Superoleophobic Properties Research Articles

Coordination-driven interfacial cross-linked graphene oxide-alginate nacre mesh with underwater superoleophobicity for oil-water separation

Inspired by the seashell nacre and seaweed, a novel GO-Ca2+-SA nacre-inspired hybrid mesh was prepared via an interfacial layer-by-layer self-assembly and cross-linking, using graphene oxide (GO) and sodium alginate (SA) as the building blocks and calcium chloride as the coordination agent, respectively. Hybrid mesh was characterized by FTIR, XPS, XRD, SEM and contact angel instrument, showing superhydrophilic and underwater superoleophobic property and low oil adhesion, due to its wrinkle and rough surface, and high hydration ability of GO-Ca-alginate nanohydrogels. The separation efficiencies of various oil-water mixtures were above 99 %, with a highest flux of 119,426 L m−2 h−1. Hybrid mesh showed an orderly layered “brick and mortar” microstructure with many ultrasmall nanoscaled protuberances. Ca2+ ions could chelate with SA to form the “egg-box” structure, and interact with GO nanosheets. Hybrid mesh possessed high salt/acid/alkaline tolerance, abrasion resistance, mechanical property with Young's modulus of 35.8 ± 4.9 GPa, and excellent cycling stability.

Simple Amphoteric Charge Strategy to Reinforce Superhydrophilic Polyvinylidene Fluoride Membrane for Highly Efficient Separation of Various Surfactant-Stabilized Oil-in-Water Emulsions.

Long-term efficient separation of highly emulsified oily wastewater is challenging. Reported herein is the preparation of a reinforced superhydrophilic, underwater superoleophobic membrane with demulsification properties using active iron nanoparticles in situ generated on a polydopamine (PDA)/polyethylenimine (PEI)-modified polyvinylidene fluoride (PVDF) membrane surface. A stable zwitterionic structure is fabricated on the membrane surface and provides it with an excellent capability of binding a hydration layer, leading to enhanced superhydrophilic/underwater superoleophobic properties. The interaction between the membrane surface and water is quantified using the relaxation time of water. After iron nanoparticles in situ anchoring, the superhydrophilic, underwater superoleophobic PDA/PEI modified PVDF membrane shows more stable flux behaviors, higher oil separation efficiency, demulsification, and excellent antioil-fouling properties for various anionic, nonionic, and cationic surfactant-stabilized oil-in-water emulsions in a crossflow filtration system. The reinforced hydration layer and the amphoteric charged demusification properties of the membrane play important roles in enhancing the membrane separation performance. The reinforced membrane also exhibits excellent cleaning and reusability performance in long-term operations. The outstanding separation performance, as well as the simple and cost-effective fabrication process of the membrane with various favorable properties, highlight its promise in practical emulsified oily water applications.

Quartz Sand Filter Media with Special Wettability for Continuous and Efficient Oil/Water Separation and Dye Adsorption

For continuous and efficient oil/water separation and adsorption of dyes, coconut shell powder was grafted onto the surface of quartz sand by dip-coating method to make coconut shell powder-covered quartz sand filter media (CSQS) with superhydrophilic and underwater superoleophobic properties and superoleophilic and underoil highly hydrophobic properties. The contact angles of the underwater oil and underoil water with CSQS were more than 151.2° and 134.2°, respectively. A continuous oil/water separation device was designed. The separation device filled with CSQS can separate oil/water mixture (whether heavy or light oil) into water and oil at the same time with a separation efficiency of above 99.92%. The filter layer can be recovered through reverse extrusion even after lyophobic liquid penetrated the filter layer; hence, the separation efficiency of the filter layer was still above 99.99% for diesel and water mixture. Simultaneously, CSQS can effectively adsorb methylene blue with the highest removal rate as 98.94%. CSQS can maintain stable wettability under harsh environment conditions. This paper provides a new idea on continuous and efficient oil/water separation and simultaneous dye adsorption.

Scalable, fluorine free and hot water repelling superhydrophobic and superoleophobic coating based on functionalized Al2O3 nanoparticles

Hot water droplet and oils induced air cushion failure, intensively used fluorine-containing chemicals, tedious preparation process, etc. are the main bottlenecks of the current artificially fabricated superhydrophobic materials, restricting their large-scale production and real-world applications. Herein, a facile, scalable, fluorine-free spray-coating strategy was employed to achieve superhydrophobic and superoleophobic polymerized organosilanes/Al2O3 nanoparticles (POS/Al2O3 NPs) coatings. The POS/Al2O3 NPs coating was achieved through hydrolytic condensation of tetraethyl orthoilicate (TEOS) and hexadecyltrimethoxysilane (HDTMS) in the presence of Al2O3 NPs. A variety of analytical techniques including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray photoelectron spectroscopy (EDS) were used to investigate the fabricated coatings. The POS/Al2O3 NPs coating features high contact angle (>158°) and low sliding angle (<5°) for water, glycerol, and ethylene glycol droplets with different surface tensions, verifying both superhydrophobic and superoleophobic properties. Moreover, the coatings present extremely low surface adhesion force, excellent liquid-driven self-cleaning ability, and hot water repellency. The superamphiphobic POS/Al2O3 NPs coating exhibits promising applications in various fields including self-cleaning, corrosion resistance, and preventing scald as this strategy is applicable on various substrates.

Zwitterionic nanogels modified nanofibrous membrane for efficient oil/water separation

Membrane fouling caused by surfactant-stabilized oil-in-water emulsions is a great challenge for oily water treatment. In this work, we fabricated a sulfobetaine-based zwitterionic nanogels modified polyacrylonitrile (ZPAN) nanofibrous membrane with superwetting surfaces. The zwitterionic nanogels were grafted on the surface of electrospun PAN nanofibers to construct hierarchical structure which can enhance surface roughness and antifouling performance of the membrane. The ZPAN membrane possesses superhydrophilic and underwater superoleophobic properties under a wide range of salt concentrations and pH values. Driven solely by gravity (applied pressure = 1 kPa), the ZPAN membrane can successfully separate oil and water emulsions. The oil content in the collected filtrates was below 20 ppm with a high separation efficiency of >99.6%, meanwhile, the permeation fluxes can reach 32800 L m−2 h−1 bar−1. Moreover, the ZPAN membrane exhibit strong mechanical property and stable reusability, indicating a great potential for efficient low-pressure-driven separation of oil-in-water emulsions.

Micro/Nanoscale Structured Superhydrophilic and Underwater Superoleophobic Hybrid-Coated Mesh for High-Efficiency Oil/Water Separation.

A novel micro/nanoscale rough structured superhydrophilic hybrid-coated mesh that shows underwater superoleophobic behavior is fabricated by spray casting or dipping nanoparticle–polymer suspensions on stainless steel mesh substrates. Water droplets can spread over the mesh completely; meanwhile, oil droplets can roll off the mesh at low tilt angles without any penetration. Besides overcoming the oil-fouling problem of many superhydrophilic coatings, this superhydrophilic and underwater superoleophobic mesh can be used to separate oil and water. The simple method used here to prepare the organic–inorganic hybrid coatings successfully produced controllable micro-nano binary roughness and also achieved a rough topography of micro-nano binary structure by controlling the content of inorganic particles. The mechanism of oil–water separation by the superhydrophilic and superoleophobic membrane is rationalized by considering capillary mechanics. Tetraethyl orathosilicate (TEOS) as a base was used to prepare the nano-SiO2 solution as a nano-dopant through a sol-gel process, while polyvinyl alcohol (PVA) was used as the film binder and glutaraldehyde as the cross-linking agent; the mixture was dip-coated on the surface of 300-mesh stainless steel mesh to form superhydrophilic and underwater superoleophobic film. Properties of nano-SiO2 represented by infrared spectroscopy and surface topography of the film observed under scanning electron microscope (SEM) indicated that the film surface had a coarse micro–nano binary structure; the effect of nano-SiO2 doping amount on the film’s surface topography and the effect of such surface topography on hydrophilicity of the film were studied; contact angle of water on such surface was tested as 0° by the surface contact angle tester and spread quickly; the underwater contact angle to oil was 158°, showing superhydrophilic and underwater superoleophobic properties. The effect of the dosing amount of cross-linking agent to the waterproof swelling property and the permeate flux of the film were studied; the oil–water separation effect of the film to oil–water suspension and oil–water emulsion was studied too, and in both cases the separation efficiency reached 99%, which finally reduced the oil content to be lower than 50 mg/L. The effect of filtration times to permeate flux was studied, and it was found that the more hydrophilic the film was, the stronger the stain resistance would be, and the permeate flux would gradually decrease along with the increase of filtration times.

Tuning the Wettability of Metal-Organic Frameworks via Defect Engineering for Efficient Oil/Water Separation.

Zirconium-based metal-organic frameworks (MOFs) have attracted interest due to their chemical and thermal stabilities and structural tunability. In this work, we demonstrate the tuning of the wettability of a UiO-66 structure via defect-engineering for efficient oil/water separation. UiO-66 crystals with controlled levels of missing-linker defects were synthesized using a modulation approach. As a result, the hydrophilicity of the defect-engineered UiO-66 (d-UiO-66) can be varied. In addition, a thin layer of hydrophilic d-UiO-66 was successfully fabricated on a series of stainless steel meshes (d-UiO-66@mesh), which exhibited excellent superhydrophilic and underwater superoleophobic properties and displayed interesting separation performance for various oil/water mixtures.

Facile fabrication of hydrophilic-underwater superoleophobic poly(N-isopropylacrylamide) coated PP/LPET nonwoven fabrics for highly efficient oil/water separation

Oil/water separation has become an urgent issue in environmental protection. Superhydrophilic and underwater superoleophobic membrane is promising materials for effective oil/water separation. In this paper, a novel oil/water separation nonwoven fabric with robust tensile strength and hydrophilic-underwater superoleophobic is successfully fabricated. This nonwoven fabric using low melt point polyester (LPET) fibers with a unique sheath-core structure to incorporate thermal bonding as reinforcement. Moreover, poly(N-isopropylacrylamide) (PNIPAM) dip-coated is also employed to modify the nonwoven fabrics to acquire the hydrophilic-underwater superoleophobic properties. The mechanical property, microstructure, water and underwater oil contact angle, and oil/water separation properties of PP/LPET nonwoven fabrics are measured, examining the effects of LPET fiber ratio and PNIPAM concentration. The test results show that an improvement in the mechanical properties after increasing the LPET content. The coated of PNIPAM endows the nonwoven fabric with a low water contact angle of from 80° to 0° (within 8 s), and underwater superoleophobicity with a high oil contact angle of 150°. This nonwoven fabric can effective separation oil/water mixture with high permeate flux (∼21850 L∙m−2∙h−1) and high separation efficiency (∼99%), solely driven by gravity. This kind of nonwoven fabrics is suggested as a promising candidate for oil/water separation and water purification.

NIR triggered healable underwater superoleophobic coating with exceptional anti-biofouling performance

Although quite some self-healing coatings have been reported to date, underwater healable coatings were involved very limited. Here, we report a novel underwater healable superoleophobic coating through depositing functional SiO2@PDA@Ag particles on the TPA/EVA-70% film. The obtained coating not only possess excellent underwater superoleophobic and antifouling properties, but also quick healable performance by remote NIR irradiation. Thus, it may provide stable and long-lasting underwater antifouling properties against marine growth and oil contamination.

Superhydrophobic and superoleophobic properties enhancement on PDMS micro-structure using simple flame treatment method

In this research, a simple flame treatment method was explored to generate micro−/nano-structures on polydimethylsiloxane (PDMS) micro-patterns. Ethanol soaked paper wipes were used as a flame source at a temperature of 700 ± 20 °C. After flame-treated for 30 s, a unique flower petal nano-structures were formed on all surface types: flat PDMS (PDMS-FLT) and PDMS with square pillar pattern (PDMS-PIL) and PDMS with rectangular ridge patterns (PDMS-REC). The flower petal nano-structures, which acts like a re-entrant micro−/nano-structure, was formed by an aggregation of organosilicon compounds in PDMS matrix. Averaged values of surface roughness of the PDMS-FLT, the PDMS-REC and the PDMS-PIL have increased to 298.9, 662.3, and 731.1 nm, respectively. The PDMS-PIL surface that was flame-treated for 30 s exhibited superhydrophobic and superoleophobic properties with water and ethylene glycol contact angle greater than 150°. Those properties led to liquid droplets spreading out instantly and rolling off very fast. Therefore, the flame treatment is expected to be one promising method to fabricate biomimetic surface with good reproducibility and stability on a large-scale antifouling surface for various applications.

Ultrafast separation of oil/water mixtures with layered double hydroxide coated stainless steel meshes (LDH-SSMs)

With the frequent discharge of wastewater and leakage of oil accidents, it has gained much attention to treat oil and organic pollutants from water. Herein, a facile and environmentally friendly approach is presented to fabricate MgAlZn layered double hydroxide-coated stainless steel mesh (LDH-SSM) via hydrothermal method, which could be used to separate various oil/water mixtures due to its superhydrophilic and underwater superoleophobic property. The as-prepared mesh possesses selective separation performance for oil/water mixtures with separation efficiency higher than 99.2% and high water flux of ∼ 44.5 L m−2 s-1 under gravity-driven force. Such membrane shows an effective separation for oil/water mixtures and recyclability, as well as exhibit excellent superhydrophilicity, making it a prominent candidate for oily water remediation.

The Manipulation of Molecular Aggregation Behavior: Underwater Superoleophobic/Underoil Superhydrophobic Gels from the Same Matrix for Oil/Water Separation

AbstractManipulating the molecular aggregation behavior plays an important role in many fields. Here, by manipulating the molecular aggregation behavior, it is the first time that the same benzoxazine molecule is used to synthesize two kinds of gel materials with underwater superoleophobic and underoil superhydrophobic properties. Meanwhile, these materials are successfully used to separate surfactant‐stabilized water‐in‐oil and oil‐in‐water emulsions. The relationship between the surface properties and molecular aggregation behavior is analyzed. Controlling molecular aggregation behavior is essential to allow the molecules reach the most stable state spontaneously (where the Gibbs free energy is the smallest under constant temperature and pressure) under different environmental conditions. This research may open a new pathway to construct different functional materials by using the same molecule, and also provide a basis for other fields to achieve various applications by manipulating the molecular aggregation behaviors.

Gluconacetobacter xylinus synthesized biocellulose nanofiber membranes with superhydrophilic and superoleophobic underwater properties for the high-efficiency separation of oil/water emulsions

Compared with plant-derived cellulose, developing biocellulose nanofibers (bio-CNFs) as a functional membrane material is of great interest in membrane filtration for the effective separation of emulsified oily wastewater due to its low cost, renewability, high water-holding capacity and anti-oil-fouling properties. In this work, a bio-CNF membrane was produced by cultured Gluconacetobacter xylinus through a simple biosynthetic process followed by a purification step involving alkali treatment. Herein, the bio-CNF membrane treated with 0.75 M NaOH solution formed a unique, porous nanonetwork structure with good hydrophilicity and ultralow-oil-adhesion properties, and this was successfully applied for the separation of surfactant-stabilized oil/water emulsions. The superhydrophilic and superoleophobic bio-CNF membranes exhibited superior performance for separating surfactant-stabilized oil/water emulsions, showing a separation efficiency of ~99% and a high permeate flux recovery ratio (above 94%) for long-term separation processes.

Durable Light-Driven Three-Dimensional Smart Switchable Superwetting Nanotextile as a Green Scaled-Up Oil–Water Separation Technology

Stimuli-responsive polymer architectures are attracting a lot of interest, but it still remains a great challenge to develop effective industrial-scale strategies. A single-stage and cost-effective approach was applied to fabricate a three-dimensional (3D) smart responsive surface with fast and reversibly switchable wetting between superhydrophobicity and superhydrophilicity/underwater superoleophobicity properties induced by photo and heat stimuli. Commercially available PVDF and P25TiO2 as starting materials fabricated with a scaled-up electrospinning approach were applied to prepare 3D smart switchable PVDF-P25TiO2 nanotextile superwetted by both UV and solar light that is simply recovered by heat at a reasonable time. The superhydrophilic/underwater superoleophobic photo-induced nanotextile will act in “water-removing” mode in which water quickly passes through and the oil is blocked on the surface. An acceptable recycling, reusing, and superior antifouling and self-cleaning performance arising from a TiO2 photocatalytic effect makes it highly desired in a green scaled-up industry oily wastewater treatment technology. With these advantages, a large-scale industrial production process can be simply simulated by applying a conducting mesh-like collector substrate.

Biomimetic Mineralization to Fabricate Superhydrophilic and Underwater Superoleophobic Filter Mesh for Oil–Water Separations

A filter mesh was prepared by a facile biomimetic mineralization method with excellent superhydrophilic and underwater superoleophobic properties for the gravity-driven oil-water separations. It sh...

Special wettable underwater superoleophobic material for effective simultaneous removal of high viscous insoluble oils and soluble dyes from wastewater

Special wettability materials from bio-renewable and bioinspired materials can efficiently be utilized for the treatment of water insoluble pollutants but these materials mostly failed to remove water-soluble organic pollutants because of oil contamination, low water forbearance and complex synthetic procedures. In this view, we have prepared a biocompatible, superwetting polymer composite from natural gel forming materials ĸ-carrageenan (CGN) and poly(acrylamide-co-diallyldimethylammonium chloride) (PAm-DADAc) with graphene oxide (GO) possessing superhydrophilic and underwater superoleophobic properties. Prepared CGN-PAm-DADAc-GO composite were applied to separate oil from oil-water mixture, water-soluble dye effluents and dye containing emulsion separation. The CGN-PAm-DADAc-GO coated stainless-steel meshes demonstrated efficient oil-water separation exhibiting good superhydrophilicity, antifouling property and underwater superoleophobicity. Superhydrophilic nature of CGN-PAm-DADAc-GO composite has been utilized to remove water-soluble cationic and anionic azo dyes contamination at high efficiency 96% with freeze-dried samples. Hydrated layer formation with abundant surface functional groups like sulphate, amine and hydroxyl groups may boosts the simultaneous removal of insoluble oils and soluble dyes from the dye-contaminated emulsion through simply passing via CGN-PAm-DADAc-GO coated filter paper with emulsion flux about 40 L m-2 h-1 and 96% of separation efficiency. These composite materials may hold promising multipurpose applications as featured membrane fabrication material for simultaneous removal of various types of contaminations.

Hierarchical structurized waste brick with opposite wettability for on-demand oil/water separation

Due to the variety of oily wastewater and complexity of separation system, it has put forward new challenge and requirement to separation materials for on-demand separation of various oil/water mixtures. Here, we reported a facile waste-to-resource strategy to rationally fabricate hierarchical ZnO nanopillars coating onto the surface of waste brick grains (ZnO/WBG) via simple physical process and in-situ growth technique. Specifically, the directly as-prepared ZnO/WBG possess superhydrophilic/underwater superoleophobic (UWSOB) properties and modified ZnO/WBG by organosilicon reagent possess quasi superhydrophobic/superoleophilic (SHOBI) properties. It is also worth noting that this discrete ZnO/WBG with opposite wettability can be accumulated into ZnO/WBG layer with numerous tortuous channel structure, making it feasible for on-demand separating various oil/water mixtures whether immiscible light- and heavy-oil/water mixtures or oil-in-water and water-in-oil emulsions. It has been demonstrated that the filter layers with opposite wettability exhibit high separation efficiency and flux, excellent chemical stability and admirable recyclability. Thus, this novel and cost-effective ZnO/WBG layer holds great promise for large-scale and versatile oil/water separation. Additionally, this work presents a sustainable perspective of effectively utilizing waste brick to construct workable functionalized materials with tremendous application potential, showing far-reaching value and significance in fundamental research and environmental protection.

Efficient oil/saltwater separation using a highly permeable and fouling-resistant all-inorganic nanocomposite membrane

Although it is still a great challenge, developing oil-/water-separating membranes that combine the advantages of high separation efficiency, salty environments tolerance, and fouling resistance are highly demanded for marine oil spill cleanups and oil-/gas-produced water treatment. Here, we report a new type of all-inorganic nanostructured membrane, which is composed of titanate nanofibers and SiO2 particulate gel for efficient and stable oil/saltwater separation. The nanoporous and interconnected network structure constructed with titanate nanofibers is the key to ensure the high separation efficiency and high water flux of the new membrane. The SiO2 gel is used as a binder to offer mechanical flexibility and integrity for this type of all-inorganic membrane. The new membrane displays a high oil/water separation efficiency of above 99.5% with oil content in treated effluent lower than US environmental discharge standards (42 ppm) and high water permeation flux of 1600 LMH/bar under low operation pressure. The new membrane also demonstrates outstanding durability in the environment of different salinities, and it has a good resistance for oil fouling due to its excellent underwater superoleophobicity with an oil contact angle above 150 °. Most importantly, the underwater superoleophobic properties can be well maintained after being repeatedly reused. The excellent environmental durability, oil-fouling resistance, high separation efficiency, and facile fabrication process for this new type of membrane render great potential for industrial application in treating produced water.

Fabrication of hyperbranched polyether demulsifier modified PVDF membrane for demulsification and separation of oil-in-water emulsion

Membrane-based treatment for oil-in-water emulsion remains a significant challenge. The main difficulties are to solve membrane fouling and to destroy the emulsion system to achieve high-efficiency emulsion separation. Herein, chemical demulsification combined with membrane separation technology was proposed for oil/water separation from the emulsion. A hyperbranched phenol-amine resin block polyether demulsifier (AE2311) was grafted onto surface of styrene-co-maleic anhydride (SMA) blend polyvinylidene fluoride (PVDF) membrane by alcoholysis reaction. The successful preparation of the demulsifier modified PVDF membrane was characterized by X - rayphotoelectron spectroscopy (XPS), attenuated total reflectance-fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM) and atomic force microscope (AFM). The obtained AE2311@SMA/PVDF membrane with grafting time of 9 h exhibited superhydrophilic (water contact angle of 0°) and underwater superoleophobic properties (underwater oil contact angle over 150°). The modified membrane can break the O/W emulsion and allow water to pass through. The separation efficiency for dichloroethane-in-water, kerosene-in-water, toluene-in-water and petroleum ether-in-water emulsions were all recorded over 99.0%, which indicates that the modified membrane has excellent capability for oil-water separation. Moreover, the modified membrane can be reused and exhibited long-term operation stability owing to the excellent underwater anti-fouling performance. The intrinsic mechanism for the oil/water separation is the synergistic effect of the chemical demulsification of AE2311, the hydrophilic and underwater super hydrophobic properties of the membrane surface, and the sieving effect of the ultrafiltration membrane. The demulsifier functionalized membrane provides a new idea for the fabrication membrane of oil-water emulsion separation in the future.

Smart ZIF-L mesh films with switchable superwettability synthesized via a rapid energy-saving process

Smart materials with unique surface wetting properties have attracted considerable interest, particularly for oil/water separation, where oil can cause severe environmental damage. Despite the considerable progress made in the past decade, critical challenges remain in scaling up, as smart materials are either expensive to fabricate or involve complicated, energy-intensive, and/or time-consuming production processes. In this work, an ultra-facile approach to fabricate hierarchical Zeolitic Imidazolate Framework-L (ZIF-L) mesh films with switchable superwettability for efficient oil/water separation was reported for the first time. A thick, continuous layer of well-intergrown ZIF-L nanoplates with an average aspect ratio of ~25 was successfully synthesized on various stainless steel (SS) meshes at ambient conditions. The ZIF-L mesh films exhibited extraordinary in-air superamphiphilic, underwater superoleophobic and underoil superhydrophobic properties, and showed outstanding performance in solely-gravity-driven oil/water mixture separation. Interestingly, a prewetting-induced switchable permeation function was found for the hierarchical ZIF-L surface, truly achieving “oil-blocking” and “water-blocking” separation. The ZIF-L mesh films demonstrated superior cyclic separation performance for a variety of oil/water mixtures with separation efficiencies above 99.99% and satisfactory chemical and mechanical stabilities even in harsh conditions. Their rapid and energy-efficient fabrication is therefore highly promising for cost-efficient and large-scale production for widespread applications in oil/water separation.