Underwater Mechanically Robust Oil-Repellent Materials: Combining Conflicting Properties Using a Heterostructure

Rapid Preparation Triggered by Visible Light for Tough Hydrogel Sensors with Low Hysteresis and High Elasticity: Mechanism, Use and Recycle-by-Design

Hydrogels have emerged as promising candidates for flexible devices and water resource management. However, further applications of conventional hydrogels are restricted due to their limited performance and lack of a recycling strategy. Herein, a tough, flexible, and recyclable hydrogel sensor via a visible-light-triggered polymerization is rapidly created. The Zn2+ crosslinked terpolymer is in situ polymerized using g-C3N4 as the sole initiator to form in situ chain entanglements, endowing the hydrogels with low hysteresis and high elasticity. In the use phase, the hydrogel sensor exhibited high ion conductivity, excellent mechanical properties, fast responsiveness, high sensitivity, and remarkable anti-fatigue ability, making it exceptionally effective in accurately monitoring complex human movements. At the end-of-life (EOL), leveraging the synergy between the photodegradation capacity of g-C3N4 and the adsorption function of the hydrogel matrix, the post-consumer hydrogel is converted into water remediation materials, which not only promoted the rapid degradation of organic pollutants, but also facilitated collection and reuse. This innovative strategy combined in situ entangling reinforcement and tailored recycle-by-design that employed g-C3N4 as key blocks in the hydrogel to achieve high performance in the use phase and close the loop through the reutilization at EOL, highlighting the cost-effective synthesis, specialized structure, and life cycle management.

Activated carbon fibers functionalized with superhydrophilic coated pDA/TiO2/SiO2 with photoluminescent self-cleaning properties for efficient oil-water separation

The adhesion of high-viscosity oil contamination poses limitations on three-dimensional (3D) materials' practical use in treating oilfield-produced water (OPW). In this study, we developed a hybrid pDA/TiO2/SiO2 coating (PTS) on the surface of hydrophilic activated carbon (ACF1) through a combination of dopamine (DA) polymerization, ethyl orthosilicate (TEOS) hydrolysis, and the condensation of TiO2 nanoparticles (NPs) with SiO2 NPs. This coating was designed for gravity-based oil-water separation. The inherent porosity and generous pore size of ACF1-PTS conferred it an ultra-high permeation flux (pure water flux of 3.72 × 105 L∙m-2∙h-1), allowing it to effectively separate simulated oil-water mixtures and oil-water emulsions while maintaining exceptional permeation flux and oil rejection efficiency. When compared to cleaning methods involving ethanol aqueous solutions and NaClO, ultraviolet (UV) illumination cleaning proved superior, enabling oil-contaminated ACF1-PTS to exhibit remarkable flux recovery efficiency and oil-removal capabilities during cyclic separation of actual OPW. Furthermore, the ACF1-PTS material demonstrated impressive stability and durability when exposed to acidic environments (acid, alkali, and salt), robust hydraulic washout conditions, and 25-cycle tests. This study offers valuable insights and research avenues for the development of highly efficient and environmentally friendly 3D oil-water separation materials for the actual treatment of OPW.

Fabrication of Anatase TiO2/PVDF Composite Membrane for Oil-in-Water Emulsion Separation and Dye Photocatalytic Degradation

At present, the types of pollutants in wastewater are more and more complicated, however, the multifunctional membrane materials are in short supply. To prepare a membrane with both high efficient oil-in-water emulsion separation performance and photocatalytic degradation performance of organic dyes, the bifunctional separation membrane was successfully prepared by electrostatic spinning technology of PVDF/PEMA and in situ deposition of anatase TiO₂ nanoparticles containing Ti³⁺ and oxygen vacancies (O_v). The prepared composite membrane has excellent hydrophilic properties (WCA = 15.65), underwater oleophobic properties (UOCA = 156.69), and photocatalytic performance. These composite membranes have high separation efficiency and outstanding anti-fouling performance, the oil removal efficiency reaches 98.95%, and the flux recovery rate (FRR) reaches 99.19% for soybean oil-in-water emulsion. In addition, the composite membrane has outstanding photocatalytic degradation performance, with 97% and 90.2% degradation of RhB and AG-25 under UV conditions, respectively. Several oil-in-water separation and dye degradation experiments show that the PVDF composite membrane has excellent reuse performance. Based on these results, this study opens new avenues for the preparation of multifunctional reusable membranes for the water treatment field.

Review of Artificial Nacre for Oil–Water Separation

Due to their extraordinary prospective uses, particularly in the areas of oil–water separation, underwater superoleophobic materials have gained increasing attention. Thus, artificial nacre has become an attractive candidate for oil–water separation due to its superhydrophilicity and underwater superoleophobicity properties. Synthesized artificial nacre has successfully achieved a high mechanical strength that is close to or even surpasses the mechanical strength of natural nacre. This can be attributed to suitable synthesis methods, the selection of inorganic fillers and polymer matrices, and the enhancement of the mechanical properties through cross-linking, covalent group modification, or mineralization. The utilization of nacre-inspired composite membranes for emerging applications, i.e., is oily wastewater treatment, is highlighted in this review. The membranes show that full separation of oil and water can be achieved, which enables their applications in seawater environments. The self-cleaning mechanism’s basic functioning and antifouling tips are also concluded in this review.

Robust Underwater Oil-Repellent Biomimetic Ceramic Surfaces: Combining the Stability and Reproducibility of Functional Structures

Robust underwater oil-repellent materials combining high mechanical strength and durability with superwettability and low oil adhesion are needed to build oil-repellent devices able to work in water, to manipulate droplet behavior, etc. However, combining all of these properties within a single, durable material remains a challenge. Herein, we fabricate a robust underwater oil-resistant material (Al₂O₃) with all of the above properties by gel casting. The micro/nanoceramic particles distributed on the surface endow the material with excellent underwater superoleophobicity (∼160°) and low oil adhesion (<4 μN). In addition, the substrate exhibits typical ceramic characteristics such as good antiacid/alkali properties, high salt resistance, and high load tolerance. These excellent properties make the material not only applicable to various liquid environments but also resistant to the impact of particles and other physical damage. More importantly, the substrate could still exhibit underwater superoleophobicity after being worn under specific conditions, as wear will create new surfaces with similar particle size distribution. This approach is easily scalable for mass production, which could open a pathway for the fabrication of practical underwater long-lasting functional interfacial materials.

Nacre-inspired underwater superoleophobic films with high transparency and mechanical robustness

Underwater superoleophobic materials have attracted increasing attention because of their remarkable potential applications, especially antifouling, self-cleaning and oil-water separation. A limitation of most superoleophobic materials is that they are non-transparent and have limited mechanical stability underwater. Here, we report a protocol for preparing a transparent and robust superoleophobic film that can be used underwater. It is formed by a hydrogel layer prepared by the superspreading of chitosan solution on a superhydrophilic substrate and biomimetic mineralization of this layer. In contrast to conventional hydrogel-based materials, this film exhibits significantly improved mechanical properties because of the combination of high-energy, ordered, inorganic aragonite (one crystalline polymorph of calcium carbonate) and homogeneous external hierarchical micro/nano structures, leading to robust underwater superoleophobicity and ultralow oil adhesion. Moreover, the mineralized film is suitable for neutral and alkaline environments and for containing organic solvent underwater and can be coated on different transparent materials, which has promising applications in underwater optics, miniature reactors and microfluidic devices. In this protocol, the time for the whole biomimetic mineralization process is only ~6 h, which is significantly shorter than that of traditional methods, such as gas diffusion and the Kitano method. The protocol can be completed in ~2 weeks and is suitable for researchers with intermediate expertise in organic chemistry and inorganic chemistry.

Bio-inspired robust superhydrophilic/underwater superoleophobic coating with lubrication, anti-crude oil fouling and anti-corrosion performances

The crude oil spill accidents cause numerous crude oil contaminations and oily wastewater. Underwater superoleophobic coating has excellent ability to resist crude oil contamination and separate oily wastewater. But it's hard to keep stable performance against the physical or chemical attack. Herein, a robust underwater superoleophobic coating was fabricated by spraying the mixture of polyethyleneimine (PEI) and TiO₂ on epoxy resin (E44) surface. Besides the good physical and chemical stability, the coating exhibited better drag reduction, anti-fouling performance and anti-corrosive performance in water compared with the commercially hydrophilic coating. The stainless steel mesh (SSM), coated by the E44/PEI/TiO₂ coating, could separate different oil-water emulsions with a high oil rejection greater than 99.7%.

Extra plasticity governed by shear band deflection in gradient metallic glasses

Inspired by gradient materials in nature, advanced engineering components with controlled structural gradients have attracted substantial research interests due to their exceptional combinations of properties. However, it remains challenging to generate structural gradients that penetrate through bulk materials, which is essential for achieving enhanced mechanical properties in metallic materials. Here, we report practical strategies to design controllable structural gradients in bulk metallic glasses (BMGs). By adjusting processing conditions, including holding time and/or controlling temperatures, of cryogenic thermal cycling and fast cooling, two different types of gradient metallic glasses (GMGs) with spatially gradient-distributed free volume contents can be synthesized. Both mechanical testing and atomistic simulations demonstrate that the spatial gradient can endow GMGs with extra plasticity. Such an enhanced mechanical property is governed by the gradient-induced deflection of shear deformation that fundamentally suppresses the unlimited shear localization on a straight plane that would be expected in BMGs without such a gradient.

Materials with controlled structural gradient have gained attention due to their unique combinations of properties. Here the authors report strategies to design controllable gradients in bulk metallic glasses, demonstrating extra plasticity and suppression of shear localization.

Simultaneous Realization of Superoleophobicity and Strong Substrate Adhesion in Water via a Unique Segment Orientation Mechanism

The underwater superoleophobicity of a coating is often caused by its preferential water affinity, which, however, normally weakens the substrate adhesion property. In this work, a new strategy is reported for achieving strong underwater adhesion between a well-designed amphiphilic polyurethane coating and a diverse range of substrates while also rendering the coating surface's superoleophobicity. When the coating, which is a mixture of an amphiphilic polyurethane and a water miscible solvent, is immersed in water, the hydrophobic segments aggregate to orientate and pile along the surface of substrates via a segment orientation mechanism triggered by solvent exchange with water penetration to exert strong adhesion. At the same time, the hydrophilic segments will physically crosslink to form a hydrogel coating, endowing the substrate with underwater superoleophobicity. This work provides a facile, versatile, and scalable approach for the future design of superoleophobic coatings in a water environment.

Robust Superamphiphilic Membrane with a Closed-Loop Life Cycle

Oil-spill remediation is an international environmental challenge, and superamphiphilic membranes, as a promising solution, have recently drawn lots of attention. However, the robustness of the conventional membrane design is less satisfying under severe conditions during practical applications. Additionally, it is unavoidable for the membranes to face a series of foulants in their practical working environment, for example, algae and sand. These foulants will block the membrane, which leads to a new economic and environmental problem in terms of waste management at the end of their life. To address the aforementioned challenges, a new generation of superamphiphilic vitrimer epoxy resin membranes (SAVER) to separate oil and water efficiently is reported. Similar to classical epoxy resins, SAVER shows strong mechanical robustness and sustains exposure to aqua regia and sodium hydroxide solutions. Furthermore, the blocked membrane can be easily recovered when contaminated with mixed foulants by using dynamic transesterification reactions in the polymer network. The ease with which biobased SAVER can be manufactured, used, recycled, and re-used without losing value points to new directions in designing a closed-loop superamphiphilic membrane life cycle.

Green Method for Fabrication of an Underwater Superoleophobic Phosphor-Copper Mesh and Transportation of Oily Liquids

Sea cucumber-shaped Cu₂O nanostructures are constructed on a phosphor-copper mesh by employing a one-step immersion process accomplished in distilled water without introducing any additional reagent. The phosphor-copper mesh with a Cu₂O structure thereon exhibits significant hydrophilicity and induces a large superoleophobic force at the oil/water interface. The method used for preparing the Cu₂O nanostructures represents an inexpensive, fast, and environmentally friendly approach, along with satisfying the requirements of large-scale preparation. It is found that the pickling degree of the phosphor-copper mesh during surface cleaning plays a major role in the oxidation process of the surface for the growth of Cu₂O nanostructures. Nanostructures with different morphologies can be achieved by accurately controlling the surface pickling degree. Interestingly, an underwater superoleophobic "pipe" developed using the as-prepared phosphor-copper mesh can realize gravity (buoyancy)-driven oily liquid transport in an aqueous environment, with no associated contamination by the oil. This study provides a simple method to realize surface-functionalization and demonstrates a new route for achieving liquid transportation without external energy and would help to design smart aquatic devices for diverse liquid transport thereby, enabling oil handling and oil spill cleanup.

Bioprocess-inspired synthesis of multilayered chitosan/CaCO3 composites with nacre-like structures and high mechanical properties

The formation of natural structures found in biological systems is wonderful and can be completed at ambient temperatures in contrast to artificial technologies wherein harsh conditions are common prerequisites. A new research direction, "bioprocess inspired manufacturing", is proposed for fabricating advanced materials with novel structures and functions. Nacre consists of an ordered multilayer structure of crystalline calcium carbonate lamellae separated by organic layers exhibiting mechanical toughness, which transcends that of its constituent components. Inspired by the nacre formation process, a microscale additive manufacturing mineralization method is proposed for achieving a multilayered organic-inorganic layered structure. In this work, layered calcite was synthesized on the surface of chitosan (CS) films at room temperature under the coordinated control of magnesium ions (Mg2+) and polyacrylic acid (PAA). The CS films and layered calcite are sequentially assembled in a layer-by-layer deposition approach to form an organic-inorganic hybrid structure. The nacre-like chitosan/CaCO3 (CS/CaCO3) composites exhibit high transparency and underwater superoleophobicity. Impressively, the hardness (2.35 ± 0.03 GPa) and Young's modulus (58.1 ± 0.5 GPa) of the as-prepared (CS/CaCO3) composites are comparable to those of their biological counterparts. This study provides a rational bioprocess-inspired room-temperature mineralization method to develop advanced composite materials with good performance.

Molecular Understanding and Design of Porous Polyurethane Hydrogels with Ultralow-Oil-Adhesion for Oil-Water Separation

Materials with opposite affinities toward oil and water have been extensively used to coat porous substrates for oil-water separation, but the applications of these materials have been limited by the need for complex coating processes as well as the short-term adherence of these materials onto different substrates under extreme conditions. As reported herein, the robust porous polyurethane hydrogel has been theoretically and structurally designed with ultralow-oil-adhesion properties which is free stand without depending on additional substrates. The combination of superhydrophilic properties along with the underwater superoleophobic behavior of this porous hydrogel allows gravity driven separations of oil-water mixtures, and its antiadhesion performance toward oil prevents undesirable oily fouling. The underwater superoleophobic properties were also illustrated by molecular dynamics simulation to understand the resisting effect of hydrated layers. The as-prepared porous hydrogel shows ultrahigh oil-water separation efficiencies of 99.9% for various oil-water mixtures, ranging from those containing viscous oils (pump oil and peanut oil) to organic solvents (n-hexane, n-hexadecane, and toluene). In addition, this hydrogel is durable even with exposure to various harsh conditions including acidic and basic media (pH 0-14) as well as exposure to mechanical abrasion. We believe that the combination of facile preparation, substrate independence, gravity driven separation, antifouling properties, high durability, as well as the outstanding separation flux and efficiency of this robust porous hydrogel will help to advance the design and application of materials in oil-water separation fields.

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

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

One-Step Preparation of Highly Durable Superhydrophobic Carbon Nanothorn Arrays

This study proposes a one-step method for growing superhydrophobic carbon nanothorn arrays (NTAs) directly on various substrates. The fabricated carbon material (named methyl-substituted graphdiyne (MGDY)) comprises sp and sp² carbons in a conjugated-backbone form, as well as methyl groups introduced into the framework as hydrophobic-enhanced functional groups. MGDY NTAs exhibit excellent hydrophobicity (contact angle ≥152°), substantial long-period hydrophobic durability (the contact angle decreased by only 3.2% over 800 days), and acid/alkali tolerance. Owing to the enhanced durability and specific stability of carbon, a superhydrophobic interface can easily be constructed using MGDY NTAs, which can be applied to achieve successful long-term metal-corrosion protection and efficient oil-water separation.

Controlling ice formation on gradient wettability surface for high-performance bioinspired materials

Ice-templating holds promise to become a powerful technique to construct high-performance bioinspired materials. Both ice nucleation and growth during the freezing process are crucial for the final architecture of the ice-templated material. However, effective ways to control these two very important factors are still lacking. Here, we demonstrate that successive ice nucleation and preferential growth can be realized by introducing a wettability gradient on a cold finger. A bulk porous material with a long-range lamellar pattern was obtained using a linear gradient, yielding a high-performance, bulk nacre-mimetic composite with excellent strength and toughness after infiltration. In addition, cross-aligned and circular lamellar structures can be obtained by freeze-casting on surfaces modified with bilayer linear gradient and radial gradient, respectively, which are impossible to realize with conventional freeze-casting techniques. Our study highlights the potential of harnessing the rich designability of surface wettability patterns to build high-performance bulk materials with bioinspired complex architectures.

Nacre-Inspired Mineralized Films with High Transparency and Mechanically Robust Underwater Superoleophobicity

Underwater superoleophobic materials have shown promising applications in various fields, especially in the highly frequent oil-spill accidents. However, the transparency and mechanical properties of existing underwater superoleophobic materials are generally mutually exclusive. In this work, a transparent and mechanically robust underwater superoleophobic film is presented by combining superspreading and biomineralization. Unlike the conventional hydrogel-based materials, the transparent mineralized film exhibits significantly improved mechanical properties, which lead to a robust underwater superoleophobicity and an ultralow oil adhesion. Such a bioinspired mineralized film can be coated on various transparent supporting materials such as glass, polystyrene (PS), poly(ethylene terephthalate) (PET), and polypropylene (PP), showing promising applications in various fields, such as goggles, underwater cameras, and submarines.

Superwetting Oil/Water Separation Membrane Constructed from In Situ Assembled Metal-Phenolic Networks and Metal-Organic Frameworks

Superwetting membranes with opposite wettability to oil and water have drawn intense attention in recent years for oil/water separation. Superhydrophilic and underwater superoleophobic membranes have shown unique advantages in the efficient treatment of oily wastewater containing oil-in-water emulsions. Facile interfacial engineering and microstructural design of the hierarchical architectures and the hydrophilic chemistry is of significance but still challenging. In this study, a hydrophilic hierarchical hybrid layer derived from metal-phenolic network (MPN)/metal-organic framework (MOF) synergy is constructed on the membrane surface via a proposed coordination-directed alternating assembly strategy. The assembly of MPN multilayers provides a hydrophilic chemical basis, and the assembly of MOF nanocrystals provides a hierarchical structural basis. Notably, the coordination interfacial interaction enables the formation of well-defined hydrophilic hierarchical architectures. The obtained membrane is thus endowed with robust superhydrophilicity, underwater superoleophobicity, and anti-oil-adhesion capability, which make it capable of highly efficient oil-water separation with high water permeance (above 6300 L/m² h), high oil rejection (above 99.4%), and recyclable antifouling property. The high performance of the developed superwetting membrane makes it a competitive candidate for oil/water separation. Additionally, the demonstrated MPN/MOF assembly strategy may offer new prospects for the facile and versatile design of other superwetting materials.

Robust Nacrelike Graphene Oxide-Calcium Carbonate Hybrid Mesh with Underwater Superoleophobic Property for Highly Efficient Oil/Water Separation

Inspired by the mastoid structure of the lotus leaf and the robust layered structure of the nacre, a novel nacrelike graphene oxide-calcium carbonate (GO-CaCO₃) hybrid mesh with superhydrophilic and underwater superoleophobic property was prepared for the first time, via a facile, economical, and environmentally friendly layer-by-layer (LBL) self-assembly method using commercially available stainless steel mesh (SSM) as a ready-made mask. Interestingly, GO nanosheets played a threefold role, regulating the growth of CaCO₃ nanocrystals between the GO interlamination for constructing a "brick-and-mortar" structure, improving the interface stability via coordination assembly onto SSM, and creating strong hydration derived from rich oxygen-containing functional groups. The surface hydrophilicity and hierarchically micro/nanoscale structure of GO-CaCO₃ artificial pearls imbed on the SSM, contributing to outstanding superhydrophilicity and underwater superoleophobicity. The biomimetic hybrid mesh exhibited a strong mechanical property with a Young's modulus of 25.4 ± 2.6 GPa. The optimized hybrid mesh showed a high separation efficiency of more than 99% toward a series of oil/water mixtures with high flux. The low oil-adhesion force, high fatigue-resistance, chemical stability (acid/alkali/salt resistance), and excellent recycling performance enlighten the great prospects of GO-based nacrelike material for application in oily wastewater treatment.

Robust Graphene/Poly(vinyl alcohol) Janus Aerogels with a Hierarchical Architecture for Highly Efficient Switchable Separation of Oil/Water Emulsions

Given the complexity and diversity of actual oily sewages, developing multifunctional separation materials with features of high separation efficiency and low energy consumption for separating diverse oil/water emulsions is urgently needed, yet it remains a formidable challenge till now. Herein, a superior graphene/poly(vinyl alcohol) Janus aerogel (J-CGPA), showing an intriguing three-dimensional (3D) hierarchical architecture (a dense skin-layer and a larger internal cell network) and desirable asymmetric wettability, was exploited via a simple direct freeze-shaping technique and subsequent mussel-inspired hydrophilic modification. Benefiting from the controlled unilateral decoration of dopamine, the resultant aerogels displayed completely opposite superwettability on two antithetic sides, i.e., one side is highly hydrophobic (water contact angle (WCA), 143°), whereas the other side is superhydrophilic. On the basis of the favorable 3D hierarchical structure and binary cooperative superwetting properties, the Janus aerogels achieved a remarkable switchable separation performance for both highly emulsified oil-in-water and water-in-oil emulsions as well as stratified oil/water mixtures accompanied with outstanding separation efficiencies. Particularly, an ultrahigh permeation flux of 1306 L m^-2 h^-1 along with a high rejection efficiency of 99.7% was acquired solely under the driving of gravity (<1 kPa), which is 1-2 order of magnitude higher than that of pioneering two-dimensional Janus polymeric/inorganic membranes recently reported. Moreover, together with robust reusability, this novel 3D Janus aerogel indicates a promising practical application for high-performance oily wastewater remediation.

Recent Advances in Bioinspired Gel Surfaces with Superwettability and Special Adhesion

Engineering surface wettability is of great importance in academic research and practical applications. The exploration of hydrogel-based natural surfaces with superior properties has revealed new design principles of surface superwettability. Gels are composed of a cross-linked polymer network that traps numerous solvents through weak interactions. The natural fluidity of the trapped solvents confers the liquid-like property to gel surfaces, making them significantly different from solid surfaces. Bioinspired gel surfaces have shown promising applications in diverse fields. This work aims to summarize the fundamental understanding and emerging applications of bioinspired gel surfaces with superwettability and special adhesion. First, several typical hydrogel-based natural surfaces with superwettability and special adhesion are briefly introduced, followed by highlighting the unique properties and design principles of gel-based surfaces. Then, the superwettability and emerging applications of bioinspired gel surfaces, including liquid/liquid separation, antiadhesion of organisms and solids, and fabrication of thin polymer films, are presented in detail. Finally, an outlook on the future development of these novel gel surfaces is also provided.

Synthesis of Dual-Functional and Robust Underwater Superoleophobic Interfaces

Fish-scale-mimicked super oil-repelling wettability that functions under water has emerged as an important avenue for developing various functional materials. Mainly, polymeric hydrogel, brittle metal oxides, and electrostatic multilayers have been utilized for synthesizing an artificial underwater superoleophobic interface, and most of these reported artificial bioinspired wettabilities are likely to be compromised under practically relevant severe settings. Moreover, a design of a dual-functional fish-scale-mimicked interface that would be capable of separating water-soluble organic pollutants, in addition to the eco-friendly removal of different forms of contaminated oils under severe settings, could be highly useful in addressing globally recognized severe water pollution problems. In this report, a dual-functional underwater superoleophobic membrane is introduced for simultaneous removal of  contaminated dyes and oil/oily phase, where graphene oxide (GO) nanosheets were strategically integrated with naturally abundant and environmentally friendly cotton fibers by adopting mussel-inspired chemistry. The synthesized membrane was found to exhibit fish-scale-mimicked nonadhesive underwater superoleophobicity, and this super oil repellency remained unaffected even after prolonged exposures to various practically relevant harsh chemical and physical conditions. Moreover, this material was capable of rapid (within 2 min) adsorption of water-soluble cationic organic dyes with high adsorption capacity (136 mg/g for methylene blue), following linear pseudo-second-order kinetics. The biomimicked extreme oil repellency was exploited for separating different forms (bulk and emulsion) of oil/oily (both sedimenting and floating) contaminants with high separation efficiency (above 98%), and the immobilized GO in the biomimicked membrane parallely allowed cationic organic dyes (methylene blue and crystal violet) to be removed from the aqueous phase through a single-step gravity-driven filtration process. The performance of simultaneous removal of cationic dyes and oil/oily contaminants remained unaffected even under various practically relevant severe settings including extremes of pH, sea water, river water, and so forth. Furthermore, the dual-functional biomimicked membrane was repetitively (10 times) used for successful separation of both the contaminated cationic dye and oil/oily phase from the aqueous phase, without affecting the separation efficiency. This simple approach is likely to provide a facile basis for addressing the problem of water pollution under practically relevant diverse and severe settings.

Capillary-Flow-Optimized Heat Localization Induced by an Air-Enclosed Three-Dimensional Hierarchical Network for Elevated Solar Evaporation

Solar evaporation is a cost-effective way for obtaining clean water using renewable energy. However, many solar evaporation devices still show unsatisfactory performance and suffer from inefficient utilization of absorbed solar energy. Herein, numerical simulations of solar evaporation demonstrate that the heat management is a key factor governing the solar evaporation efficiency. This prediction is confirmed through using a bilayered solar steam generation architecture [hollow glass microsphere-carbon black (HS-CB)] both in laboratory- and pilot-scale studies. The HS-CB consists of a CB film as a solar-thermal conversion layer and three-dimensional hierarchical polyvinylidene fluoride skeleton cross-linking HSs as a heat localization and water-transporting layer. A balance between thermal insulation and capillary-driven water transport can be reached by tuning the porosity of the thermal-insulating layer, thus inducing optimized heat localization. The proposed structure evaporates water with an efficiency of 82.1% under 1 sun irradiance (1 kW m^-2) in the laboratory and can even stably produce 4.63 L m^-2 d^-1 (average efficiency of 37%) of purified water from highly concentrated industrial waste water in the pilot study, demonstrating its promising potential for applications in seawater desalination and brackish water purification.

Recent advances of bioinspired functional materials with specific wettability: from nature and beyond nature

Through 3.7 billion years of evolution and natural selection, plants and animals in nature have ingeniously fulfilled a broad range of fascinating functions to achieve optimized performance in responding and adapting to changes in the process of interacting with complex natural environments. It is clear that the hierarchically organized micro/nanostructures of the surfaces of living organisms decisively manage fascinating and amazing functions, regardless of the chemical components of their building blocks. This conclusion now allows us to elucidate the underlying mechanisms whereby these hierarchical structures have a great impact on the properties of the bulk material. In this review, we mainly focus on advances over the last three years in bioinspired multiscale functional materials with specific wettability. Starting from selected naturally occurring surfaces, manmade bioinspired surfaces with specific wettability are introduced, with an emphasis on the cooperation between structural characteristics and macroscopic properties, including lotus leaf-inspired superhydrophobic surfaces, fish scale-inspired superhydrophilic/underwater superoleophobic surfaces, springtail-inspired superoleophobic surfaces, and Nepenthes (pitcher plant)-inspired slippery liquid-infused porous surfaces (SLIPSs), as well as other multifunctional surfaces that combine specific wettability with mechanical properties, optical properties and the unidirectional transport of liquid droplets. Afterwards, various top-down and bottom-up fabrication techniques are presented, as well as emerging cutting-edge applications. Finally, our personal perspectives and conclusions with regard to the transfer of micro- and nanostructures to engineered materials are provided.

Designing robust underwater superoleophobic microstructures on copper substrates

Recently, surfaces with a robust underwater superoleophobicity have attracted much attention. Although it is recognized that stable microstructures are significant for such surfaces, a clear picture of how microstructural features such as morphology, size, etc. influence their own stability and related wettability is still missing. Herein, three low adhesive underwater superoleophobic copper surfaces with different microstructures (hemispheric, pinecone-like, and honeycomb) were first prepared, and then the stability of these microstructures was examined by a series of physical and chemical damage experiments (sand grain abrasion, corrosion in acid/base solutions, etc.). The results indicate that the hemispheric microstructure is more stable than the other two microstructures and the corresponding surface has a robust underwater superoleophobicity. Theoretical simulation analysis further confirms the experimental results and reveals that different stabilities are ascribed to different stress distributions on these microstructures under an external force due to distinct microstructure shapes. Furthermore, based on the same design strategy, a robust underwater superoleophobic oil/water separation copper mesh film was also prepared. This work provides an insight into the effect of microstructural features on the stability and related underwater oil-repellent properties of superoleophobic copper surfaces, and could provide us with some fresh design ideas for robust superwetting surfaces.

Tough Reversible Adhesion Properties of a Dry Self-Cleaning Biomimetic Surface

Geckos have one of the world's most efficient reversible adhesion systems. Even walking in dusty conditions, geckos can dislodge up to 80% of contaminants and recover their adhesion capability after walking as few as four steps. Thus far, artificial dry self-cleaning materials inspired by the geckos' hierarchical fibrillar structure have been only able to remove 55% of collected large particle contaminants with 30 steps. Challenges, including low mechanical strength, low stiffness, and short fatigue time keep these materials from being used in practical applications. This study involves the novel fabrication of dry self-cleaning surfaces with a high mechanical performance and an outstanding dry self-cleaning property. Imposing a load-drag-pull process similar to a gecko's foot adhesion process, our biomimetic surfaces could dislodge up to 59% of microparticles (∼8 μm) with as few as five steps. Furthermore, the surface had an excellent screening ability at low temperatures regardless of the surface roughness similarity. The surfaces were also proven to be scratch resistant. The biomimetic surfaces exhibit enhanced dry self-cleaning and mechanical properties and could be promising in applications such as reusable adhesives, biochips, aerospace satellite waste collection, and screening equipment.

Bio-Inspired Underwater Super Oil-Repellent Coatings for Anti-Oil Pollution

Underwater superoleophobic surfaces have attracted great attention due to their broad applications such as anti-oil adhesion, oil capture and transportation, and oil/water separation. However, it is often fairly complex and time-consuming, involved in the construction of micro/nanostructures and the regulation of chemical compositions; there is an urgent need to develop new strategies to conquer these problems. Inspired by the strong anchoring capability and easy accessibility of plant polyphenols, we can readily and rapidly fabricate tannic acid (TA) coated copper surfaces with the excellent underwater super oil-repellent property. To achieve the optimal condition for TA modification, the influence of immersion time, TA concentration, and pH value on underwater-oil wettability and adhesion has been systematically explored. Furthermore, the underwater super oil-repellent feature can be widely achieved for different oils and on various metal sheets, suggesting the potential applications for plenty of fields such as anti-oil pollution.