Aqueous Phase Monomer Research Articles

Thermally stable thin-film composite nanofiltration membranes derived from 3,3′-diaminobenzidine

The rapid development of modern industrialization has put forward high demands on separation and purification technologies. To reduce energy consumption, improve efficiency, and enhance process flexibility, nanofiltration membranes for high temperature separation have become more and more important. Herein, we report the use of 3,3′-diaminobenzidine (DAB) as the aqueous phase monomer and trimesoyl chloride (TMC) as the organic phase monomer to engineer thermally resistant nanofiltration membranes via interfacial polymerization. The incorporation of DAB enhances the rigidity of the cross-linked polyamide network, reduces segmental thermal motion at high temperature, and improves the thermal stability of the composite membrane. The variations in fractional free volumes of the nanofiltration membranes were analyzed at different temperatures by molecular dynamics (MD) simulation, which have also been confirmed by experiments. The findings reveal that incorporating a rigid monomer into the polyamide layer can significantly enhance the thermal resistance. The resultant composite membrane exhibits outstanding resistance to high-temperature feed solutions, boasting a highly stable rejection rate (97.0 %) to Na2SO4 between 25–85 °C. Remarkably, even under sustained operation at 85 °C for 12 h, the rejection rate is consistently stable. This work presents a novel system for the design of thermally stable nanofiltration membranes for high temperature separation.

Synergistic preparation of organic solvent nanofiltration membranes from polydopamine/polyethyleneimine interlayers with aminated attapulgite

This study utilized polydopamine (PDA)/polyethyleneimine(PEI) as the hydrophilic interlayer and added aminated attapulgite (ATP-NH2) to the aqueous phase monomer for interfacial polymerization (IP) to synergistically create nanofiltration membranes resistant to organic solvents. The hydrophilic nature of the PDA/PEI interlayer facilitates the rapid passage of polar solvents and results in excellent adhesion, ensuring tight bonding between the ultrafiltration support membranes and the active layer. Furthermore, the incorporation of the ATP-NH2 nanoparticles played a pivotal role in regulating the IP process. The resulting nanofiltration membranes, produced through the combined efforts of these components, achieved an optimal methanol permeation flux of 14.05 L m−2h−1 bar−1, with a rejection rate of Evans blue dye maintained at 99.42 %. Despite being exposed to N, N-dimethylformamide (DMF) at 80 ℃ for a period of 5 days, the nanofiltration membranes maintained both their exceptional separation effectiveness and stability. These findings suggest promising application prospects for the developed nanofiltration membranes.

Dual-phase microporous polymer nanofilms by interfacial polymerization for ultrafast molecular separation.

Fine-tuning microporosity in polymers with a scalable method has great potential for energy-efficient molecular separations. Here, we report a dual-phase molecular engineering approach to prepare microporous polymer nanofilms through interfacial polymerization. By integrating two micropore-generating units such as a water-soluble Tröger's base diamine (TBD) and a contorted spirobifluorene (SBF) motif, the resultant TBD-SBF polyamide shows an unprecedentedly high surface area. An ultrathin TBD-SBF membrane (~20 nm) exhibits up to 220 times improved solvent permeance with a moderate molecular weight cutoff (~640 g mol-1) compared to the control membrane prepared by conventional chemistry, which outperforms currently reported polymeric membranes. We also highlight the great potential of the SBF-based microporous polyamides for hydrocarbon separations by exploring the isomeric effects of aqueous phase monomers to manipulate microporosity.

Fabrication of self-cleaning nanofiltration membranes through interfacial polymerization using PEI@CoPc monomer for Mg2+/Li+ separation

Efficient Mg2+/Li+ separation is highly demanded to address the global lithium scarcity. The nanofiltration (NF) membrane prepared with PEI-based monomer possess positively charged surface, exhibiting promise potential in lithium extraction from salt lake brines. In this work, water-soluble metal phthalocyanine (PEI@CoPc) was synthesized via grafting reaction between PEI and the (Tetracarboxyphthalocyaninato)cobalt(Ⅱ). The light-responsive NF membrane was prepared via interfacial polymerization technique using the water-soluble PEI@CoPc as aqueous phase monomer alone. This strategic modification significantly enhances the water permeance and Mg2+/Li+ selectivity of the membrane. The best-performing of PEI@CoPc-TMC/PES membrane shows a water permeance of 16.7 L m-2h−1 bar−1 and a Mg2+/Li+ selectivity of 29.5. The membranes exhibited exceptional selectivity towards magnesium ions while maintaining high lithium permeability, offering effective technical support for the efficient extraction of lithium resources from salt-lake brines. Moreover, the distinctive photocatalytic activity of PEI@CoPc can generate active oxidizing species such as superoxide radicals (•O2–) to oxidatively degrade pollutants, conferring the membrane excellent self-cleaning capability. The results indicated that the prepared composite membrane exhibit excellent fouling resistance and self-cleaning performance.

Preparation of self-healing and pH-responsive nanofiltration membranes with improved anti-fouling property for salt/dye separation

Nanofiltration (NF) membranes can inevitably suffer from external damage in the practical application process, causing the loss of their original function and performances. In this work, the β-CD-DX-S were synthesized for the first time through one-step polymerization of SBMA, DMAEMA and double bond functionalized β-CD. Subsequently, the membrane was successfully fabricated via interfacial polymerization using the constructed β-CD-DX-S as aqueous phase monomer alone. The prepared β-CD-DX-S/PES membrane exhibits novel self-healing performance attributing to the host-guest interaction between DMAEMA and β-CD. The membranes also possess excellent pH-responsive property attributing to the protonation and deprotonation behavior under different pH environments of dimethylamine unit in DMAEMA. The grafted DMAEMA and SBMA enhanced the hydrophilic property of membrane, reducing electrostatic adsorption of pollutants on the surface of membrane. The hydrophobic binding site inside the cavity of β-CD can accommodate dimethylamino group in the DMAEMA which could be regulate the spatial structure of β-CD-based materials, strengthening salt/dye selectivity of membrane. The results indicated that the prepared β-CD-DX-S/PES membranes possess good potential for NF applications.

Ethanol activation of polyester membrane for superior dye/salt separation performance

Dye wastewater poses a severe danger to the environment and human health. The purification of dye wastewater is the focus and hotspot of most researchers. In this work, ethylene glycol (EG) was selected as an aqueous phase monomer to fabricate polyester membranes through an interfacial polymerization reaction. Then the polyester membrane was activated by ethanol aqueous solution. By adjusting the activation time and concentration of the ethanol, the network of the polyester membrane can be reshaped to endow the membrane with excellent performance. The activation mechanism was also explored here. Compared to the membrane without activation (PE-0%), the permeability of the optimized membrane (PE-40%) was increased by 8.3 times, and a high rejection was maintained (CR: 99.2%). Importantly, the PE-40% membrane also presented good acid and alkali resistance, chlorine resistance, and excellent antifouling performance. Our work provides an effective and feasible strategy for the development of high-performance polyester membranes.

Micropore engineering of polyamide loose nanofiltration membrane for efficient dye/salt separation

Loose nanofiltration membranes (LNF) with efficient sieving and excellent permeance are desirable for dye/salt separation, and engineering the micropore of the LNF membranes is a promising approach to maximize membrane performance. Herein, we present a highly permeable and sieving polyamide LNF membrane with high porosity and suitable pore size that is prepared by interfacial polymerization using twisted aqueous phase monomer and subsequent alkali-treatment. The large-size, rigid and twisted structure of the adamantane-1,3-diamine effectively inhibits the dense-packing of polymer chain segments, resulting in a polyamide membrane with enhanced porosity and enlarged pore size. The alkali treatment hydrolyzes the partial amide linkage to further enlarge the membrane pore size, increasing the flux while maintaining high dye rejection. The optimum membrane exhibits a high salt/dye selective factor of 735 for Na2SO4/Evans blue and an excellent water permeance of 87.72 L m−2 h−1 bar−1. This study is expected to provide a valuable guidance for the targeted design and fabrication of LNF membranes.

Quaternary phosphonium-polyamide membranes for efficient lithium extraction from brine sources

Lithium extraction from brine sources such as salt lakes, seawater, and produced water from oil/gas fields is garnering increasing interests from the academic and industrial sectors due to its cost-effectiveness and reduced environmental impact. A critical technological challenge is the efficient separation of Mg2+ and Li+ ions. Many researchers have reported the preparation of positively charged nanofiltration membranes with quaternary ammonium groups, yet investigations about quaternary phosphonium groups are scarce. In this work, positively charged nanofiltration membranes were prepared utilizing polyethyleneimine as the aqueous phase monomer, trimesoyl chloride as the organic phase monomer, and 3-bromopropyl triphenyl phosphonium bromide as the functionalizing monomer. The TFC-P+ membranes, enriched with a high density of quaternary phosphonium groups and an enhanced Donnan effect, achieve a MgCl2 rejection of 98.9 %, a Mg2+/Li+ selectivity of 81.6, and a water flux of 50 LMH under 0.5 MPa. The membranes possess an enhanced comprehensive separation capability that exceeds that of the majority of nanofiltration membranes documented in scholarly articles. Additionally, the membranes exhibit outstanding anti-fouling and anti-bacterial characteristics, essential for their industrial applications. The preparation method proposed herein is simple and conducive to continuous production processes. In light of the abundant produced water reserves from oil and gas extraction, future work will focus on pilot-scale lithium extraction experiments.

A novel salt-swelling nanofiltration membranes for drinking water purification: High mineral ions passage and efficient organic removal

BackgroundMunicipal drinking water treatment demands nanofiltration (NF) membranes with high removal efficiency for organics, high passage for mineral ions, and low operating pressure. The development of innovative and loose NF membranes is imperative. MethodsA loose-network-structured NF membrane (L-NF) was synthesized through interfacial polymerization (IP) on a PES substrate by utilizing lysine (with a flexible aliphatic chain) as standalone aqueous phase monomers. The separation performance for typical organics and mineral ions in water, as well as the permeability of the membrane were investigated. Significant findingsThe lysine-based NF membranes exhibit a reversible and appropriate salt-induced swelling effect. The increased salt concentration leads to a significant enhancement of both permeate flux and salt passage, while maintaining unaffected removal efficiency for organics. The optimized membrane (L-NF3), synthesized with a 1 % (w/v) concentration of lysine, demonstrated remarkable retention (>98 %) for organics (humic acid and sodium alginate), while concurrently displaying low retention (5.22 %-16.40 %) for mineral ions (Mg2+ / Ca2+). Furthermore, the salts in the feed led to a substantial improvement in permeate flux (239.61 %-385.70 %) compared to salt-free feed. The Lys-TFC membrane showcased outstanding performance of separation, permeability, and operational stability, underscoring its significant potential in municipal drinking water purification.

Polyurea nanofiltration membranes with extreme-pH stability and high separation performance

Development of high-performance nanofiltration membranes with extreme-pH stability is an urgent need for treatment of wastewater from metallurgical and paper industries. In this study, we design a kind of oil phase monomer toluene diisocyanate (TDI) and the aqueous phase monomer polyethyleneimine (PEI) to prepare polyurea nanofiltration membranes. The special bonding type and dense crosslinking structure of polyurea were used to resist the attack of extreme pH conditions. The support-free interface polymerization was employed to minimize the membrane thickness. The TDI-PEI10000 composite membranes achieved rejection of 97.5% for MgCl2, with a corresponding pure water permeance of 20.0 L m-2 h-1 bar-1. After exposure to H2SO4 solution with pH=1 for 440 h or NaOH solution with pH=13 for 200 h, the MgCl2 rejection remained above 90%. Our study provides a facile approach to constructing extreme pH-stable separation membranes.

Preparation and performance of thin film composite solvent nanofiltration membrane based on fluorinated diamine monomers

The high perm-selectivity and long-term solvent resistance of organic solvent nanofiltration (OSN) membranes in various solvents pose significant challenges for their development. In this study, ultra-low content mixture of fluorinated diamine (5-trifluoromethyl-1,3-phenylenediamine or 4-trifluoromethyl-1,2-phenylenediamine) and m-phenylenediamine (MPD) as aqueous phase monomers and ultra-low content trimesoyl chloride (TMC) in n-hexane as organic phase monomer were used to perform interfacial polymerization (IP), then followed by crosslinking and solvent activation. By this way, two kinds of ultra-thin and ultra-smooth fluorinated polyamide OSN membranes were achieved. Under optimized conditions, these two kinds of OSN membranes, TFC-5F2,II and TFC-4F1,II, have surface roughness of 2.5 and 3.0 nm, respectively. They show ethanol permeance of 73.9 and 60.9 L m−2 h−1 MPa−1, and RDB rejection of 98.5% and 99.2%, respectively, using 100 mg L−1 rhodamine B / ethanol solution as feed. They show ethyl acetate permeance of 209.4 and 117.0 L m−2 h−1 MPa−1, respectively, and catalyst rejection of 98.2% and 98.8%, respectively, using 50 mg L−1 Jacobsen catalyst/ethyl acetate solution as feed. Meanwhile, they have pure n-hexane permeance of 32.5 and 36.8 L m−2 h−1 MPa−1, respectively. Moreover, they show excellent stability in highly polar solvents, thus have good application prospects in the separation and purification of various organic solvent systems.

Enhanced pervaporation dehydration performance of polyamide thin‐film composite membrane with sodium alginate hydrophilic surface modification

AbstractBased on the solution‐diffusion model of pervaporation (PV) technique, the development of thin‐film composite membranes (TFC) with a highly hydrophilic surface and hydrophobic internal structure is more conducive to the rapid adsorption and desorption of water molecules to overcome the trade‐off effect between flux and separation selectivity. Herein, the polyamide PV membrane was fabricated via interfacial polymerization (IP) with trimesoyl chloride (TMC) and polyethylenimine (PEI) as organic and aqueous phase monomer, respectively, on the hydrolyzed polyacrylonitrile (HPAN) substrate. Subsequently, the hydrophilic modification layer was prepared via sodium alginate (SA) crosslinking with Ca2+ to form the egg‐box network. The results indicated the optimized TFC membrane exhibited high separation factor of 525.1 with desirable permeation flux of 2083.9 g m−2 h−1 for the pervaporation dehydration 85 wt% ethanol/water solution at 70°C. The modification method of hydrophilic surface opens up new avenues for the preparation of PV membrane with high separation performance and low‐cost.

A novel loose nanofiltration membrane with high permeance and anti-fouling performance based on aqueous monomer piperazine-2-carboxylic acid for efficient dye/salt separation

Dye effluent is regarded as one of the most hazardous industrial effluents. Although loose nanofiltration (NF) membranes have been considered as an effective alternative technique for treating dye effluent, their development is still constrained by subpar permeance, separation efficiency and anti-fouling performance. In this work, a novel loose polyamide (PA) NF membrane was designed employing a conventional interfacial polymerization process using piperazine-2-carboxylic acid (PIP-COOH) and trimesoyl chloride as aqueous and organic phase monomers, respectively. The presence of unique electron-absorbing carboxyl groups on the PIP-COOH monomer not only provided abundant negative charge on the membrane surface, but also greatly reduced the reactivity, diffusion rate and solubility in n-hexane of the aqueous monomer, allowing for the formation of a more relaxed and smoother active layer. The balanced combination of pore size screening and Donnan effect achieved precise separations with high permeability. Moreover, the interaction of the carboxyl groups with the backbone structure increased the free volume of the PA layer and improved permeability significantly. The PIP-COOH/TMC membrane prepared under the optimal conditions exhibited high water permeance of 598.1 L·m−2·h−1·MPa−1, high reactive red rejection (99.3%) and low NaCl rejection (5.4%). Furthermore, the membrane possessed exceptional anti-fouling performance thanks to the ultra-smooth surface with crucial antifouling index flux recovery ratio as high as about 99%, which showed unexpected application possibilities. In conclusion, this study offers a potential novel membrane material for the development and application of loose NF membranes in the treatment of colored effluent.

Highly selective and permeable β-cyclodextrin based polyester nanofiltration membranes maintaining good chlorine resistance

Possessing high chlorine resistance is an important consideration for membranes to be applied for water treatment. In this study, the superior chlorine resistant β-cyclodextrin (β-CD) based polyester membranes were developed via interfacial polymerization (IP) with the β-CD and glycerol or mannitol as the aqueous phase monomers. By adjusting the compositions of the aqueous phase, the pore size and distribution of the resultant membranes were accurately controlled, thus improving the separation efficiency of the membranes. The optimized membrane (β-CD/Ma3) had the higher water flux (60.4 L‧m-2‧h-1 at 2.0 bar) and Na2SO4 retention (95.6%). After immersed in 10 ppm sodium hypochlorite (NaClO) solution for 360 h, the membrane performance in terms of water flux and salt retention was almost unaltered, mirroring a good long-term stability. In another test, the Na2SO4 retention of membrane remained at 91.7%, which was only 4.1% lower than the original value, after exposure to a high concentrated NaClO solution (2000 ppm) for 72 h. Fouling cycling test was also performed, and the flux was maintained as high as 97.2% of the original value after examination of three cycles. All these observations clearly indicate that the optimized membrane has outstanding chlorine resistance and superior antifouling property.

Tailor-made highly negatively charged nanofiltration membrane prepared by polyphenol derivatives for anionic dye/salt separation

Nanofiltration (NF) techniques are becoming increasingly advantageous for treating salt-containing dye wastewater. A novel NF membrane was successfully fabricated using grape seed oligomeric proanthocyanidins (OPC) as aqueous phase monomer by interfacial polymerization with isophorone diisocyanate (IPDI). The membrane surface exhibited an extremely high negative zeta potential. The experimental results showed that the negatively charged OPC/IPDI nanofiltration membranes could effectively remove anionic dyes and exhibited high NaCl/dye selectivity. Specifically, the optimal OPC/IPDI membrane exhibited a rejection of 99.4 % against Reactive Red 195 with a high permeance of 67.9 L m−2 h−1 bar−1 and a desirable NaCl/RR 195 selectivity factor of 85.3. In addition, the smooth and hydrophilic surface endowed the membranes with a desirable antifouling property. The optimized membrane achieved high flux recovery ratio values of 89.1 %, 85.5 %, and 24.75 % for the foulants of Reactive Red 195, humic acid, and bovine serum albumin, respectively. A 50-hour investigation of continuous cross-flow filtration processes showed the outstanding separation stability of the membranes. Furthermore, the membranes exhibited excellent anti-bacterial activity. Integrating all the findings, the strategy proposed in this paper for the use of polyphenol derivatives to prepare highly negatively charged membranes for the removal of anionic pollutants from saline wastewater is feasible.

Regulation of dopamine forward osmosis membrane via inorganic salt and macro-porous substrates for pharmaceutical concentration

Dopamine (DA) with good designability could self-polymerize into polydopamine (PDA) with various polymerization states in alkaline solution. However, the poor structural controllability of PDA leads to serious PDA hyper-polymers, making DA difficulty to be used as sole aqueous phase monomer during conventional interfacial polymerization (IP) for membrane preparation. In this work, the organic solvent forward osmosis (OSFO) membranes were fabricated via substrate-floating interfacial polymerization (SFIP) method with DA as sole aqueous phase monomer and macro-porous polyether sulfone (PES) membrane with pore size of 0.1–0.22 μm as substrates. Inorganic salt such as NaCl was employed as aqueous phase additive, which not only effectively regulated the oligomeric polymerization state of PDA but also promoted DA diffusion. The macro-porous substrate could enlarge the reaction contact area and relieve the internal concentration polarization in support layer. The resulting OSFO membranes exhibited an excellent ethanol flux of ∼10.70 L m−2 h−1 and lower reverse LiCl flux of ∼0.53 g m−2 h−1, as well as a high tetracycline concentration efficiency of >15 % for 1 h run whatever the tetracycline concentration in the feed (500–2000 mg/L). This work provides new insights into the fabrication of high-performance OSFO membrane for solvent recovery and pharmaceutical concentration.

Thin film composite membranes prepared from diaminoguanidine hydrochloride for Mg2+/Li+ separation

This study aims to prepare and investigate thin film composite (TFC) membranes with a highly positively charged rejection layer for effective separation of Mg2+/Li+. The aqueous phase monomer employed in fabricating the TFC membranes was a highly ionic and hydrophilic guanidinium, namely 1,3-diaminoguanidine hydrochloride (DAGH), using an interfacial polymerization method. Two methods were used to prepare the TFC membranes: conventional interfacial polymerization and support-free interfacial polymerization. The surface properties and morphologies of the TFC membranes were characterized by FESEM, AFM, surface zeta-potential, and water contact angle. The XPS was used to analyze the crosslinking structure of the interfacial layer. The study results revealed that the SF-TFC membrane had a higher crosslinking density and zeta-potential compared to the C-TFC membrane. Notably, SF-TFC exhibited a MgCl2 rejection of 95.09% at 7 bar, and for Mg2+/Li+ separation, the SF-TFC membrane had a Li+/Mg2+ separation factor of 23.32 at the Mg2+/Li+ mass ratio of 10. Additionally, the strong ionic and hydrophilic properties of DAGH led to the proposal of an aqueous-phase polymerization mechanism, substantiated by AFM and ESI-MS analysis.

Fabrication of polyamide hollow fiber nanofiltration membrane with intensified positive surface charge density via a secondary interfacial polymerization

In this work, a positively charged hollow fiber nanofiltration (NF) membrane based on twice interfacial polymerization (IP) reactions was developed for water soften and heavy metal ions removal. The first IP reaction was conducted on the polyethersulfone (PES) hollow fiber substrate using a mixture of branched polyethyleneimine (PEI) and piperazine (PIP) as the aqueous phase monomers in the aqueous phase reacting with trimesoyl chloride (TMC) in the cyclohexane solution. Then, a secondary IP reaction was performed between tris(2-aminoethyl) amine (TAEA) solution and the residual acyl chloride groups on the membrane to increase the positive charge density on the membrane surface. Consequently, a NF membrane with intensified positive surface charge density was successfully fabricated. The optimized membranes achieved a high rejection of MgCl2 of 97.6% while maintaining a pure water permeability (PWP) of 16.0 L m−2 h−1 bar−1. Meanwhile, the membranes exhibit high rejection values of 99.8% to Cu2+ and 99.7% to Zn2+, respectively. In conclusion, this work provides a facile way to prepare a positively charged membrane for efficient water softening and metal ions removal.

Microstructure optimization of bioderived polyester nanofilms for antibiotic desalination via nanofiltration

The successful implementation of thin-film composite membranes (TFCM) for challenging solute-solute separations in the pharmaceutical industry requires a fine control over the microstructure (size, distribution, and connectivity of the free-volume elements) and thickness of the selective layer. For example, desalinating antibiotic streams requires highly interconnected free-volume elements of the right size to block antibiotics but allow the passage of salt ions and water. Here, we introduce stevioside, a plant-derived contorted glycoside, as a promising aqueous phase monomer for optimizing the microstructure of TFCM made via interfacial polymerization. The low diffusion rate and moderate reactivity of stevioside, together with its nonplanar and distorted conformation, produced thin selective layers with an ideal microporosity for antibiotic desalination. For example, an optimized 18-nm membrane exhibited an unprecedented combination of high water permeance (81.2 liter m-2 hour-1 bar-1), antibiotic desalination efficiency (NaCl/tetracycline separation factor of 11.4), antifouling performance, and chlorine resistance.

L-Tartaric acid tailored polyamide thin-film composite membrane with enhanced performance for salt and molecular removal

High performance polyamide (PA) thin-film composite (TFC) membranes are in great demand. However, it is still a challenge to further enable PA TFC membranes to overcome the perm-selectivity tradeoff. Here, l-tartaric acid (LTA) and piperazine were first used as the aqueous phase monomers to fabricate LTA integrated PA (LTA/PA) TFC membranes via interfacial polymerization (IP) with trimesoyl chloride. The physicochemical property and separation performance of the PA TFC membranes were regulated via LTA concentrations. The introduction of LTA made the PA layer of the membrane thinner and smoother with enlarged pore size. The LTA/PA TFC membrane prepared with a higher LTA content had a maximal water flux (207.6 LMH/bar, 20 times higher than that of the control membrane), with superior rejections for the dyes (>98.0 %) and low removal rates for the salts (<4.5 %). Of note, the water flux of the membrane prepared with a low LTA content was enhanced to 18.9 LMH/bar without sacrificing the rejection of Na2SO4 (RNa2SO4 > 98.0 %). The membranes with optimal LTA content break the tradeoff towards some dyes or salts, and presented superior performance compared with most other reported polymeric membranes. This work highlights the great potential of constructing natural acid-modulated PA composite membranes in water purification.