Separation Performance Of Membranes Research Articles

Preparation of Thin Film Composite (TFC) Membrane with DESPs Interlayer and Its Forward Osmosis (FO) Performance for Organic Solvent Recovery.

To explore the application of forward osmosis (FO) technology in the organic solvent recovery field, we prepared a new solvent-resistant triple layer thin film composite (TFC) membrane on the PI (polyimide) substrate. The deep eutectic supramolecular polymers (DESPs) interlayer was constructed on the substrate to improve the separation performance and solvent resistance. DESPs interlayer was formed by mixing and heating with cyclodextrin as the hydrogen bond acceptor and L-malic acid as the hydrogen bond donor. The chemical changes, surface property and morphology of the composite membrane with DESPs interlayer were characterized. The separation performance and stability of the triple layer composite membrane in organic solvent FO were studied. For the monascorubrin-ethanol system, the permeation flux of TFC/DESPs5-PI membrane could reach 9.51 LMH while the rejection rate of monascorubrin was 98.4% (1.0 M LiCl/ethanol as draw solution), which was better than the pristine membrane. Therefore, this solvent-resistant triple layer composite FO membrane has good potential for the recovery of organic solvents.

Mixed matrix iongel membranes containing azo-porous organic polymers: Influence of temperature, pressure and water vapour on CO2 separation

The effect of temperature, pressure, and humidity content in the gas separation performance of iongel membranes are crucial parameters that should be assessed to determine the real potential of these materials to be used in CO2 separation processes. In this work, we present a detailed study on the impact of temperature (303, 323 and 353 K), pressure (2 and 4 bar), gas composition and water vapour content (between 11 and 21% of relative humidity) on the performance of iongels containing azo-porous organic polymers (azo-POPs), for CO2/N2 and CO2/CH4 binary gas separations. The iongels combining 80 wt% of the ionic liquid (IL) [C2mim][TFSI], 20 wt% of poly(ethylene glycol) diacrylate (PEGDA) and 0.5 wt% of different azo-POPs were prepared by a solvent-free UV curing method. At the lower temperature, the pressure increase seems to have a negative impact on the CO2 permeability of the prepared mixed matrix iongel membranes (MMIMs). However, the opposite behaviour was found when the temperature increases. Moreover, the presence of humidity in the feed gas stream affects the gas separation performance of the studied iongels, since the CO2 permeability greatly increases with increasing humidity in the gas mixture, while the selectivity decreases, for both gas separations under study. In general, the high pressure and temperature, and the presence of humidity have a significant influence on the separation performance of the studied iongel membranes, due to induced alterations in their structure and overall stability.

Surface coating of membrane by cationic photopolymerization of oxetane-terminal poly(ethylene glycol) for enhanced dye/salt separation and chlorine-resistant performance

Cationic photopolymerization is well-known for its tolerance with oxygen and low shrinkage of coating; however, its application for surface coating is limited due to the lack of functional oligomers. Herein, poly (ethylene glycol) (PEG) with terminal oxetane groups was prepared and used for the coating of membrane by rapid cationic photopolymerization. The structure and separation performance of membrane could be regulated by adjusting the molecular weight of PEG and the UV radiation time. The hydrophilicity and filtration performance of membrane has been significantly enhanced after cationic photopolymerization. Finally, the composite membrane showed excellent performance to dye/salt separation and superior chlorine resistance, with flux and retention remaining stable over a 14-day test.

Inhibiting Polyamide Intrusion of Thin Film Composite Membranes: Strategies and Environmental Implications.

Thin film composite polyamide (TFC) nanofiltration (NF) membranes represent extensive applications at the water-energy-environment nexus, which motivates unremitting efforts to explore membranes with higher performance. Intrusion of polyamide into substrate pores greatly restricts the overall membrane permeance because of the excessive hydraulic resistance, while the effective inhibition of intrusion remains technically challenging. Herein, we propose a synergetic regulation strategy of pore size and surface chemical composition of the substrate to optimize selective layer structure, achieving the inhibition of polyamide intrusion effective for the membrane separation performance enhancement. Although reducing the pore size of the substrate prevented polyamide intrusion at the intrapore, the membrane permeance was adversely affected due to the exacerbated "funnel effect". Optimizing the polyamide structure via surface chemical modification of the substrate, where reactive amino sites were in situ introduced by the ammonolysis of polyethersulfone substrate, allowed for maximum membrane permeance without reducing the substrate pore size. The optimal membrane exhibited excellent water permeance, ion selectivity, and emerging contaminants removal capability. The accurate optimization of selective layer is anticipated to provide a new avenue for the state-of-the-art membrane fabrication, which opens opportunities for promoting more efficient membrane-based water treatment applications.

Separation performance and fouling analyses of nanofiltration membrane for lithium extraction from salt lake brine

In this study, the separation performance of NF membrane for magnesium and lithium in salt lake brine with a high magnesium-to‑lithium mass ratio and membrane fouling properties were investigated. The results showed that the retention rates for magnesium and lithium were higher than 81 % and less than −69 %, respectively. The mass ratio of magnesium and lithium in the permeate reduced 8.5 times and the yield of lithium was 83 % after separation indicating the effective lithium recovery for DK NF membrane. However, the polyamide functional groups of the DK NF membrane showed redshift after fouling, and inorganic ions (Mg and Ca) and carboxyl groups were increased on the membrane surface. Furthermore, functional layer and spongy porous structures of the NF membrane were damaged after pollution decreasing the effective membrane area and pore size. Moreover, the hydrophilicities of the fouled membranes decreased, while their electronegativities increased. Therefore, the NF membrane exhibited a decreased separation performance after long-term recovery of lithium from brine. Nanofiltration fouling showed that trace calcium in salt lake brine with a high magnesium-to‑lithium mass ratio was the crucial factors on membrane fouling, and thus calcium could be reduced in the recovery of lithium from brine via nanofiltration.

Ionic liquid assisted interfacial polymerization of β-Cyclodextrin into thin-film composite membranes for organic solvent nanofiltration

β-cyclodextrin (β-CD), with intrinsic nano-cavity, is a promising monomer to construct thin-film composite (TFC) membranes for molecular separations. Nevertheless, interfacially polymerize β-CD into continuous membranes is challenging due to the low reactivity of hydroxyl groups. To address this issue, in this work, ionic liquid (IL) has been introduced into the interfacial polymerization (IP) process of β-CD and trimesoyl chloride (TMC), forming high-quality TFC membranes for organic solvent nanofiltration (OSN). Investigations have been done into how IL effects membrane structure and separation performance. In contrast to traditional β-CD-TMC TFC membrane, the β-CD-IL-TMC TFC membrane possesses upgraded crosslinking, continuity, stability, and OSN separation property. The best β-CD-IL-TMC membrane has an ethanol permeance of up to 57.01 L m−2h−1 MPa−1 and Naphthol green B rejection rate of 99.98% and can sustain a stable separation performance within 20-hour test, indicating the fabricated β-CD-IL-TMC membranes have advantage of separating and purifying organic solvent.

Preparation of Cross-Sectional Membrane Samples for Scanning Electron Microscopy Characterizations Using a New Frozen Section Technique.

Characterization of the cross-sectional morphologies of polymeric membranes are critical in understanding the relationship of structure and membrane separation performances. However, preparation of cross-sectional samples with flat surfaces for scanning electron microscopy (SEM) characterizations is challenging due to the toughness of the non-woven fabric support. In this work, a new frozen section technique was developed to prepare the cross-sectional membrane samples. A special mold was self-designed to embed membranes orientationally. The frozen section parameters, including the embedding medium, cryostat working temperature, and sectioning thickness were optimized. The SEM characterizations demonstrated that the frozen section technique, using ultrapure water as the embedding medium at a working temperature of -30 °C and a sectioning thickness of 0.5 µm, was efficient for the preparation of the membrane samples. Three methods of preparation for the cross-sectional polymeric membranes, including the conventional liquid nitrogen cryogenic fracture, the broad ion beam (BIB) polishing, and the frozen section technique were compared, which showed that the modified frozen section method was efficient and low cost. This developed method could not only accelerate the development of membrane technology but also has great potential for applications in preparation of other solid samples.

Mixed-linker MOF-303 membranes for pervaporation

Metal-organic frameworks (MOFs) hold great promise as porous materials for pervaporation applications. However, the exploration of MOF membranes in this field is still in its early stages. One of the main challenges is the relatively low mass flux and stability of pure MOF membranes compared to other materials used in pervaporation. In this study, we propose a novel approach to enhance the separation performance of MOF membranes for water and ethanol separation. Our strategy involves incorporating the 2,5-thiophenedicarboxylic acid (TDC) linker into the MOF-303 structure, partially replacing the 3,5-pyrazoledicarboxylic acid (PDC) linker. The goal is to increase the aperture size of the microporous channels in the pristine MOF-303 membrane, thereby improving the mass flux. X-ray diffraction characterization, combined with Rietveld refinement, confirmed that the partial substitution of PDC with TDC resulted in an increased pore-limiting diameter (PLD) of MOF-303. For instance, the pristine MOF-303 exhibited a PLD of 5.78 Å, while MOF-303(70/30) with 70% TDC replacement displayed a PLD of 6.02 Å. To fabricate the mixed-linker MOF-303 membranes, we utilized a seeded growth method, which yielded membranes with dense layers, as confirmed by scanning electron microscopy and air permeation characterization. The prepared membranes were subjected to pervaporation tests to evaluate their performance in separating 90 wt.% ethanol at 60 °C. The pristine MOF-303 membrane exhibited notable separation capabilities, with an average flux of 0.071 kg·m−2·hr−1 and a water/ethanol separation factor of 5371. Surpassing the unmodified MOF-303, the mixed-linker MOF-303(50/50) membrane demonstrated improved mass flux and water/ethanol separation factor. Specifically, the MOF-303(50/50) membrane displayed an average flux of 0.092 kg·m−2·hr−1 and a water/ethanol separation factor of 8500. Importantly, the unmodified MOF-303 membrane exhibited instability during prolonged pervaporation operation, whereas the mixed-linker MOF-303(50/50) membrane effectively addressed this issue. Further analysis using in situ Fourier transform infrared spectroscopy and water adsorption characterization revealed that MOF-303(50/50) possessed a strong affinity for water, comparable to the pristine MOF-303. Overall, our study highlights the potential of the mixed-linker approach to optimize the separation performance and stability of MOF-based membranes for pervaporation application.

Enhancing CO2/(light gases) separation performance of Pebax-based mixed-matrix membranes by [BMIM][AC] ionic liquid

Incorporating the proper additive with an affinity towards target gases is considered a helpful strategy for simultaneously improving membrane permeability and selectivity. In this research, the superior features of polyetherblockamide polymer (Pebax1657), 1–Butyl3–methylimidazolium acetate ([BMIM][AC]) ionic liquid (IL), and aluminum oxide (Al2O3) nanoparticles were blended to produce efficient ternary mixed-matrix membranes for CO2 removal from light gases. The fabricated membranes structures have been evaluated by FTIR3ATR, FESEM, XRD, and DSC analyses. The permeation rates of unmixed CH4, N2, and CO2 gases through the resulting membranes were obtained at 25 °C and a feed pressure range of 4–10 bar. The gas permeability results showed that embedding Al2O3 nanoparticles as the loading up to 6 wt% increased the CO2/(light gases) separation performance. Besides, adding the IL into the polymer matrix boosted the membranes gas separation efficiencies caused by the increased CO2 solubility and their fractional free volume. The results also revealed that the resulting membrane containing 15 wt% of [BMIM][AC] IL and 6 wt% of Al2O3 nanoparticles, which has the best gas separation efficiency, is the optimum ternary mixed-matrix membrane. The comparison between the optimized membrane and the unloaded one efficiencies demonstrated that CO2/N2 and CO2/CH4 selectivities, along with the CO2 permeability, rose from 63.40, 19.93, and 115.39 Barrer for the unloaded membrane to 81.18, 25.14, and 166.42 Barrer for the optimum membrane (around 28 %, 26 %, and 44 % increments), at 10 bar and 25 °C, respectively.

Improvement of persistent hydrophilicity and pore uniformity of polyvinyl chloride ultrafiltration membranes by in-situ crosslinking reaction assisted phase separation

A novel in-situ crosslinking reaction assisted phase separation strategy was proposed for persistent hydrophilization and pore size regulation of polyvinyl chloride (PVC) membranes. In-situ cross-linking between PVC molecular chains was achieved through grafting of 3-aminopropyltrimethoxysilane (APTMS) during the dissolution process and cross-linking reactions between siloxanes in APTMS molecules initiated by the coagulation bath (water). The effect of in-situ crosslinking reaction on the structure, separation and anti-fouling performance of the PVC membranes was studied. Through in-situ crosslinking reaction induced phase separation, the migration and curing of polymer molecular chains in the phase separation process were regulated, which endowed the modified membrane with improved hydrophilicity, higher porosity and narrow pore size distribution. The pure water flux of the obtained membrane increased 3.5 times as much as that of the pure PVC membrane. In addition, the flux recovery rate (FRR) of the obtained membrane was increased by 15.9% and the strength was also increased slightly at the same time. The stability of the membranes was also improved, without chemical agents leaching during filtration, avoiding secondary pollution to our environment.

Enhancing fouling resistance and separation performance of polyethersulfone membrane through surface grafting with copolymerized thermo-responsive polymer and copper oxide nanoparticles

Surface modification is a critical aspect for improving the efficiency of membranes and reducing the risk of fouling in applications such as wastewater treatment and oil/water separation. The objective of this study is to minimize membrane fouling and maximize its rejection rate through surface modification. Here, for the first time, we developed a dual-functionalized PES membrane using a two-step process, involving grafting with a thermo-responsive polymer (P(NIPAm-co-AAm)) and subsequent functionalization with copper oxide nanoparticles. The membranes were evaluated for any changes in their chemical composition, structural properties, porosity, surface charge, and wetting characteristics. The hydrophilicity of all the modified membranes increased as indicated by a noticeable reduction in the water contact angle. The modified membranes displayed a change in their receding water contact angle based on changes in water temperature, confirming the thermo-responsive nature of PNIPAm. The receding contact angle for the PES membrane grafted with P(NIPAm-co-AAm) was significantly low (∼13°) below 33 °C but increased to 28° when the temperature exceeded 40 °C, indicating the dependence of the surface wettability of the treated PES membranes on temperature. The dual-functionalized membrane outperformed the pristine PES membrane, with a 13% increase in flux and 26% rise in flux recovery ratio. Additionally, the CuO@PES-g-P(NIPAm-co-AAm) membrane showed significant improvements in contaminant rejection and antifouling ability, with > 98% rejection rate for both oil-water emulsion and bovine serum albumin (BSA). The achieved separation and antifouling properties make the dual-functionalized membrane an excellent candidate for water treatment and demonstrate the efficacy of our simple modification process.

Fabrication of a New Rationally Designed Mussel-Inspired Cationic Amphiphilic Terpolymer to Enhance the Separation and Anti-Fouling Performance of Membranes.

Polyvinylidene fluoride (PVDF) membrane-based systems for treating oily wastewater are prone to fouling. Herein, we introduced a novel mussel-inspired cationic amphiphilic terpolymer consisting of monomers N,N-diallyldimethylammonium chloride (DADMAC), N,N-diallyltetradecan-1-ammonium chloride (DTDAC), and mussel-inspired N,N-diallyldopamine hydrochloride (DADAHC) to improve the performance and characteristics of the PVDF membranes for oil-in-water emulsion separations. The cationic terpolymer, poly(DADMAC-co-DTDAC-co-DADAHC), shortened as PDDD, was synthesized in excellent yields via free radical polymerization and has good compatibility with the PVDF owing to the presence of hydrophobic long alkyl chains in DTDAC. The presence of dopamine motifs helps stabilize the PDDD-PVDF membrane by chelating with Fe3+ ions. The water contact angle on the PDDD-incorporated PVDF membranes was reduced from 87.6 to 54.6°, demonstrating improved hydrophilicity than pristine PVDF (M-0). The incorporation of PDDD into the PVDF improved the separation efficiencies of the membrane, which reached up to 99% while treating the oil-in-water emulsions. Incorporating PDDD into PVDF has significantly enhanced the anti-fouling characteristics of the membranes, which are indicated by their remarkable flux recovery ratio (FRR) (up to 92%). The hydrophobic and hydrophilic groups worked synergetically to enhance the performance of the fabricated membrane.

Tuning the Phase Composition of Metal-Organic Framework Membranes for Helium Separation through Incorporation of Fullerenes.

Metal-organic framework (MOF) membranes have attracted significant research interest in gas separation, but efficient helium (He) separation remains a challenge due to the weak polarizability of He and the intrinsic pore size flexibility of MOFs. Herein, incorporated fullerenes (C60 and C70) were used to tune the crystallographic phase composition of ZIF-8 membranes, thus creating small and fixed apertures for selective He permeation. The fullerene-modified ZIF-8 (C60@ZIF-8 and C70@ZIF-8) membranes contain about 20% of the rigid-lattice ZIF-8_I-43m phase and have been prepared as 200-350 nm thick supported layers through electrochemical synthesis. They show a significantly enhanced molecular sieving for He/N2,CH4 together with a satisfactory He permeance of >200 GPU. Specifically, the He/N2 selectivity of the C70@ZIF-8 membrane is up to 30.4, which is much higher than that of the fullerene-free ZIF-8 membrane (5.1) and nearly an order of magnitude higher than those of other reported He-selective MOF membranes. A continuous long-term gas permeation test over 780 h under dry and humid conditions proved the excellent stability of the fullerene-modified ZIF-8 membranes. The general validity and versatility of the proposed strategy for MOF membrane preparation are also demonstrated by the enhancement of the separation performance of a fullerene-modified ZIF-76 membrane.

A self-supported agZIF-UC-4 glass membrane for gas separation

Metal-organic framework (MOF) membranes have become promising candidates for gas separation due to their adjustable structure, high separation performance, and environmental friendliness. However, the emergence of grain boundary defects, and interface defects between the support layer and separation layer significantly decrease the gas separation performance of MOF membranes. Herein, a self-supported ZIF (zeolitic imidazolate framework) glass membrane is fabricated, eliminating grain boundary defects and cracks through the molten-liquid phase. The fluorine-based linkers with high electronegativity and polarizability are introduced to enhance agZIF-62(a and g denote amorphous and glass, respectively) interaction of CO2 and CH4. The CO2/N2 and CH4/N2 ideal selectivity of agZIF-UC-4 membrane (fluorine-based, UC-4 named by Cambridge University) reach 36 and 6.2, respectively. In addition, the CO2 and CH4 permeance of the agZIF-UC-4 membrane with an independent separation layer and the non-grain boundary has improved to 4752 and 818 GPU, respectively. Under the mixed gas condition, agZIF-UC-4 membrane exhibits good separation performance, exceeding the 2019 Mckeown upper bond of CO2/N2. Moreover, agZIF-UC-4 membrane has good stability for CO2/N2 and CH4/N2 under continuous operation and variable pressure testing. Hence, the self-supported agZIF-UC-4 membrane is a potential candidate for preparing MOF glass membranes with good gas separation performance.

Enhancing the Antimicrobial and Anti-biofouling Properties of Polyamide Composite Membrane Grafted with Polyhexamethylene Guanidine (PHMG)

In this work, a thin-film composite polyamide membrane with antimicrobial polyhexamethylene guanidine (PHMG) was fabricated by the combination of photo-induced and chemical grafting to enhance the antifouling and anti-biofouling properties of the membrane. The surface properties of the membrane were evaluated using field-emission scanning electron microscopy (FE-SEM) images, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), water contact angle (WCA) values, and antimicrobial activity of the membrane. The membrane separation performance was evaluated by the flux and the ability to retain Ca2+ ions in water. The antifouling and anti-biofouling properties were evaluated by the maintained flux ratios after 9 hour-filtration of humic acid and bovine serum albumin (BSA) solutions. The results showed that the grafted membrane’s surface became tighter (the retention increased from 97.3% to 98.6%), and no bacteria were observed on the surface of the grafted membrane. Meanwhile, the anti-fouling and anti-biofouling properties were also improved compared to the original membrane.

Screening of high-efficiency crosslinking agents for poly(N,N-dimethylaminoethyl methacrylate) and performance of its nanofiltration membranes

Poly(N,N-dimethylaminoethyl methacrylate) (PDM) is a water-soluble polymer that can be crosslinked via a quaternization reaction that takes 4–20 h. Polyhalogenated hydrocarbons with different structures were screened to identify high-efficiency crosslinking agents for PDM. For this purpose, the gelation time of bulk crosslinked PDM and the separation performance of interfacially crosslinked PDM membranes were investigated. Use of bromohydrocarbons with benzylic and allylic types and high functional group density can afford the rapid quaternization reaction of PDM. PDM nanofiltration membranes were prepared via interfacially crosslinking PDM with 1,3,5-tris(bromomethyl)benzene (TBB), and the effects of membrane preparation conditions (including PDM concentration, coating time, TBB concentration, and crosslinking time) on the permeation and separation performances of as-prepared membranes were investigated. The PDM membrane prepared at a PDM concentration of 6 g/L, TBB concentration of 40 mmol/L, coating time of 30 s, and crosslinking time of 30 s exhibited a water flux of 20.3 L/(m2·h) and a salt rejection of 90%, when the membrane was treated with a 1000 mg/L MgSO4 aqueous solution at 0.8 MPa pressure. The PDM membrane was positively charged and the extent of salt rejection followed the order MgCl2 > NaCl ≈ MgSO4 > Na2SO4. The membrane also exhibited good antifouling properties and chlorine resistance.

Facile and green synthesis of disordered mesoporous silica as biogenic filler for mixed-matrix membranes

Disordered mesoporous silica particles (MSNs) were successfully synthesized using facile sol-gel using rice husk as a silica precursor and water-soluble polymers as structure-directing agents (SDAs) under acidic conditions of gluconic acid solutions. The influence of polyvinyl alcohol/PVA, polyvinylpyrrolidone/PVP, and soluble starch on the textural properties and morphologies were studied. Besides, the impact of MSNs with considerable properties on the CO2/N2 separation performance of poly(ether-block-amide) or Pebax membranes was also investigated. SDAs could generally double the specific surface area of the original sample up to 400–600 m2/g, except PVP/starch and PVA/PVP. In addition, PVP governed spherical shape, while its combination with PVA established excellent particle size distribution (100–200 nm). MSNs prepared using PVA/PVP were even considered to upgrade Pebax membrane's CO2/N2 separation performance. CO2 permeability and CO2/N2 selectivity were enhanced up to 58% and 21%, respectively, compared to pure Pebax membranes. This finding will be promising for encouraging sustainable filler development for membrane technology.

Smoothing the wrinkle formation and improving dye rejection performance in porous graphene oxide membranes using high surface curvature hollow fiber substrates

Assembly of atomic-scale thin two-dimensional (2D) graphene oxide (GO) nanosheets into a membrane with macroscopic three-dimensional (3D) laminar structure is accompanied by the formation of wrinkles. The size and pattern of wrinkles, which depend on the substrate curvature and the thickness of the 3D laminar structure, adversely affect the separation performance of the membrane. Therefore, smoothing the formed wrinkles is essential to boost the separation performance of GO-based membranes. For the first time, we proposed a new approach to prepare porous hollow fiber (HF) yttria-stabilized zirconia (YSZ) substrates with small-diameter (660–790 μm, outer diameter (OD)) by stretching the nascent HF using gravitational force. Also, using a delayed phase inversion, a plurality of radial micro-channels opening from the interior surface of HFs can be realized. The resultant HF substrates show promising permeation characteristics and good fracture strength owing to their open microstructure and the robustness of YSZ. Small-diameter HF substrates (OD = 660 μm) with higher surface curvature ensured the fabrication of porous GO (PGO) membranes with better dye separation performance. The rejection of methyl red (MR, MW = 269.3 g mol−1) dye molecule for small-diameter HF PGO membranes (OD 660 μm) was 10%–167% higher than that of membranes fabricated using large-diameters (OD 1250–2600 μm). This study shed light on the fabrication of high-performance thin film membranes by tailoring the geometric features of substrates.

Improved separation performance, anti-fouling property and durability of polyamide-based RO membrane by constructing a polyvinyl alcohol/polyquaternium-10 surface coating layer

In this work, a novel coating layer of polyvinyl alcohol (PVA)/polyquaternium-10 (PQ10) was constructed onto the surface of polyamide-based RO membrane via the method of surface coating followed by cross-linking. Permeation tests demonstrated that the incorporation of PQ10 into PVA could efficiently improve the water permeation ability of surface coating layer, showing a significant decrease of hydraulic resistance from 5.9 × 1012 m−1 of the PVA-1.0 coating layer to 2.5 × 1012 m−1 of the PVA-1.0/PQ10-0.2 coating layer. Anti-fouling performance evaluation revealed that the PVA/PQ10-coated membrane not only possessed the good anti-fouling property of the PVA-coated membrane to negatively charged foulants and protein but also exhibited more excellent anti-fouling performance to positively charged foulant due to its relatively lower surface charge density and pseudo-zwitterionic surface character. Long-term filtration tests with dye wastewater illustrated that although the initial water permeability of membrane coated with PVA-1.0/PQ10-0.2 surface layer was lower than that of the virgin RO membrane under the same operation condition, the PVA-1.0/PQ10-0.2-coated membrane exhibited a higher salt rejection, lower flux decline rate and larger cumulative volume of permeated water during a filtration period of 48.0 h. Soaking tests further demonstrated the improvement of membrane chemical durability against acid, alkaline and chlorine by the PVA/PQ10 coating layer.

Developing a PVDF catalytic membrane with high permeability, fouling resistance and self-cleaning capability for efficient oil/water emulsion separation

To impart PVDF membranes with excellent antifouling performance and catalytic self-cleaning capability, a novel modifier PVDF-g-Py-FePc (PPF) was facilely designed and architecturally constructed through grafting 4-aminopyridine (4-NH2-Py) followed by axial coordinating iron phthalocyanine (FePc) on PVDF backbones. An original PPF@PVDF catalytic membrane has been successfully fabricated though incorporating the Fenton-like modifier PPF into PVDF matrix using the phase inversion method. The influences of the introduction of PPF on membrane micro-structure and separation performance were investigated in detail by XPS, contact angle measurement, SEM, and cross-flow filtration experiment. Owing to the introduction of the modifier PPF, the porosity, mean pore size and surface hydrophilicity of PVDF membrane were enhanced obviously, which results in PVDF membrane with high permeation and excellent fouling resistance. Most importantly, the embedded PPF possesses catalytic active and can more effectively degrade the oil foulants adsorbed on membrane surface or trapped within membrane pores. Thereby, PVDF membrane was endowed a catalytic self-cleaning capability for high-efficient oil/water emulsion separation. As a whole, the PPF@PVDF catalytic membrane as a potential candidate will be applied in the treatment of wastewater containing oil and sewage.