Controllable Oil Water Separation Research Articles

Fabricated pH-responsive sponge with switchable wettability for multitasking and controllable oil-water separation

pH-responsive smart materials with switchable wettability have a great potential application in bidirectional oil-water separation. In this work, a simple, low-cost and environmentally friendly strategy is developed to construct a pH-responsive melamine sponge (MS) with reversible wettability via polydopamine (PDA) modification followed by grafting long-chain alkanes with carboxyl (–COOH) and methyl (–CH3) groups. The as-modified sponge exhibits unique pH-responsiveness, that is, the water contact angle (WCA) is measured to be 144.9° under acidic and neutral environments, while the wettability is radically changed from hydrophobic to hydrophilic under alkaline conditions. Moreover, in alkaline environment, the pH-responsive sponge can rapidly release the absorbed oil, demonstrating a controllable desorption performance. Also, the prepared sponge is utilized to accomplish controllable separation of various oil/water mixtures, as well as to effectively separate oil-in-water emulsions. Furthermore, after 50 cycles, the oil-water separation efficiency was still higher than 92 %. This smart wettability sponge has an extensive application prospect in controlled oil-water separation and on-demand oil-spill remediation.

PH-regulated superhydrophobic quartz sands for controllable oil-water separation

pH-regulated wettability transformation materials have gained increasing attention attributing to the capacity for sustainable oil-water separation. In this work, a smart quartz sand (OD-SiO2 @sand) with controllable wettability was designed as a filter media for efficient oil-water mixtures and water in oil emulsions separation. The OD-SiO2 @sand was synthesized by grafting nano-silica and modifying with two silane couplers, including N, N-Diethyl-3-(trimethoxysilyl)− 1-propanamine (DTP) and trimethoxy(octyl)silane (OTMS). OD-SiO2 @sand featured superhydrophobicity with a water contact angle (WCA) of 151.6°, which suggests selective separation capacity for oil and high permeation flux up to 4018 L.m−2∙h−1. Meanwhile, OD-SiO2 @sand exhibits superhydrophobicity and hydrophilicity in neutral and acidic solutions resulting from the reversible protonation of grafted DTP, which was revealed by 1H NMR and molecular dynamics simulations. OD-SiO2 @sand posed controllable oil-water separation performance, which remains superhydrophobicity with a WCA of 150.4° after 10 cycles of filtration processes upon pH regulation. Furthermore, OD-SiO2 @sand demonstrated efficient demulsification and separation capacity for various water in oil emulsions, achieving a purified oil size of less than 10 nm and a permeation flux up to 1850 L.m−2∙h−1. Thus, OD-SiO2 @sand shows promising applicability in the field of oil recovery and oil quality improvement.

PH-responsive nonwoven fabric with reversibly wettability for controllable oil-water separation and heavy metal removal

Removal of organic solvents and heavy metals in effluents is of great significance to environmental pollution control and ecological civilization construction. pH-responsive materials have unique advantages in treating complicated oily wastewater. In this work, an intelligent pH-responsive nonwoven fabric with excellent reversible wettability was prepared. The pH-sensitive polymer was synthesized by free radical polymerization (FRP) technique, then dipped with SiO2 on PP fabric. The particular molecular structure of poly (dimethylaminoethyl methacrylate) (PDMAEMA) enabled the fabric surface to switch wettability rapidly between hydrophilic/underwater oleophobic and oleophobic/hydrophobic under pH stimulus and exhibit controllable selective separation of various oil/water mixtures. Furthermore, the fabric removed Pb2+ efficiently under a wide pH range. The experimetal results showed that the separation flux reached 19,229 ± 1656.43 L-h−1-m−2 for water and 19,342 ± 1796.77 L-m−2-h−1 for n-hexane. Besides, the obtained fabric effectively realized the separation and collection process of complex ternary mixtures. The fabric removed Pb2+ in solutions with efficiency up to 90.83%. After immersing in acid and alkali solutions for 24 h, no significant damage to the surface wettability. This economical and intelligent fabric is able to meet the different separation purposes of industrial wastewaters with complex compositions.

Synthesis of novel smart pH-sensitive modified silica nanoparticles for controllable oil-water separation

The newly designed superwettable polymers with external stimuli-responsive behavior have been greatly proposed a great research interest in the oil industry due to their fast and simple mechanism process. Herein, the development of the advanced silica-based pH-responsive materials linked with hydrophilic 3-(aminopropyl)triethoxysilane (APTES) and hydrophobic 1H,1H,2H,2H-perfluorooctyl-triethoxysilane (FOTS) chelating ligands have been designed for oil/water separation by a facile dip-coating process. This smart material can propose an excellent wettability conversion between superhydrophobicity-superoleophilicity and superhydrophilicity-underwater superoleophobicity, favorable stability, and durability, resulting in efficient separation for oil/water mixture. These properties were observed from the well-defined 3D porous surface of the smart materials when they were coated on the fabric surface. Furthermore, characterization described that the material compositions were chemically reacted and distributed throughout the smart fabric surface caused by the robust chemical interaction between the functional groups such as hydroxide, carboxylate, and silane. The water contact angle (pH≈10) was displayed at 167-160° and for acidic water (pH≈2) was ranging from 143-0° over 100 s denoting outstanding superhydrophobic and superhydrophilic features respectively. Underwater measurement pointed out that the smart fabric also has a great superoleophobicity for oil contact angle (150°). Moreover, the series of test results revealed a selective separation for oil/water system with efficacy > 98% and high oil flux ranging from 7200 to 7900 L.h−1.m−2 as well as water flux (5300–6200 L.h−1.m−2). Therefore, these smart materials with fabric and non-fabric preparation have a direct environmental impact on real samples and they can largely dominate various oily wastewater/oil spills clean up.

Dual-responsive polyacrylonitrile-based electrospun membrane for controllable oil-water separation

Membrane separation based on smart materials with responsive wettability has attracted great attention due to the excellent performance of controllable oil-water separation. Herein, responsive copolymer originated from N-isopropylacrylamide and 2-(dimethylamino) ethyl methacrylate was synthesized and electrospun with polyacrylonitrile to fabricate smart composite membrane. The introduction of the responsive copolymer endowed the membrane with stimuli-responsive wettability to pH and temperature. Specifically, at the initial state, water was selectively blocked while oil passed through the membrane. After treatment with acidic water or CO2, the reverse separation was realized due to the protonation of the tertiary amine group in the copolymer. Water was selectively passed through the membrane after heat treatment because of the structural change of membrane upon temperature. The developed membrane was able to separate different types of oil-water mixtures and surfactant-stabled emulsions with high efficiency. Additionally, two membranes controlled by temperature and pH were designed to construct a logic AND gate for oil-water separation, and the results demonstrated that only the temperature and acidity of the solution were simultaneously satisfied, the water could flow through the valve combination, and such capability made this smart membrane great potential for remotely controlling the oil-water separation process.

A bio-inspired green method to fabricate pH-responsive sponge with switchable surface wettability for multitasking and effective oil-water separation

Smart oil-water separation materials with stimuli-responsive wettability surfaces have attracted wide attention. In this paper, a novel, simple and low-cost method is developed to prepare a pH-responsive melamine sponge (MS) with switchable wettability. This approach involves the hydrophobic modification of hexadecyltrimethoxysilane (HDTMS) on the MS surface modified by polydopamine (PDA) and the Michael addition reaction and Schiff base reaction between 12-aminododecanoic acid (NH2(CH2)11COOH) and PDA. Hydrophobic/oleophilic HDTMS and pH-triggered NH2(CH2)11COOH enable the functionalized sponge to repeatedly switch between the two extreme wettability under different pH environments. Benefiting from the excellent 3D porous surface structure and smart wettability, the as-prepared sponge can be applied in the on-demand separation of various oil-water mixtures by adsorption or filtration with a separation efficiency over 98.5% and high absorption capacity of 72.7–161.3 g·g−1. With the assistance of pump-driven, continuous adsorption separation can be achieved in two cases by utilizing the wettability transformation. Moreover, in an alkaline solution, the sponge can quickly release most of the absorbed oil, showing a controllable desorption process. This smart wettability material with simple preparation and green has application potential in controllable oil-water separation and on-demand oil-spills treatment.

Structured Copper Mesh for Efficient Oil-Water Separation Processed by Picosecond Laser Combined With Chemical Treatment or Thermal Oxidation

Oil-water separation has great practical significance, and can be used to help cope with growing oily industrial sewage discharge or marine oil spills, avoiding water pollution. Smart artificial super-wettable materials used for oil-water separation have aroused enormous interest because of their advantages of energy efficiency and applicability across a wide range of industrial processes. Herein, we report a highly efficient, simple method for oil-water separation using copper mesh fabricated by picosecond laser processing combined with chemical treatment or thermal oxidation. After laser processing, the surfaces of copper mesh show superhydrophilicity (hydrophilicity) and underwater superoleophobicity, which can be used to separate water from oil. While, for the samples after laser and chemical treatment or laser treatment combined with thermal oxidation, the surfaces become superhydrophobic (hydrophobic) and underwater superoleophilic, which can separate oil from water. Moreover, these three kinds of super-wettability meshes show high separation efficiency, achieving more than 99% seperation. Furthermore, the as-prepared mesh can be used for various oil-water mixture separation, such as edible oil, kerosene, diesel, and so on. Thus, this work will provide insights for controllable oil-water separation, and will also be beneficial to the study of microfluidic devices, and smart filters.

Randomly heterogeneous oleophobic/pH-responsive polymer coatings with reversible wettability transition for multifunctional fabrics and controllable oil–water separation

Stimuli-responsive surfaces with wettability change between superhydrophilic and superhydrophobic are susceptible to oil contamination which often ruins the surface. Herein, a coating with pH-switchable wettability transition between superamphiphobic and superhydrophilic-superoleophobic is achieved by rationally designing oleophobic/pH-responsive polymer heterogeneous chemistry. Fabrics modified with this coating show repellency to both water and oils, while upon exposure to acidic water (pH = 1) the fabrics change to be superhydrophilic-superoleophobic within a short response time of <5 s. More importantly, the superamphiphobicity of the fabric can be restored under mild alkaline condition (pH = 10), and the transition is reversible for many cycles. The effective in situ or ex situ wettability change under acidic/alkaline water treatment makes the coated fabric capable of separating oil–water mixture or even some mixtures of immiscible organic solvents. In addition, the coated fabric is also demonstrated to be promising as a new class of functional fabrics that provide protection against water and many oils in one condition, and can change to be hygroscopic, anti-static, oil-repellent and anti-oil-fouling in the other condition for improved wear comfort and self-cleaning.

A solvent-responsive robust superwetting titanium dioxide-based metal rubber for oil-water separation and dye degradation

The sewage treatment technology of oil-water separation based on superwetting materials has been widely employed. However, the stability of substrates was rarely considered in the past few years, which greatly limited the application of superwetting materials in engineering field. As a new robust, three-dimensional porous material, metal rubber (MR) has attracted significant attention for solving this problem. To treat the wastewater containing insoluble heavy/light oil and soluble dyes, herein, MR capable of degrading organic dyes with switchable wettability and high oil-water separation efficiency was prepared. Firstly, the superhydrophilic MR was obtained by anodizing. Then, the wettability of MR surface was reversibly switched between superhydrophilic and superhydrophobic via alternate immersion in stearic acid ethanol solution and tetrahydrofuran (THF) solvent to achieve switchable oil-water separation of MR. The superwetting MR displayed excellent abrasion resistance and retained outstanding oil-water separation performance after 100 times of sandpaper abrasion. Besides, the surface of pure titanium MR was rich in titanium dioxide (TiO2) after anodic oxidation, which could effectively degrade the organic dyes under ultraviolet light. Therefore, the as-prepared superwetting MR possesses the ability to treat complex wastewater and have applications prospects in controllable oil-water separation and self-cleaning surfaces.

Fabricated smart sponge with switchable wettability and photocatalytic response for controllable oil-water separation and pollutants removal

Stimuli-responsive materials with the controllable oil-water separation and water further purification abilities show great potential in practical applications. In this paper, a highly effective and eco-friendly smart pH-responsive melamine sponge with switchable wettability and photocatalytic activity was prepared via anchoring three-dimensional cell-like BiOCl microspheres into sponge skeletons and being modified by dodecanedioic acid and lauric acid. The obtained sponge shows rapidly switchable wettability and can separate various oil/water mixtures with high efficiency up to 99%. Moreover, the as-prepared smart sponge also demonstrates reliable photocatalytic ability and could remove the soluble pollutants (such as methylene blue and Sudan III) under visible light as well as UV light (degradation efficiency around 100%). Besides, the smart pH-responsive material showed satisfactory reusability and stability. This smart multifunctional material has outstanding potential in water resource purification.

Photoluminescent, Ferromagnetic, and Hydrophobic Sponges for Oil-Water Separation.

To find a facile way to produce a hydrophobic sponge that can effectively absorb oils is urgent to resolve the environmental pollution and ecological disaster caused by oil spillage. Here, alkylated carbon dots (C dots) were prepared from pyrolysis of a mixture of dodecylamine and citric acid followed by purification through silica gel column chromatography. Polyurethane sponge was modified by alkylated C dots by a simple dip-coating method, which endows the photoluminescent and hydrophobic sponge with good absorption capacities for various oils and nonpolar organic solvents with high recyclability. The water contact angle of the modified sponge can reach 138.8°. Interestingly, the sponge enables visual absorption under UV irradiation in the dark, which has not been achieved by other carbon-based adsorbents. The sponge was further made ferromagnetic by introducing alkylated Fe3O4 nanoparticles into its structure, which allowed controllable oil–water separation.

Cellulosic sponges with pH responsive wettability for efficient oil-water separation

To obtain efficient oil-water separation materials with responsiveness, cellulosic porous materials with switchable wettability in response to pH changes were developed by reacting cellulose acetoacetate sponges with alkylamines of varying carbon chain length via dynamic covalent enamine bonds. The resulting sponges reversibly changed between being superhydrophilic (θwater = 0°) and highly hydrophobic (maximal θwater = 146°) under suitable pH conditions while maintained the favorable porous structures. Notably, the functionalized sponges exhibited high and selective oil absorption capacity (40–80 g/g) and satisfying desorption ability of 80%, and could efficiently separate oil-water mixtures and emulsions with extremely high efficiency (> 99%) in a controllable manner. With the three-dimensional micro/nano porous structure, switchable wettability and intrinsic environmentally friendliness, the pH responsive cellulosic sponges developed here hold great potential in controllable oil-water separation and oily wastewater purification.

Switchable Wettability Surface with Chemical Stability and Antifouling Properties for Controllable Oil-Water Separation.

Membrane materials with special wettability for separating oil-water mixtures have gradually become one of the research hotspots. However, oily wastewater usually has very strong corrosiveness, which puts forward high requirements for the chemical stability of the separation membrane. In addition, oil droplets may block the pores, resulting in the decrease of separation efficiency or even separation failure. Herein, biomimetic TiO2-titanium meshes (BTTMs) with switchable wettability were successfully fabricated by one-step dip coating of poly(vinylidene difluoride) and modified TiO2 suspension on the titanium meshes. The simple and efficient preparation method will facilitate the promotion of this smart material. Due to the controlled wettability, the BTTM can separate water or oil from an oil-water mixture as required. When the BTTM was immersed in strong corrosive solution or liquid nitrogen, the wettability did not change much, showing the good stability of the BTTM. Furthermore, the BTTM also has self-healing ability, self-recovery anti-oil-fouling properties, and self-cleaning behavior, which help it resist oil pollution and improve its recyclability. This study provides a simple and efficient strategy for fabricating a stable smart surface for on-demand controllable treatment of corrosive oily wastewater.

Facile fabricate a bioinspired Janus membrane with heterogeneous wettability for unidirectional water transfer and controllable oil–water separation

A novel smart Janus membrane for unidirectional water transfer and oil–water separation is facilely fabricated by coating graphene nanoplatelets (GNs) onto one side of polyethylene terephthalate (PET) fabric through high-temperature and high-pressure method and subsequently grafting phosphoric acid (HP) into the other side of PET fabric. Results suggest that the prepared HP–PET–GNs Janus membrane with heterogeneous surface wettability attributed to the hierarchical structure of membrane shows special unidirectional water transfer property. The water droplet can penetrate across the membrane from the GNs-coated (hydrophobic) side to the HP-grafted (hydrophilic) side, and be blocked to pass through the membrane from hydrophilic side to hydrophobic side. Moreover, the HP–PET–GNs Janus membrane is found to have the maximum water flux and separation efficiency of 2073 ± 207 Lm−2h−1 and 99.5 ± 0.2% for methylbenzene–water mixture, and the maximum oil flux and separation efficiency of 3113 ± 52 Lm−2h−1 and 99.6 ± 0.1% for carbon tetrachloride–water mixture, respectively. The water separation efficiency and oil separation efficiency could arrive at 99.0 ± 0.1 and 99.3 ± 0.2% even after 10 separation cycles, respectively. It is revealed that the obtained Janus membrane has excellent separation capability for separating the layered oil–water mixtures and possesses wonderful recyclability.

Electrochemical Wettability Control on Cu/CuxO Core-Shell Dendrites: In-Situ Droplet Modulation and On-Demand Oil-Water Separation

ABSTRACTStimuli-responsive materials with controlled reversible wettability find diverse application as self-cleaning surfaces, tunable optical lenses and microfluidic devices. We report on an electrochemical approach for dynamic control over the wetting properties of additive-free Cu/CuxO core-shell dendritic structures. By varying the oxidation state of the oxide shell phase, the entire wettability range spanning superhydrophobicity (contact angle &gt; 150°) to superhydrophilicity (contact angle &lt; 10°) can be precisely adjusted in-situ. During the wetting transitions, the surface transforms from a low adhesive rolling state (lotus effect) to high adhesive pinning state (petal effect), and eventually to superhydrophilic state with a water-absorbing ability (fish scale wetting). The wetting alteration is reversible via air-drying at room temperature or mild heat drying at 100°C. The reversibly redox-driven wettability switching is demonstrated for controllable oil-water separation with efficiency higher than 98 percent.

ZnO-Nanowires-Coated Smart Surface Mesh with Reversible Wettability for Efficient On-Demand Oil/Water Separation.

The rapid industrial growth has led to the large production of oily wastewater. Treatment of oily wastewater is an inevitable challenge to manage the greater demand of clean water for the rapidly growing population and economy. In the present work, we have developed a smart surface mesh with reversible wetting properties via a simple, ecofriendly, and scalable approach for on-demand oil-water separation. ZnO nanowires (NWs) obtained from the chemical vapor deposition method were coated on a stainless steel (SS) mesh. The as-synthesized ZnO-NWs-coated mesh shows superhydrophilic/underwater superoleophobic behavior. This mesh works in "water-removing" mode, where the superhydrophilic as well as underwater superoleophobic nature allows the water to permeate easily through the mesh while preventing oil. The wetting property of ZnO-NWs-coated mesh can be switched easily from superhydrophilic to superhydrophobic state and vice versa by simply annealing it at 300 °C alternatively under hydrogen and oxygen environment. The separation is solely driven by gravity. Thus, the reversible wettability of ZnO NWs provides a smart surface mesh which can be switched between "oil-removing" and "water-removing" modes. It was found that for more than 10 cycles of mesh reutilization in both modes alternatively, the separation efficiency of 99.9% stayed relatively invariant, indicating a prolonged antifouling property and excellent recyclability. This work provides a simple, fast, cost-effective, and on-demand solution for oily wastewater treatment and opens up new perspectives in the field of controllable oil-water separation.

Fluorine-Free Superhydrophobic Coatings with pH-induced Wettability Transition for Controllable Oil-Water Separation.

We present a simple, environmentally friendly approach to fabricating superhydrophobic coatings with pH-induced wettability transition. The coatings are prepared from a mixture of silica nanoparticles and decanoic acid-modified TiO2. When the coating is applied on cotton fabric, the fabric turns superhydrophobic in air but superoleophilic in neutral aqueous environment. It is permeable to oil fluids but impermeable to water. However, when the coated fabric is placed in basic aqueous solution or ammonia vapor, it turns hydrophilic but underwater superoleophobic, thus allowing water to penetrate through but blocking oil. Therefore, such a unique, selective water/oil permeation feature makes the treated fabric have capability to separate either oil or water from a water-oil mixture. It may be useful for development of smart oil-water separators, microfluidic valves, and lab-on-a-chip devices.

Photo-induced water–oil separation based on switchable superhydrophobicity–superhydrophilicity and underwater superoleophobicity of the aligned ZnO nanorod array-coated mesh films

Stimulus-responsive surface wettability, especially photoresponsive surface wettability, has been intensively studied. Meanwhile, multifunctional surfaces, especially for the treatment of oil contaminated water, have aroused worldwide attention. Recently, pH-responsive surfaces with controllable oil–water separation have also been reported. However, photoresponsive water–oil separation is still a challenge. Here we report photo-induced water–oil separation based on the switchable superhydrophobicity–superhydrophilicity and underwater superoleophobicity of aligned ZnO nanorod array-coated mesh films, which shows excellent controllability and high separation efficiency of different types of water–oil mixtures in an oil–water–solid three-phase system. The underwater superoleophobicity of the aligned ZnO nanorod array-coated stainless steel mesh film can effectively prevent the mesh film from being polluted by oils. This work is promising in photo-induced water–oil mixture treatments such as water-removal from a micro-reaction system and controllable filtration, and may also provide interesting insight into the design of novel functional devices based on controllable surface wettability.