Efficient separation of free organic liquid mixtures based on underliquid superlyophobic coconut shell coated meshes

Covalent organic framework functionalized smart membranes with under-liquid dual superlyophobicity for efficient separation of oil/water emulsions

The smart membrane with under-liquid dual superlyophobicity, which can achieve on-demand separation of oil/water emulsions only by simple liquid pre-wetting, is of essential value for the treatment of complicated real oil/water systems. Here, we first fabricated a stable suspension of imine-linked covalent organic framework nanospheres (TPB-DMTP-COF), and subsequently fabricated COF functionalized smart membranes with under-liquid dual superlyophobicity by immersing polyacrylonitrile-based (PAN-based) membranes into TPB-DMTP-COF nanosphere suspension. Accordingly, effective switchable separation of both oil-in-water and water-in-oil emulsions by TPB-DMTP-COF/PAN membranes can be achieved by employing pre-wetting processes (both the oil contact angle under water and the water contact angle under oil are over 150°). Specifically, the separation flux and the separation efficiency are higher than 1200 L/m2‧h and 98.0 %, and 2100 L/m2‧h and 97.4 % for the surfactant-stabilized oil-in-water and water-in-oil emulsions, respectively. Furthermore, the ultralow adhesions in liquid contributed to the outstanding reusability and antifouling resistance of the prepared TPB-DMTP-COF/PAN membranes. This work provides a feasible approach for fabricating a smart membrane with under-liquid dual superlyophobicity for oily wastewater treatment.

Super-amphiphobic arabic gum-based coatings on textile for on-demand oily and dye wastewater treatment

Different membrane materials have broadly been constructed for oil-containing water separation, but most of preparation routes involve corrosive or toxic chemicals and especially many materials have only single superwetting property. Herein, a novel and eco-friendly cellulose-based textile membrane is developed by incorporating the composite coating consisting of arabic gum (AG), attapulgite (APT), and iron (Fe) onto cellulose textiles. The functionalized textile is superoleophobic underwater and superhydrophobic underoil. As a result, the textile prewetted with water or oil can be employed to separate light oil layer/water and heavy oil layer/water mixtures, respectively, and the separation efficiency to the two types of mixtures is larger than 98.3 %. Results also reveal that the decorated textile possesses superior stability and recyclability in purifying oily wastewater. More importantly, such coated textile is capable of filtrating water-soluble contaminants (dyes) from polluted water. Due to the versatility and environmental compatibility of product as well as the accessibility as agricultural and forestry product as raw materials, the advanced textiles may offer effective solutions to oily wastewater purification and water-soluble contaminant removal.

Special Superwetting Materials from Bioinspired to Intelligent Surface for On-Demand Oil/Water Separation: A Comprehensive Review

Since superwetting surfaces have emerged, on-demand oil/water separation materials serve as a new direction for meeting practical needs. This new separation mode uses a single porous material to allow oil-removing and water-removing to be achieved alternately. In this review, the fundamentals of wettability are systematically summarized in oil/water separation. Most importantly, the two states, bioinspired surface and intelligent surface, are summarized for on-demand oil/water separation. Specifically, bioinspired surfaces include micro/nanostructures, bioinspired chemistry, Janus-featured surfaces, and dual-superlyophobic surfaces that these superwetting materials can possess asymmetric wettability in one structure system or opposite underliquid wettability by prewetting. Furthermore, an intelligent surface can be adopted by various triggers such as pH, thermal and photo stimuli, etc., to control wettability for switchable oil/water separation reversibly, expressing a thought beyond nature to realize innovative oil/water separation by external stimuli. Remarkably, this review also discusses the advantages of all the materials mentioned above, expanding the separation scope from the on-demand oil/water mixtures to the multiphase immiscible liquid-liquid mixtures. Finally, the prospects of on-demand oil/water separation materials are also concluded.

Smart Hierarchical Zeolitic Imidazolate Framework-Coated Stainless Steel Meshes with Switchable Wettability for Oil/Water Separation

Selective filtration based on superwetting materials has brought about widespread attention in the field of oil/water separation. In this study, a ZIF-L@8-coated stainless steel mesh (ZIF-L@8-coated SSM) was prepared via in situ growth of two-dimensional leaf-shaped ZIF-L nanosheets on SSM, followed by heterogeneous epitaxial growth of ZIF-8 on a ZIF-L coating. The synthesized ZIF-L@8-coated SSM with a hierarchical micro/nanoscale structure exhibited outstanding switchable wettability between underwater superoleophobicity and underoil superhydrophobicity upon respective prewetting using water and oil without additional external stimuli. It possessed excellent separation performances and stabilities with respect to various types of oil/water mixtures. The switchable wettability mechanism was analyzed and elucidated in detail. The synthesized ZIF-L@8-coated SSM with switchable wettability in this study would have great potential in on-demand oil/water separation.

Multifunctional Switchable Nanocoated Membranes for Efficient Integrated Purification of Oil/Water Emulsions

Surfaces with unusual under-liquid dual superlyophobicity are attractive on account of their widespread applications, but their development remains difficult due to thermodynamic contradiction. Additionally, these surfaces may suffer from limited antifouling ability, which has restricted their practical applications. Herein, we report a successful in situ growth of a hybrid zeolitic imidazolate framework-8 and zinc oxide nanorod on a porous poly(vinylidene fluoride) membrane (ZIF-8@ZnO-PPVDF) and its application as a self-cleaning switchable barrier material in rapid filtration for emulsified oily wastewater. The novel ZIF-8@ZnO-PPVDF exhibits superior mechanical strength, reversible under-liquid dual superlyophobicity, photocatalytic self-cleaning property, and an effective alternate separation capacity toward both oil-in-water (O/W) and water-in-oil (W/O) emulsions with ultrahigh fluxes and efficiencies (>99%). By simply using a "bait-hook-eliminate" method to separate the O/W emulsions containing soluble organic pollutants, we demonstrate that the ZIF-8@ZnO-PPVDF can achieve stable separation fluxes over 600 L m^-2 h^-1 with high efficiencies and be completely/nondestructively regenerated by visible-light irradiation after each cycle. This study would demonstrate a new approach to prepare an under-liquid dual superlyophobic revivable membrane for various applications.

Toward Efficient Oil Energy Recovery: Eco-Friendly Fabrication of a Biomimetic Durable Metal Mesh with a Moss-Like Silver Nanocluster Structure

With the purpose of oil energy recovery as well as achieving efficiency of oil/water separation, hydrophobic mesh materials have attracted extensive attention. However, fabrication of the current methods is not environmentally friendly, has high energy consumption, and creates serious pollution. Inspired by lotus leaves and rose petals, a biomimetic superhydrophobic surface was fabricated prepared on a stainless steel mesh by an in situ chemical reduction method with simple operation and mild conditions. The results of SEM, XRD, and XPS demonstrated that the mesh shows a stable and uniform moss-like rough structured surface. The SSM/Ag/ODA mesh, which was modified by moss-like Ag nanoclusters and low surface energy agents, has excellent superhydrophobicity with an excellent oil/water separation efficiency that reached up to 99.8%. The silver mirror phenomenon formed by the Ag nanoclusters further confirmed that silver ions were reduced and attached to the surface of the mesh. Moreover, the mesh can maintain superhydrophobicity under harsh conditions, such as a high concentration of a salty solution, organic solvents, alkaline, acidic solution, and even long-time UV irradiation, etc. More importantly, the modified mesh has excellent physical stability, in which the water contact angle on the mesh can be maintained above 150° after harsh mechanical wear. The hydrophobic mesh showed great potential to be applied for highly efficient oil/water separation and oil energy recovery even under complex and harsh conditions.

Superhydrophobic Waste Cardboard Aerogels as Effective and Reusable Oil Absorbents

As the main component of the municipal waste, waste cardboard has caused a host of environmental problems. Therefore, the reasonable disposal of waste cardboard is of great significance to global sustainable development and green economics. Herein, using waste cardboard as the raw material, a superhydrophobic aerogel has been developed with a unique three-dimensional porous network structure, which exhibits excellent selective oil absorption capacities. The aerogel was made by combining Ca2+ cross-links and postmodification with stearic acid. Superhydrophobic aerogels can absorb various organic solutions and its maximum absorption capacity can reach 47 times its own weight. Meanwhile, the size of aerogels has been further expanded, with a diameter of 21.2 cm and a height of 3.2 cm, which can absorb 34 times its own weight of kerosene. More importantly, the aerogel can also absorb oil droplets in oil/water emulsions with an adsorption efficiency of over 98.5%. Moreover, the aerogel can be employed multiple times without significantly reducing the adsorption capacity via distillation or squeezing, depending upon the type of pollutions. Consequently, we believe that these facile and inexpensive superhydrophobic aerogels can effectively adsorb oily wastewater, which matches well with the requirement for environmentally friendliness from the perspective of practical application.

Enhanced photocatalytic degradation of methyl orange by coconut shell-derived biochar composites under visible LED light irradiation

The conversion of carbon-rich biomass into valuable material is an environmental-friendly approach for its reutilization. In this study, coconut shell-derived biochar, graphitic carbon nitride (g-C₃N₄), g-C₃N₄/biochar, titanium dioxide (TiO₂)/biochar, zinc oxide (ZnO)/biochar, and ferric oxide (Fe₂O₃)/biochar were synthesized and characterized by using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), surface area analysis, UV-Vis diffuse reflectance spectroscopy (DRS), and zeta potential analysis. The g-C₃N₄ or metal oxide particles were found to be well-distributed on the coconut shell-derived biochar with the improvement in thermal stability and enlargement of specific surface area. A great reduction in band gap energy was observed in the composite materials after incorporating with the biochar. Among different biochar composites, g-C₃N₄/biochar was found to have the highest photocatalytic activity. The interactive effect of parameters such as catalyst dosage, peroxymonosulfate (PMS) oxidant dosage, and solution pH on the photocatalytic degradation of methyl orange was investigated using the response surface methodology (RSM). The highest photocatalytic degradation efficiency (96.63%) was achieved at catalyst dosage of 0.75 g/L, oxidant dosage of 0.6 mM, and solution pH 3 after 30 min.

Universal and Switchable Omni-Repellency of Liquid-Infused Surfaces for On-Demand Separation of Multiphase Liquid Mixtures

Mixtures of immiscible liquids are commonly found in the scenarios of environmental protection and many industrial applications. Compared to widely explored water-oil mixtures, small differences in the surface energy of organic liquids, especially for those in multiphase mixtures, make their separation a formidable challenge. Here, a family of versatile coatings based on the reactions between plant polyphenols and 3-aminopropyl triethoxysilane is introduced to regulate the wetting behavior of substrates by forming stable liquid-infused interfaces. The key finding is that when a coated substrate is prewetted with a liquid forming a stable liquid-infused interface, it becomes repellent to any other immiscible liquids. This phenomenon is independent of the surface energy of the initial wetting liquid. This exclusive wetting behavior can lead to distinctive repellency toward almost any liquid by the infusion of an immiscible liquid, even if the difference of surface energy and dielectric constant of a liquid pair is as small as 2.0 mJ m^-2 and 1.8, respectively, resulting in universal and switchable omni-repellency. Of particular importance is that the as-prepared coating makes possible the on-demand separation of multiphase liquid mixtures by both continuous membrane filtration and static absorption, presenting a green and cost-effective approach to addressing this major environmental and industrial challenge.

Superhydrophobic, superamphiphobic and SLIPS materials as anti-corrosion and anti-biofouling barriers

Multifunctional interfacial materials with special wettability including superhydrophobic, superamphiphobic, and SLIPS exhibited promising potentials for corrosion and biofouling resistance.

Three-dimensional superhydrophilic polyvinyl alcohol–formaldehyde composite sponges with suitable pore sizes for high efficiency emulsion separation

PVA/PVF and PVA–COOH/PVF composite sponges with excellent emulsion separation performance.

Robust Superamphiphobic Coatings Based on Raspberry-like Hollow SnO2 Composites

Good mechanical and chemical stabilities are the key factors for the wide application of superhydrophobic surfaces. In this work, we first prepared raspberry-like hollow structured SnO₂ nanoparticles using a simple hydrothermal method, followed by an annealing step. Then, the intrinsic raspberry-like hollow SnO₂ nanoparticles were combined with hydrophilic SiO₂ nanoparticles to construct rough surfaces with suitable hierarchical structures, and 1H,1H,2H,2H-perfluorodecyltriethoxysilane (FAS-17) was used as a hydrophobic modifier of SnO₂, while epoxy resin was used as an adhesive to prepare a superamphiphobic coating with good stability and durability. Such a coating can be applied on various substrates using a simple spray-coating or drop-coating method. The water contact angle and diiodomethane contact angle of the coating could reach up to ∼165 and ∼151°, respectively. After various chemical and mechanical stability tests including hot water treatment, salt water corrosion, strong adhesive tape peeling, and kneading, the coatings still remained amphiphobic. The facile fabrication of the robust superhydrophobic coating has great potential for applications in real life and industrial production.

Efficient separation of crude oil-in-water emulsion based on a robust underwater superoleophobic titanium dioxide-coated mesh

Robust underwater superoleophobic TiO₂-coated meshes were used for the separation of crude oil-in-water emulsion and photocatalytic degradation.

A facile surface modification of a PVDF membrane via CaCO3 mineralization for efficient oil/water emulsion separation

A facile modification of a PVDF membrane using CaCO₃ inorganic particles via a layer-by-layer self-assembly process for efficient oil/water separation.