Continuous Oil Water Separation Research Articles

Low-Resistance Thiophene-Based Conjugated Microporous Polymer Nanotube Filters for Efficient Particulate Matter Capture and Oil/Water Separation

Air and water pollution poses a serious threat to public health and the sustainable development of the ecological environment. Here, we report the fabrication of new low-resistance nanofilters based on thiophene-based conjugated microporous polymer (T-CMP) nanotubes to remove harmful particulate matter (PM) from air effectively. T-CMP nanotube filters feature inherent superhydrophobicity and hierarchical pores and are prepared by a facile one-pot synthesis. The PM removal efficiency of T-CMP nanotube filters at 90 ± 5% relative humidity exceeds 99.798 ± 0.055% for PM0.3 and 99.998 ± 0.002% for PM2.5, while the lowest pressure drop in the filtration system is only 5 Pa, which is 1-2 orders of magnitude lower than that of traditional fiber-based filters. Benefitting from their excellent porous feature and intrinsic superhydrophobicity, T-CMP nanotube filters also display higher flux during continuous oil-water separation. Based on this superior separation performance, better physicochemical stability, facile manufacturing, and easy scaling-up, such T-CMP nanotube filters might hold great potential for a wide range of applications even under harsh conditions, including PM removal, water treatment, and so on.

A durable, fluorine-free, and repairable superhydrophobic aluminum surface with hierarchical micro/nanostructures and its application for continuous oil-water separation

Artificial superhydrophobic surfaces have drawn a lot of attention owing to their multifunctional properties. However, the durability and environmental concerns of such surfaces are critical issues that have limited their widespread utilization in real-life applications. In this study, fluorine-free superhydrophobic aluminum surface was fabricated through a simple and cost-effective method. Its dual-scale micro-/nanostructures (MNS) was fabricated by combining chemical etching and hydrothermal processes. After modification with polydimethylsiloxane coating using a simple vapor deposition method, surface showed excellent superhydrophobicity, with a water contact angle of ~161° and sliding angle of 4°, and sustained its non-wetting properties against various food liquids. The effect of morphological change on the surface's wettability and the durability of the coating materials were investigated in sandpaper abrasion, tape-peeling, and blade-scratching tests. Compared with micro- or nanostructure surfaces, the MNS surface showed better robustness because of its dual-scale roughness. Furthermore, the abraded surface could effectively restore its superhydrophobicity after being recoated with PDMS. The surface also showed long-term superhydrophobic stability in an ambient environment for over 10 months. Finally, the method was applied to Al mesh with superhydrophobic/superoleophilic properties to separate various oil-water mixtures, yielding a high separation efficiency of up to 94% and outstanding reusability.

Multiple applications of bio-graphene foam for efficient chromate ion removal and oil-water separation

This paper presents the synthesis of bio-graphene foams (bGFs) from renewable sources, and the application of bGFs as new adsorbents in removal of chromate ions and oil contaminants from waste water. A two-step synthetic method was developed to produce bGFs with unique porous architecture and high specific surface area (up to 805 m2 g−1) that is highly desirable for environmental applications. The adsorption performance of prepared bGFs for removal of chromate ions from water was studied in relation to CrO42− concentration, adsorbent load, pH, and contact time to confirm adsorption capacity, kinetics and pH dependence. The adsorption isotherms of chromate ions were consistent with the Langmuir model, revealing an outstanding adsorption capacity of 245 mg of Cr(VI)/g bGFs (pH∼7). bGFs were capable of reducing Cr(VI) in water below the maximum permissible level (0.050 mg dm−3) for human consumption (WHO). In a second application, our results convincingly showed excellent performance of bGFs in separating organic solvents and oils from water in a continuous oil-water separation process showing 99.1% and 98.8% separation efficiency for toluene and petroleum, respectively. Our findings confirm that the outstanding performance of bGFs, and suggest their use as efficient adsorbents for environmental remediation.

Biomimetic, dopamine-modified superhydrophobic cotton fabric for oil–water separation

Oily wastewater seriously pollutes the environment, and is difficult to separate. In this work, superhydrophobic cotton fabrics were fabricated through the combination of micro–nano-binary structure of polydopamine (PDA) and grafting of octadecylamine (ODA). Herein, fluorine-free compounds were used. The PDA binary structure was rapidly deposited on cotton fabric under the catalysis of metal salts and oxidants. Then, the ODA was grafted onto the cotton fabric through Schiff base reaction with o-quinone formed by oxidation of the catechol structure of PDA, which covered the surface of PDA coated cotton fabric. The superhydrophobic cotton fabric with contact angle up to 163.7° and scroll angle around 9° was obtained. Due to the excellent adhesion of polydopamine, the superhydrophobic cotton fabric demonstrated great stability and durability under a variety of harsh environmental conditions. After coating the polyurethane (PU) sponge with the prepared superhydrophobic cotton fabric, an oil absorbing bag was made and it showed good oil–water separation even after being reused 20 times, and the prepared cotton fabric also had excellent self-cleaning performance. This facile strategy of preparation of superhydrophobic materials for continuous oil–water separation is quick, efficient and environmentally friendly, which has great prospect for application in removal of marine oil spills.

Recycling waste epoxy resin as hydrophobic coating of melamine foam for high-efficiency oil absorption

The preparation of oil absorption materials with both low-cost and high efficiency remains a great challenge. In this work, a waste epoxy resins (EPs) derived hydrophobic modifier was developed to fabricate high-efficient oil absorbents by simple dip-coating on melamine foam (MF). EPs were effectively degraded by acid digestion in mild condition to obtain the degradation products (DEPs) with a large molecular weight. DEPs can be directly used as a hydrophobic agent due to excellent hydrophobicity and processability. The resulting DEPs@MF exhibited excellent absorption performance for various oils or organic solvents with an ultrafast adsorption rate of 2 s and high oil absorption capacity of 116 g g−1. Moreover, the absorbed oils can be recovered by simple mechanical extrusion, and the adsorption capacity of the DEPs@MF did not deteriorate even after it was reused for 10 times. Besides, an oil recovery unit was successfully designed to achieve continuous oil–water separation. This research not only provides a new approach to the preparation of highly efficient and reusable oil-absorbing materials, but also provides new insight into solving the increasingly serious problem of waste thermosetting polymers.

Synthesis of superhydrophobic and high stable Zr-MOFs for oil-water separation

A universal strategy is developed to construct a superhydrophobic and superoleophilic metal-organic framework (MOF) by an amidation reaction between amino group and acid chloride of octadecanoyl chloride. The introduction of long alkyl chain reduced the surface free energy, yielding a superhydrophobic Zr-MOF (UiO-66-NH-C18) with a high water contact angle (WCA) of 151.7°. The adsorbed amount of water on the UiO-66-NH-C18 was only 5.59 mmol/g, which was just 28 % of that on the UiO-66-NH2. More importantly, the hydrophobic modification improved the stability of Zr-MOFs under strong alkaline conditions (e.g., pH = 13). Furthermore, the UiO-66-NH-C18 can selectively absorb organic solvent from water and achieve continuous oil-water separation. The oil-water separation efficiency could reach up to 99.9 %. In addition, the UiO-66-NH-C18@sponge was also prepared through dip-coating of UiO-66-NH-C18 on the melamine sponge in the presence of PDMS solution. The resulting composite shows high adsorption capacities for various oils and organic solvents ranging from 32.3–66.1 g/g. The superhydrophobic UiO-66-NH-C18@sponge has potential as a promising absorbent for treatment of oily wastewater.

Facile preparation of superhydrophobic porous wood for continuous oil-water separation

Preparation of superhydrophobic porous wood is an important avenue for realizing efficient oil-water separation, but the reported methods require the removal of hemicellulose and lignin as well as energy consuming freeze-drying process. In the present study, we report a facile strategy for cost-effective, convenient, simple, and highly effective preparation of polymethylsiloxane (POMS) modified wood. The resulting POMS modified wood is superhydrophobic, and its water contact angle is as high as 153°. The POMS modified wood is used to selectively remove the oil from bulk water. More importantly, by the combination of superhydrophobic performance, porous structure, and inherent channels, the modified wood is able to continuously separate oil-water mixture and oil-in-water emulsion, with a high separation efficiency. The superhydrophobic POMS modified wood has a good potential application in wastewater treatment, oil spill cleanup, emulsion separation, and so on.

Superhydrophilic Al2O3 composite meshes for continuous high-efficiency oil-water separation

Superhydrophilic and underwater superoleophobic alumina composite meshes (Al2O3@Meshes) were prepared by two different methods: the in-situ growth method and the impregnation method. The in-situ growth method used aluminum powder to react with sodium hydroxide and formed cluster-like Al2O3 on the sintered wire mesh after calcination. As for the impregnation method, the sintered wire mesh was impregnated with the saturated aluminum nitrate solution and formed papillary Al2O3 on the mesh after calcination. The hydrophilic and rough Al2O3 were capable of forming a water layer and endowed Al2O3@Meshes with superhydrophilicity, which made the meshes to transport water but to intercept oil. The Al2O3@Meshes exhibited excellent separation efficiency for various oil-water mixtures even under low concentrations in the intermittent device. Meanwhile, the Al2O3@Meshes performed well in recyclability and thermostability for oil-water separation at high temperature (95 °C). Furthermore, the continuous oil-water separation was achieved by assembling Al2O3@Meshes on the fabricated device. A continuous device could separate oil-water mixtures efficiently over 80 L in the consecutive 12 h and the separation efficiency maintained over 99.8% at the whole process.

Selective Wettability Membrane for Continuous Oil-Water Separation and In Situ Visible Light-Driven Photocatalytic Purification of Water.

Membrane‐based technologies are attractive for remediating oily wastewater because they are relatively energy‐efficient and are applicable to a wide range of industrial effluents. For complete treatment of oily wastewater, removing dissolved contaminants from the water phase is typically followed by adsorption onto an adsorbent, which complicates the process. Here, an in‐air superhydrophilic and underwater superoleophobic membrane‐based continuous separation of surfactant‐stabilized oil‐in‐water emulsions and in situ decontamination of water by visible‐light‐driven photocatalytic degradation of dissolved organic contaminants is reported. The membrane is fabricated by utilizing a thermally sensitized stainless steel mesh coated with visible light absorbing iron‐doped titania nanoparticles. Post annealing of the membrane can enhance the adhesion of nanoparticles to the membrane surface by formation of a bridge between them. An apparatus that enables continuous separation of surfactant‐stabilized oil‐in‐water emulsion and in situ photocatalytic degradation of dissolved organic matter in the water‐rich permeate upon irradiation of visible light on the membrane surface with greater than 99% photocatalytic degradation is developed. The membrane demonstrates the recovery of its intrinsic water‐rich permeate flux upon continuous irradiation of light after being contaminated with oil. Finally, continuous oil−water separation and in situ water decontamination is demonstrated by photocatalytically degrading model toxins in water‐rich permeate.

Corrosion-Resistant Hydrophobic MFI-Type Zeolite-Coated Mesh for Continuous Oil–Water Separation

Efficient separation of oil–water mixtures has become a critical challenge due to frequent oil-spill accidents and enormous release of oil-containing wastewater by households or catering services. Superhydrophobic coatings on metal meshes have been evidenced as the effective and energy-saving materials for oil–water separation. However, it is difficult to fabricate the separating coatings with long-term superhydrophobicity and the outstanding anticorrosion properties for practical application. In this study, we fabricated the hydrophobic Mobil five (MFI)-type zeolite coatings on the pristine stainless steel meshes via an in situ crystallization method and subsequently modified them with an environmentally safe hexadecyltrimethoxysilane compound. The as-prepared coating meshes showed good self-cleaning, antifouling, and anticorrosion properties. Furthermore, the coated meshes were capable of continuously and efficiently separating different kinds of oil–water mixtures under gravity-driven pressure and had more than 99.0% high separation efficiency. More important, the prepared hydrophobic MFI-coated meshes had equivalent separation performance compared to that of superhydrophobic coating meshes. Meanwhile, the hydrophobic MFI-coated meshes demonstrated excellent reusability performance and long-term stability. These as-prepared meshes thus have great potential for applications in separating oily wastewater from oil fields as well as recycling of waste oil from catering services.

Surface Metallization of Porous Polymer Materials for Multifunctional Applications.

Porous materials have attracted great interest in recent years, and a variety of surface modification methods have been developed to endow porous materials with multifunctional applications. Herein, multifunctional porous materials are fabricated based on surface metallization. Metallized sponges with Ag and Cu are highly hydrophobic and are still hydrophobic under oil. The metallized sponges selectively adsorb oils from oil/water mixtures and can completely remove oils from water. We further demonstrate continuous oil-water separation by the metallized sponges with the aid of a peristaltic pump. The Ag-metallized materials show high catalytic performance for both chemical reduction and dye degradation. The catalytic reduction efficiency of 4-nitrophenol reaches 97.7% within 60 min and remains as high as 96% after 15 cycles. Moreover, the metallized materials show 99.99% bactericidal efficiency for both Staphylococcus aureus and Escherichia coli. Particularly, the Cu-metallized materials exhibit stable conductivity under deformation; and metal patterns are realized via the metallization method combined with a patterned mask, which may provide a feasible approach for flexible electronics. This work provides a versatile method to introduce metal coatings to porous materials, broadening the applications of porous materials.

Fabricated superhydrophobic three-dimensional rambutan-like-β-NiOOH @sponge skeletons for multitasking oil–water separation

In this paper, oleophilic and superhydrophobic sponges were successfully constructed via a one-pot low temperature hydrothermal method anchoring three-dimensional rambutan-like-β-NiOOH microspheres into sponge skeletons and lauric acid modification. The constructed modified three-dimensional rambutan-like-β-NiOOH @sponge (the static contact angle of 153.5°) possessed outstanding oil sorption capacity (separation efficiency is nearly 99%) towards the various organics/oils and excellent recyclability after 30 cycles of adsorption-squeezing. Importantly, modified three-dimensional rambutan-like-β-NiOOH @sponge is capable of separating surfactant-stabilized water-in-oil emulsions and can be utilized for continuous oil-water separation with the aid of a peristaltic pump. This is mainly due to the fact that the three-dimensional hierarchical rambutan-like micronano structure formed by self-assembly with high specific surface area provides a large number of hydrophobic interfaces to improve the hydrophobic properties of sponges. This work presents a new strategy for the designs multitasking oil-water separation materials.

Polydopamine-Assisted Surface Coating of MIL-53 and Dodecanethiol on a Melamine Sponge for Oil-Water Separation.

A superhydrophobic and superoleophilic porous composite was successfully prepared via a polydopamine-assisted surface coating of MIL-53(Fe) and 1-dodecanethiol (DDT) on a melamine formaldehyde (MF) sponge. The as-prepared sponge composite (MIL-DDT@MF) has a high water contact angle (WCA) of 151.8°, which is probably attributed to both the rough surface derived from in situ growth of MIL-53 nanocrystals and the low surface energy due to grafting of hydrophobic 1-dodecanethiol. The MIL-DDT@MF sponge can effectively absorb oil or organic solvent with an absorption capacity of up to 54.1 (for petroleum) to 120.2 (for chloroform) times its own weight. In addition, the MIL-DDT@MF sponge retained a high absorption capacity and maintained approximately 78% of its original value after 50 cycles of reuse. Moreover, the MIL-DDT@MF sponge can selectively absorb the oil/organic solvent from water and achieve continuous oil-water separation. The separation efficiency of n-hexane, dichloromethane, and crude oil from water or seawater can reach above 95%. The superhydrophobic and superoleophilic MIL-DDT@MF sponge has potential as a promising absorbent for treatment of oily wastewater.

Preparation and oil–water separation of 3D kapok fiber‐reduced graphene oxide aerogel

AbstractBACKGROUNDOil spills from oil tankers and ships or industrial accidents have serious impacts on the ecological environment. There is an urgent need for finding effective ways to resolve these problems. The use of low‐cost and efficient adsorbents is considered to be one of the most effective ways.RESULTSIn this study, an ultra‐light 3D kapok fiber‐reduced graphene oxide (TKF‐rGO) aerogel was prepared by a simple and green one‐step hydrothermal method. The kapok fiber used as skeleton was embedded in a graphene network to successfully form a 3D aerogel structure. The as‐prepared TKF‐rGO aerogel featured low density, excellent mechanical strength, high thermal stability, and high hydrophobic lipophilicity. Furthermore, continuous oil–water separation could be achieved by the aerogel when connected to a vacuum system. The adsorption capacity of TKF‐rGO aerogel for various common oil products and organic solvents was 1.5‐fold greater than that of pure rGO aerogel and six‐fold greater than that of polypropylene melt spray, respectively. In addition, the initial adsorption capacity of the as‐prepared TKF‐rGO aerogel was maintained at 94% after eight cycles.CONCLUSIONThe TKF‐rGO aerogel could be synthesized by a low‐cost and green method, which was suitable for commercial production, and showed competitive adsorption capacities for oil removal. Thus, the TKF‐rGO aerogel is expected to be employed as a promising adsorbent in the removal of oil spill or hazardous organic solvents from water. © 2019 Society of Chemical Industry

Synthesis of a Superhydrophobic Polyvinyl Alcohol Sponge Using Water as the Only Solvent for Continuous Oil-Water Separation

Few cases of hydrophobic materials synthesized in water have been reported. In this work, water, as the only solvent, is used to prepare a superhydrophobic sponge via a facile and environment-friendly route. The as-prepared sponge, namely silylated polyvinyl alcohol (PVA) sponge, exhibits superhydrophobic and superoleophilic characters. It has the static water contact angle (WCA) of 152 ± 1 and the static oil contact angle (OCA) of 0°, which can lead to excellent selectivity for oil-water separation. Besides, the methyltriethoxysilane (MTES) can form a stable mixed structure with the PVA skeleton, resulting in the rare shedding of polymethylsiloxane nanoparticles and the long-term stability for oil-water separation. Furthermore, the silylated sponge shows a high separation efficiency (>99.6%), removing oil up to 6200∼14000 times of its own mass. The findings demonstrated that the silylated superhydrophobic sponge can be a promising candidate in water treatment application.

Superhydrophobic, compressible, and reusable polyvinyl alcohol-wrapped silver nanowire composite sponge for continuous oil-water separation

Herein, we applied a coaxial cable type polyvinyl alcohol-wrapped silver nanowire (Ag-PVAs) composite sponge as adsorbent material for oil/water separation. The Ag-PVAs sponge was prepared by two steps of hydrothermal and freeze-drying, and then modified with polydimethylsiloxane (PDMS) to reduce its surface energy. The modified Ag-PVAs sponge (f-PDMS) displayed superhydrophobic property due to its porous structure and low surface energy. Importantly, the f-PDMS has 14 times of maximum stress, compared with that of Ag-PVAs. Meanwhile, the maximum compressive stress of the f-PDMS sponge can still be maintained at 87.3% after 50 stress-strain cycles at 70% strain. Moreover, the f-PDMS sponge exhibits good adsorption properties for various oils with different densities and can be reused by extrusion and evaporation. Continuous oil/water separation can also be achieved with the aid of a vacuum pump, which will make it a powerful competitor for large-scale industrial separation of oil/organic solvents and water mixtures.

Superhydrophobic/superoleophilic natural fibres for continuous oil-water separation and interfacial dye-adsorption

The inconsistent wettability of biological superwetting materials, due to aging, morphological change, structural fragility and biodegradation, limit their practical use for highly demanding applications such as oil-water separation and dye adsorption. Herein, we present a new source of superwetting materials harvested from waste chestnut-shell. The material is in the form of micro-fibres which are intrinsically oleophilic/hydrophobic, chemically stable, lightweight and structurally robust. The harvested microfibres, laying between inner-liner and outer shell of the chestnut, are naturally enriched with aliphatic and aromatic hydrocarbon that results in their high oleophilicity. We demonstrated that these superoleophilic fibre-networks could be used as oil-absorbent exhibiting outstanding absorption efficiency with a maximum capacity of ~94% of their own weight. Afterwards, an efficient filtration membrane was engineered using these micro-fibres showing their ability for continuous oil-water separation process for a series of organic solvents (toluene, canola oil, engine oil, hexane, turpentine oil, petrol and olive oil) co-existing with water. Furthermore, the fibres were realized to be capable of adsorbing organic dyes at oil-water interfaces in both static (slow adsorption) and dynamic (instant adsorption) condition suggesting their multifunctionality in wastewater treatments. A small amount of fibres (0.75 g/L) could efficiently remove water miscible dyes of Rhodamine-B and Methylene blue with a maximum removal efficiency of 88% and ~91%, respectively. These low-cost natural fibres from biowaste with outstanding oil-water separation and organic dye-adsorption capacity have considerable advantages compared to other low-cost materials reported earlier for industrial wastewater-treatment and environmental remediation.

Fabrication of superhydrophobic marigold shape LDH films on stainless steel meshes via in-situ growth for enhanced anti-corrosion and high efficiency oil-water separation

A superhydrophobic marigold shape layered double hydroxide (LDH) film coated stainless steel mesh (SSM) was prepared by in-situ growth followed chemical modification in this work. The obtained SSM exhibited excellent superhydrophobicity, self-cleaning ability, physical and chemical durability, indicating the superior ability of adapting to outdoor environment. In addition, the obtained SSM also exhibited excellent corrosion resistance and the efficiency reached up to 97.3%. As for application evaluation, the obtained SSM could be applied in continuous oil-water separation with a high efficiency and flux after 50 times reuse (98.5% and 1800 L m−2 h−1 for chloroform-water mixture). More importantly, the obtained SSM exhibited a high intrusion pressure (5.39 kPa), which was helpful to the rapid separation of oil-water mixture. Consequently, the obtained superhydrophobic SSM offered a promise in solving practical application problems of oil-water separation in outdoor and thereby showed great potential in large-scale industrial applications.

Biomass‐Derived Lignocellulosic Graphene Composite: Novel Approach for Removal of Oil and Organic Solvent

AbstractNovel approach to develop a biomass derived lignin‐cellulose based, ultra‐light, hydrophobic graphene supported spongy composite was synthesized to absorb oil and organic solvents from wastewater. Spongy composite was synthesized by a facile and highly efficient one‐pot hydrothermal method from the natural precursor. Lignin‐cellulose functionalized graphene (LCG) sponge was synthesized from graphene oxide (GO) and sugarcane waste powder (SCwP) in presence of natural latex. LCG successfully demonstrated separation of oil from oil‐water mixture. LCG has high oil sorption capacity in the range of 25–50 g of oil per gram of sorbent. This material showed high efficiency as a sorbent to separate organic chemicals from wastewater. The absorption capacity of LCG sponge was enhanced thrice in comparison with SCwP and could be reused up to 10 cycles. The continuous oil water separation process was demonstrated using LCG sponge from the oil‐water mixture, which can be applied for large scale oil recovery from the waste stream.

Dual-channel separation system based on platanus fruit-like Ni@Ni(OH)2 hierarchical architecture for fast, efficient and continuous light/heavy oil–water separation

Realization of fast, efficient and continuous oil–water separation is of great significance for solving the problem of oil pollution. We present here a facile hydrothermal strategy to synthesize a superhydrophilic platanus fruit-like Ni@Ni(OH)2 hierarchical architecture (SI-PFHA). Additionally, superhydrophobic platanus fruit-like Ni@Ni(OH)2 hierarchical architecture (SO-PFHA) is obtained through stearic acid modification of SI-PFHA. Dual-channel separation system is integrated based on two superwetting membranes. Such separation system is competent for continuous light/heavy oil–water separation with high flux and high separation efficiency. Importantly, outstanding durability and reusability make this separation system a promising strategy for practical application in remediation of oily wastewater.