Membranes For Oil-water Separation Research Articles

Development of a Novel ECTFE Melt-blown Nonwoven Material and Its Application in Oil-Water Separation

The removal of oil from water surfaces is crucial for protecting the environment and living organisms from the hazards posed by industrial oily wastewater and offshore oil spills. However, achieving enhanced mechanical robustness, corrosion resistance, and durability in oil-water separation membranes presents a significant challenge. In this study, poly(ethylene chlorotrifluoroethylene) (ECTFE) resin, a novel semicrystalline polymer material composed of alternating ethylene and chlorotrifluoroethylene molecules, was fabricated into melt-blown fabric (MB) by melt-blowing technology. By optimizing the side wind temperature, collector distance, roller speed, and hot air pressure, ECTFE MB with superior mechanical properties was established. Additionally, the obtained ECTFE MB exhibited excellent hydrophobicity with a water contact angle reaching 127.8°. The separation efficiency for various oil-water mixtures (oil phase including carbon tetrachloride, petroleum ether, dichloromethane, n-hexane, and isooctane) exceeded 99%. Furthermore, after 90 cycles of oil-water separation, ECTFE MB maintained high flux (72183.16 L m−2 h−1) and separation efficiency of 99.40% when carbon tetrachloride was used as oil phase. Notably, ECTFE MB demonstrated exceptional resistance to harsh environments, including strong acids, bases, and mild high temperature. The investigation of failure modes of ECTFE MB revealed that the primary failure mode of ECTFE MB was the disruption of the oil-water interface. The maximum water height that the ECTFE MB could withstand was 1376 mm. Consequently, ECTFE MB exhibit excellent mechanical properties, chemical stability, and cycling stability, indicating the potential application in the field of oil-water separation.

PEEK-PANI bi-functional oil-water separation membrane based on structural switchable wettability

PEEK-PANI bi-functional oil-water separation membrane based on structural switchable wettability

Dopamine triggered the polymerization and co-deposition of HEMA on PVDF membranes to prepare oil-water separation membranes

A one-step co-deposition method based on dopamine and hydrophilic hydroxyethyl methacrylate (HEMA) was proposed for the modification of polyvinylidene fluoride (PVDF) membrane, which could ameliorate its oil-water separation performances and hydrophilicity. A range of modified membranes were prepared by adding different content of HEMA in the reaction solution. For the improved membrane, the minimum water contact angle can reach 13.63°, and the maximum underwater oil contact angle can reach about 150°. The pure water flux for the improved membrane reaches 9668 L·m-2·h-1·bar-1, showing excellent hydrophilicity. In addition, the separation efficiency of the improved membrane for a variety of oil-water emulsions exceeds 98%, indicating good permeability and circulating oil resistance. At the same time, this approach is also applicable to other membranes on account of the extensive availability of dopamine.

Long-lived superhydrophobic micro/nano-locked fiber membranes for long-lasting oil-water separation effectiveness

Superhydrophobic/superoleophilic oil-water separation membranes have great potential for treating industrial, domestic, and marine oily wastewater. However, the robustness of these membranes remains a challenge that restricts their ability to maintain long-lasting oil-water separation effectiveness. Inspired by the adhesion mechanisms of snail and tree frog, exploiting the synergistic effects of interfacial hydrogen bonding and mechanical interlocking, we herein achieved strong adhesion between hydrophobicized in-situ nanoparticles and textile fibers to fabricate a long-lived superhydrophobic micro/nano-locked fiber membrane (LSMFM). LSMFM maintains excellent superhydrophobicity even when exposed to mechanical and chemical damage, such as continuous sandpaper abrasion, tape-peeling, weight impact, water jet, and acid/alkali/salt erosion. Additionally, LSMFM efficiently separates various light/heavy oil-water mixtures, achieving a remarkable separation flux of >10,000 L·m−2·h−1 and an efficiency >98 %, even after 200 cycles with n-hexane. Importantly, such membranes still maintain a high separation flux >19,000 L·m−2·h−1 and efficiency >97 % after sequentially being subjected to acids, alkalis, freezing, and high temperatures, and even the adsorption bag formed by wrapping LSMFM with superhydrophilic wood pulp cotton can adsorb oil at fixed-point and continuously recover pure oil from oily wastewater. This study paves a new way for the sustainable purification of oily wastewater in extreme environments.

In situ microbubble-mediated strategy for highly efficient anti-crude oil-fouling membrane with parallel nanosheet structure

Membrane fouling caused by highly viscous oils severely hampers the long-term application of oil–water separation membranes. In situ aeration, achieved by applying a voltage to the membrane to produce bubbles, can effectively reduce the adhesion of oil contaminants. Herein, the parallel NiFe-layered double hydroxide arrays were successfully constructed on Ni foam using a hydrothermal method. Compared with NF@NFLDH having randomly aligned nanosheet arrays, NF@NFLDH-P can produce more numerous micro-size bubbles. A substantial number of the microbubbles spontaneously coalesced with oil droplets, and the synergy of buoyancy and kinetic energy significantly hindered oil fouling on the NF@NFLDH-P membrane. Specifically, this microbubble–mediated anti-oil-fouling strategy substantially reduced the flux attenuation and maintained a high flux recovery ratio during long-term crude oil–water separation, exhibiting a great operational life. This study suggests an innovative way to design future anti-fouling membranes with bubble-mediated capabilities.

Nickel-cobalt hydrogen phosphate membrane with outstanding anti-crude oil-fouling capability and its microscopic anti-fouling mechanism

Oil/water separation membranes with superior anti-fouling properties against highly viscous oils are crucial for the efficient treatment of oily wastewater. Herein, the effects of functional groups in an inorganic superhydrophilic membrane on the anti-fouling properties of the membrane are investigated. Using a facile one-step electrochemical deposition method, Ni1-xCoxHPO4·3H2O membranes were formed on a Cu(OH)2 microneedle-coated copper mesh (CCNC–P) with superhydrophilic and underwater superoleophobic properties. All CCNC–P membranes with different Co2+ contents showed outstanding anti-fouling capability for oily wastewater such as those containing crude oil. The CCNC–P(x = 0.5) membrane exhibited high separation efficiency reaching 99.7 % across five oil–water mixtures and oil-in-water emulsions, concurrently presenting an ultrahigh flux of 61695 L m−2 h−1 for crude oil–water mixture. Moreover, the membrane consistently maintained its separation performance during the long-term crude oil–water separation process. The flux decline ratio was below 1 %, and the flux recovery ratio approached 99.4 %. The CCNC–P membranes possessed superior chemical, thermal, and mechanical stability, suggesting significant potential for the industrial treatment of oily wastewater. Density functional theory calculation revealed that the HPO42− group in CCNC–P can strongly adsorb water molecules. The resultant stabilized hydration layer impeded the contact between the membrane surface and oil droplets, while the metal ions scarcely influenced the adsorption of water molecules on CCNC–P. These findings provide new insights into the development of novel oil–water separation membranes with higher anti-fouling capabilities against high-viscosity oils.

Stearic acid modified Fe3O4/Y2O3 composite membranes for efficient oil-water separation

Traditional oil-water separation methods have low separation efficiency and are prone to environmental pollution. The development of low-cost and environmentally friendly novel oil-water separation membranes is of wide interest nowadays. In this work, stearic acid modified Fe3O4/Y2O3 (Fe3O4/Y2O3/SA) composite membranes are prepared on PET and cotton fabric using spraying and impregnation methods. Both Y2O3 and Fe3O4 nanoparticles are compounded on the surface of the substrate and modified using stearic acid impregnation. The results show that Fe3O4/Y2O3/SA composite membrane has a water contact angle of 152.5° and exhibits super hydrophobicity/lipophilicity. At the same time, the composite membrane has excellent oil-water separation performance, including high separation efficiency (99.92 %) for a variety of oil-water mixtures, and good stability in 15 cycles of separation tests. The mechanism of oil-water separation is discussed.

Degradable polyvinyl alcohol/chitosan@carnauba wax superhydrophobic composite membrane for water-in-oil emulsion separation and heavy metal adsorption

At present, many oil-water separation membranes are being developed to purify oily wastewater. However, oily wastewater often contains heavy metal, which are often difficult to dispose during separation. Furthermore, most of the oil-water separation membranes cannot be degraded after scrap, producing pollution to environment. Herein, the polyvinyl alcohol/chitosan@carnauba wax (PCGCW) membrane with heavy metal adsorption and biodegradation performance was acquired by electrospinning and spraying process. The acquired PCGCW membrane had excellent mechanical properties after crosslinking glutaraldehyde (GA). Furthermore, the composite membrane had excellent superhydrophobic property (WCA = 154°) with a rolling angle of 2°, due to the introduction of carnauba wax. Exhilaratingly, for emulsions with surfactant, it had a high separation flux with 19,217 L·m−2·h−1·bar−1 and splendid an oil purity over 99.9 %. Besides, the efficiency of oil purity and separation flux remained stable even after 10 separations. In addition, the PCGCW membrane had the ability to adsorb heavy metals with adsorption capacity of 51–106 mg/g for Cu2+, Fe3+, Co2+ ions. Foremost, the superhydrophobic PCGCW membrane was biodegradable, with degrading 29.76 % within 40 days. The prepared composite membrane had the advantages of low cost, high separation flux, great repeatability, adsorbable heavy metals and degradability, which had a vast application prospect.

Smart anti‐fouling and self‐repairing polymer brushes for efficient oil–water separation

AbstractThe increasing water pollution problem poses a demand for oil–water separation materials, but preparing separation materials with high efficiency and excellent durability remains a great challenge. In this work, we use a diblock polymer brush of polydimethylsiloxane (PDMS) and poly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA) based on cotton fabric to prepare oil–water separation membranes with high efficiency, good durability, and intelligent self‐repairing properties. Lubricating PDMS brushes reduces the fouling adhesion due to its low surface energy and high flexibility. pH‐responsive PDMAEMA brushes provide good hydrophobicity and an intelligent self‐repairing effect. The prepared Co‐PDMS‐PDMAEMA has high oil flux (>30,000 L m−2 h−1) and high separation efficiency (>99%) even after 10 cycles and its surface character can be recovered under acidic conditions. Overall, the modified cotton fabric made by such a versatile technique is promising in oil–water separation.

Interfacial charge demulsification endowed dual-network photocatalytic hydrogen-bonded PVA@agarose membranes for oil-water separation

Hydrogel materials with hydrophilic cross-linked network exhibit remarkable super-wettability, enabling their widespread application in oily wastewater treatment. However, the single and loose structure lacks sufficient strength and porosity to resist long-term degradation. Herein, a structural synergistic molecular strategy was reported to introduce reinforcing phase structures and interfacial active sites into the polymer networks for long-term oil-water emulsion separation. The carbon skeleton was uniformly interspersed through the strongly hydrogen-bonded polymer chains via covalent bonds, resulting in a hydrogel network with high mechanical strength and exceptional flow conductivity, which maintained a separation flux of 1233 L m−2 h−1 after 20 separation cycles under gravitational force. Dense negative charges on the surface disrupted the internal charge stability of the oil-water emulsion, leading to remarkable demulsification with a separation efficiency exceeding 99 %. Simultaneously, the strong redox reaction of the photoheterojunction effectively removed organic dyes under visible light, enhancing the overall antifouling performance. This study provided a feasible strategy at the molecular level for optimizing the suitability of hydrogels for oil-water emulsion separation.

Multi‐Scenario Applications of Fluoro‐Free Super Liquid‐Repellent Particles Prepared Through Excluded Volume Effect

AbstractSuperhydrophobic surfaces garner tremendous research attention due to their potential applications in the fields of oil–water separation membrane, self‐cleaning, and anti‐icing systems. However, the reported superhydrophobic materials that achieve low‐surface‐tension (<60 mN m−1) liquid repellency are typically prepared using perfluorinated compounds (PFCs), which pose significant risks to the natural environment and human health. Here a concept based on the excluded volume effect in polymer dilute solutions is explored to achieve a hydrophobic flexible polymer‐chain wrapping of multidimensional particles, which forms a nonadherent soft‐shell‐hard‐core structure and maintains the original structural integrity of particles. The prepared fluoro‐free super‐repellent multidimensional particles can be spray‐coated and dip‐coated on different substrates to prepare large‐scale superhydrophobic coatings, which exhibit excellent low‐surface‐tension (42.6−50 mN m−1) liquid repellency superior to the reported fluoro‐free superhydrophobic materials. Benefiting from the strong interaction of super‐repellent particles with flexible polymer chains, the superhydrophobic coatings show unexpected wear resistance and durability. This first demonstration of hydrophobic polymer‐wrapped particles for repelling low‐surface‐tension liquids provides insights into next‐generation fluoro‐free superhydrophobic materials.

CMPs membranes prepared using electrostatic spinning as a template for efficient oil-water separation

The development of efficient oil-water separation membrane technology is of great important for elimination of the serious environmental pollution issues caused by the frequent oils-spill or organics leakages in modern industry. Herein, we report the creation of conjugated microporous polymer membranes (CMPs@PMMA/PVDF), which were synthesized by a Sonogashira-Hagihara cross-coupling reaction using 1,3,5-triethynylbenzene and 2,6-dibromophenol as monomers in the presence of a template membrane prepared using poly (vinylidene fluoride) and poly (methyl methacrylate) as mixed solution via electrostatic spinning method, for efficient oil-water separation. The as-synthesized CMPs membrane shows excellent hydrophobicity with a water contact angle (WCA) of 150.8º and high permeate flux ( 865.8 L m−2 h−1). The tensile strength of CMPs@PMMA/PVDF was measured to be 3.13 MPa with an elongation of 10.32%. The TGA curve of CMPs@PMMA/PVDF membranes shows high thermal stability with mass loss decreasing by only 15.89% when the temperature rises to 414.3 ºC. Driven by gravity alone, the resulting membrane shows outstanding oil-water selectivity for oil-water separation (with a separation efficiency of up to 99.9%), its separation efficiency almost remains unchanged after 10 cycles with cyclohexane as the oil phase, and the separation efficiency still maintains up to 98.9% even after 50 cycles. In addition, the 3D-CMPs membrane also performs well in the separation of oil-water mixtures, and the separation efficiencies of various water-in-oil mixtures are maintained above 98.6% after ten cycles, showing that the CMPs membrane materials may have great potential for a broad application in the field of separation of oil-water mixtures.

Effect of multi-walled carbon nanotubes on the properties of DLP 3D printing photosensitive resin

To improve the mechanical properties of photosensitive resin, a technique for manufacturing multi-walled carbon nanotubes (MWCNTs) composite resin using DLP 3D printing was proposed. MWCNTs were used as reinforcing materials for photosensitive resins. The molding accuracy and comprehensive mechanical properties of the resin were significantly improved, and the content of MWCNTs was 0.06 wt%, which obtained the best properties. Tests with different thickness layers further confirmed the advantages of MWCNTs as reinforcing materials. The oil–water separation membrane was prepared by DLP 3D printing with the optimum content.

Enhanced superhydrophobicity and durability of modified cotton cloth for efficient oil-water separation

The development of simple, low-cost, and efficient oil/water separation membranes is still a major challenge in the field of wastewater treatment. In this study, an oil/water separation membrane is prepared based on low-cost cotton cloth (CF) through a simple solution soaking treatment without using organic solvents. Pristine CF is treated first with concentrated alkali and then chemically grafted by sodium methyl silicate (SMS) onto the surface to obtain oil/water separation membrane (SMS-O-CF). This process not only increases the roughness of the CF but also endows the surface with superhydrophobicity due to the outward extension of methyl groups, resulting in a water contact angle (WCA) of 155° and good self-cleaning ability. The SMS-O-CF achieves efficient separation for various oil/water mixtures and maintains a separation efficiency up to 96 % and a flux of over 11,557 L·m−2·h−1 after 220 cycles under neutral conditions. Moreover, the modified CF also exhibits excellent acid/alkaline resistance and wear resistance. Regardless of the 12 h acid/base immersion, 100 min water wash, or 200-cycle mechanical abrasion, SMS-O-CF still exhibits high flux and separation efficiency. Raw material cost for preparing SMS-O-CF is as low as 1.0 dollar/m2. The preparation of SMS-O-CF has provided a green manufacturing method for developing low-cost and efficient oil–water separation membranes.

Polyvinyl alcohol gel/micro-arc oxidation 3D-printed porous structural aluminium for oil-water separation

Traditional oil-water separation membranes still face challenges in designing membrane structures and pore sizes. In this study, we successfully prepared a PVA@MAO 3D-Al material with an internal porous structure using 3D printing technology and micro-arc oxidation (MAO). Compared to the base 3D-Al material, the fabricated PVA@MAO 3D-Al exhibits excellent wear resistance, with an average friction coefficient reduced by 66 % in dry friction and 22 % in water lubrication. In electrochemical experiments, corrosion current density decreased by an order of magnitude, indicating higher stability of PVA@MAO 3D-Al in corrosive environments. In oil-water separation experiments, PVA@MAO 3D-Al achieved separation efficiencies exceeding 97 % for mixtures of white oil, kerosene, liquid paraffin, and cyclohexane with water. Moreover, even after undergoing 600 cycles of reciprocating friction and exposure to various environmental solutions, the separation efficiency of PVA@MAO 3D-Al for white oil/water mixtures remained above 96 %, demonstrating outstanding physical and chemical stability. This suggests that PVA@MAO 3D-Al is suitable for use in extremely harsh environments. This study introduces a simple and efficient approach to manufacturing oil-water separation membranes using 3D printing technology, coupled with MAO technology to enhance the base material's performance. The combination of these techniques opens up new avenues in the field of oil-water separation.

Nanofiber membranes fabricated by coaxial electrospinning with porous channel structure for high-efficiency oil-water separation

The electrospinning nanofiber membranes modified by nanoparticles can effectively improve anti-oil adhesion and separation performance. However, the low stability of nanoparticles on the fiber membrane surface substantially limits the operational lifespan of the membrane. Herein, poly(vinylidene fluoride) (PVDF) nanofiber membranes with multi-scale microporous channel structures are prepared using coaxial electrospinning and a sacrificial template strategy. Subsequently, iron phytate nanoparticles are grown in situ on the fibers to fill the porous structures by utilizing the hollow and porous nanofibers as a framework. The interlocking structure between the nanoparticles and the porous fibers significantly enhances the stability and durability between nanoparticles and the fiber membrane. Even after being subjected to ultrasonic treatment for 7 h, there is no discernible shedding of nanoparticles from the fiber membrane. The prepared nanofiber membrane demonstrates exceptional superhydrophilicity and underwater superoleophobicity, exhibiting remarkable self-cleaning capability and resistance to crude oil contamination. Additionally, the membrane efficiently separates various oil-in-water emulsions, achieving a high separation efficiency of over 99%. Moreover, the membrane also demonstrates excellent adsorption capability towards cationic dyes. Therefore, this interlocking structure composed of nanoparticles and nanofibers presents new ideas and insights for the preparation of high-performance and durable oil–water separation membranes.

Engineering superhydrophobicity: a survey of coating techniques for silicone-based oil-water separation membranes.

Oil spills in the ocean and the release of contaminated wastewater from industries cause significant harm to the ecosystem and water sources. To tackle this environmental problem, oil-water mixture separation has been the subject of extensive research over the past few decades. Improving oil absorbents is crucial in removing organic contaminants from wastewater produced by industrial activities. To this end, there is an increasing need for materials that can efficiently and flexibly recover oils from contaminated ocean waters, industrial wastewater, and other sources. Silicones are often used for this purpose because of their exceptional mechanical and thermal durability, as well as their low toxicity. The materials produced from silicones, such as foam, sponge, or substrate, exhibit excellent oil-absorbing properties (maximum oil absorption range, 23.2-77g/g) and outstanding compression cycles. This article review highlights the advancements in the manufacturing of silicone-based products that have been extensively researched for oil-water separation. Understanding the interdependencies that determine the structure, performance, and manufacturing strategy is essential to producing selective oil absorbents with more commercial potential in the future. Recycling of silicones has also become increasingly important as a goal for the circular economy.

An asymmetric super-wetting Janus PVDF oil-water separation membrane fabricated by a simple method on a non-woven substrate

Membrane separation technology is an important method of treating oily wastewater with great potential for development. However, preparation of membranes for efficiently separating complex oil-water mixtures continues to be challenging. In this study, a strategy for efficient construction of asymmetric wetting surfaces was designed, and successfully prepared an asymmetric super wetting Janus polyvinylidene fluoride (PVDF) modified separation membrane to separate complex oil-water emulsion. The composite PVDF membrane was prepared using a non-woven fabric substrate and phase conversion method. Subsequently, composite membrane was rapidly hydrophilic modified on one side using tannic acid and 3-aminopropyltriethoxysilane under the strong oxidizing effect of oxidant sodium periodate. Then non-woven fabric substrate was peeled off to obtain a Janus PVDF modified separation membrane. The front and back sides of the separation membrane have highly asymmetric micromorphology and wettability. The front side has hydrophilic/underwater oleophobic wettability (with a water contact angle of 31°). The separation efficiency of oil-in-water emulsion is up to 99.5%, while the back side has super lipophilic/underoil hydrophobic wettability (with a water contact angle of 131°). The separation efficiency of water-in-oil emulsion is up to 98.6%, improving the efficiency of oil in water separation and application range.

Double-drying 3D lamellar-structured aerogel membrane for efficient oil-water separation and long-lasting antibacterial activity

Conventional oil-water separation membranes are difficult to establish a trade-off between membrane flux and separation efficiency, and often result in serious secondary contamination due to their fouling issue and non-degradability. Herein, a double drying strategy was introduced through a combination of oven-drying and freeze-drying to create a super-wettable and eco-friendly oil-water separating aerogel membrane (TMAdf). Due to the regular nacre-like structures developed in the drying process and the pores formed by freeze-drying, TMAdf aerogel membrane finally develops regularly arranged porous structures. In addition, the aerogel membrane possesses excellent underwater superoleophobicity with a contact angle above 168° and antifouling properties. TMAdf aerogel membrane can effectively separate different kinds of oil-water mixtures and highly emulsified oil-water dispersions under gravity alone, achieving exceptionally high flux (3693 L·m−2·h−1) and efficiency (99 %), while being recyclable. The aerogel membrane also displays stability and universality, making it effective in removing oil droplets from water in corrosive environments such as acids, salts and alkalis. Furthermore, TMAdf aerogel membrane shows long-lasting antibacterial properties (photothermal sterilization up to 6 times) and biodegradability (completely degraded after 50 days in soil). This study presents new ideas and insights for the fabrication of multifunctional membranes for oil-water separation.

Anti-fouling underwater superoleophobic membranes based on hierarchical double networks for high efficiency oil–water separation

Oil fouling is a key problem of superwettable oil–water separation membranes because the membranes are inevitably susceptible to varying degrees of oil contamination during the ongoing separation processes, which usually results in a severe impact on separation performance. Consequently, it is a great challenge to construct oil-removal membranes with superior resistance to oil contamination. Herein, we fabricated hierarchical double networks (HDT)-modified porous glass membrane with superhydrophilicity/underwater superoleophobicity. Firstly, a layer of silicone nanofilament (SNF) network bearing tremendous C = C double bonds were fabricated on a porous glass membrane surface by one-step chemical vapor deposition (CVD) using vinyltrichlorosilane (VTCS) as a precursor. Subsequently, the second network layer was constructed by copolymerization of the C = C double bonds on the SNF network and those in sulfobetaine-derived monomer (sulfobetaine methacrylate, SBMA), using N,N′-methylenebisacrylamide (MBA) as the cross-linkering agent. It was observed that the obtained HDT-modified glass membranes displayed excellent superhydrophilicity/underwater superoleophobicity accompanied with superior self-cleaning performance and oil-resistance properties. As a result, the HDT-modified membranes showed high separation flux and high efficiency for both oil/water mixtures (7500 L m−2h−1, above 99.98%) and surfactant-stabilized oil-in-water emulsions (1100 L m−2h−1, above 99.96%) with excellent cyclability. The outstanding advantages with characteristics of excellent oil resistance and superior separation performance enable the HDT-modified glass membrane promising applications in a wide range of industries related to oil–water separations.