Separation Mechanism and Construction of Surfaces with Special Wettability for Oil/Water Separation

Nature-Inspired Polyethylenimine-Modified Calcium Alginate Blended Waterborne Polyurethane Graded Functional Materials for Multiple Water Purification

In recent years, natural disasters such as hurricanes and floods have become more frequent, which usually leads to the pollution of drinking water. Drinking contaminated water may cause public health emergencies. The demand for healthy drinking water in disaster-affected areas is huge and urgent. Therefore, it is necessary to develop a simple water treatment technology suitable for emergencies. Inspired by nature, a fractional spray method was used to prepare graded purification material under mild conditions. The material consists of a calcium alginate isolation layer and a functional layer composed of calcium alginate, polyethylenimine, and water-based polyurethane, which can purify complex pollutants in water such as heavy metals, oils, pathogens, and micro/nano plastics through percolation. It does not require additional energy and can purify polluted water only under gravity. A disposable paper cup model was also designed, which can be used to obtain purified water by immersing in polluted water directly without other filtering devices. The test report shows that the water obtained from the paper cup was deeply purified. This design makes the material user-friendly and has the potential as a strategic material. This discovery can effectively improve the safety of drinking water after disasters and improve people's quality of life.

Systematic Design of a Flow-Through Titanium Electrode-Based Device with Strong Oil Droplet Rejection Property for Superior Oil-in-Water Emulsion Separation Performance

Oily wastewater treatment has been restricted by the existence of stable oil-in-water (O/W) emulsions containing micrometer-sized oil droplets. However, the strong adhesion and stacking of emulsified oil droplets on the surface of current separation media cause serious fouling of the treatment unit and the rapid decline of treatment efficiency. Herein, a novel flow-through titanium (Ti) electrode-based filtration device with remarkable oil droplet rejection property was well designed for the continuously separating O/W emulsion. In contrast to the pristine Ti foam, the permeance of the TiO₂ nanoarray-coated Ti foam (NATF) increased from 2538 to 4364 L m^-2 h^-1 bar^-1 through gravity-driven flow. Further, more than ∼70% permeability can be maintained after 6 h of O/W emulsion filtration using the current device, the value of which was markedly higher than that of conventional oil/water separation filters (less than 5%). According to the results of wettability test, the super-oil-repellent surface endowed by this nanoarray structure primarily avoided the formation of a compact oil fouling layer. When the voltage was applied, accompanied by the electrophoresis effect, redistribution of surfactant molecules on the surface of oil droplets induced by an electric field made them readily captured by the microbubbles continuously generated from the electrode, thereby rapidly migrating these bubble-adhered oil droplets far from the filtration medium.

A robust underwater superoleophobic aminated polyacrylonitrile membrane embedded with CNTs-COOH for durable oil/water and dyes/oil emulsions separation

Considering the emulsified oil and water-soluble dyes in wastewater, the exploitation of easy-manufacturing, energy-saving and high-efficiency separation materials is urgently required. In this work, integrating the positively charged polyethyleneimine (PEI) with negatively charged CNTs-COOH constructed the superhydrophilic Cassie-Baxter structure onto the electrospun polyacrylonitrile (PAN) membrane surface by ultrasonic, electrostatic interaction and thermal treatment. Based on it, the PEN@CNTs membrane achieved efficient separation for surfactant-free, tween 80-stabilized, SDS-stabilized, and CTAB-stabilized emulsions (the fluxes reached 508-3158 L m^-2 h^-1, the separation efficiency reached 99.42%) by the splendid water-penetration and oil-repellency, electrostatic interaction, and "aperture sieve". Moreover, because of the porosity and strong charged surface of PEN@CNTs membrane, the anionic dyes can be quickly removed by one-step filtrate method (∼403 L m^-2 h^-1). Meanwhile, the PEN@CNTs membrane also achieved synchronous and efficient remediation for oil/dye mixture emulsions after many cycles. More importantly, facing the complex physical and chemical environments, the combination of the stabilized PEN membrane, inactive CNTs-COOH layer, and the bond of embedding method between CNTs-COOH and PEN nanofibers made the PEN@CNTs membrane demonstrated robust stability and durable separation capability.

Upcycling Waste Pine nut Shell Membrane for Highly Efficient Separation of Crude Oil-in-Water Emulsion

Discharge of oily sewage and frequent oil spills have caused serious harm to human production, life, and ecological environment. Due to the presence of a large number of surfactants in water, these oil-water mixtures are easy to form oil-in-water emulsion, which is difficult to separate by traditional methods. At the same time, the water-soluble pollutants such as dyes and heavy metal ions in oily wastewater also cause great harm to the human body and the environment. A pine nut shell is a kind of common domestic waste material. Herein, an underwater superoleophobic pine nut shell membrane (PNSM) was prepared by the simple pumping filtration method, which realized the separation of oil-in-water emulsion and adsorption of dyes and heavy metal ions. In addition, the filter membrane can be used for separating corrosive emulsions of strong acid, strong alkali, and 3.5% NaCl solutions (simulated seawater). Besides, the PNSM showed excellent toughness and flexibility. Due to the abovementioned performance, this cost-efficient and environmentally friendly membrane can be a promising candidate for multifunctional oily water remediation.

Wood-Inspired Compressible Superhydrophilic Sponge for Efficient Removal of Micron-Sized Water Droplets from Viscous Oils

Efficient micron-sized droplet separation materials have become a new demand for environmental protection and economic development. However, existing separation methods are difficult to be effectively used for micron-sized water droplets surrounded by viscous oil, and common materials have difficulty maintaining hydrophilicity underoil. Here, inspired by the microstructure of tree xylem, we report a cellulose-polyurethane sponge (CP-Sponge) with wood-like pores and underoil superhydrophilicity using directional freeze-casting. The CP-Sponge has an excellent selective water absorption capacity underoil and compression resilience. This preparation strategy can flexibly control the sponge's dimensional morphology. The designed cylindrical CP-Sponge can be easily installed in the silicone tube of a peristaltic pump. During pump operation, with a simple absorption, compression, and recovery process, the CP-Sponge continuously and effectively removes micron-sized water from crude oil and lubricating oil, reducing residual water in the oil to less than 2 ppm. The absorption-saturated sponge can be dried to continue recycling. Eco-friendly, recyclable, and sustainable artificial porous sponges provide new ideas and inspiration for the practical application of deep dehydration of viscous oils.

Superamphiphilic Chitosan Cryogels for Continuous Flow Separation of Oil-In-Water Emulsions

Chitosan is a typical hydrophilic biomass building block widely used in material science and engineering. However, its intrinsic amphiphilicity has been seldom noted so far. Herein, a series of glutaraldehyde-crosslinked chitosan cryogels with superamphiphilicity are fabricated at moderately frozen conditions through a freezing-thawing process. The micron-sized porous cryogel samples display a 0° contact angle toward both water and oil, 0° water contact angle under oil, and over 120° oil contact angle underwater. By comparing the wetting behavior of the tablet compressed by pure chitosan powders, the superamphiphilicity of the chitosan sample is proven to be independent on crosslinkers. This special wettability endows the chitosan cryogels with high separation efficiency for various surfactant-stabilized oil-in-water emulsions under continuous flow mode driven by gravity as well as a peristaltic pump.

Recent Progress in Microfiltration/Ultrafiltration Membranes for Separation of Oil and Water Emulsions

Oily wastewater has become one of the leading causes of environmental pollution. A massive quantity of oily wastewater is released from industries, oil spills, and routine activities, endangering the ecosystem's sustainability. Due to the enormous negative impact, researchers put strenuous efforts into developing a sustainable solution to treat oily wastewater. Microfiltration/ultrafiltration membranes are considered an efficient solution to treat oily wastewater due to their low cost, small footprint, facile operation, and high separation efficiencies. However, membranes severely fouled during the separation process due to oil's adsorption and cake layer formation, which shortens the membranes' life. This review has critically discussed the microfiltration/ultrafiltration membrane synthesizing methods and their emulsion's separation performance. In the end, key challenges and their possible solutions are highlighted to provide future direction to synthesize next-generation membranes.

Biomass-derived oriented neurovascular network-like superhydrophobic aerogel as robust and recyclable oil droplets captor for versatile oil/water separation

Using tubular kapok fibers (KF) and sodium alginate (SA) as the natural building block, we put forward a novel oriented neurovascular network-like superhydrophobic aerogel with robust dry and wet compression resilience by directional freeze-drying and chemical vapor deposition. In the block, SA forms aligned channel structures providing space for rapid oil transmission, while KF serves as vascular-like capillaries acting as instant "tentacle" to capture the tiny oil droplets in water, facilitating fascinating oil capture efficiency for versatile oil/water separation, The aerogel after dry and wet compression (under a strain of 60%) can recover 96.0% and 97.3% its original, respectively, facilitating stable oil recovery (81.1-89.8%) by squeezing, high separation efficiency (99.04-99.64%) and permeation flux separating oil contaminants from water. A pump-supported experiment shows the aerogel efficiently collecting oil contaminants from the water's surface and bottom by 11503-25611 L·m^-2·h^-1. Particularly, the aerogel as robust oil droplets captor facilely achieves isolation of 99.39-99.68% emulsified oils from oil/water emulsions by novel oil trapping mechanism which simply involves exerting kinetic energy on emulsified oils through repeated oscillation, potentially indicating a simple and efficient alternative to membrane-based oily wastewater remediation via filtration.

Rational design of Janus nanofibrous membranes with novel under-oil superhydrophilic/superhydrophobic asymmetric wettability for water-in-diesel emulsion separation

Endowing nanofibrous membranes with special wettability has always been the dominant strategy to improve the separation performance for water-in-oil emulsions. In this work, a rational design of deacetylated cellulose acetate/polyvinylidene fluoride (dCA/PVDF) Janus nanofibrous membrane, with asymmetric wettability in either air, water or diesel environment, was developed via sequential electrospinning PVDF and CA membranes followed by alkali treatment. In the process of water-in-diesel emulsion separation, the under-diesel superhydrophilic dCA layer is able to capture the emulsified water and strengthens the demulsification ability of the Janus membrane, while the under-diesel superhydrophobic PVDF layer acts as a water barrier and further improves the separation ability. The Janus membrane therefore exhibited prominent separation performance not only for the water/diesel mixture (separation efficiency 99.98%) but also for the surfactant-stabilized water-in-diesel emulsion with l vol% water (separation efficiency 97.74%). Moreover, the Janus membrane maintained high separation efficiency over 96% after repeated use for 50 times or soaking in corrosive solutions for 24 h. The Janus dCA/PVDF nanofibrous membrane possesses competitive efficiency, reusability and acid/alkali resistance, making it a promising candidate as the separation membrane for the surfactant-stabilized water-in-diesel emulsion.

Superhydrophobic PDMS-pCA@CNWF Composite with UV-Resistant and Self-Cleaning Properties for Oil/Water Separation

Oil separation is crucial for avoiding environmental pollution originating from industrial wastewater and oil spillage; therefore, it is essential to develop techniques for oil separation. Herein, a new membrane with superhydrophilicity was synthesized by a facile, green, and low-cost method. First, cellulose non-woven fabric (CNWF) was modified by poly (catechin) (pCA), which has good antioxidant and antibacterial activities, to make it unaffected by ultraviolet light and to improve the stability of the structure. Then, hydrolyzed polydimethylsiloxane (PDMS) was coated on the pCA@CNWF surface via chemical bonding to make the composite hydrophobic. This durable superhydrophobic fabric can be used to separate various oil/water mixtures by gravity-driven forces with high separation efficiency (over 98.9%). Additionally, the PDMS-pCA@CNWF possesses the advantages of flexibility, high efficiency, and an outstanding self-cleaning performance, and demonstrates significant potential for applications in various environments, even under various harsh conditions, which make it very promising for the treatment of oil pollution in practical applications.

Photopolymerized superhydrophobic hybrid coating enabled by dual-purpose tetrapodal ZnO for liquid/liquid separation

Low-cost and scalable superhydrophobic coating methods provide viable approaches for energy-efficient separation of immiscible liquid/liquid mixtures. A scalable photopolymerization method is developed to functionalize porous substrates with a hybrid coating of tetrapodal ZnO (T-ZnO) and polymethacrylate, which exhibits simultaneous superhydrophobicity and superoleophilicity. Here, T-ZnO serves dual purposes by (i) initiating radical photopolymerization during the fabrication process through a hole-mediated pathway and (ii) providing a hierarchical surface roughness to amplify wettability characteristics and suspend liquid droplets in the metastable Cassie-Baxter regime. Photopolymerization provides a means to finely control the conversion and spatial distribution of the formed polymer, whilst allowing for facile large-area fabrication and potential coating on heat-sensitive substrates. Coated stainless-steel meshes and filter papers with desired superhydrophobic/superoleophilic properties exhibit excellent performance in separating stratified oil/water, oil/ionic-liquid, and water/ionic-liquid mixtures as well as water-in-oil emulsions. The hybrid coating demonstrates desired mechanical robustness and chemical resistance for their long-term application in large-scale energy-efficient separation of immiscible liquid/liquid mixtures.

Photo-Fenton superwettable NiFe2O4/TA/PVDF composite membrane for organic pollutant degradation with successively oil-in-water separation

With regard to the treatment of multicomponent wastewaters, to construct multifunctional super-wetting membranes is highly attractive in current decade. In this work, a low-cost and novel NiFe₂O₄/TA/PVDF composite membrane was fabricated via a facile in-situ deposition method under vacuum system. In which, photo-response NiFe₂O₄ nanoparticles were immobilized on the surface of flexible PVDF base membrane via hydrophilic tannic acid (TA) as the binder. The resulting composite membrane exhibited a special superwettability of superamphilicity in air and underwater superoleophobicity with a nanoscale rough surface structure. One the one hand, NiFe₂O₄/TA/PVDF membrane can be used a reusable catalyst in Photo-Fenton degradation of organic dyes with high efficiency. On the other hand, the composite membrane can effectively separate emulsified oils from representative oil-in-water emulsions with excellent separation efficiency all above 99 % and relatively high flux (880-1525 Lm^-2h^-1 bar^-1). More importantly, NiFe₂O₄/TA/PVDF composite membrane showed satisfactory processing efficiency, anti-fouling property and excellent reusability in deal with the mixed organic pollutants (water-insoluble emulsified oils and water-soluble organic dyes) existed in one aqueous system, which followed the procedure of initially photo-Fenton degradation of organic dyes emulsion and successively separation the remaining emulsion over the recovered membrane. This successful development of high-performance NiFe₂O₄/TA/PVDF composite membrane will provide a new candidate for both oil/water separation and organic wastewater treatment, as well as promote the utilization of spinel ferrites in the construction of multifunctional membrane for environmental purification.

Recent Developments and Advancements in Graphene-Based Technologies for Oil Spill Cleanup and Oil-Water Separation Processes

The vast demand for petroleum industry products led to the increased production of oily wastewaters and has led to many possible separation technologies. In addition to production-related oily wastewater, direct oil spills are associated with detrimental effects on the local ecosystems. Accordingly, this review paper aims to tackle the oil spill cleanup issue as well as water separation by providing a wide range of graphene-based technologies. These include graphene-based membranes; graphene sponges; graphene-decorated meshes; graphene hydrogels; graphene aerogels; graphene foam; and graphene-coated cotton. Sponges and aerogels modified by graphene and reduced graphene oxide demonstrated effective oil water separation owing to their superhydrophobic/superoleophilic properties. In addition, oil particles are intercepted while allowing water molecules to penetrate the graphene-oxide-coated metal meshes and membranes thanks to their superhydrophilic/underwater superoleophobic properties. Finally, we offer future perspectives on oil water separation that are hindering the advancements of such technologies and their large-scale applications.

The separation of oily water using low-cost natural materials: Review and development

This paper reviewed the recent progress on a number of important natural/biomass materials (fibers, leaves, woods, nutshells, algae, and sands, etc.) for the separation of oily water mixture/emulsions. Experiments were conducted with desert pristine sand samples, which were collected, sieved, characterized and tested for the separation of two surfactant-stabilized oil in water (O/W) emulsions in a simple cross-flow sand bed filter under the simulated natural gravity. The wettability of the sand samples was checked through contact angle measurements. The morphology of sands was characterized with SEM/EDX and FTIR. Experimental results revealed that natural sand filtration is a promising technology with the characteristics of: 1) a surface of superhydrophilicity and underwater superoleophobicity; 2) sands bed achieved separation efficiency and flux comparable or higher than commercial microfiltration membranes under natural gravity conditions, and 3) the separation efficiency and flux of the sand bed are relatively stable with respect to the operation parameters. This technology is technically feasible, low-cost, and environmental-benign and can play an important role in the practical applications.

The Separation of Oil/Water Mixtures by Modified Melamine and Polyurethane Foams: A Review

Melamine (MA) and polyurethane (PU) foams, including both commercial sponges for daily use as well as newly synthesized foams are known for their high sorption ability of both polar and unipolar liquids. From this reason, commercial sponges are widely used for cleaning as they absorb a large amount of water, oil as well as their mixtures. These sponges do not preferentially absorb any of those components due to their balanced wettability. On the other hand, chemical and physical modifications of outer surfaces or in the bulk of the foams can significantly change their original wettability. These treatments ensure a suitable wettability of foams needed for an efficient water/oil or oil/water separation. MA and PU foams, dependently on the treatment, can be designed for both types of separations. The particular focus of this review is dealt with the separation of oil contaminants dispersed in water of various composition, however, an opposite case, namely a separation of water content from continuous oily phase is also discussed in some extent. In the former case, water is dominant, continuous phase and oil is dispersed within it at various concentrations, dependently on the source of polluted water. For example, waste waters associated with a crude oil, gas, shale gas extraction and oil refineries consist of oily impurities in the range from tens to thousands ppm [mg/L]. The efficient materials for preferential oil sorption should display significantly high hydrophobicity and oleophilicity and vice versa. This review is dealt with the various modifications of MA and PU foams for separating both oil in water and water in oil mixtures by identifying the chemical composition, porosity, morphology, and crosslinking parameters of the materials. Different functionalization strategies and modifications including the surface grafting with various functional species or by adding various nanomaterials in manipulating the surface properties and wettability are thoroughly reviewed. Despite the laboratory tests proved a multiply reuse of the foams, industrial applications are limited due to fouling problems, longer cleaning protocols and mechanical damages during performance cycles. Various strategies were proposed to resolve those bottlenecks, and they are also reviewed in this study.

Delamination-Free In-Air and Underwater Oil-Repellent Filters for Oil-Water Separation: Gravity-Driven and Cross-Flow Operations

Separating oil-water mixtures is critical in a variety of practical applications, including the treatment of industrial wastewater, oil spill cleanups, as well as the purification of petroleum products. Among various methodologies that have been utilized, membranes are the most attractive technology for separating oil-water emulsions. In recent years, selective wettability membranes have attracted particular attention for oil-water separations. The membrane surfaces with hydrophilic and in-air oleophobic wettability have demonstrated enhanced effectiveness for oil-water separations in comparison with underwater oleophobic membranes. However, developing a hydrophilic and in-air oleophobic surface for a membrane is not a trivial task. The coating delamination process is a critical challenge when applying these membranes for separations. Inspired by the above, in this study we utilize poly(ethylene glycol)diacrylate (PEGDA) and 1H,1H,2H,2H-heptadecafluorodecyl acrylate (F-acrylate) to fabricate a hydrophilic and in-air oleophobic coating on a filter. We utilize methacryloxypropyl trimethoxysilane (MEMO) as an adhesion promoter to enhance the adhesion of the coating to the filter. The filter demonstrates robust oil repellency preventing oil adhesion and oil fouling. Utilizing the filter, gravity-driven and continuous separations of surfactant-stabilized oil-water emulsions are demonstrated. Finally, we demonstrate that the filter can be reused multiple times upon rinsing for further oil-water separations.

NaOH-Induced Fabrication of a Superhydrophilic and Underwater Superoleophobic Styrene-Acrylate Copolymer Filtration Membrane for Effective Separation of Emulsified Light Oil-Polluted Water Mixtures

Oil-polluted water mixtures are difficult to separate, and thus, they are considered as a global challenge. A superior superhydrophilic and low-adhesive underwater superoleophobic styrene-acrylate copolymer filtration membrane is constructed using a salt (NaOH)-induced phase-inversion approach. The as-fabricated filtration membrane provides a hierarchical-structured surface morphology and three-dimensional high density open-rough porous geometry with a special chemical composition including highly accessible hydrophilic -COO^- agents, which all are of great importance for long-term usage of immiscible/emulsified (light) oil-polluted wastewater separation. The separation is performed with a high efficiency and a high flux under either a gravity-driven force or a small applied pressure of 0.1 bar. The filtration membrane indicates an excellent anti-fouling property and is easily recycled during multiple cycles. The outstanding performance of the filtration membrane in separating oil-polluted water mixtures and the cost-effective synthetic approach as well as commercially scaled-up initial materials all highlight its potential for practical applications.

A dual-functional layer modified GO@SiO2 membrane with excellent anti-fouling performance for continuous separation of oil-in-water emulsion

As the most significant target of membrane separation, the inadequacy of permeability and anti-fouling frequently constrain the application of the membrane in actual oily wastewater. Herein, a novel concept of membrane surface construction was proposed to mitigate this intractable problem, using SiO₂ as the support layer and graphene oxide (GO) as the isolation layer. The best co-localization proportion of the support layer (56 mg/L) and isolation layer (3.5 mg/L) was determined by the separation performance of the modified membranes for the simulated emulsion. The thin GO layer could effectively prevent contaminants from entering the membrane pores without affecting its roughness. Based on the synergistic action of the isolation layer and support layer, the GO@SiO₂ membrane could well implement emulsion purification with a stable permeability (654.11 LMHB) and high separation efficiency (99.41%). The superior anti-fouling performance of the membrane ensures its long-term cycling stability, with the permeability recovery rate of 89.75% (low-density oil) and 90.41% (high-density oil) after 10 repeated cycles. The storage stability also indirectly increases its value in practical applications. More importantly, the GO@SiO₂ membrane also shows great potential for industrial emulsion treatment with excellent purification and cycling stability (permeability recovery rate of 84.01%).

Nanoscale silica-coated graphene oxide and its demulsifying performance in water-in-oil and oil-in-water emulsions

In current work, GO@SiO₂ nanocomposite was prepared by coating nanoscale silica onto graphene oxide (GO). GO@SiO₂ was characterized with scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (IF-IR). Additionally, the demulsifying performance of GO@SiO₂ was investigated by bottle test. The results showed that GO@SiO₂ had a good demulsifying performance in both oil-in-water (O/W) and water-in-oil (W/O) emulsions. When the concentration of GO@SiO₂ was 200 ppm in the O/W emulsion, the optimal light transmittance of aqueous phase (LTA) and corresponding oil removal rate (ORR) at room temperature could reach 86.9% and 99.48%, respectively. Also, GO@SiO₂ had an excellent salt tolerance under acidic condition. Furthermore, GO@SiO₂ also could demulsify the W/O emulsion, and the efficiency at 70 °C could reach 80.5% when the concentration was 400 ppm.

Janus sand filter with excellent demulsification ability in separation of surfactant-stabilized oil/water emulsions: An experimental and molecular dynamics simulation study

Developing efficient separation materials for surfactant-stabilized oil/water emulsions is of great importance while significantly challenging. In this work, a sand filter with Janus channels was prepared by simply mixing superhydrophilic and superhydrophobic quartz sand in a mass ratio of 1:1. Due to the imbalanced force of droplets in those Janus channels, better separation performance under gravity was achieved for both surfactant-stabilized oil-in-water and water-in-oil emulsions than the superhydrophilic or superhydrophobic sand filter alone. It also received high flux (1080.13 L m^-2 h^-1 for dichloroethane-in-water emulsion and 1378.07 L m^-2 h^-1 for water-in-dichloroethane emulsion) and high separation efficiency (99.80% for dichloroethane-in-water emulsion and 99.98% for water-in-dichloroethane emulsion). Molecular dynamics based computational work and experimental studies revealed that the Janus channels of mixed sand layer exhibited greater interaction energy with emulsion droplets for more efficient adsorption, resulting in better demulsification capability and separation performance. The as-prepared Janus sand filters retained excellent separation performance after 50 cycles of the stability test. Together with the needs on only cheap and easily accessible raw materials and its environmentally friendly preparation method, this Janus sand filtration process exhibits its great potential for the separation of surfactant-stabilized oil/water emulsions.

Cracked-earth-like titanium carbide MXene membranes with abundant hydroxyl groups for oil-in-water emulsion separation

Membrane separation technology is one of the best methods to deal with wastewater released from oil spills and industrial wastewater. Therefore, we designed and prepared hydroxyl-rich titanium carbide MXene materials and filtered them onto a commercial polyvinylidene fluoride substrate membrane to obtain a cracked-earth-like MXene membrane with abundant hydroxyl groups and excellent underwater wettability. The underwater oil contact and sliding angles were approximately 157° and less than 3°, respectively. Moreover, the membrane effectively separated a variety of surfactant-stabilized stable emulsions with a high permeation flux of up to 6385 L m^-2h^-1 bar^-1 and offered adequate performance after five cycles of the separation experiment. Additionally, the membrane exhibited remarkable resistance toward corrosive chemicals without any decrease in its underwater wettability performance. For example, the membrane was used to separate the emulsions containing alkali, salt, and acid. This study provides a new strategy to resolve the oily wastewater disposal problem by fabricating a cracked-earth-like MXene membrane with abundant hydroxyl groups.

Hyper-Cross-Linked Polymer-Decorated Surfaces with Ultrahigh Efficiency for Oil/Water Emulsion Separation and Recovery

A novel superhydrophobic/superoleophilic surface has been developed by direct surface condensation of dichloroxylene that results in a controlled coating of hyper-cross-linked polymers. Specifically, the coating was successfully applied to a melamine formaldehyde sponge and optimized by fine-tuning the reaction variables. The resulting hierarchical porous sorbents stabilized by polydimethylsiloxane exhibited an increased surface area, good physiochemical stability, high selectivity, and adsorption capacities for a variety of oils and solvents. The composite can separate oil in water emulsions with ultrahigh separation efficiency >99% over 10 cycles in liter-scale experiments, wherein the highest separation efficiency was as low as 2 ppm even with a short period of filtration, suggesting strong potential for oil/water separation and recovery.

Shape-Deformed Mushroom-like Reentrant Structures for Robust Liquid-Repellent Surfaces

Artificial liquid-repellent surfaces inspired by biomimetic structures provide a wide range of functional surfaces for various practical applications, such as self-cleaning, antisticking, oil/water separation, and droplet manipulation. However, functional biomimetic structures cannot be fabricated using conventional techniques. For example, mushroom-like topologies on the skin of springtails, which are referred to as "doubly reentrant structures," have attracted significant attention owing to their extraordinary liquid-repellent properties. Current methods of fabricating these reentrant structures have several limitations, such as complex material systems, processing steps, and additional chemical treatments. This study proposed a simple micro-shape-deformed approach to fabricate mushroom-like reentrant structures by digital light processing, a three-dimensional (3D) printing technique, with volumetric shrinkage. The nonuniform cross-linking process and light propagation during photopolymerization caused the deformation of the topological patterns atop the micropillar arrays, resulting in bent structures for mushroom-like shape-deformed microarchitectures. This 3D-printed shape-deformed microstructure exhibits a highly stable liquid repellency without perfluorinated coatings.

Designing nanofibrous membrane with biomimetic caterpillar-like structured for highly-efficient and simultaneous removal of insoluble emulsified oils and soluble dyes towards sewage remediation

Purification of insoluble emulsified oils and soluble organic pollutants from sewage has attracted tremendous attention in today's society. Herein, a stable and environmentally friendly nanofibrous membrane with hierarchical caterpillar-like structure was fabricated via in-situ hydrothermal growing the nickel-cobalt layered double hydroxides (NiCo-LDHs) on tche polyacrylonitrile (PAN) electrospun nanofibers. The wrapped hydrophilic NiCo-LDHs constructed the hierarchical structure and endowed the membrane attractive superhydrophilicity (≈ 0°)/underwater superoleophobicity (≈ 161°) and enhanced oil-repellency performance. Meanwhile, the NiCo-LDH@PANI/oPAN NFMs can display the ultra-fast flux of SSEs (xylene/water emulsion, 4175 L m^-2 h^-1) and satisfactory separation efficiency (99.07%). Moreover, the introduction of positively charged NiCo-LDHs increased plentiful adsorption active sites for membranes, which is beneficial to demulsify ionic SSEs and adsorb organic pollutants. Finally, for simultaneous purification of complex sewage by the dead-end and cross-flow filtration experiment, the composite membrane both displayed splendid removal rate of oil (> 99.0%) and dyes (> 99.0%), robust regeneration recycle-ability and no secondary pollution. Hence, it is expected that such strategy of combining electrospun and chelating-assisted in-situ hydrothermal can provide a low energy consumption and high decontamination technology for severe environmental crisis.

Janus hybrid sustainable all-cellulose nanofiber sponge for oil-water separation

Two-faced characteristics and performance of materials driven by asymmetric physical or chemical properties exist in Janus hybrid materials which show synergistic and improved properties for a variety of applications. Here, we report a facile synthesis of Janus hybrid sustainable cellulose nanofibers (CNFs) sponge with asymmetric wettability and strong mechanical property for excellent separation efficiency of oil-water emulsions. Briefly, the CNF Janus hybrid sponge was fabricated by freeze-drying of two separate CNF suspensions into one, each prepared separately by introducing CNFs in methyltrimethoxysilane (MTMS) or 3-glycidoxypropyltrimethoxysilane (GPTMS) for hydrophobic or hydrophilic performance, respectively. The sponge demonstrated satisfactory mechanical stability with an excellent recovery from 80% compressive strain and high pore tortuosity. When employed for oil-water separation, the Janus hybrid sponge could selectively be used to collect water or oil by just switching its side facing the oil-water mixture feed via unidirectional gravity-assisted separation, with recyclability. The fabrication of such Janus hybrid sponge is one of the many approaches for utilizing nanofibers in structurally adaptive, self-supported asymmetric membrane structures in a 3D network.

Multifunctional filtration membrane with anti-viscous-oils-fouling capacity and selective dyes adsorption ability for complex wastewater remediation

Multifunctional filtration membranes (MFMs), which can both effectively separate oil and selectively remove dyes from polluted aquatic system with robust anti-viscous-oil-fouling capacity, strong chemical/physical resistance, and long cycled stability, are highly required but still a challenge to be realized. Herein, a simple route has been demonstrated to address this challenge aforementioned by decorating both halloysite nanotubes (HNTs) and zwitterionic poly (sulfobetaine methyl methacrylate) (PSBMA) on the microporous polyvinylidene fluoride (PVDF) membrane surface via modified polydopamine (PDA) coating route. The as-prepared membrane exhibits super-hydrophilic/underwater super-oleophobic performance and high water permeation flux (32529 ± 278 L m^-2 h^-1 at 0.85 bar) to purify the diverse viscous oil-in-water emulsions from oily wastewater accompanying with good cycled stability (the recovery rate of permeate flux is close to 100% after 5 cycles). Moreover, the as-prepared MFM possesses not only strong chemical resistance under wide range of pH value (from 1 to 12) and high saline (NaCl: 10 wt%) environment, but also physical resistance against ultrasound bath for 30 min. Given the presence of HNTs, PDA, and PSBMA, our MFM shows enough active sites to adsorb the soluble dyes and metallic ions in wastewater. These excellent properties endow our MFM with great potential for the remediation of complex wastewater.