Nanofiltration membranes via co-deposition of polydopamine/polyethylenimine followed by cross-linking

Ultrathin Alginate Coatings as Selective Layers for Nanofiltration Membranes with High Performance

It is highly desirable to develop environmentally friendly processes for fabricating thin-film composite (TFC) nanofiltration membranes (NFMs) from natural materials. However, the nanofiltration performance of such TFC NFMs is not satisfactory for practical applications owing to the lack of efficient methods for constructing ultrathin, uniform, stable coatings as selective layers. In this study, a contra-diffusion strategy is used to fabricate TFC NFMs with ultrathin cross-linked alginate coatings as selective layers without the use of any organic solvents. The as-prepared NFMs show a water permeation flux that is nearly one order of magnitude higher than that of other alginate-based TFC NFMs with similar salt rejection, and represents the best performance among all TFC NFMs from natural materials. These NFMs also demonstrate excellent mono-/divalent ion selectivity, as well as good long-term operation stability and antifouling properties. Furthermore, this strategy maximizes the reactant usage rate, minimizes the waste discharge and provides new insight into environmentally friendly fabrication of TFC NFMs.

Polydopamine Coatings with Nanopores for Versatile Molecular Separation

The demand for highly efficient and multifunctional membranes in various separation processes is increasing. Recently, mussel-inspired polydopamine (PDA) has provided a promising way to meet these requirements because of its surface-adhesive property and film-forming ability. However, traditional PDA coatings usually suffer from the disadvantages of nonuniformity, incompactness, and instability, leading to poor molecular separation and service performance. Herein, uniform, compact, and robust PDA coatings were fabricated on an ultrafiltration substrate via a reasonable screening of oxidants for the oxidized self-polymerization of dopamine. The as-prepared PDA coatings were nanoporous (0.56 ± 0.04 and 0.93 ± 0.04 nm) with a thickness of ∼75 nm, which endows the composite membranes with a high solute rejection and solvent permeability during molecular separation. They are useful in organic solvent nanofiltration because of their superior structural stability. Moreover, the composite membranes can be used for recycling the nanometer catalyst from organic solvents for the first time, which has significantly broadened the potential applications of these mussel-inspired coatings for versatile separation processes.

Nanofiltration Membrane with a Mussel-Inspired Interlayer for Improved Permeation Performance

A mussel-inspired interlayer of polydopamine (PDA)/polyethylenimine (PEI) is codeposited on the ultrafiltration substrate to tune the interfacial polymerization of piperazine and trimesoyl chloride for the preparation of thin-film composite (TFC) nanofiltration membranes (NFMs). This hydrophilic interlayer results in an efficient adsorption of piperazine solution in the substrate pores. The solution height increases with the PDA/PEI codeposition time from 45 to 135 min due to the capillary effect of the substrate pores. The prepared TFC NFMs are characterized with thin and smooth polyamide selective layers by ATR/IR, XPS, FESEM, AFM, zeta potential, and water contact angle measurements. Their water permeation flux measured in a cross-flow process increases to two times as compared with those TFC NFMs without the mussel-inspired interlayer. These TFC NFMs also show a high rejection of 97% to Na₂SO₄ and an salt rejection order of Na₂SO₄ ≈ MgSO₄ > MgCl₂ > NaCl.

Rapid determination of six carcinogenic primary aromatic amines in mainstream cigarette smoke by two-dimensional online solid phase extraction combined with liquid chromatography tandem mass spectrometry

A fully automated, rapid, and reliable method for simultaneous determination of six carcinogenic primary aromatic amines (AAs), including o-toluidine (o-TOL), 2, 6-dimethylaniline (2, 6-DMA), o-anisidine (o-ASD), 1-naphthylamine (1-ANP), 2-naphthylamine (2-ANP), and 4-aminobiphenyl (4-ABP), in mainstream cigarette smoke was established. The proposed method was based on two-dimensional online solid phase extraction combined with liquid chromatography tandem mass spectrometry (SPE/LC-MS/MS). The particulate phase of the mainstream cigarette smoke was collected on a Cambridge filter pad and pretreated via ultrasonic extraction with 2% formic acid (FA), while the gas phase was trapped by 2% FA without pretreatment for determination. The two-dimensional online SPE comprised of two cartridges with different absorption characteristics was applied for sample pretreatment. Analysis was performed by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) under multiple reaction monitoring mode. Each sample required about 0.5h for solid phase extraction and analysis. The limit of detections (LODs) for six AAs ranged from 0.04 to 0.58ng/cig and recoveries were within 84.5%-122.9%. The relative standard deviations of intra- and inter-day tests for 3R4F reference cigarette were less than 6% and 7%, respectively, while no more than 7% and 8% separately for a type of Virginia cigarette. The proposed method enabled minimum sample pretreatment, full automation, and high throughput with high selectivity, sensitivity, and accuracy. As a part of the validation procedure, fifteen brands of cigarettes were tested by the designed method.

Nanocomposite Membranes via the Codeposition of Polydopamine/Polyethylenimine with Silica Nanoparticles for Enhanced Mechanical Strength and High Water Permeability

A defect-free and stable selective layer is of critical significance for thin film composite membrane with excellent separation performance and service durability. We report a facial strategy for fabricating thin film nanocomposite (TFN) nanofltration membranes (NFMs) based on the codeposition of polydopamine, polyetheylenimine, and silica nanoparticles. Tripled water flux can be obtained from the TFN NFMs as compared with those NFMs without silica nanoparticles. This is ascribed to the improved wettability of the membrane surfaces and the enlarged pore sizes of the selective layer. The interfacial compatibility of the inorganic fillers and the polymer matrices can be enhanced by the electrostatic interactions of silica nanoparticles with polyethylenimine and the adhesive characteristics of polydopamine, resulting in a defect-free selective layer and then good rejection for both bivalent cations and neutral solutes. The rigid silica nanoparticles also improve the surface mechanical strength of the TFN NFMs effectively and lead to structural stability and compaction resistance during the long-term filtration process.

Preparation and characterization of novel alkali-resistant nanofiltration membranes with enhanced permeation and antifouling properties: the effects of functionalized graphene nanosheets

In this study, novel alkali-resistant NF membranes were developed by incorporating two kinds of functionalized graphene nanosheets into PES matrix. PES–SG demonstrated more great promise due to its superior permeability and antifouling performance.

Polyphenol Coating as an Interlayer for Thin-Film Composite Membranes with Enhanced Nanofiltration Performance

Thin-film composite (TFC) nanofiltration membranes are prepared via interfacial polymerization with a polyphenol coating as an interlayer for the thin and smooth polyamide selective layer. The polyphenol interlayer is simply fabricated by the codeposition of tannic acid and diethylenetriamine without changing the surface morphology of the polysulfone ultrafiltration substrate. An interfacial polymerization is conducted from piperazidine and trimesoyl chloride on the polyphenol interlayer to construct the polyamide selective layer. The as-prepared TFC nanofiltration membranes show nearly tripled fold of water permeation flux as compared with those prepared at the same condition without an interlayer. They also exhibit a high rejection to Na₂SO₄ (>98%) because the thin and defect-free polyamide selective layer is formed on the polyphenol interlayer. These nanofiltration properties have high reproducibility, which means the TFC nanofiltration membranes are suitable for scale-up industrial applications.

New RO TFC Membranes by Interfacial Polymerization in n-Dodecane with Various co-Solvents

The objective of this research is to prepare and characterize a new and highly efficient polyamide TFC RO membrane by interfacial polymerization in dodecane solvent mixed with co-solvents. Three co-solvents were tested namely; acetone, ethyl acetate, and diethyl ether of concentration of 0.5, 1, 2, 3, and 5 wt %. The modified membranes were characterized by SEM, EDX, AFM and contact angle techniques. The results showed that addition of co-solvent results in a decrease in the roughness, pore size and thickness of the produced membranes. However, as the concentration of the co-solvent increases the pore size of the membranes gets larger. Among the three co-solvents tested, acetone was found to result in membranes with the largest pore size and contact angle followed by diethyl ether then ethyl acetate. Measured contact angle increases as the concentration of the co-solvent increases reaching a constant value except for ethyl acetate where it was found to drop. Investigating flux and salt rejection by the formulated membranes showed that higher flux was attained when acetone was used as a co-solvent followed by diethyl ether then ethyl acetate. However, the highest salt rejection was achieved with diethyl ether.

High-Flux Positively Charged Nanocomposite Nanofiltration Membranes Filled with Poly(dopamine) Modified Multiwall Carbon Nanotubes

The poor dispensability of pristine carbon nanotubes in water impedes their implications in thin-film nanocomposite membranes for crucial utilities such as water purification. In this work, high-flux positively charged nanocomposite nanofiltration membranes were exploited by uniformly embedding poly(dopamine) modified multiwall carbon nanotubes (PDA-MWCNTs) in polyamide thin-film composite membranes. With poly(dopamine) modification, fine dispersion of MWCNTs in polyethyleneimine (PEI) aqueous solutions was achieved, which was interracially polymerized with trimesoyl chloride (TMC) n-hexane solutions to prepare nanocomposite membranes. The compatibility and interactions between modified MWCNTs and polyamide matrix were enhanced, attributed to the poly(dopamine) coatings on MWCNT surfaces, leading to significantly improved water permeability. At optimized conditions, pure water permeability of the PEI/PDA-MWCNTs/TMC nanofiltration membrane (M-4) was 15.32 L m(-2) h(-1) bar(-1), which was ∼1.6 times increased compared with that of pristine PEI/TMC membranes. Salt rejection of M-4 to different multivalent cations decreased in the sequence ZnCl2 (93.0%) > MgCl2 (91.5%) > CuCl2 (90.5%) ≈ CaCl2, which is well-suited for water softening and heavy metal ion removal.

Composite nanofiltration membranes via the co-deposition and cross-linking of catechol/polyethylenimine

Composite NF membranes are fabricated based on the co-deposition of CCh/PEI. The optimized membranes possess high rejection of multivalent ions with acceptable flux and show excellent operational stability over long-term filtration process.

Surface chemistry, topology and desalination performance controlled positively charged NF membrane prepared by polydopamine-assisted graft of starburst PAMAM dendrimers

A novel and facile method was introduced to prepare positively charged nanofiltration membranes by PDA-assisted grafting of starburst PAMAM onto PES membranes surface.