Durable Nano-Flower Structured Foam Coupled with Electrically-Driven in Situ Aeration Enable High-Flux Oil/Water Emulsion Separation with Dynamic Antifouling Ability

The conventional membranes used for separating oil/water emulsions are typically limited by the properties of the membrane materials and the impact of membrane fouling, making continuous long-term usage unachievable. In this study, a filtering electrode with synchronous self-cleaning functionality is devised, exhibiting notable antifouling ability and an extended operational lifespan, suitable for the continuous separation of oil/water emulsions. Compared with the original Ti foam, the in situ growth of NiTi-LDH (Layered double hydroxide) nano-flowers endows the modified Ti foam (NiTi-LDH/TF) with exceptional superhydrophilicity and underwater superoleophobicity. Driven by gravity, a rejection rate of over 99% is achieved for various emulsions containing oil content ranging from 1% to 50%, as well as oil/seawater emulsions. The flux recovery rate exceeds 90% after one hundred cycles and a 4-h filtration period. The enhanced separation performance is realized through the "gas bridge" effect during in situ aeration and electrochemical anodic oxidation. The internal aeration within the membrane pores contributes to the removal of oil foulants. This study underscores the potential of coupling foam metal filtration materials with electrochemical technology, providing a paradigm for the exploration of novel oil/water separation membranes.

Zero-Oil-Fouling Membrane With High Coverage of Grafted Zwitterionic Polymer for Separation of Oil-in-Water Emulsions

Current hydrophilic modification strategies improve the antifouling ability of membranes but fail to completely eliminate the fouling of emulsified oil droplets with a wide size distribution. Constructing membranes with superior anti-oil-fouling ability to resist various oil droplets especially at high permeation fluxes is challenging. Here, the fabrication of a zero-oil-fouling membrane by grafting considerably high coverage of zwitterionic polymer and building defect-free hydration defense barrier on the surface is reported. A uniform layer of protocatechuic acid with COOH as abundant as existing in every molecule is stably deposited on the membrane so as to provide sufficient reactive sites and achieve dense grafting of the zwitterionic polymer. The coverage of zwitterionic polymer on the membrane plays a crucial role in promoting the antifouling ability to emulsified oil droplets. The poly(vinylidene fluoride) membrane with 93% coverage of the zwitterionic polymer exhibits zero oil fouling when separating multitudinous oil-in-water emulsions with ≈0% flux decline, ≈100% flux recovery, and a high water flux of ≈800 L m-2 h-1 bar-1. This membrane outperforms almost all of the reported membranes in terms of the comprehensive antifouling performance. This work provides a feasible route for manufacturing super-antifouling membranes toward oil/water separation application.

In situ construction of green multiscale nanosilicon-based sponges for stable oil-water separation

Oil and industrial wastewater spills have caused serious ecological impacts, thus superhydrophobic materials are paid much attention for their unique oil/water selective adsorption properties. Herein, we propose a green and efficient method for preparing superhydrophobic adsorbents for oil/water separation. Superhydrophobic melamine sponges (SMS) were prepared by in situ growth of nanosilica on melamine sponge skeletons followed by surface modification with hexadecyltrimethoxysilane (HTMS). The contact angle, oil-water separation, oil absorption, recyclability, acid resistance and alkali resistance of SMS were characterised to evaluate its performance. These results showed that the prepared SMS not only exhibits superhydrophobicity with a water contact angle of 152°, but also has a strong adsorption capacity of 42-105 times its own weight for various oils and organic reagents, and outstanding recoverability with a retention of adsorption capacity of about 98% after 20 repeated cycles. In addition, it exhibits excellent environmental tolerance over a wide pH range. These excellent properties make it valuable for practical applications in the field of oil-water separation.

The Design of PAN-Based Janus Membrane with Adjustable Asymmetric Wettability in Wastewater Purification

In this paper, an environmentally friendly polyacrylonitrile-based (PAN-based) composite membrane with a Janus structure for wastewater treatment was successfully fabricated. To achieve the optimum adsorption of PAN-based Janus composite membrane, the asymmetric wettability was regulated through electrospinning, resulting in TiO2 modifying PAN as the hydrophilic substrate layer, and PCL gaining a different thickness as the hydrophobic layer. The prepared Janus composite membrane (PAN/TiO2-PCL20) showed excellent oil/water separation performance for diverse surfactant-stabilized oil-in-water emulsions. For n-hexane-in-water emulsion, the permeate flux and separation efficiency reached 1344 L m-2 h-1 and 99.52%, respectively. Even after 20 cycles of separation, it still had outstanding reusability and the separation efficiency remained above 99.15%. Meanwhile, the PAN/TiO2-PCL20 also exhibited an excellent photocatalytic activity, and the removal rate for RhB reached 93.2%. In addition, the research revealed that PAN/TiO2-PCL20 possessed good mechanical property and unidirectional water transfer capability. All results indicated that PAN/TiO2-PCL20 with photocatalysis and oil/water separation performance could be used for practical complex wastewater purification.

Superhydrophilic and Underwater Superoleophobic Copper Mesh Coated with Bamboo Cellulose Hydrogel for Efficient Oil/Water Separation

Super-wetting interface materials have shown great potential for applications in oil-water separation. Hydrogel-based materials, in particular, have been extensively studied for separating water from oily wastewater due to their unique hydrophilicity and excellent anti-oil effect. In this study, a superhydrophilic and underwater superoleophobic bamboo cellulose hydrogel-coated mesh was fabricated using a feasible and eco-friendly dip-coating method. The process involved dissolving bamboo cellulose in a green alkaline/urea aqueous solvent system, followed by regeneration in ethanol solvent, without the addition of surface modifiers. The resulting membrane exhibited excellent special wettability, with superhydrophilicity and underwater superoleophobicity, enabling oil-water separation through a gravity-driven "water-removing" mode. The super-wetting composite membrane demonstrated a high separation efficiency of higher than 98% and a permeate flux of up to 9168 L·m-2·h-1 for numerous oil/water mixtures. It also maintained a separation efficiency of >95% even after 10 cycles of separation, indicating its long-term stability. This study presents a green, simple, cost-effective, and environmentally friendly approach for fabricating superhydrophilic surfaces to achieve oil-water separation. It also highlights the potential of bamboo-based materials in the field of oil-water separation.

Hydrophobic Carbon Nitride Nanolayer Enables High-Flux Oil/Water Separation with Photocatalytic Antifouling Ability

Efficient oil/water separation tackles various issues in occasions of oil leakage and oil discharge, such as environmental pollution, recollection of the oil, and saving the water. Herein, a compact superhydrophobic/superoleophilic graphitic carbon nitride nanolayer coated on carbon fiber networks (CNBA/CF) is designed and synthesized for efficient gravity-driven oil/water separation. The CNBA/CF shows excellent oil absorption and an impressive oil/water filtration separation performance. The flux reaches the state-of-art value of 4.29 × 105 L/m2/h for dichloromethane with separation efficiency up to 99%. Successive oil absorption tests, long-term filtration separation, and harsh conditions experiments confirm the remarkable separation and chemical structure stability of the CNBA/CF filter. Besides, the CNBA/CF demonstrates good photocatalytic antifouling ability thanks to the extended visible light absorption and improved charge separation. This work combines the material surface wettability modulation with a photocatalytic self-cleaning property in the fabrication of efficient oil/water separation materials while overcoming the filter fouling issue.

Engineering of Multifunctional Nanocomposite Membranes for Wastewater Treatment: Oil/Water Separation and Dye Degradation

Multifunctional membrane technology has gained tremendous attention in wastewater treatment, including oil/water separation and photocatalytic activity. In the present study, a multifunctional composite nanofiber membrane is capable of removing dyes and separating oil from wastewater, as well as having antibacterial activity. The composite nanofiber membrane is composed of cellulose acetate (CA) filled with zinc oxide nanoparticles (ZnO NPs) in a polymer matrix and dipped into a solution of titanium dioxide nanoparticles (TiO2 NPs). Membrane characterization was performed using transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), and Fourier transform infrared (FTIR), and water contact angle (WCA) studies were utilized to evaluate the introduced membranes. Results showed that membranes have adequate wettability for the separation process and antibacterial activity, which is beneficial for water disinfection from living organisms. A remarkable result of the membranes' analysis was that methylene blue (MB) dye removal occurred through the photocatalysis process with an efficiency of ~20%. Additionally, it exhibits a high separation efficiency of 45% for removing oil from a mixture of oil-water and water flux of 20.7 L.m-2 h-1 after 1 h. The developed membranes have multifunctional properties and are expected to provide numerous merits for treating complex wastewater.

Superwetting Stainless Steel Mesh Used for Both Immiscible Oil/Water and Surfactant-Stabilized Emulsion Separation

The design and fabrication of advanced membrane materials for versatile oil/water separation are major challenges. In this work, a superwetting stainless steel mesh (SSM) modified with in situ-grown TiO2 was successfully prepared via one-pot hydrothermal synthesis at 180 °C for 24 h. The modified SSM was characterized by means of scanning electron microscopy, energy spectroscopy, and X-ray photoelectron spectroscopy analysis. The resultant SSM membrane was superhydrophilic/superoleophilic in air, superoleophobic underwater, with an oil contact angle (OCA) underwater of over 150°, and superhydrophobic under oil, with a water contact angle (WCA) as high as 158°. Facile separation of immiscible light oil/water and heavy oil/water was carried out using the prewetting method with water and oil, respectively. For both "oil-blocking" and "water-blocking" membranes, the separation efficiency was greater than 98%. Also, these SSMs wrapped in TiO2 nanoparticles broke emulsions well, separating oil-in-water and oil-in-water emulsions with an efficiency greater than 99.0%. The as-prepared superwetting materials provided a satisfactory solution for the complicated or versatile oil/water separation.

Hierarchical Ni-Mn LDHs@CuC2O4 Nanosheet Arrays-Modified Copper Mesh: A Dual-Functional Material for Enhancing Oil/Water Separation and Supercapacitors

The pursuit of superhydrophilic materials with hierarchical structures has garnered significant attention across diverse application domains. In this study, we have successfully crafted Ni-Mn LDHs@CuC2O4 nanosheet arrays on a copper mesh (CM) through a synergistic process involving chemical oxidation and hydrothermal deposition. Initially, CuC2O4 nanosheets were synthesized on the copper mesh, closely followed by the growth of Ni-Mn LDHs nanosheets, culminating in the establishment of a multi-tiered surface architecture with exceptional superhydrophilicity and remarkable underwater superoleophobicity. The resultant Ni-Mn LDHs@CuC2O4 CM membrane showcased an unparalleled amalgamation of traits, including superhydrophilicity, underwater superoleophobicity, and the ability to harness photocatalytic forces for self-cleaning actions, making it an advanced oil-water separation membrane. The membrane's performance was impressive, manifesting in a remarkable water flux range (70 kL·m-2·h-1) and an efficient oil separation capability for both oil/water mixture and surfactant-stabilized emulsions (below 60 ppm). Moreover, the innate superhydrophilic characteristics of the membrane rendered it a prime candidate for deployment as a supercapacitor cathode material. Evidenced by a capacitance of 5080 mF·cm-2 at a current density of 6 mA cm-2 in a 6 M KOH electrolyte, the membrane's potential extended beyond oil-water separation. This work not only introduces a cutting-edge oil-water separation membrane and supercapacitor electrode but also offers a promising blueprint for the deliberate engineering of hierarchical structure arrays to cater to a spectrum of related applications.

Facile Preparation of Durable and Eco-Friendly Superhydrophobic Filter with Self-Healing Ability for Efficient Oil/Water Separation

The superhydrophobic feature is highly desirable for oil/water separation (OWS) operation to achieve excellent separation efficiency. However, using hazardous materials in fabricating superhydrophobic surfaces is always the main concern. Herein, superhydrophobic filters were prepared via an eco-friendly approach by anchoring silica particles (SiO2) onto the cotton fabric surface, followed by surface coating using natural material-myristic acid via a dip coating method. Tetraethyl orthosilicate (TEOS) was used in the synthesis of SiO2 particles from the silica sol. In addition, the impact of the drying temperature on the wettability of the superhydrophobic filter was investigated. Moreover, the pristine cotton fabric and as-prepared superhydrophobic cotton filters were characterised based on Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX) and contact angle (CA) measurement. The superhydrophobic cotton filter was used to perform OWS using an oil-water mixture containing either chloroform, hexane, toluene, xylene or dichloroethane. The separation efficiency of the OWS using the superhydrophobic filter was as high as 99.9%. Moreover, the superhydrophobic fabric filter also demonstrated excellent durability, chemical stability, self-healing ability and reusability.

Versatile CO2-responsive Sponges Decorated with ZIF-8 for Bidirectional Separation of Oil/Water and Controllable Removal of Dyes

The complex wastewater containing water-soluble dyes and water-insoluble oils has given rise to significant environmental concerns that demand urgent remediation. Herein, a novel "smart" multifunctional sponge (ZIF-8@PMS) stepwise decorated with ZIF-8 nanoparticles and CO2-responsive copolymer (poly(2-(diethylamino) ethyl methacrylate-co-3-(trimethoxysilyl)propyl acrylate-co-stearyl methacrylate) was successfully prepared for CO2 controllable oil/water separation and dyes removal. The results revealed that the sponge coated with CO2-responsive copolymer for three cycles (ZIF-8@PMS-3) exhibited optimal comprehensive properties. The ZIF-8@PMS-3 had excellent compressive-resilient characteristics and chemical stability. As expected, it displayed tunable wettability and charged state under the regulation of CO2. Based on these features, ZIF-8@PMS-3 presented highly efficient removal of oil and dyes, even for the dye-containing oil/water emulsions, via a synergistic combination of adsorption and separation methods. The adsorption capacity for oil and various organic solvents ranged from 21.3 to 50 g g-1. The maximum adsorption capacities toward anionic dyes: methyl orange with 1205.89 mg g-1 and methyl blue with 880.00 mg g-1 in the presence of CO2 through electrostatic interaction. In the absence of CO2, it achieved maximum adsorption capacities for cationic dyes, including malachite green with 1246.15 mg g-1 and rhodamine B with 203 mg g-1, primarily driven by π-π interactions. According to distinct adsorption mechanisms, ZIF-8@PMS-3 could selectively adsorb either anionic or cationic dyes by exploiting CO2 as a trigger. Furthermore, the separation efficiencies for both types of oil/water emulsions surpassed 99.9%, with respective fluxes of 1566.99 L m-2 h-1 (water-in-oil emulsion) and 310.37 L m-2 h-1 (oil-in-water emulsion). Additionally, the as-prepared sponges exhibited remarkable antibacterial properties and exceptional recyclability. Therefore, the ZIF-8@PMS-3 holds substantial promise for potential applications in practical industrial wastewater treatment.

Green Synthesis of a Carbon Quantum Dots-Based Superhydrophobic Membrane for Efficient Oil/Water Separation

The efficient separation of oil and water is a significant challenge worldwide due to the increasing frequency of industrial oily wastewater. Previous work by our group utilizes biological metal-organic framework-based superhydrophobic (S.P) textile fabric for oil/water separation. However, this system is limited due to the low mechanical stability, so there is a need for producing a more robust S.P membrane for oil/water separation. In this study, we report on the synthesis of carbon quantum dots (CQD) from banana leaves via a hydrothermal process and their application in producing a robust S.P coating on textile fabric for oil/water separation. The CQDs were characterized using various techniques including TEM, XRD, absorbance spectroscopy, and the BET method. The TEM images showed that the CQDs were circular in shape with a size of 4.4 nm, while the XRD micrograph indicated that the CQDs were crystalline in nature. The UV-vis graph showed a peak at a wavelength of 278 nm, suggesting strong absorption in the ultraviolet region. The BET-specific surface area of the prepared CQDs is 845 m2/g, with a pore volume of 0.33 cm3/g, and a mean pore diameter of 1.62 nm. We examined the surface wettability, morphology, composition, oil absorption capacity, oil/water separation performance, flux rate, chemical stability, and mechanical stability of the S.P membrane. Our findings indicate that the developed CQD-based S.P membrane possesses excellent S.P properties, displaying high water contact angles of 163° and low water sliding angles of 1°. The membrane demonstrated superior oil absorption capacity, separation efficiency, and flux rate towards three different oils-petroleum ether, n-hexane, and silicone oil. Petroleum ether has the highest separation efficiency (99.5%), and flux rate (13,500 L m-2 h-1), while silicone oil has the lowest. However, silicone oil has the highest absorption capacity (218.9 g/g) and petroleum ether has the lowest (194.8 g/g). For the absorption capacity and separation efficiency, a one-way ANOVA test was conducted. The statistical analyses revealed significant differences in absorption capacity and separation efficiency for the three oils, highlighting the efficacy of the superhydrophobic membrane for tailored oil/water separation. Additionally, the S.P membrane exhibited good mechanical (the membrane maintains its superhydrophobicity until an abrasion length of 850 cm) and chemical stability (the membrane maintains its superhydrophobicity in pH range 1-13), withstanding abrasion and immersion in solutions of varying pH values. The CQD-based S.P membrane shows great potential as a promising material for oil/water separation applications, with excellent performance and stability under various environmental conditions.

Microporous Organic Network: Superhydrophobic Coating to Protect Metal-Organic Frameworks from Hydrolytic Degradation

Despite the rapid development of versatile metal-organic frameworks (MOFs), the synthesis of water-stable MOFs remains challenging, which significantly limits their practical applications. Herein, a novel engineering strategy was developed to prepare superhydrophobic MOFs by an in situ fluorinated microporous organic network (FMON) coating. Through controllable modification, the resulting MOF@FMON retained the porosity and crystallinity of the pristine MOFs. Owing to the superhydrophobicity of the FMON and the feasibility of MOF synthesis, the FMON coating could be in situ integrated with various water-sensitive MOFs to provide superhydrophobicity. The coating thickness and hydrophobicity of the MOF@FMON composites were easily regulated by changing the FMON monomer concentration. The MOF@FMON composites exhibited excellent oil/water separation and catalytic activities and enhanced durability in aqueous solutions. This study provides a general approach for the synthesis of superhydrophobic MOFs, expanding the application scope of MOFs.

Preparation of Superhydrophilic/Underwater Superoleophobic and Superhydrophobic Stainless Steel Meshes Used for Oil/Water Separation

Robust membrane materials with high efficiency have attracted extensive attention in oil/water separation. In this work, carbon particles via candle combustion were firstly adsorbed on the surface of stainless steel meshes (SSMs), which formed a thin hydrophobic coating, and a rough structure was then constructed through chemical vapor deposition and high temperature calcination, with the resultant SSM surface wrapped with uniform silica coating possessing the characteristic of superoleophobicity underwater. Scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X-ray powder diffraction (XRD) were used to characterize the modified SSMs. The prepared SSMs were superhydrophilic in air, and they had superoleophobicity underwater (157.4°). The separation efficiency of five oil/water mixtures was above 98.8%, and the separation flux was 46,300 L·m^-2·h^-1. After it was immersed in 1 mol/L NaOH, 1 mol/L HCl and 3.5 wt% NaCl for 24 h, respectively, the efficiency was still above 97.3%. Further immersion in the solution of dopamine and octadecylamine resulted in the transformation of superhydrophililc/superoleophobicity-underwater SSMs to superhydrophobic SSMs, and the resultant SSMs with reverse surface wettability was also used for the oil/water separation with good separation efficiency and separation flux.

Clay-Coated Meshes with Superhydrophilicity and Underwater Superoleophobicity for Highly Efficient Oil/Water Separation

A novel clay-coated mesh was fabricated via a simple brush-coating method without the use of special equipment, chemical reagents, and complex chemical reactions and operation processes. Possessing superhydrophilicity and underwater superoleophobicity, the clay-coated mesh can be used for efficiently separating various light oil/water mixtures. The clay-coated mesh also exhibits excellent reusability, maintaining a high separation efficiency of 99.4% after 30 repeated separations of the kerosene/water mixture.

Reusable and Biodegradable Separation Membranes Prepared from Common Mushrooms for the Removal of Oily and Particulate Contaminants from Water

Mushroom chitin membranes with controllable pore structures were fabricated through a simple process with naturally abundant Agaricus bisporus mushrooms. A freeze-thaw method was applied to alter the pore structures of the membranes, which consist of chitin fibril clusters within the glucan matrix. With tunable pore size and distribution, mushroom chitin membranes could effectively separate stable oil/water emulsions (dodecane, toluene, isooctane, and chili oil) with various chemical properties and concentrations and particle contaminants (carbon black and microfibers) from water. Chitin fibrils tightly pack with each other to form a dense membrane, leading to no permeation of contaminants or water. An increasing number of applied freeze-thaw cycles confers more tortuous pore structures throughout the mushroom chitin membranes, leading to higher flux while maintaining rejection performance. The 3D simulation constructed by the X-ray computed tomography and GeoDict software also demonstrated capturing a considerable amount of contaminants within the membranes' pores, which can be easily removed by water rinsing for further successive filtration. Furthermore, mushroom chitin membranes were almost completely biodegraded after approximately a month of being buried in the soil or kept in a lysozyme solution while possessing mechanical durability demonstrated by consistent filtration performance for repeated usage up to 15 cycles under ambient and external pressure. This research is a proof of concept that mushroom-derived chitin develops functional and biodegradable materials for environmental applications with scalability.

Bioinspired Underwater Superoleophilic Two-Dimensional Surface with Asymmetric Oleophobic Barriers for Unidirectional and Long-Distance Oil Transport

Unidirectional and long-distance liquid transport is critically important to a range of practical applications, e.g., water harvesting, microfluidics, and chemical reactions. Great efforts have been made on liquid manipulation; most of which, however, are limited in the air environment. It is still a great challenge to achieve unidirectional and long-distance oil transport in an aqueous environment. Herein, we have successfully fabricated an underwater superoleophilic two-dimensional surface (USTS) with asymmetric oleophobic barriers to arbitrarily manipulate oil in aqueous medium. The behavior of oil on USTS was carefully investigated, of which the unidirectional spreading capability was originated from the anisotropic spreading resistance resulted from the asymmetric oleophobic barriers. Accordingly, an underwater oil/water separation device has been developed, which can achieve continuous and efficient oil/water separation and further prevent the secondary pollution caused by oil volatilization.

Biomass Chitosan-Based Tubular/Sheet Superhydrophobic Aerogels Enable Efficient Oil/Water Separation

Water pollution, which is caused by leakage of oily substances, has been recognized as one of the most serious global environmental pollutions endangering the ecosystem. High-quality porous materials with superwettability, which are typically constructed in the form of aerogels, hold huge potential in the field of adsorption and removal of oily substances form water. Herein, we developed a facile strategy to fabricate a novel biomass absorbent with a layered tubular/sheet structure for efficient oil/water separation. The aerogels were fabricated by assembling hollow poplar catkin fiber into chitosan sheets using a directional freeze-drying method. The obtained aerogels were further wrapped with -CH₃-ended siloxane structures using CH₃SiCl₃. This superhydrophobic aerogel (CA ≈ 154 ± 0.4°) could rapidly trap and remove oils from water with a large sorption range of 33.06-73.22 g/g. The aerogel facilitated stable oil recovery (90.07-92.34%) by squeezing after 10 sorption-desorption cycles because of its mechanical robustness (91.76% strain remaining after 50 compress-release cycles). The novel design, low cost, and sustainability of the aerogel provide an efficient and environmentally friendly solution for handling oil spills.

Unveiling the Mechanism of the in Situ Formation of 3D Fiber Macroassemblies with Controlled Properties

Electrospinning technique is well-known for the generation of different fibers. While it is a "simple" technique, it lies in the fact that the fibers are typically produced in the form of densely packed two-dimensional (2D) mats with limited thickness, shape, and porosity. The highly demanded three-dimensional (3D) fiber assemblies have been explored by time-consuming postprocessing and/or complex setup modifications. Here, we use a classic electrospinning setup to directly produce 3D fiber macrostructures only by modulating the spinning solution. Increasing solution conductivity modifies electrodynamic jet behavior and fiber assembling process; both are observed in situ using a high-speed camera. More viscous solutions render thicker fibers that own enhanced mechanical stiffness as examined by finite element analysis. We reveal the correlation between the universal solution parameters and the dimensionality of fiber assemblies, thereof, enlightening the design of more "3D spinnable" solutions that are compatible with any commercial electrospinning equipment. After a calcination step, ultralightweight ceramic fiber assemblies are generated. These inexpensive materials can clean up exceptionally large fractions of oil spillages and provide high-performance thermal insulation. This work would drive the development and scale-up production of next-generation 3D fiber materials for engineering, biomedical, and environmental applications.

Facile Fabrication of Superelastic, Hydrophobic and Hierarchical polydimethylsiloxane@nanocelluloses Aerogels for Durable Oil/Water Separation

Nanocelluloses (NCs)-based aerogels have gradually attracted attention due to their excellent performance in oil recovery for mitigating environmental pollution caused by oil spillages. However, hydrophobicity due to polyhydroxy groups and fragile in water, as well as a complicated fabricating process, significantly restrict their practical applications. Herein, we reported a facile route to fabricate superelastic polydimethylsiloxane (PDMS)@NCs aerogels through a Pickering emulsion strategy. The hierarchical PDMS@NCs aerogels exhibit function-dependent porous structures and integrated properties of hydrophobicity and lipophilicity, stemming from the synergistic effect of the hydrophobic skin layer and porous matrix. The resulting aerogels are capable of continuous oil/water filtration by adsorption-extrusion with a flux up to 4300 L·m^-2 ·h^-1 and a separation efficiency of 99.9%. Therefore, this provides a new route for the rational design of morphology-tunable NCs-based aerogels and affords a reference for its practical application in durable oil/water separation. This article is protected by copyright. All rights reserved.

Fabrication of Robust and Effective Oil/Water Separating Superhydrophobic Textile Coatings

A superhydrophobic (SH) surface is typically constructed by combining a low-surface-energy substance and a high-roughness microstructure. Although these surfaces have attracted considerable attention for their potential applications in oil/water separation, self-cleaning, and anti-icing devices, fabricating an environmentally friendly superhydrophobic surface that is durable, highly transparent, and mechanically robust is still challenging. Herein, we report a facile painting method to fabricate a new micro/nanostructure containing ethylenediaminetetraacetic acid/poly(dimethylsiloxane)/fluorinated SiO₂ (EDTA/PDMS/F-SiO₂) coatings on the surface of a textile with two different sizes of SiO₂ particles, which have high transmittance (>90%) and mechanical robustness. The different-sized SiO₂ particles were employed to construct the rough micro/nanostructure, fluorinated alkyl silanes were employed as low-surface-energy materials, PDMS was used for its heat-durability and wear resistance, and ETDA was used to strengthen the adhesion between the coating and textile. The obtained surfaces showed excellent water repellency, with a water contact angle (WCA) greater than 175° and a sliding angle (SA) of 4°. Furthermore, the coating retained excellent durability and remarkable superhydrophobicity for oil/water separation, abrasion resistance, ultraviolet (UV) light irradiation stability, chemical stability, self-cleaning, and antifouling under various harsh environments.

Oil/Water Mixtures and Emulsions Separation Methods-An Overview

Catastrophic oil spill accidents, oily industrial wastewater, and other types of uncontrolled release of oils into the environment are major global issues since they threaten marine ecosystems and lead to a big economic impact. It can also affect the public health of communities near the polluted area. This review addresses the different types of oil collecting methods. The focus of this work will be on the different approaches to materials and technologies for oil/water separation, with a special focus on water/oil emulsion separation. Emulsified oil/water mixtures are extremely stable dispersions being, therefore, more difficult to separate as the size of the droplets in the emulsion decreases. Oil-absorbent materials, such as sponges, foams, nanoparticles, and aerogels, can be adjusted to have both hydrophobic and oleophilic wettability while displaying a porous structure. This can be advantageous for targeting oil spills in large-scale environmental and catastrophic sets since these materials can easily absorb oil. Oil adsorbent materials, for example, meshes, textiles, membranes, and clays, involve the capture of the oily material to the surface of the adsorbent material, additionally attracting more attention than other technologies by being low-cost and easy to manufacture.

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.

Mussel-Inspired Robust Peony-like Cu3(PO4)2 Composite Switchable Superhydrophobic Surfaces for Bidirectional Efficient Oil/Water Separation

To alleviate the economic and environmental damage caused by industrial discharges of oily wastewater, materials applied for efficient oil/water separation are receiving significant attention from researchers and engineers. Among others, switchable wettable materials for bidirectional oil/water separation show great potential for practical applications. Inspired by mussels, we utilized a simple immersion method to construct a polydopamine (PDA) coating on a peony-like copper phosphate surface. Then, TiO₂ was deposited on the PDA coating surface to build a micro-nano hierarchical structure, which was modified with octadecanethiol (ODT) to obtain a switchable wettable peony-like superhydrophobic surface. The water contact angle of the obtained superhydrophobic surface reached 153.5°, and the separation efficiency was as high as 99.84% with a flux greater than 15,100 L/(m²·h) after 10 separation cycles for a variety of heavy oil/water mixtures. Notably, the modified membranes have a unique photoresponsiveness, transforming to superhydrophilic upon ultraviolet irradiation, achieving separation efficiencies of up to 99.83% and separation fluxes greater than 32,200 L/(m²·h) after 10 separation cycles for a variety of light oil/water mixtures. More importantly, this switch behavior is reversible, and the high hydrophobicity can be restored after heating to achieve efficient separation of heavy oil/water mixtures. In addition, the prepared membranes can maintain high hydrophobicity under acid-base conditions and after 30 sandpaper abrasion cycles, and damaged membranes can be restored to superhydrophobicity after a brief modification in the ODT solution. This simple-to-prepare, easy-to-repair, robust membrane with switchable wettability shows great potential in the field of oil/water separation.

Zero-Material Cost Production of Soil-Coated Fabrics with Underwater Superoleophobicity for Antifouling Oil/Water Separation

Soil-coated fabrics were fabricated by scrape-coating of soil slurry onto cotton fabrics. The raw materials, soil, and cotton fabrics were, respectively, obtained from farmland and waste bed sheets, making the method a zero-material cost way to produce superwetting membrane. The superhydrophilic/underwater superoleophobic soil-coated fabrics exhibit high efficiency (>99%), ultra-high flux (~45,000 L m^-2 h^-1), and excellent antifouling behavior for separating water from various oils driven by gravity. The simple fabrication and superior performance suggest that the soil-coated fabric could be a promising candidate as a filtration membrane for practical applications in industrial oily wastewater and oil spill treatments.

Hydrogel/β-FeOOH-Coated Poly(vinylidene fluoride) Membranes with Superhydrophilicity/Underwater Superoleophobicity Facilely Fabricated via an Aqueous Approach for Multifunctional Applications

Hydrogel coatings that can endow various substrates with superior properties (e.g., biocompatibility, hydrophilicity, and lubricity) have wide applications in the fields of oil/water separation, antifouling, anti-bioadhesion, etc. Currently, the engineering of multifunctional hydrogel-coated materials with superwettability and water purification property using a simple and sustainable strategy is still largely uninvestigated but has a beneficial effect on the world. Herein, we successfully prepared poly(2-acrylamido-2-methyl-1-propanesulfonic acid) hydrogel/β-FeOOH-coated poly(vinylidene fluoride) (PVDF/PAMPS/β-FeOOH) membrane through free-radical polymerization and the in situ mineralization process. In this work, owing to the combination of hydrophilic PAMPS hydrogel coating and β-FeOOH nanorods anchored onto PVDF membrane, the resultant PVDF/PAMPS/β-FeOOH membrane achieved outstanding superhydrophilicity/underwater superoleophobicity. Moreover, the membrane not only effectively separated surfactant-stabilized oil/water emulsions, but also possessed a long-term use capacity. In addition, excellent photocatalytic activity against organic pollutants was demonstrated so that the PVDF/PAMPS/β-FeOOH membrane could be utilized to deal with wastewater. It is envisioned that these hydrogel/β-FeOOH-coated PVDF membranes have versatile applications in the fields of oil/water separation and wastewater purification.

Ag-CuO-Decorated Ceramic Membranes for Effective Treatment of Oily Wastewater

Although ultrafiltration is a reliable method for separating oily wastewater, the process is limited by problems of low flux and membrane fouling. In this study, for the first time, commercial TiO₂/ZrO₂ ceramic membranes modified with silver-functionalized copper oxide (Ag-CuO) nanoparticles are reported for the improved separation performance of emulsified oil. Ag-CuO nanoparticles were synthesized via hydrothermal technique and dip-coated onto commercial membranes at varying concentrations (0.1, 0.5, and 1.0 wt.%). The prepared membranes were further examined to understand the improvements in oil-water separation due to Ag-CuO coating. All modified ceramic membranes exhibited higher hydrophilicity and decreased porosity. Additionally, the permeate flux, oil rejection, and antifouling performance of the Ag-CuO-coated membranes were more significantly improved than the pristine commercial membrane. The 0.5 wt.% modified membrane exhibited a 30% higher water flux (303.63 L m^-2 h^-1) and better oil rejection efficiency (97.8%) for oil/water separation among the modified membranes. After several separation cycles, the 0.5 wt.% Ag-CuO-modified membranes showed a constant permeate flux with an excellent oil rejection of >95% compared with the unmodified membrane. Moreover, the corrosion resistance of the coated membrane against acid, alkali, actual seawater, and oily wastewater was remarkable. Thus, the Ag-CuO-modified ceramic membranes are promising for oil separation applications due to their high flux, enhanced oil rejection, better antifouling characteristics, and good stability.

Demulsifier-Inspired Superhydrophilic/Underwater Superoleophobic Membrane Modified with Polyoxypropylene Polyoxyethylene Block Polymer for Enhanced Oil/Water Separation Properties

Demulsifiers are considered the key materials for oil/water separation. Various works in recent years have shown that demulsifiers with polyoxypropylen epolyoxyethylene branched structures possess better demulsification effects. In this work, inspired by the chemical structure of demulsifiers, a novel superhydrophilic/underwater superoleophobic membrane modified with a polyoxypropylene polyoxyethylene block polymer was fabricated for enhanced separation of O/W emulsion. First, a typical polyoxypropylene polyoxyethylene triblock polymer (Pluronic F127) was grafted onto the poly styrene-maleic anhydride (SMA). Then, the Pluronic F127-grafted SMA (abbreviated as F127@SMA) was blended with polyvinylidene fluoride (PVDF) for the preparation of the F127@SMA/PVDF ultrafiltration membrane. The obtained F127@SMA/PVDF ultrafiltration membrane displayed superhydrophilic/underwater superoleophobic properties, with a water contact angle of 0° and an underwater oil contact angle (UOCA) higher than 150° for various oils. Moreover, it had excellent separation efficiency for SDS-stabilized emulsions, even when the oil being emulsified was crude oil. The oil removal efficiency was greater than 99.1%, and the flux was up to 272.4 L·m^-2·h^-1. Most importantly, the proposed F127@SMA/PVDF membrane also exhibited outstanding reusability and long-term stability. Its UOCA remained higher than 150° in harsh acidic, alkaline, and high-salt circumstances. Overall, the present work proposed an environmentally friendly and convenient approach for the development of practical oil/water separation membranes.

Facile Fabrication of Superwetting PVDF Membrane for Highly Efficient Oil/Water Separation

A novel superhydrophilic and underwater superoleophobic modified PVDF membrane for oil/water separation was fabricated through a modified blending approach. Pluronic F127 and amphiphilic copolymer P (MMA-AA) were directly blended with PVDF as a hydrophilic polymeric additive to prepare membranes via phase inversion induced by immersion precipitation. Then, the as-prepared microfiltration membranes were annealed at 160 °C for a short time and quenched to room temperature. The resultant membranes exhibited contact angles of hexane larger than 150° no matter whether in an acidic or basic environment. For 1, 2-dichloroethane droplets, the membrane surface showed a change from superoleophilic to superoleophobic under water with aqueous solutions with pH values from 2 to 13. This as-prepared membrane has good mechanical strength and can then be applied for oil and water mixture separation.

Ultrasmall Cu3(PO4)2 Nanoparticles Reinforced Hydrogel Membrane for Super-antifouling Oil/Water Emulsion Separation

Membrane fouling is a persistent and crippling challenge for oily wastewater treatment due to the high susceptibility of membranes to contamination. A feasible strategy is to design a robust and stable hydration layer on the membrane surface to prevent contaminates. A hydrogel illustrates a distinct category of materials with outstanding antifouling performance but is limited by its weak mechanical property. In this research, we report a reinforced hydrogel on a membrane by in situ growing ultrasmall hydrophilic Cu₃(PO₄)₂ nanoparticles in a copper alginate (CuAlg) layer via metal-ion-coordination-mediated mineralization. The embeddedness of hydrophilic Cu₃(PO₄)₂ nanoparticle with a size of 3-5 nm endows the CuAlg/Cu₃(PO₄)₂ composite hydrogel with enhanced mechanical property as well as reinforced hydrate ability. The as-prepared CuAlg/Cu₃(PO₄)₂ modified membrane exhibits a superior oil-repulsive property and achieves a nearly zero flux decline for separating surfactant stabilized oil-in-water emulsions with a high permeate flux up to ∼1330 L m^-2 h^-1 bar^-1. Notably, it is capable of keeping similar permeate flux for both pure water and oil-in-water emulsions during filtration, which is superior to the currently reported membranes, indicating its super-antifouling properties.

Polyaminophosphoric Acid-Modified Ion-Imprinted Chitosan Aerogel with Enhanced Antimicrobial Activity for Selective La(III) Recovery and Oil/Water Separation

In this study, polyaminophosphoric acid (PA)-functionalized ion-imprinted chitosan (CS) aerogel was fabricated for the first time, exhibiting good antibacterial property for selective La(III) recovery and oil/water separation. The as-prepared PA-CS-IIA-2 shows a remarkable adsorption capacity of 114.6 mg/g toward La(III) and high selectivity in the competitive adsorption systems, which is attributed to its abundant imprinting sites and surface functional groups. Benefiting from the amphiphilic property, the PA-CS-IIA-2 also exhibits an excellent adsorption performance for the extractant, oils, and organic solvents. Besides, the PA-CS-IIA-2 presents excellent regeneration and reusability characteristics. Moreover, compared with CS, the PA-CS-IIA-2 exhibits a significantly improved antibacterial activity originating from the PA component. Most importantly, the PA-CS-IIA-2 aerogel is capable of removing multiple pollutants all together and effectively inhibiting bacteria in the complex wastewater environments. Therefore, this study paves the way for developing high-performance rare-earth capture materials with multiple functions to meet diverse applications.

Special Superwetting Materials from Bioinspired to Intelligent Surface for On-Demand Oil/Water Separation: A Comprehensive Review

Since superwetting surfaces have emerged, on-demand oil/water separation materials serve as a new direction for meeting practical needs. This new separation mode uses a single porous material to allow oil-removing and water-removing to be achieved alternately. In this review, the fundamentals of wettability are systematically summarized in oil/water separation. Most importantly, the two states, bioinspired surface and intelligent surface, are summarized for on-demand oil/water separation. Specifically, bioinspired surfaces include micro/nanostructures, bioinspired chemistry, Janus-featured surfaces, and dual-superlyophobic surfaces that these superwetting materials can possess asymmetric wettability in one structure system or opposite underliquid wettability by prewetting. Furthermore, an intelligent surface can be adopted by various triggers such as pH, thermal and photo stimuli, etc., to control wettability for switchable oil/water separation reversibly, expressing a thought beyond nature to realize innovative oil/water separation by external stimuli. Remarkably, this review also discusses the advantages of all the materials mentioned above, expanding the separation scope from the on-demand oil/water mixtures to the multiphase immiscible liquid-liquid mixtures. Finally, the prospects of on-demand oil/water separation materials are also concluded.

Functional Coating from Amyloid Superwetting Films

Tailoring the hydrophilicity of solid surfaces with a strong affinity to water has been extensively explored in the last 20 years, but studies have been limited to the single function of wettability. Here, the multifunctional properties of tailored surface films are extended from exhibiting superwettability to facilitating biological activities. It is shown that amyloid fibrils can be universally coated onto various substrates, such as fabrics (non-woven organic masks), metal meshes, polyethersulfone (PES), glass, and more, endowing the resulting surfaces with excellent performance in oil/water mixture and emulsion separation, antifouling, and antifogging. Moreover, the biocompatible crosslinked amyloid fibril coatings can serve as a platform for biocatalytic activities by immobilizing enzymes, as shown in the 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt (ABTS) oxidation and Reactive Black 5 (RB5) degradation by laccase from Trametes versicolor. The study provides a universal approach to modifying surface morphology and chemical properties via fibrous protein templates, opening the way to unexplored bio-based applications and functionalities.

Effect of Oxygen Plasma Pre-Treatment on the Surface Properties of Si-Modified Cotton Membranes for Oil/Water Separations

Hydrophobic and oleophilic Si-based cotton fabrics have recently gained a lot of attention in oil/water separation due to their high efficiency. In this study, we present the effect of O₂ plasma pre-treatment on the final properties of two Si-based cotton membranes obtained from dip coating and plasma polymerization, using polydimethylsiloxane (PDMS) as starting polymeric precursor. The structural characterizations indicate the presence of Si bond on both the modified cotton surfaces, with an increase of the carbon bond, assuring the success in surface modification. On the other hand, employing O₂ plasma strongly changes the cotton morphology, inducing specific roughness and affecting the hydrophobicity durability and separation efficiency. In particular, the wettability has been retained after 20 laundry tests at 40 °C and 80 °C, and, for separation efficiency, even after 30 cycles, an improvement in the range of 10-15%, both at room temperature and at 90 °C can be observed. These results clearly demonstrate that O₂ plasma pre-treatment, an eco-friendly, non-toxic, solvent-free, and one-step method for inducing specific functionalities on surfaces, is very effective in enhancing the oil/water separation properties for Si-based cotton membranes, especially in combination with plasma polymerization procedure for Si-based deposition.

Fabrication of Superhydrophobic/Superoleophilic Bamboo Cellulose Foam for Oil/Water Separation

Water is an indispensable strategic resource for biological and social development. The problem of oily wastewater pollution originating from oil spillages, industrial discharge and domestic oil pollution has become an extremely serious international challenge. At present, numerous superwetting materials have been applied to effectively separate oil and water. However, most of these materials are difficult to scale and their large-scale application is limited by cost and environmental protection. Herein, a simple, environmentally friendly strategy including sol-gel, freeze-drying and surface hydrophobic modification is presented to fabricate a bamboo cellulose foam with special wetting characteristics. The bamboo cellulose foam is superhydrophobic, with a water contact angle of 160°, and it has the superoleophilic property of instantaneous oil absorption. Owing to the synergistic effect of the three-dimensional network structure of the superhydrophobic bamboo cellulose foam and its hydrophobic composition, it has an excellent oil-absorption performance of 11.5 g/g~37.5 g/g for various types of oil, as well as good recyclability, with an oil (1,2-dichloroethane) absorption capacity of up to 31.5 g/g after 10 cycles. In addition, the prepared cellulose-based foam exhibits an outstanding performance in terms of acid and alkali corrosion resistance. Importantly, owing to bamboo cellulose being a biodegradable, low-cost, natural polymer material that can be easily modified, superhydrophobic/superoleophilic bamboo cellulose foam has great application potential in the field of oily wastewater treatment.

Atmospheric Pressure Plasma-Treated Polyurethane Foam as Reusable Absorbent for Removal of Oils and Organic Solvents from Water

This paper reports the optimization of a two-step atmospheric pressure plasma process to modify the surface properties of a polyurethane (PU) foam and, specifically, to prepare a superhydrophobic/superoleophilic absorbent for the removal of oils and nonpolar organic solvents from water. In particular, in the first step, an oxygen-containing dielectric barrier discharge (DBD) is used to induce the etching/nanotexturing of the foam surfaces; in the second step, an ethylene-containing DBD enables uniform overcoating with a low-surface-energy hydrocarbon polymer film. The combination of surface nanostructuring and low surface energy ultimately leads to simultaneous superhydrophobic and superoleophilic wetting properties. X-ray photoelectron spectroscopy, scanning electron microscopy and water contact angle measurements are used for the characterization of the samples. The plasma-treated PU foam selectively absorbs various kinds of hydrocarbon-based liquids (i.e., hydrocarbon solvents, mineral oils, motor oil, diesel and gasoline) up to 23 times its own weight, while it completely repels water. These absorption performances are maintained even after 50 absorption/desorption cycles and after immersion in hot water as well as acidic, basic and salt aqueous solutions. The plasma-treated foam can remove mineral oil while floating on the surface of mineral oil/water mixtures with a separation efficiency greater than 99%, which remains unaltered after 20 separation cycles.

Polyphenylene Sulfide Ultrafine Viscous Fibrous Membrane Modified by ZIF-8 for Highly Effective Oil/Water Separation under High Salt or Alkaline Conditions

The oil/water separation in harsh environments has always been a challenging topic all over the world. In this study, the ZIF-8/PPS fiber membranes were fabricated via the combination of hot pressing and in situ growth. The distribution of ZIF-8 in the membranes was adjusted by changing the ZIF-8 in situ growth time, which could control the oil/water separation effect. Due to the hydrophilic nature of the ZIF-8/PPS fiber membranes, the water molecules in the oil-in-water emulsion could quickly penetrate into the fiber membrane under the drive of pressure, gravity, and capillary force, forming a water layer on the surface of the fiber membranes. The coupling of the water layer and the fiber structure prevented direct contact between the oil molecules and the fiber membrane, thereby realizing the separation of the emulsion. The results show that when the ZIF-8 in situ growth time was 10 h, the contact angle, the porosity, and the pure water flux of the ZIF-8/PPS fiber membranes were 72.5°, 52.3%, and 12,351 L/h·m², respectively. More importantly, the separation efficiency of M10 was 97%, and the oil/water separation efficiency reached 95% after 14 cycles. This study provides a novel strategy for preparing MOFs/fiber materials for oil/water separation in harsh environments.

Membranes for Oil/Water Separation: A Review

Recent advancements in separation and membrane technologies have shown a great potential in removing oil from wastewaters effectively. In addition, the capabilities have improved to fabricate membranes with tunable properties in terms of their wettability, permeability, antifouling, and mechanical properties that govern the treatment of oily wastewaters. Herein, authors have critically reviewed the literature on membrane technology for oil/water separation with a specific focus on: 1) membrane properties and characterization, 2) development of various materials (e.g., organic, inorganic, and hybrid membranes, and innovative materials), 3) membranes design (e.g., mixed matrix nanocomposite and multilayers), and 4) membrane fabrication techniques and surface modification techniques. The current challenges and future research directions in materials and fabrication techniques for membrane technology applications in oil/water separation are also highlighted. Thus, this review provides helpful guidance toward finding more effective, practical, and scalable solutions to tackle environmental pollution by oils.

Introducing Polar Groups in Porous Aromatic Framework for Achieving High Capacity of Organic Molecules and Enhanced Self-Cleaning Applications

Due to the frequent oil/organic solvent leakage, efficient oil/water separation has attracted extensive concern. However, conventional porous materials possess nonpolar building units, which reveal relatively weak affinity for polar organic molecules. Here, two different polarities of superhydrophobic porous aromatic frameworks (PAFs) were synthesized with respective orthoposition and paraposition C=O groups in the PAF linkers. The conjugated structure formed by a large number of alkynyl and benzene ring structures enabled porous and superhydrophobic quality of PAFs. After the successful preparation of the PAF solids, PAF powders were coated on polyester fabrics by a simple dip-coating method, which endowed the resulting polyester fabrics with superhydrophobicity, porosity, and excellent stability. Based on the unique structure, the oil/water separation efficiency of two superhydrophobic flexible fabrics was more than 90% for various organic solvents. Polar LNU-26 PAF showed better separation performance for the polar oils. This work takes the lead in adopting the polar groups as building units for the preparation of porous networks, which has great guiding significance for the construction of advanced oil/water separation materials.

2D Nano-Mica Sheets Assembled Membranes for High-Efficiency Oil/Water Separation

Oil-polluted water has become one of the most important environmental concerns nowadays due to the increasing industrial oily wastewater and frequent oil spill accidents. Herein, a novel two-dimensional (2D) nano-mica sheets assembled composite membrane with underwater super-oleophobic properties was developed for effective oil/water separation. A 2D nano-mica sheet was synthesized by a facile solvent-assisted ultrasonic exfoliation and then the obtained 2D nano-mica sheets were co-deposited with dopamine on polyvinylidene fluoride substrate to prepare nano-mica composite membranes (NCM). The NCM is hydrophilic in air and super-oleophobic underwater (the water contact angle in the air is 37.6°, and the oil contact angle in water is 151.4°). Furthermore, the prepared NCM provided outstanding stability in different acid-base environments (pH = 1-11). Noteworthily, the oil removal rate is higher than 99.5% as the sodium dodecyl sulfate SDS-stabilized oil (soya-bean oil, mineral oil and pump oil) -in-water emulsions. Meanwhile, the NCM showed excellent reusability, as the oil removal efficiency kept at 99.0% after ten soya-bean oil-in-water or mineral oil-in-water emulsion filtration cycles. The present work paved a new way for developing a low-cost and environmentally friendly strategy for oily wastewater treatment and developed a high-increment utilization application field for natural minerals.

A multifunctional composite membrane with photocatalytic, self-cleaning, oil/water separation and antibacterial properties

Multifunctional composite materials have attracted wide attention because they can be applied in many fields, and have great potential for application. The superhydrophobic surface has been favored by scientists in recent years because of its excellent properties. In this paper, carbon fabric (CF) with high porosity, good electrical conductivity and excellent flexibility was selected as substrate. The CF/Zr-TiO₂/PDMS composites were prepared by solvo-thermal method on CF and modified by PDMS, which can be used in the fields of self-cleaning, self-healing, oil/water separation, antibacterial, anti-icing and so on. Furthermore, the PDMS modification has no or negligible adverse effect on the important textile physical properties of the CF. The effects of different process parameters on the structure and properties of CF/Zr-TiO₂were studied, and the samples with the best conditions were obtained. The results show that the sample achieves the transformation from superhydrophilic to superhydrophobic after modification. The CF/Zr-TiO₂/PDMS composite structure not only shows excellent photocatalytic activity, but also has a certain self-cleaning ability. The samples before and after modification can separate light oil/water and heavy oil/water respectively. Compared with CF/Zr-TiO₂, CF/Zr-TiO₂/PDMS has better anti-Escherichia coliability.

Synthesis of Superhydrophobic Cellulose Stearoyl Ester for Oil/Water Separation

Developing fluorine-free superhydrophobic and biodegradable materials for oil/water separation has already become an irresistible trend. In this paper, we designed two biopolymer oil/water separation routes based on cellulose stearoyl ester (CSE), which was obtained via the acylation reaction between dissolving pulp and stearoyl chloride homogeneously. The CSE showed a superhydrophobic property, which could selectively adsorb oil from the oil/water mixture. Additionally, the CSE was emulsified with an oxidized starch (OS) solution, and the resulting latex was used to impregnate commercial, filter base paper, finally obtaining a hydrophobic and oleophilic membrane. The SEM revealed the membrane had hierarchical micro/nanostructures, while the water contact angle indicated the low surface energy of the membrane, all of which were attributed to the CSE. The membrane had high strength and long durability due to the addition of OS/CSE, and the separation efficiency was more than 99% even after ten repeated uses.

A Self-Detecting and Self-Cleaning Biomimetic Porous Metal-Based Hydrogel for Oil/Water Separation

Porous materials with super-wetting surfaces (superhydrophilic/underwater superoleophobic) are ideal for oil/water separation. However, the inability to monitor the pollution degree and self-cleaning during the separation process limits their application in industrial production. In this study, a porous metal-based hydrogel is proposed, inspired by the porous structure of wood. Porous copper foam with nano-Cu(OH)₂ is used as the skeleton, and its surface is coated with a polyvinyl alcohol, tannic acid, and multiwalled carbon nanotube cross-linked hydrogel coating. The hydrogel has superhydrophilicity and excellent oil/water separation efficiency (>99%) and can adapt to various environments. This approach can also realize hydrogel pollution degree self-detection according to the change in the electrical signal generated during the oil/water separation process, and the hydrogel can also be recovered by soaking to realize self-cleaning. This study will provide new insights into the application of oil/water separation materials in practical industrial manufacturing.

Easy, Fast, Selective, and Simultaneous Separation of Hg(II) and Oil via Loofah-Sponge-Inspired Hierarchically Porous Membranes

In this work, Cu2Se/Cu membranes (CSMs) of hierarchical pores were fabricated via chemical dissolution of Cu and Se followed by redeposition of cuprous selenide (Cu2Se) on copper membranes (CMs), and applied for adsorption/removal/separation of Hg(II) among a variety of interfering metal ions. The CSM demonstrates the best comprehensive performance among previous Hg(II) adsorption membranes, having high selectivity (KHg/M = 2.9 × 104-3.0 × 105), high efficiency (>99%, 5 s to 3 min), high adsorption capacity (505 mg/g), and high flux (2.0 × 106 L m-2 h-1). Meanwhile, effects of Hg(II) concentration, flow rate, and the number of membrane layers and adsorption cycles were also investigated on the removal of Hg(II). Moreover, a Cu2Se/Cu membrane-plasma (CSM-p) with superhydrophilicity/underwater superoleophobicity was prepared on the basis of CSM, and simultaneous removal of Hg(II) and oil was realized by using CSM and CSM-p in combination. This work not only provides a new reference for design of highly selective, efficient metal ion adsorption/enrichment/separation materials but also presents a novel approach to the removal/enrichment/separation of multiple complex contaminants by the combination of different functional membranes.

Facile Preparation of Hydrophobic PLA/PBE Micro-Nanofiber Fabrics via the Melt-Blown Process for High-Efficacy Oil/Water Separation

Polylactic acid (PLA) micro-nanofiber fabrics with a large specific surface area and excellent biodegradability are commonly used in oil/water separation; however, challenges remain due to their poor mechanical properties. Herein, a thermoplastic polylactic acid/propylene-based elastomer (PLA/PBE) polymer was prepared by blending PLA with PBE. Then, PLA/PBE micro-nanofiber fabrics were successfully prepared using a melt-blown process. The results show that the PLA/PBE micro-nanofiber fabric has a three-dimensional porous structure, improving the thermal stability and fluidity of the PLA/PBE blended polymers. The PLA/PBE micro-nanofiber fabric demonstrated a significantly reduced average fiber diameter and an enhanced breaking strength. Moreover, the water contact angle of the prepared samples is 134°, which suggests a hydrophobic capacity. The oil absorption rate of the fabric can reach 10.34, demonstrating excellent oil/water separation performance. The successful preparation of PLA/PBE micro-nanofiber fabrics using our new method paves the way for the large-scale production of promising candidates for high-efficacy oil/water separation applications.

Poly(ethylene-co-vinyl alcohol) Electrospun Nanofiber Membranes for Gravity-Driven Oil/Water Separation

Fabrication of highly efficient oil/water separation membranes is attractive and challenging work for the actual application of the membranes in the treatment of oily wastewater and cleaning up oil spills/oil leakage accidents. In this study, hydrophilic poly(ethylene-co-polyvinyl alcohol) (EVOH) nanofiber membranes were made using an electrospinning technique for oil/water separation. The as-prepared EVOH electrospun nanofiber membranes (ENMs) exhibited a super-hydrophilic property (water contact angle 33.74°) without further treatment. As prepared, ENMs can provide continuous separation of surfactant-free and surfactant-stabilized water-in-oil emulsions with high efficiency (i.e., flux 8200 L m−2 h−1 (LMH), separation efficiency: >99.9%). In addition, their high stability (i.e., reusable, mechanically robust) would broaden the conditions under which they can be employed in the real field oil/water separation applications. Various characterization techniques (including morphology investigation, pore size, porosity, mechanical properties, and performance test) for gravity-driven oil/water separation were employed to evaluate the newly prepared EVOH ENMs.

A Simple Approach to Fabricate Composite Ceramic Membranes Decorated with Functionalized Carbide-Derived Carbon for Oily Wastewater Treatment

Membrane-based oil−water separation has shown huge potential as a remedy to challenge oily wastewater with ease and low energy consumption compared to conventional purification techniques. A set of new composite ceramic membranes was fabricated to separate surfactant-stabilized oil/water (O/W) emulsion. Carbide-derived carbon (CDC) was functionalized by 3-aminopropyltriethoxy silane (APTES) and subsequently deposited on a ceramic alumina support and impregnated with piperazine as an additional amine. The APTES functionalized CDC-loaded membrane was then crosslinked using terephthalyol chloride (TPC). Different loadings of functionalized CDC (50 mg, 100 mg and 200 mg) were employed on the ceramic support resulting in three versions of ceramic membranes (M-50, M-100 and M-200). The fabricated membranes were thoroughly characterized by Scanning electron microscopy (SEM), X-ray diffraction (XRD), Attenuated total teflectance Fourier transform infrared (ATR-FTIR) spectroscopy, Energy dispersive x-ray spectroscopy (EDX) and elemental mapping. The highest permeate flux of 76.05 LMH (L m−2 h−1) at 1 bar using 67.5 ppm oil-in-water emulsion (as feed) was achieved by the M-50 membrane, while an oil separation efficiency of >99% was achieved by using the M-200 membrane. The tested emulsions and their respective permeates were also characterized by optical microscopy to validate the O/W separation performance of the best membrane (M-100). The effect of feed concentration and pressure on permeate flux and oil−water separation efficiency was also studied. A long-term stability test revealed that the M-100 membrane retained its performance for 720 min of continuous operation with a minor decrease in permeate flux, but the O/W separation efficiency remained intact.

Constructing Environmental-Friendly "Oil-Diode" Janus Membrane for Oil/Water Separation

Oil leakage is a global environmental issue and happens frequently, resulting in a waste of oil resources and even threatening the safety of marine creatures and humans. Because of unidirectional oil transportation performance, "oil-diode" Janus membranes have attracted lots of attention for oil/water separation. However, the hydrophobic side of traditional "oil-diode" Janus membrane is completely hydrophobic, resulting in an easy permeation of oil, which hampers light oil recycling. Herein, we provide a facile approach to develop "oil-diode" Janus membranes with the special wettable structure for fast oil refining. The material characteristics and surface wettability of the membranes that generate superimposed efforts are vital to fabricate "oil-diode" Janus membranes. Interestingly, the manufactured membranes exhibit extra-high oil intrusion pressure up to 12 kPa and present high permeance of about 2993 L m^-2 h^-1 bar^-1 in separating stable water-in-oil emulsion containing surfactant and separation efficiency up to 99.6%, thereby showing promising potential in oil recovery and refining.

Bioinspired Superhydrophobic/Superhydrophilic Janus Copper Foam for On-Demand Oil/Water Separation

Superwettable Janus membranes with unique interfacial characteristics have versatile applications in oil/water separation, microfluid transportation, and membrane distillation. However, it remains a significant challenge to simply fabricate three-dimensional (3D) metallic foams with Janus superwettability using a facile and environment-friendly method. In this study, a novel method is present to construct a Janus copper foam (CF) by combining superhydrophobicity and superhydrophilicity into CF. Based on gravity, the water in the light oil (LO)/water mixture can be transported from the superhydrophilic (SHL) side to the superhydrophobic (SHB) side, while the heavy oil (HO) in the HO/water/mixture can be transported from the SHB side to the SHL side. Therefore, cylindrical Janus oil/water separation devices with superior separation efficiency and excellent repeatability can achieve on-demand oil/water separation effortlessly. This design and fabrication method offers a novel avenue for the preparation of Janus interface materials for practical applications in liquid transportation, sensor devices, energy materials, and oil spills.

Flexible, Elastic, and Superhydrophobic/Superoleophilic Adhesive for Reusable and Durable Water/Oil Separation Coating

This study investigates a highly flexible/stretchable and mechanically durable superhydrophobic/superoleophilic coating for efficient oil/water separation and oil absorption. The coating is applied via a simple immersion process using a mixed solution of a biocompatible adhesive (ethyl cyanoacrylate, ECA), a highly stretchable polymer (polycaprolactone, PCL), and superhydrophobic/superoleophilic nanoparticles (fluorine-coated silica nanoparticles, F-SiO₂ NPs) in a solvent, followed by solvent evaporation and ECA polymerization. Polymerized ECA (poly-ECA) in the coating material strongly adheres the F-SiO₂ NPs to the substrate surface, while PCL bestows the rigid poly-ECA with high flexibility. A coated polyurethane sponge exhibits superhydrophobicity (water contact angle of >150°), while retaining robust mechanical stability and flexibility/elasticity. This provides an efficient means of cleaning oil spills with high selectivity, even after mechanical abrasion (>99% separation efficiency is retained after 120 tape test cycles and 50 rubbing test cycles), with excellent reusability.