Oil Rejection Rate Research Articles

Solventless Polymer-Grafted Mesh for Rapid and Efficient Oil–Water Separation

We report a solventless bilayer strategy for grafting hydrophilic poly(methacrylic acid) (PMAA) onto metal meshes. The bilayer nanocoating consisted of ultrathin PMAA brushes grafted onto a highly crosslinked primer that binds to each mesh wire. The enrichment of hydrophilic functionalities on the PMAA-grafted mesh surface improved the surface hydration and underwater oil repellency over the PMAA-crosslinked mesh, which contributed to the formation and stabilization of continuous water films between mesh wires to reject oil penetration in repeated uses. The vapor-based nanocoating process maximized the retention of pore openings for high-flux oil–water separation. The retained permeability, together with the enhanced oil repellency, enabled the PMAA-grafted mesh to achieve excellent gravity-driven oil–water separation, with an oil rejection rate higher than 99%, water flux exceeding 50,000 L m–2 h–1, and flux decay less than 3% after 20 cycles of reuse. More importantly, the PMAA-grafted mesh preserved high separation efficiency and flux stability under conditions of high salinity and extreme pH.

Fabrication and characterization of a novel mullite-stainless steel composed hollow fibre membrane for oil/water separation

Low-cost mullite-kaolinite material has recently received more attention as an alternative to conventional ceramic materials such as alumina and silica to prepare ceramic hollow fibre membranes (CHFMs) due to its high alumina contents and silica and thermal/chemical stability. However, weak bending strength is still one of the key bottlenecks that delay their commercial applications. In this work, we successfully fabricate a novel mullite-SS HFM with enhanced bending strength using mullite-kaolinite power with different stainless steel alloy (SS) 316 L contents of 0.0, 2.5, 5.0, 7.5, 10 and 12 % (w/w) as a reinforcement material by phase inversion/sintering techniques. The SS alloy was a potential material to enhance the mechanical strength of mullite HFMs due to its excellent mechanical properties. The effects of the major fabrication parameters of SS contents, mullite contents, and fabrication parameters such as air gap distance and bore fluid flow rates were well studied and evaluated through the fabrication process. Fabricated mullite-SS HFMs were characterized by morphology, porosity, pore size/pore size distribution, and bending strength. Afterwards, they were evaluated in an oil/water separation system regarding water flux and oil rejection rate. Based on the findings, there was a gradual increase in the bending strength from 32.1 to 79.8 MPa with increased SS contents from 0 to 12 % (w/w). At 10 % (w/w) SS, the satisfactory morphology with the balance between the bending strength of 66.7 MPa and porosity of 29 % was obtained. This bending strength was significantly higher than reported for mullite-kaolinite HFMs in previous works. Moreover, At 10 % (w/w) SS, the oil–water rejection performance of 96.9% and the water permeation of 290 L/m2. h was satisfactory at the sintering temperature of 1300 °C. These findings suggest the advantage of this membrane for various water treatment applications, such as oil/water separation, due to its outstanding physical properties.

Effect of sintering temperature on functional properties of mullite-kaolinite and stainless steel composed hollow fibre membrane for oil-in-water emulsion separation

BackgroundThe commercialization of mullite-kaolinite hollow fibre HFMs is still obstructed due to the weakness of their mechanical strength. MethodsThis study investigates the effect of different sintering temperatures (i.e., 1350, 1400, 1450 and 1500 °C) on the mechanical strength and other functional properties of ceramic HFMs composed of mullite-kaolinite and stainless steel (SS). The membranes were tested and evaluated through an oil-in-water separation process using three oily emulsions (i.e. 1000, 1500, and 2000 ppm) in a filtration system for 120 min. Significant findingsThe results showed a successful preparation for mullite-SS HFMs with asymmetrical and sponge-like structures. Increased sintering temperatures from 1350 to 1500 °C significantly integrated mullite and SS particles, and forming robust bonds improved the mechanical strength. Amongst all mullite-SS HFMs, the membrane sintered at 1450 °C was the most suitable for oil-in-water separation due to its optimum properties compared to other mullite-SS HFMs. As compared to mullite HFMs counterparts, the mullite-SS HFM at 1450 °C exhibited higher mechanical strength, oil rejection rate and permeate flux of 106.4 MPa, 99.05% and 345 L/m2.h, respectively. In addition, it showed higher mechanical stability and separation performance for a longer filtration time of 120 min than other CHFMs prepared from different low-cost materials reported in previous works. This membrane offers an advantage in mechanical strength, water flux, and rejection performance, making it suitable for various water treatment applications.

A novel glue attachment approach for precise anchoring of hydrophilic EGCG to enhance the separation performance and antifouling properties of PVDF membranes

A novel glue attachment approach was proposed to form a durable hydration layer on a hydrophobic PVDF hollow fiber membrane (PVDF HFM) surface to improve its hydrophilicity and antifouling ability during wastewater filtration. The functional glue was synthesized from reclaimed styrene butadiene rubber (SBR) and a hydroxyl group was created with an epoxidation reaction (ESBR). The hydrophilic epigallocatechin-s-gallate (EGCG) was then precisely anchored via hydrogen bonding with multiple phenolic hydroxyl groups in the ESBR without penetrating into the inner matrix of the PVDF to prevent flux decline. The hydrophilicity of the PVDF membrane increased drastically and the water contact angle decreased from 62.7° to 45.1° with only a 25% decline in the pure water flux. Furthermore, due to precise anchoring of the EGCG, the modified EGCG-ESBR/PVDF membrane showed a higher pure water flux (110.6 L m−2h−1) and much higher BSA and oil (kerosene) rejection rates (approximately 94.5% and 99.5%, respectively) compared to membranes directly coated with EGCG (EGCG-PVDF). Moreover, the modified membrane also showed higher water flux recovery after multiple filtration cycles. This promising and efficient hydrophilic modification suggests great potential for application of the eco-friendly material in wastewater treatment.

Modification of PVDF membrane by post-modified NH2-MIL-88B(Fe) showing improved permeability and oil/water separation performance

Metal organic frameworks (MOFs) possess excellent post-modification characteristics, high specific surface area, diversity of skeleton composition and pore tunability, have been increasingly applied in membrane modifications. In this work, NH2-MIL-88B(Fe) (NM88B) was first fixed onto polyvinylidene fluoride (PVDF) membrane by polyethyleneimine (PEI) through a vacuum-assisted self-assembly process, and the deposited NM88B was subsequently grafted with perfluoroalkyl polyethoxyacetic acid (FPEOAA) via a condensation reaction to realize the surface modifications. The modified membranes (named as N1Fx) showed improved hydrophilicity and underwater-oleophobicity. In addition, very high pure water flux (up to 9403 L‧m−2‧h−1) was obtained for the N1Fx membranes due to the high porosity of introduced NM88B. In the dead-end filtration experiments of n-hexadecane-water emulsion, the optimum membrane N1F20 showed a good oil rejection rate (98.3%) and high permeation flux (667 L‧m−2‧h−1) which is approximately seven times of the pure PVDF membrane, indicating that the surface-modified membranes had excellent permeability and good separation performance. Even after four filtration cycles of oil-water emulsion, the rejection rate maintained higher than 97%, showing good reusability. Furthermore, the study found that N1F20 had certain acid and alkaline resistance and great potential for engineering applications.

Tunable nanostructured stainless-steel coating for high-selective and high-permeable separation membranes for oil/water emulsions

This paper demonstrates a stainless-steel (SS) nano-pyramid structure (diameter of ~20–50 nm and pore size of 156.1 nm) sputter-coated on mixed cellulose ester (MCE) membrane for the use in separation of oil/water emulsions. SS-coated MCE membrane presented a superhydrophilic, antifouling surface as well as underwater superoleophobicity. The coated membrane achieved excellent separation efficiency of >99% when applied to light oil-water emulsions with a range of viscosities and densities. The highest permeation flux measured was 1,555 L m−2 h−1 when applied to toluene-in-water emulsions. The membrane also presented outstanding recyclability, as evidenced by oil rejection rate retaining at >99% through four separation cycles. The coated membrane was also shown to work well under harsh conditions including salty water, extreme pH values (1–14), and high temperatures (60 °C). In addition, our fabrication route of SS-coated MCE employs low process temperature while being highly scalable, which is favorable for industrial-scale applications.

3D printing titanium dioxide-acrylonitrile-butadiene-styrene (TiO2-ABS) composite membrane for efficient oil/water separation

The oily water treatment is becoming one of the hottest topics due to that increase of offshore oil transportation and the various accident oil leakages. In this study, a functional TiO2-ABS composite membrane was generated through the three-dimensional (3D) printing strategy for the first time and was conducted to simulated oily water treatment. The TiO2-ABS composite membrane demonstrated a significant promotion in hydrophilicity and oleophobicity which were evidenced by the water contact angle of 14.8° and the underwater oil contact angle of 144.7°, respectively. The optimal modified membrane had both exceedingly high flux (1.8 × 105 L m−2·h−1) and oil rejection rate (99.5%). Moreover, the results of filtration cycles of 10 days and extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory demonstrated that the modified membranes took possession of excellent stability and antifouling property. What was more, the TiO2-ABS composite membrane revealed over 99% rejection to all five types of oil/water systems. The interestingly experimental results indicated that the prepared membrane possessed a broad development trend and application prospect in the field of oily water treatment.

Plasma surface modification of graphene oxide nanosheets for the synthesis of GO/PES nanocomposite ultrafiltration membrane for enhanced oily separation

AbstractIn this study, two different monomers, namely hexafluorobutyl acrylate (HFBA) and diethylaminoethyl methacrylate (DEAEMA) were individually used to modify graphene oxide (GO) nanosheets via environmentally friendly plasma enhanced chemical vapor deposition (PECVD) method. The results from instrumental analyses confirmed the successful deposition of respective functional material onto the nanomaterials. Modified GOs were used as the nano‐fillers to develop composite polyethersulfone (PES) ultrafiltration (UF) membrane with improved surface properties for oily solution treatment. All the developed membranes were characterized with a series of analytical instruments to support the findings of membrane filtration performance. The results indicated that the membrane incorporated with DEAEMA‐GOs (coated with hydrophilic polymer) could achieve better results in terms of oil rejection, antifouling resistance and water recovery rate than the membrane incorporated with HFBA‐GOs (coated with hydrophobic polymer). This is due to the reduced agglomeration between modified GOs as well as better interaction of hydrophilic‐coated GOs with polymer membrane. Compared to the pure water flux of the membrane incorporated with unmodified GO, the membrane incorporated with DEAEMA‐GO achieve approximately 85% higher value with oil removal rate remained almost unchanged (98.94% rejection).

Lignin: Excellent hydrogel swelling promoter used in cellulose aerogel for efficient oil/water separation

HypothesisSuper-hydrophilic/underwater super-oleophobic materials composed of biomass show great advantages for the treatment of oily wastewater due to their inherent fouling resistance. However, the development of three-dimensional materials from biomass for oil–water separation is still a challenge. It is universally acknowledged that constructing a rough structure on the surface of hydrophilic substrates would significantly improve the underwater oleophobicity and oil–water separation performance. ExperimentsIn this work, a three-dimensional lignin/cellulose aerogel (LCA) was developed through sol–gel method with freeze-drying. The rough microstructure and 3D interconnected network composed of lignin and cellulose impart excellent underwater superoleophobicity to LCA for efficient oil–water separation. FindingsThe introduction of lignin to cellulose aerogel could effectively enhance its surface roughness, water permeation speed and underwater oil contact angle. Especially, the swelling properties of the hydrogel could be regulated by modulating the content of lignin, which could further control the pore size of aerogels to optimize the separation flux. The as-prepared aerogel showed remarkable performance in separating various oil–water mixtures and oil-in-water emulsions, with a separation flux of 7646 ± 167 L·m−2·h−1 and oil rejection rate >99 %. These excellent properties combined with its facile fabrication make LCA a promising candidate for the treatment of oily wastewater.

Removal of Scale-Forming Ions and Oil Traces from Oil Field Produced Water Using Graphene Oxide/Polyethersulfone and TiO2 Nanoribbons/Polyethersulfone Nanofiltration Membranes.

Treatment of produced water in oil fields has become a tough challenge for oil producers. Nanofiltration, a promising method for water treatment, has been proposed as a solution. The phase inversion technique was used for the synthesis of nanofiltration membranes of polyethersulfone embedded with graphene oxide nanoparticles and polyethersulfone embedded with titanium nanoribbons. As a realistic situation, water samples taken from the oil field were filtered using synthetic membranes at an operating pressure of 0.3 MPa. Physiochemical properties such as water flux, membrane morphology, flux recovery ratio, pore size and hydrophilicity were investigated. Additionally, filtration efficiency for removal of constituent ions, oil traces in water removal, and fouling tendency were evaluated. The constituent ions of produced water act as the scaling agent which threatens the blocking of the reservoir bores of the disposal wells. Adding graphene oxide (GO) and titanium nanoribbons (TNR) to polyethersulfone (PES) enhanced filtration efficiency, water flux, and anti-fouling properties while also boosting hydrophilicity and porosity. The PES-0.7GO membrane has the best filtering performance, followed by the PES-0.7TNR and pure-PES membranes, with chloride salt rejection rates of 81%, 78%, and 35%; oil rejection rates of 88%, 85%, and 71%; and water fluxes of 85, 82, and 42.5 kg/m2 h, respectively. Because of its higher hydrophilicity and physicochemical qualities, the PES-0.7GO membrane outperformed the PES-0.7TNR membrane. Nanofiltration membranes embedded with nanomaterial described in this work revealed encouraging long-term performance for oil-in-water trace separation and scaling agent removal.

Transformation of hazardous zinc sludge into highly porous spinel/whisker-form mullite membranes for the separation of oil-in-water emulsions

Heavy metal waste poses an environmental and health hazard. Zinc-containing sludge is a particular problem. However, the conversion of this sludge into a spinel-based ceramic material is an environmentally friendly, space-saving, and cost-effective method for preventing heavy-metal pollution. However, silicates are frequently present in such sludge, and can reduce the porosity of the produce ceramic material, which limits their potential applications in membrane-separation technology. To ensure the conversion of the zinc component into a highly porous spinel-based ceramic, in this study, additives were used to convert the silica component to whisker-form mullite. Thus, a primary pore structure was formed between spinel particles, and secondary pore channels were formed by the mullite whiskers in the primary pores. Crucially, the oriented growth of a ceramic containing 15% ZnO at 1150 °C resulted in a porosity of 40.5%. In contrast, the unmodified ceramic had a porosity of 6.3%. The unique structure also reduced the tortuosity of the ceramic to less than unity, which improved the permeation flux for membrane applications. The optimal ceramic was tested for the separation of oil-in-water emulsions, yielding a promising oil-rejection rate of 96%.

Silicon carbide microfiltration membranes for oil-water separation: Pore structure-dependent wettability matters

Both the pore size and surface properties of silicon carbide (SiC) membranes are demonstrated to significantly affect their separation efficiency when used for oily water treatment. However, the potential influences of open porosity together with the pore size of SiC membranes on their surface properties and oil-water separation performance have rarely been investigated. In this work, porous SiC ceramic membranes with tunable open porosity and pore size were purposely prepared and selected to systematically study the effect of pore structure-dependent wettability on the oil-water separation performance. The measured pure water flux of selected membranes as a function of open porosity (34–48%) and pore size (0.43–0.67 μm) was well-fitted by using a modified H-P equation. Interestingly, the hydrophilicity of SiC membranes was improved with the increase in open porosity and pore size, as evidenced by the gradually decreased dynamic water contact angle and underwater adhesion of oil droplets. Further, the open porosity of SiC membranes was found to contribute more to the improved surface wettability. As a result, the stable flux of SiC membranes in oil-in-water (O/W) emulsions was increased by 24% with the increased open porosity while the oil rejection rate remained above 90%. This work quantitatively reveals the contributions of the pore structure to the surface wettability of ceramic membranes, and thus provides an effective pathway to improve their performance in oil-water separation.

Anti-fouling performance investigation of micron-submicron hierarchical structure PVDF membranes in water-in-oil emulsion separation

Membrane technology was widely used in the field of oil-water separation. In the process of water-in-oil emulsion treatment, surface contamination of hydrophobic and lipophilic membranes was a difficult problem. Therefore, the effect of hydrophobic membrane surface micro-rough structure on oil-water separation performance and its anti-fouling behavior has been investigated as a major focus of current research. Superhydrophobic-superoleophilic polyvinylidene fluoride (PVDF) membranes with micron-submicron hierarchical structure were prepared by combining thermally induced phase separation (TIPS) with rolling embossing. The influence of the roller temperature on the structure and performance of the membrane were discussed. The best achieved superhydrophobicity with a high water contact angle (WCA) of 154.8° and rolling angle (SA) of 1.9°, which was similar with lotus-effect. Meanwhile, the N2 flux was 197 L m−2 s−1 and LEP was 4.08 bar. Besides, the tensile strength of PVDF membrane was 1.89 MPa. The embossed membrane showed good lipophilicity, and the residence time of kerosene on the membrane surface was only 0.14 s. PVDF membranes with lotus leaf effect showed excellent demulsification performance and high recyclability in water in oil emulsion. The oil flux and rejection rate were 1258 L m−2 h−1 and 99.14%, respectively. In the separation experiment of PVDF membranes in diesel emulsion containing inorganic pollutant CaCO3, the results showed that the anti-fouling effect of PVDF membranes by cross-flow filtration method was obviously better than that by dead-end filtration method. When the operating temperature and pressure were 0.1 MPa and 45 °C, respectively, embossed membrane showed relatively excellent separation performance in cross-flow filtration. This study provided some guidance for the anti-fouling performance of roughened surface superhydrophobic-superoelophilicity membrane in oil-water separation experiment.

Study on Treatment of Low Concentration Oily Wastewater Using Alumina Ceramic Membranes

In this study, alumina ceramic plate microfiltration membranes (ACMs) were used for the treatment of oily wastewater with different concentrations. The permeate oil concentration of the system was basically less than 5 mg·L−1, and the oil rejection rate was up to 97.6%. The effects of raw oil concentration on permeation flux and oil rejection rate of oily wastewater were studied. The results showed that with the increase of raw oil concentration, the oil rejection rate increased slightly due to the existence of oil film on the surface of filtered ACMs. Moreover, the existence of oil film had little effect on the flux change of ceramic membranes. The results showed that the permeability of ACMs mainly depended on their own oleophobic properties. In this system, physical cleaning technology is used to remove oil droplets and particles blocked in membrane pores. The results showed that physical cleaning could significantly recover the permeation flux as well as improve the oil rejection rate. On this basis, a system is proposed as a potential technique for oily wastewater treatment.

Bio-inspired mineral-hydrogel hybrid coating on hydrophobic PVDF membrane boosting oil/water emulsion separation

Membrane fouling is one of the difficult challenges that restrict the efficient application of membrane separation technology in oil/water separations. Hydrogel with strong hydration capability has been considered as an ideal material for preparing anti-oil-fouling coating for membranes. Although some hydrogel-based coatings have been developed for the membrane interface hydrophilization modification, controlling the morphology of gel layers and improving the flux of hydrogel coated membranes remains a difficult matter to resolve. In this study, we elegantly designed a new mineral-hydrogel coating with nanostructures to modify hydrophobic polyvinylidene fluoride (PVDF) microfiltration membranes by an alternate quaternary soaking strategy. Compared with the merely hydrogel-coated membrane, the pure water flux of novel mineral-hydrogel coating membrane increased by 214% and the permeation increased by 127% with the oil rejection rate of 99.6% at 0.4 bar. Most importantly, the newly-built mineral-hydrogel layer on porous support possessed excellent hydrophilicity, underwater super-oleophobic properties and superior anti-oil-fouling performance, which is greatly promising in oily sewage remediation. In addition, this mineral-hydrogel coating could also be constructed on other hydrophobic substrates successfully, such as commercial melamine resin. Our facile strategy for designing and constructing synergetic mineral-hydrogel architecture may also inspire other functional coatings with nanostructures.

Effect of Curing Temperature on the Properties of Latex Based Membrane for Oily Wastewater Filtration

Oily wastewater pollution has always been part of the most serious worldwide environmental disaster. Thus, the treatment of oily wastewater is notably crucial. In this work, nitrile butadiene rubber/graphene oxide (NBR/GO) membranes were fabricated by latex compounding and curing method which is comparatively brand-new technique to produce membranes for wastewater treatment. Therefore, the steps in the production need to be studied to enhance the performance of the membrane. Curing temperature is an important factor in the production of the latex-based membrane. In this paper, the effect of curing temperature in the range of 90 °C – 110 °C on the morphology, tensile properties, permeation flux, and oil rejection rate performance of the membrane was studied. The curing temperature was found to affect the surface morphology and integrity of the membranes which sequentially affects the performance of the membrane in terms of strength, permeation flux, and oil rejection rate. NBR/GO membranes cured at the temperature of 100 °C exhibit the highest flux of 491.84 L/m2.hr with an oil rejection rate of 95.44 %, with the ultimate tensile strength (UTS), elongation break (EB%), and E-Modulus (E-mod) of 34.490 MPa, 1627.11 %, and 1.309 MPa, respectively.

Spider silk bioinspired superhydrophilic nanofibrous membrane for efficient oil/water separation of nanoemulsions

Membrane separation has been acknowledged as an effective strategy to treat oily emulsions based on size-sieving. For separating nanoemulsions, smaller membrane pores are required to reject nano-sized oil droplets; however, the permeate flux would be significantly restrained. Herein, bioinspired by spider silk, a novel superhydrophilic electrospun nanofibrous membrane with spindle-knotted structures (SK-ENM) was constructed for highly efficient separation of nanoemulsions. The special spindle-knotted structures were constructed with 3–3.5 wt% polyacrylonitrile utilizing electrospinning based on Rayleigh instability. The prepared SK-ENM possessed a highly porous structure with a mean pore size of 0.634 μm, and strong superhydrophilicity/underwater superoleophobicity with rich micro/nano-hierarchical structures. For separating the surfactant-stabilized paraffin-in-water nanoemulsion with a mean droplet size of 325.7 nm, the oil rejection, permeate flux, and flux recovery rate were 95.68%, 1143.3 LMH/bar, and 99.98%, respectively. Thus, the SK-ENM with larger pores achieved both high oil rejection and high permeate flux for separating nano-sized oil droplets, which is a breakthrough achievement in overcoming the limitations of size-sieving. This could be attributed to the directional migration and coalescence of nano-sized oil droplets on spindle-knotted structures driven by Laplace force, which was calculated to be 8.7 × 10-8N. Meanwhile, the resulting large oil droplets were proved to be rejected by the superhydrophilic nanofibrous membrane with negligible fouling. This study provides insights into the design of novel functional superhydrophilic membranes for separation of emulsions. The as-prepared SK-ENM can be effectively applied to treating various nanoemulsions and complex oily wastewater in practical.

Super‐Wetting Porous g‐C3N4 Nanosheets Coated PVDF Membrane for Emulsified Oil/Water Separation and Aqueous Organic Pollutant Elimination

AbstractSuper‐wetting multifunctional membranes are highly attractive in the current decade in the environmental remediation of wastewater containing water‐insoluble emulsified oils and water‐soluble hazardous organic pollutants. Herein, hydroxyl modified porous g‐C3N4 nanosheets (CNNS) coated polyvinylidene fluoride (PVDF) membrane is fabricated by a facile vacuum pumping process. Hydroxyl modified porous g‐C3N4 nanosheets are firmly immobilized on flexible PVDF substrate via sodium alginate (SA) adhesive to create a stable surface micro/nanohierarchical structure. The fabricated CNNS/SA/PVDF membrane achieves the desired surface wettability of superhydrophilicity/underwater superoleophobicity with an anti‐oil‐fouling property. The functionalized membrane exhibits above 99% emulsified oil rejection rate with excellent stability and recyclability when separating oil‐in‐water emulsions. Besides, visible‐light‐response CNNS endow the as‐prepared membrane with excellent photocatalytic activity. The resulted CNNS/SA/PVDF membrane can eliminate organic dye both in static and dynamic water with high flux recovery ratio and renewability, which conducted the procedures of photodegradation of organic dye adsorbed on the membrane surface after filtering the contaminative flowing aqueous solution, and directly the photodegradation of organic dye in stationary aqueous solution, respectively. This facile‐fabrication and high‐performance CNNS/SA/PVDF membrane provides a promising practical application toward oily and organic wastewater treatment. It also promotes the utilization of surface wettability modified g‐C3N4 nanomaterial in the construction of multifunctional interface membrane for environmental purification.

Reusable membrane with multifunctional skin layer for effective removal of insoluble emulsified oils and soluble dyes

The organic pollutants, typical of emulsified oils and soluble organic dyes, is commonly found in wastewater, however simultaneous removal of them remains challenging because of their difference in surface charge, molecule size, and solubility in water. Inspired by the water purification of the earth's multilayer strata, a fibrous membrane with multifunctional skin is fabricated by coupling sub-micrometer pores layer of polyaniline (PANI) and nano molecular brush of polyacrylic acid (PAA)/polyethyleneimine (PEI) on polyacrylonitrile membrane, for cross-scale organic pollution/water separation. This ultrathin skin of PANI/PAA/PEI is endowed with sub-micrometer pores and strong hydration, which can effectively prevent tiny oil droplets from entering or adhering the membrane pores. Furthermore, this skin with double electric layer can selectively adsorb and even filtrate anionic/cationic dyes by protonation and deprotonation effect in different pH solutions. The synergy of these features enables this membrane with ultra-high water flux (>3000 L m−2 h−1 bar−1), oil rejection rates (>99.6%), and anionic/cationic dyes adsorbability (>49.1 mg/g). Besides, the membrane also exhibits desirable reusability, excellent mechanical durability and outstanding acid/alkali resistance, promising for removal of insoluble emulsified oils and soluble organic dyes in wastewater.

Sulfonic nanohydrogelled surface-modified microporous polyvinylidene fluoride membrane with excellent antifouling performance for treating water-oil separation of kitchen wastewater

Kitchen wastewater containing high concentration of suspended solids, salt and oil is a comprehensive wastewater that requires urgent treatment. Organic fouling limits the use of membranes for treating kitchen wastewater. Herein, we propose a novel sulfonic nanohydrogel membrane with superhydrophilicity and underwater-superoleophobicity. A 32-nm-diameter sulfonic nanohydrogel Poly(SPP-co-MA-co-FLUORAL-P), developed by the polymerization technique in an aqueous medium, was grafted onto the polyvinylidene difluoride (PVDF) microfiltration membranes. The developed PVDF-g-Poly(SPP-co-MA-co-FLUORAL-P) membrane exhibited excellent antifouling properties for treating kitchen wastewater. The influence of organics (edible oil, surfactant, protein and humic acid) and salts on the membrane filtration was thoroughly investigated. The Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy techniques were used to confirm the successful surface modification. The experimental results revealed that the pure water flux was 2161 L m−2 h−1. A high oil rejection rate was achieved when the fabricated membrane was used for treating the simulated kitchen wastewater (˃99.7%). The excellent antifouling properties of the membrane significantly improved the circulation stability of the simulated kitchen wastewater filtration. The recovery rate of permeation flux was up to 100%. The chemical oxygen demand removal rate of the real kitchen wastewater was 61% and the flux recovery rate arrived at 98%. The PVDF-g-Poly(SPP-co-MA-co-FLUORAL-P) membrane can be potentially used for treating kitchen wastewater.