Underwater Superoleophilicity Research Articles

Upcycling of waste brick powder and PET as robust and flexible Janus membrane with asymmetric wettability for switchable emulsion separation

Superwetting membranes were widely studied in the field of oil/water separation due to their excellent separation efficiency and good recoverability, but they still suffer from the disadvantages of expensive reagents, complicated processes, and narrow scope of application. Herein, a robust and flexible Janus membrane with asymmetric wetting properties was constructed using discarded PET and bricks powder as building blocks, for various types of emulsions separation. Given the cross-linking effect of acrylic resin, the superhydrophilic crushed waste bricks powder (WBP) was orderly assembled on the electrospinning PET nanofiber membrane, achieving asymmetric wettability on each side: the high-hydrophobic PET side had underwater superoleophilicity, while superhydrophilic WBP side had underwater superoleophobicity. Janus membrane exhibit excellent corrosion resistance and can maintain stable contact angles in different pH environments. Due to its highly porous and surface anisotropic nature, Janus membrane showed excellent separation efficiency and separation flux for both oil-in-water emulsions (separation efficiency up to 99.4%, separation flux up to 196 L m−2 h−1) and oil-in-water emulsions (separation efficiency up to 99.3%, separation flux up to 792 L m−2 h−1 bar−1). More importantly, Janus membranes exhibited outstanding reusability. This Janus membrane shows great potential in the fields of waste upcycling and emulsion separation.

Facile preparation of hydrophilic PVDF membrane via tea polyphenols modification for efficient oil-water emulsion separation

Facile preparation of hydrophilic membranes is essential for achieving efficient separation of oil-water emulsion. In this paper, a hydrophilic PVDF@TP membrane was prepared by very simple direct modification using green tea (The main extract is tea polyphenols, TP). The PVDF@TP membrane exhibits good hydrophobicity in air and underwater superoleophilicity. The oil-water separation potential of this membrane was studied using several model oil-in-water emulsions. The resulting membrane exhibitd high separation efficiency (above 99 %) and separation fluxes (955–1672 L m−2 h−1 bar−1) for various oil-in-water emulsions. Additionally, separation efficiency of PVDF@TP membrane was still above 98 % even after 10 times continuous separation, demonstrating its good antifouling ability and stability. In addition, bending, ultrasonic and stirring treatments showed that the membrane has good mechanical durability. In view of the advantages of facile preparation, economy and high-performance, the hydrophilic PVDF@TP membrane has a very broad application potential in industrial oily wastewater and oil spill treatment.

Reactive Multilayer Coating As Versatile Nanoarchitectonics for Customizing Various Bioinspired Liquid Wettabilities.

In last few decades, multilayer coatings have achieved enormous attention owing to their unique ability to tune thickness, topography, and chemical composition for developing various functional materials. Such multilayer coatings were mostly and conventionally derived by following a simple layer-by-layer (LbL) deposition process through the strategic use of electrostatic interactions, hydrogen bonding, host-guest interactions, covalent bonding, etc. In the conventional design of multilayer coatings, the chemical composition and morphology of coatings are modulated during the process of multilayer constructions. In such an approach, the postmodulations of the porous multilayers with different and desired chemistries are challenging to achieve due to the lack of availability of readily and selectively reactive moieties. Recently, the design of readily and selectively reactive multilayer coatings (RMLCs) provided a facile basis for postmodulating the prepared coating with various desired chemistries. In fact, by taking advantage of the inherent ability of co-optimizing the topography and various chemistries in porous RMLCs, different durable bioinspired liquid wettabilities (i.e., superhydrophobicity, underwater superoleophobicity, underwater superoleophilicity, slippery property, etc.) were successfully derived. Such interfaces have enormous potential in various prospective applications. In this review, we intend to give an overview of the evolution of LbL multilayer coatings and their synthetic strategies and discuss the key advantages of porous RMLCs in terms of achieving and controlling wettability properties. Recent attempts toward various applications of such multilayer coatings that are strategically embedded with different desired liquid wettabilities will be emphasized.

Amphibious superamphiphilic polystyrene monolith with underwater superoleophilicity: Capture of underwater oil

Three-dimensional porous polystyrene monolith was fabricated by emulsion templating and it showed superamphiphilicity in the air by absorption of both water and oil droplets rapidly (within seconds). When as-prepared polystyrene monolith was immersed in water, similar behaviors were observed, demonstrating its amphibious superamphiphilicity. In underwater environment, the monolith can be easily filled with water which can be completely displaced by oil as contact with oil droplets, referred to as underwater superoleophilicity. Those interesting properties can be attributed to high porosity provided in emulsion templating and the hydrophilic and oleophilic domains which remain at the interface of interconnected pores after polymerization. The as-prepared monolith was able to absorb at least twenty types of solvents and the maximum uptake capacity was comparable to the performances of other polystyrene absorbents. Moreover, the absorbing capacity remained unchanged after 10 cycles of water and decane absorption and desorption, indicating its good reusability. With the high affinity toward oil, the monolith was able to remove oil spillage and organic pollutants from water and it can be used as an advanced absorbent for underwater oil capture.

Pickering emulsion strategy to control surface wettability of polymer microspheres for oil–water separation

Surface wettability, one of the most important parameters for oil–water separation, depends on the chemical composition and surface roughness of a material. Herein, the Pickering emulsion template method is proposed to control the surface wettability of polymer microspheres. Upon the dispersion of modified diatomite particles in the aqueous phase, a superhydrophobic surface was formed on the polymer microspheres via Pickering emulsion polymerization, with a water contact angle of 152°. When the initial dispersion location of the modified diatomite particles changed from water to oil, a hydrophilic/underwater superoleophilic surface with micro/nanoscale hierarchical structures formed on the polymer microspheres. This special wettability enabled the microsphere layer to serve as an adsorbent with underwater superoleophilicity, achieving efficient oil separation from various oil-in-water emulsions with high separation efficiency of >99.8%. Hence, this study provides a valuable strategy based on the Pickering emulsion template method to design materials with special wettability for realizing promising emulsion separation.

Sucrose solution assisted femtosecond laser ablation of aluminum film to induce nanospikes for efficient and stable oil-water separation

The fabrication of functional surface covered with novel nanostructures for various applications has attracted much attention in recent years. A large area of randomly distributed nanospikes can be induced on the surface of aluminum (Al) film in sucrose solution by using femtosecond (fs) laser, and the distribution density of nanospikes varies with laser pulse energy and mass ratio for sucrose to water. After modification with polydimethylsiloxane (PDMS), the Al film covered with nanospikes exhibits the characteristics of tunable wettability, underwater superoleophilicity (~0°), superhydrophobicity (~155.3°), high water adhesion and environmental stability. Further, an oil-water separation filter was prepared by using fs laser direct writing (LDW) on one side of the Al film in air and then inducing nanospikes in sucrose solution as well as PDMS modification on the other side. After the above treatment, the filter has low water adhesion similar to “lotus effect” and can be used for highly efficient (99.61% ~ 99.63%) and recyclable oil-water separation. In addition, the filter exposed to air for more than 7 months still remains high oil-water separation efficiency (99.46% ~ 99.57%), showing strongly environmental stability. This functional filter fabricated by fs laser can be applied in the separation process of chemical products, biomedical device, and environmental protection fields.

Is superhydrophobicity equal to underwater superoleophilicity? Hydrophilic wetting defects on a superhydrophobic matrix with switchable superdewetting in both air and water

A simultaneous in-air superhydrophobic and underwater superoleophobic state is realized on a superhydrophobic matrix after incubation in weakly alkaline aqueous media.

Relationship and Interconversion Between Superhydrophilicity, Underwater Superoleophilicity, Underwater Superaerophilicity, Superhydrophobicity, Underwater Superoleophobicity, and Underwater Superaerophobicity: A Mini-Review.

Superwetting surfaces have received increasing attention because of their rich practical applications. Although various superwettabilities are independently achieved, the relationship between those superwettabilities is still not well-clarified. In this mini-review, we show that superhydrophilicity, underwater superoleophilicity, underwater superaerophilicity, superhydrophobicity, underwater superoleophobicity, and underwater superaerophobicity can be obtained on a same structured surface by the combination of hierarchical surface microstructures and proper chemistry. The relationship and interconversion between the above-mentioned different superwettabilities are also well-discussed. We believe that the current discussion and clarification of the relationship and interconversion between different superwettabilities has important significance in the design, fabrication, and applications of various superwetting materials.

Robust and switchable superwetting sponge-like membrane: Towards on-demand emulsion separation and aqueous pollutant degradation

There remains a great challenge to integrate reversible separation of emulsified oil/water mixtures and treatment of organic contaminants in complex oily wastewaters. Herein, sponge-like Co(OH)2 nanosheets coated stainless steel mesh (SSM) was designed through electrodeposition route within only 20 min. Due to the highly porous hierarchical architecture, the membrane displays superhydrophilicity and underwater superoleophilicity with water contact angle of nearly 0° and underwater oil contact angle greater than 160.1°, achieving high-efficient separation of surfactant-stabilized oil-in-water emulsion (≥99.9%) and fast permission flux up to 540 L m−2 h−1. Interestingly, reversible wettability transition for on-demand emulsified oil/water separation can be easily manipulated for at least 10 cycles by the alternation treatment with stearic acid and NaOH/tetrahydrofuran in turn. The membrane reveals outstanding superwetting stability against mechanical abrasion, heat treatment and harsh corrosive conditions. Importantly, the Co(OH)2/SSM exhibits a high catalyzing potential to effectively oxidize the aqueous contaminant (i.e. Acid Orange 7) with a maximum degradation efficiency of almost 100% in 6 min. All these attractive features make the smart membrane a promising candidate for potential extensive application in oil spill cleanup and industrial emulsified oily wastewater treatment.

Fine Switching between Underwater Superoleophilicity and Underwater Superoleophobicity while Maintaining Superhydrophobicity.

Switching between superhydrophobicity/underwater superoleophilicity and superhydrophilicity/underwater superoleophobicity has been widely designed. Recently, superwettability is subdivided into multiple extreme wetting states for oil, water, and air as wetting and medium phases. However, fine switching among the multiple superwettability is rare. Here, a pH-responsive case is presented to demonstrate the fine switching between underwater superoleophilicity and underwater superoleophobicity while maintaining superhydrophobicity. The surface chemistry of silver-roughened copper coatings is elaborately manipulated by water-repellent perfluoroalkyl and alkyl chains and the smart terminal carboxyl group. By adjusting the pH value of water, the completely opposite extreme wetting states for oil in water are precisely controlled. Simultaneously, the extreme repellence for water in the air can be kept owing to the fairly low surface energy of the perfluoroalkyl chain. This discovery accelerates the subdivision of superwettability and the achievement of unusual superwetting switching.

Hydrophobicity or superhydrophobicity—which is the right choice for stabilizing underwater superoleophilicity?

Hydrophobic multilayers chemically optimized with discontinuous metastable trapped air displayed highly unusual and superior oil wettability underwater in comparison to the superhydrophobic interface and were unprecedentedly extended for filtration-based oil-in-water emulsion separation at diverse and severe settings.

Underwater superoleophobic biomaterial based on waste potato peels for simultaneous separation of oil/water mixtures and dye adsorption

Underwater superoleophilicity involves interactions between a solid surface and two immiscible liquids, viz., water and oils, in which water remains in the completely wetted and oils in the non-wetted state. Materials with underwater superoleophilicity have drawn significant interest due to their superior performance in selective separation of oil and organic solvents from an aqueous phase. However, the development of such materials with special wettability for water and oils are hindered by (1) complex fabrication process (2) long processing duration with high cost, and (3) use of environmentally unfriendly and expensive fluorochemicals to lower the surface energy. Herein, we demonstrate the use of waste potato peels (WPP) to fabricate simple, economical and eco-friendly materials with superhydrophilic (water contact angle ~ 0°) and underwater superoleophobic (oil contact angle > 150°) properties. Initially, powder of WPP was prepared and accumulated into a layer via a simple cleaning, smashing, one step inexpensive chemical treatment and stacking procedures. The developed WPP layer was efficient for the gravity-driven separation of various oil/water mixtures (including hexane, toluene, dodecylbenzene, and kerosene) and water-in-oil emulsions, with high efficiency (> 98%) in single unit operation. During the oil/water separation process, the WPP layer was also found to serve as an adsorbent material for efficient removal of various water-soluble dyes (methylene blue and rhodamine B, 50 mg L−1) contaminants, simultaneously. Thus, the developed WPP layer is not only a good biomaterial for water remediation by the oil/water separation and dye adsorption simultaneously, but can also contribute in reducing environmental pollution and wastage.

In situ reversible underwater superwetting transition by electrochemical atomic alternation

Materials with in situ reversible wettability have attractive properties but remain a challenge to use since the inverse process of liquid spreading is normally energetically unfavorable. Here, we propose a general electrochemical strategy that enables the in situ reversible superwetting transition between underwater superoleophilicity and superoleophobicity by constructing a binary textured surface. Taking the copper/tin system as an example, the surface energy of the copper electrode can be lowered significantly by electrodeposited tin, and be brought back to the initial high-energy state as a result of dissolving tin by removing the potential. Tin atoms with the water depletion layer inhibit the formation of a hydrogen-bonding network, causing oil droplets to spread over the surface, while copper atoms, with a high affinity for hydroxyl groups, facilitate replacing the oil layer with the aqueous electrolyte. The concept is applicable to other systems, such as copper/lead, copper/antimony, gold/tin, gold/lead and gold/antimony, for both polar and nonpolar oils, representing a potentially useful class of switchable surfaces.

Amphibious superamphiphilic fabrics with self-healing underwater superoleophilicity

A fabric with novel amphibious superamphiphilicity and self-healing underwater superoleophilicity has been developed using a single-step wet-chemical coating technique.

Remarkably simple achievement of superhydrophobicity, superhydrophilicity, underwater superoleophobicity, underwater superoleophilicity, underwater superaerophobicity, and underwater superaerophilicity on femtosecond laser ablated PDMS surfaces

Six different super-wettabilities were achieved on the same femtosecond laser ablated PDMS surface.

Photoinduced switchable underwater superoleophobicity–superoleophilicity on laser modified titanium surfaces

A one-step way to achieve smart reversible switching between the underwater superoleophobicity and underwater superoleophilicity of femtosecond laser ablated Ti materials.

PH-Induced Reversible Wetting Transition between the Underwater Superoleophilicity and Superoleophobicity

Surfaces with controlled oil wettability in water have great potential for numerous underwater applications. In this work, we report a smart surface with pH-responsive oil wettability. The surface shows superoleophilicity in acidic water and superoleophobicity in basic water. Reversible transition between the two states can be achieved through alteration of the water pH. Such smart ability of the surface is due to the cooperation between the surface chemistry variation and hierarchical structures on the surface. Furthermore, we also extended this strategy to the copper mesh substrate and realized the selective oil/water separation on the as-prepared film. This paper reports a new surface with excellently controllable underwater oil wettability, and we believe such a surface has a lot of applications, for instance, microfluidic devices, bioadhesion, and antifouling materials.

Underwater Superoleophilic to Superoleophobic Wetting Control on the Nanostructured Copper Substrates

Surfaces with controlled underwater oil wettability would offer great promise in the design and fabrication of novel materials for advanced applications. Herein, we propose a new approach based on self-assembly of mixed thiols (containing both HS(CH2)9CH3 and HS(CH2)11OH) on nanostructured copper substrates for the fabrication of surfaces with controlled underwater oil wettability. By simply changing the concentration of HS(CH2)11OH in the solution, surfaces with controlled oil wettability from the underwater superoleophilicity to superoleophobicity can be achieved. The tunable effect can be due to the synergistic effect of the surface chemistry variation and the nanostructures on the surfaces. Noticeably, the amplified effect of the nanostructures can provide better control of the underwater oil wettability between the two extremes: superoleophilicity and superoleophobicity. Moreover, we also extended the strategy to the copper mesh substrates and realized the selective oil/water separation on the as-prepared copper mesh films. This report offers a flexible approach of fabricating surfaces with controlled oil wettability, which can be further applied to other ordinary materials, and open up new perspectives in manipulation of the surface oil wettability in water.

Underwater superoleophilicity to superoleophobicity: role of trapped air

The interesting oil-wetting behavior to a superamphiphobic surface in water has been investigated. We demonstrated that the trapped air can tune the underwater wettability of the surface, changing from superoleophilic to superoleophobic. The trapped air in the grooves of the superamphiphobic surface can cause the significant change of the three-phase contact line (TCL).