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Oil/water separation processes have garnered significant global attention due to the quick growth in industrial development, recurring chemical leakages, and oil spills. Hence, there is a significant demand for the development of inexpensive superwetting materials in an eco-friendly manner to separate oil/water mixtures and emulsions. In this study, a superwetting melamine sponge (SMS) with switchable wettabilities was prepared by modifying melamine sponge (MS) with sodium dodecanoate. The as-prepared SMS exhibited superhydrophobicity, superoleophilicity, underwater superoleophobicity, and underoil superhydrophobicity. The SMS can be utilized in treating both light and heavy oil/water mixtures through the prewetting process. It demonstrated fast permeation fluxes (reaching 108,600 L m−2 h−1 for a light oil/water mixture and 147,700 L m−2 h−1 for a heavy oil/water mixture) and exhibited good separation efficiency (exceeding 99.56%). The compressed SMS was employed in separating surfactant-stabilized water-in-oil emulsions (SWOEs), as well as surfactant-stabilized oil-in-water emulsions (SOWEs), giving high permeation fluxes (reaching 7210 and 5054 L m−2 h−1, respectively). The oil purity for SWOEs' filtrates surpassed 99.98 wt% and the separation efficiencies of SOWEs exceeded 98.84%. Owing to their remarkable capability for separating oil/water mixtures and emulsions, eco-friendly fabrication method, and feasibility for large-scale production, our SMS has a promising potential for practical applications. [ABSTRACT FROM AUTHOR]

Although membrane separation technology has been widely used in the treatment of oily wastewater, the complexity and high cost of the membrane preparation, as well as its poor stability, limit its further development. In this study, via the vacuum-assisted suction filtration method, polydopamine (PDA)-coated TiO2 nanoparticles were tightly attached and embedded on both sides of laboratory filter paper (FP). The resultant FP possessed the typical wettability of high hydrophilicity in the air with the water contact angle (WCA) of 28°, superoleophilicity with the oil contact angle (OCA) close to 0°, underwater superoleophobicity with the underwater OCA greater than 150°, and superhydrophobicity under the water with the underoil WCA over 150° for five kinds of organic solvents (carbon tetrachloride, toluene, n-hexane, n-octane, and iso-octane). The separation efficiency of immiscible oil/water, oil-in-water, and water-in-oil emulsions using the modified FP is higher than 99%. After 17 cycles of emulsion separation, a high separation efficiency of 99% was still maintained for the FP, along with good chemical and mechanical stability. In addition, successful separation and purification were also realized for the oil-in-water emulsion that contained the methylene blue (MB) dye, along with the complete degradation of MB in an aqueous solution under UV irradiation. [ABSTRACT FROM AUTHOR]

Emulsified oily wastewater threatens human health seriously, and traditional technologies are unable to separate emulsion containing small sized oil droplets. Currently, oil–water emulsions are usually separated by special wettability membranes, and researchers are devoted to developing membranes with excellent antifouling performance and high permeability. Herein, a novel, simple and low-cost method has been proposed for the separation of emulsion containing surfactants. Polyacrylonitrile (PAN) nanofibers were prepared via electrospinning and then coated by polydopamine (PDA) by using self-polymerization reactions in aqueous solutions. The morphology, structure and oil-in-water emulsion separation properties of the as-prepared PDA@PAN nanofibrous membrane were tested. The results show that PDA@PAN nanofibrous membrane has superhydrophilicity and almost no adhesion to crude oil in water, which exhibits excellent oil–water separation ability. The permeability and separation efficiency of n-hexane/water emulsion are up to 1570 Lm−2 h−1 bar−1 and 96.1%, respectively. Furthermore, after 10 cycles of separation, the permeability and separation efficiency values do not decrease significantly, indicating its good recycling performance. This research develops a new method for preparing oil–water separation membrane, which can be used for efficient oil-in-water emulsion separation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

To address the problem of ever-increasing oily wastewater management, due to its directional liquid transport property, membranes with asymmetric wettability can be effectively used for emulsion separation. This study reports the synthesis of electrospun polymer–clay nanocomposite nanofibers, using co-polyamide polymer (COPA) and halloysite nanotubes (HA) as filler. The influence of clay content on the morphological, thermal and dielectric properties of the polymer composite nanofiber was investigated comprehensively to address the material characteristics of the developed system. The surface structure analysis and contact angle measurements of the electrospun composite nanofibers confirms the change in surface roughness and wettability when the fillers are added to the polymer. The porosity of the composite electrospun nanofiber membrane was found to be 85% with an oil adsorption capacity of 97% and water permeability of 6265 L/m2 h. Furthermore, the asymmetric wettability-driven oil/water emulsion separation abilities of the as-synthesized membranes shows that the separation efficiency of the composite fiber membrane is 10% improved compared to that of the neat fiber membrane, with improved separation time. [ABSTRACT FROM AUTHOR]

A novel ultralight superhydrophobic-superoleophilic hybrid Carbon Nanotubes (CNTs) film with double-layer structures is fabricated by using vacuum filtration method. The CNTs film can separate various surfactant-stabilized water-in-oil emulsions with a separation efficiency higher than 99.3%. Moreover, the hybrid films can be regenerated through a simple and rapid combustion process within 2 s. In addition, the CNTs film still retains good hydrophobic properties under the conditions of physical abrasion, and strong acidic and alkaline solutions, which shows the excellent durability. The hybrid CNTs film is ultralight, stable, and easily stored and reused. The outstanding features of the obtained CNTs films we present here may find many important applications in various fields like oil purification and wastewater treatment. [ABSTRACT FROM AUTHOR]

In this paper, a novel superhydrophobic magnetic sawdust (SMSD) was fabricated as an oil sorbent. The SMSD was functionalized with Fe3O4 nanoparticles using melamine formaldehyde resin (MFR) as a coupling agent and subsequently hydrophobically-treated with hexadecyltrimethoxysilane (HDTMS). The SMSD showed excellent superhydrophobicity with the water contact angle of 155.3 ± 0.9°. Meanwhile it had remarkable environmental durability, long-term stability, and mechanical durable properties. Taking advantage of its magnetic characteristics, the SMSD could be easily controlled to absorb oil to separate oil–water mixtures with high oil absorption capacity and good reusability. Moreover, the emulsion was successfully separated by SMSD, including water-in-oil and oil-in-water emulsions. This study developed an effective oil absorbent, which was low cost and environmentally-friendly. [ABSTRACT FROM AUTHOR]

The pollution of water resources has become a worldwide concern. The primary pollutants including insoluble oil, toxic dyes, and heavy metal ions. Herein, we report a polymer adsorbent, named SPCT, to remove the above three contaminants from water simultaneously. The preparation process of SPCT contains two steps. Firstly, a hydrogel composed of sulfonated phenolic resin (SMP) and polyethyleneimine (PEI) was synthesized using glutaraldehyde (GA) as the crosslinking agent, and the product was named SPG. Then SPCT was prepared by the reaction between SPG and citric acid (CA) at 170 °C. SPCT exhibited an excellent performance for the removal of methylene blue (MB) and Cu(II) from aqueous solution. For a solution with a pollutant concentration of 50 mg L−1, a removal efficiency of above 90% could be obtained with a SPCT dosage of 0.2 g L−1 for MB, or a SPCT dosage of 0.5 g L−1 for Cu(II), respectively. SPCT also presented an interesting wettability. In air, it was both superhydrophilic and superoleophilic, and it was superoleophobic underwater. Therefore, SPCT could successfully separate oil-in-water emulsion with high separation efficiency and resistance to oil fouling. Additionally, SPCT was easily regenerated by using dilute HCl solution as an eluent. The outstanding performance of SPCT and the efficient, cost-effective preparation process highlight its potential for practical applications. [ABSTRACT FROM AUTHOR]

In this study, a method that can simultaneously separate oil/water mixtures and water-in-oil emulsions were developed. Various substrates (synthetic polymers and stainless steel meshes) were coated by rough hydrophobic polymer films. The prepared materials possessed superhydrophobicity and superoleophilicity. These superhydrophobic sponges can isolate extensive amounts of oil from water when connected to a related vacuum framework. Moreover, the superhydrophobic meshes (SHM) can separate both surfactant-free and -stabilized water-in-oil emulsions via gravity with high separation efficiency (oil purity: >99.99%) and flux (up to 4760 L m−2 h−1). The extraordinary performance of our materials and their low-energy, efficient, low-cost preparation propose that they have great potential for real-time applications. [ABSTRACT FROM AUTHOR]