Underwater Superoleophobic Membranes Research Articles

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.

Reusable Underwater Superoleophobic Polyacrylamide Membranes for Effective Oil‐Water Separation and Dye Removal

AbstractWater contamination by oily wastes continues to rise with industrialization and pose a threat to marine ecosystem and public health. Water repellent special wettability membranes have been fabricated for oil removal. These superhydrophobic membranes have been fabricated utilizing hazardous chemicals such as fluorinated compounds, which again have shown toxicity. In contrast, environmentally friendly separation membranes are required for oily wastewater treatment. In this regard, we fabricated underwater superoleophobic membrane based on β‐cyclodextrin and acrylamide for efficient and effective water‐oil separation. Acrylamide polymeric membrane was prepared by free radical co‐polymerisation by incorporating acrylic acid and β‐cyclodextrin as monomer via crosslinking with N,N‐methylene bis‐acrylamide. FT‐IR and PXRD used for characterizing the prepared hydrogel and studied for morphological analysis by FE‐SEM. The oil and water wetting characterization of gels were evaluated, in ambient and submerged conditions. The dried gel showed gradual decrease of contact angle for both oil and water indicating liquid absorption with time. However, in completely water wetted state hydrogel was superoleophobic with a very high oil contact angle of ≥170°. The pre‐wetted hydrogel efficiently and effectively separated oil/water mixtures with ~99 % separation efficiency. Additionally, its effectiveness was monitored over several days of continuous separation operation. Interestingly, the hydrogel was also able to remove dye from water. The underwater superoleophobic acrylamide‐β‐cyclodextrin hydrogel demonstrated high oil recovery efficiency and indicated the potential for repeated oil‐water separation process.

Robust superwetting polytetrafluoroethylene membranes with interlayer-bridged inorganic nanocoating for efficient oil/water separation

Treating oily wastewater is of great importance and urgency worldwide. The superhydrophilic and underwater superoleophobic (SUS) membrane is an effective alternative to realize such a goal. However, most SUS membranes are vulnerable in harsh environments, such as strong acidic/alkaline solutions or physical abrasion, resulting in a limited lifespan. In this work, a robust SUS membrane was developed by depositing in situ a TiO2 nanocoating onto the polytetrafluoroethylene (PTFE) porous membrane with (3-[(perfluorohexyl sulfonyl) amino] propyltriethoxy silane) (PFSS) as an intermediate layer. In the preparation process, the fibrils and nodes of the PTFE membrane were integrally enclosed with the chemical networks generated by hydrolysis and self-condensation of the PFSS. Then, the nano-TiO2 was in situ bonded with the sulfonyl amide group of the PFSS via bidentate coordination. As a result, an ultrathin and continuous nano-TiO2 coating (∼20 nm) was created, and the coating covered throughout the porous PTFE matrix. The resultant PTFE membranes demonstrated typical SUS characteristics, while their pore structure was almost unchanged. The PTFE SUS membranes exhibited a high emulsion permeance (up to 18,700 L m–2h−1 bar−1) with a separation efficiency above 99.3%. Attributed to the soldering effect of the PFSS between TiO2 nanoparticles and the PTFE membrane, the developed SUS membranes exhibited excellent stability against strong acid/alkali washing and hydraulic shearing, all of which outperformed the majority of current SUS membranes.

Sugarcane-based superhydrophilic and underwater superoleophobic membrane for efficient oil-in-water emulsions separation

The development of ecological, low cost, easy preparation, especially high performance materials for emulsions separation is of great importance due to the rise in pollution of oil-water emulsions from industrial production and domestic waste. Straws as agricultural wastes, including plenty of hydrophilic groups and multi-level pore structures, can be prepared as biomass membranes for oil-water emulsion separation. Herein, a novel super-hydrophilic sugarcane-based (SHS) membrane was prepared using a facile and eco-friendly method including chemical treatment and freeze-drying. The as-prepared SHS membrane has unique wettabilities due to the hydrophilic property of the internal cellulose and the micro-nano pores, including superhydrophilicity (water contact angle of 0°) and underwater superoleophobicity (underwater oil contact angles of over 150°). The SHS membrane has good durability and stability against ultraviolet (UV) irradiation, corrosion by acids and alkalis, mechanical abrasion and especially mould adhesion. Importantly, the SHS membrane can be used for separation of various oil-in-water emulsions, and exhibits excellent separation performances such as high separation efficiency (> 99 %) and good separation flux (above 891 L m−2 h−1 bar−1). The SHS membrane also exhibits excellent recyclability over 10 continuous separation cycles. Furthermore, the SHS membrane can be utilized to selectively absorb water from oils as a water absorbent material. Hence, SHS membrane is a promising and practical material for applications in treatment of wastewater containing oil-water emulsions.

Underwater superoleophobic polyvinylidene fluoride membranes using sulfonated dopamine and polyethyleneimine as additives for the separation of oily water

AbstractOil‐fouling of the membranes limits further application in the separation and purification of oil‐in‐water emulsions. Here, anti‐oil fouling membranes are engineered by the method of non‐solvent induced phase separation (NIPS) which enriches the polysulfonated dopamine (PSDA) and polyethyleneimine (PEI) (PSDA‐PEI) to the top surface from mixed casting solution. The obtained membrane achieves excellent anti‐oil fouling property as high as 98.2% oil rejection, yet it still possesses good flux of 2362.5 ± 110.9 and 1252.3 ± 71.8 L m−2 h−1 for the separation of 1,2‐dichloroethane‐in‐water and toluene‐in‐water emulsions. This can be attributed to outstanding hydrophilicity and super underwater superoleophobicity for mussel‐inspired PSDA‐PEI layer. In addition, the membrane also has excellent stability in acid (pH 1, 3, and 5) or alkali (pH 10 and 12) solutions. This work provides a facile method to engineer underwater superoleophobic membranes with excellent anti‐oil fouling by mussel‐inspired chemistry for oily water treatment.

Synergistic effect of underwater superoleophobicity and photo-Fenton oxidation on improving anti-fouling performances of filtration membranes for oily wastewater separation

Underwater superoleophobic membranes can inhibit the adhesion of oil droplets and efficiently reduce oil-fouling. However, under the action of transmembrane pressure, the oil inevitably adheres to the membranes, which is difficult to be removed by facile washing. Here, an excellent coupling of underwater superoleophobicity and photo-Fenton oxidation is reported for desired anti-fouling performances. Briefly, composite polypropylene (PP) membranes with stable underwater superoleophobicity and excellent photo-Fenton oxidation efficiency were constructed by depositing hydrophilic α-FeOOH nanorods and mussel-inspired coating in turn. Various stable water-in-oil emulsions can be effectively separated with the obtained membranes. Most importantly, in the presence of H2O2 and visible light, α-FeOOH nanorods can photo-Fenton oxidize oil and dye that break through the underwater superoleophobic defense layer. Therefore, the reversible fouling ratio (Rr-L) and the flux recovery ratio (FRR-L) improve to 76.8 ± 3.2% and 87.2 ± 2.4% respectively, while the irreversible fouling ratio (Rir-L) decreases to 9.9 ± 0.2% for separation pump oil-in-water emulsion containing methylene blue. This work has great potential and strategic value in the treatment of oily wastewater and the preparation of advanced filtration and anti-fouling membranes.

Underwater superoleophobic membrane with hydrophobic bump and hydrophilic sublayer structure for effective oil-in-water emulsions separation

Underwater superoleophobic membranes are competitive strategy for accomplishing efficient oil-in-water emulsions separation. However, permeating flux of water probably may be dropped with the reduction of pore size. Moreover, the plenty of oil phase may block pore canal resulting the decrease of separation performance. Herein, an underwater superoleophobic membrane with hydrophobic bump and hydrophilic sublayer structure was fabricated through spinning hexadecyltrimethoxysilane (HDTMS) modified SiO2 (H-SiO2) micro-particles on polydopamine (PDA) hydrophilized polyvinylidene fluoride (PVDF, PDP) membrane. Therefore, the sieving of hydrophilic PDP membrane sublayer and oil absorption-flotation of hydrophobic H-SiO2 bump are ongoing simultaneously in separation processes, thus effective decreasing oil fouling to break the trade-off effect between separation efficiency and permeation flux. Interestingly, the PDPS membrane not only could efficiently separate diverse emulsions involving low and high-viscosity oil/water emulsions, but also possessed excellent mechanical (200 times of bending test) and chemical (separation of oil-in-corrosive waster emulsions) stabilities. More importantly, the separation performance of PDP-H-SiO2 (PDPS) membrane with bump-sublayer structure is obviously superior to the single PDP membrane. The idea of rationally combing opposite wetting and bump-sublayer structures has certain significance towards the fabrication and development about oil/water separation materials.

Green electrospun poly(vinyl alcohol)/silicon dioxide nanofibrous membrane coated with polydopamine in the presence of strong oxidant for effective separation of surfactant-stabilized oil-in-water emulsion

Most nanofibrous membranes were electrospun from organic solutions. Because organic solvents are usually volatile and poisonous, they can cause unfavorable influence on the natural environment and human health. In this work, poly(vinyl alcohol)/silicon dioxide@polydopamine (PVA/SiO2@PDA) membrane was fabricated by green electrospinning of aqueous dispersion of PVA and SiO2 combined with deposition of PDA in the presence of strong oxidant sodium periodate. Notably, PDA coating with distinguished superhydrophilic and underwater superoleophobic property was obtained due to producing carboxyl components during degradation of quinone units. When the PVA/SiO2@PDA membrane was immersed in water, a stable hydrated layer produced on the membrane surface due to the presence of hydrophilic groups. The hydrophilicity of this hydrated layer could make water molecules pass through the membrane successfully and effectively prevent infiltration of oil droplets. This superhydrophilic and underwater superoleophobic membrane showed excellent oil/water separation performance for various oil-in-water emulsions. The maximum permeate flux reached 4413.96 L·m−2·h−1 with separation efficiency higher than 99.2 %. Moreover, excellent chemical stability as well as outstanding antifouling performance of the PDA-modified electrospun membrane provided long-term durability for oil/water separation. The developed PVA/SiO2@PDA membrane with superwetting property and good reusability exhibited prospective potential in the remediation of oily wastewater.

Superhydrophilic and underwater superoleophobic Graphene oxide-Phytic acid membranes for efficient separation of oil-in-water emulsions

The increase in oily wastewater generation from industrial effluents and accidental oil spills has become a severe environmental concern today. Recently, tailored wettability materials have received extensive research interest due to their potential applications in remediation of oily wastewater. Herein, a superhydrophilic and underwater superoleophobic membrane was synthesised by a two-step approach: surface coating of graphene oxide-phytic acid (GO-PA) mixture on a polyvinylidene fluoride (PVDF) support membrane followed by Fe3+ deposition via metal-organophosphate coordination interaction. The optimised GO-PA-Fe3+/PVDF membrane possessed a water contact angle of 1.4° and an underwater oil contact angle of 163.4°. In the separation of surfactant-stabilised sub-micron sized oil-in-water emulsions (of 0.01 – 1 µm) at 0.4 bar, a permeation flux of up to 43.7 LMH/bar and separation efficiency of > 99.5% were achieved with the synthesised GO-PA-Fe3+/PVDF. This permeation flux was also observed to be six times higher than pristine GO/PVDF. The robust membrane exhibited excellent recyclability with a separation efficiency of > 99% and permeation flux of 38.2 – 41.8 LMH/bar for ten cycles. The research establishes a promising avenue towards tuning Graphene-oxide membranes for treatment of sub-micron sized oily wastewater, while maintaining a high permeation flux.

Constructing a Hierarchical Hydrophilic Crosslink Network on the Surface of a Polyvinylidene Fluoride Membrane for Efficient Oil/Water Emulsion Separation

Oil/water mixtures from industrial and domestic wastewater adversely affect the environment and human beings. In this context, the development of a facile and improved separation method is crucial. Herein, dopamine was used as a bioadhesive to bind tea polyphenol (TP) onto the surface of a polyvinylidene fluoride (PVDF) membrane to form the first hydrophilic polymer network. Sodium periodate (NaIO4) is considered an oxidising agent for triggering self-polymerisation and can be used to introduce hydrophilic groups via surface manipulation to form the second hydrophilic network. In contrast to the individual polydopamine (PDA) and TP/NaIO4 composite coatings for a hydrophobic PVDF microfiltration membrane, a combination of PDA, TP, and NaIO4 has achieved the most facile treatment process for transforming the hydrophobic membrane into the hydrophilic state. The hierarchical superhydrophilic network structure with a simultaneous underwater superoleophobic membrane exhibited excellent performance in separating various oil-in-water emulsions, with a high water flux (1530 L.m-2 h-1.bar) and improved rejection (98%). The water contact angle of the modified membrane was 0° in 1 s. Moreover, the steady polyphenol coating was applied onto the surface, which endowed the membrane with an adequate antifouling and recovery capability and a robust durability against immersion in an acid, alkali, or salt solution. This facile scale-up method depends on in situ plant-inspired chemistry and has remarkable potential for practical applications.

Fabrication of novel zwitterionic copolymer high performance membrane applied for oil/water mixtures and emulsions separation

The separation of oily wastewater is important for the ecological environment. Due to all kinds of defects in traditional methods, membrane technology shows outstanding merit for separating oil contaminants from water. In this work, a novel zwitterionic monomer 2-(3-carboxyacryloyloxy)-N-(Carboxyethyl)-N, N-dimethyl ethanaminium (DMAAA) was synthesized and characterized. Then, a novel zwitterionic copolymer, poly(2-(3-carboxyacryloyloxy)-N-(Carboxyethyl)-N, N-dimethyl ethanaminium-co-2-hydroxyethyl acrylate) (P(DMAAA-co-HEA)) was prepared by free radical polymerization. The superhydrophilic and underwater-superoleophobic membranes were prepared using stainless steel mesh (SSM) with different pore sizes as substrate, P(DMAAA-co-HEA) as superhydrophilic component, nano-silica (SiO2) as micro-nano porous structure, and tetraethyl orthosilicate (TEOS) as cross-linking agent by the one-step dip-coating method. P(DMAAA-co-HEA)-TEOS-SiO2 coated 400 mesh SSM(PTS-SSM400) exhibits ultra-high separation flux (243,600 L·m−2·h−1) and separation efficiency (>99.88%) in separating oil/water mixtures. And the coated 2000 mesh SSM (PTS-SSM2000) can separate various surfactant-stabilized emulsions with high water flux and efficiency only under gravity. Moreover, the membranes have excellent chemical stability and wear resistance. Even having been successively immersed for seven days in acidic, alkaline, and saline environments, respectively, and after 50 wear resistance cycle tests, the coated membranes can still effectively separate oil/water mixtures. The simple and facile preparation method is especially suitable for large-scale practical industrial applications.

Discarded Cigarette Butts Regenerated Superhydrophilic/ Underwater Superoleophobic Chitosan–Cellulose Membrane for Oil/ Water Emulsion Separation

With the rapid development of the chemical industry, oil/ water emulsion separation is receiving global attention. It is particularly important to find a low-cost, convenient, economical and environmentally friendly method to prepare superhydrophilic/ underwater superoleophobic membranes for oil/ water emulsion separation. In this paper, discarded cigarette butts were used as raw materials, combined with chitosan to form a superhydrophilic/ underwater superoleophobic membrane through a phase inversion method. The performance of CA/CS membrane is controlled by adjusting the ratio of cellulose acetate and chitosan. The cigarette butts are washed in ethanol solution to remove impurities to obtain cellulose acetate, and then chitosan and polyvinylpyrrolidone (PVP) are added to build the micro–nano structure on the surface of the membrane. The prepared CA/CS composite membrane was superhydrophilic/ underwater superoleophobic. For the oil-in-water emulsion, the filtrate of the CA/CS membrane can hardly see the oil droplets through electron microscope. CA/CS membrane has a higher emulsion permeation flux (more than 340 L m[Formula: see text] h[Formula: see text] and a higher separation efficiency (more than 97.1%). In addition, the membrane has good reusability within 10 cycles. This method can reduce the harm of cigarette butts to nature and can also be used for oil–water separation. The method of turning discarded cigarette butts into treasure is worthy of social advocacy.

A super-hydrophilic and underwater super-oleophobic membrane with robust anti-fouling performance of high viscous crude oil for efficient oil/water separation

In recent years, crude oil-spill accidents released millions of tonnes of crude oil into the environment worldwide. Oily wastewater has persistent harmful influences on the marine environment and animal health. It is essential to dispose of crude-oil contained wastewater. The high adhesion of crude oil is easy to adhere to the surface of separation materials, and traditional separation equipments always become invalidation when used for treating the oily wastewater containing crude oil. To solve this problem, we have successfully prepared super-hydrophilic chitosan hydrogel coated metal mesh (CS-SSM) via a simple coating method and the cross-linking reaction of chitosan and glutaraldehyde, which exhibits robust anti-high viscous crude oil-fouling performance. The super-hydrophilic CS-SSM showed excellent separation performance for various oil/water mixtures, and the separation efficiency and flux for the high viscous crude oil/water mixture exceed 99.99% and 12,000 L·m−2·h−1 respectively. Moreover, the molecular dynamics simulation clarified that the chitosan hydrogel coating the surface of metal mesh can dramatically decrease the interaction between crude oil molecules and metal mesh, resulting in the robust anti-high viscous crude oil-fouling performance for CS-SSM. In addition, the oil skimmer fabricated with the super-hydrophilic CS-SSM was demonstrated to effectively deal with large-area spills of crude oil.

Micro-dissolved fabrication of robust superhydrophilic and underwater superoleophobic membranes based on cotton fabrics for oil/water separation

The superhydrophilic and underwater superoleophobic membranes based on textile possessed excellent separation efficiency as well as outstanding anti-oil fouling property, while the poor stability caused by nanoparticle (NP) shedding had severely limited the practical application in oily water separation. In this paper, a feasible method of fabricating the robust membranes based on cotton fabric (CF), which was decorated with TiO2 NP and citric acid (CA) through micro-dissolution method, was reported. Firstly, the CF was slightly dissolved in the NaOH/Urea solution at low temperature, accelerating the destruction of the cellulose macromolecule on the superficial layers of the fabrics. Then, the vacuum filtration process promoted the TiO2 NP to distribute uniformly on the CF surface. In the subsequent coagulation process, the TiO2 NP were firmly anchored on the fabric surface because of self-glue effect of micro-dissolved CF. Finally, the esterification reaction between CA and CF was carried out to enhance the hydrophilic property of CF. The prepared membranes were characterized by fourier transform infrared spectroscopy, scanning electron microscopy (SEM), X-ray diffraction and thermogravimetric analysis. Additionally, the separation performance and stability of membranes were systematically evaluated. The results of SEM indicated that the TiO2 NP were uniformly anchored on the membrane surface. Especially, the prepared membranes could not only separate traditional oil/water mixture but also treat complicated oil-in-water (O/W) emulsion with excellent separation efficiency. What’s more, the membranes could withstand various harsh condition and exhibit excellent application stability. In terms of separation performance and stability, the CA/TiO2 decorated cotton fabrics have the potential to be used in the practical oily water separation.Graphical abstract

Remediation of saline oily water using an algae-based membrane

Petrochemical industry generates large amounts of oily wastewater that requires effective treatment methods. Among all, membrane filtration techniques have been receiving more attention, due to easy operation and low energy consumption. One of the issues is that the oily wastewater also contains high level of salinity. Thus, preparation of dual function membrane to be used for purification of saline oily wastewater is an attractive option. Inspired from fish scales, we prepared an underwater superoleophobic membrane using microalgae coated on steel mesh which can also be used in water desalination. In order to fix microalgae biofilm on the surface of steel mesh, PVA polymer and glutaraldehyde as crosslinking reagent was used. The salts can also be removed using microalgae biomass coated on steel mesh by the adsorption process. The prepared membrane demonstrated high efficiency (above 98%) for oil-water separation with the highest water flux of 30225.0 L m−2 h−1. Under optimized conditions, algae-based mesh exhibited salt rejection of (98.6 ± 0.5) %. Due to its simplicity, low cost and great performance in both oil-water separation and water desalination, the as-prepared membrane could find broad applications for commercial purposes.

Engineering a superwetting membrane with spider-web structured carboxymethyl cellulose gel layer for efficient oil-water separation based on biomimetic concept

Superhydrophilic and underwater superoleophobic membranes have recently attracted significant interest as materials for effective oil-water emulsion separation.In this work, a superwetting membrane with a spider web structured gel layer was designed for efficient oil-water separation. Biomaterial, carboxymethyl cellulose (CMC), was used as the raw material, a spider web structured gel layer was constructed on the PVDF membrane surface by heat-treatment and chemical cross-linking. The hydrophilic gel layer imparted excellent superhydrophilic and underwater superoleophobic properties to the membrane, while the special spider web structure improved the membrane mechanical stability. The fabricated membrane exhibited superhydrophilicity and underwater superoleophobicity. Among different CMC concentration-modified membranes, the M-0.5 membrane containing 0.5 wt% CMC exhibited a flux of 612 L·m−2 h−1 during dichloromethane oil-water emulsion separation, which was 4.2-fold higher than that of the pristine PVDF membrane, while the membrane showed efficient oil-water separation capacity. Additionally, the water flux recovery reached as high as 93.3 %, and oil rejection attained 99.1 %. Meanwhile, the spiderweb-structured gel layer on the membrane surface displayed good mechanical stability. In summary, this novel membrane-modification method, inspired by the spider web structure, was simple, cost effective and environmentally friendly, thereby making it promising for future preparation of highly efficient oil-water emulsion separation membranes.

Multifunctional fly ash-based GO/geopolymer composite membrane for efficient oil-water separation and dye degradation

Membrane fouling and separation materials with low cost and high efficiency are challenges for membrane separation technology in wastewater treatment. Superhydrophilic and underwater superoleophobic membranes show broad application prospects in oily wastewater treatment because of their high permeability, selectivity, and antifouling performance; however, they are generally ineffective for organic pollutant molecules. In this study, a novel graphene oxide (GO)/geopolymer composite membrane with superhydrophilic and underwater superoleophobic characteristics was prepared by dipping a mixed slurry of GO and fly ash-based geopolymer onto a stainless steel mesh via a facile self-assembly process. The results show that GO could adjust the hydrophilicity and water flux of composite membranes. The composite membrane containing 0.4 wt% GO (4GO/GCM) had the best hydrophilic, water flux of 1363 kg/(m2·h), and high separation efficiencies (≥98.2%) for oil-water mixtures and oil-in-water emulsions under gravity-driven. In addition, the 4GO/GCM sample exhibited excellent stability under harsh conditions, including hot water and strong acid, alkali, and salt solutions. Importantly, the sample derived from fly ash exhibited unique photocatalytic degradation performance for organic dye molecules under simulated solar-light irradiation. Thus, it is believed to this strategy has substantial potential for high-value utilization of fly ash and the sustainable treatment of oily and dye wastewater.

Super hydrophilic modified biaxially oriented polypropylene microporous membrane for excellent gravity-driven oil/water emulsion separation

Considering the protection of our natural environment from oily wastewater toxicity, the biaxially orientated polypropylene (PP) microporous membrane is taken as a suitable substrate to prepare a super hydrophilic and underwater superoleophobic membrane for oily wastewater separation. It is designed as a large-scale, cost-effective, and stable technology with the minimum possible environmental pollution to prepare the membrane for oily wastewater emulsion separation. The hydrophobic PP membrane is initially treated via corona discharge treatment followed by a grafting reaction with hydrophilic acrylamide monomer to generate rough micro-nano structures and polar functional groups. The permanent super hydrophilicity and underwater oleophobicity properties are accomplished by measuring the water contact angle (∼ 0°) and the underwater-oil contact angle (∼ 153°) over 10 weeks. Due to its excellent mechanical properties with a uniform modified micro-nano porous structure, significant separation flux with high efficiency is achieved for layered mixtures, surfactant-free, and surfactant-stabilized emulsions over 10 times reusability. Consequently, all separation processes are handled by the energy-saving gravity-driven separation method. Overall, this study demonstrated the super hydrophilic and underwater superoleophobic biaxially oriented polypropylene membrane, prepared in a stable and large-scale approach with outstanding separation performance, which can be widely used in emulsion separation and practically as an excellent solution for water separation from oily wastewater.

Underwater superoleophobic mesh with robust Anthurium andraeanum-like attapulgite coating layer for effective oil spill recovery

It is highly desired to develop an efficient and stable approach to recover water from oil-water mixtures. In this work, we reported the facile fabrication of superhydrophilic and underwater superoleophobic membranes by coating a layer of Anthurium andraeanum-like attapulgite (ARATP) on commercially available wire meshes via sintering. The ARATP was obtained through anchoring nano-Fe3O4 on attapulgite (ATP), and its micro nano-structures can be adjusted by varying Fe3O4 content. Molecular dynamic simulations revealed the benefits of Fe3O4 in constructing superwetting coating layer with oil droplet repulsion larger than 227 KJ·mol−1. The membrane exhibited underwater superoleophobicity (with underwater oil contact angle at 157°) and was proven to treat various oil-water mixtures effectively (with a water permeation flux above 3249 L·m−2·h−1 and oil content in filtrate less than 2 mg·L−1). Furthermore, the chemical, mechanical stability and easy-cleaning property of the as-prepared membrane was demonstrated by different tests.

A stable underwater superoleophobic membrane constructed by CuO oriented rods and PAA water-adsorbent resin for fast and high efficient oil–water separation

The practicalapplication of filter membranes for oil–water separation requires high efficient, large flux and excellent stability. Hydrogel membrane with superhydrophilicity and underwater superoleophobicity has been considered as an ideal material for efficient separation of oil–water mixture. However, hydrogel materials are generally fragile and easy to dehydrate. In this work, inorganic CuO oriented-rods framework was used to support water-adsorbent polyacrylic acid (PAA) resin for constructing superhydrophilic-superoleophobic composite hydrogel membrane. The as-prepared composite membrane displayed stable underwater superoleophobicity during swelling-drying cycles and abrasion test. In “bottom-injection” filter apparatus, the CuO@PAA membrane exhibited high separation efficiencies, above 99.90%, for kerosene-water, hexadecane-water, soybean oil–water and rapeseed oil–water mixtures with water penetration fluxes larger than 5700 L•m−2•h−1. The excellent separation efficiency and flux were capable of maintaining for 200 separation processes. This work paved the way for designing and constructing economical and practical oil–water separation equipment for industrial application.