Smart candle soot coated membranes for on-demand immiscible oil/water mixture and emulsion switchable separation

Preparation of multifunctional PET membrane and its application in high-efficiency filtration and separation in complex environment

Nowadays, effluent treatment is a severe challenge mainly because of its complex composition, which includes oil, heavy metal ions, and dyes. Developing new intelligent membranes is one of the strategies to tackle these significant challenges in wastewater treatment. In this study, we fabricated asymmetric polyethylene glycol terephthalate (PET) membranes by grafting cross-linked poly (itaconic anhydride) (CL-PITA) nanoparticles onto the irradiated face. These nanoparticles were then functionalized with polyethyleneimine (PEI) and protonated with HCl to introduce numerous active electropositive amine groups. The fundamental purpose was to increase surface roughness, introduce numerous hydrophilic groups, and modify it to create a multi-functional PET membrane to separate complex environments. The promising results demonstrated that the protonated PET-g-ITA/DVB(10)-cat membrane exhibited excellent separation efficiencies (SE) for water/light oil, water/heavy oil and oil-in-water (O/W) emulsion. Compared to PET-g-ITA/DVB(0)-cat, it showed superior performance in SE for O/W emulsion and flux decay for water/light oil after 10 cycles. More interestingly, owing to numerous positively charged active amino groups and negativley charged carboxylate groups, the intelligent membrane exhibited a high removal rate of ca. 90 % for anionic dye (congo red) and heavy metals (Cu2+ and Co2+), showing great potential in complex water treatment environments.

Dual Superlyophobic Materials for Under-Liquid Microfluid Manipulation, Immiscible Solvent Separation, and CO2 Blockage

Oily water purification, immiscible solvent separation, sensitive microreaction, and CO₂ blockage are of great interest because of their importance for the environment and demands of controllable microreactions. However, one specific material that can meet all the requirements has yet to be reported. Herein, we developed a simple environment-benign method to prepare specific dual superlyophobic materials to solve the problems mentioned earlier. The dual superlyophobic materials can maintain their dual superoleophobicity in various oil/water systems, and no additional surface modifications were required when the oil/water system was changed. Moreover, the materials can be used to separate oil/water mixtures with separation efficiencies greater than 99.50% even after 40 separation cycles and separate immiscible organic solvents with efficiencies over than 99.25% after 20 cycles. Separations of meal waste oily water at 60 °C and crude oil/water were also successfully performed. The materials can be further applied to manipulate and block CO₂ bubbles under liquid. The materials can also act as a platform for microdrop manipulation/microreaction under liquid.

Recent advances in superwetting materials for separation of oil/water mixtures

Engineering surfaces or membranes that allow an efficient oil/water separation is highly desired in a wide spectrum of applications ranging from oily wastewater discharge to offshore oil spill accidents. Recent advances in biomimetics, manufacturing, and characterization techniques have led to remarkable progress in the design of various superwetting materials with special wettability. In spite of exciting progress, formulating a strategy robust enough to guide the design and fabrication of separating surfaces remains a daunting challenge. In this review, we first present an overview of the wettability theory to elucidate how to control the surface morphology and chemistry to regulate oil/water separation. Then, parallel approaches are considered for discussing the separation mechanisms according to different oil/water mixtures, and three separation types were identified including filtration, adsorption and other separation types. Finally, perspectives on the challenges and future research directions in this research area are briefly discussed.

Turbo-Synergistic Oily Wastewater Remediation in Bio-Inspired Cone Array Barrel

Oily wastewater discharge causes not only the pollution of environment but also the waste of resources. Existing technologies for wastewater remediation, such as membrane and particle methods, are variable and effective, but are difficult for achieving continuous and rapid oil-water separation. Here, with the synergy of turbo stirring, a strategy for emulsion separation is demonstrated based on the bio-inspired cone array barrel. Under the centrifugal force, oil droplets in emulsion are thrown onto the cones arrayed on inner wall due to the Coriolis effect, captured by microstructures on cone surface and then penetrate out through the superhydrophobic pores, while only the remediated water remains. The separation technique maintains a high efficiency of above 99.5% for over 30 times of use, as well as for emulsions with variable ingredients. This structure-dynamics synergistic separation strategy evolves the future technologies on water purification in industrial and daily processes.

Textured ceramic membranes for desilting and deoiling of produced water in the Permian Basin

Oil production in the Permian Basin gives rise to large volumes of produced water contaminated by silt, emulsified oil, and additives used for enhanced oil recovery. There is intense interest in the design of membrane modules as sustainable alternatives for produced water treatment to enable the reuse of produced water for agricultural applications, injection into aquifers, and redeployment in oil recovery. Here, we report a hierarchically textured cement-based membrane exhibiting orthogonal wettability, specifically, superhydrophilic and underwater superoleophobic characteristics. The in situ formation of ettringite needles accompanied by embedding of glass spheres imbues multiscale texturation to stainless-steel mesh membranes, enabling the separation of silt and oil from produced water at high flux rates (1600 L h⁻¹۰m⁻², at ca. 2.7 bar). Oil concentration is reduced as low as 1 ppb with an overall separation efficiency of 99.7% in single-pass filtration. The membranes show outstanding mechanical resilience and retention of performance across multiple cycles.

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Multiscale 3D texturation of a metal mesh membrane engenders orthogonal wettability

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High separation efficiency of ca. 99% was achieved for produced water

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Oil concentration reduced to ≤1 ppb in a single pass at a high flux rate

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Desiliting and deoiling demonstrated for real produced water streams

Destructing surfactant network in nanoemulsions by positively charged magnetic nanorods to enhance oil-water separation

The separation of ultrafine oil droplets from wasted nanoemulsions stabilized with high concentration of surfactants is precondition for oil reuse and the safe discharge of effluent. However, the double barriers of the interfacial film and network structures formed by surfactants in nanoemulsions significantly impede the oil-water separation. To destroy these surfactant protective layers, we proposed a newly-developed polyethyleneimine micelle template approach to achieve simultaneous surface charge manipulation and morphology transformation of magnetic nanospheres to magnetic nanorods. The results revealed that positively charged magnetic nanospheres exhibited limited separation performance of nanoemulsions, with a maximum chemical oxygen demand (COD) removal of 50%, whereas magnetic nanorods achieved more than 95% COD removal in less than 30 s. The magnetic nanorods were also applicable to wasted nanoemulsions from different sources and exhibited excellent resistance to wide pH changes. Owing to their unique one-dimensional structure, the interfacial dispersion of magnetic nanorods was significantly promoted, leading to the efficient capture of surfactants and widespread destruction of both the interfacial film and network structure, which facilitated droplet merging into the oil phase. The easy-to-prepare and easy-to-tune strategy in this study paves a feasible avenue to simultaneously tailor surface charge and morphology of magnetic nanoparticles, and reveals the huge potential of morphology manipulation for producing high-performance nanomaterials to be applied in complex interfacial interaction process. We believe that the newly-developed magnetic-nanorods significantly contribute to hazardous oily waste remediation and advances technology evolution toward problematic oil-pollution control.

Candle Soot-Based Electrosprayed Superhydrophobic Coatings for Self-Cleaning, Anti-Corrosion and Oil/Water Separation

The interest in candle soot (CS)-based superhydrophobic coatings has grown rapidly in recent years. Here, a simple and low-cost process has been developed for the fabrication of CS-based superhydrophobic coatings through electrospraying of the composite cocktail solution of CS and polyvinylidene fluoride (PVDF). Results show that the superhydrophobicity of the coating closely relates to the loading amount of CS which results in coatings with different roughnesses. Specifically, increasing the CS amount (not more than 0.4 g) normally enhances the superhydrophobicity of the coating due to higher roughness being presented in the produced microspheres. Further experiments demonstrate that the superhydrophobicity induced in the electrosprayed coating results from the synergistic effect of the cocktail solution and electrospray process, indicating the importance of the coating technique and the solution used. Versatile applications of CS-based superhydrophobic coatings including self-cleaning, anti-corrosion and oil/water separation are demonstrated. The present work provides a convenient method for the fabrication of CS-based superhydrophobic coatings, which is believed to gain great interest in the future.

Upcycling Waste Pine nut Shell Membrane for Highly Efficient Separation of Crude Oil-in-Water Emulsion

Discharge of oily sewage and frequent oil spills have caused serious harm to human production, life, and ecological environment. Due to the presence of a large number of surfactants in water, these oil-water mixtures are easy to form oil-in-water emulsion, which is difficult to separate by traditional methods. At the same time, the water-soluble pollutants such as dyes and heavy metal ions in oily wastewater also cause great harm to the human body and the environment. A pine nut shell is a kind of common domestic waste material. Herein, an underwater superoleophobic pine nut shell membrane (PNSM) was prepared by the simple pumping filtration method, which realized the separation of oil-in-water emulsion and adsorption of dyes and heavy metal ions. In addition, the filter membrane can be used for separating corrosive emulsions of strong acid, strong alkali, and 3.5% NaCl solutions (simulated seawater). Besides, the PNSM showed excellent toughness and flexibility. Due to the abovementioned performance, this cost-efficient and environmentally friendly membrane can be a promising candidate for multifunctional oily water remediation.

The local electric field effect of onion-like carbon nanoparticles for improved laser desorption/ionization efficiency of saccharides

It is still a challenge to improve ionization efficiency of saccharides in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Herein, the highly curved onion-like carbon nanoparticles (OCS) were synthesized from the low-price candle raw via a facile strategy. The unique nanostructure of OCS showed large surface area with plentiful mesoporous architecture, highly curved sp² carbon with regulating electronic effect, and good hydrophilicity, which could be beneficial to facilitate the desorption and ionization efficiency in MS process. The prepared OCS material as MALDI matrix exhibited the superior performance for the detection of xylose, glucose, maltose monohydrate, and raffinose pentahydrate in positive-ion mode with low background noise, enhanced ion intensities, uniform distribution, excellent reproducibility, good salt-tolerance, and high sensitivity compared to control candle soot (CS) and traditional α-cyano-4-hydroxycinnamic acid (CHCA) matrices. This highly effective LDI of OCS matrix was attributed to its enhancing local electric field effect, strong UV absorption ability, and high photo-thermal conversion performance. Furthermore, the OCS-assisted LDI MS approach was employed to quantitatively detect glucose in rat serum. This LDI MS platform may have valuable for the analysis of metabolites in clinical research.

A Materials Science Perspective of Midstream Challenges in the Utilization of Heavy Crude Oil

An increasing global population and a sharply upward trajectory of per capita energy consumption continue to drive the demand for fossil fuels, which remain integral to energy grids and the global transportation infrastructure. The oil and gas industry is increasingly reliant on unconventional deposits such as heavy crude oil and bitumen for reasons of accessibility, scale, and geopolitics. Unconventional deposits such as the Canadian Oil Sands in Northern Alberta contain more than one-third of the world's viscous oil reserves and are vital linchpins to meet the energy needs of rapidly industrializing populations. Heavy oil is typically recovered from subsurface deposits using thermal recovery approaches such as steam-assisted gravity drainage (SAGD). In this perspective article, we discuss several aspects of materials science challenges in the utilization of heavy crude oil with an emphasis on the needs of the Canadian Oil Sands. In particular, we discuss surface modification and materials' design approaches essential to operations under extreme environments of high temperatures and pressures and the presence of corrosive species. The demanding conditions for materials and surfaces are directly traceable to the high viscosity, low surface tension, and substantial sulfur content of heavy crude oil, which necessitates extensive energy-intensive thermal processes, warrants dilution/emulsification to ease the flow of rheologically challenging fluids, and engenders the need to protect corrodible components. Geopolitical reasons have further led to a considerable geographic separation between extraction sites and advanced refineries capable of processing heavy oils to a diverse slate of products, thus necessitating a massive midstream infrastructure for transportation of these rheologically challenging fluids. Innovations in fluid handling, bitumen processing, and midstream transportation are critical to the economic viability of heavy oil. Here, we discuss foundational principles, recent technological advancements, and unmet needs emphasizing candidate solutions for thermal insulation, membrane-assisted separations, corrosion protection, and midstream bitumen transportation. This perspective seeks to highlight illustrative materials' technology developments spanning the range from nanocomposite coatings and cement sheaths for thermal insulation to the utilization of orthogonal wettability to engender separation of water-oil emulsions stabilized by endogenous surfactants extracted during SAGD, size-exclusion membranes for fractionation of bitumen, omniphobic coatings for drag reduction in pipelines and to ease oil handling in containers, solid prills obtained from partial bitumen solidification to enable solid-state transport with reduced risk of damage from spills, and nanocomposite coatings incorporating multiple modes of corrosion inhibition. Future outlooks for onsite partial upgradation are also described, which could potentially bypass the use of refineries for some fractions, enable access to a broader cross-section of refineries, and enable a new distributed chemical manufacturing paradigm.

Dynamic Anti-Icing Surfaces (DAIS)

Remarkable progress has been made in surface icephobicity in the recent years. The mainstream standpoint of the reported antiicing surfaces yet only considers the ice-substrate interface and its adjacent regions being of static nature. In reality, the local structures and the overall properties of ice-substrate interfaces evolve with time, temperature and various external stimuli. Understanding the dynamic properties of the icing interface is crucial for shedding new light on the design of new anti-icing surfaces to meet challenges of harsh conditions including extremely low temperature and/or long working time. This article surveys the state-of-the-art anti-icing surfaces and dissects their dynamic changes of the chemical/physical states at icing interface. According to the focused critical ice-substrate contacting locations, namely the most important ice-substrate interface and the adjacent regions in the substrate and in the ice, the available anti-icing surfaces are for the first time re-assessed by taking the dynamic evolution into account. Subsequently, the recent works in the preparation of dynamic anti-icing surfaces (DAIS) that consider time-evolving properties, with their potentials in practical applications, and the challenges confronted are summarized and discussed, aiming for providing a thorough review of the promising concept of DAIS for guiding the future icephobic materials designs.

NaOH-Induced Fabrication of a Superhydrophilic and Underwater Superoleophobic Styrene-Acrylate Copolymer Filtration Membrane for Effective Separation of Emulsified Light Oil-Polluted Water Mixtures

Oil-polluted water mixtures are difficult to separate, and thus, they are considered as a global challenge. A superior superhydrophilic and low-adhesive underwater superoleophobic styrene-acrylate copolymer filtration membrane is constructed using a salt (NaOH)-induced phase-inversion approach. The as-fabricated filtration membrane provides a hierarchical-structured surface morphology and three-dimensional high density open-rough porous geometry with a special chemical composition including highly accessible hydrophilic -COO^- agents, which all are of great importance for long-term usage of immiscible/emulsified (light) oil-polluted wastewater separation. The separation is performed with a high efficiency and a high flux under either a gravity-driven force or a small applied pressure of 0.1 bar. The filtration membrane indicates an excellent anti-fouling property and is easily recycled during multiple cycles. The outstanding performance of the filtration membrane in separating oil-polluted water mixtures and the cost-effective synthetic approach as well as commercially scaled-up initial materials all highlight its potential for practical applications.

Insights into Regional Wetting Behaviors of Amphiphilic Collagen for Dual Separation of Emulsions

Industrial manufacture generates a huge quantity of emulsion wastewater, which causes serious threats to the aquatic ecosystems. Water-in-oil (W/O) and oil-in-water (O/W) emulsions are two major types of emulsions discharged by industries. However, dual separation of W/O and O/W emulsions remains a challenging issue due to the contradictory permselectivity for separating the two emulsions. In the present investigation, the amphiphilicity-derived regional wetting mechanism of water and oil on the amphiphilic collagen fibers was revealed based on the combination of numerous experiments and molecular dynamics (MD) simulations. Electrostatic interactions and van der Waals force were manifested to be the driving forces of regional wetting in the hydrophilic and hydrophobic regions, respectively. The regional wetting endowed amphiphilic collagen fibers with underwater oleophobicity and underoil hydrophilicity, which enabled dual separation of emulsions by selectively retaining the dispersed water phase of W/O emulsions in the hydrophilic regions while the dispersed oil phase of O/W emulsions in the hydrophobic regions. The achieved separation efficiency was higher than 99.98%, and the flux reached 3337.6 L m^-2 h^-1. Initial wetting status significantly affects the regional wetting-enabled dual separation. Based on the MD simulations, amphiphilic intramolecular conformations of tropocollagen were suggested to be the origins of regional wetting on collagen fibers. Our findings may pave the way for developing high-performance dual separation materials that are promising to be utilized for the practical treatment of emulsion wastewater.

Multifunctional superhydrophobic adsorbents by mixed-dimensional particles assembly for polymorphic and highly efficient oil-water separation

Supra-wetting materials, especially superhydrophobic absorption materials, as an emerging advanced oil-water separation material have attracted extensive concern in the treatment of oil spillage and industrial oily wastewater. However, it is still a challenge to fabricate robust and multifunctional superhydrophobic materials for the multitasking oil-water separation and fast clean-up of the viscous crude oil by an environment-friendly and scalable method. Herein, a solid-solid phase ball-milling strategy without chemical reagent-free modification was proposed to construct heterogeneous superhydrophobic composites by using waste soot as the solid-phase superhydrophobic modifier. A series of covalent bond restricted soot-graphene (S-GN) or soot-Fe₃O₄ (S-Fe₃O₄) composite materials with a peculiar micro-nano structure are prepared. Through "glue+superhydrophobic particles" method, the prepared soot-based composite particles are facilely loaded on the porous skeleton of the sponge to obtain multifunctional superhydrophobic adsorbents. The reported superhydrophobic adsorbents exhibited robust chemical and mechanical stability, convenient magnetic collection, the high oil absorption capacity of 60-142 g g^-1, durable recyclability (>250 cycles), efficient separation efficiency (>99.5%) and outstanding self-heated performance, which enable them to be competent for oil-water separation in multitasking and complex environment (floating oils, continuous oil collection, oil-in-water emulsion, and viscous oil-spills).

Simple preparation of a durable and low-cost load-bearing three-dimensional porous material for emulsion separation

Superhydrophobic MR–C composites were used for the separation of water-in-oil emulsions. Under a load of 500 N with a reciprocating wear, the contact angle was kept at 146 ± 2°. The oil-in-water emulsion can still be separated efficiently.

Multiple functional materials from crushing waste thermosetting resins

Novel applications of waste thermosetting resins are developed by facile mechanical crushing, and their excellent performances are demonstrated in oil-water separation, superhydrophobic coatings with diverse water adhesion, acid liquid/gas monitoring and information storage. This work provides new ideas for waste treatments and functional material design, as well as speeds up the transformation of waste resins from laboratory achievements to industrial applications. Moreover, it can also improve the utilization efficiency of non-renewable resources and meet the requirements of energy conservation and environmental protection.

Self-Concentrated Surface-Enhanced Raman Scattering-Active Droplet Sensor with Three-Dimensional Hot Spots for Highly Sensitive Molecular Detection in Complex Liquid Environments

In this work, a surface-enhanced Raman scattering (SERS)-active droplet with three-dimensional (3D) hot spots prepared from a superhydrophobic SERS substrate, which is inspired by the nut wizard strategy, was developed for ultrasensitive detection in complex liquid environments. The SERS substrate was composed of silver-capped parylene C-coated carbon nanoparticles (Ag-PC@CNPs). Such a SERS substrate was prepared by candle-soot deposition to provide a porous carbon nanoparticle layer followed by deposition of a parylene C film to protect the CNPs and then sputtering of silver nanoparticles. Similar to a nut wizard, a droplet rolling on the Ag-PC@CNP-coated substrate picked up the Ag-PC@CNPs. In this way, a self-concentrated and extremely sensitive SERS-active droplet sensor with 3D hot spots was formed. The sensor did not require precise laser focusing and showed relatively high repeatability and much higher sensitivity than those of a corresponding SERS substrate with two-dimensional hot spots. The sensor also achieved high sensitivity and specificity in complex liquid environments; in addition, bovine serum albumin with a concentration as low as 1 pM can be achieved. Consequently, an extremely simple, flexible, and highly sensitive SERS detection technique applicable to liquid biopsy analysis is anticipated.

PVDF-Modified TiO2 Nanowires Membrane with Underliquid Dual Superlyophobic Property for Switchable Separation of Oil-Water Emulsions

Separation membranes with underliquid dual superlyophobicity have recently caused widespread concern due to their switchable separation of oil-water mixtures and emulsions. However, the fabrication of the reported underliquid dual superlyophobic membranes is difficult, and the design of the underliquid dual superlyophobic surface of these membranes is challenging because of their complex surface composition. Theoretically, underliquid dual superlyophobicity is an underliquid Cassie state attainable by the synergy of the underliquid dual lyophobic surface and the construction of a high-roughness surface. Herein, we fabricated an underliquid dual superlyophobic membrane by combining underliquid dual lyophobic polyvinylidene fluoride (PVDF) and TiO₂ nanowires. PVDF-modified TiO₂ nanowire membranes with underliquid dual superlyophobicity were prepared via a simple adsorption and filtration approach. PVDF was coated onto TiO₂ nanowires to form a PVDF layer with a thickness of 6 nm. The PVDF modification provided flexibility to the fragile TiO₂ nanowires membrane and changed its wettability from underwater superoleophobicity/underoil superhydrophilicity to underliquid dual superlyophobicity. The PVDF-modified TiO₂ nanowires membrane efficiently separated both oil-in-water and water-in-oil emulsions. The binary cooperative effect between the TiO₂ nanowires and the coated PVDF layer was responsible for the underliquid dual superlyophobicity.

One-step, low-cost, mussel-inspired green method to prepare superhydrophobic nanostructured surfaces having durability, efficiency, and wide applicability

Various oils discharged from daily life and industrial production, as well as frequent oil spillages, have led to severe water pollution and ecological problems. Mussel-inspired polydopamine has been widely applied for fabrication of superhydrophobic materials for oil/water separation. However, the need of additional nanoparticles via tedious steps to construct nanostructures, and the high cost of dopamine itself limit its practical applications. Moreover, the application modes of superhydrophobic materials for oil/water separation are monotonous, which will limit the applied range of the superhydrophobic materials. For example, superhydrophobic sponge was usually used for adsorbing oil droplets or oil spills from water, while superhydrophobic fabric or mesh was usually used for separating bulk layered oil/water mixture. Therefore, developing simple and low-cost mussel-inspired surface modification strategy toward superhydrophobic materials, as well as diverse application modes for oil/water separation, is still highly desired. In this study, superhydrophobic sponge and fabric with nanostructures, which exhibits excellent performance for diverse oil/water separation, have been fabricated through a novel one-step and cost-effective mussel-inspired approach. The resultant superhydrophobic sponge exhibits outstanding oil absorption capability (weight gains up to 8860%), while the superhydrophobic fabric can effectively separate oil/water mixture. Moreover, diverse modes for oil/water separation have been developed for the first time. For example, water-in-oil emulsion can be highly-efficient separated by a compressed superhydrophobic sponge (~1800L m^-2h^-1 bar^-1 for water-in-oil emulsion, and above 99% rejection rate for water droplets), while crude oil spills can be efficiently collected by a superhydrophobic boat (above 98%).

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

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

Water deteriorates lubricating oils: removal of water in lubricating oils using a robust superhydrophobic membrane

Water is recognized as a contaminant in lubricating oils. Recently, interfacial materials with special wettability have been broadly developed for oil-water separation. However, solving lubricating oil failure caused by water remains a challenge. Here, a robust superhydrophobic membrane is presented to effectively remove water in lubricating oils to recover their lubricating capability. Compared to pure lubricating oils without or with an additive, lubricating oils collected from their emulsions using the superhydrophobic membrane have an equivalent friction coefficient and wear volume, which are much lower than that of lubricating oils contaminated by water. Water in lubricating oils accelerates the oxidation of metallic substrates and wear corrosion. Moreover, the metallic ions dissolved in water-containing lubricating oils induce the catalytic dehydrogenation of lubricating oils, leading to the deposition of a good deal of carbon-based wear debris. Importantly, the prepared membrane shows steady performance in regard to extreme water repellency, high-efficiency purification of lubricating oils, and low wear volume even after harsh mechanical damage. Robust interfacial materials have potential advantages in practically solving lubricating oil failure caused by water.

Beetle-like droplet-jumping superamphiphobic coatings for enhancing fog collection of sheet arrays

Fog collection from atmosphere is an effective way to solve the water resource crisis in arid or semi-arid areas. Inspired by the bumpy surface of the desert beetle, this work provides a beetle-like superamphiphobic coating by adding silicon carbide particles to nano-SiO2 superamphiphobic coating in proportion, which shows excellent superamphiphobic performance, high nucleation rate, efficient drop removal efficiency and recommendable fog collection effect. In this work, drop removal is facilitated by the collisions of water droplets between the array sheets, and when the as-prepared samples are placed parallel to each other and with a space of ∼2 mm, the jumping drop collisions between two sample surfaces could promote the departure of droplets, and the water collection rate of the collision surface increased by ∼217% compared to that of the non-collision surface, which provides a new idea to promote water droplet removal. This work findings are instrumental in water collection and have wide application prospects in desalination, heat transfer, anti-fogging and other fields.

Reversibly switching water droplets wettability on hierarchical structured Cu2S mesh for efficient oil/water separation

Surfaces with reversible wettability have broad applications but remain challenging since the switching process is usually energy intensive and complex. In this paper, a pyramid shaped Cu2S film with hierarchical micro/nanostructures is formed on a commercial copper mesh. This film is formed by a spontaneous redox sulfuration reaction and results in a roughened surface, which enables reversible wetting transition between superhydrophilicity to superhydrophobicity. This switching occurs by simple processes such as alternately storing in air or using an ethanol solution treatment and yields cyclic wettability switching for many cycles. This convenient wetting transition behavior, as well as strong stability and efficient oil/water separation with efficiency exceeding 98%, renders it as a potentially useful mesh material for switchable surfaces.

Expanded Graphite-Polyurethane Foams for Water-Oil Filtration

Herein, expanded graphite is successfully combined with waterborne polyurethane to develop porous foams with underwater oleophobic properties for the separation of surfactant-free, oil-in-water mixtures and emulsions. To obtain foams with different pore sizes and therefore with different performances in the oil-water filtration process, two solvent-free fabrication processes are adopted. In the first one, the expanded graphite granules are mixed with the waterborne polyurethane (PUEGr), and in the second method, calcium carbonate is introduced to the two-component mixture (PUEGr_t). In both cases, the obtained foams exhibit hydrophilicity and oleophilicity in air and oleophobicity underwater, and they have porous interconnected networks, while their pore size distribution differs significantly. The foams can be used as 3D filters, able to separate, through gravity, surfactant-free, oil-in-water mixtures (10% w/w oil in water) with high oil rejection efficiencies and flow rates that depend on the type of foam. In particular, in the gravity-driven filtration process using 100 mL of the feed liquid, the PUEGr foams have an oil rejection efficiency of 96.85% and flow rate of 9988 L m^-2 h^-1, while for the PUEGr_t foams the efficiency is higher (99.99%) and the flow rate is lower (8547 L m^-2 h^-1) due to their smaller pore size. Although the PUEGr_t foams have slower separation performance, they are more efficient for the separation of surfactant-free emulsions (1% w/w oil in water) reaching an oil rejection efficiency of 98.28%, higher than the 95.66% of the PUEGr foams of the same thickness. The foams can be used for several filtration cycles, as well as in harsh conditions without deteriorating their performance. The nature of raw materials, the simple solvent-free preparation method, the effective gravity-driven filtration even in harsh conditions, and their reusability suggest that the herein engineered foams have great potential for practical applications in oil-water separation through highly energy-efficient filtration.

Wool-Like Fibrous Nonwoven Mesh with Ethanol-Triggered Transition between Antiwater and Antioil Superwetting States for Immiscible and Emulsified Light Oil-Water Separation

Superwetting antiwater and antioil textiles are not only very attractive for efficient and cost-effective oil-water separation but also very challenging to be prepared. A well-designed polystyrene wool-like fibrous mesh was fabricated by a controlled electrospinning setup to provide simple and quick reversible ethanol-triggered switching between antiwater and antioil superwetting states in various media such as air, water, and oil. Additionally, it exhibits a long-term stability against acid, alkaline, and salt at high concentrations. Such characteristics will prove unusual capabilities for controllable gravity-driven separation of both immiscible and emulsified oil-water mixtures with a separation efficiency more than 99.0%, as well as a prolonged antifouling property and an excellent recyclability; all will be advantageous for technical applications including oil removing and water removing. Furthermore, light oil-polluted water and water-soluble pollutants can be simultaneously cleaned well by the antioil mesh acting in the water-removing mode.

Underliquid Superlyophobic Copper-Coated Meshes for the Separation of Immiscible Organic Liquid Mixtures

Superwettable materials have been studied extensively and successfully applied in various forms liquid separation. However, because of low surface tension differences, organic liquids (OLs) exhibit approximate wettability on most of the material surfaces, and the separation of OL mixtures remains a challenge. The current separation method for OL mixtures is mainly dependent on covalent modification to precisely control the surface energy of the membranes, which is extremely complicated. Herein, we demonstrate a novel concept of underliquid superlyophobicity for the separation of immiscible OLs mixtures, which only depend on a relatively stable liquid-repellent interface. Furthermore, the minimum system's free-energy principle was used to explain this wetting behavior. Different from the previous reports, the method of separation of OL mixtures does not involve various low-surface-energy materials, thus it is facile and eco-friendly. Our research provides a general strategy for the efficient separation of immiscible OLs mixtures and is expected to promote the development of superwettable materials for multiphase liquid separation.

Waste cigarette filter as nanofibrous membranes for on-demand immiscible oil/water mixtures and emulsions separation

The rapid industrial growth and the frequent oil spill accidents have led to the large production of oily wastewater. Thus, it is urging to develop a low-cost and eco-friendly material to purify the oily wastewater. In our work, the waste cigarette filter as the raw material was used to prepare cigarette filter coated meshes (CFCMs) by a facile electrospinning approach. The as-prepared CFCMs prewetted with water or oil achieved the special wetting performance of underwater superoleophobicity or underoil superhydrophobicity without any further chemical modification. Hence, the cigarette filter coated meshes with larger or smaller pore size can be applied to on-demand immiscible oil/water mixtures (light or heavy oil/water mixtures) and oil/water emulsions separation (water-in-oil or oil-in-water emulsions), respectively. Moreover, the CFCMs still exhibited high separation efficiency larger than 99.9% for immiscible oil/water mixtures and emulsions after many cyclic testing. The work provides an application in oil/water separation for waste cigarette filters and contributes to reduce the pollution for environment from the waste cigarette filters.

Switchable Wettability Surface with Chemical Stability and Antifouling Properties for Controllable Oil-Water Separation

Membrane materials with special wettability for separating oil-water mixtures have gradually become one of the research hotspots. However, oily wastewater usually has very strong corrosiveness, which puts forward high requirements for the chemical stability of the separation membrane. In addition, oil droplets may block the pores, resulting in the decrease of separation efficiency or even separation failure. Herein, biomimetic TiO₂-titanium meshes (BTTMs) with switchable wettability were successfully fabricated by one-step dip coating of poly(vinylidene difluoride) and modified TiO₂ suspension on the titanium meshes. The simple and efficient preparation method will facilitate the promotion of this smart material. Due to the controlled wettability, the BTTM can separate water or oil from an oil-water mixture as required. When the BTTM was immersed in strong corrosive solution or liquid nitrogen, the wettability did not change much, showing the good stability of the BTTM. Furthermore, the BTTM also has self-healing ability, self-recovery anti-oil-fouling properties, and self-cleaning behavior, which help it resist oil pollution and improve its recyclability. This study provides a simple and efficient strategy for fabricating a stable smart surface for on-demand controllable treatment of corrosive oily wastewater.