Functional interface based on silicon artificial chamfer nanocylinder arrays （CNCAs） with underwater superoleophobicity and anisotropic properties

A functional interface based on silicon chamfer nanocylinder arrays （CNCAs） was successfully fabricated by carrying out secondary etching of silicon nanopillar arrays via a facile inclined etching method. The structure of the novel CNCAs was finely modulated by varying the nanopillar array structure and the etching conditions. The underwater oil wetting behavior of this CNCAs-based interface can be easily modulated from superoleophilic （oil contact angle （OCA） of -8.13°） state to superoleophobic （OCA of ~163.79°） state by modifying the surface using different substances. Moreover, a reversible transformation of underwater oil wetting behavior from superoleophobic （OCA of -155.67°） state to oleophilic （OCA of ~31.27°） state was achieved by grafting a temperature-responsive polymer onto this specific asymmetric structure. The functional interface exhibited isotropic wetting behavior under certain oleophilic conditions. Chemically heterogeneous structures, obtained via asymmetry modification of CNCAs, exhibited amphiphobic properties while maintaining their anisotropic wetting ability.

Efficient oil-water separation by novel biodegradable all cellulose composite filter paper

Industrial production and domestic discharge produce a large amount of oily wastewater, which seriously affects the stability of the ecological environment. Membrane separation technology provides another path to treating oily wastewater. And appropriate surface modification of the membrane helps to achieve high efficiency of treating oily wastewater. With green, economy and stability been more concerned.The focal research reports a completely biodegradable all cellulose composite filter paper(ACCFP) composed of Ⅰ-cellulose macrofibers and Ⅱ-cellulose matrix. It is a simple one-step impregnation method to adjust the surface microstructure of the pristine filter paper(PFP), and it does not involve with chemical reaction. The pre-wetted ACCFP consist of Ⅱ-cellulose hydrogel and Ⅰ-cellulose reinforcement in the process of oil-water separation. This layer of hydrogel is the fundamental to underwater superoleophobicity, which determines their eligibility for applications of efficient oil-water mixture or oil-in-water(oil/water) emulsion separation. The separation efficiency of oil-water mixture and oil/water emulsion exceed 95% and 99.9%, respectively. In addition, excellent mechanical properties of ACCFP in dry and wet conditions ensure its stability in service and prolong service life in applications. The focal study provides a new method for high-performance oil-water separation and it is more in line with sustainable chemistry.

Femtosecond laser micro/nano fabrication for bioinspired superhydrophobic or underwater superoleophobic surfaces

The preparation of superhydrophobic or underwater superoleophobic interface materials has become a research hotspot because of their wide application in self-cleaning, drag reduction, oil-water separation, anti-oil pollution and so on. The unique wettability of organisms gives inspiration to design and create new interface materials. This review focuses on the recent research progress of femtosecond laser micro/nano fabrication for bioinspired superhydrophobic or underwater superoleophobic surfaces. This review starts with a presentation of the related background including the advantages of femtosecond laser and wettability theoretical basis. Then, organisms with unique wettability in nature, the preparation of superhydrophobic or underwater superoleophobic surfaces by femtosecond lasers on different materials, and their related important applications are introduced. Finally, the current challenges and future prospects with regard to this field are provided.

Green Fabrication of Underwater Superoleophobic Biopolymeric Nanofibrous Membranes for Effective Oil-Water Separation

Currently,most of the materials for oil-water separation membranes are limited to fluorine-based polymers with low surface energy.However,it is not biodegradable and requires large amounts of organic and toxic solvents in the membrane manufacturing process.Therefore,interest in the development of a new eco-friendly oil-water separation membrane that does not cause secondary pollution and exhibits selective wettability characteristics in water or oil is increasing.The biopolymeric nanofibrous membranes inspired by fish skin can provide specific underwater oleophobicity,which is effective for excellent oil-water separation efficiency and prevention of secondary contamination.Fish gelatin,which is highly soluble in water and has a low gelation temperature,can be electrospun in an aqueous solution and has the same polar functional groups as the hydrophilic mucilage of fish skin.In addition,the micro/nanostructure of fish skin,which induces superoleophobicity in water,introduces a bead-on-string structure using the Rayleigh instability of electrospinning.The solubility of fish gelatin in water was removed using an eco-friendly crosslinking method using reducing sugars.Fish skin-mimicking materials successfully separated suspended oil and emulsified oil,with a maximum flux of 2086 Lm^(−2) h^(−1) and a separation efficiency of more than 99%.The proposed biopolymeric nanofibrous membranes use fish gelatin,which can be extracted from fish waste and has excellent biodegradability with excellent oil-water separation performance.In addition,polymer material processing,including membrane manufacturing and crosslinking,can be realized through eco-friendly processes.Therefore,fish skin-inspired biopolymeric membrane is expected to be a promising candidate for a sustainable and effective oil-water separation membrane in the future.

Easily-manufactured paper-based materials with high porosity for adsorption/separation applications in complex wastewater

A multi-functional porous paper-based material was prepared from grass pulp by simple pore-forming and green cross-linking method.As a pore-forming agent,calcium citrate increased the porosity of the paper-based material from 30%to 69%while retaining the mechanical strength.The covalent cross-linking of citric acid between cellulose fibers improved both the wet strength and adsorption capacity.In addition,owing to the introduction of high-content carboxyl groups as well as the construction of hierarchical micro-nano structure,the underwater oil contact angle was up to 165°.The separation efficiency of the emulsified oil was 99.3%,and the water flux was up to 2020 L·m^(–2)·h^(–1).The theoretical maximum adsorption capacities of cadmium ion,lead ion and methylene blue reached 136,229 and 128.9 mg·g^(–1),respectively.The continuous purification of complex wastewater can be achieved by using paper-based materials combined with filtration technology.This work provides a simple,low cost and environmental approach for the treatment of complex wastewater containing insoluble oil,organic dyes,and heavy metal ions.

Laser Ablation and Chemical Oxidation Synergistically Induced Micro/Nano Re-entrant Structures for Super-Oleophobic Surface with Cassie State

Generally,re-entrant structures are a key part of fabricating superoleophobic surfaces,and this structure appears in almost all kinds of published research articles regarding superoleophobicity.However,the application of related fabrication methods is usually too complex and costly in real practice.In this paper,we present a simple method to generate micro-cauliflower structures,which work as re-entrant structures in microcone arrays,to promote the formation of superoleophobic surfaces.The heating process after alkali-assisted surface oxidation is the main reason for the appearance of a micro-ball structure,and the oxidation time can influence the size of the micro-ball.To the best of our knowledge,the influence of the heating process after alkali-assisted surface oxidation on the birth of the micro-ball structure is seldom researched.A low-surface-energy treatment was also analyzed in influencing the size of the re-entrant structure and its relative wettability.Droplets of 5μl of n-decane show contact angles of 155±1°on the as-prepared superoleophobic surface,and air pockets can be clearly seen underneath,indicating a stable Cassie contacting state and a promising application value in the near future.

Biomimetic Superlyophobic Metallic Surfaces: Focusing on Their Fabrication and Applications

Metals are indispensable engineered materials for day-to-day life.Researches focused on metallic surfaces with superlyophobicity(superhydrophobicity,superoleophobicity,underwater superoleophobicity and slippery characteristic)have attracted much attention recently.Nature is a magician that gives each organic life a unique advantage.Researchers have created a large number of biomimetic superlyophobic metallic surfaces through various approaches.These biomimetic superlyophobic metallic surfaces exhibit advantages in many applications,such as self-cleaning,corrosion resistance,anti-icing,and drag reduction.In this review,the specific fabrication and applications of biomimetic superlyophobic metallic surfaces were reported.The remaining challenges and future outlook of biomimetic superlyophobic metallic surfaces were preliminarily analyzed.It is hoped that the review will be essential for broadening the scope of potential applications of metals and providing a powerful reference for future research on metal-based advanced functional materials.

A stable ZIF-8-coated mesh membrane with micro-/nano architectures produced by a facile fabrication method for high-efficiency oil-water separation

With the possibility of large-area processing, the ZIF-8-coated mesh membranes with rough micro-/nanostructures and underwater superoleophobic properties were successfully fabricated at ambient temperature and pressure.These membranes exhibited excellent separation efficiency over 99.99% for various oil-water mixtures with the residual oil content in the collected water less than 4 ppm, and high water flux of 10.2×104 L m-2 h-1. Furthermore, the ZIF-8-coated mesh membrane displayed outstanding stability towards high temperature and various organic solvents immersion. More importantly, based on its facile fabrication method, this kind of ZIF-8-coated mesh membrane can be easily enlarged, which is critical for the practical oil-water separation applications.

An unusual superhydrophilic/superoleophobic sponge for oil-water separation

Development of porous materials with anti-fouling and remote controllability is highly desired for oil-water separation application yet still challenging. Herein, to address this challenge, a sponge with unusual superhydrophilicity/superoleophobicity and magnetic property was fabricated through a dip-coating process. To exploit its superhydrophilic/superoleophobic property, the obtained sponge was used as a reusable water sorbent scaffold to collect water from bulk oils without absorbing any oil. Owing to its magnetic property, the sponge was manipulated remotely by a magnet without touching it directly during the whole water collection process, which could potentially lower the cost of the water collection process. Apart from acting as a water-absorbing material, the sponge can also be used as affiliation material to separate water from oil-water mixture and oil in water emulsion selectively, when fixed into a cone funnel. This research provides a key addition to the field of oil-water separation materials.

TiO_(2) Coated Polypropylene Membrane by Atomic Layer Deposition for Oil-Water Mixture Separation

Polypropylene(PP)membrane has been widely used in water purification and other fields owing to special pore structure,excellent mechanical properties and resistance to acids,alkalis and organic solvents.However,it is difficult for PP to introduce the hydrophilic chemical compositions for oil-water separation.Herein,superhydrophilic and underwater superoleophobic PP membranes were prepared by ALD for efficient gravity-driven oil-water separation.Owing to synergistic effect,oil contact angle of TiO_(2) coated PP membrane under water can reach above 150°.Hence,TiO_(2) coated PP membrane has great oil-repelling performance.Because of the superwetting property,TiO_(2) coated PP membrane can easily separate oil-water mixture and have high separation efficiency(more than 95%).The outstanding recyclability and mechanical stability of TiO_(2) coated PP membrane suggest the promising potential application in practical oil-water separation.

Twofold bioinspiration of TiO_(2)-PDA hybrid fabrics with desirable robustness and remarkable polar/nonpolar liquid separation performance

The fundamental relationship between microstructure,constituent,processing and performances of separating materials is really a vital issue.Traditional preparation methods for separation membranes are complex,time-consuming and easy to be fouled.Also,the durability of conventional coatings on membrane is poor.By combination of bioinspiration from mussel adhesive and fish scales’underwater superoleophobicity,we propose a general route to prepare organic-inorganic hybrid coatings,while no complex apparatus is needed.Specifically,based on the biomimetic adhesion of polydopamine(PDA),we used it as a binder to adhere TiO_(2)nanoparticles and built rough microstructure on fabric.In this way,we obtained TiO_(2)-PDA treated fabric with special wettability.These TiO_(2)-PDA treated samples owned superamphiphilicity in air,underwater superoleophobicity(underwater oil contact angles(OCAs)>150°),underoil superhydrophobicity(underoil water contact angles(WCAs)>150°),excellent multiresistance;and can separate polar/nonpolar liquid mixture effectively.It also owned superaerophobicity underwater(underwater bubble contact angles(BCAs)>150°).The proposed TiO_(2)-PDA coatings are highly expected to be employed for real situation of water pollution remediation,self-cleaning,oil extraction and harsh chemical engineering issues.

An antifouling catechol/chitosan-modified polyvinylidene fluoride membrane for sustainable oil-in-water emulsions separation

Low-pressure membrane filtrations are considered as effective technologies for sustainable oil/water separation.However,conventional membranes usually suffer from severe pore clogging and surface fouling,and thus,novel membranes with superior wettability and antifouling features are urgently required.Herein,we report a facile green approach for the development of an underwater superoleophobic microfiltration membrane via one-step oxidant-induced ultrafast co-deposition of naturally available catechol/chitosan on a porous polyvinylidene fluoride(PVDF)substrate.Membrane morphology and surface chemistry were studied using a series of characterization techniques.The as-prepared membrane retained the original pore structure due to the ultrathin and uniform catechol/chitosan coating.It exhibited ultrahigh pure water permeability and robust chemical stability under harsh pH conditions.Moreover,the catechol/chitosan hydrophilic coating on the membrane surface acting as an energetic barrier for oil droplets could minimize oil adhesion on the surface,which endowed the membrane with remarkable antifouling property and reusability in a cyclic oil-in-water(O/W)emulsion separation.The modified membrane exhibited a competitive flux of~428 L/(m^(2)·h·bar)after three filtration cycles,which was 70%higher than that of the pristine PVDF membrane.These results suggest that the novel underwatersuperoleophobic membrane can potentially be used for sustainable O/W emulsions separation,and the proposed green facile modification approach can also be applied to other water-remediation materials considering its low cost and simplicity.

Nonswellable hydrogels with robust micro/nano-structures and durable superoleophobic surfaces under seawater

Hydrogels, composed mainly of water trapped in three dimensional cross-linked polymer networks, have been widely utilized to construct underwater superoleophobic surfaces. However, the swelling nature and instability of hydrogels under complex marine environment will weaken their underwater superoleophobicity. Herein, we synthesize structured poly （2-hydroxyethylmethacrylate） （PHEMA） hydrogels by using sandpaper as templates. The robust non-swelling of PHEMA hydrogel ensures that micro/nano-structures on the surface of PHEMA hydrogels can be well maintained. Moreover, when roughness Ra of about 3-4 bun, the surface has superior oil-repellency. Additionally, even after immersing in seawater for one-month, their breaking strength and toughness can be well kept. The non-swellable hydrogels with long-term stable under seawater superoleophobicity will promote the development of robust superoleophobic materials in marine antifouling coatings, biomedical devices and oil/water separation.

Hydrophilic/underwater superoleophobic graphene oxide membrane intercalated by TiO2 nanotubes for oil/water separation

Membrane technology for oil/water separation has received increasing attention in recent years. In this study, the hydrophilic/underwater superoleophobic membrane with enhanced water permeability and antifouling ability were fabricated by synergistically assembling graphene oxide （GO） nanosheets and titanium dioxide （TiO2） nanotubes for oil/water separation. GO/TiO2 membrane exhibits hydrophilic and underwater superoleophobic properties with water contact angle of 62° and under water oil contact angle of 162.8°. GO/TiO2 membrane shows greater water permeability with the water flux up to 531 L/ （m^2·h·bar）, which was more than 5 times that of the pristine GO membrane. Moreover, GO/TiO2 membrane had excellent oil/water separation efficiency and anti-oil-fouling capability, as oil residual in filtrate after separation was below 5 mg/L and flux recovery ratios were over 80%.The results indicate that the intercalation of TiO2 nanotubes into adjacent GO nanosheets enlarged the channel structure and modified surface topography of the obtained GO/TiO2 membranes, which improved the hydrophilicity, permeability and anti-oil-fouling ability of the membranes, enlightening the great prospects of GO/TiO2 membrane in oil-water treatment.

Underwater Superoleophobic Crucian Fish Scale:Influence of Ontogeny on Surface Morphologies and Wettability

Recent development concerning underwater superoleophobic surface has been motivated by fish scales,which are rendered capable of preventing their surfaces from contamination in oil-polluted water.In this paper,for the first time,the variations in surface topography and chemical composition of crucian fish scales at different growth stages have been investigated.The water and oil contact angles,surface morphology and chemical composition of the fish scales were measured by means of contact angle measurements,scanning electron microscopy and Fourier transform infrared spectroscopy,respectively.It is found that surface morphology and chemical composition both have influences on surface wettability of fish scales;fish scale at infant period seems to possess better hydrophilicity than that of fish scales at mature and senescent period.What is more,it is believed that the wettability heavily depends on the surface structures during their growth procedure,which enlightens us to design and fabricate biomimetic multifunctional underwater superoleophobic surfaces inspired by nature.

Bioinspired cellulose-based membranes in oily wastewater treatment

It is challenging to purify oily wastewater, which affects water-energy-food production. One promising method is membrane-based separation. This paper reviews the current research trend of applying cellulose as a membrane material that mimics one of three typical biostructures: superhydrophobic, underwater superoleophobic, and Janus surfaces. Nature has provided efficient and effective structures through the evolutionary process. This has inspired many researchers to create technologies that mimic nature’s structures or the fabrication process. Lotus leaves, fish scales, and Namib beetles are three representative structures with distinct functional and surface properties: superhydrophobic, underwater superoleophobic, and Janus surfaces. The characteristics of these structures have been widely studied and applied to membrane materials to improve their performance. One attractive membrane material is cellulose, whichhas been studied from the perspective of its biodegradability and sustainability. In this review, the principles, mechanisms, fabrication processes, and membrane performances are summarized and compared. The theory of wettability is also described to build a comprehensive understanding of the concept. Finally, future outlook is discussed to challenge the gap between laboratory and industrial applications.