Conventional Interfacial Polymerization Research Articles

Modulating low-temperature interfacial polymerization with NaHCO3 for high-performance ultrathin nanofiltration membranes

Conventional interfacial polymerization (IP) encounters significant challenges in achieving the desired nanofiltration (NF) membrane structure, owing to uncontrolled diffusion and ultrafast polymerization. Our study introduced carbonates into the low-temperature interfacial polymerization (LTIP) process to precisely regulate the diffusion of amine monomers and polymerization kinetics. Carbonates in the aqueous phase restrict the diffusion of amine monomers while promoting the generation of nanobubbles. Further utilization of the low-temperature oil phase not only retards polymerization but also facilitates the formation of foam nanostructures in the polyamide layer. Density functional theory calculations and molecular dynamics simulations revealed the mechanisms underlying the regulation of amine monomer diffusion and gas-bubble release by carbonates and LTIP. The fabricated membrane has a smoother, ultrathin separation layer while maintaining a high permeability of 35.0 L·m−2·h−1·bar−1 (nearly doubled compared with the pristine membrane) and high Na2SO4 rejection of 99.5 %. This study confirms the practicality of the carbonate-modulated LTIP strategy.

Bis-tris-based polyester nanofiltration membranes fabricated via one-step interfacial polymerization for desalination

To obtain high-performance polyester (PE) nanofiltration (NF) membranes for desalination, most PE NF membranes are fabricated with high aqueous monomer concentration, or high reaction temperature, or long reaction time. The interfacial polymerization (IP) reaction rate between hydroxyl groups and acyl chloride groups is promoted but the cost of membrane fabrication is also increased. In this work, Bis-tris (bis(2-hydroxyethyl)-amino-tris(hydroxymethyl)methane) with rich hydroxyl groups is first utilized as an aqueous monomer to fabricate PE membranes under conventional IP conditions. The fabricated Bis-tris PE membranes feature strong hydrophilicity, excellent electronegativity, and ultra-thin selective layers, which are conducive to improving desalination performance. The optimized Bis-tris PE membrane shows excellent water permeance of 22.5 L m−2 h−1 bar−1 and a satisfactory Na2SO4 rejection of 96.9 %. Additionally, the Bis-tris PE membrane displays superior long-term stability and chlorine resistance under 96 h cross-flow filtration. This research enlightens the promising potential of Bis-tris as a novel and economic aqueous monomer for the fabrication of high-performance PE NF membranes.

Organic-organic interfacial polymerization for the ultrathin polyamide organic solvent nanofiltration membranes

There is an increasing demand for advanced membranes that exhibit both high perm-selectivity and good stability in organic solvents, particularly for organic solvent nanofiltration (OSN). Traditional methods of synthesizing thin films using conventional interfacial polymerization (CIP) have been limited by the use of water-soluble monomers, which has hindered the development of high-performance membranes. To address this issue, a new method called organic-organic interfacial polymerization (OOIP) has been proposed. This method allows for the use of aromatic amines that are not water-soluble in the fabrication of ultrathin polyamide (PA) (<40 nm) thin film composite (TFC) membranes. By investigating five different organic solvents (tetrahydrofuran, acetone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide) with varying water content as the organic phase for a water-insoluble benzidine monomer, two diffusion models of monomers were identified that resulted in different membrane structures and degrees of network crosslinking. The ultrathin PA membranes produced using tetrahydrofuran-H2O and N,N-dimethylformamide-H2O, along with solvent activation, demonstrated high methanol permeances of 11.4 L m−2 h−1 bar−1 and 6.0 L m−2 h−1 bar−1, respectively, while maintaining exceptional rejections of over 99.0 % for small molecules with molecular weights greater than 452 g mol−1. The OOIP method is scalable and reproducible, making it suitable for large-scale membrane production. This innovative approach shows great potential for advancing OSN technology and providing efficient and cost-effective separation solutions for various industries.

A novel high temperature resistance thin film composite polyamide reverse osmosis membrane with covalent organic frameworks intermediate layer

Both salt rejection and pressure-bearing properties of the conventional thin film composite (TFC) polyamide reverse osmosis (RO) membrane are easily weakened at high temperature. In order to improve the high temperature resistance, in this work, a polyamide TFC RO membrane with covalent organic frameworks (COFs) intermediate layer was prepared. Firstly, the COFs layer was decorated on polyether sulfone (PES) support membrane by a unidirectional diffusion method and further modified for shrinking the micropore via the chemical crosslinking reaction with 1,3-diamino-2-propanol (DAPL) or ethylenediamine (EDA), and then continued the conventional interfacial polymerization of m-phenylene diamine (MPD) and trimesoyl chloride (TMC) on the resultant COFs layer for preparing the RO membrane. Furthermore, the correlationship between the microstructure of COFs layer and the separation performance of modified RO membrane was systematically investigated. Due to the introduction of the COFTpPa-DAPL intermediate layer with more regular microstructure and specific hydrophilicity, the resultant TFC-COFTpPa-DAPL RO membrane exhibited improvement in water flux by 30 ​% (reached to 50.5 ​L ​m−2 ​h−1) and higher salt rejection (>99.5 ​%) as compared with the conventional polyamide RO membrane and other reported temperature resistance RO membranes. Meanwhile, this TFC-COFTpPa-DAPL membrane showed good long-term separation stability during the RO process for 160 ​h. Especially, its water flux increased to 98.8 ​L ​m−2 ​h−1 without weakening salt rejection (about 99.4 ​%) at 70 ​°C. This study provides an effective way to fabricate the high temperature resistance TFC polyamide RO membrane with good comprehensive separation performance based on COFs intermediate layer.

A sub-10 nm polyamide nanofiltration membrane from polyvinylpyrrolidone-mediated interfacial polymerization

In conventional interfacial polymerization (IP) for thin-film composite nanofiltration membranes, the separation layer is typically thick (∼100 nm), which limits its water permeance. In this study, we successfully synthesized an ultrathin polyamide layer (∼8.6 nm) from polyvinylpyrrolidone (PVP)-mediated IP. With the surfactant concentration over its critical micelle concentration, PVP not only formed a monolayer at the water-heptane interface, but also stayed in the aqueous solution. The CO groups of PVP formed the N–H⋯O hydrogen bond interactions with N–H bonds of piperazine (PIP) monomers in the aqueous phase to slow down the diffusion of PIP monomers. Besides, PVP with amphiphilic groups minimized the interfacial tension at the water-heptane interface to regulate IP processes. By adjusting the concentration of PVP, we obtained a sub-10 nm polyamide nanofiltration membrane. Moreover, hydrophilic PVP macromolecules improved the membrane surface hydrophilicity. Due to the ultrathin thickness and improved hydrophilicity, the optimized polyamide membrane demonstrated a threefold increase in permeance compared to that of the pristine polyamide membrane without PVP addition, and maintained 98.4% rejection for 1000 ppm Na2SO4 solution. This study provides a new insight into fabricating sub-10 nm polyamide membranes for nanofiltration processes.

Ultrahighly Li-selective nanofiltration membranes prepared via tailored interfacial polymerization

Nanofiltration (NF) membrane-based separation has gained significant attention as an efficient technology for recovering lithium (Li) from salt-lake brines. However, many previously developed NF membranes are not commercially feasible because they lack sufficient Li selectivity and require the use of new monomers/chemicals or complicated fabrication processes. Herein, we propose a commercially viable method to fabricate ultrahighly Li-selective polyamide (PA) membranes by carefully tailoring a conventional interfacial polymerization process using an established piperazine (PIP)/trimesoyl chloride monomer system. The use of excess PIP endowed the fabricated membrane with enhanced PA crosslinking density and a positive surface charge, reinforcing both its size and Donnan exclusion mechanisms. Furthermore, the addition of benzyltributylammonium chloride, a cationic surfactant, to the PIP solution effectively improved the water permeance of the membrane without impairing its magnesium ion (Mg2+) rejection by loosening its PA network while enhancing its positive surface charge. Consequently, our tailor-made PA membranes with the proper pore structures and strong positive surface charges exhibited ultrahigh Li+/Mg2+ selectivity of up to 150 (under single-salt conditions) and 887 (under mixed-salt conditions), significantly outperforming commercial and other reported laboratory-made NF membranes. Our strategy provides a facile and effective means to manufacture Li-selective membranes with high commercial viability.

Decoupling synthesis and crystallization of covalent organic frameworks (COFs) for more crystalline layer targeting high efficiency dye separation

Covalent organic frameworks (COFs) are crystalline porous materials composed of organic building blocks linked by covalent bonds, which have attracted great attention for membrane–based separation applications. However, fabrication of COF membranes with high quality and performance remains a challenge, especially for the β–ketoenamine linked COFs. In the conventional IP methods, the synthesis process (the Schiff–base reaction of the monomers and the tautomerism of the oligomers) and the crystallization process (the self–assembly of the oligomers) of the COFs materials occur simultaneously on the surface of the support membrane, which can result in low crystallinity, high defect density, and poor separation performance of the COF layer. In this study, a novel strategy for fabricating large-area, defect–free COFs composite membranes by interfacial polymerization (IP) was presented to overcome this problem. By incorporating both the amine and aldehyde monomers in one organic phase, and dissolving organic acid catalyst in another phase (the water), the synthesis process mostly take place in the bulk of the organic phase, while the crystallization occurs on the surface of the support membrane under the influence of the organic acid catalyst. This strategy effectively decoupled the synthesis process with the crystallization, providing a stable growth region for crystalline layer, ultimately leading to the formation of a thin, defect–free and highly ordered COF layer on the support membrane. The strategy was demonstrate by synthesis of triformylphloroglucinol phenylenediamine (TpPa)–Ⅱ/Poly(m–phenylene isophthalaminde) (PMIA) composite membrane. We characterize the structure and morphology of the TpPa–Ⅱ/PMIA composite membrane by various analytical techniques to verify our hypothesis, and evaluate its separation performance using pure water permeance and dyes retention rate as indicators. The results show that the TpPa–Ⅱ/PMIA composite membrane has an 80 nm thick top-layer with regular COF structure and orderly pores. It exhibits an excellent dye separation performance, with a (pure water permeance) PWP of 105.6 L·m−2·h−1·bar−1 and CR rejection of 99.2 %, which surpasses most of the TpPa–type COFs composite membranes reported in literature, as well as the reference (TpPa–I/PMIA membrane) in this work. Moreover, the TpPa–Ⅱ/PMIA composite membrane maintains both its performance and structural stability during a 240–hour cross–flow filtration of the dye solution, demonstrating its excellent potential in the dye wastewater treatment.

Highly selective Mg2+/Li+ separation membranes prepared by surface grafting of a novel quaternary ammonium bromide

The efficient separation of Mg2+ and Li+ is the crucial step in the process of extracting lithium from salt lake brine. Nanofiltration (NF) membranes exhibit promising application potential in Mg2+/Li+ separation but the Mg2+/Li+ selectively of negatively charged NF membranes prepared by conventional interfacial polymerization process is far from desirable. In this study, a novel positively charged quaternary ammonium bromide, 3-bromopropyl trimethylammonium bromide (BTAB), is grafted on the polyethyleneimine (PEI)/trimesoyl chloride (TMC) NF membrane surface. This is achieved by a chemical reaction known as nucleophilic substitution, which involves the replacement of a bromine atom (-Br) with an amine group. Owing to the enhanced Donnan effects, the BTAB-modified NF membranes exhibit a MgCl2 rejection of up to 99.2 %, while maintaining a water flux of approximately 50 LMH under 5 bar. Meanwhile, the LiCl rejection is only ∼ 30 %. The Mg2+/Li+ selectively of the BTAB-modified NF membranes reaches 95.9 when filtrating a simulated brine with a Mg2+/Li+ ratio of 20 (2000 ppm MgCl2 and LiCl mixture), which is a twofold improvement compared with the pristine NF membranes. The working stability of the BTAB-modified NF membranes is confirmed by a 50-h continuous operation process. A two-stage NF treatment is conducted using a simulated East Taijinar salt lake brine, achieving Li2CO3 powder with a purity level of 99.4 %. The nucleophilic substitution reaction between -Br and the amine groups offers a good reference for the surface functionalization of NF membranes.

Polytetrafluoroethylene hollow fiber membranes with thru hydrophilic channels for enhancing water transfer and anti-oil-fouling properties

Herein, a feasible method for hydrophilic modification of polytetrafluoroethylene (PTFE) hollow fibers via interfacial polymerization (IP) was proposed. 1, 3-Diamino-2-propanol (DAP) and trimesoyl chloride (TMC) were selected as monomers and a three-time IP method was adopted to construct hydrophilic channels within the membrane pores, thus effectively improving the hydrophilicity and permeability of membranes. The solvent of aqueous phase in conventional IP process was replaced by ethanol for better introducing amine monomers into membrane pores. The characterization results of Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and water contact angle (WCA) tests indicated the successful formation of polyamide (PA) layer within the membrane pores. In comparison to the ethanol pre-wetted control membrane, the PTFE hollow fibers modified under optimal IP conditions exhibited higher water flux (from 136.8 to 1059.1 kg m−2 h−1) and showed better resistance to both BSA (FRR from 53.4% to 92.3%) and soybean oil (FRR 16.4% from to 78.1%) after four cycles of filtration and cleaning. Simultaneously, the modified membranes demonstrated a favorable oil removal capacity (≥ 92%), and still maintained good stability after 24 h ultrasonic treatment and 8 d immersion tests in acid, alkali and oxidation solutions. This membrane holds significant application value in the treatment of oily wastewater.

Constructing nanofiltration membrane on hydrophobic PVDF and PTFE substrates via reverse interfacial polymerization

Polyvinylidene fluoride (PVDF) and polytetrafluoroethylene(PTFE) porous membranes are ideal substrates for preparing thin-film composite (TFC) polyamide (PA) membranes with improved solvent resistance. However, it remains difficult to construct PA skin layers on PVDF and PTFE substrates via conventional interfacial polymerization (IP) due to the hydrophobic nature of these materials. To address this challenge, a reverse IP process was proposed to construct a defect-free PA skin layer on PVDF and PTFE substrates, in which the hydrophobic PVDF and PTFE substrates were soaked with the organic phase to ensure uniform coverage of reacted solution on the substrates. This novel strategy can effectively tackle the issue of uneven wetting of the aqueous phase on hydrophobic substrates in the conventional IP process. The resultant TFC membranes (i.e. Mrev-PVDF and Mrev-PTFE) exhibit excellent nanofiltration (NF) performance in both aqueous and organic solutions. Mrev-PVDF and Mrev-PTFE have MgCl2 rejections of 96.12% and 95.17%, alongside the water permeances of 12.8 LMH/bar and 11.2 LMH/bar, respectively (Mrev-PTFE was activated with DMF). It is further shown that Mrev-PVDF and Mrev-PTFE could also reject 99.4% and 98.5% of Congo red in methanol solution at solvent permeances of over 3.3 LMH/bar, while they also perform excellently in other polar protic solvents. Consequently, this work opens a new window for constructing high-performance TFC PA membranes on hydrophobic substrates and expands the application of the TFC PA NF membrane.

Sustainable β- and γ-cyclodextrins for development of highly permeable thin film composite nanofiltration membranes

The use of macromolecules, such as cyclodextrins (CDs), given their porosity and compatibility with organic materials, are very attractive for the progress of polymeric membranes in nanofiltration (NF) of aqueous dye solutions. Two types of membranes were fabricated. Firstly, β- and γ-CDs were incorporated to polyamide (PA) thin film composite (TFC) membranes. These membranes, named CD/MPD-TMC, were prepared by conventional interfacial polymerization —i.e., an aqueous solution of m-phenylenediamine (MPD) followed by a solution of trimesoyl chloride (TMC) in hexane— by replacing a certain amount of the MPD monomer with varying proportions of CDs. Secondly, two-step double-IP (TD-IP) membranes were fabricated as follows: CDs were deposited atop the polymer support, followed by addition of TMC —forming a polyester (PE) layer—, and subsequently the membrane surface was modified with MPD molecules. In both CD/MPD-TMC and TD-IP membranes, the presence of CDs improved the membrane performance, the latter configuration leading to much higher water permeances. The TD-IP membrane using β-CD achieved the highest water permeance of 10 L m−2 h−1·bar−1 (LMH bar−1) and a rejection of acridine orange dye (265 Da) greater than 98 %. This represents a 6-fold increase in water permeance compared to bare PA (1.6 LMH bar−1). The enhanced water transport was mainly attributed to the more hydrophilic nature of the membranes and the presence of a PE layer with a porous structure and high pore connectivity. High dye rejection resulted from electrostatic and Donnan repulsions due to surface modification with MPD molecules.

Support-free assembled molecular layer by layer - HPAN forward osmosis membranes

The internal concentration polymerization (ICP) phenomenon may hinder the flux of forward osmosis (FO) membranes. The mitigation of ICP can be achieved by employing a porous support layer structure. Nevertheless, conventional interfacial polymerization (IP) methods encounter challenges in establishing a dense selective layer upon a highly porous support layer. In this study, the support-free assembled molecular layer-by-layer (SF-mLbL) was suggested to manufacture the thin-film composite (TFC) membrane by combining the separately fabricated polyamide (PA) selective layer with a tunable thickness and the highly porous support layer. The SF-mLbL (8 wt%) membrane had a higher water flux and selectivity (43.52 ± 0.89 LMH/0.15 ± 0.01 g L−1) than those (10.34 ± 0.48 LMH/0.75 ± 0.02 g L−1 and 7.41 ± 0.18 LMH/0.81 ± 0.01 g L−1) of IP-PA and commercial cellulose triacetate membranes as 0.5 M NaCl draw solution in FO mode. Consequently, the SF-mLbL membranes exhibited significant improvement in the FO process with well-balanced permselectivity.

Hydrophilic-hydrophobic bilayer interlayer for high performance thin-film composite reverse osmosis membranes

The strategy of modifying substrates with hydrophilic interlayers has been widely used to improve the performance of thin-film composite (TFC) nanofiltration (NF) membranes. However, the preparation of TFC reverse osmosis (RO) membranes with excellent performance on hydrophilic substrates through conventional interfacial polymerization (IP) method has proven to be very challenging. In this work, a hydrophilic polycarboxylic acid – hydrophobic ZIF-8 nanoparticles bilayer interlayer was developed to enhance the performance of TFC RO membranes. Based on this, the interlayer was designed to improve the performance of TFC RO membranes by creating a synergistic effect between the hydrophilic polycarboxylic acid and the hydrophobic ZIF-8 nanoparticles. The hydrophilic polycarboxylic acid interlayer was used to heal defects in the PSF substrate and provide growth sites for the in-situ growth of ZIF-8 nanoparticles. Hydrophobic ZIF-8 nanoparticles weakened the inhibition of the hydrophilic polycarboxylic acid interlayer on the diffusion of MPD, thus promoting the IP reaction and forming a dense PA separation layer (NaCl rejection 98.8%). The modulation of MPD erupted from the pores of the modified substrate by the bilayer interlayer results in the formation of an asymmetric PA layer, which has a dense PA in the upper region and loose PA encapsulating ZIF-8 nanoparticles in the lower region. ZIF-8 nanoparticles encapsulated by PA not only provided a low-resistance channel for water to pass through the separation layer but also enhanced the compaction resistance of the RO membrane, thus improving the permeance of the TFC RO membrane (4.2 L m−2 h−1·bar−1). In addition, thanks to the good compatibility between ZIF-8 nanoparticles and the PA matrix, as well as the smoother PA layer, TFC RO membranes with the bilayer interlayer presented excellent long-term stability and antifouling ability. This work presents a new idea to improve the performance of TFC RO membranes using interlayer strategies.

Support-free interfacial polymerized polyamide membrane on a macroporous substrate to reduce internal concentration polarization and increase water flux in forward osmosis

Macroporous substrates have great potential in the development of high performance thin film composite forward osmosis (TFC FO) membranes. This paper reports on the preparation of TFC FO membrane via support-free interfacial polymerization (SFIP) technology on a macroporous substrate. SFIP technology can effectively break the bottleneck of conventional interfacial polymerization (IP) technology, which makes it difficult to form a complete polyamide (PA) film on the macroporous substrate. Briefly, the complete PA film is formed at the free water-organic phase interface and then attached to the macroporous substrate by vacuum filtration. The monomer concentration and filtration pressure were adjusted to form the optimal SFIP-PA film. Meanwhile, we chose a macroporous polyvinylidene fluoride (PVDF) microfiltration substrate and screened the pore size to reduce the structural parameters and then the internal concentration polarization, which caused the improvement of water flux. The performance of SFIP-PVDF membranes was investigated and discussed. Under the AL-FS mode with DI water and 1.0 M NaCl solution as the feed solution and draw solution, respectively, the SFIP-PVDF membrane, which used a macroporous PVDF substrate with a pore size of 0.45 μm exhibited a water flux (20 L/m2·h) and a reverse salt flux (2.5 g/m2·h). Besides, the membrane showed good stability in the 72 h test. The specific salt flux (Js/Jw) of SFIP-PVDF membranes was much lower than that of IP-PVDF membranes prepared via IP technology, which were incomplete and defective, suggesting that SFIP technology was superior to IP technology. This work effectively exploits the potential of macroporous substrates for the development of high performance TFC FO membranes and provides an insight into the high performance FO membrane design.

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.

Loose Nanofiltration Membrane Incorporating CeZnFe Layered Double Hydroxide with Enhanced Dye/Salt Separation Performance and Self-Cleaning Ability.

The high-salinity wastewater from the textile industry faces a significant challenge in effectively separating dyes and salts. In this study, a CeZnFe-layered double hydroxide (LDH)-incorporated nanofiltration (LNF) membrane was fabricated using the conventional interfacial polymerization (IP) technique to fractionate dyes and salts within the wastewater. The impact of CeZnFe LDH on various aspects of membrane performance was examined, including water flux, dye removal efficiency, dye/salt separation capability, self-cleaning ability, and membrane integrity. The addition of LDHs resulted in improved membrane surface hydrophilicity, thereby enhancing water flux. The optimized TFN membrane (0.050 wt% LDH in PIP solution) significantly improved pure water flux, exceeding 150%. All TFN membranes exhibited excellent performance in dye and salt fractionation (93% for Congo red, 2.6% for NaCl, and 40.7% for Na2SO4). Also, excellent self-cleaning ability was observed for the optimized membrane, exhibiting a remarkable water flux recovery rate after three operation cycles. Moreover, including CeZnFe LDH in the optimized TFN membrane played a significant role in enhancing membrane integrity. This study provides new inspiration for fabricating self-cleaning loose NF membranes using CeZnFe LDH for effective dye/salt separation.

Spray coating as a novel, versatile tool to prepare membranes via IP

Polyamide (PA) thin-film composite (TFC) membranes, synthesized by interfacial polymerization (IP), are commonly applied in NF and RO. However, they have a high tendency to foul due to the rough ridge and valley surface. IP requires utilization of toxic solvents and hydrolysis of acyl chlorides can occur as undesired side reaction due to the presence of water. Therefore, a new approach to synthesize TFC membranes is now introduced: spray-based interfacial polymerization prior to solidification (s-IPS). IP is performed on a still liquid polymer film containing a first (amine) monomer while the second monomer (acyl chloride) is sprayed on top. The susceptibility of the liquid cast film to defects due to the impact of spraying, is minimized by the increased viscosity resulting from charge-transfer complex formation between the amine monomer (MPD) and the polymer (PI). This new s-IPS process is more time-efficient, uses less chemicals and produces less waste than the conventional IP. Additionally, problems in conventional IP associated with non-wetted support pores and bad adhesion of the IP layer to the support are eliminated and water-free IP is enabled, limiting hydrolysis of TMC. Properties such as high viscosity and interfacial stability lead to controllable IP and smooth PA top-layer surfaces.

Nano-wrinkled polyamide membrane preparation via heterogeneous surface-regulated interfacial polymerization for enhanced desalination performance

Nano-wrinkled morphology and ultrathin thickness are desirable membrane structures in polyamide membranes, particularly for high-performance applications in desalination and wastewater treatment. In this study, we present the fabrication of a nano-wrinkled polyamide membrane with ultrathin thickness on a heterogeneous surface that features hydrophilic UiO-66-NH2 nanoparticles embedded on a hydrophobic polyethersulfone surface using a heterogeneous surface regulated interfacial polymerization approach. The presence of the heterogeneous surface induces the formation of aqueous phase microphases under the organic phase due to the unbalanced interfacial tension, which serves as a template for the formation of the polyamide film. This results in the creation of a nano-wrinkled polyamide layer upon drying. Furthermore, the hydrogen bonding interaction between the UiO-66-NH2 and piperazine (PIP) slows down the PIP release, which contributes to the ultrathin thickness of the polyamide layer. The polyamide membrane obtained in this study exhibits a pure water permeance (PWP) of 26.1 L bar−1·h−1·m−2 and a Na2SO4 rejection of 97.5 %. The PWP is 6.15 times higher than that of a control membrane fabricated through conventional interfacial polymerization. Our work offers a novel approach to tailor the structure of polyamide membranes via heterogeneous surface regulated interfacial polymerization, which has potential applications in environmental desalination.

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.