Interfacial Polymerization Reaction Research Articles

Positively charged nanofiltration membranes with gradient structures for enhancing separation properties

Creating a gradient structure in a separation layer is an effective approach for enhancing separation performance of thin film composite membranes. Here we present the preparation of a positively charged nanofiltration membrane with a gradient structure. An inner layer consisting of a loose polyester separation layer with large pores was formed through the interfacial polymerization (IP) reaction between triethanolamine (TEA) and trimesoyl chloride (TMC). And a dense and thin top layer composed of a polyamide separation layer was obtained by secondary interfacial polymerization (SIP) reaction using polyethyleneimine (PEI) along with unreacted TMC and residual acyl chloride groups of IP reaction. The influences of TEA concentration, PEI concentration and SIP time on the physicochemical properties and separation performances of the membrane were systematically analyzed. Our results show that the presence of the gradient structure optimized mass transfer pathways and reduced mass transfer resistance, resulting in significantly improved permeability of 13.0 ± 0.5 L·m−2·h−1·bar−1 (over 3 times compared with control-PEI), high MgCl2 rejection of 91.7 ± 0.6 %, and an excellent stability and anti-fouling performance. Our work provides valuable insights and guidance for developing high-performance positively charged NF membrane with gradient structures.

Effect and mechanism of solution flow rate during interfacial polymerization on morphology and performance of hollow fiber membranes

Interfacial polymerization (IP) using m-phenylenediamine and trimesoyl chloride (TMC) is an essential method for producing thin-film composite (TFC) membranes. Nevertheless, IP is highly sensitive to changes in process parameters, especially the TMC solutions flow rate during inside-out TFC hollow fibers (HF) production. Research on the impact of flow conditions (i.e., laminar vs. turbulent flows) of these organic solutions on the final membrane characteristics and corresponding mechanism is still lacking. This research tested different TMC flow rates (0.1–2 mL/min) to produce inside-out TFC HF. With a TMC flow rate increase, (i) the leaf-like structures of the polyamide (PA) layer decreased in size, (ii) the thickness of the PA layer slightly increased, and (iii) the pure water permeability decreased. However, the elemental composition, chemical bonds, and NaCl rejection remained stable. Different fluid regimes are considered to affect the performance of HF membranes by affecting the heat dissipation process during IP reaction. A TMC flow rate in the laminar flow state (i.e., low flow rates) is recommended for synthesizing HFs. The current research provides new insights into the IP reaction mechanism of HF membrane, thus offering valuable guidance to optimize and produce membrane products with better performance.

Combined effect of polyelectrolyte assisted interfacial polymerization and tannic acid protective surface modification to boost organic solvent nanofiltration performance

Organic solvent nanofiltration (OSN) is an effective technology for separating solute with molecular weight of 200–1000 Da (Da) from organic solvents. However, as the core of this technology, most of OSN membranes exhibit a low solvent permeance. Herein, a highly permeable OSN membrane was prepared via a poly (sodium 4-styrenesulfonate) (PSSNa)-assisted interfacial polymerization reaction using ultra-low content of aqueous monomer solution, followed by a protective modification using tannic acid (TA) grafting onto the nascent polyamide surface, and a post chemical crosslinking treatment as well as an activation treatment. PSSNa manipulates the diffusion and distribution of the m-Phenylenediamine monomers, leading to a looser and thinner polyamide layer. TA molecules successfully reacted with the remaining acyl chloride groups on the nascent polyamide layer surface and formed ester, thus preventing the surface from subsequent crosslinking reaction and also making the selective layer looser, which is beneficial for solvent permeation. Moreover, the TA modification makes the surface more hydrophilic, thus further helps to improve the solvent permeance of OSN membrane. The optimal membrane possesses an excellent ethanol permeance of 71.5 L m−2 h−1 MPa−1, an increment of 41.6 % as compared with the baseline OSN membrane, while keeping a rejection of 98.2 % for rhodamine B (RDB). Meanwhile, the surface of optimal membrane is ultra-smooth, with an average roughness of 4.4 nm, which is much beneficial for antifouling. Moreover, the OSN membrane possesses a brilliant durability performance, with only a 1.5 % decrease of the RDB rejection after being immersed in N, N-Dimethylformamide (DMF) at room temperature for 115 d, and only a further 0.3 % decrease of the RDB rejection after being further immersed in DMF at 80 °C for another 11 d, indicating its superior solvent resistance, which makes it a promising candidate for treating organic solutions from pharmaceutical and textile industries.

Synergistic interfacial polymerization between hydramine/diamine and trimesoyl chloride: A novel reaction for NF membrane preparation

Polyester-amide (PEA) thin film composite (TFC) NF membranes have rapidly evolved towards a competitive performance, benefiting from their remarkable antifouling capability and superior chlorine resistance. In this report, a new concept of synergistic interfacial polymerization is explored, which promptly triggers the reaction between hydramines and trimesoyl chloride (TMC) in the presence of a trace amount of diamines. This rapid-start mode enables the formation of defect-free PEA films without the requirement of catalysis. A comprehensive characterization of physicochemical properties using high-resolution mass spectrometer (HRMS) reveals that the recombination and formation of a “hydramine-diamine” coupling unit plays a decisive role in activating the synergistic interfacial polymerization reaction with TMC molecules. Taking the pair of serinol and piperazine (PIP) as an example, the PEA-NF membrane fabricated with 0.1 w/v% serinol mixed with 0.04 w/v% PIP as water-soluble monomer and 0.1 w/v% TMC as oil phase monomer was found to have a pure water permeability (PWP) of 18.5 L·m−2·h−1·bar−1 and a MgSO4 rejection of 95.5 %, which surpasses almost all the reported PEA NF membranes. Findings of the current research provide more possibilities for the low-cost and rapid synthesis of high-performance PEA membranes aiming for water purification.

Structurally tuned polyamide membranes via the polyvinylpyrrolidone-modulated interfacial polymerization reaction for enhanced forward osmosis performance

Controllable interfacial polymerization (IP) reaction is an important strategy to fabricate high-performance polyamide (PA) thin-film composite (TFC) membranes. In this work, a new TFC membrane was successfully fabricated by incorporating polyvinylpyrrolidone (PVP) with different molecular weights (K15, K30 and K60) at different concentrations into the aqueous phase of IP process. Due to an increased solution viscosity and interaction between PVP and amine monomers, the lower diffusion rate of amine monomers resulted into a thin (the thinnest basal PA layer of approximately 30 nm) and smooth PA layer with a high crosslinking degree. Among, the optimum PVP K60–0.25 TFC membranes with the highest molecular weights and lower incorporating concentrations had a more positive effect on forward osmosis performance, which presented a pure water flux of 11.2 L m−2 h−1, 25 % higher, and a specific salt flux of 0.04 g L−1, 43 % lower than the original membrane. Our work provides a low-cost and simple approach to obtain high-performance TFC membrane with an improved trade-off effect, and helps to deeply understand the role played by additives in PA layer modulation.

Manipulating the monomers supply of interfacial polymerization towards the ultrathin polyamide composite membrane for CO2 capture

Preparing polyamide (PA) composite membranes with high gas separation performance requires rational control for the interfacial polymerization (IP) process. In this study, the monomer supply of piperazine (PIP) and trimesoyl chloride (TMC) in the IP process was precisely manipulated to generate an ultrathin PA film on the polydimethylsiloxane (PDMS) gutter layer for CO2 separation. Concretely, the PIP supply was regulated from the homogeneous, slow, and excess mode to the inhomogeneous, fast, and small mode by constructing a sodium dodecyl sulfate (SDS) array at the phase interface; subsequently, the TMC supply was increased by elevating the TMC concentration. Therefore, the amine-to-acid chloride concentration ratio in the reaction zone was optimized and, as a consequence, the IP reaction rate was significantly increased. As a result, the thickness of the PA film was reduced from ∼92 nm to ∼37 nm through the optimization of SDS and TMC concentrations, and accordingly, the CO2 permeance was increased from 501 GPU to 1498 GPU under 0.1 MPa without sacrificing selectivity. Moreover, the membrane preparation efficiency was greatly improved with an IP reaction time of less than 30 s. The insights provided could promote the industrial application of interfacial polymerization in the scale-up preparation of high-performance CO2 separation membranes.

The effect of PEG-content and molecular weight of PEG-PPG-PEG block copolymers on the structure and performance of polyphenylsulfone ultra- and nanofiltration membranes

Thin-film composite (TFC) membranes obtained by forming a selective polyamide (PA) layer on a surface of a porous membrane-substrate via interfacial polymerization (IP) technique are the most effective membranes for nanofiltration (NF). The idea of this study is that addition of polyethylene glycol-polypropylene glycol-polyethylene glycol (PEG-PPG-PEG) block copolymers to the polyphenylsulfone (PPSU) casting solution tunes the pore structure (pore size and porosity), water contact angle and topology of the selective layer of ultrafiltration (UF) membranes. This influences the formation of PA layer via IP since membrane-substrate significantly effects the first stage of IP reaction. For the first time the effect of PEG-PPG-PEG copolymer molecular weight, content of PEG blocks and copolymer concentration in the PPSU casting solution on the structure, hydrophilicity and performance of ultrafiltration and TFC NF membranes was revealed. It was found that increase in PEG block content and PEG-PPG-PEG molecular weight led to the increase in pore size, porosity and hydrophilicity of selective layer of ultrafiltration membranes which results in the formation of thinner and more uniform PA layer with higher cross-linking degree of NF membranes via IP. It was revealed that NF membrane flux increased with the rise in the content of PEG units from 10 to 80 wt% and increase in molecular weight of PEG-PPG-PEG block copolymer. Modification of PPSU membrane-substrate yielded the increase in selectivity of the corresponding TFC NF membranes due to the formation of more uniform and denser defect-free PA layer attributed to the rise in hydrophilicity of membrane-substrate. It was found that membrane-substrate modification by PEG-PPG-PEG results in the enhancement of antifouling performance toward bovine serum albumin (flux recovery ratio is 99–100 %) and long-term stability during 48 h operation compared to the reference membrane. Modification of PPSU membrane-substrate by F38 PEG-PPG-PEG block copolymer (Mn = 5000 g mol−1, PEG block content of 80 wt%) was found to yield the TFC NF membranes with the best combination of permeation, separation and antifouling performance and long-term stability.

Preparation of N-MG-modified PVDF-CTFE substrate composite nanofiltration membrane and its selective separation of salt and dye.

Poly(vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE) is considered an ideal membrane material for the treatment of complex environmental water due to its exceptional thermal stability and chemical resistance. Thus, to expand its application in the field of nanofiltration (NF) membranes, in this study, N-methylglucamine (N-MG) was used to hydrophilically modify PVDF-CTFE, overcoming the inherent hydrophobicity of PVDF-CTFE as a porous substrate membrane, which leads to difficulties in controlling the interfacial polymerization (IP) reaction and instability of the separation layer structure. The -OH present in N-MG could replace the C-Cl bond in the CTFE chain segment, thus enabling the hydrophilic graft modification of PVDF-CTFE. The influence of the addition of N-MG on the surface and pore structure, wettability, permeability, ultrafiltration separation, and mechanical properties of the PVDF-CTFE substrate membrane was studied. According to the comparison of the comprehensive capabilities of the prepared porous membranes, the M4 membrane with the addition of 1.5 wt% N-MG exhibited the best hydrophilicity and permeability, indicating that it is a desirable modified membrane for use as an NF substrate membrane. The experiments showed that the rejection of Na2SO4 by the NF membrane was 96.5% and greater than 94.0% for various dyes. In the test using dye/salt mixed solution, this membrane exhibited a good separation selectivity (CR/NaCl = 177.8) and long-term operational stability.

Incorporation of dendritic silica nanoparticles for the preparation of high‐performance thin‐film nanocomposite membranes

AbstractThe development of thin‐film nanocomposite (TFN) membranes with high performance is conducive to efficient desalination and wastewater treatment. In this work, dendritic mesoporous silica nanoparticles (DLSiO2) were synthesized by a dual‐templating strategy. Afterward, they were introduced into the aqueous phase to fabricate TFN membranes via in situ interfacial polymerization (IP) reaction. Powerful techniques as scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, Nano zetasizer‐DLS, x‐ray photoelectron microscopy, electrokinetic analyzer, and contact angle were used in the characterization of dendritic structures and nanocomposite membranes. Results revealed that DLSiO2 with special structural characteristics can effectively regulate the IP process, promoting the enhancement of the crosslinking degree, surface hydrophilicity, and surface negative charge of polyaimde (PA) selective layers. It is also beneficial for constructing extra water channels within the PA selective layer to boost the transport of water molecules. As a consequence, the prepared TFN membrane with 0.3 mg/mL DLSiO2 exhibits optimal separation performance and good pressure resistance, acid–base resistance, and anti‐fouling properties. It also exhibited a water permeability of 4.17 L m−2 h−1 bar−1 (increased by 61.7% compared with thin film composites (TFC) membrane) and a NaCl rejection of 99.0%, which were better than those of TFN membranes prepared by introducing other types of silica in other studies.

Engraving Polyamide Layers by In Situ Self-Etchable CaCO3 Nanoparticles Enhances Separation Properties and Antifouling Performance of Reverse Osmosis Membranes.

Nanovoids within a polyamide layer play an important role in the separation performance of thin-film composite (TFC) reverse osmosis (RO) membranes. To form more extensive nanovoids for enhanced performance, one commonly used method is to incorporate sacrificial nanofillers in the polyamide layer during the exothermic interfacial polymerization (IP) reaction, followed by some post-etching processes. However, these post-treatments could harm the membrane integrity, thereby leading to reduced selectivity. In this study, we applied in situ self-etchable sacrificial nanofillers by taking advantage of the strong acid and heat generated in IP. CaCO3 nanoparticles (nCaCO3) were used as the model nanofillers, which can be in situ etched by reacting with H+ to leave void nanostructures behind. This reaction can further degas CO2 nanobubbles assisted by heat in IP to form more nanovoids in the polyamide layer. These nanovoids can facilitate water transport by enlarging the effective surface filtration area of the polyamide and reducing hydraulic resistance to significantly enhance water permeance. The correlations between the nanovoid properties and membrane performance were systematically analyzed. We further demonstrate that the nCaCO3-tailored membrane can improve membrane antifouling propensity and rejections to boron and As(III) compared with the control. This study investigated a novel strategy of applying self-etchable gas precursors to engrave the polyamide layer for enhanced membrane performance, which provides new insights into the design and synthesis of TFC membranes.

Exploiting sulfonated covalent organic frameworks to fabricate long-lasting stability and chlorine-resistant thin-film nanocomposite nanofiltration membrane

Incorporating hydrophilic and charged porous nanofillers to prepare high-performance thin film nanocomposite (TFN) nanofiltration (NF) membranes is an effective method to achieve efficient water treatment. In this study, we synthesize the sulfonated covalent organic framework nanosheets (S-CONs) with higher hydrophilicity and electronegativity by immobilizing sulfonic acid groups (–SO3H) on TpPa-1 nanosheets. The S-CONs are incorporated in the PA layer by interfacial polymerization (IP) reaction. The results indicated that the S-CONs could modulate the hydrophilicity, thickness, and electronegativity of TFN-NF membranes. At the optimal addition of S-CONs (0.006 g), the pure water permeance increases to 8.84 L⋅m−2⋅h−1⋅bar−1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\rm{L}}\\cdot{\\rm{m}}^{-2}\\cdot{\\rm{h}}^{-1}\\cdot{\\rm{bar}}^{-1}$$\\end{document}, which is about 1.75 times than the TFC membrane, with a high Na2SO4 rejection reaching 98.97%. The improvement of the separation performance mainly results from the reduction of PA layer thickness (from ~178.00–198.00 to ~100.00–128.00 nm) and the increase of surface electronegativity (from −20.37 to −44.41 mV at pH = 7.00). More interestingly, the amide bond formed between the S-CONs and TMC improved the chlorine resistance of the membranes. This study reveals the potential of using functionalized 2D CONs as nanofillers to modify TFC membranes for efficient nanofiltration.

Dissecting the impacts of nanobubbles and heat generated in polymerization on polyamide nanofiltration membranes

In the preparation of nanofiltration (NF) membranes, the introduction of acid acceptors into the aqueous phase generates heat through their interaction with the byproduct HCl from interfacial polymerization (IP), potentially leading to the formation of bubbles. This work aims to dissect the combined influences of heat and nanobubbles on NF membrane structure and performance. Three representative alkalis (i.e., NaHCO3, NaOH, and Ca(OH)2) were employed as acid acceptors into the aqueous phase, resulting in an increase of the consumption of PIP in the IP reaction from 10.75% to 23.65%, 19.35%, and 12.90%, respectively. The use of NaOH and Ca(OH)2 released more heat led to a thicker polyamide layer which reduced flux. While the use of NaHCO3 simultaneously released heat and bubbles, which promoted the development of a rougher surface polyamide layer, resulting in an increased flux from 20.3 to 28.3 L/m2 h bar, while maintaining a salt rejection rate of 97.7%. The attendance of acid acceptors also enhanced the degree of crosslinking and resulted in a decrease in negative charge of the prepared membrane. This study advances the understanding of the impact of heat and bubbles release induced by the addition of acid acceptors on NF membrane structure and performance.

Amphiphilic Interlayer Regulated Interfacial Polymerization for Constructing Polyamide Nanofiltration Membranes with High Perm-Selectivity of Mono-/Divalent Salts.

High-quality thin-film composite (TFC) membranes with high selectivity and permeability have great significance owing to their practical applications, specifically for the accurate differentiation of monovalent and divalent ions. However, the trade-off effect between selectivity and permeability is still a big challenge due to the difficult structure adjustment of the selective layer. Herein, polydopamine (PDA) functionalized with a hydrophobic long alkane chain was first explored as a functional amphiphilic interlayer to synthesize high-quality TFC membranes via a confined interfacial polymerization (IP) reaction. The amphiphilic interlayer not only restricted the formation of the polyamide (PA) matrix in the pores of the substrate but also accelerated spatially more homogeneous polymerization and formed a PA active layer with a more uniform pore size distribution. The method may provide an effective principle for the construction of versatile polyamide-based membranes with high perm-selectivity on various supports. The NaCl/Na2SO4 separation factor of the D-8/PA membrane reached as high as 204.07, while the flux increased up to 25.71 L m-2 h-1 bar-1. This progress provides a more feasible way for the construction of high-quality TFC membranes with a devisable and creative amphiphilic interlayer for industrial application.

Surface modification of nanofiltration membrane using polyoxometalates for improved separation and antifouling performance.

In this study, polyoxometalates (POMs) as a core-modifying material was used to fabricate the nanofiltration (NF) membrane on the polyvinylidene fluoride (PVDF) microfiltration membrane substrate via a novel interfacial polymerization (IP) method. The formation mechanism of the POMs-modified composite membrane was proposed. The separation and antifouling properties were further investigated. After cross-linking with POMs through the new IP reaction, the modified composite membrane showed improved hydrophilicity, water flux, and salt rejection. In the humic acid fouling experiment, the POMs-modified membrane exhibited the best antifouling performance, with a flux recovery rate of up to 91.3%. Electrochemical impedance spectroscopy was further used to investigate the antifouling performance of the membranes. Nyquist and Bode plots of the POMs-modified membranes showed no significant change before and after fouling compared to the PVDF membrane substrate, indicating reduced fouling attachment on the modified membrane, which was consistent with the fouling index and flux variation observed during the fouling experiment. Our findings provide a simple and valuable route for fabricating POMs-functionalized NF membranes with desirable separation and antifouling performance.

Micelles regulated thin film nanocomposite membrane with enhanced nanofiltration performance

The desalination performance of thin film nanocomposite (TFN) membranes is significantly influenced by the nature of nanofillers and the structure of the polyamide (PA) layer. Herein, a micelles regulated interfacial polymerization (MRIP) strategy is reported for the preparation of TFN membranes with enhanced nanofiltration (NF) performance. Specially, stable and ultrafine micelles, synthesized from the poly(ethylene oxide)-b-poly(4-vinyl pyridine)-b-polystyrene (PEO-PVP-PS) triblock copolymers, were utilized as regulators in the aqueous phase during the interfacial polymerization (IP) process. TFN membranes were fabricated with varying concentrations of micelles to improve their properties and performances. The structure of the PA layer was further regulated by modulating the content of trimesoyl chloride (TMC), which significantly enhances the performance of the TFN membrane with micelles. Attributable to the homogeneously dispersed micelles and the modified PA layer, the optimized membrane denoted as TFN-2–0.3 exhibits an improved separation performance of 20.7 L m-2h−1 bar−1 and 99.3 % Na2SO4 rejection, demonstrating nearly twice the permeance and 2.7 % higher rejection than that of the original control membrane, respectively. The mechanism of this MRIP strategy was investigated through the diffusion experiments of piperazine (PIP) and interfacial tension tests. The incorporated micelles effectively lower the interfacial tension, promote the diffusion of PIP and accelerate the IP reaction, resulting in a denser and thinner PA layer. Collectively, these findings demonstrate that TFN membranes with micelles exhibit increased roughness, enhanced hydrophilicity, superior rejection to divalent salts, and better acid-base resistance, highlighting their potential applications in the design of TFN membranes.

Conductive nanofiltration membranes via in situ PEDOT-polymerization for electro-assisted membrane fouling mitigation

Nanofiltration (NF) membranes play a pivotal role in water treatment; however, the persistent challenge of membrane fouling hampers their stable application. This study introduces a novel approach to address this issue through the creation of a poly(3,4-ethylenedioxythiophene) (PEDOT)-based conductive membrane, achieved by synergistically coupling interfacial polymerization (IP) with in situ self-polymerization of EDOT. During the IP reaction, the concurrent generation of HCl triggers the protonation of EDOT, activating its self-polymerization into PEDOT. This interwoven structure integrates with the polyamide network to establish a stable selective layer, yielding a remarkable 90 % increase in permeability to 20.4 L m−2 h−1 bar−1. Leveraging the conductivity conferred by PEDOT doping, an electro-assisted cleaning strategy is devised, rapidly restoring the flux to 98.3 % within 5 min, outperforming the 30-minute pure water cleaning approach. Through simulations in an 8040 spiral-wound module and the utilization of the permeated salt solution for cleaning, the electro-assisted cleaning strategy emerges as an eco-friendly solution, significantly reducing water consumption and incurring only a marginal electricity cost of 0.055 $ per day. This work presents an innovative avenue for constructing conductive membranes and introduces an efficient and cost-effective electro-assisted cleaning strategy to effectively combat membrane fouling.

Narrowing the pore size distribution of a piperazine-based ultrathin polyamide film with the addition of 1,3-diamino-2-propanol (DAP)

Sharpening the pore size distribution is challenging but highly efficacious to boost the performance of polyamide (PA) membranes in nanofiltration (NF). Herein, a facile and applicable strategy for narrowing the pore size distribution of a piperazine (PIP)-based NF membrane is proposed by introducing 1,3-diamino-2-propanol (DAP) into the aqueous phase. The results show that the selective layer can be effectively remodeled via the incorporation of DAP. A thicker, rougher and more hydrophilic selective layer with a narrowed pore size distribution can be attained by adding 0.03 w/v% DAP to the 0.1 w/v% PIP solution, which exhibited a pure water permeance (PWP) of 20.7 L m−2 h−1·bar−1 and a MgSO4 rejection up to 97.4 %. This transformation can be attributed to the stronger polarity and higher reactivity of DAP compared to PIP. During the IP process modified by DAP, the strong polarity of DAP could result in a slower and more homogeneous diffusion of PIP into the organic phase through hydrogen interaction to facilitate a uniform interfacial polymerization reaction. Meanwhile, the higher reactivity of DAP could remedy the probably produced defects. This work provides a straightforward route for the regulation of NF membrane structure and performance.

Tailoring the pore size distribution of nanofiltration membranes via surfactants with different alkyl chain lengths: Towards efficient molecular separation

The diffusion of amine monomer during interfacial polymerization (IP) directly affects the structure and properties of the polyamide (PA) separation layer. Surfactants can regulate the diffusion rate of monomers and change the microstructure of the PA layer. In this study, a PA nanofiltration (NF) membrane with the tailor-made pore size is fabricated by modulating the diffusion rate of 1, 4, 7, 10-tetraazacyclododecane (Cyclen). Surfactants with different alkyl chain lengths are used to precisely regulate the diffusion rate of Cyclen monomer. The longer the alkyl chain length of the surfactant is, the faster the diffusion rate of the Cyclen monomer is, resulting in the formation of a PA layer with a narrow pore size distribution. The prepared composite membrane is qualified for on-demand desalting and antibiotic/salt separation performance by changing the length of the alkyl chain. For example, surfactants with short alkane chains (C4) endow the NF membranes with a high water permeance of 30.7 L−1 m−2h−1 bar−1 for tetracycline separation. Surfactants with long alkane chains (C12) endow the NF membranes with a high selectivity of 84.8 for tetracycline/NaCl separation. This study provides further evidence for surfactant-regulated IP reactions and offers new ideas for the tailor-made regulation of NF membrane properties.

Porous Zn-TCPP interlayer with active reaction sites modulates membrane physicochemical properties to improve nanofiltration performance

For nanofiltration (NF) membranes, constructing the interlayer between the substrate and polyamide (PA) layer could balance the trade-off effect between the selectivity and permeability. However, the influencing mechanism of the interlayer to the PA layer is mostly indirect, and how to regulate the physicochemical properties of the PA layer to improve the membrane property remains to be investigated. In this study, porous Zn-TCPP nanosheets with active reaction sites were used to construct interlayer and directly participated in interfacial polymerization (IP) reaction through the edge COOH of nanosheets reacting with piperazine (PIP) to further regulate PA layer physicochemical properties. Controlling the amount of nanosheets involved in the reaction, NF membranes with striated Turing structures, higher negatively charged surface and larger effective filtration area were obtained. The NF membrane permeability with Zn-TCPP interlayer was significantly improved by 123 % while the Cl−/SO42− selectivity was greatly enhanced to 72.69, meanwhile it showed excellent performance stability. This study presents a new perspective that the interlayer can modulate the NF membrane physicochemical properties to improve its performance by directly participating in the IP reaction.

Commercial polyethylene supported thin-film composite membranes within 10 µm thickness for organic solvent forward osmosis

Organic solvent forward osmosis (OSFO) as a promising separation process for the pharmaceutical industry. The practicality and suitability of OSFO membrane are significant for the OSFO process. In this study, we developed and characterized an ultrathin (<10 µm) and solvent-resistant thin-film composite (TFC) membrane for use in the OSFO process. The commercialized polyethylene (PE) membrane with thicknesses of 5 and 9 μm were selected as a novel substrate, and hydrophilic polyvinyl alcohol was introduced on its surface to enhance hydrophilicity and structural attributes. After interfacial polymerization reaction, the utilization of the 5 μm PE substrate elevates water and alcohol fluxes, while the 9 μm PE substrate possesses the higher rejection for salts and APIs. Notably, following a 2-hour DMF activation process, the resulting TFC5-0.05 membrane attains a noteworthy ethanol flux of 2.6 L m–2h−1, along with a robust oxytetracycline rejection of > 95 % during 10-hour continuous operation. These findings underscore the favorable permselectivity of the ethanol and oxytetracycline and solvent stability of the ultrathin PE-PA TFC membrane on the commercial substrates for OSFO process.