Underwater Superoleophobic Surfaces Research Articles

Mixed superoleophilic/superoleophobic hard granular media for coalescence of oil-in-water-emulsion

To enhance the coalescence separation efficiency of oil/water emulsions, the coalescence mechanism of oil droplets between two media of opposite wettability was investigated. A coalescent-bed comprising a mix of superhydrophobic and superoleophilic quartz sand, along with superhydrophilic and underwater superoleophobic quartz sand, was constructed in a coalescer. Single-factor and response surface experiments were used to study the effects of oleophilic/oleophobic sand mixing ratio, apparent velocity, initial oil concentration, bed thickness, sand particle size on coalescence-separation performance, and to determine the optimal experimental conditions. Employing the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, the agglomeration mechanism of oil droplets within the mixed particle bed was analyzed based on interfacial energy dynamics. Results indicate that the mixing ratio of the two sands significantly influences coalescence separation performance. An optimal oleophilic/oleophobic sand mixing ratio of 1:1 yielded a mass factor of 0.69 kPa−1, showcasing superior coalescence separation efficiency and an optimal balance of separation efficiency and pressure drop. Under the optimal conditions of apparent velocity of 2.7 m/h, initial oil concentration of 471.9 mg/L, bed thickness of 12.6 cm and mixed sand particle size of 0.5 mm, the oil/water separation efficiency reached 98.08 % ± 0.87 %, with effluent oil droplet size being 2.5 to 3 times larger than at the inlet. Analysis of the oil droplet coalescence mechanism revealed a synergistic effect between the two quartz sands, enhancing oil removal performance. The strong affinity of oil to the superhydrophobic and superoleophilic sand surface increases oil droplet wetting and coalescence efficiency, while the water attraction on the superhydrophilic and underwater superoleophobic sand surface forms a stable water film, improving the flux of the continuous water phase and reducing pressure drop across the bed. This study demonstrates that combining quartz sands of opposite wettability not only overcomes the limitations of single-wettability surfaces in coalescing oil removal but also achieves high efficiency and low energy consumption in oil removal.

Facile fabrication of polymeric-inorganic hybrid coated membrane with super-hydrophilic and underwater super-oleophobic properties for highly efficient crude oil-in-water emulsion separation

The oily wastewater is a huge wastewater stream that can potentially serve as an enormous source of clean water for water reuse applications such as groundwater recharge or irrigation. Given the huge potential of cleaning oily wastewater, we have developed an amino-functionalized nickel oxide nanoparticles coated inorganic-polymeric hybrid membrane with superhydrophilic and underwater superoleophobic properties for excellent crude oil-in-water (O/W) emulsion separation potential using a cross-flow filtration system. The use of ceramic alumina (Al2O3) support offers increased chemical, thermal, and mechanical stability while nickel oxide (NiO) decoration equips the membrane with special surface wettability to avoid membrane fouling. Moreover, the amino-functionalized NiO-coated polyamide network (F-NiO/PA) offers an active layer dense enough to separate the oil from water when the surfactant-stabilized crude oil-in-water emulsion was used as feed during separation experiments. Hence fabricated F-NiO/PA@Alumina membrane was studied by using different membrane characterization techniques to explore the features and understand the structure of F-NiO/PA@Alumina membrane. The F-NiO/PA@Alumina membrane possessed a superhydrophilic (water contact angle; θW, A = 0°) and underwater superoleophobic (oil contact angle; θO, W = 161°) surface wettability which is an ideal feature required for O/W emulsion separation. The F-NiO/PA@Alumina membrane demonstrated a high O/W emulsion separation efficiency of >99 % even with crude oil concentrations as high as 200 ppm using a cross-flow filtration system. The stability test of the separation performance of the F-NiO/PA@Alumina membrane also revealed a separation performance of >99 % for the duration of the test using a cross-flow filtration system.

Quantifying droplet–solid friction using an atomic force microscope

AbstractControlling the wetting and spreading of microdroplets is key to technologies such as microfluidics, ink‐jet printing, and surface coating. Contact angle goniometry is commonly used to characterize surface wetting by droplets, but the technique is ill‐suited for high contact angles close to . Here, we attach a micrometric‐sized droplet to an atomic force microscope cantilever to directly quantify droplet–solid friction on different surfaces (superhydrophobic and underwater superoleophobic) with sub‐nanonewton force resolutions. We demonstrate the versatility of our approach by performing friction measurements using different liquids (water and oil droplets) and under different ambient environments (in air and underwater). Finally, we show that underwater superoleophobic surfaces can be qualitatively different from superhydrophobic surfaces: droplet–solid friction is highly sensitive to droplet speeds for the former but not for the latter surface.

Constructing green, smart wettability-switchable and antibacterial Caragana cellulose filter by cooperative regulation of texture and surface for on-demand purification of emulsions

The efficient on-demand purification of complex oily emulsions containing multiple pollutants and bacteria by a green filter has always been desired, but also extremely challenging. The abundant and renewable natural cellulose biomass is the best choice for developing green separation materials, but the limited separation capability of raw biomass restricts its application. To resolve this problem, this paper proposed a synergetic texture-surface regulation strategy to improve the liquid-locking ability and amphiphilicity of Caragana cellulose fiber, and thus prepared an intelligent multifunctional filter with an arbitrarily switchable underoil superhydrophobic (WCA = 152.1°) and underwater superoleophobic (OCA = 151.6°) surface. The surface wettability of the filter can be switched randomly by changing the wetting liquid, thus achieving efficient separation of different types of emulsions. As expected, both simulated different oils-in-water and different actual waters-in-oil emulsions, and all types of practical industrial oily complex emulsion sewage were purified by the filter at a high level (separation efficiency: 99.9 %). In addition, the filter can simultaneously remove 99.1 % of the Methylene blue and 98.6 % of the Oil red O in emulsions and has excellent antibacterial activity against E. coli (efficiency: 99.87 %) and S. aureus (efficiency: 99.43 %). The spent filter can be regenerated as an adsorbent capable of dynamically adsorbing 99.9 % of Orange II and 99.8 % of Methylene blue. This study provides a new method to modulate natural renewable cellulose and thus produce a multifunctional separation material for on-demand purification of complex and stubborn emulsions.

Probing the physical origins of droplet friction using a critically damped cantilever.

Previously, we and others have used cantilever-based techniques to measure droplet friction on various surfaces, but typically at low speeds U < 1 mm s-1; at higher speeds, friction measurements become inaccurate because of ringing artefacts. Here, we are able to eliminate the ringing noise using a critically damped cantilever. We measured droplet friction on a superhydrophobic surface over a wide range of speeds U = 10-5-10-1 m s-1 and identified two regimes corresponding to two different physical origins of droplet friction. At low speeds U < 1 cm s-1, the droplet is in contact with the top-most solid (Cassie-Baxter), and friction is dominated by contact-line pinning with Ffric force that is independent of U. In contrast, at high speeds U > 1 cm s-1, the droplet lifts off the surface, and friction is dominated by viscous dissipation in the air layer with Ffric ∝ U2/3 consistent with Landau-Levich-Derjaguin predictions. The same scaling applies for superhydrophobic and underwater superoleophobic surfaces despite their very different surface topographies and chemistries, i.e., the friction scaling law derived here is universal.

Designing effective underwater self-cleaning surfaces by investigating the oil dewetting ability of hydrophobic and underwater superoleophobic Poly(Diisobutyl Glycolide)-Silica composite surfaces

This study introduces composite thin films of amphiphilic structures to fabricate underwater superoleophobic surfaces. The hydrophobic part of the structure is created by poly(diisobutyl glycolide) thanks to a side chain of isobutyl groups, while the hydrophilic component is formed with hydrophilic silica nanoparticles. Poly(diisobutyl glycolide), having a 77° water contact angle, was obtained through ring-opening polymerization of l-diisobutyl glycolide in a bulk medium, resulting in excellent conversion (97.9 %) and narrow polydispersity (1.47), while maintaining the chiral center. The investigation revealed a notable increment in the underwater hexadecane contact angle from 110° to 160° In contrast, the water contact angle exhibited partial constancy in the air environment because of the augmenting silica content. At a silica content reached up to 30 %, the self-cleaning underwater oil-repellent surface was accomplished, attributable to the phenomenon of the underwater Cassie state, which effectively trapped air within the hierarchical rough structure. Moreover, the surface free energy (SFE) of the composite films was evaluated using both the van Oss-Chaudary-Good and Owens-Wendt methods. Notably, the contact angle of underwater hexadecane decreased with the increase of polar interactions as determined by both methods, owing to the influence of the underwater Cassie state of the hierarchical composite surface.

Robust Superhydrophilic/Underwater Superoleophobic Surface with Anti-Abrasion and Anti-Corrosion Performances Based on Laser Ablation

Preparing underwater superoleophobic surface is an effective method to solve the problems of oil adhesion on the underwater surfaces and oil spill in water. However, the underwater superoleophobic surfaces at present are not reliable in practical application due to their poor stability under corrosion and abrasion. Herein, we proposed a facile method to fabricate a robust superhydrophilic/underwater superoleophobic surface. The surface is combined with micro honeycomb frame structure and nanostructure, which was fabricated by laser ablation. The surface with the honeycomb pattern shows strong hydrophilicity with a water contact angle of 0° and stable underwater oil repellency with an underwater oil contact angle of 164.9°. Furthermore, it can maintain its excellent underwater superoleophobic performance after 120 cycles of abrasion and corrosion of 6 h at pH = 1–14.

A scalable method toward robust underwater superoleophobic surfaces with microstructure arrays on 304 stainless steel substrates

Underwater superoleophobic surfaces have huge application prospects due to their multiple functions such as antifouling, self-cleaning, manipulation of oil microdroplets, and oil − water separation. However, efficient and low-damage methods for the scalable fabrication of robust underwater superoleophobic surfaces on stainless steel substrates are still lacking. Here, a maskless electrochemical machining technology was developed to fabricate robust underwater superoleophobic surfaces on 304 stainless steel substrates. The square micro pit array was obtained on the surface, and the surface showed excellent superoleophobicity with a contact angle of 154.93 ± 1.42° when submerged in water. In addition, the fabricated underwater superoleophobic surface with the square micro pit array showed good chemical stability, mechanical stability, and anti-friction performance. The friction coefficient of the fabricated underwater superoleophobic surface was 0.0748, which was 60.7% lower than the friction coefficient of a smooth surface. Compared with traditional methods, the proposed technology will promote the practical applications of underwater superoleophobic surfaces in complex underwater environments.

Modification of polyacrylonitrile (PAN) membrane with anchored long and short anionic chains for highly effective anti-fouling performance in oil/water separation

Conventional polymeric membranes are usually prone to fouling by oily substances and therefore are greatly hindered in their applications for oil/water separation. In this study, we carried out a new strategy of modifying PAN membrane for highly effective anti-oil fouling performance. The modified membrane surface was anchored with negatively charged long and short chains, where the long chains could reject oil droplets at far away from the membrane surface while the short chains near the membrane surface could increase its hydrophilicity and thus enhance the permeate flux during the filtration of oil emulsion. The negatively charged long chains were constructed with sulfonate-terminated units and the short chains with carboxylate units. The prepared PAN membranes were tested to show both superhydrophilic and underwater superoleophobic surface properties, and displayed very high resistance to the adhesion of various types of oils. In the membrane separation experiments with 1000 mg‧L-1 surfactant-stabilized oil-in-water emulsion, the developed PAN membrane exhibited an initial water flux of 115.4 L·m−2·h−1, and less than 16% of flux decay but higher than 97% in flux recovery after 3 filtration cycles (45 min each). Furthermore, in a challenging test, the membrane also showed excellent recovery in its performance after being fouled by a heavy fuel oil but cleaned simply by the action of soaking it into water. Therefore, the current study appeared to provide a new and effective alternative in the modification of conventional PAN membrane to enhance or expand its anti-oil fouling performance, especially for oil recovery or oil removal in oily wastewater treatment.

Controllable construction of the underwater superoleophobic surface from superhydrophilicity to superhydrophobicity in oil

Superwetting that is being subdivided to multiple superlyphobic states exists unique superiority in a specific interfacial application. Fine controlling superwetting surface is lack of systematic research. Due to the harsh conditions on the creation of underoil superhydrophilicity and suerhydrophobicity in oil of underwater superoleophobic surface, so far controllable fabrication strategies of the underwater superoleophobic surfaces in oil still remain a challenge. Herein, underwater superoleophobic surfaces from superhydrophilicity to superhydrophobicity in oil are controllable constructed by mixing commercial titanium dioxide nanoparticles, aluminum phosphate, and n-Alkyl acids, where the surface heterogeneous chemistry is finely controlled by changing the chain length of n-alkanoic acids. Under the rational surface energy, underoil superhydrophilicity and underoil superhydrophobicity of the underwater superoleophobic surfaces can be efficiently regulated via simply adjusting the chain length of n-alkanoic acids. The under-liquid dual superlyophobic surface can be achieved when an appropriate parameter denoted chain length of n-Alkyl acids (n) is between 14 and 16. However, when the parameter (n) is to be within 4 and 6, the superhydrophilicity in oil of underwater superoleophobic surface can be realized. This finding can connect the molecular-level conformational transformation and the conversion of macroscopic surface alternative wettability, providing the molecular-level design principle of superwetting interfacial in under-liquid environments.

Fabrication of metal-based superhydrophilic and underwater superoleophobic surfaces by laser ablation and magnetron sputtering

Fabricating underwater superoleophobic surfaces is an advanced technique for controlling undesirable oil and wax adhesion on engineering structures and household appliances. This article presented a facile method based on the combination of laser ablation of stainless steel substrates followed by magnetron sputtering of a metallic tungsten target to fabricate superhydrophilic and underwater superoleophobic surfaces. The results showed that the laser-ablated stainless steel substrate without coatings exhibited hydrophilicity and underwater oleophobicity. However, its transition to superhydrophilicity and underwater superoleophobicity with a 0° water contact angle and higher than 156° underwater oil contact angles occurred after the deposition of a thin tungsten film followed by annealing at 300 °C. The prepared surface maintained its wetting behavior for more than 4 weeks, even in corrosive aqueous HCl and NaOH solutions. According to the data from SEM and XPS, this distinguished wetting behavior resulted from the presence of the regular microscale texture patterns, abundant hydroxyl content, and low carbon content on the tungsten layer after annealing at 300 °C. Thus, laser ablation combined with magnetron sputtering of tungsten demonstrated effective results in fabricating superhydrophilic and underwater superoleophobic surfaces that are independent of the initial wetting of the substrates.

Janus Fabric with Asymmetric Wettability for Switchable Emulsion Separation and Controllable Droplets with Low Friction.

Superwetting surfaces have recently attracted extensive attention in oil-water emulsion separation and droplet manipulations, which are widely used in various situations ranging from wastewater treatment, to flexible electronics, to biochemical diagnosis. However, it still remains challenging to obtain asymmetric materials with high efficiency during oil-water separation. Meanwhile, excellent robustness of the superhydrophobic surface is of significance but retards the mobility of droplets due to increased lateral adhesion of small spacing between solid protrusions. Herein, a facile approach is demonstrated to obtain the excellent robustness of Janus fabrics with asymmetric wettability. As for one side of water-in-oil emulsion separation, mimicking the soft earthworm with periodically wrinkled skin, an adaptive superhydrophobic fabric was fabricated by wrapping soft wrinkled poly(dimethylsiloxane) (PDMS) polymer with a cross-linking structure on woven fabric fibers induced by Ar plasma treatment. In addition, inspired by the desert beetle's structure but with reversed wettability, the other side of the Janus fabric was constructed for treating emulsion of oil-in-water. In addition, the underwater superoleophobic surface consisting of magnetically responsive PDMS microcilia with slippery heads, which shows robustness against pH, improved water drop mobility and lowered the resistance of fluid friction similar to the intrinsic hydrophobic Salvinia molesta with additional slippery performance. Hence, we propose a novel and easy approach that optimizes enhanced emulsion separation and reduced fluid drag properties simultaneously, which actively broadens their widespread applications.

Bioinspired superhydrophilic/underwater superoleophobic surfaces with robust wax-prevention, self-cleaning, and oil/water separation functions

A superhydrophilic and underwater superoleophobic surface with excellent anti-wax, self-cleaning and oil/water separation performances was fabricated by a facile post-crosslinking process.

Super-hydrophilic electrospun PAN nanofibrous membrane modified with alkaline treatment and ultrasonic-assisted PANI in-situ polymerization for highly efficient gravity-driven oil/water separation

Polyaniline (PANI) is utilized in numerous membrane-based oil/water emulsion separation systems due to its simple synthesis, low cost, chemical stability, and abundant amino functional groups. However, it is still challenging to benefit from the highest efficiency of the PANI-modified membrane in oil/water separation. Herein, PANI was favorably functionalized electrospun polyacrylonitrile (PAN) nanofiber through the establishment of electrostatic interaction and hydrogen bonding between aniline monomer and alkalinized PAN (APAN) nanofibers followed by aniline polymerization under ultrasonic irradiation (APAN/PANI-S) for high-performance oil/water emulsion separation. The uniform and efficient coating of PANI on APAN nanofiber led to the APAN/PANI-S nanofibrous membrane demonstrating outstanding physical stability in harsh acidic and basic conditions. In addition, the APAN/PANI-S nanofibrous membrane illustrated a super-hydrophilic and underwater super-oleophobic surface nature, which resulted in an extraordinary water flux of about 2289 LMH and oil rejection of around 99.69 % in oil/water separation under the gravity driving force. Furthermore, the homogenous penetration of PANI across the APAN nanofibrous membrane as a result of ultrasound-assisted polymerization caused the APAN/PANI-S nanofibrous membrane to show excellent mechanical stability (∼14.07 MPa) and antifouling properties (water flux of>981 LMH and oil rejection above 98 %) during 15-cycle oil/water emulsion separation. These results indicate that the APAN/PANI-S nanofibrous membrane with superior oil/water separation performance could be a promising candidate from a practical application point of view.

CoFe2O4 functionalized PVDF membrane for synchronous oil/water separation and peroxomonosulfate activation toward aromatic pollutants degradation

Effective synchronous removal of water-immiscible oils and water-miscible refractory aromatic pollutants from wastewater is of great significance for water remediation. In this work, a low-cost and easy-prepared composite membrane was fabricated by vacuum assisted assembling of CoFe2O4 and tannic acid on polyvinylidene fluoride (PVDF) substrate. The CoFe2O4 functionalized PVDF membrane (CoFe2O4@PVDF) exhibited in-air superamphiphilic and underwater superoleophobic surface wettability. The resultant membrane displayed relatively favorable permeation flux (811.5 to 1837.5 Lm−2h−1) and high separation efficiency (above 99 %) in the separation of a series of emulsified oils ranged from nanoscale to microscale from water. Meanwhile, the as-fabricated CoFe2O4@PVDF membrane coupled with peroxymonosulfate (PMS) exhibited an extensive oxidizing capacity and high degradation efficiency towards aromatic contaminants with desired mineralization ability. More importantly, considering that the fabricated CoFe2O4@PVDF membrane possessed special super-wettability as well as PMS activation-based catalytic ability, it also applied in the treatment of simulated complex wastewater. The process achieved effectively synchronous oil/water separation and PMS activation toward pollutants degradation. Besides, in five cyclic continuous “degradation-separation” tests, the recovered CoFe2O4@PVDF membrane after PMS-based degradation in each cycle could separate oil/water emulsions as usual. It exhibited almost complete oil rejection and flux recovery property under multicycle filtration, demonstrating its excellent durability and stability. This flexible integration of PMS-based AOP catalytic capability and super-wettability into a composite membrane can provide inspiration for effective complicated wastewater rehabilitation.

In-situ self-compensation strategy for superhard, universal superhydrophilic/underwater superoleophobic coatings

Superhydrophilic and underwater superoleophobic surfaces are considered promising to maintain clean surfaces and sustain their functionalities. These surfaces, however, are often substrate specific, mechanically weak and can be damaged easily, resulting in short lifetimes. To address this, we propose a novel in situ self-compensation strategy for preparing a reconstructable hybrid polysiloxane network. This network can enhance surface roughness when hydrophilic chemistry is lost due to progressive water erosion, thus affording long-period superhydrophilic and underwater superoleophobic coatings that can survive rainfall or long-term underwater applications. For a diverse range of substrates with sustainable superhydrophilicity and underwater superoleophobicity, we developed a waterborne suspension containing metal nanoparticles and inorganic silicate adhesive applicable for the industrially viable spray-, dip-, or paint-coating techniques. This universal, superhard (exceeding 9H), long-period coating represents an applicable solution for preventing dirt or oil contamination and oil–water separation. It is expected to be widely used in industries and daily life.

Performance design of a highly anti-fouling porous membrane with dual pH-responsiveness

With the increasingly extensive application of membrane technology, facing the wastewater system with complex components, it is urgent to develop a porous membrane with excellent pollution-resistant and easily cleaned after pollution. Herein, a membrane with dual pH-responsiveness effects was successfully fabricated via a facile and eco-friendly method. The isoelectric point of zeta potential of the modified membrane (M-D-IA) appeared at pH = 4.31. It exhibited positive-charged and the water intake rate reached 427% under strongly acidic conditions, while it showed negative-charged with the water intake rate reaching 492% under strongly alkaline conditions, showing an excellent dual pH-responsiveness. Meanwhile, the membrane M-D-IA possessed good super-hydrophilic and underwater super-oleophobic surface characteristics. Furthermore, the membrane M-D-IA displayed an excellent oil-fouling resistance in the treatment of hexadecane/water mixed emulsion, with the water flux decay rate (FDR) only 17.5% after 7 cycles of operation and the water flux recovery rate (FRR) remained above 99.7% after alkali cleaning. Notably, the membrane M-D-IA also had excellent dual pH-responsiveness when treating typical polluted wastewater HA/CaCO3 feed solution. The FRR was as high as 98.3% after washing with alkali and acid solution in turn, indicating that the membrane not only possessed a significant resistance to organic/inorganic pollution but also had an outstanding recovery of membrane flux after cleaning. Moreover, the water flux of the membrane M-D-IA was maintained at 850 L m−2 h−1 during 30 days of storage, displaying an excellent resistance to biological pollution.

Green and rapid fabrication of superhydrophilic and underwater superoleophobic coatings for super anti-crude oil fouling and crude oil-water separation

The development of surfaces with super anti-crude oil-fouling behavior and crude oil-water separation properties is still a global challenge owing to the high viscosity of crude oil. Herein, superhydrophilic and underwater superoleophobic surfaces were successfully prepared by a simple, green and environmentally friendly one-step dip coating method. In the whole process, microcrystalline cellulose with hydrophilic hydroxyl functional groups was introduced into the coating with the help of inorganic adhesives, water was the only solvent, and no other organic solvents or surface modifiers was added. Besides being highly resistant to low viscosity oils and achieving effective oil-water separation (more than 98.3% separation efficiency after 30 cycles), the surface effectively resisted crude oil adhesion and achieved high viscosity crude oil-water separation. In addition, the underwater oil contact angle can still reach 147.5° and 152.5° after 20 cycles of sandpaper friction tests and 50 cycles of finger pressure tests, respectively, which indicates excellent durability. Furthermore, the method can achieve excellent superhydrophilicity and underwater superoleophobicity on varieties of substrates (such as copper foil, aluminum sheet and glass), showing very extensive applicability. It is expected that such fabrication strategy can provide a low cost, green and environmentally friendly approach to construct a series of superhydrophilic and underwater superoleophobic surfaces to achieve super anti-crude oil-fouling and (crude) oil-water separation.

Waste-derived carbon fiber membrane with hierarchical structures for enhanced oil-in-water emulsion separation: Performance and mechanisms

A superhydrophilic and underwater superoleophobic membrane based on waste-derived carbon fibers was prepared with the assistance of tannic acid and (3-Aminopropyl)triethoxysilane. The surface morphology, chemistry, roughness and wettability of the membranes were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, atomic force microscopy, water contact angle (WCA) and underwater oil contact angle (UWOCA) measurements, respectively. Carbon fibers enabled the construction of micro-nano hierarchical structures on the membrane surface, which significantly increased the membrane surface roughness (2.1 times higher than the control) and effective surface area (1.6 times higher than the control). The carbon fiber membrane exhibited superhydrophilicity (WCA = 0°) with ultrafast water spreading in air and underwater superoleophobicity (UWOCA = 157.2°) with little oil adhesion. The carbon fiber membrane showed effective surfactant stabilized oil-in-water emulsion separation using various oils (permeation flux up to 713 Lm-2h-1 and separation efficiency up to 99.8%). We also proposed an integrated model to elucidate how the superhydrophilic and underwater superoleophobic property and surface roughness interact with the size exclusion mechanism by considering dynamic flows near the membrane surface, which further reveals the anti-fouling and self-cleaning properties of our carbon fiber membrane. Our model provides new insights into developing specially-wettable membranes with high fouling resistance for wide wastewater treatment applications based on surface wettability and roughness.

Zwitterionic polyvinylidene fluoride membranes with strong underwater superoleophobicity and oil-fouling resistance for oily water purification

Polyvinylidene fluoride (PVDF) membrane offers excellent potential for efficient separation and purification of O/W emulsions. However, oil-fouling presents a major obstacle to its further application. Herein, a strong underwater superoleophobic surface was engineered to efficiently inhibit oil-fouling. PVDF-graft-poly(2-(dimethylamino) ethyl methacrylate) (PVDF-g-PDMAEMA) membranes were first fabricated via vapor-induced phase separation (VIPS), in which the nascent liquid film was left in a vapor bath for a predesigned time (te). The surface roughness increases by an order of magnitude when te increases from 0 to 240 s, and the underwater oil contact angle (UWOCA) correspondingly increases to more than 150°. However, it declines with time gone until the oil droplets on the underwater membranes were swallowed up. After surface zwitterionicalization by the reaction between PDMAEMA and 1, 3-propane sulfonate, a strong underwater superoleophobic surface was obtained, even after being soaked in water for 24 h. It endows the zwitterionic membrane with superior crude oil/water emulsion separation (with a flux of 749.7 ± 44.8 L m−2 h−1 and separation efficiency of 99.4 ± 0.1%) and excellent oil-fouling resistance (with a flux recovery rate of more than 90%), improving the potential value of porous membranes in oily water treatment.