M-phenylenediamine Research Articles

Elastic modulus of polyamide thin films formed by molecular layer deposition

Molecular layer deposition (MLD) is a gas-phase deposition technique that can create ultra-thin films with precisely controlled chemical composition and thickness by depositing one monolayer at a time. This makes MLD an attractive technology for desalination membranes among other applications. Given its relatively recent development, little information has been reported regarding the properties of MLD thin films. We present the results of an initial mechanical property study of MLD films with thicknesses ranging from ∼50 to 2000 nm. MLD was utilized to create crosslinked polyamide films grown using either m -phenylenediamine (MPD) and trimesoyl chloride (TMC) reactants or piperazine (PIP) and TMC reactants. The elastic modulus of the films was determined using atomic force microscopy (AFM). The results show that the modulus was independent of film thickness with values of 4.36 ± 1.19 GPa and 5.24 ± 1.06 GPa for the MLD films grown using the MPD-TMC and PIP-TMC chemistries, respectively. These values are of the same order of magnitude as those reported for much thicker polyamide films, but higher than the modulus of polyamide films fabricated using interfacial polymerization. • All-organic polyamide thin films were fabricated using molecular layer deposition. • The elastic modulus of the films was measured using atomic force microscopy. • Two film chemistries with thicknesses between ∼50 and 2000 nm were evaluated. • Modulus was independent of chemistry and film thickness. • Modulus values of ∼3–6 GPa were similar to those of bulk polyamides.

Tannic acid reinforced interfacial polymerization fabrication of internally pressurized thin-film composite hollow fiber reverse osmosis membranes with high performance

Internally pressurized thin-film composite (TFC) hollow fiber (HF) reverse osmosis (RO) membranes have the merits of easy scaling-up and no flow dead zone, etc. In this work, we used tannic acid (TA) as a reinforced additive in m-phenylenediamine (MPD) aqueous solution to assist the interfacial polymerization process to construct a polyamide separation skin layer with high separation performance on the inner surface of polysulfone hollow fiber substrate. Due to many phenolic hydroxyl groups on tannic acid molecules, they could form hydrogen bonds with MPD molecules and thus greatly hinders MPD diffusion towards the interface, and greatly helps to manipulate the interfacial polymerization process. In this way, we obtained a TA-reinforced TFC HF RO membrane having super hydrophilicity (contact angle of merely 26.4°), much thinner skin layer (about 100 nm in thickness), as well a much smoother surface (roughness of about 35 nm) under the optimized ultra-low concentration (100 mg L−1) for tannic acid in the MPD solution. The prepared TA-reinforced membrane achieves a water permeance of 20.4 L m−2 h−1 MPa−1, which is more than 50 % higher than that of the TA-free membrane, and a NaCl rejection of about 98 % with 2000 mg L−1 NaCl solution as feed. The TA-reinforced membrane has excellent fouling resistance, chlorine resistance, as well as long-term operation stability, thus showing a broad application prospect in brackish water desalination and tap water treatment.

Cosolvent-Assisted Interfacial Polymerization toward Regulating the Morphology and Performance of Polyamide Reverse Osmosis Membranes: Increased m-Phenylenediamine Solubility or Enhanced Interfacial Vaporization?

Cosolvent-assisted interfacial polymerization (IP) can effectively enhance the separation performance of thin film composite (TFC) reverse osmosis (RO) membranes. However, the underlying mechanisms regulating the formation of their polyamide (PA) rejection films remain controversial. The current study reveals two essential roles of cosolvents in the IP reaction: (1) directly promoting interfacial vaporization with their lower boiling points and (2) increasing the solubility of m-phenylenediamine (MPD) in the organic phase, thereby indirectly promoting the IP reaction. Using a series of systematically chosen cosolvents (i.e., diethyl ether, acetone, methanol, and toluene) with different boiling points and MPD solubilities, we show that the surface morphologies of TFC RO membranes were regulated by the combined direct and indirect effects. A cosolvent favoring interfacial vaporization (e.g., lower boiling point, greater MPD solubility, and/or higher concentration) tends to create greater apparent thickness of the rejection layer, larger nanovoids within the layer, and more extensive exterior PA layers, leading to significantly improved membrane water permeance. We further demonstrate the potential to achieve better antifouling performance for the cosolvent-assisted TFC membranes. The current study provides mechanistic insights into the critical roles of cosolvents in IP reactions, providing new tools for tailoring membrane morphology and separation properties toward more efficient desalination and water reuse.

Vacuum-assisted MPD loading toward promoted nanoscale structure and enhanced water permeance of polyamide RO membrane

Thin-film composite (TFC) reverse osmosis (RO) membranes fabricated by interfacial polymerization (IP) have been widely applied in seawater desalination. Nevertheless, their separation performance is limited by the permeance-selectivity upper bound. Compared to conventional synthesis/modification techniques, the manipulation of amine monomer distribution for the IP reaction has been far less investigated. In this study, we systematically investigated three classical approaches for m-phenylenediamine (MPD) loading during the IP reaction, i.e., vacuum filtration (TFC-V), roller (TFC-R), and air gun (TFC-A). Our results suggested that the vacuum-assisted approach can greatly enhance the availability of MPD monomers, which could, in turn, result in enhanced “ridge-and-valley” morphology of the polyamide rejection layer as a result of the enhanced nanofoaming effect. Furthermore, the TFC-V membrane demonstrated the highest water permeance of 2.8 ± 0.4 L m-2 h−1 bar−1 compared to TFC-R and TFC-A membranes of 2.1 ± 0.2 L m-2 h−1 bar−1 and 2.1 ± 0.4 L m-2 h−1 bar−1, respectively. This study provided mechanistic insights to facilitate an improved understanding of membrane synthesis–structure–performance relationships.

Amino-functionalized hypercrosslinked polymer as sorbent for effective extraction of nitroimidazoles from water, drink and honey samples

The three hypercrosslinked polymers (HCP) materials, designated as OPD-HCP, MPD-HCP and PPD-HCP, were synthesized by using o-phenylenediamine (OPD), m-phenylenediamine (MPD) and p-phenylenediamine (PPD) as monomers. They were characterized by infrared spectroscopy, powder X-ray diffraction, nitrogen sorption isotherms, and scanning electron microscopy. Then, the HCPs were explored as solid-phase extraction (SPE) adsorbent for the extraction of five nitroimidazoles (NDZs) (metronidazole, ronidazole, secnidazole, dimetridazole and ornidazole). Among the three HCPs, the MPD-HCP has the best adsorption performance for the NDZs. With the help of high-performance liquid chromatography with ultraviolet detection (HPLC-UV), good linear response range (0.07-40.0 ng mL-1), high method recovery (86.8%-113.3%), low limits of detection (0.02-0.15 ng mL-1) and good precision with the relative standard deviations of less than 8.1% were achieved for the determination of the NDZs in water samples. The effective determination of the NDZs in peach juice, honey tea, and honey samples were also realized by the developed method with satisfactory results. Based on both the experimental results and density functional theory calculation, the adsorption mechanism can be attributed to multiple interactions between the MPD-HCP and the NDZs, including hydrogen bonding, hydrophilic, and electrostatic interactions. The method provides a new alternative of choice for the determination of some NDZs in real samples.

Enhancement and Mechanism of NH3 Plasma Treatment on Interfacial Combination of PMTA and Cellulose Insulation Matrix

Interfacial bonding is significant in determining the mechanical properties and dielectric loss of polymer composites. In this study, NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> plasma treatment is used to reinforce the interfacial bonding between polyisophthaloyl metaphenylene diamine (PMTA) and the cellulose matrix. The mechanism of modification is investigated via x-ray photoelectron spectroscopy (XPS) and density functional theory (DFT). Additionally, molecular dynamics (MD) simulations are performed to explore the microscopic mechanism of the performance improvement of the composite insulation paper. The experimental results show that the mechanical property is improved and dielectric loss decreased to a certain extent after treatment. According to the results of XPS and DFT, the treatment introduces a polar group, −NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , into the C18 position of PMTA. PMTA treated with NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> plasma (T-PMTA) is conducive to form H-bonds with cellulose. It increases the interaction energy and strengthens the interfacial bonding, causing the T-PMTA molecules to penetrate wider and deeper on the cellulose surface. Thus, the mechanical properties are improved. Additionally, the improved interfacial bonding impedes the rotation and movement of molecules at the interface, which reduces the degree of freedom of the dipole steering and the resulting low dielectric loss. This study reveals the mechanism of NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> plasma treatment and provides insights into the microscopic mechanism of the improvement of properties of composite insulation paper at the molecular level.

Performance evaluation of polyamide reverse osmosis membranes incorporated silica nanoparticles for concentrating peach juice: An invitro evaluation

In this study, a mixture of water and peach juice is used as feed for the reverse osmosis (RO) device. Polyester sheet, polyester sulfone polymer and polyamide from interfacial polymerization of m-phenylenediamine (MPD) and trimesoyl chloride (TMC) monomers with silica nanoparticles are used to produce the membrane. A solution of Poly (ether sulfone) (PES) is prepared in N-Methyl-2-pyrrolidone (NMP) solvent with 10 wt%, 15 wt%, and 20 wt% and the addition of 0.5 wt%, 1.5 wt%, and 3 wt% of silica nanoparticles. Scanning electron microscope (SEM) and Fourier transform infrared (FTIR) analysis are used to evaluate the morphology and functional groups of the prepared membranes. According to the SEM images, it is observed that the membrane consists of three layers and the polyamide layer (surface) of the membrane, is responsible for the main separation is dense hills and valleys' surface morphology. The polyester sulfone layer (middle) has finger-shaped porosity and the obtained results of the contact angle test show that with increasing silica nanoparticles, the membrane becomes more hydrophilic and the angle decreases as the polyester sulfone layer (middle) have finger-shaped porosity. Chemical bonds formed in the resulting membrane structure were identified, including sulfonylide, polyamide, and silica nanoparticles. The results of the contact angle test show that as the silica nanoparticle increases, the membrane became more hydrophilic and the angle was decreased. The sample with 3% nanoparticles has the lowest angle and the highest level of hydrophilicity, followed by the membrane 151.5, which has 1.5% nanoparticles, and then the membrane 150 without nanoparticles.

Polymer types regulation strategy toward the synthesis of carbonized polymer dots with excitation-wavelength dependent or independent fluorescence

Three kinds of carbonized polymer dots (CPDs) synthesized via a one-pot process from o-phenylenediamine (OPD), m-phenylenediamine (MPD) and p-phenylenediamine (PPD) exhibit excitation-wavelength independent yellow, green and red emissions, respectively. In sharp contrast, two kinds of CPDs prepared via a hydrothermal process from citric acid (CA) and diethylenetriamine (DETA) exhibit obvious excitation-wavelength dependent emissions. Through the characterization and comparison of the two types of CPDs, it is concretely revealed that the polymer structure types during the formation of CPDs can effectively control the fluorescence excitation-wavelength independence/dependence. The homogeneous polymer structures contained in CPDs contribute to excitation-wavelength independence, whereas random copolymer structures contribute to excitation-wavelength dependence. These studies are of great significance for further understanding the polymer structures and designing unique optical properties of CPDs.

New cross‐linked poly(methyl methacrylate): Synthesis, characterization, and inhibitory effects against selected bacteria and cancer cells

AbstractNovel cross‐linked poly(methyl methacrylate) (PMMA) derivatives with different ratios of crosslinkers (2, 5, 10, 20, 30, 40, and 50 wt%) were synthesized using the condensation method between PMMA and bifunctional amino derivative cross‐linkers, o‐phenylenediamine (OPD), and m‐phenylenediamine (MPD). The final products were tested for antibacterial and anticancer activities. Various techniques were used to characterize the cross‐linked polymers. Fourier transform infrared (FTIR) spectroscopy was used to identify interactions between PMMA and diamine derivatives. The scanning electron microscope (SEM) images show that the smooth PMMA surface was totally changed after cross‐linking. Thermogravimetric analysis (TGA) results show that when the percentage of cross‐linked PMMA (C‐PMMA) increased, the decomposition temperature at 25%, 50%, and 75% weight loss increased. C‐PMMA/2% OPD, C‐PMMA/20% OPD, and C‐PMMA/20% MPD have an antibacterial effect on both Escherichia coli (gram‐negative) and Staphylococcus aureus (gram‐positive) with an inhibitory zone ranged from 9 to 16 mm. In addition, C‐PMMA/2% OPD showed anticancer activities, reducing the number of HepG2 cancer cells significantly. A positive correlation between the concentrations of the product and the reduction of HepG2 cells has been detectedr.

Semi-aromatic polyamide membrane incorporated with yolk-shell mesoporous hybrid nanospheres for ultrahigh permeability and improving comprehensive property

In this report, yolk-shell (YS) organic-inorganic hybrid nanospheres (YSHNs) with radially ordered mesopores were synthesized by a co-assembly strategy using 1,2-bis(triethoxysilyl)ethane and tetraethoxysilane as precursors, and cetyltrimethylammonium bromide as a soft template. Then, Silver nanoparticles (AgNPs) were uniformly embedded in the hollow cavities of the YSHNs. The semi-aromatic polyamide (SAP) based nanocomposite membrane was fabricated using 1,3,5-cyclohexane tricarbonyl chloride as an organic phase, meta-phenylene diamine as an aqueous phase, and the mesoporous YS hybrid nanospheres as nanoadditives by an interfacial polymerization approach. The results show that the YS nanospheres were successfully incorporated into the polyamide (PA) separation layer, and the membrane becomes very hydrophilic. The membrane incorporated with the aminated YS mesoporous nanospheres exhibits ultrahigh pure water permeability (PWP, 9.34 L m−2 h−1 bar−1) and comparable NaCl rejection (96.1%), which is dramatically higher than the membrane with common mesoporous nanospheres. It is because that the hollow cavity of the YS nanosphere further decreases the membrane resistance, and the aminated spherical surface improves the interfacial compatibility between the PA matrix and the YS nanospheres. Furthermore, the flexible YS hybrid structure and the mesoporous core could play an important buffering for avoiding the shell fracture under a high operation pressure. The chlorine resistance of the YS-nanosphere incorporated membrane is significantly improved compared to the pristine SAP membrane in a strong chlorination strength (5500 ppm h, pH = 5). The confined AgNPs in the YS mesostructure endow the membrane with a sustainable antibiofouling property. Moreover, the polylysine modification improves the membrane fouling resistance and performance stability.

Removal of arsenic from water using a novel polyamide composite hollow fiber membrane by interfacial polymerization on lumen side

A novel mixed polyamide based composite membrane was prepared by interfacial polymerization (IP) of chitosan (CS) and m-phenylenediamine (MPD) mixture with trimesoyl chloride (TMC) for low pressure hollow fiber nanofiltration (NF). A uniform thin selective layer of polyamide was chemically coated on the lumen side of the polysulfone (PSF) based ultrafiltration support membrane. Permeability of the prepared hollow fiber NF membrane improved appreciably by incorporation of a small amount of CS into the MPD solution during IP process. The properties of prepared hollow fiber membranes were characterized using scanning electron microscope (SEM), contact angle, molecular weight cut off (MWCO), permeability, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and surface zeta potential. Pure water permeability of mixed polyamide composite membrane enhanced from 3.8 l/m2h bar to 32.5 l/m2h bar, which corroborated an increase in MWCO from 673 Da to 2553 Da and pore radius from 6.8 to 12.9 Å as CS was incorporated in polyamide layer. However, this drastic increase in permeate flux was not compromised with the arsenate rejection, which changed from 74.68% to 73.16% only. Thus, the prepared hollow fiber membrane performance was suitable and competent for low pressure driven hollow fiber membrane based arsenate rejection, which has many advantages over the conventional resin based filtration to remove arsenic from water. Performance of the developed hollow fiber membrane was also tested with arsenic contaminated natural groundwater prepared artificially with a rejection of 66–71% arsenate, 45–47% total dissolved solids (TDS), 47–48% hardness and 46–50% iron at 1 bar pressure with 25 l/m2h permeate flux.

Physical structure, TD-DFT computations, and optical properties of hybrid nanocomposite thin film as optoelectronic devices

HCl doped-copolymer of ortho phenylene diamine and meta phenylene diamine was prepared by using oxidative polymerization method with ferric chloride as an oxidizing agent in the existence of sodium dedocyl sulphate as a soft template. The microporous structure thin films of hybrid copolymer/ZrO2 nanocomposite [copolymer/ZrO2]NC were fabricated using a physical vapor deposition (PVD) method. The effect of addition of zirconium oxide nanoparticles [ZrO2]NPs on the physical properties of the copolymer was discussed in the light of crystallinity and optical properties. The average crystallite size of [ZrO2]NPs is around 40 nm. The copolymer showed an absorbance of 1.18 at the wavelength (λ) 374 nm, which increased to 1.26 at λ = 440 nm after glycine addition, also increased to 1.53 at λ = 486 nm after [ZrO2]NPs loading. Also, the significant changes in the absorption index and indirect/direct bandgap of the copolymer have been detected. The materials Studio 7.0 program on TDDFT/DMol3 was used to optimize the molecular structure and perform the frequency calculations for the crystal models and isolated molecules. The DFT-Gaussian09W-vibration values are quite similar to the experimental data either in the structure or in the optical properties. The improvements in optical properties were achieved and revealed the possibility of using the hybrid nanocomposite films in the polymers solar cell application.

Modification of polyamide reverse osmosis membranes for the separation of urea

Reverse osmosis (RO) membranes are the gold standard for water desalination and have been in use for over three decades. Even though RO membranes exhibit excellent performance rejecting monovalent and divalent salt ions, they do not reject small, neutral, and uncharged molecules, such as urea, to a level to produce potable water, especially at near-neutral pH. Due to the fast, uncontrolled nature of the interfacial polymerization reaction, the polyamide layer contains both network and aggregate free volume holes (pores). Because urea rejection is dominated by the size exclusion mechanism, reducing the free volume to reduce the passage of the urea through the membrane is needed. In this regard, the modification of RO membranes to increase the degree of cross-linking and/or decrease the free volume hole size is an ideal approach. We hypothesize that if the polyamide layer can be modified with a diamine, then the urea rejection will be increased. In this work, we modified polyamide RO membrane separation layers of commercial membranes (Dupont XLE and BW30XFR) using the carbodiimide chemistry followed by the application of m-phenylenediamine (MPD) and heat treatment in the post-modification stage. The modified membranes were characterized using ATR-FTIR, XPS, SEM, contact angle goniometry, and electrokinetic analyzer. Membranes were performance tested for water permeance, NaCl rejection, and urea rejection using a dead-end stirred cell. Compared to the control membranes, the modified XLE membranes and modified BW30XFR membranes improved the urea rejection from 16.8% to 54.9% and from 48.4% to 64.6%, but a reduction in water permeance by a factor of up to 4.7 and 2.7 respectively. The results show that combining the application of MPD and heat treatment can enhance the urea rejection of the membranes significantly.

Hybrid nanofiltration thin film hollow fiber membranes with adsorptive supports containing bentonite and LDH nanoclays for boron removal

This study focused on removal of boron from water via hybrid nanofiltration (NF) thin film composite (TFC) hollow fiber (HF) membranes. To do so, nanocomposite polyvinyl chloride (PVC) HF membranes containing bentonite and layered double hydroxide (LDH) nanoparticles as natural and synthetic adsorbents were fabricated as the adsorptive support layers with high efficiency in boron removal. The phase inversion behavior of dope solutions and mechanical strength of the adsorptive nanocomposite PVC HF membranes were investigated and the results showed that LDH interacts better with PVC polymeric chains than bentonite. It was found that LDH with smaller pores and better adsorption capability in comparison with bentonite results in more hydrophilic membranes with better performance. On the other hand, bentonite tends to become agglomerated at above 1.5 wt%. Moreover, the fabricated membranes containing LDH have lower MWCO and more uniform pore size distribution which make them better options as support for the TFC layer formation to fabricate NF TFC membranes. The selective TFC layer was then fabricated via interfacial polymerization of m-phenylenediamine (MPD) and 1,3,5- benzenetricarbonyl trichloride (TMC) on the outer layer of the nanocomposite PVC HF membranes. Boron removal, and recovery and reusability of the fabricated NF TFC membranes were investigated by Na₂CO₃ solution. It was found that the NF TFC membranes containing LDH with boron removal of more than 83.6% and water flux of 16.1 L/m2.h at 4 bar operational pressure exhibit better performance than the NF TFC membranes containing bentonite.

Effects of Polyamide Chemistry on Solution Permeance in Molecular Layer-By-Layer Desalination Membranes

We present a series of polyamide membranes synthesized via molecular layer-by-layer (mLbL) deposition using a combination of two acid chlorides, trimesoyl chloride (TMC) and isophthaloyl chloride (IPC), and one of two diamines, m-phenylenediamine (MPD) or 3,5-diaminobenzoic acid (BA). These monomer combinations permit comparison of the conventional reverse osmosis chemistry, TMC combined with MPD, against a variant with a higher concentration of polar acid groups, TMC combined with BA, and a variant with reduced cross-link density via the addition of a linear monomer, a 50%/50% mixture by mass fraction of TMC and IPC combined with MPD. Water permeance, NaCl rejection, and water swelling are compared across the series. Although efficient NaCl rejection appears to be dependent on the formation of a sufficiently cross-linked polyamide network, we find that water permeance is more strongly controlled by the concentration of hydrophilic moieties in the membrane than by the cross-link density. The enhanced permeance in polar membranes is associated both with increased membrane swelling and with elevated water mobility.

A method to quantify composition, purity, and cross-link density of the active polyamide layer in reverse osmosis composite membranes using 13C cross polarization magic angle spinning nuclear magnetic resonance spectroscopy

A method for harvesting and purifying the thin polyamide (PA) active layer from thin-film composite (TFC) reverse osmosis (RO) membranes was developed, enabling quantitative nuclear magnetic resonance (NMR) measurements of the composition and cross-linking in the PA layer that can be directly related to membrane performance. Using our chemical separation process, we report on four trimesoyl chloride (TMC)/isophthaloyl chloride (IPC)/ m -phenylene diamine (MPD)-based TFC membranes in which the cross-link density was intentionally reduced by replacing trifunctional cross-linking TMC monomers with their linear IPC difunctional analog. While the NMR results show a two-fold decrease in cross-linking that causes a 30% increase in salt passage, the addition of the difunctional analog leads to increased polar amine groups that reduce water permeance due to tighter binding of water in the PA membrane. Our results demonstrate that 13 C cross polarization magic angle spinning (CPMAS) is a powerful method for quantitatively monitoring the purity, cross-linking, and chemical composition in PA membranes and will be an essential tool in ascertaining atomistic models of PA structure. • A method for purifying the polyamide layer from TFC RO membranes was developed. • 13 C CPMAS quantifies composition and crosslinking in harvested polyamide TFC RO films. • Crosslinking is controlled by IPC/TMC ratio. • With a two-fold decrease in crosslinking, a 30% increase in salt passage. • With a two-fold increase of amine content, a 30% decrease in water permeance.

Ultra-smooth and ultra-thin polyamide thin film nanocomposite membranes incorporated with functionalized MoS2 nanosheets for high performance organic solvent nanofiltration

Organic solvent nanofiltration (OSN) membranes are the key factors for the treatment of organic solution via OSN technology. In this work, we fabricated a kind of ultra-thin and ultra-smooth thin-film nanocomposite (TFN) OSN membrane using interfacial polymerization (IP) process with ultra-low concentration for both the aqueous and the organic monomers, together with doped tannic acid (TA) functionalized Molybdenum disulfide (MoS2) nanosheets of ultra-low content in the aqueous monomer solution, and followed by post-IP chemical crosslinking and solvent activation procedures. The results demonstrated that the incorporated TA-MoS2 nanosheets not only help to promote the solvent permeation, but also help to increase the solvent resistance and fouling resistance of the fabricated membrane. The optimal TFN OSN membrane fabricated using 0.05 wt% aqueous m-phenylenediamine (MPD) solution doped with TA-MoS2 nanosheets content of 50 mg L−1 and 0.0025 wt% trimesoyl chloride (TMC) / n-hexane solution has an ultra-thin barrier layer, with an average thickness of about 15 nm. This endows it a much higher pure DMF permeance of 219.1 L m−2 h−1 MPa−1, which is much superior over most of literature works. Meanwhile, the fabricated TFN OSN membrane achieves a rejection of 99.1 % for rhodamine B (RDB, 479 Dalton), which is about 10.1 % increment compared with that of the baseline thin-film composite (TFC) membrane. The TFN OSN membrane also features an ultra-smooth skin layer, with a surface roughness of merely about 2.0 nm, which is quite beneficial for its fouling resistance performance. Moreover, the TFN OSN membrane features outstanding high solvent resistance. It remained a nearly constant and extremely high rejection for Rose Begal (RB, 1017 Dalton), about 99.9 %, and a much higher DMF permeance, 101 ± 2 L m−2 h−1 MPa−1, after cross-flow filtration for more than 200 h using 100 mg L−1 RB / DMF solution as feed, which is seldomly reported in literature. Even being immersed in DMF at 80 °C for more than 144 h, it remained a rejection of higher than 98 % for Rhodamine B (479 Dalton), indicating its superior solvent resistance and promising industrial application prospect.

Facile fabrication of hydroxyl-rich polyamide TFC RO membranes for enhanced boron removal performance

The insufficient boron removal performance is a conspicuous infirmity of reverse osmosis (RO) membranes for seawater desalination. Herein, RO membranes with high boron removal performance were prepared by adding 2-hydroxyethyl acrylate (HEA) and acrylamide (AA) into the m-phenylenediamine (MPD) solution and employing ultraviolet (UV) irradiation during the interfacial polymerization (IP) process. During the UV-imported IP process, the radical polymerization between HEA and AA was triggered to produce hydroxyl-containing HEA-co-AA copolymers, while polyamide polymers were simultaneously generated. Attributed to the interspersion of hydroxyl-containing copolymers in the polyamide chain segments, the superior dense and tight structure of the hybrid separation layer was achieved. Crucially, the high electron density hydroxyl groups enriched in the hybrid separation layer could specifically interact with the electron-deficient boric acid via electrostatic interaction and hydrogen bond. Therefore, in the modified membrane, the diffusion of boric acid was inhibited. Consequently, for the modified membrane, the boric acid retention rate was dramatically increased from 84.42% to 92.80%. Additionally, NaCl retention rate and water flux were also promoted. The UV-imported IP process was neither process-intensive nor time-consuming, exhibiting high compatibility with the continuous membrane production. It was expected that this work would guide the innovation of high boron removal RO membranes and other types of IP-made membranes.

Highly efficient size-sieving-based removal of arsenic(III) via defect-free interfacially-polymerized polyamide thin-film composite membranes

Serious health problems have been linked to the consumption and exposure of arsenic-contaminated groundwater. In comparison to As(V), As(III) is smaller and predominantly present in its neutral form in groundwater, which hinders its efficient removal by conventional nanofiltration and reverse osmosis membranes. In this study, the removal of As(III) was investigated at different pH conditions using three defect-free interfacially polymerized thin-film composite (TFC) membranes made by an optimized in-house developed interfacial polymerization process (KRO). The membranes were fabricated from aromatic para-phenylenediamine (PPD) or meta-phenylenediamine (MPD) and cycloaliphatic piperazine (PIP) by reaction with trimesoyl chloride (TMC). The PPD-KRO, MPD-KRO, and PIP-KRO polyamide membranes were tested with a feed containing 5 ± 1 mg L−1 (ppm) As(III). Two commercial TFC membranes, a seawater (Sepro RO4) and a nanofiltration (DOW NF270) membrane, were also evaluated for comparison. At natural conditions (pH 6–8), the defect-free fully aromatic TFC membranes demonstrated unprecedented size-sieving performance for As(III) removal with a rejection of ∼99.5 and > 99.8% for PPD-KRO and MPD-KRO, respectively, in comparison to ∼95% for the commercial Sepro RO4 seawater membrane tested under the same conditions. In contrast, As(III) rejection of semi-aromatic piperazine-based TFCs, PIP-KRO and NF270, showed a strong dependence on the charge-exclusion mechanism with maximum As(III) rejections of 69.5 and 46.3% at pH 10, respectively. Most notably, we demonstrated that the MPD-KRO membrane achieved an As(III) concentration ∼5 μg L−1 in the permeate (less than the WHO permissible arsenic standard level of 10 μg L−1), whereas PPD-KRO achieved a slightly higher value of ∼14 μg L−1. Our results are very promising considering the arsenic standard level in highly As(III) contaminated groundwater in Bangladesh and India is set at 50 μg L−1.

Deciphering the Role of Amine Concentration on Polyamide Formation toward Enhanced RO Performance

Polyamide surface morphology and its underneath nanosized voids have crucial influence on the separation performance of thin film composite (TFC) polyamide reverse osmosis membranes. Although there have been numerous studies reporting the impact of amine monomer concentration on polyamide formation and membrane performance, the observations and interpretations in the existing literature remain controversial. In this study, we performed interfacial polymerization (IP) of polyamide films over a wide range of m-phenylenediamine (MPD) concentration (0.05–8.0 w/w %). For the first time, we demonstrate that the water permeance of the resultant TFC membranes is governed by the competing effects of (1) promoted polyamide film growth for forming thicker polyamide films and (2) improved nanofoaming effect that results in more extensive nanovoids at higher MPD concentrations. To dissect these competing mechanisms, we further adopted a free-interface IP strategy to suppress the nanofoaming effect. The corresponding polyamide nanofilms had negligible nanovoids and monotonously increased film thickness, leading to decreased water permeance at high MPD concentrations. In contrast, the conventional TFC membranes exhibited optimal water permeance at the intermediate MPD concentration of 2.0 w/w %, which results from the trade-off between improved nanovoid formation (which promotes higher permeance) and increased film growth (which limits permeance). On the other hand, the better film growth at greater MPD concentration was generally beneficial for achieving better membrane rejection. The current study unveils the fundamental chemistry–morphology–performance relationship of TFC polyamide membranes and provides important implications on their synthesis and environmental applications.