhancing dye rejection performance of PVDF@rGO/TiO2 membrane. Interestingly, in terms of antifouling properties, PVDF@GO-MWCNTs/TiO2 possessed better antifouling properties as indicated by its higher flux recovery ratio (FRR) value of 95.30%. The existence of hydration layer on membrane surface endowed by oxygen-functional groups prevents the contaminant accumulation thus resulted high FRR value.

Effect of Diameter of Carbon Nanotubes in Nanocomposite Membrane for Methyl Orange Dye Removal

It is worth noticing that structure of nanomaterials affects the membrane performance, however, the effect of diameter of multiwalled carbon nanotubes (MWCNTs) has not been discussed in the past. This research aims to investigate the effect of diameter of MWCNTs on the performance of graphene oxide (GO)/ MWCNTs nanocomposite membrane for methyl orange dye removal. MWCNTs with different diameters (12-15 nm, 30-50 nm) with the same length (< 10 µm) are used to synthesize the nanocomposite membrane. The characteristics of the synthesized nanocomposite membrane were determined by surface hydrophilicity, pore size and porosity, zeta potential, and Fourier-transfer infrared (FTIR) spectroscopy. Besides, the membrane performance was evaluated by the water permeability test, dye rejection test, and antifouling test. The result showed that pure MWCNTs (30-50 nm) nanocomposite membrane (M2b) has the best performance among the synthesized membrane. The dye rejection of M2b membrane reached 86.77% and the normalized flux was approximately 0.82. Lower dye rejection (83.37%) and normalized flux (0.76) were attained by M2a membrane with smaller diameter MWCNTs (12-15 nm). This was due to M2b membrane having a smaller pore size (0.032 nm), which helped reduce the tendency of dye to pass through the membrane. Besides, M2b membrane has a more negative surface charge (-10.93 mV) that produces larger repulsion force, resulting in more dye being rejected. In conclusion, the performance of the synthesized nanocomposite membrane particularly antifouling properties can be enhanced with the addition of MWCNTs with larger diameter.

Low-pressure thin-film composite nanofiltration membranes with enhanced selectivity and antifouling property for effective dye/salt separation

For better sustainable resource recovery and elevating the separation efficiency of dye/salt mixture, it is essential to develop an appropriate nanofiltration membrane for the treatment of textile dyeing wastewater containing relatively smaller molecule dyes. In this work, a novel composite polyamide-polyester nanofiltration membrane was fabricated by tailoring amino functionalized quantum dots (NGQDs) and β-cyclodextrin (CD). An in-situ interfacial polymerization occurred between the synthesized NGQDs-CD and trimesoyl chloride (TMC) on the modified multi-carbon nanotubes (MWCNTs) substrate. The incorporation of NGQDs significantly elevated the rejection (increased by ∼ 45.08%) of the resultant membrane for small molecular dye (Methyl orange, MO) compared to the pristine CD membrane at low pressure (1.5 bar). The newly developed NGQDs-CD-MWCNTs membrane exhibited enhanced water permeability without compromising the dye rejection compared to the pure NGQDs membrane. The improved performance of the membrane was primarily attributed to the synergistic effect of functionalized NGQDs and the special hollow-bowl structure of CD. The optimal NGQDs-CD-MWCNTs-5 membrane expressed pure water permeability of 12.35 L m-2h−1 bar−1 at the pressure of 1.5 bar. Noteworthily, the NGQDs-CD-MWCNTs-5 membrane not only showed high rejection for the larger molecular dye of Congo Red (CR, 99.50%) but also for the smaller molecular dye of MO (96.01%) and Brilliant Green (BG, 95.60%) with the permeability of 8.81, 11.40, and 6.37 L m-2h−1 bar−1, respectively at low pressure (1.5 bar). The rejection of inorganic salts by the NGQDs-CD-MWCNTs-5 membrane was 17.20% for sodium chloride (NaCl), 14.30% for magnesium chloride (MgCl2), 24.63% for magnesium sulfate (MgSO4), and 54.58% for sodium sulfate (Na2SO4), respectively. The great rejection of dyes remained in the dye/salt binary mixed system (higher than 99% for BG and CR, <21% for NaCl). Importantly, the NGQDs-CD-MWCNTs-5 membrane exhibited favorable antifouling performance and potential good operation stability performance. Consequently, the fabricated NGQDs-CD-MWCNTs-5 membrane suggested a prospective application for the reuse of salts and water in textile wastewater treatment owing to the effective selective separation performance.

Exploring impacts of water-extractable organic matter on pre-ozonation followed by nanofiltration process: Insights from pH variations on DBPs formation

This study investigated the influence of pH (4–10) on the treatment of water-extractable organic matter (WEOM), and the associated disinfection by-products (DBPs) formation potential (FP), during the pre-ozonation/nanofiltration treatment process. At alkaline pH (9–10), a rapid decline in water flux (> 50 %) and higher membrane rejection was observed, as a consequence of the increased electrostatic repulsion forces between the membrane surface and organic species. Parallel factor analysis (PARAFAC) modeling and size exclusion chromatography (SEC) provides detailed insights into the WEOM compositional behavior at different pH levels. Ozonation at higher pH significantly reduced the apparent molecular weight (MW) of WEOM in the 4000–7000 Da range by transforming the large MW (humic-like) substances into small hydrophilic fractions. Fluorescence components C1 (humic-like) and C2 (fulvic-like) exhibited a predominant increase/decrease in concentration for all pH conditions during pre-ozonation and nanofiltration treatment process, however, the C3 (protein-like) component was found highly associated with the reversible and irreversible membrane foulants. The ratio C1/C2 provided a strong correlation with the formation of total trihalomethanes (THMs) (R2 = 0.9277) and total haloacetic acids (HAAs) (R2 = 0.5796). The formation potential of THMs increased, and HAAs decreased, with the increase of feed water pH. Ozonation markedly reduced the formation of THMs by up to 40 % at higher pH levels, but increased the formation of brominated-HAAs by shifting the formation potential of DBPs towards brominated precursors.

Pore flow and solute rejection in pilot-scale air-gap membrane distillation

Membrane distillation (MD) is a desalination technology with promising applications in treating brines generated by reverse osmosis. Theoretically, MD can achieve 100% rejection of non-volatile contaminants such as organic and inorganic solutes and pathogens because only the vapor phase permeates through the membrane. However, polymeric membranes are subject to a wide distribution of pore sizes that may result in pore flow or liquid flux through even a new membrane resulting in poor contaminant rejection. In pilot-scale MD systems, a larger membrane area increases the hydraulic pressure in the flow channel and the transmembrane hydraulic pressure difference, thus increasing the probability of pore flow of non-volatile contaminants through the membrane and providing enhanced resolution of contaminant detection. This work reports membrane rejection of organic and inorganic non-volatile solutes in a pilot-scale air-gap MD (AGMD) element and quantifies, for the first time, transport of non-volatile solutes through the membrane because of pore flow. Pathogen rejection in the pilot-scale MD system was also measured using enteric virus surrogates MS2 and PhiX174 as tracers. Organic and inorganic solutes and both viruses were detected in the distillate, suggesting the presence of pore flow. No difference between organic and inorganic solute rejection was observed, and both decreased (from 2.5-log10 to 1.5-log10) with an increase in air-gap vacuum (from 50 to 500 mbar). At 50 mbar and low evaporator inlet temperature (40 °C), virus rejection (2.4 -log10) was higher than organic and inorganic solute rejection (1.7-log10).

Antifouling thin-film nanocomposite NF membrane with polyvinyl alcohol-sodium alginate-graphene oxide nanocomposite hydrogel coated layer for As(III) removal

Removal of As(III) from the polluted waters is a challenge. It should be oxidized to As(V) for increasing its rejection by RO membranes. However, in this research, As (III) is directly removed by a high permeable and antifouling membrane prepared through the surface coating and in-situ crosslinking procedure of polyvinyl alcohol (PVA) and sodium alginate (SA) as coating materials containing graphene oxide as a hydrophilic additive on a polysulfone support with glutaraldehyde (GA) chemical crosslinking agent. The properties of the prepared membranes were evaluated through contact angle, zeta potential, ATR-FTIR, SEM, and AFM. The addition of GO in the polymeric networks of SA and PVA hydrogel coating layers led to a better hydrophilicity and a smoother surface and a higher negative surface charge resulted in improvment of permeability and rejection of membranes. Among the prepared hydrogel-coated modified membranes, SA-GO/PSf indicated the highest pure water permeability (15.8 L m−2 h−1 bar−1) and BSA permeability (9.57 L m−2 h−1 bar−1), respectively. The best desalination performance (NaCl, MgSO4, and Na2SO4 rejections of 60.0%, 74.5%, and 92.0%, respectively) and As(III) removal (88.4%) along with satisfactory stability and reusability in cyclic continuous filtration was reported for PVA-SA-GO membrane. In addition, the PVA-SA-GO membrane indicated improved fouling resistance toward BSA foulant with the lowest flux decline of 7%.

High-Performance Polyamide Reverse Osmosis Membrane Containing Flexible Aliphatic Ring for Water Purification

A reverse osmosis (RO) membrane with a high water permeance and salt rejection is needed to reduce the energy requirement for desalination and water treatment. However, improving water permeance while maintaining a high rejection of the polyamide RO membrane remains a great challenge. Herein, we report a rigid-flexible coupling strategy to prepare a high-performance RO membrane through introducing monoamine with a flexible aliphatic ring (i.e., piperidine (PPR)) into the interfacial polymerization (IP) system of trimesoyl chloride (TMC) and m-phenylenediamine (MPD). The resulted polyamide film consists of a robust aromatic skeleton and soft aliphatic-ring side chain, where the aliphatic ring optimizes the microstructure of polyamide network at a molecular level. The obtained membranes thereby showed an enhanced water permeance of up to 2.96 L·m-2 h-1 bar-1, nearly a 3-fold enhancement compared to the control group, meanwhile exhibiting an ultrahigh rejection toward NaCl (99.4%), thus successfully overcoming the permeability-selectivity trade-off limit. Furthermore, the mechanism of the enhanced performance was investigated by molecular simulation. Our work provides a simple way to fabricate advanced RO membranes with outstanding performance.

Highly permeable and durable mixed-matrix reverse osmosis membranes filled with cellulose nanofibers-hybridized Ti3C2Tx

Exploration of optimized nanomaterial fillers has been highly realized as a key to improve the comprehensive performance of reverse osmosis (RO) membranes. In this study, a new kind of high-separating efficient mixed-matrix RO membrane is proposed by filling cellulose nanofibers (CNFs)-hybridized Ti3C2Tx with an enlarged layer distance and enhanced negative electronegativity due to a strong hydrogen-bond-interaction. Therefore, the two-phase monomer interfacial polymerization (IP) process of the polyamide (PA) membranes was mediated to change the RO membrane surface from a leaf-like to a nodular-like morphology with additional water molecular channels, increased hydrophilicity and enhanced roughness. With such a special microstructure, the maximum water flux of the Ti3C2Tx-CNFs/PA membrane was elevated up to 64 L m−2 h−1, 1.4 times that of the pristine PA membrane without reducing the salt rejection (98.8 %) at all. In addition, the incorporation of Ti3C2Tx-CNFs was also found to elevate the antifouling and chlorine resistance of the RO membrane effectively. Interestingly, the Ti3C2Tx-CNFs/PA membrane exhibited both organic protein and inorganic salt pollution resistance. At a chlorination intensity of 10,000 ppm·h, the salt rejection of the PA membrane at this time had dropped to 67.4 %, while that of the TC10/PA membrane still remained at 92.3 %, which could be ascribed to the chlorine adsorption/substitution reaction on the surface of Ti3C2Tx-CNFs and the protective effect on the membrane surface. This study thus has validated the beneficial effects of nanomaterial incorporation and pointed out a new perspective for promoting the real applications of high-performance and long-life RO membranes.

Improved oily wastewater rejection and flux of hydrophobic PVDF membrane after polydopamine-polyethyleneimine co-deposition and modification

The surface structure and properties of a membrane largely determine its in-service performance during a filtration process. Polyvinylidene fluoride (PVDF) hydrophobic membrane is widely used in the separation of oily wastewater because of its mechanical strength, but is susceptible to oil fouling, whereas hydrophilic membranes are easily damaged in water due to their wettability but are resistant to oil. The advantages of the two membranes are then combined by modifying the hydrophobic membrane to be hydrophilic to maintain stability, mechanical strength, and antifouling performance. PVDF ultrafiltration membranes were modified with a mixture of different concentrations of polydopamine (PDA) and polyethyleneimine (PEI) using different deposition times (6, 12, and 24 h) and characterized using SEM, FTIR, and contact angle. Membrane performance was tested using a dead-end module for 60 min. The PDA-modified membrane showed a decrease in hydrophilicity from 88.1° to 77.7° after being coated with 0.5 g/L PDA for 6 h, while with the addition of 2 g/L PEI, the hydrophilicity reached 64.6° SEM characterization showed the presence of aggregates formed during the PDA polymerization process and decreased with the addition of PEI. This is in line with the results obtained from the performance test with the dead-end module where the smaller the aggregate, the greater the flux produced. FTIR characterization showed a strong bond between PDA and PDA-PEI with the membrane as the concentration and coating time increased.

Preparation of High Flux Chlorinated Polyvinyl Chloride Composite Ultrafiltration Membranes with Ternary Amphiphilic Copolymers as Anchor Pore-Forming Agents and Enhanced Anti-Fouling Behavior

N-Phenylmaleimide-styrene-maleic anhydride (NSM) copolymer, an inexpensive and commercial heat-resistant agent, was used as an additive in this work to tune the properties of chlorinated polyvinyl chloride (CPVC) composite ultrafiltration membranes. The NSM chains did not agglomerate in the casting solution, but increased the thermal instability, leading to faster phase separation and changing the cracked pores to rounded pores on the membrane surface. Moreover, the cross-section appeared with sub-layered finger-like macropores and micropores, which facilitated the rapid passage of water through the membrane. Notably, NSM copolymers were anchored to the membrane surface and the cyclic groups (maleic anhydride and maleamide) were not hydrolyzed during the phase separation as demonstrated by ATR-FTIR and XPS analysis. This may affect the membrane separation behavior. The results indicated that the pure water permeability of NSM-tuned membranes increasing by 350% that of pristine membrane. The rejection of all NSM-tuned membranes was higher than 90% for humic acid (HA) and 85% for sodium alginate (SA), which still outperformed the pristine membrane. With a NSM content of 5 or 10 wt % for two foulants (20 mg/L SA and 100 mg/L HA), the FRR of the NSM-tuned membrane exceeded 90.0% and the reversible flux decline ratio reached 50%, exhibiting better anti-fouling performance. Extended Derjaguin–Landau–Verwey–Overbeek theoretical model was utilized to evaluate and analyze the fouling mechanisms of the NSM-tuned membrane. Therefore, NSM can not only play a role of pore-forming but also significantly enhance the separation behavior of the CPVC membrane, providing a reference for future environmentally friendly membrane manufacturing processes.

Triethanolamine-based zwitterionic polyester thin-film composite nanofiltration membranes with excellent fouling-resistance for efficient dye and antibiotic separation

Water pollution and scarcity caused by small organic compounds (dyes and antibiotics) have attracted considerable attention due to their potential adverse effects on ecological environment and human body. Nanofiltration membranes with high performance, such as high rejection and fouling resistance, are expected to address these challenges. Herein, a new zwitterionic triethanolamine-based (Z-TEOA) monomer is proposed for the fabrication of zwitterionic polyester thin-film composite nanofiltration (ZNF) membranes. Z-TEOA is successfully synthesized via the ring-open reaction between TEOA and 1,3-propane sultone. ZNF membranes are fabricated via the interfacial polymerization under alkaline conditions. All fabricated membranes exhibit enhanced hydrophilicity and permeability due to the introduction of the zwitterionic functionality in the thin film layers. Specifically, the optimum membrane (ZNF1.5-5) shows an ultralow water contact angle (WCA) of 20.2°, high rejections to Congo red (CR, 99.9%), methyl blue (MB, 99.7%), orange G (OG, 95.9%), and tetracycline (TC, 96.7%). The uncompromised MB rejection of the ZNF membrane after a chlorine exposure (10,000 ppm.h) indicates its excellent chlorine resistance. Furthermore, the achieved ultrahigh flux recovery ratio (FRR, 97.8%) for MB demonstrates its outstanding fouling-resistant performance. All results reveal its potential for applications in the treatment of wastewaters from textile and pharmaceutical industries.

Study on boron removal performance of covalent organic skeleton membrane by hydroxyl groups

Growing demand for water desalination promoted the vigorous development of reverse osmosis (RO) membrane. How to effectively remove boron from seawater is the key problem to be solved by RO membrane. It is important to select suitable membrane materials for experimental design before complicated and expensive experimental attempts. In this paper, we demonstrate that pore chemistry plays a key role in boron removal capability of RO membranes via nonequilibrium molecular dynamics simulations. This study shows that the introduction of hydroxyl (-OH) groups into the Covalent organic frameworks (COFs) pore allows for better boron removal without changing water permeability. The optimal boron rejection of AB-COF membranes is 76.67%, and that of ATFG-COF membranes with hydroxyl groups can achieve 90%. This is caused by the hydrophilic pore of ATFG-COF that will preferentially adsorb water molecules to prevent the passage of boric acid molecules through membrane zone. Additionally, -OH groups on the pore will also adsorb a part of boric acid in the membranes, reducing the amount of boric acid entering into the permeate side. The results obtained in this paper can provide guidance for the rational design of RO membranes to achieve more efficient boron removal.

Preparation, enhancement of permeability, and anti-biofouling properties of PEES/nano-silver/PVP mixed-matrix membrane

This study investigated the separation of bovine serum albumin using a novel matrix mixed membrane composed of poly vinyl pyrrolidone and poly (phenylene ether ether sulfone)/Nano-silver. The responsive bare and modified PEES/Nano-silver membranes were evaluated using morphology, wettability, XRD and ATR-FTIR. The molecular weight cut-off (MWCO), water content, mean pore radius, porosity, and pure water flux were used to evaluate the presentation of mixed matrix membranes. The outcomes show that the membranes wettability is increased by the addition of PVP, which promotes the formation of hydrogen bonds. Its clear that the membranes are more hydrophilic than the PEES/Nano-silver membrane based on their performance. In addition, model foulants such bovine serum albumin (BSA) and E. coli were used to assess the efficacy of mixed matrix membranes anti-fouling properties. PVP loading results in more diversified surface morphology with asymmetric structure and higher water flux (4.35 × 10−5 ms−1) than the pristine membrane (2.23 × 10−5 ms−1) as a reference at 3.5 bar without compromising the rejection of membrane. The flux recovery ratio for PEES/PVP/Nano-Silver membranes is 97%, which is significantly higher than the ratio for PEES/Nano-Silver membranes (62%). Furthermore, The results of fluorescence microscopy showed that, compared to clean membranes, the modified membranes have biofouling activities.

Positively charged nanofiltration membranes for efficient Mg2+/Li+ separation from high Mg2+/Li+ ratio brine

Nanofiltration has gained increasing attention in lithium extraction from salt lake brine with high Mg2+/Li+ ratio. However, conventional nanofiltration membranes with negatively charged surfaces suffer from low Mg2+/Li+ selectivity. Herein, positive nanofiltration membranes with high charge density were fabricated via a two-step charge enhancement strategy. High concentration of polyethylenimine was used as the aqueous monomer to ensure the abundant amino groups on the membrane surface. To further enhance the electro-positivity, 2, 3-epoxypropyl trimethyl ammonium chloride was grafted through ring-opening reactions. The as-obtained membranes demonstrated positive zeta potentials over a large pH range (3-10), leading to significantly strengthened Donnan exclusion for Mg2+. The membrane rejection to MgCl2 was up to 99.3% while the rejection to LiCl was only ∼30%. The Mg2+/Li ​+ ​separation factor was 167 when filtration simulated brine with a Mg2+/Li+ ratio of 20 (2000 ​ppm MgCl2 and LiCl mixture), which is the highest value achieved among polyamide-based nanofiltration membranes. In addition, the membranes exhibited good stability in 40 ​h’ continuous testing. The modification strategy proposed in the present work is highly compatible with current industrial membrane preparation processes and easy to scale up with cost effectiveness.

Single Vs Multichannel Silica-Pectin Ultrafiltration Membranes for Treatment of Natural Peat Water

A comparative study was undertaken to investigate the potential of silica-pectin ultrafiltration membrane on varied operation pressure (0.1-0.3 MPa). Cross-flow ultrafiltration works were explored with tubular alumina substrates in single and multichannel configuration. The silica-pectin sol was prepared from TEOS as silica precursor by sol-gel method, afterward pectin was templated into the silica sol to induce carbon on it. Thereafter, both of single and multichannel alumina substrates was coated by the silica-pectin sol via inner coating technique. The study exhibited better performance of multichannel silica-pectin ultrafiltration membrane (with 4 bores) compared to the single channel membrane in terms of the permeate quality of UV254 rejection, as well as the permeate flux. The UV254 rejection of multichannel silica-pectin ultrafiltration membranes conducted over 84% in compliance with highest permeate fluxes of 234.3 L.m-2.h-1.bar-1 at high operation pressure (TMP 0.3 MPa). The multichannel ultrafiltration membrane permeate flux in this work is slightly high 60-75% over single channel. Hence, both single and multichannel silica-pectin membranes exhibited steady neutralized permeate fluxes under TMP 0.3 MPa conditions for natural 100% peat water concentration, which indicates that fouling is not occurred during filtration time up to 60 min. Therefore, multichannel silica-pectin ultrafiltration membrane in this work is success to treatment of natural peat water, that the natural organic matter removal was found to be fit for uses as clean water sources.

Improvements of ferrate(VI) pretreatment on membrane flux and membrane rejection using cheap NaClO reagent

Ferrate(VI) pretreatment can effectively alleviate membrane fouling during the ultrafiltration (UF) process, while instability and high expenditure limit its application. This study discovered that the cheap NaClO reagent would improve the performance of ferrate(VI) pretreatment, i.e., establishing Fe(VI)/NaClO (FC) process. 20 μM of Fe(VI) group can increase J/J0 from 0.323 to 0.391, while the optimization process of 20 μM Fe(VI)/4 μM NaClO [FC (5:1)] increased it to 0.491 at the end of cycle 1 filtration. Meanwhile, the reversible and irreversible membrane fouling resistance decreased by 50% and 56% in FC (5:1). This was attributed to the suppression of ferrate(VI) decomposing and in-situ formation of more dispersed ferric nanoparticles in FC process [730.33 nm in Fe(VI) and 606.80 nm in FC (5:1)] by applied NaClO. The rejection ratio of dissolved organic carbon (DOC) increased from 27.18% of Fe(VI) group to 40.34% of FC (5:1) due to the repulsive interaction amplification of acid-base (AB) interaction energy. That was derived from the hydrophilia promotion of the treated sample and the electrical property evolution of in-situ formed ferric nanoparticles by NaClO. It suggested that AB interaction energy, presenting repulsive interaction in membrane-foulants and foulants-foulants, was a major role in Fe(VI) group and FC process. There was no more side effect induced by FC pretreatment, which was confirmed by the result that FC caused no increase in the disinfection by-products (DBPs) formation potential. The present study provided insight into improving the effect of ferrate(VI) pretreatment without inducing side effect, and reduced the costs of ferrate(VI) pretreatment during the process of UF.

Robust and highly hydrophilic ultrafiltration membrane with multi-branched cellulose nanocrystals for permeability-selectivity anti-trade-off property

To overcome challenges associated with the “trade-off” effect and membrane fouling, the high-performance ultrafiltration membranes were prepared by blended multi-branched nanocellulose (Multi CNC) into polyethersulfone (PES) matrix using non-solvent induced phase separation (NIPS) technology. The as-prepared composite ultrafiltration membranes have high hydrophilicity, thicker skin layer and lower negative charge due to the abundant polar groups of carboxyl (COOH) in Multi CNC. As the results, the water flux and Bovine serum albumin (BSA) rejection of the composite membranes with 1 wt% Multi CNC reached to 961.65 L/m2·h and 96.4 %, while the flux and rejection of the original PES membrane was only 702.04 L/m2·h and 86.2 % respectively, thus the “trade-off” was effectively improved by loading of Multi CNC. Moreover, the flux recovery ratio (FRR) of MCP1 (FRR = 74.08 %) was 2.1 times as much as the original PES membranes (FRR = 34.81 %) in the water-BSA-water filtration process, verified that the introduction of Multi CNC could effectively improve the anti-fouling ability of composite membranes. Such hydrophilic composite ultrafiltration membranes with robust mechanical performance could be developed for pharmaceutical and biotechnological industries.