Superwetting surfaces require micro-/nanohierarchical structures but are mechanically weak. Moreover, such surfaces are easily polluted by amphiphiles. In this work, inorganic adhesives are presented as a building block for construction of superwetting surfaces and to promote robustness. Nanomaterials can be selected as fillers to endow the functions. We adopted a simple procedure to fabricate underwater superoleophobic surfaces by spraying a titanium dioxide suspension combined with aluminum phosphate binder on stainless steel meshes. The surfaces maintained their excellent performance in regard to oil repellency under water, oil/water separation, and self-cleaning properties after even 100 abrasion cycles with sandpaper. Robust superwetting surfaces favored by inorganic adhesives can be extended to other nanoparticles and substrates, which are potentially advantageous in practical applications.Keywords: inorganic adhesives; oil/water separation; robust surfaces; self-cleaning; underwater superoleophobic;

Structural colours and superwettability are of great interest due to their unique characteristics. However, the application of materials with either structural colours or superwettability is limited. Moreover, materials possessing both structural colours and superwettability are crucial for many practical applications. The combination of structural colours and superwettability can result in materials for use various applications, such as in sensors, detectors, bioassays, anti-counterfeiting, and liquid actuators, by controlling surfaces to repel or absorb liquids. Regarding superwettability and structural colours, surface texture and chemical composition are two factors for the construction of materials with superwettable structural colours. This review aims at offering a comprehensive elaboration of the mechanism, recent biomimetic research, and applications of biomimetic superwettable materials with structural colours. Furthermore, this review provides significant insight into the design, fabrication, and application of biomimetic superwettable materials with structural colours.

Understanding the complementary roles of surface roughness and energy in natural super-non-wetting surfaces has greatly promoted the development of biomimetic superhydrophobic surfaces that repel water at a much greater rate than oils. These surfaces that are highly repellent to low-surface-tension oils and organic liquids, termed superoleophobic surfaces, are poorly understood. Inspired by springtails (collembolan), a third factor, re-entrant surface curvature, has been introduced to the design and fabrication system of superoleophobic surfaces in conjunction with two other factors of surface chemical composition and roughness. Over the past decade, superoleophobic surfaces have attracted tremendous attention with respect to their design, fabrication and applications due to their extraordinary properties. This review focuses on these aspects and thus summarizes recent research progress in superoleophobic surfaces. Starting from the origin, features of natural oil-resistant creatures have been introduced, and fundamental theories for surface design have been discussed. Calculations suggest that creation of these surfaces requires specific re-entrant structures and fluoride modifiers. Based on this principle, various fabrication methods, from top-down to bottom-up approaches, have been used, and some derivative structures with desirable properties have been produced. A precise and detailed classification has been provided in this review that includes representative methods and structures as well as functions (i.e., transparence and self-healing). Significantly, superoleophobic materials have many valuable applications, including oil pollution resistance, oil transportation, and synthesis of mesoporous supraparticles. However, their complicated manufacturing techniques, poor physical–chemical properties and environmentally unfriendly surface chemicals jointly impede their real-life applications. Therefore, it is highly necessary to optimize the craft and performance of theses surfaces for industrial operation and practical applications. To this end, some challenges and perspectives will be provided regarding the future research and development of superoleophobic surfaces.

When deposited on a superheated surface, a droplet can be levitated by its own vapour layer, a phenomenon that is referred to as the Leidenfrost effect. This dynamic effect has attracted interest for many potential applications, such as cooling, drag reduction and drop transport. A lot of effort has been paid to this mechanism over the past two and half centuries. Herein, we not only review the classical theories but also present the most recent theoretical advances in understanding the Leidenfrost effect. We first review the basic theories of the Leidenfrost effect, which mainly focuses on the relationship between the drop shape, vapour layer and lifetime. Then, the shift in the Leidenfrost point realized by fabricating special surface textures is introduced and the mechanisms behind this are analyzed. Furthermore, we present the reasons for the droplet transport in both classical Leidenfrost and pseudo-Leidenfrost regimes. Finally, the promising breakthroughs of the Leidenfrost effect are briefly addressed.

A superhydrophobic/self-lubricating fabric with double hierarchical structure was prepared by first etching pristine ultrahigh molecular weight polyethylene (UHMWPE) fibers with air-plasma, followed by a facile in situ growth method. Scanning electron microscopy (SEM) showed that the air-plasma etching treatment generated pits on the fiber surface and TiO2 was grafted onto the etched fiber, which greatly improved its surface roughness. The fabric was further modified by 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PTES), which possesses a low surface free energy. The results showed the PTES-TiO2@UHMWPE fabric possessed superhydrophobic properties with a water contact angle (WCA) of 157.75°, enhanced thermal resistance, and exhibited excellent antiwear properties with a friction coefficient of 0.05. In addition, the PTES-TiO2@UHMWPE fabric retained its superhydrophobicity without an apparent reduction after 30 cycles of washing or 5 minutes of friction treatment, revealing its good mechanical properties. Meanwhile, the mechanical strength of the fabric had little reduction after UV irradiation, which is helpful in enlarging the fabric applications in industry.

•A robust superhydrophilic/underwater superoleophobic polyacrylonitrile (PAN) ultrafiltration membrane is prepared.•The employed method is a hydroxylamine-induced phase inversion process, which is so simple.•The obtained membrane shows a high flux for various oil/water emulsions.•The obtained membrane shows good anti-fouling properties.Suffering from terrible membrane fouling and flux decline caused by foulants absorption or plugging, conventional ultrafiltration membranes are hampered in treating oil/water emulsions. In this work, a novel superhydrophilic/underwater superoleophobic polyacrylonitrile (PAN) ultrafiltration membrane is prepared by a hydroxylamine-induced phase inversion process. The obtained PAN membrane displays a high flux ranging from 2200 to 3806 L m−2 h−1 bar−1 and desirable separation efficiency for various oil-in-water emulsions. Additionally, the PAN membrane shows superior antifouling property and recyclability due to its ultralow-oil-adhesion property. Therefore, the superhydrophilic/underwater superoleophobic PAN ultrafiltration membrane provides a promising potential for treating oily wastewater.A novel strategy for fabricating a superhydrophilic and underwater superoleophobic polyacrylonitrile ultrafiltration membrane is presented through a hydroxylamine-induced phase inversion process. The robust oil/water emulsion separation performance of the superwetting polyacrylonitrile ultrafiltration membrane shows a great potential to be used for treating oily wastewater.Download high-res image (84KB)Download full-size image

•The aligned Cu(OH)2 nano-needles are successfully constructed on the sand gain surfaces;•The as-prepared functional sands show superior superhydrophobicity;•The discrete superhydrophobic sand is a good candidate for oil-water separation•This work is expected to change our traditional understanding of sand and the reutilization of natural desert sand.Desert sand as an abundant natural resource rarely has been reconsidered and reutilized due to its superhydrophilicity. Aiming at the combination of super-wettability with sand resource, we successfully design the aligned Cu(OH)2 nano-needles on the sand grain surfaces through a skillful strategy and conferred superhydrophobic properties on them in this study. The water contact angle and rolling angle are shown to be ~ 158° and ~ 6°, which break our traditional understanding towards desert sand, i.e., superhydrophilicity. More importantly, the selective superhydrophobic-superoleophilic wettability and the cavities between nano-needles and sand grains allow the sand to be a good candidate for efficient oily water treatment. The as-prepared superhydrophibic sand can not only absorb light oils from water surface, but separate heavy oils from oil/water mixtures. The speed of oil/water separation is up to 16,985 L m− 2 h− 1 when a 0.35 cm thickness of superhydrophobic sand layer is used. Significantly, it exhibits both high separation rate and high separation efficiency (> 99.5%). The as-prepared superhydrophobic sands are expected to become a new candidate of highly efficient oil/water separation material and to realize the reutilization of desert sand resource.This new work provides some information for the reutilization of natural sand resource for oily water treatment through surface structuration with aligned Cu(OH)2 nano-needles and surface functionalization with superhydrophobic property.Download high-res image (156KB)Download full-size image

Transition metals and their oxide materials have been widely employed to fabricate superhydrophobic surfaces, not only because of their surface topography with controllable microstructures leading to water-repellence, diverse adhesion even tunable wettability, but also due to a variety of special properties like optical performance, magnetism, anti-bacterial, transparency and so on. At the meantime, biomimetic superhydrophobic surfaces have attracted great interest from fabricating hierarchical micro-/nano-structures inspired by nature to imitate creature's properties and many potential applications, including self-cleaning, antifogging, antireflection, low drag and great stability and durability. In this review, natural surfaces and biomimetic materials with special wettability are introduced by classification according to the similar microstructure of morphology, like array structure, sheet overlapped structure, high density hairs and seta shaped structure. Not only do we exhibit their special performances, but also try to find out the true reasons behind the phenomenon. Then, the recent progress of a series of superhydrophobic transition mental and their oxide materials, including TiO2, ZnO, Fe3O4, CuO, Ag, Au and so on, is presented with a focus on fabricating methods, microstructures, wettability, and other properties. As followed, these superhydrophobic surfaces can be applied in many fields, such as oil/water separation, self-cleaning, photo-controlled reversible wettability, surface-enhanced Raman scattering, antibacterial, anticorrosion, and synthesis of various applications. However, few of them have been applied in practical life. Hence, we discuss the remaining challenges at present and the development tendency in future at the end of this article. This review aims to present recent development of transition metals and their oxides applied in biomimetic superhydrophobic surfaces about fabrication, microstructure, water repellence, various properties, and potential applications.

•Annealing, proton irradiation and atomic oxygen exposure are employed as the post-treatment processes.•The sensing behaviors of all samples are evaluated in a multi-channel test system at the same time.•The different gas sensing behaviors of hierarchical hollow WO3 are certified.•The response value can be greatly improved by annealing and AO while it’s worse by proton irradiation.Hierarchical hollow tungsten trioxide is fabricated by a facile method. Annealing, proton irradiation and atomic oxygen exposure are employed as the three different post-treatment processes. Effect of different post-treatment processes on microstructures and gas sensing behaviors of the as-prepared WO3 are investigated by various characterization analyses. We have demonstrated that the response amplitude can be greatly improved by annealing and AO treatment while it became worse after proton irradiation process. The results indicate that the post-treated WO3 can be used as a promising material for detecting acetone.Effect of different post-treatment processes on microstructures and gas sensing acetone behaviors of the as-prepared WO3 are investigated.Download high-res image (151KB)Download full-size image

Superhydrophobic (SHP) coatings inspired by lotus have great application prospect for our daily life. Regrettably, three formidable challenges, namely, complex fabrication, weak mechanical stability and large-scale fabrication, have already existed for a long time in this research field. Here, a robust micro-nanoscale P25 (Nano TiO2)/MgO/epoxy resin (ER) SHP coating has been fabricated via facile one-pot route, which can be applied to arbitrary substrates through multiples methods. P25/MgO/ER SHP coating not only displays excellent mechanical stability but also shows unique repairable ability to recover its superhydrophobicity under various damages by extreme environment such as low temperature, strong acid or alkali and this repairable process can be repeated for many times. P25/MgO/ER SHP coating also is easy to large-scale fabrication with very low cost.We have demonstrated one kind of micro-nanoscale superhydrophobic coating via a novel one-pot route on arbitrary substrates. This coating has avoided complex process, noxious chemicals and high cost successfully. It not only displays excellent mechanical stability but also shows unique repairable ability to recover its superhydrophobicity under various damages.Download high-res image (96KB)Download full-size image

Green fluoride-free superhydrophobic hierarchical flowerlike iron-containing MnO2 particles were synthesized by a simple one-pot approach and subsequently modified by stearic acid. The special selective wettability toward water and oil makes the particle can be used in oil-in-water emulsion separation. In addition, the particle also can be applied as absorption material to remove dyes which are serious water contaminants. More importantly, as for the mixture of emulsion and dye, the particles also have the ability to remove both oil and dye, making the particles potential for wastewater purification in the future.Low cost and non-fluorine flowerlike superhydrophobic particles were prepared for both emulsions separation and dyes removal.Download high-res image (95KB)Download full-size image

Superhydrophobic materials have triggered large interest due to their widespread applications, such as self-cleaning, corrosion resistance, anti-icing, and oil/water separation. However, suffering from weak mechanical strength, plenty of superhydrophobic materials are limited in practical application. Herein, we prepared hierarchical carbon microflowers (CMF) dispersed with molybdenum trioxide (MoO3) nanoparticles (MoO3/CMF) via a two-step preparation method. Taking advantage of high-adhesion epoxy resin and the modification with 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PDES), the modified MoO3/CMF (PDES-MoO3/CMF) coating on various substrates shows great waterproof ability, excellent chemical stability, good mechanical durability, and self-cleaning property. More significantly, the prepared PDES-MoO3/CMF powder with high thermal stability (250 °C) can be used for oil/water separation due to its special flower-like structure and superhydrophobicity/superoleophilicity. All of these advantages endow the superhydrophobic powders with huge potential in the practical applications.Multifunctional superhydrophobic PDES-MoO3/CMF powders created by a two-step method can be used in robust, heated-resistant superhydrophobic coating and separate oil/water mixture.Download high-res image (232KB)Download full-size image

•A multifunctional superamphiphobic cotton fabric was fabricated;.•The prepared cotton fabrics exhibited high liquid repellency to water, colza oil and n-hexadecane;.•The superamphiphobic cotton fabric possessed desirable chemical and mechanical durability, self-cleaning and self-healing property.A multifunctional superamphiphobic cotton fabric was fabricated by coating silica nanoparticles on the cotton fabric surface and further modification by 1H,1H,2H,2H-perfluorooctyltrichlorosilane (FOTS). The fluctuant woven fabric and the fluffy spherical SiO2 nanoparticles constructed a dual micro/nano-structures. The surface free energy of the fabric composite was reduced by FOTS modifier. The interplay of the structured and perfluorinated SiO2 nanoparticles could not only endow the fabric highly liquid repellent ability, but could also to enhance the coating stability. The prepared cotton fabrics exhibited high liquid repellency to water, colza oil and n-hexadecane with lower surface tension, showing a contact angle of 158°, 152°, and 153°, respectively. The results demonstrated that superamphiphobic cotton fabric possessed desirable chemical and mechanical durability, self-cleaning and self-healing property, the robust and multifunctional fabric would find innovative opportunities for practical applications.The structured and perfluorinated modification SiO2 nanoparticles coated on the cotton fiber endow the fabric highly superamphiphobic ability, meanwhile the superamphiphobic fabric also shows excellent durability against various severe damages.Download high-res image (284KB)Download full-size image

•The recent advances of the synthesis, fabrications, and properties of these “different kinds of silica” are reviewed totally.•The related properties about anti-reflection, oil-water separation, environmental applications, etc, are briefly introduced.•The challenge about this filed is proposed.With years of explorations, researchers have achieved great success in fabricating superhydrophobic materials, herein, silica-based materials play an important role. In general, silica exists in three different morphologies when constructing superhydrophobic materials, they are silica particles, silica micro-string networks, and silica gels. Based on this, we give out a panoramic presentation about the synthesis, fabrications, and properties of these “different kinds of silica”. Besides, some of recent applications, such as anti-reflection, oil-water separation, environmental applications, etc, are briefly introduced. This review is aimed at setting up a system for the silica-based superhydrophobic materials, summarizing the previous works of this domain, and more importantly, providing reference for the subsequent studies.Inspired by creatures in nature, lots of studies on superhydrophobic materials have been carried out, and silica-based materials with different sizes and morphology play an important role. In this reveiw, the related research advances are reviewed and some challenges and the potential promising breakthroughs are also succinctly highlighted in this field.Download high-res image (134KB)Download full-size image

Numerous research studies have contributed to the development of mature superhydrophobic systems. The fabrication and applications of polymeric superhydrophobic surfaces have been discussed and these have attracted tremendous attention over the past few years due to their excellent properties. In general, roughness and chemical composition, the two most crucial factors with respect to surface wetting, provide the basic criteria for yielding polymeric superhydrophobic materials. Furthermore, with their unique properties and flexible configurations, polymers have been one of the most efficient materials for fabricating superhydrophobic materials. This review aims to summarize the most recent progress in polymeric superhydrophobic surfaces. Significantly, the fundamental theories for designing these materials will be presented, and the original methods will be introduced, followed by a summary of multifunctional superhydrophobic polymers and their applications. The principles of these methods can be divided into two categories: the first involves adding nanoparticles to a low surface energy polymer, and the other involves combining a low surface energy material with a textured surface, followed by chemical modification. Notably, surface-initiated radical polymerization is a versatile method for a variety of vinyl monomers, resulting in controlled molecular weights and low polydispersities. The surfaces produced by these methods not only possess superhydrophobicity but also have many applications, such as self-cleaning, self-healing, anti-icing, anti-bioadhesion, oil–water separation, and even superamphiphobic surfaces. Interestingly, the combination of responsive materials and roughness enhances the responsiveness, which allows the achievement of intelligent transformation between superhydrophobicity and superhydrophilicity. Nevertheless, surfaces with poor physical and chemical properties are generally unable to withstand the severe conditions of the outside world; thus, it is necessary to optimize the performances of such materials to yield durable superhydrophobic surfaces. To sum up, some challenges and perspectives regarding the future research and development of polymeric superhydrophobic surfaces are presented.

Sand, an abundant natural resource, is the cause behind the harsh environmental conditions of the desert, such as water shortages and sand storms. Because of the strong hydrophilicity of sand itself, water can be quickly absorbed by sand, which greatly impedes desert greening, water storage and transportation projects. In contrast to this conventional understanding of sand (i.e., superhydrophilicity), we propose the design of “superhydrophobic sand”, aimed to address issues associated with the desert environment and sand resource utilization. In our experiments, three kinds of hydrophobic sands with different surface structures and wettability properties were successfully prepared by cladding nonmetal (SiO2) and metal (Ag and Cu) inorganic materials on sand grain surfaces and then modifying them with low-surface-energy chemicals. Combining superhydrophobicity with desert sand, superhydrophobic sand (PFDS-sand@SiO2) is shown to have excellent water repellency, allowing water to stably remain and flow on such a sand surface without any wetting or permeation. Furthermore, the superhydrophobic sand demonstrates a great water-holding capacity, such that a sand layer with a thickness of 2 cm can sustain a water column height of 35 cm. Very significantly, PFDS-sand@SiO2 exhibits extremely high thermal stability up to 400 °C when used for water storage. This result is unprecedented and sufficient for facing the high-temperature conditions of the desert environment and some others. In addition to reliable water storage, such superhydrophobic sand also demonstrates a great anti-flow-dragging effect during water transportation, whereby a water droplet can smoothly and quickly roll down a simulated sand channel (13 cm length) within 0.3 s (∼0.45 m s−1). All of these manifestations imply the significant potential of such “superhydrophobic sand” in its application to desert water storage and transportation.

Inspired by the strong adhesion of mussel, taking advantage of a simple one-pot approach, we designed a robust and boiling-water resistant superhydrophobic polydopamine@SiO2(PDA@SiO2) coated cotton fabric through copolymerization reaction and trimethyl silyl modified process at room temperature. The as-prepared fabric not only shows great resistance to mechanical abrasion, wear and ultrasonic treatment but also has excellent superhydrophobicity stability towards UV irradiation, high temperature and organic solvents immersion. More importantly, the superhydrophobic fabric also exhibits boiling water (99 °C) repelling properties, while several superhydrophobic surfaces lose their superhydrophobicity when exposed to hot water with temperature more than 50 °C. It is also noticeable that the purity of all the collected oil is as high as 99.9% when superhydrophobic fabric is used to separate oil/water mixture for 20 cycles, indicating the high oil/water separation efficiency of the fabric. We believe that the modified fabric is environmentally friendly, low cost and easy to fabricate, and thus exhibits great potential applications in solving the serious problems of oily waste water and scald-protection clothes.

In this work, superhydrophobic fabrics were prepared through an in-situ growth method for fabricating hierarchical flower-like MnO2 nanoparticles on cotton fabric surface and subsequent STA modification, which exhibited multifunction for self-healing, self-cleaning, oil/water separation and wear resistance. After air-plasma treatment, the self-healing MnO2@fabric could restore superhydrophobicity by a short time heat treatment, and the water CA without obvious reduction after 8 cycles. Moreover, the MnO2@fabric could selectively filtrate oil from a mixture of oil and water repeatedly, and demonstrated high efficiency for oil/water separation capability and excellent self-cleaning property. Furthermore, the MnO2@fabric composite possessed high mechanical strength and good wear resistance, its wear rate could be reduced to 1.21 × 10−14 m3 (N m)−1. The MnO2@fabric still maintained superhydrophobicity even was seriously damaged after the friction test.MnO2 nanoparticles were grafted on the cotton fabrics by an in-situ growth method, then modified by STA. The as-prepared superhydrophobic MnO2@fabric showed durable superhydrophobicity, stable self-healing, self-cleaning, efficient oil/water separation, excellent wear resistance and high tensile strength.Download high-res image (106KB)Download full-size image

Superhydrophobic surfaces demonstrate remarkable advantages involving interfacial issues but limited practical applications due to their poor mechanical robustness and environmental durability. The required micro-/nano-hierarchical structures and low-surface-energy nanocomponents are very vulnerable to physical and chemical destruction. Moreover, harsh conditions fundamentally weaken the mechanical strength of already-constructed robust superhydrophobic surfaces. In this work, inorganic adhesives are proposed to strengthen the bonding force between superhydrophobic coatings and various substrates. A simple spray-coating method is adopted to fabricate superhydrophobic surfaces using an all-in-one suspension that contains an aluminum phosphate binder, titanium dioxide nanoparticles, and alkylsilane. The surfaces benefitting from inorganic adhesives still extremely repel water after physical abrasion, and greatly endure harsh conditions including hot oil (80 °C), hot water (80 °C), and hot acetone (50 °C) for 24 h to preserve their high mechanical strength. The prepared coatings also have a self-healing ability against boiling-water treatment, O2-plasma etching, and amphiphilic pollution. Superhydrophobicity can be rapidly regenerated after multiple cycles of high-temperature repairing for 5 min. In addition, the robust interfacial materials exhibit a very reliable performance in oil–water separation after 100 abrasion cycles. Benefiting from the distinctive advantages of inorganic adhesives, interfacial materials will be broadly developed for practical applications in related fields.

Lamellar compounds such as the disulfides of molybdenum and tungsten are widely used as additives in lubricant oils or as solid lubricants in aerospace industries. The dioxides of these two transition metals have identical microstructures with those of the disulfides. The differences in the lubrication behaviors of disulfide and dioxides were investigated theoretically. Tungsten dioxide and molybdenum dioxide exhibit higher bond strengths at the interface and lower interlayer interactions than those of the disulfides which indicates their superlubricity. Furthermore, the topography of the electron density of the single layer nanostructure determined their sliding potential barrier; the dioxides showed a weaker electronic cloud distribution between the two neighboring oxygen atoms, which facilitated the oxygen atoms of the counterpart to go through. For commensurate friction, the dioxides exhibited nearly the same value of friction work, and same was the case for the disulfides. The lower positive value of friction work for the dioxides confirmed their improved lubricity than the disulfides and the higher mechanical strength of the bulk dioxides demonstrated that they are excellent solid lubricants in vacuum.

Superhydrophobic coating has extremely high application value and practicability. However, some difficult problems such as weak mechanical strength, the need for expensive toxic reagents, and a complex preparation process are all hard to avoid, and these problems have impeded the superhydrophobic coating’s real-life application for a long time. Here, we demonstrate one kind of omnipotent epoxy resins @ stearic acid-Mg(OH)2 superhydrophobic coating via a simple antideposition route and one-step superhydrophobization process. The whole preparation process is facile, and expensive toxic reagents needed. This omnipotent coating can be applied on any solid substrate with great waterproof ability, excellent mechanical stability, and chemical durability, which can be stored in a realistic environment for more than 1 month. More significantly, this superhydrophobic coating also has four protective abilities, antifouling, anticorrosion, anti-icing, and flame-retardancy, to cope with a variety of possible extreme natural environments. Therefore, this omnipotent epoxy resins @ stearic acid-Mg(OH)2 superhydrophobic coating not only satisfies real-life need but also has great application potential in many respects.

It is widely known that natural examples like lotus leaves can only repel room-temperature water but cannot repel hot water and oils. Even though superamphiphobic surfaces composed of re-entrant “mushroom-like” or “T-shaped” structures are promising, they are generally regarded as substrate-dependent and difficult to fabricate, and hence, their practical use on various materials has been limited. Here, we synthesize a flower-like superamphiphobic FOTS-TiO2 powder by solvothermal process and self-assembly functionalization. These structured and functionalized submicron particles can repel the liquids with surface tension as low as 23.8 mN·m–1 (n-decane), which is the lowest among powder samples. With respect to the biomimetic aspect, the surface morphology of FOTS-TiO2 particle is similar to the hierarchical micro/nano-structures of the lotus leaf surface, but it is beyond the lotus leaf for superoleophobic capacity. The difference in the oleophobicity is suggested to be the interplay of quasi-spherical re-entrant structure and perfluorined modification. Because of superior superamphiphobicity of the powder, a facile yet versatile strategy is developed, adhesive-assisted sieve deposition fabrication (AASDF), for preparing superamphiphobic coatings on various substrates. The investigation results pertaining to the water/oil proofing, mechanical durability, self-cleaning, and antifouling performances prove that the FOTS-TiO2 coating is robust and multifunctional, which will enable more opportunities for practical applications. Apart from these general applications, we find that the superamphiphobic FOTS-TiO2 powders when coated on sponge as anti-icing surface have good ice delay and icephobic performances. Furthermore, they can be used to prepare magnetic Fe3O4&FOTS-TiO2 composite particles through liquid marbles, implying significant scientific value.Keywords: anti-icing; biomimetic; lotus leaf; multifunctional; self-cleaning; superamphiphobic; TiO2

Inspired by Namib Desert beetles, a hybrid superhydrophobic surface was fabricated, showing highly efficient fog harvesting with a water collection rate (WCR) of 1309.9 mg h−1 cm−2. And, the surface possessed an excellent robustness and self-cleaning property.

Nowadays, water shortage is a severe issue all over the world, especially in some arid and undeveloped areas. Interestingly, a variety of natural creatures can collect water from fog, which can provide a source of inspiration to develop novel and functional water-collecting materials. Recently, as an increasingly hot research topic, bioinspired materials with the water collection ability have captured vast scientific attention in both practical applications and fundamental research studies. In this review, we summarize the mechanisms of water collection in various natural creatures and present the fabrications, functions, applications, and new developments of bioinspired materials in recent years. The theoretical basis related to the phenomenon of water collection containing wetting behaviors and water droplet transportations is described in the beginning, i.e., the Young's equation, Wenzel model, Cassie model, surface energy gradient model and Laplace pressure equation. Then, the water collection mechanisms of three typical and widely researched natural animals and plants are discussed and their corresponding bioinspired materials are simultaneously detailed, which are cactus, spider, and desert beetles, respectively. This is followed by introducing another eight animals and plants (butterfly, shore birds, wheat awns, green bristlegrass, the Cotula fallax plant, Namib grass, green tree frogs and Australian desert lizards) that are rarely reported, exhibiting water collection properties or similar water droplet transportation. Finally, conclusions and outlook concerning the future development of bioinspired fog-collecting materials are presented.

Polyaniline (PANI) decorated commercial filtration membranes, such as stainless steel meshes (SSMs) with 5 μm pore size and polyvinylidene fluoride (PVDF) membranes with 2–0.22 μm pore sizes, were fabricated by a simple one-step dilute polymerization at low temperature. Lots of short PANI nanofibers were firmly and uniformly coated onto the membrane surfaces, forming rough micro- and nanoscale structures and leading to underwater superoleophobicity with low oil-adhesion characteristic. Furthermore, we systematically studied the effect of pore size and pressure difference on oil–water separation ability of the obtained membranes. It was found that the PANI-modified SSMs with 5 μm pore size were suitable for the separation of non-surfactant emulsions with water fluxes of more than 1000 L m−2 h−1 under gravity only. The PANI-modified PVDF membranes were used for the effective separation of surfactant-stabilized emulsions with water fluxes up to 3000 L m−2 h−1 for 2 μm pore size under 0.1 bar or 0.22 μm pore size under 0.6 bar. In addition, the superhydrophilic membranes with PANI coatings were demonstrated for high oil rejection, stable underwater superoleophobic properties after ultrasonic treatment and immersing in oils and various harsh conditions, and high and steady water permeation flux after several cycles.Polyaniline-coated filtration membranes with different pore sizes are used to effectively separate various oil-in-water emulsions with high water flux and oil rejection under gravity or a low pressure difference.

•SnO2 architectures with unitary or binary structure were tuned by a facile approach.•The samples of S1 and S2 with the specific surface area being 10.48 and 18.46 m2/g.•Both these two sensors exhibit good selectivity and high sensitiveness.•The response time of S2 sensor are both sub-20 s to 100 and 250 ppm ethanol.Different SnO2 architectures with unitary or binary structure were successfully assembled utilizing the assistance of Polyvinyl pyrrolidone (PVP). The microstructure, surface topography, specific surface area and gas sensing property were investigated with X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Brunauer–Emmett–Teller (BET) and WS-60A gas sensing apparatus, respectively. The sensing amplitude, selectivity, response time and recovery time were carefully studied. The possible mechanism of crystallization and gas sensing behavior were also discussed. The present study could be potentially applied to the ethanol or acetone detection and referenced by other researchers and engineers.Different SnO2 architectures with unitary or binary structure were successfully assembled utilizing the assistance of polyvinyl pyrrolidone.

Recycled paper with superhydrophobicity and flame-retardancy has been demonstrated here due to the synergistic action of dopamine-silica trimethylsilyl modified gel powder and stearic acid modified Mg(OH)2. This multifunctional recycled paper displays great self-cleaning and anti-fouling ability and can be used for oil-water separation. Surprisingly, the absorbed organic can be reused as fuel via simple combustion method for multiple cycles. This work will not only expand the usable range of paper but also ease the energy and environment crisis.Eco-friendly functionalized recycled paper with superhydrophobicity and flame-retardancy has been demonstrated which can put up with the invasion of water and fire. What is more, this multifunctional recycled paper display great self-cleaning and anti-fouling ability and can be used to oil-water separation. Surprisingly, the absorbed oil or organic can be reused as fuel via simple combustion method for multiple cycles.

We report a simple and rapid method to fabricate superhydrophobic films on copper substrates via Fe3+ etching and octadecanethiol (ODT) modification. The etching process can be as short as 5 min and the ODT treatment only takes several seconds. In addition, the whole process is quite flexible in reaction time. The superhydrophobicity of as-prepared surfaces is mechanically durable and chemically stable, which have great performance in oil–water separation and ice-over resistance.A chemically stable and mechanically durable superhydrophobic surface on copper substrates with excellent performance in oil spill clean and ice-over delay was fabricated.

With the development of surface science, surface with special wettability, such as reversible or gradient, gradually becomes the focus of the field of science now. Here, via a facile, green organic solvent-free route, we have fabricated superhydrophobic hybrid MWCNTs membrane on mixed cellulose ester filter with great flexibility and tailorability. Importantly, induced by acetic acid vapour and NH3 vapour without external energy, wettability of it can be reversibly switched between superhydrophobic (low adhesion) to hydrophobic (high adhesion). Furthermore, hybrid MWCNTs membrane can achieve diverse range of gradient wettability. The principle of theory behind phenomenon also has been explained through surface chemical composition and microscopic surface topography by means of Field-emission scanning electron microscope (FESEM) images, X-ray photoelectron spectroscopy (XPS) and Fourier transformer infrared spectra (FTIR) spectroscopy. This work has solved some critical problems in this field. The limitations and potential application of our work also be summarized.A superhydrophobic hybrid MWCNTs membrane on mixed cellulose ester filter with well-tunable wettability was fabricated via a facile, green organic solvent-free route.

Ongoing interest in oxide semiconductor as components of gas sensing devices is motivated by environmental monitoring and intelligent control. NiO with different precursor solution were synthesized by aqueous chemical deposition and pyrolysis process. Here the method is quite facile, green and free of surfactant. Their morphology, crystal structure and chemical composition have been systemically characterized by various techniques. Interestingly, the microstructures of NiO can be engineered by different nickel salt (nitrate or chloride). These NiO based gas sensors showed substantially enhanced responses to benzaldehyde target analyte and exhibited fast response-recover feature. The observed gas sensing behavior is explained in terms of oxygen ionosorption mechanism.The microstructures of NiO gas sensing device for benzaldehyde detection can be engineered by a quite facile, green and surfactant-free method.

Surfaces equipped with controllable wetting behaviours have received extraordinary attention recently due to their great importance in both fundamental research and practical applications. Through introducing stimuli-sensitive materials whose chemical compositions and/or topological structures can be controlled by external stimuli, different types of smart responsive surfaces that switch reversibly between superhydrophobicity and superhydrophilicity can be effectively fabricated, even though these are two fundamentally opposite wetting states. In this paper, we summarized the most frequently employed methods for the fabrication of surfaces with switchable wettability, focussing on smart materials and recent developments in this field. According to their responsiveness to different external stimuli, smart materials are divided into several groups, including photo-responsive materials, thermally responsive materials, pH-responsive materials, and electricity-responsive materials. Additionally, potential applications of smart materials, such as oil–water separation, biosensors, drug delivery and smart windows are also mentioned. Finally, current challenges for both intelligent surfaces and smart responsive materials and the future prospects for this research field are also mentioned. The purpose of this review is to give a brief and crucial overview of smart surfaces with wettability that is responsive to external stimuli.

The papermaking industry always causes many disastrous problems to humans, such as energy consumption, environmental pollution and destruction to the ecosystem. However, paper is not only one kind of life's necessities but also a necessity of the office. But the service life of paper is reduced easily because of the invasion of water. Here we creatively prepared one kind of multifunctional inner and outer uniform-superhydrophobic paper by the secondary use of waste paper inspired by nature and traditional papermaking knowledge, which not only has a great water proof ability for various liquids, but also has wonderful self-cleaning, anti-fouling and oil absorption abilities. It is worth mentioning that superhydrophobic recycled paper still has good writability, suppleness, foldability and tailorability to meet our daily needs. Unique outer and inner uniform-superhydrophobicity make this paper able to tolerate any degree of abrasion. This groundbreaking work will not only avoid harm by the water invasion and expand the usable range of paper, but also it will ease the energy and environment crisis.

•Interconnected NiCo2O4 nanoflakes were prepared by H2O-EG solvothermal synthesis.•The resultant NiCo2O4 network-like films show a honeycomb-like morphology.•They exhibit outstanding supercapacitive performance due to their specific porous structure.Honeycomb-like NiCo2O4 films consisting of interconnected nanoflakes were directly grown on conductive substrates via a H2O-EG assisted synthesis. After being annealed at different temperatures, the resultant NiCo2O4 nanoflakes possess abundant pores, which are more favorable for enhanced electrochemical properties. In particular, when evaluated as a binder-free electrode of supercapacitors, such porous structures annealed at 300 °C manifest a relatively high pseudocapacitance of 920 F/g at a very high current density of 40 A/g, the great capacitance retention at 16 A/g after 3000 charge/discharge cycles and high rate capability, which holds great promise for high-performance supercapacitors.

•The developments of several models were introduced.•A most classic mathematic method was elucidated.•The theoretical achievements on metals solid–solid interfaces were reviewed.•A new theoretical study was proposed.It is important to explain the triboligical mechanism of solid interfaces at the atomic scale. Theoretical models developments involving atomic-scale tribology and the most classical first-principles theory for atomic-scale friction have been described. The construction of potential energy surface based on first-principle calculation is found extremely useful to unveil the tribological mechanism for atomic-scale solid sheets. Furthermore, atomic-scale tribological mechanisms exploring achievements for metals interfaces, tribo-chemisty, carbon-based solid lubrication material and 2h-MoS2 have also been reviewed.

Although the superhydrophobicity and transparence are generally two contradictory characters as the roughness factor, it is literature abundant for achieving both of these two purposes. To our knowledge, the integration multipurpose (transparent, superhydrophobic, superhydrophilic, underwater superoleophobicity, anti-fogging, and photo-controllable ability) in one has not been reported so far and these are vital for their promising applications in various aspects which can attract broad attention from scholars to engineers. In this work, we are successful to bio-inspired design of a kind versatile transparent nanocoating with superhydrophobic or superhydrophilic/underwater superoleophobic properties. The TiO2/SiO2 nanocoatings can be transformed from superhydrophobicity into superhydrophilicity and underwater superoleophobicity after heat treatment (450 °C and 2 h). If it was coated on conductive glass, the electrical conductivity was impervious, while the wettability can be manipulated. Importantly, both these superhydrophobic and superhydrophilic TiO2/SiO2 composite nanocoatings were endowed with photo-induced self-cleaning nature and these antifouling coatings could prolong their service life.

In order to increase the life of spacecraft, it is important to improve the comprehensive lubrication performance. Multiple alkylated cyclopentane (MAC) lubricants are presently gaining wide acceptance for actual space applications; adding extreme pressure additive is a strategy to improve lubrication performance. In this study, taking 1,3,4-tri-(2-octyldodecyl) cyclopentane as base oil, tricresol phosphate (traditional additive) and tri-(2-octyldodecyl) phosphate (developmental additive) have been screened computationally for compatibility, shear film forming and energy dissipation. Theoretical results indicate that (a) tricresol phosphate additive is not suited for addition to 1,3,4-tri-(2-octyldodecyl) cyclopentane lubricant due to limited compatibility; (b) tri-(2-octyldodecyl) phosphate is an excellent lubricant additive due to its perfect compatibility, ease of forming a shear film on the surface of friction pairs, higher strength, and low energy dissipation; and (c) lubrication occurs through the solid-liquid composite lubrication mechanism. These theoretical results were confirmed experimentally.

Oil spills and industrial organic pollutants have induced severe water pollution and threatened every species in the ecological system. To deal with oily water, special wettability stimulated materials have been developed over the past decade to separate oil-and-water mixtures. Basically, synergy between the surface chemical composition and surface topography are commonly known as the key factors to realize the opposite wettability to oils and water and dominate the selective wetting or absorption of oils/water. In this review, we mainly focus on the development of materials with either super-lyophobicity or super-lyophilicity properties in oil/water separation applications where they can be classified into four kinds as follows (in terms of the surface wettability of water and oils): (i) superhydrophobic and superoleophilic materials, (ii) superhydrophilic and under water superoleophobic materials, (iii) superhydrophilic and superoleophobic materials, and (iv) smart oil/water separation materials with switchable wettability. These materials have already been applied to the separation of oil-and-water mixtures: from simple oil/water layered mixtures to oil/water emulsions (including oil-in-water emulsions and water-in-oil emulsions), and from non-intelligent materials to intelligent materials. Moreover, they also exhibit high absorption capacity or separation efficiency and selectivity, simple and fast separation/absorption ability, excellent recyclability, economical efficiency and outstanding durability under harsh conditions. Then, related theories are proposed to understand the physical mechanisms that occur during the oil/water separation process. Finally, some challenges and promising breakthroughs in this field are also discussed. It is expected that special wettability stimulated oil/water separation materials can achieve industrial scale production and be put into use for oil spills and industrial oily wastewater treatment in the near future.

We report a novel and facile route to synthesize a 1D needlelike CuO gas sensor utilizing simple solution-treatment, heat-treatment and sonication processes based on copper meshes (CMs) for the first time. We have demonstrated that the architectural 1D CuO sensor displays a substantial improvement of response magnitude toward a series of toxic organic molecules. We expect that our work may provide a new inspiration for synthesizing 1D semiconductor nanowires for gas sensing application.

Superoleophobic surfaces have drawn wide attention because of their special wetting behaviour. By adjusting surface chemical composition and surface structure, different kinds of superoleophobic surfaces (in air, underwater and others) can be obtained. This account mainly focuses on the recent progress of the fabrication and applications of superoleophobic surfaces. There are various methods to fabricate superoleophobic surfaces, which are generally divided into two ways. One is the top-down method, which includes etching, lithography, anodization and laser processing. The other is the bottom-up method, which contains electrodeposition, the hydrothermal method, sol–gel process and electro-spinning. However, each has its own merits and demerits. Hence, choosing the proper method in different conditions is quite important. These superoleophobic surfaces can be applied in many areas, such as self-cleaning, anti-corrosion, oil transportation, anti-bio-adhesion devices, oil capture, anti-smudge, chemical shielding, micro-droplet manipulation and oil–water separation. In fact, few of them have been put into practice. The development of superoleophobic surfaces is still in the experimental stage. Current and further challenges for superoleophobic surfaces are proposed. Beyond that, some creatures with typical structures are also referred, for instance, the lotus leaf, butterfly wing, rice leaf, desert beetle, rose petal, mosquito eyes, springtail, fish scale, shark skin, snail shell, the lower surface of the lotus leaf and a clam's shell.

There is a critical need for a practical all-solution approach to bulk-scale graphene materials, which is of great advantage for both fundamental studies and potential applications. Here we report a facile route to low-oxygen graphene nanosheets (GNs) by slight oxidation of graphite in concentrated perchloric acid. The resultant GNs can be dispersed in most polar solvents with concentrations from 2 to 20 g L−1. The good dispersibility of GNs favors investigation of their chemical properties and fabrication of transparent conductive films and high-rate supercapacitors via all-solution approaches. Compared to GO counterparts, the GN suspensions are less sensitive to the pH value and electrolyte concentration, and maintain better stability and dispersibility even after the hydrothermal reaction and hydrazine reduction. The GN film after annealing has a conductivity of as high as 1488 S cm−1, and the bandgap of GNs can be effectively opened even at low oxidation levels. Supercapacitors of GNs deposited on nickel foams allow for operations at a high rate up to 200 V s−1, and possess high capacitance and cycling stability. Our solution processing method offers a suitable way to fabricate conductive GNs with significant advantages, which creates more opportunities for various applications.

Superhydrophobic nanocoatings, a combination of nanotechnology and superhydrophobic surfaces, have received extraordinary attention recently, focusing both on novel preparation strategies and on investigations of their unique properties. In the past few decades, inspired by the lotus leaf, the discovery of nano- and micro-hierarchical structures has brought about great change in the superhydrophobic nanocoatings field. In this paper we review the contributions to this field reported in recent literature, mainly including materials, fabrication and applications. In order to facilitate comparison, materials are divided into 3 categories as follows: inorganic materials, organic materials, and inorganic–organic materials. Each kind of materials has itself merits and demerits, as well as fabrication techniques. The process of each technique is illustrated simply through a few classical examples. There is, to some extent, an association between various fabrication techniques, but many are different. So, it is important to choose appropriate preparation strategies, according to conditions and purposes. The peculiar properties of superhydrophobic nanocoatings, such as self-cleaning, anti-bacteria, anti-icing, corrosion resistance and so on, are the most dramatic. Not only do we introduce application examples, but also try to briefly discuss the principle behind the phenomenon. Finally, some challenges and potential promising breakthroughs in this field are also succinctly highlighted.

Controlling oil of wettability behavior in response to the underwater out stimulation has shown promising applications in understanding and designing novel micro- or nanofluidic devices. In this article, the pH-manipulated underwater–oil adhesion wetting phenomenon and superoleophobicity on the micro- and nanotexture copper mesh films (CMF) were investigated. It should be noted that the surface exhibits underwater superoleophobicity under different pH values of the solution; however, the underwater–oil adhesion behavior on the surface is dramatically influenced by the pH value of the solution. On the basis of the thermodynamic analysis, a plausible mechanism to explain the pH-controllable underwater–oil adhesion and superoleophobic wetting behavior observed on a micro- and nanoscale semicircular structure has been revealed. Furthermore, variation of chemistry (intrinsic oil contact angle (OCA)) of the responsive surface that due to the carboxylic acid groups is protonated or deprotonated by the acidic or basic solution on free energy (FE) with its barrier (FEB) and equilibrium oil contact angle (EOCA) with it hysteresis (OCAH) are discussed. The result shows that a critical intrinsic OCA on the micro- and nano- semicircular texture is necessary for conversion from the oil Cassie impregnating to oil Cassie wetting state. In a water/oil/solid system, the mechanism reveals that the differences between the underwater OCA and oil adhesive force of the responsive copper mesh film under different pH values of solution are ascribed to the different oil wetting state that results from combining the changing intrinsic OCA and micro-/nanosemicircular structures. These results are well in agreement with the experiment.Keywords: Cassie impregnating; equilibrium oil contact angle; free energy; oil adhesion; superoleophobic;

We established four kinds of good dispersing systems of graphene and its derivatives with different structural characteristics to estimate their peroxidase-like activity. Besides graphene oxide (GO), it is demonstrated that defect-free graphene, low-oxygen graphene, and iron(III)-doped graphene oxide (GO-Fe) are all capable of H2O2 activation to oxidize peroxidase substrates. As for defect-free graphene, the dispersibility in reaction medium exerts great impact on its catalytic activity and our further judgements concerning the nature of active sites. Improved stability and further exfoliation of defect-free graphene in reaction medium are beneficial to the access of reactants to active sites on the basal planes and enhance its peroxidase-like activity, which is superior to that of low-oxygen graphene and much higher than that of GO. In addition, their peroxidase-like activity can be greatly inhibited by the addition of iron chelators. Interestingly, the introduction of trace ferric ions into GO does not lead to an apparent change except for remarkable increase of its peroxidase-like activity. Therefore, we propose that the observed iron impurities rather than the doped nonmetallic heteroatoms play an important role in the peroxidase-like activity of graphene and its derivatives. In this light, saturated iron(III) was immobilized onto the oxygen-donor coordination of GO to immensely promote its activity. The peroxidase-like activity of the prepared GO-Fe was systematically evaluated by using 3,3′,5,5′-tetramethylbenzidine and pyrogallol as peroxidase substrates and was compared to that of horseradish peroxidase and hemin. As a result, GO-Fe shows excellent peroxidase-like catalytic activity, which is comparable to that of hemin. Furthermore, GO-Fe was used for the quantitative detection of H2O2 and glucose.Keywords: defect-free graphene; graphene oxide; iron-doped graphene oxide; low-oxygen graphene; peroxidase-like activity;

Inspired by mussels we designed a novel green superhydrophobic gel nanocoating with good transparency and stability through a facile copolymerization reaction at room temperature and a subsequent trimethyl silyl modified process, which is applicable to various substrates via a simple spray process without requiring toxic substances. Importantly, this well-designed nanocoating has rapid self-healing superhydrophobicity induced by usual organic solvents to face complicated work conditions, which satisfies the need of daily life and can be applied in industry as well.

As important and irreplaceable engineering materials, metals are widely used in our daily life. Therefore, fabricating superhydrophobic surfaces on metal materials is of great significance, and applicable methods for industrial production are in urgent need. In this work, we provide a rapid and easy route for fabricating superhydrophobic films on metal materials through simple displacement deposition. This method includes two simple steps with each step being as short as one second. The obtained superhydrophobic surfaces are homogeneous and easy to repair. A miniature boat and a miniature box were used to test the buoyancy-increasing and oil absorption properties, respectively. This method is feasible for massive production of superhydrophobic metal materials applied to water transportation and oil spill clean-up areas.

It is well known that high optical transparency is one of the most crucial criteria for the overwhelming majority of optical devices and correlative functions, including smart windows, camera lenses, solar cell systems and optoelectronic devices. With the frequent exposure of this equipment to all sorts of environments, such as outdoor conditions, a surface with self-cleaning properties can guard against fouling, humidity, bacterial growth and so forth. That is one type of application of the big family of superhydrophobic coatings. Therefore, integrating high transparency with self-cleaning characteristics is of great importance for such applications. In this review, the recent developments in designing, synthesizing and manufacturing transparent and superhydrophobic surfaces are reviewed. Firstly, the established theoretical aspects of surface wetting properties are summarized and then several natural and bio-inspired superhydrophobic surfaces of diverse microcosmic structures are presented as representative examples. With a focus on distinctively employed materials and the corresponding fabrication of superhydrophobic coatings with high transparency, the promising research directions and application prospects of this rapidly developing field are briefly addressed as well.

In this work, non-doped SnO2 samples, and SnO2 samples doped with Zn(II), Cu(II), or Mn(II), having hierarchical microstructures, were prepared using an otherwise identical hydrothermal process, followed by annealing. The morphological and structural characteristics of the samples were systematically characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) measurements, and X-ray photoelectron spectroscopy (XPS). Ten gas sensors were constructed from each material, and compared as to detection of gas-phase ethanol, acetone, glacial acetic acid, methanol, and ammonia. The results indicated, for example, that SnO2 containing 2.91% Mn dopant exhibited a 2.5-fold higher gas detection response toward ethanol at 100 ppm than that of the non-doped material. The fastest response time for 100 ppm ethanol was found for Cu(II)-doped SnO2 (9.7 s), compared with 12.4 s for non-doped SnO2. Graphs of sensor response versus operating temperature for SnO2 containing different types and quantities of dopant exhibited quite different morphologies. The gas-sensing mechanism appears to involve reactions between the detected gases and the various oxygenous ions, such as O, O2−, and O2−, present at the surface of the sensor.

It has been revealed experimentally that some superhydrophobic surfaces in nature, such as rice leaf, show strong anisotropic wetting behavior. In this work, based on a thermodynamic approach, the effects of profile shape of parallel grooved microstructure on free energy (FE) with its barrier (FEB) and equilibrium contact angle (ECA) with its hysteresis (CAH) for various orientations of different parallel micro texture surface have been systematically investigated in detail. The results indicated that the anisotropy of wetting properties strongly depended on the specific topographical features and wetting state. In particular, a paraboloidal profile of parallel micro-texture surface is used as an important example to theoretically establish the relationship between surface geometry and anisotropic wetting behavior for optimal design, showing that the wetting behavior of the composite state is similar to that of the non-composite state and the anisotropy will possibly be appeared with the decrease of height or intrinsic contact angle of paraboloidal profile of micro texture.

Frequent oil spillages and the industrial discharge of organic solvents have caused severe environmental and ecological damage. Besides, as another common phenomenon in industry, corrosion of various active metals is of great importance in deciding the service life of such materials. Therefore, for the sake of solving such problems, it is imperative, but also challenging, to find suitable materials with good performance. On the other hand, the complicated fabrication procedures generally hinder practical applications of superhydrophobic and superoleophilic materials. Here, we present a simple method for preparing a three-dimensional material based on a commercially available sponge and other substrates functionalized by depositing nanoscale polypyrrole (PPy) particles, which is followed by modification of a low-surface-energy material such as fluoroalkylsilane (FAS). Such superhydrophobic samples can efficiently separate oils and organic solvents from water and are endowed with good anti-corrosion properties of several metals to a greater extent as well.

Here we demonstrated that high-content nitrogen endowed polyaniline (PANI) and polypyrrole (PPy) have not only a doping–dedoping ability but also an inherent hydrophilic property. Combining their rigid chain structures, rough surfaces can be easily achieved by uniformly and firmly coating PANI and PPy onto the surfaces of stainless steel meshes via a simple modified dilute polymerization. Compared to the pristine meshes, the modified meshes become hydrophilic in air and superoleophobic underwater, and maintain stability in various harsh conditions. Taking advantage of this unique wetting feature, PANI and PPy coated meshes were used to separate mixtures of oil and water efficiently.

The mixed modifiers of methyl-terminated thiol and carboxyl-terminated thiol were successfully assembled on stainless steel meshes (SSM) utilizing polydopamine as the adhesion layer and the strong thiol ligand with Ag. The microstructure, surface topography, chemical composition and wettabilities were investigated with X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS) and contact angle meter, respectively. Importantly, the surface modified by mixed thiol show different responsive behavior to nonbasic and basic water droplets. Plus, the selectiveness of high water–oil repellence reveals the unique and smart tendencies of as-prepared functional stainless steel mesh. The reversible pH-response and stability have also been investigated. Based on stainless steel material widely used in engineering, this prepared smart material is expected to be used in many industrial applications, such as pH controllable dual oil–water on–off switch and diversified oil–water separation.

Metal nanoparticles are known as extremely hydrophilic substances due to their high surface energy. Hydrophobic properties of the metal nanoparticles can be realized only if the nanoparticles are pretreated with low-surface-energy chemicals. In this paper, two adjacent transition metals, i.e. Fe and Co, were selected and coated on a commercially available fabric via a facile in situ growth method. n-Octadecyl thiol, which possesses low surface energy, was selected as the modifier to obtain a superhydrophobic–superhydrophilic hybrid fabric depending on the thiol's selective modification to Fe and Co nanoparticles on the fabric. The surface Co nanoparticles can be modified by n-octadecyl thiol and transform to hydrophobic nanoparticles; however, the surface Fe nanoparticles could not be modified by n-octadecyl thiol in our experimental condition; thus, they retained the hydrophilic property. An as-prepared fabric with these two kinds of nanoparticles evenly distributed on the surface is termed as a superhydrophobic–superhydrophilic hybrid fabric because it shows superhydrophobic property and possesses many superhydrophilic spots. This material is expected to realize water harvesting similar to the desert beetle that collects micro droplets of water from the morning fog without using any external energy source.

Hydrophilic graphene oxide (GO) nanosheets can be easily coated onto stainless steel meshes. Compared to neat meshes, GO coated meshes become more hydrophilic in air and superoleophobic under water. Taking advantage of this completely opposite wettability, GO coated meshes were used for gravity-driven oil–water separation.

The adhesion behaviors of superhydrophobic surfaces have become an emerging topic to researchers in various fields as a vital step in the interactions between materials and organisms/materials. Controlling the chemical compositions and topological structures via various methods or technologies is essential to fabricate and modulate different adhesion properties, such as low-adhesion, high-adhesion and anisotropic adhesion on superhydrophobic surfaces. We summarize the recent developments in both natural superhydrophobic surfaces and artificial superhydrophobic surfaces with various adhesions and also pay attention to superhydrophobic surfaces switching between low- and high-adhesion. The methods to regulate or translate the adhesion of superhydrophobic surfaces can be considered from two perspectives. One is to control the chemical composition and change the surface geometric structure on the surfaces, respectively or simultaneously. The other is to provide external stimulations to induce transitions, which is the most common method for obtaining switchable adhesions. Additionally, adhesion behaviors on solid–solid interfaces, such as the behaviors of cells, bacteria, biomolecules and icing on superhydrophobic surfaces are also noticeable and controversial. This review is aimed at giving a brief and crucial overview of adhesion behaviors on superhydrophobic surfaces.

Open porous NiO films prepared by a simple green solvothermal approach on ITO/glass substrate show a high-rate specific capacitance, Coulombic efficiency of ≈100% at high current rates and good cycling stability, suggesting their promising application in supercapacitors.

•Using the wetting criteria, paraboloid microtexture is considered as optimal microtexture for ideal superhydrophobicity.•How all geometrical parameters for paraboloid microtexture affect superhydrophobic behavior is presented.•Such a paraboloid microtexture has excellent mechanical and controllable fabrication properties.Due to the crucial role of surface roughness, it has been recently proposed to design optimal and extract geometrical microstructures for practical fabrications of superhydrophobic surfaces. In this work, a paraboloid microtexture is employed as a typical example to theoretically establish a relationship between surface geometry and superhydrophobic behavior for a final optimal design. In particular, based on a thermodynamic approach, the effects of all the geometrical parameters for such a paraboloid microtexture on free energy (FE) and free energy barrier (FEB) as well as equilibrium contact angle (ECA) and contact angle hysteresis (CAH) of a superhydrophobic surface have been systematically investigated in detail. It is interestingly noted that the droplet position for metastable state is closely related to the intrinsic CA of the surface. Furthermore, the paraboloid base steepness plays a significant important role in ECA and CAH, and a critical steepness is necessary for the transition from noncomposite to composite states, which can be judged using a proposed criterion. Moreover, the superhydrophobicity depends strongly the surface geometrical dimension for noncomposite state, while it is not sensitive for composite state. Additionally, both vibrational energy and geometrical dimension affect the transition from noncomposite to composite wetting states, and a comprehensive criterion for such transition can be obtained. Finally, using such criterion, it is revealed that the paraboloidal protrusion is the most optimal geometry among the three typical microtextures for ideal superhydrophobicity.

The micro erosion processes of atomic oxygen for 1,3-didecyl cyclopentane and 1,3-dioctyldodecyl cyclopentane lubricants have been investigated by using a Reaxff molecular dynamics method. Simulation results showed that the creation of H2, CO, and CO2 is the main reason for the quality loss of lubricants. O-atom addition and H abstraction are the main mechanisms. Furthermore, singlet and triplet atomic oxygen erosion mechanisms for two kinds of alkylated cyclopentanes have been investigated utilizing density functional theory (DFT) methods. DFT calculation demonstrated that different spin states of atomic oxygen correspond to different erosion mechanisms, and no non-adiabatic reaction phenomenon appears. Alkylated cyclopentanes are damaged by insertion of triplet oxygen atoms among the C–C bonds, the branched chain in alkylated cyclopentane is easier to be removed due to the lower activation barrier. Erosion products are H, CO, CO2, and CH2O, organic oxygen radicals are the main intermediates in the 3O erosion process. However, 1O erosion originates from the elimination mechanism and the extent of lubricant degradation is lower. Finally, the diffusion coefficient of atomic oxygen in 1,3-didecyl cyclopentane is 1.63 times that of 1,3-dioctyldodecyl cyclopentane, which is the fundamental reason for the 1,3-dioctyldodecyl cyclopentane having better atomic oxygen resistance performance.

Utilizing the strong coordination interactions between phenolic hydroxyls of polydopamine (Pdop) and silver oxide nanoparticles (Ag2O NPs), Ag2O NPs were successfully assembled on a dual-layer film composed of a polydopamine outer layer and 3-aminopropyltriethoxy silane (APS) sub-layer, on silicon (Si) substrate. The morphologies, structures and chemical compositions of Ag2O NPs and the tri-layer film were confirmed by various instruments, including ultraviolet absorption spectrum (UV), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Furthermore, the micro adhesion forces and macro tribological performances were evaluated using AFM and UMT-2M tribometer (CETR), respectively. The results indicated that the tri-layer film displays favourable friction reduction and wear resistance ability. Hence, this renders the self-assembly attractive for constructing the multilayer-structure films with favourable tribological performances for nano/microelectromechanical systems (NEMS/MEMS).

•The latest methods to fabricate encapsulated cells were discussed.•Examples of different types of artificial shells were listed.•Their advantages and disadvantages were compared.•The biomedical applications of encapsulated cells were also described.In nature, most single cells do not have structured shells to provide extensive protection apart from diatoms and radiolarians. Fabrication of biomimetic structures based on living cells encapsulated with artificial shells has a great impact on the area of cell-based sensors and devices as well as fundamental studies in cell biology. The past decade has witnessed a rapid increase of research concerning the new fabrication strategies, functionalization and applications of this kind of encapsulated cells. In this review, the latest fabrication strategies on how to encapsulate living cells with functional shells based on the diversity of artificial shells are discussed: hydrogel matrix shells, sol-gel shells, polymeric shells, and induced mineral shells. Classical different types of artificial shells are introduced and their advantages and disadvantages are compared and explained. The biomedical applications of encapsulated cells with particular emphasis on cell implant protection, cell separation, biosensors, cell therapy and tissue engineering are also described and a recap of this review and the future perspectives on these active areas is given finally.This tutorial review describes the development of novel methods for encapsulation of biological cells with polymers and nanomaterials, focusing on the areas of potential applications of functionalized cells.

One-dimensional (1D) titania (TiO2) in the form of nanorods, nanowires, nanobelts and nanotubes have attracted much attention due to their unique physical, chemical and optical properties enabling extraordinary performance in biomedicine, sensors, energy storage, solar cells and photocatalysis. In this review, we mainly focus on synthetic methods for 1D TiO2 nanostructures and the applications of 1D TiO2 nanostructures in dye-sensitized solar cells (DSCs). Traditional nanoparticle-based DSCs have numerous grain boundaries and surface defects, which increase the charge recombination from photoanode to electrolyte. 1D TiO2 nanostructures can provide direct and rapid electron transport to the electron collecting electrode, indicating a promising choice for DSCs. We divide the applications of 1D TiO2 nanostructures in DSCs into four parts, that is, 1D TiO2 nanostructures only, 1D TiO2 nanostructure/nanoparticle composites, branched 1D TiO2 nanostructures, and 1D TiO2 nanostructures combined with other materials. This work will provide guidance for preparing 1D TiO2 nanostructures, and using them as photoanodes in efficient DSCs.1D TiO2 nanostructures which can provide direct and rapid pathways for electron transport have promising applications in dye-sensitized solar cells (DSCs). The synthetic methods and applications of 1D TiO2 nanostructures in DSCs are summarized in this review article.

•Facile fabrication of dual-functional Fe3O4@PDA-FS microspheres.•The product has the properties of mechanical stability and easy-repairability.•Desirable magnetic response, high absorption capacity and excellent recyclability.•Potential applications in smart microfluidic systems and solving oil leakage.Functional Fe3O4@polydopamine (Fe3O4@PDA) core shell composite microspheres with magnetic response and special wetting properties were successfully assembled utilizing the strong coordination interactions between these two versatile materials. The microstructures, morphologies, and chemical constitute of the synthesized Fe3O4 microspheres and Fe3O4@PDA core shell composite microspheres were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), transmission electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), respectively. It was demonstrated that the as-obtained product with designed functionality has favorable superhydrophobic and superparamagnetic properties, showing significant advantages in both magnetic control behavior and oil/water separation. Therefore, the study of Fe3O4@PDA in this perspective is of great importance for environmental friendly-related and transportation of fluid in micro-fluidic system applications.Fe3O4@PDA-FS composite microspheres with magnetic responsive and superhydrophobic properties were successfully prepared by a general route and possessed high absorption capacity and excellent recyclability for oil/water separation.

•MFI-type zeolite membranes were synthesized by the seed growth hydrothermal method.•The separation of oil/water mixture was demonstrated by the contact angle and movie.•The film can be used for several times keeping the high separation efficiency.Silicalite-1 (structure type MFI), an important type of zeolite, was prepared on the porous stainless steel wire by seed growth hydrothermal synthesis, forming an amazing film. The coated film consists of well-intergrown crystals with hexagonal prismatic shape (coffin shape), which shows superamphiphilic in air and superoleophobic underwater. This prepared film can effectively collect the oil from oil/water mixture underwater driven by gravity for several times, showing good durability and high separation efficiency, which is very helpful in the promising application of energy-efficient membrance for reducing the environmental impacts of oil spills. This work provides an alternative solution to current separation mesh based-on the surface wettability.

Graphene as an important two-dimensional one-atom-thick nanosheet can be regarded as a solid and also a molecule. In this paper, we focused attention on the coordination ability of doping-induced defects, micro-scale size and atomic thickness of graphene, and anchored oxygen-donor coordination of graphene oxide to ferric ions, forming a giant flat iron complex. As well as graphene oxide, as-obtained graphene oxide–Fe(III) complexes were characterized by transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and so on. It was demonstrated that graphene oxide–Fe(III) complexes could be well dispersed in water, with size up to micrometers and atomically thin. Under visible-light irradiation, graphene oxide–Fe(III) complexes displayed homogeneous catalytic ability of H2O2 activation, and could be easily removed by simple filtration or centrifugation, showing significant advantages in both homogeneous and heterogeneous catalysis.

Solid surfaces possessing both superhydrophobic and superoleophilic properties have attracted significant interest in fundamental investigations and potential applications in the fields of self-cleaning surfaces, oil/water separation, and microfluidic channels. In this paper, a general methodology for robust superhydrophobic fabrics and sponges was proposed via the in situ growth of both transition-metal oxides and metallic nanocrystals, including the simple neutralization reaction and oxidation–reduction reaction. The porous surfaces coated with Group VIII and IB nanocrystals (such as Fe, Co, Ni, Cu, and Ag) can not only present multiscale surface roughness, but also readily coordinate with thiols, leading to special wettability. In our previous work, it has been confirmed that the interaction between the nanocrystals and thiols plays a significant role in the introduction of hydrophobic ingredients. In this work, it has been demonstrated that the efficient control of the nucleation and growth of Group VIII and IB nanocrystals on the porous surfaces becomes the key factor in the formation of multiscale surface roughness, resulting in the achievement of controllable special wettability. In addition, these as-prepared superhydrophobic and superoleophilic fabrics and sponges were successfully used for application in oil/water separation.Keywords: fabric; in situ growth; oil/water separation; sponge; superhydrophobic; thiol;

A superhydrophobic copper mesh film (CMF) with pH-responsive property was synthesized via an electrochemical deposition strategy, followed by Au sputter-coating process and surface modification with a thiol mixture of HS(CH2)9CH3 and HS(CH2)10COOH. As-prepared CMF can be applied to separate an oil-and-water mixture bidirectionally.

A thin film of polyaniline (PANI) nanofibers on the stainless steels with fluoro-thiol modification was prepared through an optimal polymerization time of aniline using HClO4 as a dopant, showing robust superhydrophobic, transparent and anti-fingerprint properties.

•Natural color effects found in nature that are fascinating are pointed out.•Research progress on the fabrication methods of photonic crystals is presented.•Some possible applications for the photonic structures are described.•The prospects for the future development of these materials are introduced.Nature is a huge gallery of art involving nearly perfect structures and forms over the millions of years developing. Inspiration from natural structures exhibiting structural colors is first discussed. We give some examples of natural one-, two-, and three-dimensional photonic structures. This review article presents a brief summary of recent progress on bio-inspired photonic materials with variable structural colors, including the different facile and efficient routes to construct the nano-architectures, and the development of the artificial variable structural color photonic materials. Besides the superior optical properties, the excellent functions such as robust mechanical strength, good wettability are also mentioned, as well as the technical importance in various applications. This review will provide significant insight into the fabrication, design and application of the structural color materials.Graphical abstract

In this paper, polyaniline nanofibers were deposited on the surface of fabrics and generated a rough structure similar to the micromorphology of a lotus leaf via the oxidative chemical polymerization of aniline. After modification with n-octadecyl thiol, water-repellent fabrics were obtained. Interestingly, the as-prepared fabrics showed stable and robust superhydrophobic properties towards many corrosive solutions (acidic, basic, salt liquids), hot water, and mechanical abrasion. In addition, it was proven that this method can also be applied to other porous materials with different pore diameters and chemical compositions, such as stainless steel meshes with different pore diameters and sponges. More importantly, the as-obtained diverse superhydrophobic/superoleophilic porous materials can successfully and effectively be applied to separate oil-and-water mixtures. It is expected that this general route to fabricating superhydrophobic porous materials could have many more practical applications, especially in oil/water separation.

•Novel thermo-responsive hollow silica microgels (THSMGs) were prepared.•The porosity is still in the THSMGs after the coverage of PNIPAAm gels.•THSMGs possess good thermosensitive performance in spite of rigid silica layer.•THSMGs have good biocompatibility and achieve controlled release of RHB.•THSMGs are a type of promising targeted drug delivery carriers.Thermo-responsive hollow silica microgels (THSMGs) consisting of a hollow core, an intermediate silica supporting layer and a smart polymer gel corona were fabricated via organic–inorganic hybridization. Hollow silica particles and PNIPAAm microgels were successfully combined by utilizing the cross-linking reaction between 3-(trimethoxysilyl) propyl methacrylate (TMSPMA) and silanol groups on the silica surface, and then the copolymerization of TMSPMA and N-isopropylacrylamide (NIPAAm). The morphology and chemical composition were systematically examined by field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), energy dispersive X-ray spectroscopy (EDS) and the Brunauer–Emmett–Teller (BET) measurement. The thermo-responsive phase transition behavior was investigated by the determination of the lower critical solution temperature (LCST), and particle size measurement using dynamic light scattering. THSMGs remain porous even after the coverage of PNIPAAm gels, and also have obvious hydrophilic/hydrophobic transition property and good swelling/collapse capability in spite of the rigid silica layer. The results of in vitro cytotoxicity evaluation and Rhodamine B (RHB) release study demonstrated that THSMGs have good biocompatibility, and achieve a thermo-responsive controlled-release behavior. The prepared THSMGs show considerable potential for applications as targeted and ambient temperature responsive drug delivery system.

The mechanisms of activation of CH4 catalyzed by 1/3Hf2+ and oxidation of CO by N2O catalyzed by 1/3HfO2+ or 2/4TaO2+ have been investigated using the B3LYP level of theory. For the activation of methane, the TSR (two-state reactivity) mechanism has been certified through the spin–orbit coupling (SOC) calculation and the Landau–Zener-type model. In the vicinity of the minimum energy crossing point (MECP), SOC equals 900.23 cm–1 and the probability of intersystem crossing is approximately 0.62. Spin inversion makes the activation barrier decline from 1.63 to 0.57 eV. NBO analysis demonstrates that empty 6s and 5d orbitals of the Hf atom play the major role for the activation of C–H bonds. Finally, CH4 dehydrogenates to produce Hf–CH22+. For oxidation of CO by N2O catalyzed by HfO2+ or TaO2+, the covalent bonds between transition metal atoms and the oxygen atom restrict the freedom of valence electrons. Therefore, they are all SSR (single-state reactivity). The oxygen atom is directly extracted during the course of oxygen transfer, and its microscopic essence has been discussed. The detailed kinetic information of two catalytic cycles has been calculated by referencing the “energetic span (δE)” model. Finally, TOF(HfO2+)/TOF(TaO2+) = 2.7 at 298.15 K, which has a good consistency with the experimental result.

The underlying theories interpreting wetting phenomena are still mainly focused on the Young's equation, the Wenzel equation, and the Cassie–Baxter equation, despite the fact that wetting phenomena have been studied over the past decades. Based on these theories, people have understood that both surface chemical composition and its morphology can influence the contact angle of liquid droplets on solid surfaces. However, such equations are not sufficient to thoroughly explain the mechanisms of wetting phenomena, although they are still necessary. In this feature article, we review the theory, from the classical wetting models to the most recent theoretical advances, of superhydrophobic surfaces with regard to the wetting process, and some promising breakthroughs in the advance of the theory are proposed in the final section.

Stable superhydrophobic coatings were successfully achieved from thiol-ligand nanocrystals. Nanocrystals included VIII and IB metals and oxide nanoparticles, such as Fe, Co, Ni, Cu and Ag. We present a simple and available method that facilitates the synthesis of superhydrophobic textiles and sponges, in which the interaction between the nanocrystals and thiol plays a significant role in the formation of a special wetting surface. Meanwhile, the superhydrophobic textiles could also be endowed with new functionalities. For example, textiles with Fe3O4 nanocoatings possess magnetic properties, and Ag nanocrystals provide an antibacterial effect. If perfluoroalkyl thiol was used to replace alkyl thiol, the as-modified surfaces became oleophobic from superoleophilic. The proposed strategy was fit for various nanoparticles from as-established methods, including the preparation in different polar solvents, and the usage of surfactants as capping agents. As-prepared superhydrophobic nanocoatings show good durability towards hot water, surfactant aqueous solutions, and ultrasonic treatment in nonpolar solvents. The superhydrophobic and superoleophilic nanocoatings were effectively used for application in oil/water separation.

It is well known that properties of materials are largely determined by their structures. Here we introduce the special double-structural materials, which are composed of micrometre and nanometre building blocks and commonly exist in nature. This review mainly focuses on recent developments of double-structural and functional materials with special wettability. We highlight excellent properties possessed by micro- and nanostructures which initially originated from the organisms with special functions in the biological world. The excellent properties shown by such structures are discussed in three parts: special wettability, mechanical properties, and optical properties, primarily including superhydrophobicity, superhydrophilicity, superoleophobicity, low and high adhesion, low friction, structural color, antireflection and so on. We will also briefly address the research prospects and directions of micro- and nano-structures. Further study on the relationship between structures and properties will be conducive to better transfer micro- and nanostructures to the engineering materials so as to obtain desired performances and a wide range of applications.

Tribological phenomena abundantly exist in living beings, especially in human beings, such as in teeth, eyes, bones, skins, heart valves and so on, and it is meaningful to reveal the mechanism of tribology in human body and fabricate artificial biomaterials to replace the damaged tissues to release the pain of patients. Alloys, ceramics and polymers are three uppermost materials used in engineering and some of them play a crucial role in biomedicine. In the paper, we provide an overview of the tribological behaviors of artificial biomaterials including alloys, ceramics and polymers. We aim to provide fundamental mechanistic and applications of tribological biomaterials, while emphasizing the advantages and disadvantages of various kinds of tribological biomaterials. Finally, some challenges and the potential promising breakthroughs are also succinctly highlighted in this field.

Nature is a huge gallery of art involving nearly perfect structures and properties over the millions of years of development. Many plants and animals show water-repellent properties with fine micro-structures, such as lotus leaf, water skipper and wings of butterfly. Inspired by these special surfaces, the artificial superhydrophobic surfaces have attracted wide attention in both basic research and industrial applications. The wetting properties of superhydrophobic surfaces in nature are affected by the chemical compositions and the surface topographies. So it is possible to realize the biomimetic superhydrophobic surfaces by tuning their surface roughness and surface free energy correspondingly. This review briefly introduces the physical-chemical basis of superhydrophobic plant surfaces in nature to explain how the superhydrophobicity of plant surfaces can be applied to different biomimetic functional materials with relevance to technological applications. Then, three classical effects of natural surfaces are classified: lotus effect, salvinia effect, and petal effect, and the promising strategies to fabricate biomimetic superhydrophobic materials are highlighted. Finally, the prospects and challenges of this area in the future are proposed.

As the frequent oil spill accidents happens and large quantities of oily wastewater from all kinds of industries are being discharged, the environment has been seriously polluted and our living areas have been horribly threatened. To deal with these issues, attentions have been aroused on the treatments of the oily wastewater. Recently, numerous superwettable materials have been fabricated. In this review, we summarize the new development of the materials for the separation of oil/water mixtures, mainly including the immiscible and emulsified mixtures. For the separation of immiscible ones, special materials with fixed wettability are firstly detailed, where three types of materials can be classified based on their wettability, i.e. superhydrophobic and superoleophilic materials, superhydrophilic and underwater superoleophobic materials, and superhydrophilic and superoleophobic materials. Then, the smart materials with switchable wettabilities responsive to external stimulus, for instance, light, solvent, pH, temperature, and electrical potential, are presented. Meanwhile, the single, dual, and multiple stimulus-responsive materials are also described. As for the separation of emulsified oil/water mixtures, the materials for the separation of water-in-oil (W/O), oil-in-water (O/W), and both water-in-oil (W/O) and oil-in-water (O/W) emulsions are sequentially introduced. Finally, some challenges are discussed and the outlook in this filed is proposed.

The aim of this paper is to characterize the microrelief and wettability of lotus leaf, waterlily leaf and biomimic ZnO surface with potential engineering applications. The characterizations of morphologies reveal that the top surface of lotus leaf is textured with 4 μm – 10 μm size protrusions and 70 nm – 100 nm nanorods, while the top surface of waterlily leaf is textured with wrinkle and decorated with concave coin-shaped geometric structure. The wettabilities of water and oil on lotus leaf and waterlily leaf under different surroundings were systematically researched. It is indeed interesting that the leaves of the two typical plants both living in the aquatic habitats possess opposite wettabilities: superhydrophobicity for top surface of lotus leaf (156°) while quasi-superhydrophilicity for top surface of waterlily leaf (15°). We have succeeded in fabricating the superhydrophobic ZnO nanorods semiconductor material (151°) employing a simple method inspired by the detailed structures and chemical composition of lotus leaf.

Oilseed rape, widely cultivated all over the world, plays an important role for our daily life due to its high nutritional and economic values. In this paper, for the first time we discuss the surface wettability of oilseed rapes with special surface structures. It is found that the fresh rape flowers are superhydrophobic with a low Adhesion Force (AF), showing the self-cleaning properties similar to lotus leaves. In contrast, the fresh rape leaves also exhibit hydrophobicity but a high AF, which resemble rose petals. Furthermore, we study the effect of storage time on the wetting properties of rape leaves. The high hydrophobicity of rape leaves gradually switches to hydrophilicity. Meanwhile, the AF intensely increases after placement at room temperature for 10 days. This research offers a profound inspiration to artificially fabricate biomimetic materials with high hydrophobicity and different adhesion characterizations.

Superhydrophobic materials have drawn great attention due to its’ remarkable non-wetting properties and applications in many fields. In this paper, we synthesize a hollow superhydrophobic SiO2 powder by typical template method and self-assembly functionalization. Robustness of many superhydrophobic surfaces has become the development bottleneck for industrial applications. Aiming at this problem, the adhesive epoxy resin is specially taken to use as the binding layer between superhydrophobic SiO2 powder and substrates to create robust superhydrophobic coating. The mechanical durability of the obtained superhydrophobic coating is evaluated by a cyclic sandpaper abrasion. Also, the chemical stability of this superhydrophobic coating is assessed by exposuring it to different pH conditions and UV irradiation, respectively. Significantly, because of the special structure and superhydrophobicity/superoleophilicity of the hollow microspheres, these hollow superhydrophobic SiO2 powders manifest great oil-adsorbing capacity, which thus can be used to separate oil/water mixtures and remove oil from oil-in-water emulsions.Multifunctional hollow superhydrophobic SiO2 microspheres created by template method and self-assembly functionalization can be used in stable superhydrophobic coating and removal of oil from water.Figure optionsDownload full-size imageDownload high-quality image (76 K)Download as PowerPoint slide

Paper is kind of essential materials in our daily life. However, it can be easily destroyed by water owing to its superhydrophilic surface. Here, we reported a simple and green fabrication of coloured superhydrophobic paper via swelling and approximate dissolution of cotton followed by precipitation of cellulose and doping coloured stearates. The obtained paper exhibited uniform colour and superhydrophobicity, of which the colour was consistent with the doped stearates owing to the adhesion of stearate powders to the tiny floc fiber surface and we proved that the superhydrophobicity could not be damaged after abrasion resulting from the inner and outer superhydrophobicity and the increased surface roughness. This coloured superhydrophobic paper would be avoided from moisture damage and may be useful in different fields.The green coloured superhydrophobic paper was fabricated from native cotton cellulose via swelling and approximate dissolution of cotton followed by precipitation of cellulose and doping coloured stearates. The process contains no toxic modifier and the obtained paper exhibits satisfactory inner and outer uniform superhydrophobicity and colour.

The adhesion behaviors of superhydrophobic surfaces have become an emerging topic to researchers in various fields as a vital step in the interactions between materials and organisms/materials. Controlling the chemical compositions and topological structures via various methods or technologies is essential to fabricate and modulate different adhesion properties, such as low-adhesion, high-adhesion and anisotropic adhesion on superhydrophobic surfaces. We summarize the recent developments in both natural superhydrophobic surfaces and artificial superhydrophobic surfaces with various adhesions and also pay attention to superhydrophobic surfaces switching between low- and high-adhesion. The methods to regulate or translate the adhesion of superhydrophobic surfaces can be considered from two perspectives. One is to control the chemical composition and change the surface geometric structure on the surfaces, respectively or simultaneously. The other is to provide external stimulations to induce transitions, which is the most common method for obtaining switchable adhesions. Additionally, adhesion behaviors on solid–solid interfaces, such as the behaviors of cells, bacteria, biomolecules and icing on superhydrophobic surfaces are also noticeable and controversial. This review is aimed at giving a brief and crucial overview of adhesion behaviors on superhydrophobic surfaces.

Hydrophilic graphene oxide (GO) nanosheets can be easily coated onto stainless steel meshes. Compared to neat meshes, GO coated meshes become more hydrophilic in air and superoleophobic under water. Taking advantage of this completely opposite wettability, GO coated meshes were used for gravity-driven oil–water separation.

There is a critical need for a practical all-solution approach to bulk-scale graphene materials, which is of great advantage for both fundamental studies and potential applications. Here we report a facile route to low-oxygen graphene nanosheets (GNs) by slight oxidation of graphite in concentrated perchloric acid. The resultant GNs can be dispersed in most polar solvents with concentrations from 2 to 20 g L−1. The good dispersibility of GNs favors investigation of their chemical properties and fabrication of transparent conductive films and high-rate supercapacitors via all-solution approaches. Compared to GO counterparts, the GN suspensions are less sensitive to the pH value and electrolyte concentration, and maintain better stability and dispersibility even after the hydrothermal reaction and hydrazine reduction. The GN film after annealing has a conductivity of as high as 1488 S cm−1, and the bandgap of GNs can be effectively opened even at low oxidation levels. Supercapacitors of GNs deposited on nickel foams allow for operations at a high rate up to 200 V s−1, and possess high capacitance and cycling stability. Our solution processing method offers a suitable way to fabricate conductive GNs with significant advantages, which creates more opportunities for various applications.

We report a novel and facile route to synthesize a 1D needlelike CuO gas sensor utilizing simple solution-treatment, heat-treatment and sonication processes based on copper meshes (CMs) for the first time. We have demonstrated that the architectural 1D CuO sensor displays a substantial improvement of response magnitude toward a series of toxic organic molecules. We expect that our work may provide a new inspiration for synthesizing 1D semiconductor nanowires for gas sensing application.

Stable superhydrophobic coatings were successfully achieved from thiol-ligand nanocrystals. Nanocrystals included VIII and IB metals and oxide nanoparticles, such as Fe, Co, Ni, Cu and Ag. We present a simple and available method that facilitates the synthesis of superhydrophobic textiles and sponges, in which the interaction between the nanocrystals and thiol plays a significant role in the formation of a special wetting surface. Meanwhile, the superhydrophobic textiles could also be endowed with new functionalities. For example, textiles with Fe3O4 nanocoatings possess magnetic properties, and Ag nanocrystals provide an antibacterial effect. If perfluoroalkyl thiol was used to replace alkyl thiol, the as-modified surfaces became oleophobic from superoleophilic. The proposed strategy was fit for various nanoparticles from as-established methods, including the preparation in different polar solvents, and the usage of surfactants as capping agents. As-prepared superhydrophobic nanocoatings show good durability towards hot water, surfactant aqueous solutions, and ultrasonic treatment in nonpolar solvents. The superhydrophobic and superoleophilic nanocoatings were effectively used for application in oil/water separation.

The underlying theories interpreting wetting phenomena are still mainly focused on the Young's equation, the Wenzel equation, and the Cassie–Baxter equation, despite the fact that wetting phenomena have been studied over the past decades. Based on these theories, people have understood that both surface chemical composition and its morphology can influence the contact angle of liquid droplets on solid surfaces. However, such equations are not sufficient to thoroughly explain the mechanisms of wetting phenomena, although they are still necessary. In this feature article, we review the theory, from the classical wetting models to the most recent theoretical advances, of superhydrophobic surfaces with regard to the wetting process, and some promising breakthroughs in the advance of the theory are proposed in the final section.

It is well known that properties of materials are largely determined by their structures. Here we introduce the special double-structural materials, which are composed of micrometre and nanometre building blocks and commonly exist in nature. This review mainly focuses on recent developments of double-structural and functional materials with special wettability. We highlight excellent properties possessed by micro- and nanostructures which initially originated from the organisms with special functions in the biological world. The excellent properties shown by such structures are discussed in three parts: special wettability, mechanical properties, and optical properties, primarily including superhydrophobicity, superhydrophilicity, superoleophobicity, low and high adhesion, low friction, structural color, antireflection and so on. We will also briefly address the research prospects and directions of micro- and nano-structures. Further study on the relationship between structures and properties will be conducive to better transfer micro- and nanostructures to the engineering materials so as to obtain desired performances and a wide range of applications.

Graphene as an important two-dimensional one-atom-thick nanosheet can be regarded as a solid and also a molecule. In this paper, we focused attention on the coordination ability of doping-induced defects, micro-scale size and atomic thickness of graphene, and anchored oxygen-donor coordination of graphene oxide to ferric ions, forming a giant flat iron complex. As well as graphene oxide, as-obtained graphene oxide–Fe(III) complexes were characterized by transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and so on. It was demonstrated that graphene oxide–Fe(III) complexes could be well dispersed in water, with size up to micrometers and atomically thin. Under visible-light irradiation, graphene oxide–Fe(III) complexes displayed homogeneous catalytic ability of H2O2 activation, and could be easily removed by simple filtration or centrifugation, showing significant advantages in both homogeneous and heterogeneous catalysis.

Metal nanoparticles are known as extremely hydrophilic substances due to their high surface energy. Hydrophobic properties of the metal nanoparticles can be realized only if the nanoparticles are pretreated with low-surface-energy chemicals. In this paper, two adjacent transition metals, i.e. Fe and Co, were selected and coated on a commercially available fabric via a facile in situ growth method. n-Octadecyl thiol, which possesses low surface energy, was selected as the modifier to obtain a superhydrophobic–superhydrophilic hybrid fabric depending on the thiol's selective modification to Fe and Co nanoparticles on the fabric. The surface Co nanoparticles can be modified by n-octadecyl thiol and transform to hydrophobic nanoparticles; however, the surface Fe nanoparticles could not be modified by n-octadecyl thiol in our experimental condition; thus, they retained the hydrophilic property. An as-prepared fabric with these two kinds of nanoparticles evenly distributed on the surface is termed as a superhydrophobic–superhydrophilic hybrid fabric because it shows superhydrophobic property and possesses many superhydrophilic spots. This material is expected to realize water harvesting similar to the desert beetle that collects micro droplets of water from the morning fog without using any external energy source.

Superoleophobic surfaces have drawn wide attention because of their special wetting behaviour. By adjusting surface chemical composition and surface structure, different kinds of superoleophobic surfaces (in air, underwater and others) can be obtained. This account mainly focuses on the recent progress of the fabrication and applications of superoleophobic surfaces. There are various methods to fabricate superoleophobic surfaces, which are generally divided into two ways. One is the top-down method, which includes etching, lithography, anodization and laser processing. The other is the bottom-up method, which contains electrodeposition, the hydrothermal method, sol–gel process and electro-spinning. However, each has its own merits and demerits. Hence, choosing the proper method in different conditions is quite important. These superoleophobic surfaces can be applied in many areas, such as self-cleaning, anti-corrosion, oil transportation, anti-bio-adhesion devices, oil capture, anti-smudge, chemical shielding, micro-droplet manipulation and oil–water separation. In fact, few of them have been put into practice. The development of superoleophobic surfaces is still in the experimental stage. Current and further challenges for superoleophobic surfaces are proposed. Beyond that, some creatures with typical structures are also referred, for instance, the lotus leaf, butterfly wing, rice leaf, desert beetle, rose petal, mosquito eyes, springtail, fish scale, shark skin, snail shell, the lower surface of the lotus leaf and a clam's shell.

Oil spills and industrial organic pollutants have induced severe water pollution and threatened every species in the ecological system. To deal with oily water, special wettability stimulated materials have been developed over the past decade to separate oil-and-water mixtures. Basically, synergy between the surface chemical composition and surface topography are commonly known as the key factors to realize the opposite wettability to oils and water and dominate the selective wetting or absorption of oils/water. In this review, we mainly focus on the development of materials with either super-lyophobicity or super-lyophilicity properties in oil/water separation applications where they can be classified into four kinds as follows (in terms of the surface wettability of water and oils): (i) superhydrophobic and superoleophilic materials, (ii) superhydrophilic and under water superoleophobic materials, (iii) superhydrophilic and superoleophobic materials, and (iv) smart oil/water separation materials with switchable wettability. These materials have already been applied to the separation of oil-and-water mixtures: from simple oil/water layered mixtures to oil/water emulsions (including oil-in-water emulsions and water-in-oil emulsions), and from non-intelligent materials to intelligent materials. Moreover, they also exhibit high absorption capacity or separation efficiency and selectivity, simple and fast separation/absorption ability, excellent recyclability, economical efficiency and outstanding durability under harsh conditions. Then, related theories are proposed to understand the physical mechanisms that occur during the oil/water separation process. Finally, some challenges and promising breakthroughs in this field are also discussed. It is expected that special wettability stimulated oil/water separation materials can achieve industrial scale production and be put into use for oil spills and industrial oily wastewater treatment in the near future.

A superhydrophobic copper mesh film (CMF) with pH-responsive property was synthesized via an electrochemical deposition strategy, followed by Au sputter-coating process and surface modification with a thiol mixture of HS(CH2)9CH3 and HS(CH2)10COOH. As-prepared CMF can be applied to separate an oil-and-water mixture bidirectionally.

A thin film of polyaniline (PANI) nanofibers on the stainless steels with fluoro-thiol modification was prepared through an optimal polymerization time of aniline using HClO4 as a dopant, showing robust superhydrophobic, transparent and anti-fingerprint properties.

Open porous NiO films prepared by a simple green solvothermal approach on ITO/glass substrate show a high-rate specific capacitance, Coulombic efficiency of ≈100% at high current rates and good cycling stability, suggesting their promising application in supercapacitors.

Inspired by mussels we designed a novel green superhydrophobic gel nanocoating with good transparency and stability through a facile copolymerization reaction at room temperature and a subsequent trimethyl silyl modified process, which is applicable to various substrates via a simple spray process without requiring toxic substances. Importantly, this well-designed nanocoating has rapid self-healing superhydrophobicity induced by usual organic solvents to face complicated work conditions, which satisfies the need of daily life and can be applied in industry as well.

It is well known that high optical transparency is one of the most crucial criteria for the overwhelming majority of optical devices and correlative functions, including smart windows, camera lenses, solar cell systems and optoelectronic devices. With the frequent exposure of this equipment to all sorts of environments, such as outdoor conditions, a surface with self-cleaning properties can guard against fouling, humidity, bacterial growth and so forth. That is one type of application of the big family of superhydrophobic coatings. Therefore, integrating high transparency with self-cleaning characteristics is of great importance for such applications. In this review, the recent developments in designing, synthesizing and manufacturing transparent and superhydrophobic surfaces are reviewed. Firstly, the established theoretical aspects of surface wetting properties are summarized and then several natural and bio-inspired superhydrophobic surfaces of diverse microcosmic structures are presented as representative examples. With a focus on distinctively employed materials and the corresponding fabrication of superhydrophobic coatings with high transparency, the promising research directions and application prospects of this rapidly developing field are briefly addressed as well.

Inspired by Namib Desert beetles, a hybrid superhydrophobic surface was fabricated, showing highly efficient fog harvesting with a water collection rate (WCR) of 1309.9 mg h−1 cm−2. And, the surface possessed an excellent robustness and self-cleaning property.

Nowadays, water shortage is a severe issue all over the world, especially in some arid and undeveloped areas. Interestingly, a variety of natural creatures can collect water from fog, which can provide a source of inspiration to develop novel and functional water-collecting materials. Recently, as an increasingly hot research topic, bioinspired materials with the water collection ability have captured vast scientific attention in both practical applications and fundamental research studies. In this review, we summarize the mechanisms of water collection in various natural creatures and present the fabrications, functions, applications, and new developments of bioinspired materials in recent years. The theoretical basis related to the phenomenon of water collection containing wetting behaviors and water droplet transportations is described in the beginning, i.e., the Young's equation, Wenzel model, Cassie model, surface energy gradient model and Laplace pressure equation. Then, the water collection mechanisms of three typical and widely researched natural animals and plants are discussed and their corresponding bioinspired materials are simultaneously detailed, which are cactus, spider, and desert beetles, respectively. This is followed by introducing another eight animals and plants (butterfly, shore birds, wheat awns, green bristlegrass, the Cotula fallax plant, Namib grass, green tree frogs and Australian desert lizards) that are rarely reported, exhibiting water collection properties or similar water droplet transportation. Finally, conclusions and outlook concerning the future development of bioinspired fog-collecting materials are presented.

As important and irreplaceable engineering materials, metals are widely used in our daily life. Therefore, fabricating superhydrophobic surfaces on metal materials is of great significance, and applicable methods for industrial production are in urgent need. In this work, we provide a rapid and easy route for fabricating superhydrophobic films on metal materials through simple displacement deposition. This method includes two simple steps with each step being as short as one second. The obtained superhydrophobic surfaces are homogeneous and easy to repair. A miniature boat and a miniature box were used to test the buoyancy-increasing and oil absorption properties, respectively. This method is feasible for massive production of superhydrophobic metal materials applied to water transportation and oil spill clean-up areas.

A superhydrophilic surface with two superhydrophobic circular patterns was fabricated via a simple and rapid route, showing outstanding fog harvesting properties with a water collection rate (WCR) of 1316.9 mg h−1 cm−2. Water collection can be repeated on the sample 10 times without obvious change in the WCR.

Oil/water emulsion separation is a worldwide challenge because of frequent oil spill accidents and the large quantities of oily wastewater generated in various industrial processes. Among the many methods employed in separating oil/water emulsions, biomimetic thin membranes with a superwetting property have attracted tremendous interest because of their high separation efficiency, low energy consumption, scalable productivity, good stability and durability. In this paper, the typical superwettable materials in nature and the basic rules for constructing biomimetic thin membranes are summarised. In terms of the different categories of membrane materials, recent developments in biomimetic thin membranes, including polymer-based membranes, metallic mesh-based membranes, ceramic membranes and carbon nanotube-based composite membranes, are presented in this review. For each filtration membrane, its fabrication methods are introduced in detail and the role of each method in the fabrication and performance of membrane is discussed comprehensively. Finally, some challenges and prospects concerning the future development of filtration are discussed. This review is aimed to give a brief and systematic overview of biomimetic thin membranes fabrication applied in oil/water emulsion separation.

Understanding the complementary roles of surface roughness and energy in natural super-non-wetting surfaces has greatly promoted the development of biomimetic superhydrophobic surfaces that repel water at a much greater rate than oils. These surfaces that are highly repellent to low-surface-tension oils and organic liquids, termed superoleophobic surfaces, are poorly understood. Inspired by springtails (collembolan), a third factor, re-entrant surface curvature, has been introduced to the design and fabrication system of superoleophobic surfaces in conjunction with two other factors of surface chemical composition and roughness. Over the past decade, superoleophobic surfaces have attracted tremendous attention with respect to their design, fabrication and applications due to their extraordinary properties. This review focuses on these aspects and thus summarizes recent research progress in superoleophobic surfaces. Starting from the origin, features of natural oil-resistant creatures have been introduced, and fundamental theories for surface design have been discussed. Calculations suggest that creation of these surfaces requires specific re-entrant structures and fluoride modifiers. Based on this principle, various fabrication methods, from top-down to bottom-up approaches, have been used, and some derivative structures with desirable properties have been produced. A precise and detailed classification has been provided in this review that includes representative methods and structures as well as functions (i.e., transparence and self-healing). Significantly, superoleophobic materials have many valuable applications, including oil pollution resistance, oil transportation, and synthesis of mesoporous supraparticles. However, their complicated manufacturing techniques, poor physical–chemical properties and environmentally unfriendly surface chemicals jointly impede their real-life applications. Therefore, it is highly necessary to optimize the craft and performance of theses surfaces for industrial operation and practical applications. To this end, some challenges and perspectives will be provided regarding the future research and development of superoleophobic surfaces.

Sand, an abundant natural resource, is the cause behind the harsh environmental conditions of the desert, such as water shortages and sand storms. Because of the strong hydrophilicity of sand itself, water can be quickly absorbed by sand, which greatly impedes desert greening, water storage and transportation projects. In contrast to this conventional understanding of sand (i.e., superhydrophilicity), we propose the design of “superhydrophobic sand”, aimed to address issues associated with the desert environment and sand resource utilization. In our experiments, three kinds of hydrophobic sands with different surface structures and wettability properties were successfully prepared by cladding nonmetal (SiO2) and metal (Ag and Cu) inorganic materials on sand grain surfaces and then modifying them with low-surface-energy chemicals. Combining superhydrophobicity with desert sand, superhydrophobic sand (PFDS-sand@SiO2) is shown to have excellent water repellency, allowing water to stably remain and flow on such a sand surface without any wetting or permeation. Furthermore, the superhydrophobic sand demonstrates a great water-holding capacity, such that a sand layer with a thickness of 2 cm can sustain a water column height of 35 cm. Very significantly, PFDS-sand@SiO2 exhibits extremely high thermal stability up to 400 °C when used for water storage. This result is unprecedented and sufficient for facing the high-temperature conditions of the desert environment and some others. In addition to reliable water storage, such superhydrophobic sand also demonstrates a great anti-flow-dragging effect during water transportation, whereby a water droplet can smoothly and quickly roll down a simulated sand channel (13 cm length) within 0.3 s (∼0.45 m s−1). All of these manifestations imply the significant potential of such “superhydrophobic sand” in its application to desert water storage and transportation.