Anchoring metal organic frameworks on nanofibers via etching-assisted strategy: Toward water-in-oil emulsion separation membranes

A facile method for separating fine water droplets dispersed in oil through a pre-wetted mesh membrane

To achieve the successful separation of emulsions containing fine dispersed droplets and low volume fractions, a membrane with pore sizes comparable to or smaller than the droplet size is typically required. Although this approach is effective, its utilization is limited to the separation of emulsions with relatively large droplets. To overcome this limitation, a secondary membrane can be formed on the primary membrane to reduce pore size, but this can also be time-consuming and costly. Therefore, a facile and effective method is still required to be developed for separating emulsions with fine droplets. We introduce a pre-wetted mesh membrane with a pore size significantly larger than droplets, easily fabricated by wetting a hydrophilic stainless-steel mesh with water. Applying this membrane to emulsion separation via gravity-driven flow confirms a high efficiency greater than 98%, even with droplets approximately 10 times smaller than the pore size.

One-Step Prepared Multifunctional Polyacrylonitrile/MIL-100(Fe) Membrane with High-Density Porous Fibers for Efficient Dye/Oil Wastewater Remediation

With environmental pollution becoming more serious, developing efficient treatment technologies for all kinds of organic wastewater has become the focus of current research. In this work, the coaxial electrospinning technology was used to one-step fabricate a porous and underwater superoleophobic polyacrylonitrile nanofibrous membrane with an Fe-based metal-organic framework (MIL-100(Fe)). Benefiting from the synergistic effect of two jets, the nanofibers are smaller and denser, which prompt the exposure of more nanomaterial additives (MIL-100(Fe)). The BET surface area increased to 202.888 m2/g, and the membranes demonstrated outstanding underwater superoleophobicity. Moreover, compared with traditional blended matrix membranes by the single-axis method, separation of the modifier and membrane matrix material by coaxial methods also maintained excellent mechanical properties, which enhanced Young's modulus 3.4 times (∼1.34 MPa). As a result, facing soluble dyes, the porous C-PAN/MIL-100(Fe) membrane can demonstrate outstanding and fast adsorptive property (the Qm of MB and CR reached 44.71 and 88.74 mg g-1, respectively). For oily emulsion, the hydrophilic and oleophobic nanofibrous reticular surface provided excellent separation performance (flux: 1124.0-1549.3 L m-2 h-1, R > 98%). Moreover, the porous and underwater superoleophobic C-PAN/MIL-100(Fe)-0.5 membrane can synchronously purify the dye/oil mixture emulsions by one-step filtration. Based on the above performance, we believe that the modified nanofibrous membrane prepared by one-step coaxial electrospinning technology can promote more studies of the development of membrane preparation technology in the field of oily wastewater treatment.

Effective separation of water-in-oil emulsions using an under-medium superlyophilic membrane with hierarchical pores

Separating water-in-oil emulsions is important in terms of environmental protection and resource recovery. To address the challenges posed by the water-oil interface, superwetting materials have been designed to accomplish separation through filtration and adsorption. Superhydrophobic membranes prevent the permeation of water droplets owing to extreme repellence and their size-sieving abilities. However, their use in remediating water-contaminated oil is limited by high oil viscosities. Meanwhile, in-air superhydrophilic sorbents are rarely employed for the separation of water-in-oil emulsions due to the thermodynamic and kinetic limitations of water adsorption in oil. Herein, the integration of an under-medium superlyophilic membrane with the hierarchical porous structure of wood is presented for filtration-driven selective adsorption of water from surfactant-stabilized (10 g/L) water-in-oil emulsions. Compared to filtration through a natural wood membrane or direct adsorption using an under-oil superhydrophilic wood membrane, the under-medium superlyophilic wood membrane demonstrated high separation efficiencies of > 99.95% even when applied to the regeneration of high-viscosity lubricating (6.3 mPa s) and edible (50.5 mPa s) oils, exhibiting viscosity-dependent fluxes and excellent stability. Moreover, the cost of purifying 200 mL of lubricating oil using the modified wood membrane was much lower than the oil's market price and required a low energy consumption of ca. 1.72 kWh. ENVIRONMENTAL IMPLICATION: The ever-growing use of petroleum and industrial/domestic oil products has led to excessive (estimated at a million tons per year) output of waste oils. Because direct discharge of waste oils into the environment causes serious pollution problems, separating water-in-oil emulsions is important in terms of environmental protection and resource recovery. Here filtration-driven water adsorption has been demonstrated to be a feasible method for the remediation of water-contaminated waste oils, even those that are highly viscous.

Facile fabrication of organic superhydrophobic corn silk-derived cellulose acetate nanofiber for the effective sequestration of oil from oil-water mixture

Oil spills and subsequent cleanup by oil-water separation remain a global concern. For the first time, corn silk-derived cellulose acetate (CSCA) and polyacrylonitrile (PAN) composite nanofiber are reported to create a superhydrophobic oil-water sequestration membrane. CA : PAN solutions with various PAN concentrations were evaluated for viscosity and conductivity. A CSCA nanofiber membrane was fabricated through electrospinning, which was superhydrophobic and oleophilic in water. Scanning electron microscope, energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and thermogravimetric analysis/differential scanning calorimetry were used to analyze the membrane's morphological features. CSCA nanofibers formed a highly spherical bead with a maximum contact angle of 156° (>120°) in pure water solutions, demonstrating their superhydrophobicity. This study found that membranes can remove oil from oil-water mixtures and emulsions, as gravity is the only force required for propelling the system. Mineral oil had the highest oil sorption capability (908%), while toluene had the lowest (664%). For mineral oil-water mixtures, the CSCA membrane has the greatest separation flux at a maximum of 442 L/m2/h and the best separation efficiency at up to 99.67%. These findings provide strong support for using an as-prepared CSCA nanofiber membrane as a viable reusable oil sorbent in oil spill cleaning.

Solar-Assisted Superhydrophobic MoS2/PDMS/MS Sponge for the Efficient Cleanup of Viscous Oil

Industrialization releases many high-viscosity oil pollutants into the environment, requiring a hydrophobic recyclable oil-absorbing material. Therefore, a self-heating and superhydrophobic melamine sponge (MS) by connecting polydimethylsiloxane (PDMS) was coated with functionalized molybdenum disulfide (MoS₂) nanosheets on a three-dimensional microstructure of a commercial MS (MoS₂/PDMS/MS) via a simple and low-cost dip-coating method. The prepared sponge showed a water contact angle of 151.8°, indicating that the modified sponge exhibited superhydrophobicity. Due to the addition of MoS₂, the modified sponge can convert light into heat, and its surface could be heated to 59.7 °C within 30 s. Because of the excellent MoS₂/PDMS/MS photothermal performance, the sponge could decrease the viscosity of the high-viscosity oil, absorbing the high-viscosity oil efficiently. After simultaneous thermal analysis and repeated compression tests, the modified sponge exhibited high thermochemical stability, mechanical property, and reusability. This superhydrophobic multifunctional sponge shows excellent potential for high-viscosity oil absorption.

Wettability Improvement in Oil-Water Separation by Nano-Pillar ZnO Texturing

The nanostructure-based surface texturing can be used to improve the materials wettability. Regarding oil−water separation, designing a surface with special wettability is as an important approach to improve the separation efficiency. Herein, a ZnO nanostructure was prepared by a two-step process for sol−gel process and crystal growth from the liquid phase to achieve both a superhydrophobicity in oil and a superoleophobic property in water. It is found that the filter material with nanostructures presented an excellent wettability. ZnO-coated stainless-steel metal fiber felt had a static underwater oil contact angle of 151.4° ± 0.8° and an underoil water contact angle of 152.7° ± 0.6°. Furthermore, to achieve water/oil separation, the emulsified impurities in both water-in-oil and oil-in-water emulsion were effectively intercepted. Our filter materials with a small pore (~5 μm diameter) could separate diverse water-in-oil and oil-in-water emulsions with a high efficiency (>98%). Finally, the efficacy of filtering quantity on separation performance was also investigated. Our preliminary results showed that the filtration flux decreased with the collection of emulsified impurities. However, the filtration flux could restore after cleaning and drying, suggesting the recyclable nature of our method. Our nanostructured filter material is a promising candidate for both water-in-oil and oil-in-water separation in industry.