Oil Contact Angle Research Articles

Chitosan interpenetrating polymer network hydrogels for oil–water and emulsion separation

AbstractHydrogels have obtained extensive attention in oil–water separation due to their high hydrophilicity and weak viscosity. However, most hydrogels have limited applications due to their subpar mechanical qualities. The interpenetrating network gives the hydrogel material high mechanical properties due to the presence of physical and chemical crosslinking. Hence, polyvinyl alcohol/chitosan/polyacrylamide interpenetrating polymer network hydrogel (HAPC‐Gel) was created in this study. HAPC‐Gel coating filter cloth showed underwater super‐oleophobic (the oil contact angles about 159°) and could stably separate oil–water mixtures in different oil phases and complex environments (acids, bases, salts), and the removal rate is still above 99% after 20 cycles of separation. Furthermore, the water could be divided from the oil‐in‐water emulsion. These results indicate that HAPC‐Gel composites have promising applications in oil–water separation.

OGF nanocomposite foam for enhanced recyclability and oil-recovery

Continuous oil spills around the world not only affect the air and water quality but also lead to massive destruction of the natural ecosystem of shallow and deep-waters. Existing methods for oil sorption lack ease of reusability, selectivity and mass production. Thus, there is an urgent need to develop economical, scalable, and efficient oil sorbent material. Here, we report a polymer nanocomposite foam of oxidised graphene frameworks (OGFs) derived using agro-waste. The OGFs impart porosity, hydrophobicity, and super-oleophilicity to the foam, resulting in enhanced sorption capacity of different categories of oils such as lubricants, organic solvents, vegetable oils and locomotive oils. Sorption capacity for DCM, diesel and mustard oil was found to be 27.4, 6.18 and 6.4 gg-1 respectively. Surface-wetting properties improved to super-oleophilic and hydrophobic, with an oil contact angle of 0° and water contact angle of 120 ± 3°, respectively. Compared to pristine polymeric foam, the nanocomposite foam shows ∼80% increase in tensile modulus and compressive strength, making it durable during handling and recycling. It is found to be stable in highly acidic, basic and saline conditions and shows excellent sorption performance even after 500 cycles, making it attractive for commercial applications. OGF-incorporated nanocomposite foam has demonstrated superb sorption and mechanical with excellent recycling properties, which makes it suitable for recovering oils and organic solvents from spills and resolving the problem of oil pollution in sea and surface water with recovery of precious resources. Our findings pave the way for the direct implementation of developed nanocomposite foam for commercial application.

Superhydrophilic and underwater superoleophobic ceramic membranes grafted by layered polydopamine and polydopamine encapsulated silica particles for efficient separation of oil-in-water emulsions

Owing to frequent oil spills and the increasing discharge of oily wastewater, oil pollution has threatened the sustainability of the ecosystem. Ceramic membranes (CM) have been employed for oily wastewater treatment because of their mechanical and chemical stability, but a suitable separating layer is required to treat surfactant-stabilized oil-in-water emulsions effectively. Herein, a separating layer was rationally designed on the CM surface by combining cross-linked layered polydopamine (CL-LPDA) and polydopamine-encapsulated silica particles (SiO2@PDA) with appropriate permeation flux and antifouling characteristics. The resulting CL-LPDA-SiO2@PDA-CM demonstrated superhydrophilicity with a water contact angle of 0° and underwater superoleophobicity with an underwater oil contact angle of 157°, making it an ideal membrane for separating oil-in-water emulsions. The designed membrane could treat a surfactant-stabilized oil-in-water emulsion with a maximum separation efficiency of 97 % and a permeation flux of 109.76 L m−2h−1. The CL-LPDA-SiO2@PDA-CM has also shown significant resistance to fouling under 20 cycles of observation, and the flux recovery ratio (FRR) was higher than 90 %, indicating that pore-clogging could be effectively prevented in the separating layer.

Preparation of superhydrophilic-underwater superoleophobic silica nanorods modified fiber membrane for efficient oil-in-water emulsion separation

Silica nanorods modified fiber membranes were successfully fabricated for the separation of emulsions by filtration deposition method. Compared to the unmodified membranes, the arithmetic mean and root mean square of the membranes were 5.69 μm and 9.71 μm, with an improvement of 39.8% and 46.0%, respectively. Roughness increases improved hydrophilicity and underwater oleophobicity of the membrane. The instantaneous water contact angle (WCA) and underwater oil contact angle (UOCA) reached 0° and 151.92°, showing excellent superhydrophilic and underwater superoleophobic properties. The structural stability of the membranes was demonstrated by testing the mass and microstructural changes after continuous ultrasonic treatment, where the mass loss was only 5.42% and no significant changes in the microstructure were observed. Moreover, following immersion treatment with acid, alkali, and saline solutions, the maximum loss of membrane mass was only 1.20% and it remained underwater oleophobic, displaying excellent chemical stability. The separation efficiency of the silica nanorods modified fiber membrane for oil-in-water emulsions was as high as 96%, and the separation flux was above 1900 L m−2 h−1·bar−1. The separation efficiency of the membranes was consistently maintained above 96% for 5 cycles.

Control the hydrophilic layer thickness of Janus membranes by manipulating membrane wetting in membrane distillation

Janus membranes with asymmetric wettability have attracted wide attentions for their robust anti-oil-wetting/fouling abilities in membrane distillation (MD). Compared to traditional surface modification approaches, in this study, we provided a new approach which manipulated surfactant-induced wetting to fabricate Janus membrane with a controllable thickness of the hydrophilic layer. The membranes with 10, 20, and 40 μm of wetted layers were obtained by stopping the wetting induced by 40 mg L−1 Triton X-100 (J = 25 L m−2 h−1) at about 15, 40, and 120 s, respectively. Then, the wetted layers were coated using polydopamine (PDA) to fabricate the Janus membranes. The resulting Janus membranes showed no significant change in porosities or pore size distributions compared with the virgin PVDF membrane. These Janus membranes exhibited low in-air water contact angles (< 50°), high underwater oil contact angles (> 145°), and low adhesion with oil droplets. Therefore, they all showed excellent oil-water separation performance with ∼100% rejection and stable flux. The Janus membranes showed no significant decline in flux, but a trade-off existed between the hydrophilic layer thicknesses and the vapor flux. Utilizing membranes with tunable hydrophilic layer thickness, we elucidated the underlying mechanism of such trade-off in mass transfer. Furthermore, the successful modification of membranes with different coatings and in-situ immobilization of silver nanoparticles indicated that this facile modification method is universal and can be further expanded for multifunctional membrane fabrication.

Efficient oily wastewater treatment by a novel electroflotation-membrane separation system consisting a Ni-Cu-P membrane prepared by electroless nickel plating

Electroflotation-membrane separation system with a conductive membrane has recently emerged as a promising technology for oily wastewater treatment. However, the conductive membrane prepared by electroless plating often suffers the problems of low stability and high activation cost. To solve these problems, this work proposed a new strategy regarding surface metallization of polymeric membrane by surface nickel-catalyzed electroless nickel plating of nickel‑copper‑phosphorus alloys for the first time. It was found that, addition of copper source remarkably enhanced the membranes' hydrophilicity, corrosion resistance and fouling resistance. The Ni-Cu-P membrane had an underwater oil contact angle of up to 140°, and simultaneously possessed rejection rate > 98 % with rather high flux of 65,663.0 L·m−2·h−1 and excellent cycling stability when separating n-hexane/water mixtures under gravity drive. The permeability is higher than the state-of-the-art membranes for oil/water separation. The Ni-Cu-P membrane as the cathode can be assembled into an electroflotation-membrane separation system, allowing to separate oil-in-water emulsion with 99 % rejection. Meanwhile, the applied electric field significantly improved membrane flux and fouling resistance (flux recovery up to 91 %) when separate kaolin suspensions. Polarization curve and Nyquist curve analysis further confirmed that addition of Cu element obviously enhanced corrosion resistance of the Ni modified membrane. This work provided a novel strategy to make up high-efficiency membranes for oily wastewater treatment.

Oil–Water Separation on Hydrophobic and Superhydrophobic Membranes Made of Stainless Steel Meshes with Fluoropolymer Coatings

In this work, membranes were synthesized by depositing fluoropolymer coatings onto metal meshes using the hot wire chemical vapor deposition (HW CVD) method. By changing the deposition parameters, membranes with different wetting angles were obtained, with water contact angles for different membranes over a range from 130° ± 5° to 170° ± 2° and a constant oil contact angle of about 80° ± 2°. These membranes were used for the separation of an oil–water emulsion in a simple filtration test. The main parameters affecting the separation efficiency and the optimal separation mode were determined. The results reveal the effectiveness of the use of the membranes for the separation of emulsions of water and commercial crude oil, with separation efficiency values that can reach over 99%. The membranes are most efficient when separating emulsions with a water concentration of less than 5%. The pore size of the membrane significantly affects the rate and efficiency of separation. Pore sizes in the range from 40 to 200 µm are investigated. The smaller the pore size of the membranes, the higher the separation efficiency. The work is of great economic and practical importance for improving the efficiency of the membrane separation of oil–water emulsions. It lays the foundation for future research on the use of hydrophobic membranes for the separation of various emulsions of water and oil products (diesel fuel, gasoline, kerosene, etc.).

A superhydrophobic/superoleophilic rGO modified melamine sponge for efficient oil sorption under static, continous and photothermal condition

Sponges have been widely studied as common adsorbent materials. There is little research on sponges that can be used for comprehensive treatment of oil-water mixtures, emulsions and high viscosity oils. We prepared a graphene melamine sponge (rGOMS) adsorbent material with special wettability for oil water separation by loading rGO on melamine sponge. The results showed that the water contact angle of the rGOMS prepared with GO concentration of 4.5 mol/mL (4.5-rGOMS) was 153.3° and the oil contact angle in air was 0°, indicating that 4.5-rGOMS has superhydrophobicity and superlipophilicity. The 4.5-rGOMS possessed a high saturation sorption capacity, which had values between 54.6 g/g and 132.9 g/g, and did not decrease significantly after several cycles. 4.5-rGOMS had a fast separation capacity for carbon tetrachloride/water mixtures and water-in-oil emulsions, and could achieve efficient continuous separation of n-hexane-water mixtures by connecting a peristaltic pump.

Highly robust separation for aqueous oils enabled by balsa wood-based cellulose aerogel with intrinsic superior hydrophilicity

Owing to the strong adsorption capacity, cellulose aerogel has emerged as a promising material in the field of oil–water separation. In this study, we have taken advantage of the inherent superior hydrophilicity of balsa wood-based cellulose aerogel for the separation of various aqueous oils. A facile approach to preserve inherent hydrophilic cellulose nanofibers was achieved by removing lignin and hemicellulose fractions from natural wood, resulting in flexible cellulose aerogel with lamellar architecture. As a result, the separation efficiency of cellulose aerogel can achieve 99.97% for immiscible aqueous oils, and 98.45% even for water-in-oil emulsions. Moreover, the as-prepared cellulose aerogel exhibits remarkable mechanical properties, with stress decay of 7% after 60 compression cycles making it recycle feasible. When exposed to several complex environments including acid, alkaline and salt for a long time, the cellulose aerogel remains stable superoleophobicity with underwater oil contact angle of 153.2 ± 1.2°. Given the low operating cost, high separation efficiency and durability and stability of cellulose aerogel, this work provides a promising material for aqueous oils purification.

Robust Superhydrophobic PDMS@SiO2@UiO66-OSiR Sponge for Efficient Water-in-Oil Emulsion Separation.

A major challenge in oil/water separation is the processing of surfactant-stabilized emulsions from the water medium. One of the feasible schemes of emulsion separation is the porous melamine sponge coupled with functional particles. Here, we proposed a novel superhydrophobic metal-organic framework (MOF)-based sponge for water-in-oil emulsion separation. The porous melamine sponge was combined with poly(dimethylsiloxane) (PDMS)-coated hydrophobic SiO2 and UiO66-OSiR particles were prepared for demulsification via the one-step dipping method for the first time. The PDMS@SiO2@UiO66-OSiR sponge revealed excellent superhydrophobicity at a water contact angle of 160.7° and superlipophilicity at an oil contact angle of 0°. Compared with the pristine melamine sponge, the size-controllable PDMS@SiO2@UiO66-OSiR sponge could separate stabilized water-in-oil emulsions with ultrahigh separation efficiency (>98.64%) and high flux (e.g., 970 L·m-2·h-1). Meanwhile, the PDMS@SiO2@UiO66-OSiR sponge exhibited superior durability and mechanical reusability. Under harsh conditions such as strong acid and alkali, organic solvent corrosion, etc., all water contact angles of the PDMS@SiO2@UiO66-OSiR sponge were over 152°. Furthermore, the stress decreased by 5% when the sponge was subjected to 10 loading/unloading compression cycles at a constant strain of 60%. These results demonstrate that the PDMS@SiO2@UiO66-OSiR sponge can efficiently separate water-in-oil emulsions through its adjustable porous structure coupled with demulsification and hydrophobic particles. This study provides a step forward in developing a feasible strategy for the MOF-based sponge for emulsion separation.

Temperature and pH endurable self-assembled camellia-like nanostructure achieved on zinc sheet with superamphiphobicity for fog harvesting

Easy-implement and low-cost fabrication of super-hydrophobic/super-oleophobic materials is of great significance for efficient fog harvesting. Herein, we propose a simple two-step procedure based on Cu/1-octadecanethiol (ODT) self-assembled monolayer (SAM) modified zinc plates. Interestingly, the whole process mimics the blooming process of flowers in nature: the deposition of copper particle and the subsequent formation of SAM drives the surface undergo gradually stretches and finally blooms to camellia-like nanostructures. The water contact angle (WCA) and oil contact angle (OCA) reach 160 ± 1° and 159 ± 1° respectively, as a result of the formation of layered petal structure that traps air effectively, which is attributed as one of the most important factors for the superamphiphobic effect. In addition to much enhanced facility in fog collection, the materials maintain excellent performance in acid/base environments (1 ≤ pH ≤ 14), broad temperature conditions ranging from −18 °C to 240 °C, and the artificial sea environment, and exhibit capable wear resistance as well as self-cleaning property. The cooperation of all these multiple properties ensures the robustness and stability for efficient fog collection.

Controlling Superhydrophobicity and Oleophobicity of Polydimethylsiloxane-Coated Silica Hybrid Particles

Hierarchical functional organic-inorganic hybrid particles for versatile control of surface wettability have attracted much attention in a wide range of applications from makeup cosmetics to anti-smudging optoelectronic devices. In this study, superhydrophobic and oleophobic organic-inorganic hybrid particles were prepared by a simple and systematic fabrication strategy using the synergistic combination of commonly available silica particles and polydimethylsiloxanes (PDMSs) with hydrophobic chain ends. Various types of PDMSs with different chain lengths and chemical structures were surface-grafted to silica microparticles through facile physical dispersion and subsequent thermal treatment to form hydrogen bonds or covalent bonds between the inorganic silica and organic PDMS polymers and thus induce a core-shell structure for the hybrid particles, which imparts superhydrophobicity and oleophobicity to the surface of silica particles. The prepared PDMS-coated silica hybrid particles with long PDMS chains exhibited a water contact angle of 151.2° and an oil contact angle of 15.2° due to the rough surface morphology and hydrophobic long-chain effects. Furthermore, the resulting organic-inorganic hybrid particles were thermally stable up to 420 °C. This controlled approach endowed the organic-inorganic hybrid particles with both superhydrophobic and oleophobic surfaces and, therefore, these particles were proven to be suitable for waterproof applications.

Underwater superoleophobic cellulose/acrylamide-modified magnetic polyurethane foam for efficient oil/water separation

A superhydrophilic/underwater superoleophobic magnetic cellulose and acrylamide-modified polyurethane foam (Fe₃O₄-CE-AM@PUF) was prepared for effective gravity-driven oil/water separation. The prepared materials were characterized for their structure and morphology using various characterization techniques. The prepared carbohydrate polymeric composite showed excellent superhydrophilic/underwater superoleophobic properties with a good static underwater oil contact angle of 160°. Furthermore, it exhibited remarkable oil-repellent properties in acidic, basic, and saline water. Fe₃O₄-CE-AM@PUF could also be used after immersion in water for 100 h, and also delivered an excellent underwater superoleophobic performance with an underwater oil contact angle of 155°. Moreover, it demonstrated a high separation efficiency (>99.15%) and an excellent flux up to 31181 Lm−2h−1 for various kinds of oil-water mixtures. The separation flux and efficiency of n-Hexane have not significantly changed after 50 cycles of separation. Fe₃O₄-CE-AM@PUF's high porosity, superhydrophilic, and superoleophobic properties allowed it to continuously absorb water from oils. Its magnetic properties made it easy to remove the absorbent material with a magnet.

Decomposition of Fingerprints on Porous TiO2 Thin Films

This study investigated the effect of the mixing ratio of TiO2 nanoparticles (P25) and titanium alkoxide (T-sol) on various properties of TiO2 films. The specific surface area of the TiO2 film was determined using BET analysis, while the microstructure and thickness were analyzed by field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM), respectively. Transmittance and pencil hardness tests were conducted to evaluate the transparency and durability of the coating layer, respectively. The results showed that, as the P25 content increased, the specific surface area of the TiO2 film also increased, but this effect decreased as the ratio of T-sol to P25 increased. Additionally, the thickness and surface roughness (Ra) of the coating layer increased as the P25 content increased, with the thickness increasing from 210 to 950 nm and Ra increasing from 51 to 88 nm. However, the transmittance of the coating layer decreased as the P25 content increased, indicating that the films became less transparent. Furthermore, the pencil hardness of the coating layer decreased as the P25 content increased, indicating that the films became less durable. Finally, the oil contact angle decreased as the P25 content increased, indicating that the films became more hydrophilic.

Eco-Friendly Fluorine Functionalized Superhydrophobic/Superoleophilic Zeolitic Imidazolate Frameworks-Based Composite for Continuous Oil-Water Separation.

Superhydrophobic metal-organic framework (MOF)-based sponges have received increasing attention in terms of treating oil-water mixtures. However, highly fluorinated substances, commonly used as modifiers to improve the hydrophobicity of MOFs, have aroused much environmental concern. Developing a green hydrophobic modification is crucial in order to prepare superhydrophobic MOF-sponge composites. Herein, we report the preparation of a porous composite sponge via a polydopamine (PDA)-assisted growth of zeolitic imidazolate frameworks (ZIF-90) and eco-friendly hydrophobic short-chain fluorinated substances (trifluoroethylamine) on a melamine formaldehyde (MF) sponge. The composite sponge (F-ZIF-90@PDA-MF) exhibited superhydrophobicity (water contact angle, 153°) and superoleophilicity (oil contact angle, 0°), which is likely due to the combination of the low surface energy brought on by the grafted CF3 groups, as well as the rough surface structures that were derived from the in situ growth of ZIF-90 nanoparticles. F-ZIF-90@PDA-MF showed an excellent adsorption capacity of 39.4-130.4 g g-1 for the different organic compounds. The adsorbed organic compounds were easily recovered by physical squeezing. Continuous and selective separation for the different oil-water mixtures was realized by employing the composite sponge as an absorbent or a filter. The separation efficiency and flux reached above 99.5% and went up to 7.1 ×105 L m-2 h-1, respectively. The results illustrate that the superhydrophobic and superoleophilic F-ZIF-90@PDA-MF sponge has potential in the field of water-oil separation, especially for the purposes of large-scale oil recovery in a water environment.

Three dimension-printed membrane for ultrafast oil/water separation as driven by gravitation

Facing millions of tons of discharged oily wastewater each year worldwide, it is highly desired to develop eco-friendly, cost-effective and high-efficiency oil/water separation technology with antifouling performance. Herein, three-dimensional (3D) printing technology is applied to develop an eco-friendly acrylonitrile-butadiene-styrene (ABS) membrane that is modified by an eco-friendly plasma strategy without chemical consumption. The modified membrane demonstrates excellent hydrophilicity and oleophobicity, with a water contact angle of 8.8° and underwater oil contact angle of 137.6°. Only driven by tiny gravitation force, the modified membrane exhibits an ultra-high flux of 1.17 × 105 L·m-2·h-1 with 99.60% rejection for five typical oil/water systems. The rejection maintains 99.40% after 100 cycling tests during a four-month period, demonstrating superior stability and recyclability of the membrane. To our knowledge, this membrane largely outperforms all the state-of-the-art membranes for oil/water separation. In particular, the electron transfer of liquid and solid (L-S) surface during the contact electrification (CE) process is firstly introduced to interpret the membrane separation process. This work opens an avenue to fabricate appealing performance membranes for oil/water separation.

Durable superhydrophobic/superoleophilic melamine foam based on biomass-derived porous carbon and multi-walled carbon nanotube for oil/water separation

In the present study, fabrications of two eco-friendly superhydrophobic/superoleophilic recyclable foamy-based adsorbents for oil/water mixture separation were developed. Hierarchically biomass (celery)-derived porous carbon (PC) and multi-walled carbon nanotube (MWCNT) were firstly synthesized and loaded on pristine melamine foam (MF) by the simple dip-coating approach by combining silicone adhesive to create superhydrophobic/superoleophilic, recyclable, and reusable three-dimensional porous structure. The prepared samples have a large specific surface area of 240 m2/g (MWCNT), 1126 m2/g (PC), and good micro-mesoporous frameworks. The water contact angle (WCA) values of the as-prepared foams, PC/MF and MWCNT/MF, not only were 159.34° ± 1.9° and 156.42° ± 1.6°, respectively but also had oil contact angle (OCA) of equal to 0° for a wide range of oils and organic solvents. Therefore, PC/MF and MWCNT/MF exhibited superhydrophobicity and superoleophilicity properties, which can be considered effective adsorbents in oil/water mixture separations. In this context, superhydrophobic/superoleophilic prepared foams for kind of different oils and organic solvents were shown to have superior separation performance ranges of 54–143 g/g and 46–137 g/g for PC/MF and MWCNT/MF, respectively, suggesting a new effective porous material for separating oil spills. Also, outstanding recyclability and reusability of these structures in the ten adsorption-squeezing cycles indicated that the WCA and sorption capacity has not appreciably changed after soaking into acidic (pH = 2) and alkaline (pH = 12) as well as saline (3.5% NaCl) solutions. More importantly, the reusability and chemical durability of the superhydrophobic samples made them good opportunities for use in different harsh conditions for oil-spill cleanup.

Anisotropic cellulose nanocrystalline sponge sheets with ultrahigh water fluxes and oil/water selectivity

Oily sewage caused by oil spill accidents has become a severe problem in the last decades. Hence, two-dimensional sheet-like filter materials for oil/water separation have received widespread attention. Porous sponge materials were developed using cellulose nanocrystals (CNCs) as raw materials. They are environmentally friendly and easy to prepare, with high flux and separation efficiency. The 1,2,3,4-butane tetracarboxylic acid cross-linked anisotropic cellulose nanocrystalline sponge sheet (B-CNC) exhibited ultrahigh water fluxes driven by gravity alone, depending on the aligned structure of channels and the rigidity of CNCs. Meanwhile, the sponge gained superhydrophilic/underwater superhydrophobic wettability with an underwater oil contact angle of up to 165.7° due to its ordered micro/nanoscale structure. B-CNC sheets displayed high oil/water selectivity without additional material doping or chemical modification. For oil/water mixtures, high separation fluxes of approximately 100,000 L·m−2·h−1 and separation efficiencies of up to 99.99 % were obtained. For a Tween 80-stabilized toluene-in-water emulsion, the flux reached >50,000 L·m−2·h−1, and the separation efficiency was above 99.7 %. B-CNC sponge sheets showed significantly higher fluxes and separation efficiencies than other bio-based two-dimensional materials. This research provides a facile and straightforward fabrication method of environmental-friendly B-CNC sponges for rapid, selective oil/water separation.

Selective and Continuous Oil Removal from Oil-Water Mixtures Using a Superhydrophobic and Superoleophilic Stainless Steel Mesh Tube.

The development of continuous oil-water separation processes has applications in the treatment of industrial oily wastewater and effective management of oil spills. In this research, the performance of a superhydrophobic-superoleophilic (SHSO) membrane in oil-water separation is investigated through dynamic tests. We investigate the effects of the total flow rate and oil concentration on the separation efficiency using an as-fabricated SHSO mesh tube. To construct the SHSO membrane, a tubular stainless steel mesh is dip-coated into a solution, containing a long-chain alkyl silane (Dynasylan F8261) and functionalized silica nanoparticles (AEROSIL R812). The as-prepared SHSO mesh tube illustrates a water contact angle of 164° and an oil contact angle of zero for hexane. A maximum oil separation efficiency (SE) of 97% is obtained when the inlet oil-water mixture has the lowest flow rate (5 mL/min) with an oil concentration of 10 vol %, while the minimum oil SE (86%) is achieved for the scenario with the highest total flow rate (e.g., 15 mL/min) and the highest oil concentration (e.g., 50 vol %). The water SE of about 100% in the tests indicates that the water separation is not affected by the total flow rate and oil concentration, due to the superhydrophobic state of the fabricated mesh. The clear color of water and oil output streams also reveals the high SE of both phases in dynamic tests. The outlet oil flux increases from 314 to 790 (L/m2·h) by increasing the oil permeate flow rate from 0.5 to 7.5 (mL/min). The linear behavior of the cumulative amounts of collected oil and water with time demonstrates the high separation performance of a single SHSO mesh, implying no pore blocking during dynamic tests. The significant oil SE (97%) of the fabricated SHSO membrane with robust chemical stability shows its promising potential for industrial-scale oil-water separation applications.

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.