Rational design of materials interface at nanoscale towards intelligent oil-water separation

Preparation of temperature-dependent flux controllable cellulose nanofiber-based films and their application in oil-water separation

The discharge of industrial oily wastewater causes a significant waste of resources and serious environmental pollution problems. Oil- water separation and recycling waste oil are effective ways for human society to achieve sustainable development. In this work, a series of temperature dependent flux adjustable "dehydration type" cellulose nanofiber-based (CNFS) films was constructed for achieving efficient oil-water separation, which were obtained by using physical blending of polyvinyl alcohol (PVA) and cellulose nanofibers (CNF) modified by sulfobetaine fragment (SB). CNFS-based films with high SB content had high water flux. At room temperature, after 20 cycles, the water flux of CNFS-5/15%PVA film was 881 L m-2 h-1 for separating petroleum ether/water lotion, and the oil-water separation efficiency was 93.4 %. CNFS-based films exhibited higher water fluxes at high temperatures. For example, at 35 °C, the water flux of CNFS-5/15%PVA film was 1.5 times that at room temperature. The higher water flux of CNFS-based films at high temperatures was attributed to their higher hydrophilicity. In this work, SB was used to endow CNF with temperature response. And the CNFS-based films can effectively separate oil lotion by regulating the water fluxes through temperature, which provides a new idea for oil-water separation and recycling waste oil.

Durable PVA-based hydrogel sponge with cellulose whiskers embedded in the 3D interconnected channels for efficient oil/water separation

Superhydrophilic hydrogel was typically used as the membrane coating on various substrates for oil/water separation. Nevertheless, these coatings may suffer from such limitations as poor adhesion strength and abrasion-resistance. Thus, the facile construction of hydrogel sponge with 3D connecting channels would be an ideal choice. Herein, we reported a free-standing polyvinyl alcohol (PVA)/cellulose nanocrystal (CNC) hydrogel sponge for controllable oil/water separation. In the design, the salt/CNC hybrid crystals instead of conventional salt particles were employed as the sacrificial template, thus CNC was creatively integrated into the long and tortuous 3D interconnected channels via the solvent displacement combined template-leaching strategy. The resultant microstructure woven by CNC bundles in sponge channels could alleviate severe pore collapse in leaching process and oil intrusion. Moreover, it could serve as the superhydrophilic "sieve", promoting the separation efficiency significantly. The gravity-based separation efficiencies for PC5-HL hydrogel sponge in processing of diverse oil/water mixture and oil-in-water emulsions could achieve up to 99.7 and 99.4 %, respectively. In addition, this hydrogel sponge can be used for continuous oil/water separation without obvious decline upon several cycles. This work provides a different way to fabricate the eco-friendly, low-cost and energy-saving filtration hydrogel sponge, showing high potential in oily wastewater treatment.

Regulation of Oil/Water Separation Using Pyridinium-Based Poly(ionic liquid)s with Prewetted Induced Responsive Transition

The development of affordable, intelligent dual-separation technology is crucial for the treatment of oil-water mixtures. Pyridinium-based poly(ionic liquid)s (PILs), designed using molecular theory, exhibit unique switching wettability properties, making them ideal for use in both aqueous and oily environments. By prewetting the material's surface with water or oil, the targeted separation of these components becomes feasible. PILs are synthesized through the cross-linking of [Pyr]Cl with various cross-linkers and auxiliary agents. Studies on the wetting mechanism of these materials have identified bursting pressure and surface structure as key factors influencing their wetting properties. They exhibit hydrophilic and lipophilic properties in air, hydrophobic properties under oil, and oleophobic properties under water, achieving a 99% separation efficiency. A reusability study demonstrated maintenance of 90% efficiency after 10 cycles, highlighting their sustained high performance. This research presents promising avenues for the application of PIL-based materials in oil-water separation, environmental remediation, and industrial processing.

Advanced strategies for controlling three-phase boundaries in photocatalysis

This review delves into the latest advancements in controlling three-phase boundaries (TPBs) in photocatalytic systems, with a focus on photo(electro)catalytic processes for nitrogen reduction, oxygen reduction, and water reduction. We critically analyze various strategies and advanced materials designed to enhance TPB performance, evaluating their impact on catalytic efficiency and identifying gaps in the existing literature. By examining sophisticated triphasic systems that integrate superwetting materials, we emphasize their essential role in improving light absorption, charge separation, and mass transfer. Key challenges in TPB optimization are discussed, and future research directions are proposed to advance photocatalytic technologies for sustainable energy applications. This review highlights the crucial importance of TPBs in photo(electro)catalysis, aiming to inspire further innovation for more efficient and scalable solutions.

Research progress on biomass-based materials for oil/water separation: Designing strategy and efficiency mechanism

The treatment of water contaminated with oil or organic solvents has always been a thorny challenge, considering the complexity of water pollution, the susceptibility to secondary pollution and the consequent depletion of resources. Biomass is a versatile, green and self-circulating natural material that shows important potential in designing high-performance oil/water separation materials. This review highlights the recent research progress on biomass-based materials (BBMs) in the field of oil-water separation. Firstly, related properties for displaying definitions, sources and specificities on biomass materials are introduced, and the basic wetting theory of interfacial wettability is discussed. Secondly, representative nature-inspired designing strategies for oil-water separation materials are summarized. Finally, the current development prospects, future challenges and trends on BBM for oil-water separation are discussed as well. Hopefully, this review will provide some essential guidelines for the researchers to design novel oil/water separation materials with green, self-degradable, low-toxicity and readily available raw materials.

Self-standing membranes for separation: Achievements and opportunities

Supported membranes and mixed matrix membranes have a limitation of harming the mass transfer due to the incompatibility between the support layer or the matrix and the active components of the membrane. Self-standing membranes, which could structurally abandon the support layer, altogether avoid the adverse effect, thus greatly facilitating the transmembrane mass transfer process. However, the abandonment of the support layer also reduces the membrane's mechanical properties and formability. In this review, our emphasis will be on self-standing membranes within the realm of materials and separation engineering. We will explore the materials employed in the fabrication of self-standing membranes, highlighting their ability to simultaneously enhance membrane performance and promote self-standing characteristics. Additionally, we will delve into the diverse techniques utilized for crafting self-standing membranes, encompassing interfacial polymerization, filtration, solvent casting, Langmuir-Blodgett & layer-by-layer assembly, electrospinning, compression, etc. Throughout the discussion, the merits and drawbacks associated with each of these preparation methods were elucidated. We also provide a brief overview of the applications of self-standing membranes, including water purification, gas separation, organic solvent nanofiltration, electrochemistry, and membrane reactor, as well as a brief description of the general strategies for performance enhancement of self-standing membranes. Finally, the current status of self-standing membranes and the challenges they may encounter were discussed.

Vertically Grown Bioinspired Diphenylalanine Nanowire-Coated Fabric for Oil-Water Separation

Due to the pervasive use of oil for energy and other industrial applications, solutions to oil-water separation have received a great deal of attention lately to address the environmental damage of oil spills and groundwater contamination. However, many of these separation methods are materially expensive and environmentally hazardous, require elaborate fabrication, or rely on large amounts of energy to function. Herein, we provide an effective low-cost method for oil-water separation based on the hydrophobicity induced by self-assembled bioinspired diphenylalanine peptide nanowires grown on polyester fabric. This modified polyester fabric mesh exhibits parahydrophobicity and oleophilicity due to the hierarchical nano-to-microscale surface roughness. This mesh also achieves consistent high water separation efficiencies of over 99% and an ultrahigh oil flux of up to 26.7 ± 5 kLm-2·h-1. The growth of bioinspired peptide-based nanostructures on fabrics using facile technique and their application in oil-water separation presents the potential for using bioinspired materials for environmental remediation while minimizing environmental footprint.

Fabrication and Applications of Nature-Inspired Surfaces with Selective Wettability

Inspired by the Stenocora beetle, selective wettability surfaces incorporate alternating wettable and nonwettable surface features that have received substantial attention over the past two decades. These surfaces are sought after for their very promising potential to drive progress in numerous application fields, including ecological protection, biomedical sciences, and industrial technologies. However, despite ongoing efforts to produce such surfaces in commercial quantities, understanding their basic fabrication concepts for practical applications can be challenging, especially for novices, given the vast technical literature in this area. This review, therefore, aims to elucidate the principles of wettability, along with the evolution of selective wettability surfaces and their uses. Beginning with a summary of the essential history and theory of wetting, we explore naturally occurring surfaces that have influenced wetting studies. We then detail state-of-the-art methods for fabricating these unique biwetting surfaces and show how contemporary science employs such designs in solving real-world problems. Finally, we offer an outlook for future research prospects on scalable, printing-based fabrication methods.

An Eco-Friendly Manner to Prepare Superwetting Melamine Sponges with Switchable Wettability for the Separation of Oil/Water Mixtures and Emulsions

Oil/water separation processes have garnered significant global attention due to the quick growth in industrial development, recurring chemical leakages, and oil spills. Hence, there is a significant demand for the development of inexpensive superwetting materials in an eco-friendly manner to separate oil/water mixtures and emulsions. In this study, a superwetting melamine sponge (SMS) with switchable wettabilities was prepared by modifying melamine sponge (MS) with sodium dodecanoate. The as-prepared SMS exhibited superhydrophobicity, superoleophilicity, underwater superoleophobicity, and underoil superhydrophobicity. The SMS can be utilized in treating both light and heavy oil/water mixtures through the prewetting process. It demonstrated fast permeation fluxes (reaching 108,600 L m-2 h-1 for a light oil/water mixture and 147,700 L m-2 h-1 for a heavy oil/water mixture) and exhibited good separation efficiency (exceeding 99.56%). The compressed SMS was employed in separating surfactant-stabilized water-in-oil emulsions (SWOEs), as well as surfactant-stabilized oil-in-water emulsions (SOWEs), giving high permeation fluxes (reaching 7210 and 5054 L m-2 h-1, respectively). The oil purity for SWOEs' filtrates surpassed 99.98 wt% and the separation efficiencies of SOWEs exceeded 98.84%. Owing to their remarkable capability for separating oil/water mixtures and emulsions, eco-friendly fabrication method, and feasibility for large-scale production, our SMS has a promising potential for practical applications.

Recent advances in hydrophobic nanocellulose aerogels for oil spill applications: A review

In a rapidly growing world, petroleum is used extensively in various industries, and the extraction, processing, and transportation of petroleum generates large amounts of petroleum-containing wastewater. Conventional oil/water separation methodologies are often ineffective and costly. Nanocellulose-based aerogels (NA) have emerged as a possible solution to this problem. However, hydrophobic modification is required for effective use in oil/water separation. This review on materials commonly used in these processes and outlines the requirements for adsorbent materials and methods for creating unique lipophilic surfaces. New trends in hydrophobization methods for NA are also discussed. Additionally, it includes the development of composite nanocellulose aerogels (CNAs) and cellulose based membrane specially developed for oil/water (o/w) separation considering different separation requirements. This analysis also examines how CNAs have evolved by introducing special properties that facilitate oil collection or make the adsorbent recyclable. We also discuss the difficulties in creating effective NAs for these important applications in a changing society, as well as the difficulties in creating oil recovery equipment for oil spill cleanup.

Dynamic Regulation Achieving High-Performance La-Containing Prussian Blue Analogues for Aqueous K+ Storage

Lanthanum (La), an "industrial aginomoto" element, exhibits that a small amount of introduction would greatly improve performance. However, La-containing Prussian blue analogues (PBAs) would be dissolved into aqueous solutions, which cannot act as a potassium-ion (K+) storage host. Here, an effective dynamic regulating strategy (chemical components and structures) is developed to overcome the high solubility of La-containing PBA in aqueous electrolytes and achieve high structural stability and superior aqueous K+ storage. For chemical component regulation, Fe3+ ions in the electrolyte fill the La3+ vacancies on the surface and the modified surface hinders the La atoms from further dissolving, and the remaining La atoms in bulk phase improve electron/ion transfer ability and amount of K+ storage. For the structure regulation, the material is transferred from the hexagon to the cubic lattice during charging-discharging procedures, achieving a highly thermodynamically optimal structure. The cathode presents ultrahigh capacities of 171, 155, 132, and 116 at current densities of 1, 2, 3, and 4 A g-1 respectively, and the capacity remains almost constant after 1000 cycles. The mechanism is revealed by experiments and density functional theory (DFT).

Robustly Adherable Hierarchical Nanostructures via Self-Bonding and Self-Texturing of Aluminum Nitride for Applications in Highly Efficient Oil/Water Separation

The release of wastewater containing oily contaminants into water bodies and soils severely threatens the environment and human health. Although several conventional techniques are used in treating oil/water mixtures and emulsions, these methods are often expensive, time-consuming, and inefficient. Porous membranes or sponges are widely used in filtration or absorption, but their use is limited by their low separation efficiencies and secondary contamination. Recently, a novel technology that is designed to selectively separate oil from oil/water mixtures or emulsions by using materials with special wetting surfaces was developed. Superwetting surfaces may be used to selectively separate oils from emulsions. This approach enables the use of materials with relatively large pores, resulting in high throughput properties and efficiencies. In this study, a facile method is proposed for use in preparing a superhydrophobic-superoleophilic felt fabric for utilization in separating oil/water mixtures and emulsions. By hydrolyzing aluminum nitride nanopowders, the desired micro-/nanostructures may be successfully fabricated and firmly attached to a fabric surface without using a binder resin. This results in various materials with special wetting properties, regardless of their sizes and shapes and the successful separation of oil and water from oil/water mixtures and emulsions in harsh environments. This approach exhibits promise as a low-cost, scalable, and efficient method of separating oily wastewater, with the potential for use in wider industrial applications.

Molecular transport and water condensation inside mesopores with wettability step gradients

The wettabilities of nanoscale porous surfaces play important roles in the context of molecular and fluid transport or oil-water separation. The wettability pattern along a nanopore strongly influences fluid distribution throughout the membrane. Mesoporous silica thin films with gradually adjusted wettabilities were fabricated via cocondensation. With consecutive mesoporous layer depositions, double-layer mesoporous silica films with asymmetric or so-called Janus wettability patterns were generated. The effects of these wetting gradients on mass transport, water imbibition, and water vapor condensation were investigated with ellipsometry, cyclic voltammetry (CV), drop friction force instrument (DoFFIs), fluorescence microscopy and interferometry. By increasing the film thickness of the hydrophobic mesoporous silica top layer deposited on a hydrophilic mesoporous silica layer up to 205 nm, molecular transport through both the layers was prevented. However, water was observed to condense onto the bottom layer, and transport occurred for thinner top layers.

A biomimetic design for efficient petrochemical spill disposal: CoFe-PBA modified superhydrophobic melamine sponge with mechanical/chemical durability and low fire risk

Due to frequent petrochemical spills, environmental pollution and the threat of secondary marine fires have arisen, necessitating an urgent need for petrochemical spill treatment strategies with high-performance oil-water separation capabilities. To address the challenges of poor durability, instability in hydrophobic conditions, and difficulty in absorbing high-viscosity crude oil associated with hydrophobic absorbent materials, the authors of this study took inspiration from the unique micro and nanostructures of springtails' water-repellent skin. We engineered a superhydrophobic melamine sponge using interfacial assembly techniques designated as Si@PBA@PDA@MS. This material demonstrated improved mechanical and chemical durability, enhanced photothermal performance, and reduced fire risk. The metal-organic framework (MOF)-derived cobalt-iron Prussian blue analog (CoFe-PBA) was firmly anchored to the sponge framework by the chelation of cobalt ions using polydopamine (PDA). The results demonstrated that Si@PBA@PDA@MS demonstrated excellent superhydrophobicity (WCA=163.5°) and oil absorption capacity (53.4-97.5 g/g), maintaining high durability even after 20 cycles of absorption-squeezing. Additionally, it could still exhibit excellent mechanical properties, hydrophobic stability, and absorption performance across a wide temperature range (0-100 °C), pH range (1-14), and high compression strength (ε = 80%), with excellent mechanical/chemical durability. Furthermore, Si@PBA@PDA@MS demonstrated remarkable photothermal performance and low fire risk, offering efficient, safe, and sustainable practical value for effective petrochemical spill treatment.

Robust Superhydrophobic PDMS@SiO2@UiO66-OSiR Sponge for Efficient Water-in-Oil Emulsion Separation

A major challenge in oil/water separation is the processing of surfactant-stabilized emulsions from the water medium. One of the feasible schemes of emulsion separation is the porous melamine sponge coupled with functional particles. Here, we proposed a novel superhydrophobic metal-organic framework (MOF)-based sponge for water-in-oil emulsion separation. The porous melamine sponge was combined with poly(dimethylsiloxane) (PDMS)-coated hydrophobic SiO₂ and UiO66-OSiR particles were prepared for demulsification via the one-step dipping method for the first time. The PDMS@SiO₂@UiO66-OSiR sponge revealed excellent superhydrophobicity at a water contact angle of 160.7° and superlipophilicity at an oil contact angle of 0°. Compared with the pristine melamine sponge, the size-controllable PDMS@SiO₂@UiO66-OSiR sponge could separate stabilized water-in-oil emulsions with ultrahigh separation efficiency (>98.64%) and high flux (e.g., 970 L·m^-2·h^-1). Meanwhile, the PDMS@SiO₂@UiO66-OSiR sponge exhibited superior durability and mechanical reusability. Under harsh conditions such as strong acid and alkali, organic solvent corrosion, etc., all water contact angles of the PDMS@SiO₂@UiO66-OSiR sponge were over 152°. Furthermore, the stress decreased by 5% when the sponge was subjected to 10 loading/unloading compression cycles at a constant strain of 60%. These results demonstrate that the PDMS@SiO₂@UiO66-OSiR sponge can efficiently separate water-in-oil emulsions through its adjustable porous structure coupled with demulsification and hydrophobic particles. This study provides a step forward in developing a feasible strategy for the MOF-based sponge for emulsion separation.

Recent Advances in Biomass-Based Materials for Oil Spill Cleanup

Oil spill on sea surfaces, which mainly produced by the oil leakage accident happened on tankers, offshore platforms, drilling rigs and wells, has bring irreversible damage to marine environments and ecosystems. Among various spill oil handling methods, using sorbents to absorb and recover spill oils is a perspective method because they are cost-effective and enable a high recovery and without secondary pollution to the ecosystem. Currently, sorbents based on biomass materials have aroused extensively attention thanks to their features of inexpensive, abundant, biodegradable, and sustainable. Herein, we comprehensively review the state-of-the-art development of biomass-based sorbents for spill oil cleanup in the recent five years. After briefly introducing the background, the basic theory and material characteristics for the separation of oil from water and the adsorption of oils is also presented. Various modification methods for biomass materials are summarized in section three. Section four discusses the recent progress of biomass as oil sorbents for oil spill cleanup, in which the emphasis is placed on the oil sorption capacity and the separation efficiency. Finally, the challenge and future development directions is outlined.

Special Superwetting Materials from Bioinspired to Intelligent Surface for On-Demand Oil/Water Separation: A Comprehensive Review

Since superwetting surfaces have emerged, on-demand oil/water separation materials serve as a new direction for meeting practical needs. This new separation mode uses a single porous material to allow oil-removing and water-removing to be achieved alternately. In this review, the fundamentals of wettability are systematically summarized in oil/water separation. Most importantly, the two states, bioinspired surface and intelligent surface, are summarized for on-demand oil/water separation. Specifically, bioinspired surfaces include micro/nanostructures, bioinspired chemistry, Janus-featured surfaces, and dual-superlyophobic surfaces that these superwetting materials can possess asymmetric wettability in one structure system or opposite underliquid wettability by prewetting. Furthermore, an intelligent surface can be adopted by various triggers such as pH, thermal and photo stimuli, etc., to control wettability for switchable oil/water separation reversibly, expressing a thought beyond nature to realize innovative oil/water separation by external stimuli. Remarkably, this review also discusses the advantages of all the materials mentioned above, expanding the separation scope from the on-demand oil/water mixtures to the multiphase immiscible liquid-liquid mixtures. Finally, the prospects of on-demand oil/water separation materials are also concluded.

PDMS/PVDF Electrospinning Membranes for Water-in-Oil Emulsion Separation and UV Protection

With industry development, the separation of oily wastewater is becoming more critical. Inspired by organisms such as lotus leaves, biomimetic superhydrophobic surfaces with micro-nano structures have shown great potential in this regard. In this work, PDMS/PVDF oil-water separation membranes with designed microstructures were prepared by electrospinning technology. The membrane-forming effect of electrospinning with different ratios of PDMS and PVDF was studied. The study found that membranes with high PDMS content were more likely to form microspheres, and PDMS tended to concentrate on the microspheres. The results also showed that the microspheres would bring better hydrophobicity to the membrane. When the ratio of PDMS to PVDF is 1:2, the membrane has a water contact angle of up to 150° and an oil contact angle of 0°. At this ratio, the separation efficiency of the membrane for the water-in-oil emulsion is 98.7%, and it can still maintain more than 98% after ten separation cycles, which is a good candidate for oil-water separation. Furthermore, microspheres enable the membrane to achieve macroscopic uniformity and microscopic phase separation so that the membranes have both good elongation and fracture strength. In addition, the PDMS/PVDF membranes also exhibit excellent UV resistance, and their UV protection factor is greater than 185, making them a potential UV protective material.

Facile and simple fabrication of superhydrophobic and superoleophilic MS/PDA/DT sponge for efficient oil/water separation

To overcome the problems of frequent leakage accidents during oil exploitation, a superhydrophobic and superoleophilic porous MS/PDA/DT sponge was successfully prepared via mild solvent evaporation method, and a polydopamine assisted surface coating of 1-dodecanethiol (DT) on a melamine sponge (MS) substrate. Surface structure and performance of the MS/PDA/DT sponge were characterized by Scanning Electron Microscope (SEM), Fourier transform infrared spectrometer (FTIR), and Video Optical Contact Angle (CA) metre. The results showed that the as-prepared MS/PDA/DT sponge has a high-water contact angle (WCA) of 147.2°, which is probably attributed to both the rough surface derived from in situ growth and the low surface energy due to grafting of hydrophobic 1-dodecanethiol. The durability of the as-constructed MS/PDA/DT sponge was studied by repeated abrasion tests. After 50 abrasion cycles, the superhydrophobicity of the MS/PDA/DT sponge good mechanical durability. The MS/PDA/DT sponge can effectively absorb oil with an absorption capacity of up to 24 times its weight. The superhydrophobic and superoleophilic MS/PDA/DT sponge has the potential as a promising adsorbent for oil/water separation.Highlights The MS/PDA/DT sponge was prepared via the mild solvent evaporation method.The contact angle of the MS/PDA/DT sponge was 147.2^o.The adsorption capacity of the MS/PDA/DT sponge was 24 times their weight.The cost-efficient, environmentally friendly porous materials show high oil/water separation efficiency.

Superhydrophobic nanofibrous sponge with hierarchically layered structure for efficient harsh environmental oil-water separation

Oil leakage has posed serious threat to the environment, but still remain a great challenge to be solved especially for harsh environmental conditions. Herein, robust superhydrophobic nickel hydroxide grown by hydrothermal method and stearic acid modification on a blow-spun polyacrylonitrile (PAN)/Al₂O₃ nanofibrous sponge was proposed, so that the nickel hydroxide-modified polyacrylonitrile sponge (NPAS) was successfully obtained for efficient oil-water separation. The porous NPAS with a distinctive hierarchically layered structure, which exhibited excellent separation efficiency and mechanical elasticity. Due to its superhydrophobic and high porosity, the absorption capacity of NPAS could reach as high as 45 g g^-1. It could not only separate a series of oil-water mixture with a high steady flux of 12,413 L m^-2 h^-1 (dichloromethane-water), but also separate stabilized emulsions with a superior flux 2032 L m^-2 h^-1 (water-in-dichloromethane) under gravity, all of that with above 99.92% separation efficiencies, which was higher than that of the most reported sponges. Most importantly, its strong acid/alkali resistance enable it is suitable for hazardous materials treatment applications in harsh environmental conditions. This novel NPAS via facile large-scale blow-spinning provide an efficient strategy for oil-containing wastewater treatment and environmental protection.

Aqueous construction of raspberry-like ZIF-8 hierarchical structures with enhanced superhydrophobic performance

Materials with super-wetting ability have attracted wide attention from both academia and industry due to their great potential applications. A straightforward and versatile route was proposed for the large-scale synthesis of a monodisperse raspberry-like metal-organic framework (ZIF-8) using zinc nitrate as a zinc source and dimethylimidazole as an organic ligand in aqueous solution. After hydrophobic treatment with hexadecyltrimethoxysilane, the ethanolic suspension of three-dimensional raspberry-like ZIF-8 showed excellent superhydrophobic properties. Furthermore, commercial adhesives were used to blend with the suspension to improve the bonding strength to different substrates. These surfaces retained their water resistance after 50 finger-wipe cycles, 40 sandpaper abrasions and knife scratches. Moreover, the prepared hydrophobic surface can withstand the impact of water flow for 10 minutes. The formulations developed can be used for superhydrophobic coating applications on different substrate surfaces such as aluminum foil, glass, paper and cotton.

Introducing Polar Groups in Porous Aromatic Framework for Achieving High Capacity of Organic Molecules and Enhanced Self-Cleaning Applications

Due to the frequent oil/organic solvent leakage, efficient oil/water separation has attracted extensive concern. However, conventional porous materials possess nonpolar building units, which reveal relatively weak affinity for polar organic molecules. Here, two different polarities of superhydrophobic porous aromatic frameworks (PAFs) were synthesized with respective orthoposition and paraposition C=O groups in the PAF linkers. The conjugated structure formed by a large number of alkynyl and benzene ring structures enabled porous and superhydrophobic quality of PAFs. After the successful preparation of the PAF solids, PAF powders were coated on polyester fabrics by a simple dip-coating method, which endowed the resulting polyester fabrics with superhydrophobicity, porosity, and excellent stability. Based on the unique structure, the oil/water separation efficiency of two superhydrophobic flexible fabrics was more than 90% for various organic solvents. Polar LNU-26 PAF showed better separation performance for the polar oils. This work takes the lead in adopting the polar groups as building units for the preparation of porous networks, which has great guiding significance for the construction of advanced oil/water separation materials.

Superhydrophilic–superhydrophobic patterned surfaces: From simplified fabrication to emerging applications

Superhydrophilic–superhydrophobic patterned surfaces constitute a branch of surface chemistry involving the two extreme states of superhydrophilicity and superhydrophobicity combined on the same surface in precise patterns. Such surfaces have many advantages, including controllable wettability, enrichment ability, accessibility, and the ability to manipulate and pattern water droplets, and they offer new functionalities and possibilities for a wide variety of emerging applications, such as microarrays, biomedical assays, microfluidics, and environmental protection. This review presents the basic theory, simplified fabrication, and emerging applications of superhydrophilic–superhydrophobic patterned surfaces. First, the fundamental theories of wettability that explain the spreading of a droplet on a solid surface are described. Then, the fabrication methods for preparing superhydrophilic–superhydrophobic patterned surfaces are introduced, and the emerging applications of such surfaces that are currently being explored are highlighted. Finally, the remaining challenges of constructing such surfaces and future applications that would benefit from their use are discussed.

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.

Self-powered aligned porous superhydrophobic sponge for selective and efficient absorption of highly viscous spilled oil

Crude oil spills have caused catastrophic damage to marine ecosystems and become a global challenge. Although various liquid absorption materials have been developed, manual operations such as pumping and electric heating are still required in the face of highly viscous spilled oils. Efficient and autonomous crude oil spill cleanup methods are urgently needed. Here, inspired by the unidirectional microstructure of tree xylem, we report a sponge (SPC-Sponge), which combines superhydrophobic property and aligned porous structures, prepared from a ternary suspension (hydrophobic silica nanoparticles, polyurethane, and cellulose nanofibers) by single-step directional freeze casting. SPC-Sponge not only effectively overcome the limitations of traditional synthetic modification methods on the shape and size of porous sponge materials, but also has excellent oil-water selection function, liquid absorption speed, and liquid absorption capacity compared with common porous materials. Moreover, the sponge can self-absorb highly viscous crude oil of around 80,000 mPa‧s on seawater without external energy and human intervention. By adding multi-walled carbon nanotubes, the sponge can implement in-situ solar heating of crude oil, and the absorption speed is further improved. Given its unique structural design and superwetting property, this SPC-Sponge provides an efficient remediation approach for viscous oil spills.

Bis-Pyridine-Based Organogel with AIE Effect and Sensing Performance towards Hg2

A novel gelator (1) based on a bis-pyridine derivative was designed and synthesized, which could form stable gels in methanol, ethanol, acetonitrile, ethyl acetate, DMF/H₂O (4/1, v/v) and DMSO/H₂O (4/1, v/v). The self-assembly process of gelator 1 was studied by field emission scanning electron microscopy (FESEM), UV–vis absorption spectroscopy, fluorescence emission spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction and a water contact angle experiment. Gelator 1 exhibited obvious AIE behavior. On the base of its AIE, the gel of 1 could detect Hg²⁺, which resulted in fluorescence quenching and a gel–sol transition. ¹H NMR titration experiments with Hg²⁺ revealed that the metal coordination interaction induced the fluorescence quenching and the breakdown of the noncovalent interaction in the gel system. This research provides a new molecular mode for designing a functional self-assembly gel system.

Separate Reclamation of Oil and Surfactant from Oil-in-Water Emulsion with a CO2-Responsive Material

Oil-in-water (O/W) emulsion is one type of oily wastewater produced by many industries. The treatment of and resource recovery from O/W emulsions are very challenging. Unlike bulk or floating oil, which can be successfully abstracted from wastewater by hydrophobic/oleophilic materials, the abstraction of emulsified oil is not easy because of its highly hydrophilic surface composed of dense surfactants. Separate reclamation of miscible oil and surfactant through a green approach is even more difficult. Here, we report that a CO₂-responsive material can abstract emulsified oil and demulsify the oil droplets. Moreover, it can release the abstracted oil and surfactant separately. This material exhibited a very high adsorption capacity for emulsified oil (14 g g^-1). Upon switching the surface wettability of the material under CO₂ or synthetic flue gas sparging, coalesced oil was reclaimed while the surfactant was retained inside the pores. The hydrophobic character of the material was retrieved when CO₂ was purged with nitrogen sparging or air heating. Then, the surfactant was reclaimed by elution with diluted alkali/ethanol. Oil and surfactant were thus separately reclaimed from the O/W emulsion. High rates of oil removal, oil recovery, and surfactant recovery were maintained during repeated adsorption/desorption operations. This work provides a potentially sustainable and green way for O/W emulsion treatment and resource recovery.

Adhesion behaviors of water droplets on bioinspired superhydrophobic surfaces

The adhesion behaviors of droplets on surfaces are attracting increasing attention due to their various applications. Many bioinspired superhydrophobic surfaces with different adhesion states have been constructed in order to mimic the functions of natural surfaces such as a lotus leaf, a rose petal, butterfly wings, etc. In this review, we first present a brief introduction to the fundamental theories of the adhesion behaviors of droplets on various surfaces, including low adhesion, high adhesion and anisotropic adhesion states. Then, different techniques to characterize droplet adhesion on these surfaces, including the rotating disk technique, the atomic force microscope cantilever technique, and capillary sensor-based techniques, are described. Wetting behaviors, and the switching between different adhesion states on bioinspired surfaces, are also summarized and discussed. Subsequently, the diverse applications of bioinspired surfaces, including water collection, liquid transport, drag reduction, and oil/water separation, are discussed. Finally, the challenges of using liquid adhesion behaviors on various surfaces, and future applications of these surfaces, are discussed.

A Multi-Omics Approach to Evaluate the Toxicity Mechanisms Associated with Silver Nanoparticles Exposure

Silver nanoparticles (AgNPs) are currently used in many different industrial, commercial and health fields, mainly due to their antibacterial properties. Due to this widespread use, humans and the environment are increasingly exposed to these types of nanoparticles, which is the reason why the evaluation of the potential toxicity associated with AgNPs is of great importance. Although some of the toxic effects induced by AgNPs have already been shown, the elucidation of more complete mechanisms is yet to be achieved. In this sense, and since the integration of metabolomics and transcriptomics approaches constitutes a very useful strategy, in the present study targeted and untargeted metabolomics and DNA microarrays assays have been combined to evaluate the molecular mechanisms involved in the toxicity induced by 10 nm AgNPs. The results have shown that AgNPs induce the synthesis of glutathione as a cellular defense mechanism to face the oxidative environment, while inducing the depletion of relevant molecules implicated in the synthesis of important antioxidants. In addition, it has been observed that AgNPs completely impair the intracellular energetic metabolism, especially affecting the production of adenosine triphosphate (ATP) and disrupting the tricarboxylic acids cycle. It has been demonstrated that AgNPs exposure also affects the glycolysis pathway. The effect on such pathway differs depending on the step of the cycle, which a significant increase in the levels of glucose as way to counterbalance the depleted levels of ATP.

Honeycomb-like cobalt hydroxide nanosheets induced basalt fiber fabrics with robust and durable superhydrophobicity for anti-icing and oil-water separation

The fiber-based membranes with superhydrophobic/superoleophilic features are highly desirable for oil-water separation applications. Herein, a superhydrophobic/superoleophilic basalt fiber fabric is constructed by using a general strategy of surface KMnO₄ pre-oxidation, honeycomb-like cobalt hydroxide nanosheets in-situ deposition, and hydrophobization. The influence of morphology change on wettability and roughness of the fabric surface were investigated. Benefiting from the dual-scale micro-/nanostructures, the obtained composite fabric has outstanding superhydrophobicity (water contact angle > 161°) and sustains non-wettability against multifarious food liquids. Meanwhile, the fabric displays substantial superhydrophobic durability during sandpaper abrasion, tape-peeling, and bending treatment. Moreover, the fabric also demonstrates excellent anti-wetting, self-cleaning and anti-icing performance. With these properties, the fabric has outstanding separation efficiencies (> 99.31%) and recyclability for various oil-water mixtures and emulsions under gravity. Therefore, this work provides an idea for development of superhydrophobic fabrics with potential application in the rapid treatment of oily wastewater.

The optimization effect of different parameters on the super hydrophobicity of prickly-shaped carbonyl iron particles

In this study, the effects of glucose concentration, temperature, and time parameters of the hydrothermal reaction on the growth of prickly-shaped carbonyl iron were studied by using an experimental design to obtain the maximum superhydrophobicity of the magnetic particles. The experimental design was carried out by Response Surface Methodology (RSM) analysis using the Central Composite Design (CCD) method. Field Emission Scanning Electron Microscopy (FESEM) analysis was performed to qualitatively assess the growth of the prickly-shaped carbonyl iron, and Water Contact Angle (WCA) analysis was used to quantify the superhydrophobicity of the resulting particles. The results revealed that the elevation of the concentration and time increased the roughness (prickly shape) of the particle surface and contact angle up to a point, after which it did not affect them. The temperature elevation caused an increase in the prickly shape of the particles and contact angles and then reduced them. The optimum concentration, temperature, and time were 0.75 Mol L⁻¹, 170 °C, and 4 hours, respectively, for the maximum growth of prickly-shaped particles and the maximum contact angle was 169.7°. Fourier-Transform Infrared Spectroscopy (FT-IR) and thermogravimetric analysis (TGA) results confirmed the presence of glucose and stearic acid chemically bonded to the carbonyl iron particles. The X-ray Diffraction (XRD) results showed that the carbonyl iron had been not converted into iron oxide during the synthesis procedures of the superhydrophobic particles. Vibrating Sample Magnetometer (VSM) analysis showed that making the particles superhydrophobic had little effect on the magnetization reduction.

The effects of glucose concentration, temperature, and time parameters of the hydrothermal reaction on the growth of prickly-shaped magnetic particles were studied by using an experimental design to obtain the maximum superhydrophobicity.

Review of the Recent Advances in Electrospun Nanofibers Applications in Water Purification

Recently, nanofibers have come to be considered one of the sustainable routes with enormous applicability in different fields, such as wastewater treatment. Electrospun nanofibers can be fabricated from various materials, such as synthetic and natural polymers, and contribute to the synthesis of novel nanomaterials and nanocomposites. Therefore, they have promising properties, such as an interconnected porous structure, light weight, high porosity, and large surface area, and are easily modified with other polymeric materials or nanomaterials to enhance their suitability for specific applications. As such, this review surveys recent progress made in the use of electrospun nanofibers to purify polluted water, wherein the distinctive characteristics of this type of nanofiber are essential when using them to remove organic and inorganic pollutants from wastewater, as well as for oil/water (O/W) separation.

Preparation of polymer-based foam for efficient oil-water separation based on surface engineering

The leakages of a large number of organic solvents and oil spills not only cause extensive economic losses, but also destroy the ecological environment. However, there were few studies on the surface engineering of adsorption materials for efficient oil-water separation in complex environments. In this research, through surface engineering, the polymer-based foam exhibited high efficiency oil-water separation performance in different pH environments. Hydrophobic groups were introduced onto the surface of nano-sized SiO₂ particles via hydrolysis and polycondensation reactions, and then the modified SiO₂ was loaded on the foam. After modification, the water contact angle of the modified foam increased from 116.4° to 152.5°, and the oil-water separation performance was obviously enhanced. The oil removal rate of the modified foam remained above 96%. The highest capacity of petroleum diesel was 33.4 g^-1, which was much higher than other similar adsorption materials. In addition, the modified foam maintained good hydrophobicity and oil removal rate in a wide pH range. The efficient oleophilic and hydrophobic foam prepared by combining green physical foaming with surface engineering was expected to be widely used in large-scale organic solvent recovery and oil leakage emergency treatment.

Solvent‐Influenced Fragmentations in Free‐Standing Three‐Dimensional Covalent Organic Framework Membranes for Hydrophobicity Switching

The ordered open organic frameworks membranes are attractive candidates for flow‐assisted molecular separations. The physicochemical properties of such membranes mostly depend on their selectively chosen functional building blocks. In this work, we have introduced a novel concept of functional switchability of three‐dimensional covalent organic framework (3D‐COF) membranes through a simple solvent‐influenced fragmentation method. This room‐temperature interfacial synthesis provides free‐standing 3D‐COF membranes with distinct physicochemical properties from the same building monomers. Notably, the change of solvent from chloroform to ethyl acetate switches the membrane property from hydrophilic (water contact angle 60°) to hydrophobic (water contact angle 142°) nature. The hydrophobic 3D‐COF membrane selectively passes oil molecules from an oil–water emulsion with a gravitational flux of 1536 L m⁻² h⁻¹.

Wood-Inspired Compressible Superhydrophilic Sponge for Efficient Removal of Micron-Sized Water Droplets from Viscous Oils

Efficient micron-sized droplet separation materials have become a new demand for environmental protection and economic development. However, existing separation methods are difficult to be effectively used for micron-sized water droplets surrounded by viscous oil, and common materials have difficulty maintaining hydrophilicity underoil. Here, inspired by the microstructure of tree xylem, we report a cellulose-polyurethane sponge (CP-Sponge) with wood-like pores and underoil superhydrophilicity using directional freeze-casting. The CP-Sponge has an excellent selective water absorption capacity underoil and compression resilience. This preparation strategy can flexibly control the sponge's dimensional morphology. The designed cylindrical CP-Sponge can be easily installed in the silicone tube of a peristaltic pump. During pump operation, with a simple absorption, compression, and recovery process, the CP-Sponge continuously and effectively removes micron-sized water from crude oil and lubricating oil, reducing residual water in the oil to less than 2 ppm. The absorption-saturated sponge can be dried to continue recycling. Eco-friendly, recyclable, and sustainable artificial porous sponges provide new ideas and inspiration for the practical application of deep dehydration of viscous oils.