Membrane Separation Layer Research Articles

Fabrication of POSS-centered polyester network as high anti-chlorine and anti-fouling separation layer of membrane via successive Photo-ATRP and interfacial polymerization for molecular separation

The incorporation of polyhedral oligomeric sesquisiloxane (POSS), a distinctive nanoparticle, into the membrane separation layer represents an effective strategy for enhancing the chlorine resistance of membranes. This modification contributes to both the durability of the membrane and its separation efficiency. However, POSS is easy to agglomerate, which affects the separation performance of the membrane. In this paper, POSS-centered polyhydroxy polymer (OMEPOSS-P(GMA-NMDG)) was synthesized via photo-induced atom transfer radical polymerization and used as water-soluble monomer to prepare polyester separation layer on porous substrates through interfacial polymerization with trimelanoyl chloride. The obtained POSS-centered polyester membrane exhibits a high dye removal rate exceeding 99 %, and it can realize the screening of dye molecules with different molecular weight and different charge. Notably, the membrane demonstrates excellent chlorine resistance, maintaining effective separation efficiency after exposure to sodium hypochlorite solutions at concentrations of 10 000 ppm for 96 h and 1000 ppm for 7 days. It is worth noting that the membrane showed high anti-fouling performance. This method provides a useful guideline for the development of chlorine-resistant and anti-fouling separation membranes.

Controllable Design of Polyamide Composite Membrane Separation Layer Structures via Metal-Organic Frameworks: A Review.

Optimizing the structure of the polyamide (PA) layer to improve the separation performance of PA thin-film composite (TFC) membranes has always been a hot topic in the field of membrane preparation. As novel crystalline materials with high porosity, multi-functional groups, and good compatibility with membrane substrate, metal-organic frameworks (MOFs) have been introduced in the past decade for the modification of the PA structure in order to break through the separation trade-off between permeability and selectivity. This review begins by summarizing the recent progress in the control of MOF-based thin-film nanocomposite (TFN) membrane structures. The review also covers different strategies used for preparing TFN membranes. Additionally, it discusses the mechanisms behind how these strategies regulate the structure and properties of PA. Finally, the design of a competent MOF material that is suitable to reach the requirements for the fabrication of TFN membranes is also discussed. The aim of this paper is to provide key insights into the precise control of TFN-PA structures based on MOFs.

Catalytic pre-coat on ceramic nanofiltration membranes for segregation and Fenton cleaning of high-resistance colloids in direct surface water treatment

Ceramic nanofiltration (NF) is a promising alternative for direct surface water treatment, but is hampered for full-scale applications by fouling and a lack of eco-friendly cleaning regimes. In this work, an innovative reactive pre-coat layer, consisting of an iron oxychloride catalyst, was constructed on top of commercial ceramic NF membranes, for segregating a large-sized colloid fraction in canal water and Fenton cleaning with a hydrogen peroxide (H2O2) solution. The large-sized colloids (3−30 μm) were identified as dominant substances fouling the TiO2 separation layer of the pristine membranes, leading to a fast increase in their filtration resistance, in contrast to the small-sized colloids (<0.04 μm) and natural organic matter (NOM). As a consequence, the catalyst pre-coat layer with a pore size of 0.1–0.5 μm was able to segregate the large-sized colloids from the TiO2 separation layer during direct filtration of the raw water. Moreover, filtration under an acceptable flux of around 23 L m−2 h−1 did not cause pore clogging in the catalyst pre-coat. In addition, Fenton oxidation initiated by the catalytic pre-coat efficiently restored the filtration resistance, whereas sole H2O2 flush of the pristine membrane was not effective. In the meantime, the TiO2 separation layer of the membrane exerted a high NOM rejection of approximately 90%, measured as dissolved organic carbon, while the catalyst pre-coat on the membrane remained active in Fenton cleaning, over five one-day cycles. The findings of this work may provide guidance on the structural and functional design of a catalytic pre-coat layer for a dual purpose of foulant segregation and oxidative removal, particularly in response to key fouling-causing substances, during membrane-based treatment of real water matrices.

Quantification of overcompensated cations in layer-by-layer membrane by Orange yellow II

The charge density of the nanofiltration (NF) membrane separation layer is critical for ion separation because the charge-based Donnan exclusion plays a critical role. To quantified the charge density has been an important but difficult task. We recently discovered the excellent performance of poly(styrene sulfonate) (PSS)/ poly (allylamine hydrochloride) (PAH) layer-by-layer (LBL) NF membranes for Mg2+/Li+ separation. The overcompensated amine groups (R-NH3+) in PAH were assumed to be the main contribution, but lacked a quantification of the charge density for further proof. Here, a simple quantitative experimental method by Orange yellow II staining was reported for the first time to measure the overcompensated amine groups in the separation layer. The sulfonic acid group (R-SO3-) in Orange yellow II stoichiometrically adsorbed to the excessive R-NH3+ at pH = 3 by electrostatic interaction, and desorbed at pH = 12. Thermodynamics and kinetics analysis of the sorption process demonstrated a Langmuir monolayer sorption and the sorption was controlled by sorption reaction not diffusion. The pore size distribution and rejection measurement confirmed that Orange yellow II sorption did not disrupt the original PSS/PAH layer. A linear relationship was observed between the charge density and the coating bi-layers or PAH layers. The accurate, easy assessment of charge density of LBL NF membrane provides future possibility for understanding overcompensation during LBL assembly and a bottom-up understanding of the charges to the NF performance in separation.

Magnetic‐field‐inducedFe3O4@CNTsdispersion in the separation layer to improve the performance of composite ultrafiltration membrane

AbstractIt is of great significance to regulate carbon nanotubes (CNTs) dispersed in the separation layer of membranes to improve the properties of membranes. In this work, ferric oxides coated carbon nanotubes (Fe3O4@CNTs) are prepared by solvothermal method, and then are added to the casting solution to prepare Fe3O4@CNTs/poly(ethersulfone)/sulfonated polysulfone composite ultrafiltration membranes. The result shows that Fe3O4@CNTs migrate to the separation layer of membranes under the induction of a low‐intensity magnetic field. The surface and overall porosity of the membranes increase and the surface roughness of the membranes decreases. The contact angle of composite ultrafiltration membranes decreases from 78.0° to 60.1°, indicating an improvement of hydrophilicity. The pure water permeance of the composite ultrafiltration membranes increases from 240.1 to 524.7 L m−2 h−1while retaining a high bovine serum albumin rejection (&gt;96.8%). Moreover, the antifouling property of the composite ultrafiltration membranes is significantly improved, and the flux recovery ratio increased from 56.2% to 80.9%.

Preparation of disc ceramic membrane by a printing and dip-coating method for oil-water separation

Efficient separating oil-water emulsion, it is required that ceramic membranes have the suitable membrane pore size, narrow pore size distribution and low membrane fouling. To realize it, thin and defect-free membrane separation layer should be directly prepared on the large pore size support surface, and the membrane under a dynamic filtration mode. In the present work, disc ceramic membrane without any transition layer was fabricated directly on the surface of support with a pore-size of 3.8 µm via a printing and dip-coating method. The mesh aperture and printing times regulate the thickness of printing layer, preventing the small alumina particles from penetrating into the support. Meanwhile, Dip-coating layer effectively eliminate the defects of the printing layer. Compared with common ceramic membranes, the prepared disc ceramic membrane has a low-cost and high permeability of 1946.6 L/m2·h·bar. Furthermore, the disc ceramic membrane can significantly mitigate membrane fouling and improve the oil-water separation efficiency (>99.5%) under a dynamic membrane filtration mode. This study suggests the practicability of printing and dip-coating method to prepare the disc ceramic membrane with high performance.

Advanced Mg2+/Li+ separation nanofiltration membranes by introducing hydroxypropyltrimethyl ammonium chloride chitosan as a co-monomer

In recent years, the global demand for lithium resources has been constantly rising thanks to the rapid development of the new energy industry. Nanofiltration (NF) membranes with positive charge could achieve high efficiency separation performance of magnesium ion (Mg2+)/ lithium ion (Li+), which provides a useful solution for the extraction and recovery of lithium resources from brine. In this work, hydroxypropyltrimethyl ammonium chloride chitosan (HACC) was introduced into the interfacial polymerization (IP) as co-monomer with piperazine (PIP) to react with trimesoyl chloride (TMC) for preparing positively charged NF membranes. Based on the modulation of IP process by HACC, the thickness of the modified NF membrane separation layer reduced and the hydrophilicity increased, while the pore size had no obvious variation. In addition, the introduction of the quaternary ammonium group in HACC also increased the antibacterial properties of the NF membrane. The optimized NF-HACC-0.3 not only improved the separation factor significantly, but also increased the flux by 2 times compared with the original membrane. This strategy provides a new valuable idea and insight for the preparation and development of Mg2+/Li+ separation NF membranes.

Microstructure adjustment of an asymmetric ceramic membrane with high permeation performance

Abstract An asymmetric alumina ceramic membrane was prepared by secondary dip coating. The influence of different dispersants and dip coating parameters on the microstructure of the membrane separation layer was explored. Meanwhile, the pure water fluxes of the membranes with various microstructures were also studied. The results show that a separation layer with a defect-free thickness of 16.5 μm and high surface flatness can be obtained when using polycarboxylate as a dispersant and twice dip coating within 2 s + 1 s and the pure water flux of an asymmetric membrane up to 1153 L × m-2 × h-1 × bar-1. The present work provides a simple and effective method for controlling the morphology and permeation performance of an asymmetric alumina membrane.

Development of cellulose acetate-chitosan-metal organic framework forward osmosis membrane for recovery of water and nutrients from wastewater

Aluminium fumarate (AlFu) metal organic framework (MOF) incorporating forward osmosis (FO) membrane prepared by coating chitosan (CS)-AlFu MOF mix on cellulose acetate (CA) membrane. AlFu MOF in the membrane separation layer enhanced hydrophilicity and resulted in higher water flux and lower reverse salt flux than CA or the CA-CS membranes. The M-1–0.06 membrane with 1% CS coating and 0.06 wt% AlFu MOF addition identified to be optimal. Using MgCl2.6 H2O as the draw, the membranes tested for concentration of nutrients from synthetic wastewater (SW) and real wastewater (RW) from a cowshed. For the SW feed, M-1–0.06 displayed enhanced water flux (18 LMH compared to 11.8 LMH for CA membrane) and accumulation (concentration) of components as follows: COD (2X), NH4-N (1.9X), NO3-N (0.76X) and PO4 (0.85X). With RW feed, the water flux was lower (8.75 LMH), but components concentration was higher: COD (3.75X), NH4-N (4.46X), NO3-N (3.35X) and PO4 (5.1X). Fouling due to cake layer deposits on the membrane surface could be removed by physical cleaning. Over 80% water recovery obtained in FO, and 85% salt rejection was obtained from diluted draw solution using reverse osmosis (RO). The nutrients in concentrated feed wastewater recovered as struvite (NH4MgPO4.6 H2O) by precipitating, using the RO reject, which was also the re-concentrated draw solution for the next FO experiment.

High flux polysulfone braided hollow fiber membrane for wastewater treatment role of zinc oxide as hydrophilic enhancer

Incorporation of zinc oxide (ZnO) nanoparticles has played an important role on the improvement of unique membrane characterization and performance, most notably the hydrophilic modification of the membrane for higher pure water permeability. Additionally, the permeability of the membrane can be improved via introduction of braid support by reducing the thickness of the membrane separation layer. Moreover, the braided hollow fiber membrane (BHFM) is able to perform under higher pressure conditions compared to hollow fiber membranes. In this paper, hybrid polysulfone (PSf)/ZnO BHFMs were fabricated via phase inversion method. Hydrophilic 10 ± 1.8 nm polycrystalline ZnO nanoparticles synthesized via sol-gel method were incorporated on BHFM to improve the hydrophilicity and increase flux with constant rejection under high pressure and the effect of the ZnO loading on the membrane properties and performance were thoroughly studied. The fabricated BHFMs with 0.0, 0.5, 1.0 and 1.5 wt% of ZnO nanoparticles concentration were defined as BHFM1, BHFM2, BHFM3 and BHFM4 respectively. Scanning electron microscopy (SEM), contact angle, mechanical strength, flux performance, rejection with bovine serum albumin (BSA) and fouling of best performed membrane were conducted to achieve the target of this paper. The performance of these hybrid ZnO/PSf BHFMs were compared with neat PSf hollow fiber membrane (HFM) and previous studies. The findings from this research work shows that BHFM4 has the most desired properties for wastewater treatment application. The ZnO nanoparticles in BHFM4 have improved hydrophilicity from 108.79° to 71.02°, and thus BHFM4 has increased flux performance from 36.20 to 919.12 L/m2 h at 1.0 bar pressure and 193.48 to 1909.11 L/m2h at 4.0 bar pressure when compared with BHFM1. Constant BSA rejection rates (> 90%) were observed in all BHFMs. The improved hydrophilicity and pure flux performance with constant rejection rate in high pressure conditions illustrates the suitability of fabricated ZnO/PSf BHFMs in wastewater treatment applications.

Efficient removal of dyes and proteins by nitrogen-doped porous graphene blended polyethersulfone nanocomposite membranes

Nitrogen-doped porous graphene oxide (N-PGO) was synthesized, characterized, and applied as a hydrophilic nanomaterial in fabrication of polyethersulfone (PES) membrane for Reactive Red 195 dye and bovine serum albumin (BSA) protein separation. The N-PGO nanosheets not merely showed a good adhesion towards polymers, but simultaneously promoted hydrogen bonding action. Therefore, high-efficiency permeation passageway in the separation layer of membranes was attained. X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDX) and Fourier transform infra-red spectroscopy (FTIR) analyses approved nitrogen doping, which increased hydrophilicity and hydrogen bonding ability of PGO in water filtration. The pure water permeation of nanocomposite membranes could reach as high as 190 L m−2 h−1 at 3 bar. A dye rejection efficiency higher than 92% and BSA rejection higher than 95% were accordingly obtained. Atomic force microscopy (AFM) images approved formation of a rough surface that was decreased by addition of low amounts of the PGO. SEM images provided from the surface also confirmed enlarged pore size and increased porosity. Antifouling properties were investigated by BSA filtration, and results showed that the flux recovery ratio of the N-PGO membrane was improved. Overall, the N-PGO hybrid membranes exhibited potential for application in separation of typical proteins and dyes with good antifouling properties.

Effects of gamma-ray irradiation on separation and mechanical properties of polyamide reverse osmosis membrane

This study investigates the effects of gamma rays at different total irradiation doses on polyamide reverse osmosis (RO) membranes under aqueous or anhydrous conditions. ATR–FTIR, XPS, Raman, SEM and AFM microscopes are used to observe the chemical structure and morphology of the membrane separation layer before and after irradiation. The effects of irradiation on the filtration properties (water flux and salt rejection), mechanical properties and hydrophilic properties of RO membranes are examined. Results show that the degradation mechanism or path of the membrane separation and support layers are different under aqueous and anhydrous conditions. The results of different analyses reveal that the rupture of amide bond under anhydrous conditions is significantly higher than that under aqueous conditions. Under both conditions, when the total radiation dose was less than 100 kGy, the performance of polyamide membrane is slightly improved. Thus, irradiation positively affects the membrane. When the dose reached 200 kGy, chain breakage and collapse due to radiation are widespread, thereby yielding prominent changes in the properties and morphology of the membrane, most seriously under the anhydrous condition. This study provides a reference for the application of polyamide RO membrane in radioactive liquid waste and an effective method for the modification of polyamide membranes.

Continuous gas-phase hydroformylation of but-1-ene in a membrane reactor by supported liquid-phase (SLP) catalysis

The development of a supported liquid phase (SLP) gas-phase hydroformylation catalyst combined with a monolithic membrane separation layer is reported.

Next-Generation Asymmetric Membranes Using Thin-Film Liftoff.

For the past 30 years, thin-film membrane composites have been the state-of-the-art technology for reverse osmosis, nanofiltration,ultrafiltration, and gas separation. However, traditional membrane casting techniques, such as phase inversion and interfacial polymerization, limit the types of material that are used for the membrane separation layer. Here, we describe a novel thin-film liftoff (T-FLO) technique that enables the fabrication of thin-film composite membranes with new materials for desalination, organic solvent nanofiltration, and gas separation. The active layer is cast separately from the porous support layer, allowing for the tuning of the thickness and chemistry of the active layer. A fiber-reinforced, epoxy-based resin is then cured on top of the active layer to form a covalently bound support layer. Upon submersion in water, the cured membrane lifts off from the substrate to produce a robust, freestanding, asymmetric membrane composite. We demonstrate the fabrication of three novel T-FLO membranes for chlorine-tolerant reverse osmosis, organic solvent nanofiltration, and gas separation. The isolable nature of support and active-layer formation paves the way for the discovery of the transport and selectivity properties of new polymeric materials. This work introduces the foundation for T-FLO membranes and enables exciting new materials to be implemented as the active layers of thin-film membranes, including high-performance polymers, two-dimensional materials, and metal-organic frameworks.

New Generation of Mesoporous Silica Membranes Prepared by a Stöber-Solution Pore-Growth Approach.

Membranes consisting of uniform and vertically organized mesopores are promising systems for molecular filtration because of the possibility to combine high-flux and high-rejection properties. In this work, a new generation of mesoporous silica membranes (MSMs) have been developed, in which an organized mesoporous layer is directly formed on top of a porous ceramic support via a Stöber-solution pore-growth approach. Relevant characterization methods have been used to demonstrate the growth of the membrane separation layer and the effect of reaction time and the concentration of the reactants on the microstructure of the membrane. Compared to previous studies using the evaporation-induced self-assembly method to prepare MSMs, an important increase in water permeability was observed (from 1.0 to at least 3.8 L m–2 h–1 bar–1), indicating an improved pore alignment. The water permeability, cyclohexane permporometry tests, and molecular cut-off measurements (MWCO ≈ 2300 Da) were consistent with membranes composed of 2–3 nm accessible pores.

Photocatalytic self-cleaning carbon nitride nanotube intercalated reduced graphene oxide membranes for enhanced water purification

Crumpled laminar nanostructures with nanoscale water transport channels constructed by two-dimensional (2D) reduced graphene oxide nanosheets (rGO NS) have been considered as a promising membrane separation layer for water purification. However, efficient tuning of rGO laminar structures with enhanced membrane performance remains challenging. In this work, we report a novel 1D graphitic carbon nitride nanotube (g-C3N4 NT) intercalated rGO nanofiltration (NF) membrane with enhanced photo-induced self-cleaning performance. The g-C3N4 NT photocatalyst could not only enlarge the rGO interlayer spacing for improved water permeability, but also endow the composite membrane with visible-light photocatalytic activity for efficient removal of organic dyes from polluted water. Our g-C3N4 NT/rGO membrane exhibits superior water permeability (4.87 L·m−2·h−1·bar−1) and synergetic Rhodamine B (RhB) removal rate (>98%) for long-term operation, compared with pristine rGO membrane and 2D g-C3N4 NS intercalated rGO membrane prepared by the same method. The RhB removal mechanism on the as-prepared composite membranes under integrated photocatalytic filtration process is presented. Our findings offer new insights into designing and tuning laminar structures of photocatalytic graphene-based NF membranes for enhanced water purification.

Porous graphene nanosheets functionalized thin film nanocomposite membrane prepared by interfacial polymerization for CO2/N2 separation

The inherent defects of porous graphene (PG) formed during reduction etching process could serve as nanopores, making PG emerge a potential application for the preparation of micrometre-sized separation membranes. Here, we introduced PG as inorganic nanofiller to fabricate thin film nanocomposite (TFN) membranes for CO2 capture via interfacial polymerization technique. The PG selective nanolayers not only possessed a good adhesion with polymers but also benefited from hydrogen bonding actions, simultaneously, thus ensuring the formation of high-efficiency molecular sieving passageway in the separation layer of membranes. Furthermore, the thin PG nanosheets were verified to have an significantly affect for permeability and selectivity of membranes (PG, 0.05wt%, 1bar), with exhibiting about 21% and 20.8% enhancement of the CO2 permeance and the CO2/N2 selectively compared to that of the membrane without PG separately. Simultaneously, the membrane also showed higher stability and the porous surface morphology of PG shortened greatly the gas transfer path. The approach offers a potential promising to exploit the ultra-thin film composite membrane for efficient gas separation.

Investigations on the behaviour of ceramic micro- and mesoporous membranes at hydrothermal conditions

Hydrothermal processes can be used for extraction, reaction or analytical purposes. In combination with membrane technologies, energy consumption of such processes can be reduced considerably in terms of a nearly isobaric and isothermal regeneration of the hot and pressurized fluid. However, investigations on the performance of this hybrid process concept require experimental data on the use of membrane processes under hydrothermal conditions.Consequently, the main objective of this work is the determination of characteristics such as permeation and filtration behaviour for several ceramic, asymmetric micro- and mesoporous membranes (TiO2/ZrO2) with average pore diameters from 0.9 to 3.0nm at hydrothermal conditions. Performed studies are comprised of experimental investigation of pure water permeance and organic model substance retention in dependence on feed pressure (200–375bar), feed temperature (40–140°C) and transmembrane pressure (5–25bar). All investigations were carried out in a newly developed stainless steel membrane separation apparatus.Due to seriously corrosive hydrothermal conditions, a degradation of the glass coated membrane end seals and the membrane separation layer at temperatures above 140°C has been observed. Subsequently, an inorganic and more stable end seal has been designed. Moreover, this work gives a first promising approach for stabilizing the membrane separation layer by Y2O3 modification. As a result, pure water permeance has been found to be independent of feed and transmembrane pressure, but showed an almost linear dependence on feed temperature.In a following step, the filtration characteristic towards organic model substances such as Inulin and Neohesperidin dihydrochalcone (NHDC) has been studied. Experimental results showed retention up to 88% for Inulin and 75% for NHDC.

Effects of ordered mesoporous silica on the performances of composite nanofiltration membrane

Surface modified composite nanofiltration (MCNF) membrane was prepared by traditional interfacial polymerization approach using trimesoyl chloride and piperazine as reacting monomers, mesoporous silica SBA-15 as a surface modification additive, for investigating the influences of mesoporous-silica introduction on the membrane performances. Its surface properties and microstructures were carefully characterized by various analyzing instruments. Furthermore, the rejection performance was tested using 2000ppm of MgSO4 aqueous solution under 1MPa working pressure. Its fouling-resistance performance was also evaluated by using bovine serum albumin as an organic pollutant model, based on the changes of permeate flux in the running process. The experimental results show that the introduction of SBA-15 material can obviously enable the permeate flux of the NF membrane to be increased from 32.4 to 45.6L/h·m2, accompanied with slight decrease of MgSO4 rejection from 97.88 to 85.23%. The SBA-15 modified MCNF membrane exhibits excellent fouling-resistance performance, with the permeate flux still retaining 72.53% of the initial flux value, after the anti-fouling test running for 270min. The introduction of SBA-15 significantly improves the hydrophilicity, effective surface area and pore size of the membrane separation layer, which is favorable for the enhancement of permeate flux and fouling-resistance performances.

Solvent sorption measurements in polymeric membranes with ATR-IR spectroscopy

Long-term stability and performance of polymeric membranes in solvent and mixed solvent media can be reduced due to sorption and swelling of the membrane matrix. For this reason quantification of sorption and swelling is of major importance for the development of future applications of membrane processes in solvent and mixed solvent media. In this work a method is discussed, based on attenuated total reflectance infrared spectroscopy (ATR-IR), to establish sorption and sorption selectivity of a cellulose acetate (CA) membrane in water/methanol and water/ethanol mixtures. By analysis of specific peaks from the ATR-IR spectra of the solvents, the preferential sorption of water in CA membranes can be quantified. In the presence of methanol, the selectivity for water ranges from 2.5 to 3.5 between 52 and 90% of methanol. For ethanol, the selectivity for water ranges from about 1 (30% ethanol) to 2 (90% ethanol). From the work it follows that ATR-IR provides an easy and non-destructive method to study the sorption behavior of the polymeric membrane separation layer.