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In this work, a green route for the preparation of S-2-amino-1-butanol in the post-treatment for direct enantioseparation for the antituberculosis drug ethambutol hydrochloride has been explored. T...

The performance of nanofiltraton (NF) membranes are characterized by a high selectivity for multivalent anions, whereas poor selective separation capacity for multivalent cations and heavy metal ions. In this work, a new positively charged NF membrane was prepared by using 2-chloro-1-methyliodopyridine as an active agent to graft polyimide polymer onto the membrane surface via covalent bonding with surface carboxylic groups. The results showed that the prepared membranes had a high selective separation for divalent and monovalent salts (MgCl2 97.1%, CaCl2 96.8%, Na2SO4 83.5%, MgSO4 87.3%, NaCl 49%, LiCl 32%), and also exhibited a high removal efficiency for toxic heavy metal ions and dyes (CuCl2 96%, NiCl2 95.8%, CrCl3 98.0%, Tropaeolin O 98.3%, Victoria blue B 99.2%, Semixylenol orange 99%, Neutral 98.2%).

A novel industrial lithium-containing wastewater depth concentrating process integrating reverse osmosis (RO) and electrodialysis (ED) into a system is presented. A systematic analytical study was accomplished to optimize the studied parameters and minimize the energy consumption. The tested parameters were as follows: RO recovery by adding pressure, ED voltage drop, the concentration of RO retentate in ED feed solution, ED volume ratio, and ED operating mode. By using RO retentate instead of initial wastewater in the ED process, water energy consumption was reduced by 3.41 times from 26.67 to 7.81 kW h/m3, while optimizing the RO retentate concentration for the ED feed solution reduced the cost to 0.47 $/kg. The results showed that RO is crucial to preconcentrate lithium salt and save energy. Furthermore, the final LiCl concentration can approach as high as 87.09 g/L with the secondary ED process (Vd:Vc = 3:1), while the energy consumption can be saved as 7.71 kW h/m3 when the experiments stopped in regi...

Environmental stimuli-responsive membranes have many latent applications in numerous fields, for example, chemical/biological separations, water treatment, drug delivery, self-cleaning material and chemical sensor. In this study, a pH-responsive membrane with in-situ assembled stimuli-responsive microgels on membrane surface and internal channels wall was fabricated by the coagulation step of the phase-inversion process. Interestingly, it was found that poly(4-vinyl pyridine) (P4VP) microgel can be mobilized onto the membrane surface by using an acidic coagulation bath. Meanwhile, the membrane-based materials with different hydrophobic properties showed a great effect on the migration of microgel onto the channel surface. The inner pores of these responsive membranes can self-adjust its size with the changes of outside pH stimulus. Moreover, the gate-controlled water permeability of pH-responsive membranes was explored at the pH interval from pH 2 to pH 6. Investigations revealed that the P4VP microgel-assembled membrane had excellent pH-responsive performance. In addition, these pH-responsive membranes with embedded microgels on surface and inner pores wall also exhibited excellent reversible behaviors and self-cleaning properties.

Exploring a desirable cross-linker applied in cation exchange membranes (CEMs) to improve dimensional stability as well as electrochemical performance has a great signifcance for the current membrane science and technology. In this investigation, a sequence of crosslinked sulphonated polysulfone (SPSF) CEMs has been prepared to explore the influence of the crosslinking functionality on the dimensional stability and electrodialysis (ED) performance of modified membranes. Different cross-linker structures were obtained according to the cross-linker agent content added during the synthesis route. As expected, the membrane surface became smoother with increasing cross-linker content, presumably as result of the denser structure established. The dimension stability increases according to the crosslinking degree applied, whereas the permselectivity of membranes depends on the conjunction of many important and interlinked factors, including the formation of narrow ion transport channels and the variations in the exchanges sites concentration. It was observed that the optimized CEM (60SPSF-C2#) showed the highest NaCl removal ratio (91.7%) during the desalination experiments and exhibited the higher current efficiency (95.7%) and lowest energy consumption (6.55 kWh kg−1). These results suggest the formation of the optimum three-dimensional network configuration for the membrane structure determined by the functionality of cross-liker selected in this investigation.

The present work reports the preparation of a series of novel highly durable imidazolium-decorated anion exchange membranes (AEMs), with 3D network structure, via ultraviolet crosslinking reaction between 1-vinylimidazole and 1,6-hexanedithiol. AEM modified with trimethylamine (TMA) groups (no crosslinking, 45.7%) showed a significantly reduced water uptake within a range of 14.4–23.6% at 80 °C. Due to relatively good alkali-resistant of imidazolium groups and the compact structure stemmed from crosslinking network, the optimum cross-linked AEM (BPPO-Im 0.3) can retard the degradation and exhibits superior alkaline stability in 1.0 M NaOH at 60 °C for over 15 days, compared with TMA modified AEM. In ED application, BPPO-Im 0.3 AEM has a higher NaCl removal ratio of 77.82% than that of commercial AEM-Type II (74.13%) within 3 h experimental time. Accordingly, it shows higher current efficiency (67.43%) and lower energy consumption (1.94 kWh kg−1 NaCl), compared to commercial one (62.83%; 2.05 kWh kg−1). The facile fabrication process and the better-performance are suggestive of that BPPO-Im 0.3 is potentially applicable in ED.

The preparation of quaternary ammonium polysulfone anion exchange membranes (AEMs) with good dimensional stability and alkaline stability is an urgent problem to solve. In response, a series of cross-linked based on polysulfone and 4, 4′-trimethylenedipiperidine (TMDP) as crosslinkers with different degrees AEMs were developed in this work through a simple process. Among the fabricated AEMs, CAPSF-5 exhibits superb alkaline stability in a 1 M KOH aqueous solution at 60 °C for 15 days, whereas the non-crosslinked APSF membrane became tremendously brittle within 24 h and could not be further studied under the same conditions. In addition, even at 60 °C, CAPSF-5 demonstrates a superior dimensional stability compared to the non-crosslinked APSF membrane due to the formation of a dense internal network structure. These observations demonstrate that crosslinked CAPSF membranes can be a viable strategy to improve the deficiency of the polysulfone backbone, especially in terms of alkaline stability.

Anion exchange membrane (AEMs) fouling is a serious problem influencing membrane performance during electrodialysis process(ED), which would increase power consumption and reduce water recovery. In this paper, an aliphatic anion-exchange membrane was prepared from quaternized polyvinyl alcohol (QPVA) via dual cross-linking through annealing treatment and condensation reaction to restrain the membrane water swelling. The Wu% of QPVA membrane could be reduced to 22.87 ± 0.81%. Due to the hydrophilia (59.86 ± 0.21°), negative ζ-potential surface and aliphatic matrix of QPVA, no transition time appeared under our experiment condition, indicating the QPVA membrane was scarcely fouled by SDBS. And the existence of SDBS in dilute solution generated slightly effect on the QPVA membrane resistance and only 7.47 ± 0.21% reduction of the desalination rate in ED process. Furthermore, only distilled water was used as solution or reaction media, without any harmful organic solvents, presenting an environmentally friendly route for the preparation of water-based anion-exchange membrane. So, the excellent anti-fouling performance along with green preparation of QPVA showed its remarkable prospect for desalination purpose in ED process.

Novel anion exchange membranes with enhanced ion exchange capacity, dimensional stability and alkali stability were prepared by a facile synthesis method. Internal crosslinking networks in the resulting membranes were achieved by reacting chloromethylated polysulfone with 4,4′-trimethylene bis(1-methylpiperidine) (BMP), where BMP was used as both a quaternization reagent and crosslinker without requirement of post-functionalization. In order to evaluate the alkali resistance and dimension stability performance of the resulting membranes, the molar ratio of BMP in the resulting membranes was fixed at four different contents: 40%, 60%, 80% and 100%. The obtained membranes were accordingly denoted as CAPSF-N, in which N = 40, 60, 80 and 100, respectively. Due to the dense internal network structure and spatial conformation of the six-membered rings, the resulting CAPSF-N AEMs showed enhanced dimensional structures (at 60 °C, the water uptakes and swelling ratios of CAPSF-N were 8.42% to 14.84% and 2.32% to 5.93%, respectively, whereas those for the commercial AEM Neosepta AMX were 44.23% and 4.22%, respectively). In addition, after soaking in 1 M KOH solution at 60 °C for 15 days, the modified membranes exhibited excellent alkaline stability. The CAPSF-100 membrane showed the highest alkali stability (retained 85% of its original ion exchange capacity and 84% of its original OH− conduction after the alkaline stability test), whereas the non-crosslinked APSF broke into pieces. Additionally, compared to the commercial Neosepta AMX membrane under the same test conditions, the desalination efficiency of CAPSF-100 was enhanced, and the energy consumption was lower.

Developing a durable and antifouling monovalent selective anion exchange membrane is critical in practical electrodialysis (ED) process. Herein, a commercial anion exchange membrane was modified by sulfonated reduced graphene oxide (S-rGO) and polydopamine (PDA). Inspired by biological adhesion from mussels, the PDA coating on the surface of S-rGO-PDA membrane enhanced the stability of S-rGO nanosheets due to strong adhesion. The monovalent anion selectivity was evaluated by means of the Cl - / SO 4 2 - permeselectivity, and stability property was measured by the ion concentration changes of Cl - and SO 4 2 - for a long time application of ED. Moreover, antifouling property was measured by recording the time course of the potential difference in the presence of sodium dodecyl benzene sulfonate (SDBS). The results show that permselectivity of S-rGO-PDA membrane is 2.50, which is higher than pristine membrane (1.08). In addition, S-rGO-PDA membrane is stable, the permselectivity did not change significantly during 70 h ED process. Besides antifouling property of S-rGO-PDA membranes is improved compared with S-rGO membranes.

Self-regulation of membrane permeability performance is highly desirable for porous membrane applications. Inspired by the stomatal closure behaviour of plant leaves in response to environmental changes, here we report a series of dual thermo- and pH-responsive membranes based on the poly(4-vinyl pyridine) (P4VP) core/poly(N-isopropylacrylaminde) (PNIPAM) shell microgels. The stimuli-responsive microgels underwent in situ surface segregation and uniformly decorated on the surface of internal channels during the phase inversion process. The hydraulic permeability performance of the dual responsive membranes (DRMs) has been investigated within a temperature range of 20–50 °C and a wide pH range (spanning pH 2–6). The water flux of optimized membrane (M2) varied from 1.94 kg m−2 h−1 at 20 °C/pH 2–474.91 kg m−2 h−1 at 50 °C/pH 6 with a high gating ratio of 245. Investigations revealed that microgels based on different thickness of PNIPAM shell conferred different thermo-/pH-responsive properties to the DRMs. For example, the thicker PNIPAM shell enhanced the thermo-response performance, while the pH-response performance was restrained. These optimum smart gating membranes with enhanced gating coefficient and reversibility are potential for the applications in water gating and controlled release systems.

In this work, we have investigated a series of anion exchange membranes (AEMs) based on brominated poly(2,6-dimethyl-1,6-phenylene oxide) (BPPO) tethered with three saturated heterocyclic quaternary ammonium groups (QAs) of 1-methylpyrrolidine (MPY), N-methylpiperidine (MPRD), and 4-methylmorpholine (MMPH) for electrodialysis (ED) applications, respectively, along with BPPO with trimethylamine (TMA) and Neosepta AMX made for comparison. Our investigations demonstrate that the optimized BPPO-MPRD, having an ion exchange capacity of 1.67 mmol g−1, is highly stable in aqueous KOH (1 mol L−1) with ion exchange capacity retention ratio of 85.1% and hydroxide conductivity retention ratio of 80.3% at 60 °C for over 15 days, relative to other heterocyclic amine decorated AEMs. In ED application process, BPPO-MPRD shows the NaCl removel ratio of 98.8% and energy consumption of 12.58 kWh kg−1, outperforming the Neosepta AMX (97.4% & 15.76 kWh kg−1). The results demonstrate that the as-prepared BPPO-MPRD AEM can be applied in ED.

Membrane fouling is an urgent problem needing to be solved for practical application of nanofiltration membranes. In this study, an amphiphilic nanofiltration membrane with hydrophilic domains as well as low surface energy domains was developed, to integrate a fouling-resistant defense mechanism and a fouling-release defense mechanism. A simple and effective two-step surface modification of a polyamide NF membrane was applied. Firstly, triethanolamine (TEOA) with abundant hydrophilic functional groups was grafted to the membrane surface via reacting with the residual acyl chloride group of the nanofiltration membrane, making the nanofiltration membranes more hydrophilic; secondly, the 1H,1H,2H,2H-perfluorodecyltrichlorosilane (PFTS), well-known as a low surface energy material, was covalently grafted on the hydroxyl functional groups through hydrogen bonding. Filtration experiments with model foulants (bovine serum albumin (BSA) protein solution, humic acid solution (HA) and sodium alginate solution (SA)) were performed to estimate the antifouling properties of the newly developed nanofiltration membranes. As a result of surface modification proposed in this study the antifouling properties of an amphiphilic modified F-PA/PSF membrane were enhanced more than 10% compared to the PA/PSF specimen in terms of flux recovery ratio.

Inspired by stomata, a series of single or dual thermo-/pH-responsive smart gating membranes (SGMs) were prepared with in situ assembled stimuli-responsive microgels as gates. Highly cross-linked poly(N-isopropylacrylamide-co-methylacrylic acid) P(NIPAM-co-MAA) microgels underwent in situ surface segregation during the acetic acid-assisted phase inversion process, and they were uniformly decorated on the surface of the membranes and the channels. The hydraulic permeability performance of SGMs was studied within the temperature range of 25–70 °C and a wide pH range (spanning pH 3–11). Investigations revealed that microgels based on different NIPAM/MAA ratios provided different thermo/pH-responsive properties to SGMs. Higher NIPAM/MAA ratios determined the thermo-responsive performance, and higher MAA/NIPAM ratios determined the pH-responsive performance. Moreover, the SGMs with in situ assembled microgels on the surface and channel surface have enhanced gating coefficients, stimuli-reversible behaviours and self-cleaning performance.

Layer-by-layer deposition of polycations and polyanions multilayers on the surface of anion exchange membranes (AEMs) is a simple and versatile method to obtain monovalent anion selectivity. However, the stability of the polyelectrolyte multilayers (PEMs) can be compromised by the weak interactions formed between the deposited barrier and the pristine membrane surface. In this sense, cross-linking appears as an efficient method to improve the chemical stability of PEMs by covalent bonding. In this investigation, polyelectrolyte multilayers was coated on commercial AEMs by alternating electro-deposition with polystyrene sulfonate (PSS) and 2-hydro-xypropyltrimethyl ammonium chloride chitosan (HACC). Subsequently, photosensitive molecules (4,4-diazostilbene-2,2-disulfonic acid disodium salt (DAS)) were mixed into the loose multilayers by soaking in the DAS solution and chemical bonds were formed in the membrane by UV irradiation. The chemical composition and structure of the membrane were confirmed and observed by infrared spectroscopy, atomic force microscopy and scanning electron microscopy. The monovalent selectivity and durability were evaluated by electrodialysis (ED) in a Cl - /SO 4 2- system. The optimized membrane was found to have a stable selectivity during the entire duration of testing (76 h), and while a conventional multilayer modified AEMs completely loses its selectivity after 30 h. Furthermore, the modification process improved the monovalent anion selectivity from 0.39 to 4.36. The experimental results demonstrate the effectivity and feasibility of the modified strategy.

In this work, a novel zero liquid discharge technology combining of electrodialysis (ED), electrochemical catalytic oxidation (ECO), reserve osmosis (RO) and bipolar membrane electrodialysis (BMED) was developed for sustainable recovery of high-saline papermaking wastewater. The effect of membrane type, volume ratio, membrane fouling and voltage were investigated in ED process; subsequently parameter such as electrolyte conductivity was studied in ECO process. The FKB/FAB stack shows good separation performance for the salts and organics, allowing a relatively high COD rejection of 97.80%. Meanwhile, membrane fouling was investigated through a comparison between virgin and fouled membranes. To achieve a high-saline solution with low organics, a second-stage ED process was applied. The concentration factor was increased to 1.799 with a COD rejection of 96.54% at voltage of 12 V. Simultaneously, the ECO process exhibited superior COD removal of 94.99% at the electrolyte conductivity of 4 mS/cm. Through the application of BMED at Vf:Vb:Va (volume ratio of feed, base and acid solution) of 4:1:1, the final acid and base content could approach a high value of 12.30 wt% and 10.60 wt%, respectively. Therefore, this hybrid ED-ECO-RO-BMED combined process demonstrates a strongly technical applicability for sustainable resource recovery from high-saline papermaking wastewater.

Anion exchange membranes (AEMs) with a high ion exchange capacity, striking water uptake and excellent dimensional stability were prepared via an internal crosslinking networks strategy. Internal crosslinking networks were formed by reacting 4,4′-bipyridine with brominated poly (2,6-dimethyl-1,4-phenylene oxide) (BPPO). 4,4′-bipyridine not only provides a functional group but also comprises a cross-linking agent without requirements of post-functionalization. The variation of the 4,4′-bipyridine amount into the casting polymer solution was explored to regulate the performance of the anion exchange membranes, and the membrane properties were evaluated by AFM, ion exchange capacity (IEC), water uptake, the linear expansion ratio, tensile strength, thermal stability, membrane area resistance and electrodialysis experiments, etc. The results showed that the cross-linked membrane with the IEC of 1.98 mmol/g has much more outstanding dimensional stability (water uptake: 11.68%; swelling ratio: 3.8%) than non-cross-linked BPPO-Tri membrane (water uptake: 53.26%; swelling ratio: 7.71%) and commercial Neosepta AMX membrane (water uptake: 60.29%; swelling ratio: 5.08%), at the high temperature (50 °C). When being applied in ED application, the cross-linked BPPO-20 membrane (NaCl remove: 59.7%; energy consumption: 5.97 kWh/kg NaCl) exhibits slightly higher desalination efficiency and lower energy consumption than commercial Neosepta AMX membrane (NaCl remove: 58.3%; energy consumption: 6.51 kWh/kg NaCl), suggesting its promising application in ED.

In this study, a process design consisting of chemical precipitation, electrodialysis with monovalent-selective membranes, and bipolar membrane electrodialysis (BMED) is proposed to valorize seawater concentrate discharged from an RO (reverse osmosis) plant for the production of acid/base and coarse salt with high purity. After pre-precipitation and electrodialysis with monovalent-selective membranes, a high purity of coarse salt (∼92%) was obtained. Furthermore, the effect of current density and feed concentration of the BMED process on the production of acid/base with high purity was investigated. It is acceptable to attain acid/base with a purity of ∼95%/∼85% when operating at a current density of 10 mA/cm2 and a feed conductivity of 100 mS/cm by applying the screened BMED stack. Finally, the total process cost for the acid/base production was estimated at $0.50/kg at the current density of 10 mA/cm2, which is appropriate and competitive for industrial application.

In this study, an electrodialysis (ED) system which was divided into three-stage operation was designed to treat seawater concentrate. The experiment was carried using a laboratory ED-cell with an effective area of 189 cm2. Two types of monovalent selective ion-exchange membranes were investigated: CIMS/ACS and CSO/ASV. The effect of applied current density during ED process was also studied. The experimental results indicate that the separation performance for divalent ions (i.e., Ca2 +, Mg2 +) with CIMS/ACS membranes stack was superior to CSO/ASV membranes stack; furthermore, a lower current density can increase the selectivity in monovalent ions to divalent ions with either the CIMS membrane or the CSO membrane. The current efficiency and energy consumption were optimal at a current density of 4 mA/cm2 by using CIMS/ACS membranes stack as the first stage of system in this experiment. Furthermore, the desalination rate (70%) was chosen as the experimental operation endpoint of the first-stage ED operation based on the experimental results. Moreover, the latter two-stage operation was used to concentrate brine to produce coarse salt after evaporation process. Finally, the repeated batch experiments confirmed the system feasibility for treating seawater concentrate to produce coarse salt with the purity of ~ 85% under continuous operation.

Hybrid polyethersulfone-based ultrafiltration membranes were prepared by incorporating metal (Ag and Cu) and/or amine-functionalized mesostructured SBA-15 silica particles. The doping particles were included into the casting solution to obtain a total solids load of 3.6 wt% in the final membranes. The physicochemical characterization of particles and membranes showed a good dispersion of metals inside the mesoporous structure of silica as well as a reduced skin layer, higher pore interconnectivity, and a larger amount of pores in membranes doped with the hydrophilic fillers. Membrane surface was also slightly less hydrophobic in hybrid membranes. Membrane performance was significantly improved as result of considerable increase of water permeation without affect negatively the membrane selectivity. The organic antifouling properties were enhanced with significant permeability improvement without compromising membrane rejection performance. In addition to it, metal-loaded silica allowed preparing membranes with high antibacterial activity. The removal of colonies of Escherichia coli and Staphylococcus aureus was complete either on membrane surface or in the liquid in contact with membranes when exposed to a 1/500 nutrient broth medium for 20 h at 36 °C. The rate of metal release depended on metal speciation and represented a 0.1–0.6% of the total metal content of membranes.

Polymeric membranes enhanced by nanoparticles have received great attention over the past decade due to their abilities to meet the growing demand in addressing the global scarcity and pollution of water resources. Many efforts have been devoted to improve the membrane performance using this strategy, and to develop novel applications via molecular-level design for nanoparticle-polymer systems. Recent advances in applying in situ preparative techniques in polymeric membrane can potentially lead to new classes of nano-enhanced membranes for advanced water purification. Considering the increasing interest in this field related to the potential for controlling the dispersion and stability of nanoparticles, we review the progress of in situ preparative techniques for water purification. Categories of in situ preparative techniques are elaborated in detail, primarily focusing on the mechanism of the sol-gel process and in situ chemical reduction, which are considered as the most common applications of in situ preparative techniques. We also describe the effect of binding styles of nanoparticles ( in situ formation in the membrane matrix or on the membrane surface) on the structure-property relationship in nano-enhanced membranes, discussing recent applications of in situ formed metal nanoparticles, metal oxide nanoparticles, polymeric nanoparticles and other nanoparticles in water treatment. Finally, we suggest the antifouling mechanisms of in situ preparative techniques and give a further perspective for the next-generation nano-enhanced membranes. Further development of nano-enhanced membranes must go hand in hand with strict regulations for drinking water consumption and environmental safety.

Functionalized SBA-15 mesoporous materials were newly developed and embedded as inorganic additive into polyethersulfone (PES) membrane. Doping the SBA-15 mesoporous materials improved membrane permeability without significant change in morphological structure of PES membrane. However, low dosage of SBA-15 of 0.3 wt.% increased fouling rate of PES membrane with BSA compound. The fouling potential in PES membrane was reduced by increasing concentration of SBA-15 materials to 0.6 wt.%. Antifouling properties of PES membrane were associated with lower BSA membrane adsorption due to the improvement of membrane hydrophilicity by SBA-15 addition.

A novel anion exchange membrane (AEM) is developed through poly (sodium 4-styrene sulfonate) (PSS) and hydroxypropyltrimethyl ammonium chloride chitosan (HACC) alternate electro-deposition to enhance the monovalent selectivity. Compared to the commercial original AEM, coating of the (PSS/HACC)N alternate electro-deposition multilayer on the membrane surface dramatically enhance the selectivity of anions. In addition, the permselectivity for monovalent anions of the membranes was investigated by electrodialysis experiments. For comparison, the corresponding Cl−/SO42− were chosen and the average values of permselectivity and separation efficiency of commercial AEM are 0.66 and −0.19 respectively. As result of alternate electro-deposition of PSS/HACC layers, the permselectivity raised up to 2.90 and the separation efficiency also increased up to 0.28 for nine PSS/HACC bilayers needed. Under the optimal fabricating conditions, the area resistance of membrane arrived at 4.52 Ω cm2 with nine PSS/HACC bilayers. Meanwhile, the polarization current-voltage curves and ζ-potential of membranes were also tested to characterize the electrochemical behavior of the modified membrane. The high selectivities of these membranes may enable electrodialysis applications in separation of monovalent and divalent anions.

New polyethersulfone (PES) ultrafiltration hybrid membranes were prepared by doping with different amine-functionalized mesostructured silica (SBA-15) particles added at low weight concentration (0.6% in the synthesis medium). 3-(aminopropyl) trimethoxysilane, N -(3-trimethoxysilylpropyl)ethylenediamine, and N -(3-trimethoxysilylpropyl)diethylenetriamine were used as amine precursors of the fillers obtained by co-condensation and denoted as SBA-15/Monoamine, SBA-15/Diamine, and SBA-15/Triamine, respectively. SBA-15 material functionalized with polyethylenimine was synthetized by hyperbranching polymerization with aziridine. Physicochemical characterization of fillers was achieved by nitrogen sorption, X-ray diffraction, TEM, dynamic light scattering, and elemental analysis. Membrane morphology was assessed in terms of overall porosity by water uptake and surface pore size distribution from FEG-SEM. Hydrophilicity of the membranes was determined by measuring water contact angle. Significant increase of porosity and hydrophilicity was found in all doped membranes, which exhibited substantial improve in water flux in comparison with neat PES membrane. Filtration experiments conducted with BSA protein aqueous solutions (1 g L −1 ) revealed that antifouling ability of doped membranes was gradually enhanced with amine functionalization, especially against reversible fouling. PES/SBA-15/Triamine appeared as the best specimen in both water flux and antifouling behavior with excellent long time permeation performance in repeated cleaning/filtration cycles.

The development of a facile approach to fabricate anion exchange membranes (AEMs) with efficient ionic transport and desirable stabilities (mechanical and dimensional) for various applications is meaningful. In this work, a two-step strategy for the preparation of AEMs with 3D network structure, via cross-linking reaction between 2-chloroacetamide (CAA) modified poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and N,N,N′,N′-tetramethyl-1,4-diaminobutane (TMDAB) has been reported. The as-prepared AEMs with ion-exchange capacity (IEC) in the range of 1.38–1.84 mmol g−1, exhibit the much lower water uptake (13.14–22.45%, 80 °C) relative to the un-crosslinked AEM (35.89%, 80 °C). In addition, due to the presence of fluorine-based 3D network structure, the as-prepared AEMs show much enhanced mechanical and thermal stability in comparison with the un-crosslinked AEM. In the electrodialysis (ED) application, the optimized AEM shows the higher current efficiency (78.6%) and lower energy consumption (2.01 kWh kg−1 NaCl) than those of commercial AEM AEM-Type II (76.4%; 2.26 kWh kg−1), respectively, within 150 min of operation interval. The proposed facile fabrication protocol and the better-performance of optimized PVDF-HFP -based AEM demonstrate the potential ED application.

：Organic solvent nanofiltration (OSN) membranes have gained increasing attention for their wide applications in organic phase system. However, the fabrication method rather than the swelling behavior receives more attention during the OSN testing. In this work, a thin-film composite membrane with an internal cross-linking network by reacting 4,4-bipyridine with brominated poly (2,6-dimethyl-1, 4-phenylene oxide) (BPPO) has been prepared for organic solvent nanofiltration (OSN). The bipyridine groups substituted on the polyphenylene oxide polymer backbone act as cross-linkers and cationic channels for remarkable chemical stability and high solvent permeability. The permeability of the cross-linked BPPO (CBPPO) thin-film membranes exhibited high related to the viscosity and solubility parameter of solvents. The stability of CBPPO membrane was studied via various organic solvent immersing experiments. The result demonstrated that the composite membrane swelling changed to an extent of no more than 2.01%. It can be attributed to the low conformational flexibility of polymer chains with a high crosslinking degree. The ethanol permeation and dye rejection were compared before and after soaking. The calculation of the MWCO and membrane potential of modified CBPPO membranes showed that the swelling behavior of the CBPPO composite membranes is mainly affected by the membrane charge densities rather than the pore size.

This study reports the fabrication of mixed matrix membranes (MMMs) using immersion precipitation phase inversion for promising application in desalination of dye solutions. Aromatic poly(m-phenylene isophthalamide) is used as the polymer material, and the metal–organic framework MIL-53(Al) is added to develop integrally skinned asymmetric membranes. Successful dispersion of MIL-53(Al) particles into the membrane-separating layer is confirmed by scanning electron microscopy. The optimum performance of the membranes is obtained at 0.5 wt % MIL-53(Al) concentration. In particular, the M-0.5 membrane is planned for use in separating dye/salt aqueous mixtures. It is observed that the M-0.5 membrane has a rejection for NaCl and Na2SO4 below 11% and 37%, respectively, in mixed salt/dye solutions. Additionally, the M-0.5 membrane is found to have a rejection rate of 83.9%, 98.3%, and 99.8% for nitroso-R salt, xylenol orange, and ponceau S, respectively, in mixed Na2SO4/dye solutions. The rejection rate for Na2SO...

SiO 2 nanoparticles offer promising prospects as additives for the synthesis of organic–inorganic hybrid composite membranes due to their facile synthesis procedure with low cost and toxicity to aqueous systems. This requires silica nanoparticles with good monodispersity to form a regular hydrophilic surface. In this study, monodisperse silica synthesized by the Stober method was explored as an additive in ultralow concentration for the synthesis of organic–inorganic composite membranes based on polyethersulfone, aiming at potential application in water treatment. The results indicate the polyethersulfone membrane doped with monodisperse silica has an enhanced performance. The hydrophilicity of the modified membranes was also enhanced due to the high water affinity of nano-SiO 2 , resulting in a higher permeability. However, in the high concentration interval of nano-SiO 2 , the permeability of modified membranes decreases due to pore plugging and the alteration of macrovoids in the sublayer of membranes. Simultaneously, the selectivity of the modified membranes was improved, which is an indicator for a more narrow pore size. The optimum permselectivity was obtained with the addition of 0.30% nano-silica. Additionally, the fouling resistance increased by ca. 70%. Thus, doping of nano-silica in the membranes is an alternative method to enhance permselectivity and fouling property for water treatment.

Nanofiltration (NF) membranes have been used previously for the recovery of dyes, salts, and water from textile wastewaters with high salinity. However, commercially available NF membranes have a high rejection for divalent salts (i.e., Na2SO4), substantially reducing the salt recovery and membrane flux when treating textile wastewater containing Na2SO4. In this study, a tight ultrafiltration membrane (UH004, Microdyn-Nadir) was proposed to fractionate the dye and Na2SO4 in the textile wastewater. The UH004 membrane with a molecular weight cutoff of 4700 Da provided complete passage of monovalent salts, with little rejection of Na2SO4. This significantly increases the filtrate flux that can be achieved with high-salinity wastewater since osmotic pressure and concentration polarization effects are minimized. Furthermore, the retention behavior of four different dyes was evaluated to determine the efficiency of this membrane process. This tight ultrafiltration membrane offered the high retention for direct dyes (i.e., direct red 80, direct red 23, and Congo red) and reactive blue 2. For instance, the UH004 membrane yielded >98.9% rejection for all of the dyes at a pressure of 4 bar even in the presence of 60 g L−1 Na2SO4. Subsequently, an ultrafiltration-diafiltration process was designed to separate a dye/Na2SO4 aqueous mixture with 98% desalination efficiency and greater than 97% dye recovery after 5 diavolumes. These results clearly demonstrate that tight ultrafiltration membranes can be a stand-alone alternative to NF membranes for the effective fractionation of dye and Na2SO4 in the direct treatment of high-salinity textile wastewater.

A series of semi-interpenetrating polymer network (sIPN) composite anion exchange membranes were fabricated depending on immobilized linear PVDF and cross-linked polyepichlorohydrin (PECH), 1,4-diazabicyclo[2.2.2]octane, (DABCO) network through in situ synthetic pathway. A cyclic diamine (DABCO) was used as cross-linking agent and simultaneously improved the ion-exchange capacity by amination. Scanning electron microscopy (SEM) indicated that the composite membranes exhibited a dense and homogeneous structure. Successful formation of PECH-DABCO copolymer within the sIPN membranes was also confirmed by Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). The PVDF percentage and inherent properties of membranes such as ion exchange capacity (IEC), water uptake (WR), thermal stability, mechanical property, and area resistance were investigated to evaluate their applicability in electrodialysis (ED). The experimental results showed that the composite membrane maintained a good perspec...

Novel nanofiltration (NF) membranes were prepared by interfacial polymerization using four different nanocomposite membranes as sublayers. The nanocomposite sublayers were prepared by immersion precipitation method, dispersing nanoparticles such as TiO 2 , SBA-15 and functionalized SBA-15 with carboxylic groups (SBA-15(COOH)). The physico-chemical properties of the sublayers were studied by means of cross section morphology, pore diameter, pore density, contact angle and roughness by SEM and FEG-SEM. The successful incorporation of the thin film layer was evaluated by FT-IR. The addition of the nanoparticles increased the pore density and hydrophilic character of the ultrafiltration (UF) sublayers. Results showed that the nanocomposite sublayers can improve the process performance of the thin film composite membrane. In this study, the most significant performance improvement was observed on the NF with SBA-15(COOH) doped sublayer, achieving permeability values in the UF range (56.3 dm 3 /m 2 hbar) and successful MgSO 4 rejection coefficients (68.3%). Results also show that there is no strong influence between the physical parameters of the sublayers and NF process performance. Therefore, it was concluded that the COOH functional group of the nanoparticle SBA-15(COOH) might have interfered in the interfacial polymerization process, leading to more permeable and selective NF membranes.

Nanofiltration (NF) membranes, especially loose NF membranes, trigger a growing interest for the fractionation of concentrated organic matters/salt mixtures in addition to the production of pure water. This study presents an in-depth characterization of two superhydrophilic loose NF membranes (Sepro NF 6 and 2A, Ultura). The physical characterization included the determination of the molecular weight cut-off (MWCO), pore size distribution, membrane morphology, surface charge, roughness and hydrophilicity. This was combined with a chemical characterization, i.e., by Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), to determine the intrinsic membrane properties. The chemical characterization demonstrates that both Sepro NF membranes are poly(piperazineamide) based, showing the modification chemistry for the top layer through XPS measurement. Specifically, Sepro NF 6 and NF 2A membranes were found to have a superhydrophilic surface (contact angle for Sepro NF 6: 14.3±0.9°; that for Sepro NF 2A: 21.7±1.4°) with a low roughness, offering a potential advantage over conventional NF membranes in minimizing membrane fouling. Sepro NF 6 and NF 2A membranes had a mean effective pore size of 0.64±0.03 nm and 0.52±0.01 nm (corresponding to MWCOs of 862±80 Da and 493±53 Da), respectively. In terms of filtration performance, Sepro NF 6 showed a high permeability of 16.7 L m −2 h −1 bar −1 with 88.9% salt transmission for 0.01 mol L −1 NaCl solution, and a slightly lower permeability and salt transmission was obtained for Sepro NF 2A, which is desired for an effective fractionation of target organic matter/salt mixtures.

Selectivity for monovalent cations is an important property of cation exchange membranes (CEMs). The cation exchange membranes of the CSO modified with polyethyleneimine type have a higher selectivity for monovalent cations than the multivalent cations. Unfortunately, the loss of selectivity for these kinds of CSO seems to be unavoidable due to fouling and degradation of polyethyleneimine groups. In this situation, a “re-modification” technique was developed for recovery of fouled CSO, activating the fouled CSO by methanol and a sulfuric acid solution with ultrasonic vibration, followed by a layered surfacial electro-deposition method to prolong the lifetime of cation exchange membranes. A series of electrodialysis experiments for Na+/Ca2+ separation was performed for evaluating and comparing the monovalent cation selectivity of the samples. The restoration of the surface and cross section morphology after “re-modification” was demonstrated by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). As a result of the re-modification method the membranes with chemically degraded polyethyleneimine were again made functional. The ion exchange groups of the CSO modified with polyethyleneimine were successfully recovered, giving the membrane a high permselectivity again.

Poly(vinyl chloride) (PVC) ultrafiltration membranes with improved antifouling and antibiofouling properties were prepared by non-solvent induced phase inversion using a hyperbranched polyamidoamine as additive. PVC reacted into the casting solution with the commercial polyamidoamine nanomaterial Helux-3316 by means of a nucleophilic substitution reaction. The composition of neat and functionalized membranes was studied by ATR-FTIR and elemental composition. Amino groups were tracked using the fluorescent dye fluorescamine. Surface ζ-potential and water contact angles were used to measure surface charge and hydrophilicity of tested membranes. The incorporation of amino groups increased membrane hydrophilicity and surface porosity, which resulted in enhanced permeability. Functionalized membranes displayed antifouling behaviour revealed upon filtering BSA solutions and lower irreversible fouling than PVC membranes. The attachment of Helux moieties to PVC yielded membranes with antibiofouling functionality explained by the interaction of positively charged Helux moieties with the negatively charged cell envelopes. Growth reduction for cells attached to the membrane surface during filtration reached up to 1-log for the gram-positive bacterium S. aureus. This investigation revealed that the incorporation of the hyperbranched nanomaterial in concentrations in the order of 1 wt% in the casting solution provides significant benefits to membrane performance, in terms of permeability and antifouling potential.

In digital printing, a high salt content in dye solutions is detrimental, which calls for effective strategy for dye/salt fractionation. In this study, a loose nanofiltration (NF) membrane Sepro 2A was employed to desalinate diverse dye species (2 reactive dyes and 4 cationic dyes). This membrane, with a molecular weight cutoff of 490 Da, showed consistently high rejections to all the reactive and cationic dyes (>97.7%). Operational conditions such as dye concentrations and applied pressures have limited effects on the rejection of the membrane. An integrated NF-diafiltration process, involving a pre-concentration and a diafiltration step, was specifically designed for the fractionation of dye/NaCl mixtures. This loose NF membrane showed >99.7% rejection to reactive dyes (reactive blue 2 and reactive orange 16) and ca. 99.3% salt removal with ca. 2.0% dye loss after 5.0 diavolumes. However, the NF membrane experienced a 15.9% loss to methylene blue due to the lower rejection to this model cationic dye (97.2%). The current study provides important insights into dye/salt fractionation by loose NF membranes for digital ink-jet printing. © 2017 Elsevier B.V.

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