Advanced Materials with Special Wettability toward Intelligent Oily Wastewater Remediation

Biomimetic materials for efficient emulsion separation: Based on the perspective of energy

Purifying emulsified oily wastewater is particularly crucial for solving environmental pollution and water scarcity. Membrane separation shows great potential for emulsified wastewater treatment. However, realizing continued effective emulsion separation remains a significant challenge. Fortunately, various kinds of creative schemes have been proposed to overcome the current dilemma. In this paper, biomimetic emulsion separation materials with unique wettability are introduced. Besides, This article summarizes the recently advanced emulsion separation strategies. First, we analyze the typical wettability theory and explore the trade-off between separation flux and efficiency. After that, based on emulsion types, the current common emulsion separation materials are summarized and analyzed. Notably, the integration of natural biological inspiration has made separation materials full of potential. Further, from the perspective of external energy input or no-external energy input, this article provides an overview of advanced emulsion separation materials and analyzes the potential separation mechanism. Encouragingly, efficient emulsion separation can be realized by membrane characteristics (microstructure, superwettability, electrostatic interaction) or the appropriate external stimulus (photo, electricity, magnetic). Finally, the challenges and trends are summarized. We hope that this article will provide inspiration for the advancement of novel generations of separation materials.

Next-generation stimuli-responsive smart membranes: Developments in oil/water separation

Effective treatment of oil-contaminated wastewater is essential due to its severe environmental and health impacts. The membrane-based separation is cost-effective, energy-efficient, and eco-friendly; however, fouling has remained a pressing issue. Stimuli-responsive membranes, which adjust their pore structure and surface properties in response to external triggers such as light, pH, and temperature, offer enhanced fouling resistance and improved separation performance. This review provides a comprehensive analysis of stimuli-responsive membranes for oil/water separation, emphasizing the role of smart polymeric materials engineered for controllable separation processes. We critically assess the strengths of these advanced membranes, including their tuneable wettability and energy-efficient operation, while identifying key limitations such as long-term stability, response time, scalability, and cost-effectiveness. Furthermore, the review explores various polymer types, synthesis methods, and fabrication techniques, evaluating their effectiveness in separation applications. Finally, the review concludes by outlining the challenges and proposing future directions to enhance the performance of stimuli-responsive membranes. By offering valuable insights into the dynamic control of membrane structures and properties, this study aims to inspire the development of next-generation stimuli-responsive membranes, drive their commercialization, and promote sustainable water treatment solutions.

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.

Janus Composite Porous Structure with Asymmetric Selective-Wettability for Unidirectional Liquid Transportation and High-Efficiency Oil-Water Separation

Selective-superwetting surfaces exhibiting diametrically opposed superwettability toward oil and water have been widely used in the filtration-based separation of oil-water mixtures. But further reducing energy consumption and improving separation flux and separation efficiency still remain challenges. Janus composite porous structures with asymmetric wettability have capacities of driving liquid unidirectional penetration and blocking liquid opposite transmission. This "liquid diode" functionality has proven to be effective for high-efficiency separation in past studies. However, most of the existing Janus porous structures exploit only the capacity of blocking liquid opposite transmission, leaving their capacity of driving liquid unidirectional penetration underutilized. Herein, we propose a selective (super)wetting surface-based configuration of Janus composite porous structure and fabricate two kinds of Janus composite porous structures. The Janus composite porous structures with asymmetric selective (super)wettability exhibit capacities of driving water/oil unidirectional penetration and blocking water/oil opposite transmission. The oil-water separation efficiency is over 99%, and the separation flux is significantly higher than conventional homogeneous selective-superwetting porous structures. This work provides insights into the design of Janus porous structures with significant potential applications in selective unidirectional actuation of multiphase liquids, oil-water separation, wastewater treatment, and marine oil spill recovery. Furthermore, this scalable fabrication methodology opens avenues for developing next-generation smart membranes for osmotic energy harvesting and adaptive interface materials.

Development of high-throughput electrospun chitosan/PEO-CNC composite membranes with enhanced antibacterial and oil-water separation properties

Untreated waste liquid mixtures often support large bacterial populations, posing challenges to effective purification due to high volume and limited filtration efficiency. This study aims to develop a multifunctional filtration membrane that combines both filtration and sterilization, enhancing overall purification efficiency. Using electrospinning technology, we fabricated a superhydrophilic, oil-repellent membrane by integrating the hydrophilic properties of chitosan, antibacterial N-halamine groups, and the mechanical strength of cellulose nanocrystals (CNC). The chitosan's -NH₂ groups were chlorinated to form N-halamine groups, significantly enhancing the membrane's bactericidal properties. Experimental results demonstrated that the CS/PEO-CNC-2-Cl membrane achieved complete inactivation of E. coli (108 CFU/mL) and S. aureus within 1 min of contact. Furthermore, under a filtration rate of up to 1273 L·m-2·h-1, the membrane fully inactivated a 106 CFU/mL S. aureus bacterial solution. These findings indicate that the superhydrophilic, antibacterial membrane developed in this study holds considerable promise for applications in water treatment, particularly in addressing oil and microbial contamination.

Solvation enabled highly efficient gradient assembly creates robust metal-phenolic coatings

Metal-phenolic networks (MPNs) are supramolecular materials that have received interest in various fields, including biomedicine, separations, environmental remediation, and catalysis. Despite recent advances, the construction of thick and robust MPN coatings that withstand harsh conditions (e.g., acidic, alkaline) remains challenging. In addition, the interfacial assembly of MPNs in mixed solvents (e.g., water and nonaqueous solvents) has not been investigated. Herein, a solvent-regulated (water/ethylene glycol) gradient assembly strategy that can regulate the coordination kinetics of MPNs to realize thick (up to 1.5 μm) and robust MPN coatings on various substrates is presented. Through mediating interactions between polyphenols, a balance is achieved between the aggregation, precipitation, and continuous assembly of well-dispersed precursors. The gradient assembly of polyphenols and metal ions results in lateral and longitudinal cross-linking leading to the formation of robust MPN coatings. The potential application of the coatings in oil/water separation is demonstrated by their excellent performance (oil intrusion pressure of 2.0 kPa and water flux of 2.59 × 105 L m-2h-1), long-term stability, tolerance to various harsh conditions, and thick oil fouling. This study provides further insight into the assembly mechanism of MPNs.

Ultra-Antifouling Liquid-Like Surfaces for Sustainable Viscous Water-in-Oil Emulsions Separation and Oil Recovery

The demand for efficient separation techniques in industries dealing with high viscosity emulsions has surged due to their widespread applications in various scenarios, including emulsion-based drug delivery systems, the removal of emulsified impurities in formulations and oil spill remediation. However, membrane fouling is a major challenge for conventional separation methods, leading to decreased efficiency and increased maintenance costs. Herein, a novel approach is reported by constructing liquid-like surfaces with double anti-fouling structure, incorporating soft nanomicelles within a rigid, chemically cross-linked network for both anti-membrane-fouling and effective viscous water-in-oil emulsion separation. The coating significantly outperforms perfluorinated and commercial polytetrafluoroethylene (PVDF) membranes, effectively preventing the adhesion of viscous oils like crude oil and pump oil, and alleviating severe membrane fouling. For high-viscosity emulsions (97.3 cP and 52.8 cP), it maintains over 99% separation efficiency after 3 h continuous use. Even after 15 h immersion in strong acids, alkalis, salts, or organic solvents, its separation efficiency remains above 95%. In addition, thanks to the anti-membrane-fouling ability, this work achieved 6 h continuous emulsion separation performance for the first time, demonstrating unparalleled long-term stability. Overall, this study offers valuable insights into the development of innovative coatings for efficient and eco-friendly separation of high-viscosity emulsions.

Effect of micro-granular activated carbon on bacteriophage MS2 removal and fouling control in flat-plate MBR

Pathogenic microorganisms pose a severe risk to the aquatic environment and human health. Membrane bioreactors (MBRs) have attracted much attention due to their simultaneous biological treatment and virus retention, but membrane fouling is the main obstacle. This study explored the effect of micro-granular activated carbon (μGAC) on bacteriophage MS2 removal efficiency and membrane fouling in a flat-plate MBR. The results showed that the μGAC addition with a particle size of 180-300 μm improved the removal of MS2 (LRVMBR of 4.77 log) and enhanced the removal of COD and ammonia nitrogen. The μGAC integrated MBR (μGAC-MBR) exhibited a higher MS2 retention rate by the membrane filter layers with an average LVRMem of 2.03 log compared to that of a control reactor (C-MBR) of 1.89 log. Meanwhile, the total membrane filter layer resistance of μGAC-MBR was significantly lower than that of C-MBR, particularly in terms of cake layer resistance and organic pore-blocking exclusion. The μGAC addition slightly reduced MS2 adsorption by the activated sludge while significantly altering the extracellular polymeric substances (EPS) profiles. The fluorescent components in the bound EPS and PN/PS ratio of the activated sludge were reduced. We found that μGAC enhanced membrane surface roughness and hydrophilicity. Notably, the μGAC significantly influenced the quorum sensing (QS) systems, reducing the abundance and synthesis of AHL-related genes. The synthase luxI in the AHL-QS system was reduced by 93.21% in μGAC-MBR. The AHL-QS system is closely related to biofilm formation, and the total EPS of the surface filer layer of μGAC-MBR decreased by 57.73%, and PN in LB-EPS and TB-EPS decreased by 91.33% and 54.44% compared with C-MBR, indicating a significant reduction in biofilm formation. This study exhibited a new perspective on promoting MS2 removal with the synergistic effect of alleviating fouling in the MBR process.

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.

Perfluoroalkyl Functionalized Superhydrophobic Covalent Organic Frameworks for Excellent Oil-Water Membrane Separation and Anhydrous Proton Conduction

Rapid economic development has led to oil pollution and energy shortage. Membrane separation has attracted much attention due to its simplicity and efficiency in oil-water-separation. The development of membrane materials with enhanced separation properties is essential to improve the separation-efficiency. Proton exchange membrane fuel cells (PEMFCs) are expected to replace conventional engines due to their high-power-conversion rates and other favorable properties. Anhydrous-proton-conducting materials are vital components of PEMFCs. However, developing stable proton-conducting materials that exhibit high conductivity at varying temperatures remains challenging. Herein, two covalent organic frameworks (COFs) with long-side-chains are synthesized, and their corresponding COF@SSN membranes. Both membranes can effectively separate oil-water mixtures and water-in-oil emulsions. The TFPT-AF membrane achieves a maximum oil-flux of 6.05 × 105 g h-1 m-2 with an oil-water separation efficiency of above 99%, which is almost unchanged after 20 consecutive uses. COF@H3PO4 doped with different ratios of H3PO4 is prepared, the results show that the perfluorocarbon-chain system has  excellent anhydrous proton conductivity , achieving an ultra-high proton-conductivity of 3.98 × 10-1 S cm-1 at 125 °C. This study lays the foundation for tailor-made-functionalization of COF through pre-engineering and surface-modification, highlighting the great potential of COFs for oil-water separation and anhydrous-proton-conductivity.

Pioneering technologies over time to rehabilitate crude oil-contaminated ecosystems: a review

The unremitting pollution of our environment induced by crude oil spillage and drilling site accidents has jeopardized every living species in the biological ecosystem. Removing heavy crude oil constituents with the help of traditional and mainstream oil sorbents because of their ingrained raised viscosities is a strenuous venture. Lighter distillates of crude oil, like condensate, do not aggregate with tremulous shine on the aquatic surface nor settle at the bottom sediment of the water bodies like the heavier components do with time. Fabricating optimally designed materials capable of capturing, degrading, or removing toxic chemical constituents of this fossil fuel is critical in this modern era. This review comprehensively discusses the evolution of scientific technologies developed to separate these constituents from land and aquatic bodies. We provide an overview of the latest physical and chemical strategies and prevalent biological remediation schemes for removing these pollutants from soils and water for environmental protection. The article highlights the urgency of preventing oil spill accidents, whose anticipation is challenging to harness. A spectrum of advanced functional methodologies is also discussed to adequately treat discharged hydrocarbon contaminants, establish public safety, and pave the path to enhancing the circular economy metrics linked with oil industries.

Next-Generation BiOCl/MXene Nanocomposites: Optimized for Dye Removal and Supercapacitor Applications

The study focuses on the development of an efficient and sustainable solution for synthetic dye degradation through the hydrothermal synthesis of BiOCl and BiOCl/MXene heterostructures. Structural and compositional properties were analyzed by using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS) techniques. A significant reduction in the band gap of BiOCl/MXene to 2.97 eV from 3.62 eV for BiOCl was observed via UV spectroscopy, leading to enhanced photocatalysis with 89% degradation efficiency in just 12 min. The mechanism involved and reactive species were confirmed by LC-HRMS and radical trapping tests, while ICP-MS verified metal content in water before and after degradation. Additionally, the nanocomposite demonstrated a specific capacitance of 431.24 F g-1 at a current density of 1 mA cm-2, with an excellent capacitance retention of 94.35% after 2000 cycles. This study highlights BiOCl/MXene as a promising material for both photodegradation and supercapacitor applications.

Design of carboxymethyl cellulose/alginate aerogels with anti-fouling and light-driven self-cleaning for enhanced oily wastewater remediation

With the increase of oily wastewater discharge and the growing demand for clean water supply, high throughput green materials for oil-water separation with anti-pollution and self-cleaning ability are urgently needed. Herein, the polysaccharide-based composite aerogels of CMC/SA@TiO2-MWCNTs (CSTM) with fast photo-driven self-cleaning ability have been prepared by a simple freeze-drying and ionic cross-linking strategy. The introduction of TiO2 /MWCNTs nanocomposites effectively improves the underwater oleophobic and mechanical properties of polysaccharide aerogels and enables their photo-driven self-cleaning ability for efficient oil-water separation and purification of complex oily wastewater. For immiscible oil-water mixtures, a high separation flux of about 7650 L m-2 h-1 and a separation efficiency of up to 99.9 % was obtained. For surfactant-stabilized oil-in-water emulsion, a flux of 3952 L m-2 h-1 was achieved with a separation efficiency of up to 99.3 %. More importantly, the excellent photoluminescent self-cleaning ability and low oil adhesion contribute to the high contamination resistance, excellent reusability, and robust durability of CSTM aerogel. With the advantages of simple preparation, remarkable performance, and recyclability, this aerogel is expected to provide a green, economical, and scalable solution for the purification of oily wastewater.

A Hydrogel-coated Wood Membrane with Intelligent Oil Pollution Detection for Emulsion Separation

Considering the potential threats posed by oily wastewater to the ecosystem, it is urgently in demand to develop efficient, eco-friendly, and intelligent oil/water separation materials to enhance the safety of the water environment. Herein, an intelligent hydrogel-coated wood (PPT/PPy@DW) membrane with self-healing, self-cleaning, and oil pollution detection performances is fabricated for the controllable separation of oil-in-water (O/W) emulsions and water-in-oil (W/O) emulsions. The PPT/PPy@DW is prepared by loading polypyrrole (PPy) particles on the delignified wood (DW) membranes, further modifying the hydrogel layer as an oil-repellent barrier. The layered porous structure and selective wettability endow PPT/PPy@DW with great separation performance for various O/W emulsions (≥98.69% for separation efficiency and ≈1000 L m-2 h-1 bar-1 for permeance). Notably, the oil pollution degree of PPT/PPy@DW can be monitored in real-time based on the changed voltage generated during O/W emulsion separation, and the oil-polluted PPT/PPy@DW can be self-cleaned by soaking in water to recover its separation performance. The high affinity of PPT/PPy@DW for water makes it effective in trapping water from the mixed surfactant-stabilized W/O emulsions. The prepared eco-friendly and low-cost multifunctional hydrogel wood membrane shows promising potential in on-demand oil/water separation and provides new ideas for the functional improvement of new biomass oil/water separation membrane materials.

Dual-capable spinel cobalt oxide nanoparticles for electrocatalytic oxygen evolution and water contaminant removal

This study investigates the synthesis and electrocatalytic performance of cobalt oxide (Co3O4) nanoparticles for the oxygen evolution reaction (OER) and their role in water treatment as contaminant removal agents. Cobalt oxide nanoparticles are recognized as promising materials in electrocatalysis due to their tunable properties and nanoscale engineering potential. Here, fine cobalt oxide nanoparticles are synthesized using the sol-gel method followed by various sintering temperatures to achieve precise control over surface morphology, size, and shape. Characterization via high-resolution scanning electron microscopy (HRSEM) and high-resolution transmission electron microscopy (HRTEM) elucidates the impact of sintering temperature on nanoparticle properties. Thin film electrodes of cobalt oxide are fabricated using the doctor blade method and evaluated using linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). Among the tested sintering temperatures, cobalt oxide electrodes sintered at 600 °C exhibit superior catalytic activity, demonstrating an overpotential of 258 mV (vs RHE) at 10 mA cm-2 current density and a Tafel slope of 17.33 mV dec-1. Furthermore, these electrodes demonstrate excellent stability, maintaining OER performance for 10 h in 1 M NaOH electrolyte. Additionally, the role of cobalt oxide nanoparticles in water treatment is explored using inductively coupled plasma atomic emission spectrometry (ICP-AES). Experimental results reveal that lower sintering temperatures enhance the electrocatalytic properties of cobalt oxide nanoparticles, highlighting their potential contribution to sustainable energy and water treatment technologies. This work underscores the significance of cobalt oxide nanoparticles as dual-functional materials for advancing electrocatalysis and water purification applications, thus paving the way for the development of efficient and environmentally friendly technologies.

Preparation of Newly Polymer-Coated Microbial Pellets and Their Adsorption and Degradation Properties for Oil-Containing Wastewater

Water is the lifeblood of everything on earth, nourishing and nurturing all forms of life, while also contributing to the development of civilization. However, with the rapid development of economic construction, especially the accelerated process of modern industrialization, the pollution of oily sewage is becoming increasingly serious, affecting the ecological balance and human health. The efficient elimination of pollutants in sewage is, therefore, particularly urgent. In this paper, a core-shell microbial reactor (MPFA@CNF-SA-AM) was fabricated by using nanocellulose and sodium alginate (SA) particles embedded with microorganisms as the core and lipophilic and hydrophobic fly ash as the outer shell layer. Compared with that of free microorganisms and cellulose and SA aerogel pellets loading with microorganisms (CNF-SA-AM), which has a degradation efficiency of 60.69 and 82.89%, respectively, the MPFA@CNF-SA-AM possesses a highest degradation efficiency of 90.60% within 240 h. So that this self-floating microbial reactor has selective adsorption properties to achieve oil-water separation in oily wastewater and high effective degradation of organic pollutants with low cost. The adsorption curves of MPFA@CNF-SA-AM for diesel and n-hexadecane were studied. The results showed that the adsorption follows the Freundlich model and is a multimolecular layer of physical adsorption. In addition, the degradation mechanism of diesel oil was studied by gas chromatography-mass spectrometry. The results showed that diesel oil was selectively adsorbed to the interior of MPFA@CNF-SA-AM, and it was degraded by enzymes in microorganisms into n-hexadecanol, n-hexadecaldehyde, and n-hexadecanoic acid in turn, and finally converted to water and carbon dioxide. Compared with existing oily wastewater treatment methods, this green and pollution-free dual-functional core-shell microbial reactor has the characteristics of easy preparation, high efficiency, flexibility, and large-scale degradation. It provides a new, effective green choice for oily wastewater purification and on-site oil spill accidents.

Fabrication of a Janus Copper Mesh by SiO2 Spraying for Unidirectional Water Transportation and Oil/Water Separation

Massive discharge of oily wastewater and frequent occurrence of offshore oil spills have posed an enormous threat to the socioeconomic and ecological environments. Janus membranes with asymmetric wettability properties have great potential for oil/water separation applications and have attracted widespread attention. However, existing Janus membranes still suffer from complex and costly manufacturing processes, low permeability, and poor recyclability. Herein, a novel and facile strategy was proposed to fabricate a Janus copper mesh with opposite wettability for unidirectional water transport and efficient oil/water separation. The hydrophilic side of the Janus copper mesh was prepared by coating it with Cu(OH)2 nanoneedles via a chemical oxidation method. The hydrophobic side was fabricated by coating it with hydrophobic SiO2 nanoparticles via a facile spraying method. The as-prepared Janus copper mesh showed asymmetric surface wettability, which can achieve unidirectional water transport and efficient oil/water separation with excellent recyclability, exhibiting great application potential for droplet manipulation and wastewater purification.

Superhydrophilic Photothermal-Responsive CuO@MXene Nanofibrous Membrane with Inherent Biofouling Resistance for Treating Complex Oily Wastewater

MXene, a recently emerged 2D material, has garnered substantial attention for a myriad of applications. Despite the growing interest, there remains a noticeable gap in exploring MXene-based membranes for the simultaneous achievement of photomodulated oil/water separation, bacterial resistance, and the removal of pollutants in the treatment of oily wastewater. In this work, we have successfully synthesized a novel multifunctional CuO@MXene-PAN nanofibrous membrane (NFM) featuring unique nanograin-like structures. Benefitting from these unique structures, the resultant membrane shows excellent superwetting properties, significantly enhancing its performance in oil/water separation. In addition, the membrane's photothermal property boosts its permeance by 40% under visible light illumination within 30 min. Furthermore, the resultant membrane shows decent dye removal efficiency in an aqueous solution, e.g., Rhodamine B (RhB), promoting efficient degradation with high reusability under visible light. Most remarkably, the resultant membrane exhibits superior anti-biofouling capability and consistently resists the adhesion of microorganisms such as cyanobacteria over a 14 day period. Thus, the combined effect of superior superwetting properties, photothermal responsivity, photocatalytic activity, and the antibacterial effect in CuO@MXene-PAN NFM contributes to the efficient treatment of intricate oily wastewater. This synergistic combination of superior properties in the membrane could be an appealing strategy for the broad development of multifunctional materials to prevent fouling during actual separation performance.

One-Step Prepared Multifunctional Polyacrylonitrile/MIL-100(Fe) Membrane with High-Density Porous Fibers for Efficient Dye/Oil Wastewater Remediation

With environmental pollution becoming more serious, developing efficient treatment technologies for all kinds of organic wastewater has become the focus of current research. In this work, the coaxial electrospinning technology was used to one-step fabricate a porous and underwater superoleophobic polyacrylonitrile nanofibrous membrane with an Fe-based metal-organic framework (MIL-100(Fe)). Benefiting from the synergistic effect of two jets, the nanofibers are smaller and denser, which prompt the exposure of more nanomaterial additives (MIL-100(Fe)). The BET surface area increased to 202.888 m2/g, and the membranes demonstrated outstanding underwater superoleophobicity. Moreover, compared with traditional blended matrix membranes by the single-axis method, separation of the modifier and membrane matrix material by coaxial methods also maintained excellent mechanical properties, which enhanced Young's modulus 3.4 times (∼1.34 MPa). As a result, facing soluble dyes, the porous C-PAN/MIL-100(Fe) membrane can demonstrate outstanding and fast adsorptive property (the Qm of MB and CR reached 44.71 and 88.74 mg g-1, respectively). For oily emulsion, the hydrophilic and oleophobic nanofibrous reticular surface provided excellent separation performance (flux: 1124.0-1549.3 L m-2 h-1, R > 98%). Moreover, the porous and underwater superoleophobic C-PAN/MIL-100(Fe)-0.5 membrane can synchronously purify the dye/oil mixture emulsions by one-step filtration. Based on the above performance, we believe that the modified nanofibrous membrane prepared by one-step coaxial electrospinning technology can promote more studies of the development of membrane preparation technology in the field of oily wastewater treatment.

Applications of graphene oxide (GO) in oily wastewater treatment: Recent developments, challenges, and opportunities

The treatment of oily wastewater has become a serious environmental challenge, for which graphene oxide has emerged as a promising material in solving the problem. The ever-growing utilization of graphene oxide (GO) in the treatment of oily wastewater necessitates a constant review. This review article employs a comprehensive literature survey methodology, systematically examining peer-reviewed articles, focusing on, but not entirely limited to, the last five years. Major databases such as EBSCOhost, Scopus, ScienceDirect, Web of Science and Google Scholar were searched using specific keywords related to GO and oily wastewater treatment. The inclusion criteria focused on studies that specifically address the application, efficiency, and mechanisms of GO in treating oily wastewater. The data extracted from these sources were then synthesized to highlight the most important developments, challenges, and prospects in this field. As far as oily wastewater treatment is concerned, the majority of the studies revolve around the use of GO in mitigating fouling in membrane processes, improving the stability, capacity and reusability of sorbents, and enhancing photodegradation by minimizing charge recombination.

Reusable Solid-form Phase-Selective Organogelators for Rapid and Efficient Remediation of Crude Oil Spill

Phase-selective organogelators (PSOGs) are considered as a prospective tool for their application in oil spill remediation. However, the number of reports on the PSOGs that can be used in powder form for prompt phase-selective gelation of crude oils is still limited. In this study, a series of compounds with l-mandelic acid as the scaffold bearing different amino acid fragments have been prepared. Also, the gelation behaviors and properties of these derivatives toward organic liquids, product oils, and a type of Chinese crude oil were investigated via heating-and-cooling process, stirring, or resting operation. Besides, the micromorphologies of the resulting gels and the driving forces for the gel formation have been studied by scanning electron microscopy, Fourier transform infrared, UV spectroscopy, concentration-dependent 1H NMR, and X-ray diffraction. Particularly, gelator C15-Phe-Mac-Nap was shown to have the capability of congealing the Chinese crude oil selectively from water in powder form with a relatively lower gelator dosage, as compared with the other gelators we reported in the current and previous works. Moreover, gelator C15-Phe-Mac-Nap displayed some advantageous behaviors such as the reusability of gelator, excellent mechanical and chemical stability of the crude oil gels, and nontoxicity of the gelator in the aquatic environment, indicating its great potential application value for marine oil spill remediation.

Flame retardant, heat insulating and hydrophobic chitosan-derived aerogels for the clean-up of hazardous chemicals

Leakage of hazardous chemicals often causes significant casualties, enormous economic losses, and negative social benefits. Presently, fire rescue personnel lack efficient and eco-friendly disposal materials for hazardous chemical leakage accidents. In this study, chitosan (CS) aerogels with excellent flame-retardant performance were prepared via cross-linking by two phosphorus-containing vanillin-based compounds (DV and TV). The as-prepared chitosan aerogels were lightweight and porous. The introduction of DV and TV greatly enhanced the residual char yields of CS at 700 °C and the flame-retardant performance of chitosan aerogels. TCS-5.0 possessed the best flame-retardant performance, indicating that TV was more effective than DV in enhancing the flame-retardant performance of chitosan aerogels. The greatly improved flame-retardant properties could be attributed to TV effectively promoting the residual char formation of chitosan aerogels and reducing the formation of combustible gas phase products. To improve the hydrophobicity of chitosan aerogels, TCS-5.0 was treated with solution immersion to load siloxane molecules on its surface. The water contact angle of HTCS-5.0 was 136.1°. HTCS-5.0 had a high oil absorption multiplicity, absorbing up to 31 times its own weight of chloroform. HTCS-5.0 could continuously absorb organic solvents on the water surface with the assistance of a vacuum pump, indicating that HTCS-5.0 could be used for the clean-up of hazardous chemical leakage accidents.

Robust PVA/GO@MOF membrane with fast photothermal self-cleaning property for oily wastewater purification

The poor mechanical durability and weak fouling resistance of oil/water separation membranes severely restrict their applications in industry. Herein, a robust PVA/GO@MOF membrane with fast photothermal self-cleaning capability was developed through facile chemical crosslinking and suction-filtration strategies. Attributed to the powerful underwater superoleophobicity, the PVA/GO@MOF membrane exhibited extraordinary anti-oil adhesion even for high-viscosity crude oil and continuous crude oil emulsion purification capability with stable flux (1020 L m-2 h-1 bar-1) and exceptional efficiency (> 99.3%) even after 60 min. Most importantly, in comparison to reported photocatalytic self-cleaning oil/water separation membranes, the PVA/GO@MOF membrane can degrade organic contaminants more rapidly with a higher degradation rate (99.9%) in 50 min due to the superior photothermal conversion capacity. The synergistic photothermal and photocatalytic effects significantly enhanced photodegradation efficiency, which created opportunities for in-depth treatment of complex oily wastewater. Besides, the obtained membrane displayed excellent chemical and mechanical durability with underwater oil contact angle (UWOCA) above 150° even in harsh environments, such as corrosive solutions, UV irradiation, ultrasound treatment, abrasion experiment and bending test. Therefore, the developed PVA/GO@MOF membrane with robust durability and fast photocatalytic self-cleaning property is highly expected to purify oily wastewater and degrade organic pollutants.

Hydrophobic organogel sorbent and its coated porous substrates for efficient oil/water emulsion separation and effective spilled oil remediation

Frequent offshore oil leakage accidents and large quantities of oily-wastewater produced in industry and daily life bring huge challenges to global water purification. The adaptability and stability of organogels as adsorbent materials have shown wide application prospects in the field of oil-water separation. Herein, the organogels displayed stable hydrophobic/lipophilic properties with high absorption ability (1200 wt./wt%), efficient sorption of multiple emulsions (>99.0%), and good reusability. More importantly, the organogels were successfully assembled with 2D/3D substrates to achieve excellent sorption capacity (102.5 g/g) and recycling performance (50 cycles). The gel-carbon black assembled on MS (GCB-MS) sorbent with excellent photothermal conversion performance, and can rapidly heat the surface to 70.4 °C under 1.0 sunlight radiation (1.0 kW/m2) and achieved an ultra-high sorption capacity of about 103 g/g for viscous crude oil. Meanwhile, the GCB-MS was combined with a pump to build continuous oil spill cleaning equipment to achieve a super-fast cleanup rate of 6.83 g/min. The developed hydrophobic organogels had been expanded unprecedentedly to realize the comprehensive treatment of oily-wastewater in complex environments, including layered oils, emulsions, and viscous crude oil spill, which provided an effective path for the comprehensive treatment of oily wastewater in complex environments.

Facile construction of multifunctional bio-aerogel for efficient separation of surfactant-stabilized oil-in-water emulsions and co-existing organic pollutant

The deep treatment of robust oily emulsion wastewater has long been an arduous challenge. Herein, a biomass-derived PEI-TiO2@Gelatin aerogel (PEI-TiO2@GA) with honeycomb-like porous structure was fabricated. The interface wetting characteristics of PEI-TiO2@GA could be selectively switched between the superlipophilicity and superoleophobicity through the merely pre-wetting process. Combined with extraordinary structure and superwetting properties, PEI-TiO2@GA was proved to be ideal for oils absorption (17-26 g/g) and MO dye adsorption (73.549 mg/g) with high up-taking rate. Simultaneously, as-prepared PEI-TiO2@GA could realize various surfactant-stabilized oil-in-water emulsions separation simply under gravity with the separation efficiency as high as 99.25%. In addition, PEI-TiO2@GA was highly resistant toward mechanical compression (1.952 MPa), and exhibited acceptable regenerability within 5 cycles by performing solvent replacement approach. Combining with the newly developed separator and dynamic emulsion separation device, the continuous deep separation of the emulsion and the synergistic removal of co-existing pollutants can be achieved with the enhanced separation efficiency and permeation flux. Most importantly, the mechanism results show that the transition of interface wetting properties was a reversible multi-step process, and the demulsification separation of emulsion and the adsorption removal of co-existing pollutants were two independent processes. This work opens up a new avenue to customize advanced bio-aerogels for industrial effluent treatment and environmental remediation.

Superhydrophilic and Underwater Superoleophobic Copper Mesh Coated with Bamboo Cellulose Hydrogel for Efficient Oil/Water Separation

Super-wetting interface materials have shown great potential for applications in oil-water separation. Hydrogel-based materials, in particular, have been extensively studied for separating water from oily wastewater due to their unique hydrophilicity and excellent anti-oil effect. In this study, a superhydrophilic and underwater superoleophobic bamboo cellulose hydrogel-coated mesh was fabricated using a feasible and eco-friendly dip-coating method. The process involved dissolving bamboo cellulose in a green alkaline/urea aqueous solvent system, followed by regeneration in ethanol solvent, without the addition of surface modifiers. The resulting membrane exhibited excellent special wettability, with superhydrophilicity and underwater superoleophobicity, enabling oil-water separation through a gravity-driven "water-removing" mode. The super-wetting composite membrane demonstrated a high separation efficiency of higher than 98% and a permeate flux of up to 9168 L·m-2·h-1 for numerous oil/water mixtures. It also maintained a separation efficiency of >95% even after 10 cycles of separation, indicating its long-term stability. This study presents a green, simple, cost-effective, and environmentally friendly approach for fabricating superhydrophilic surfaces to achieve oil-water separation. It also highlights the potential of bamboo-based materials in the field of oil-water separation.

Biomimetic materials in oil/water separation: Focusing on switchable wettabilities and applications

Clean water resources are crucial for human society, as the leakage and discharge of oily wastewater not only harm the economy but also disrupt our living environment. Therefore, there is an urgent need for efficient oil-water separation technology. Surfaces with switchable superwetting behavior have garnered significant attention due to their importance in both fundamental research and practical applications. This review introduces the fundamental principles of wettability in the oil-water separation process, the basic theory of switchable wettability, and the mechanisms involved in oil-water separation. Subsequently, the review discusses the research progress, challenges, and issues associated with three conventional types of special wettability materials: superhydrophobic/superoleophilic materials, superhydrophilic/superoleophobic materials, and superhydrophilic/underwater superoleophobic materials. Most importantly, it provides a detailed exploration of recent advancements in switchable wettability smart materials, which combine elements of traditional special wettability materials. These include stimulus-responsive smart materials, pre-wetting-induced materials, and Janus materials. The discussion covers key response factors, detailed examples of representative works, design concepts, and fabrication strategies. Finally, the review offers a comprehensive summary of switchable superwetting smart materials, encompassing their advantages and disadvantages, persistent challenges, and future prospects.

A comprehensive review on the behavior and evolution of oil droplets during oil/water separation by membranes

Membrane separation technology has significant advantages for treating oil-in-water emulsions. Understanding the evolution of oil droplets could reveal the interfacial and colloidal interactions, facilitate the design of advanced membranes, and improve the separation performances. This review on the characteristic behavior and evolution of oil droplets focuses on the advanced analytical techniques, and the subsequent fouling as well as demulsification effects during membrane separation. A detailed introduction is provided on microscopic observations and numerical simulations of the dynamic evolution of oil droplets, featuring real-time in-situ visualization and accurate reconstruction, respectively. Characteristic behaviors of these oil droplets include attachment, pinning, wetting, spreading, blockage, intrusion, coalescence, and detachment, which have been quantified by specific proposed parameters and criteria. The fouling process can be evaluated using Hermia and resistance models. The related adhesion force and intrusion pressure as well as droplet-droplet/membrane interfacial interactions can be accurately quantified using various force analysis methods and advanced force measurement techniques. It is encouraging to note that oil coalescence has been achieved through various effects such as electrostatic interactions, mechanical actions, Laplace pressure/surface free energy gradients, and synergistic effects on functional membranes. When oil droplets become destabilized and coalesce into larger ones, the functional membranes can overcome the limitations of size-sieving effect to attain higher separation efficiency. This not only bypasses the trade-off between permeability and rejection, but also significantly reduces membrane fouling. Finally, the challenges and potential research directions in membrane separation are proposed. We hope this review will support the engineering of advanced materials for oil/water separation and research on interface science in general.

Studies on the Functional Properties of Titanium Dioxide Nanoparticles Distributed in Silyl-Alkyl Bridged Polyaniline-Based Nanofluids

In the present work, a new kind of nanocomposite (NC)-based solid component was prepared for formulating nanofluids (NFs). The NC comprised metal oxide (titanium dioxide, TiO2) dispersed in a conducting polymer with polyaniline (PANI) and chemically linked silyl-alkyl units in it (PSA) that were designated as T-PSA NC. The NFs with ethylene glycol (EG) as a base fluid were prepared with T-PSA NCs with various compositions of TiO2 and PSA as well for various concentrations of T-PSA NCs. The scanning electron microscopic evaluation of the NC revealed that PSA deposition on TiO2 nanoparticles (NPs) decreased particle agglomeration. The PSA coating on the TiO2 NPs did not influence the crystalline structure of the TiO2 NPs, according to the X-ray diffraction patterns. The thermophysical characterization and molecular interaction features of the NFs at 303 K including a novel inorganic-organic T-PSA NC, were detailed. Furthermore, the stability of the T-PSA NC-based NFs was investigated experimentally using the zeta potential, and the particle size distribution change was analyzed using the dynamic light scattering (DLS) method. The T-PSA NCs had particle sizes that were significantly bigger than pristine PSA and pure TiO2. Most of the preparation conditions used to produce the T-PSA NCs resulted in moderately stable suspensions in EG. The results revealed that the ultrasonic velocity increased with the increase in the concentration of T-PSA NC mass % in the NFs, the refractive index and thermal conductivity increased with the increase in the concentration, and the surface tension exhibited a linear change when the ratio of mass % concentration of the T-PSA NCs increased. The combined presence of components that synergistically contribute to the electro, thermal, optical, and rheological properties is expected to attract advanced applications for NFs.

Non-Stop Switching Separation of Superfine Solid/Liquid Dispersed Phases in Oil and Water Systems Using Polymer-Assisted Framework Fiber Membranes

Fabricating filtration membranes with wide applicability and high efficiency is always a challenge in the precise separation of small colloidal particles under mild conditions. For this purpose, a strategy mixing supramolecular framework fiber with polymer is adopted. The fibrous assembly in the gel state provides uniform nanopores for both channel and interception and controlled wettability for lyophilic/lyophobic switching. The used polymer fills the gaps between fiber assemblies and improves the mechanical property. The composite membrane shows both under-oil superhydrophobic and underwater superoleophobic nature, which allows the conversions via in situ modulation of joystick solvents. Based on surface wetting and size-sieving, ultrafine hard nanoparticles dispersing in both hydrophobic organic solvents and water are selectively sieved. In addition, on-demand separation of water-in-oil and oil-in-water microemulsions without and with surfactants as systems containing soft droplets are realized. The smallest cut-off size of ≈3 nm is achieved for both hard and soft emulsions, while separation efficiency maintains during sustained in situ reversible switches.

Highly compressible and hydrophobic nanofibrillated cellulose aerogels for cyclic oil/water separation

Nanofibrillated cellulose (NFC)-based aerogels are ideal oil-sorbent materials, but the poor structural stability and hydrophilicity restrain their practical applications in the fields of oil/water separation. In the present work, we report a facile strategy for constructing a hydrophobic nanofibrillated cellulose aerogel for cyclic oil/water separation. Briefly, an aerogel matrix of C-g-PEI with multiple cross-linked network structures was constructed via the combined use of oxidized-NFC (ONC), polyethyleneimine (PEI), and ethylene glycol diglycidyl ether (EGDE), followed by rapid in situ deposition of poly(methyl trichlorosilane) (PMTS) through a low-temperature gas-solid reaction. The resulting ONC-based aerogel (C-g-PEI-PMTS) exhibits the advantages of ultralight (53.80 mg/cm³), high porosity (95.73 %), hydrophobicity (contact angle of 130.0°) and remarkable elasticity (95.86 %). Meanwhile, the composite aerogel of C-g-PEI-PMTS is extremely suitable for oil sorption-desorption by a simple mechanical squeezing method. After 10 cycles of sorption-desorption, the sorption capacity of the aerogel towards various oils reached almost the same level as in the first cycle. The filtration separation efficiency for the trichloromethane-water mixtures remained at 99 % after 50 cycles, demonstrating encouraging reusability. In summary, an efficient strategy to prepare NFC-based aerogel with highly compressible and hydrophobic properties is developed, which expands the applications of NFC in the fields of oil/water separation.

Dimensionality effects of g-C3N4 from wettability to solar light assisted self-cleaning and electrocatalytic oxygen evolution reaction

Unique interfacial properties of 2D materials make them more functional than their bulk counterparts in a catalytic application. In the present study, bulk and 2D graphitic carbon nitride nanosheet (bulk g-C₃N₄ and 2D-g-C₃N₄ NS) coated cotton fabrics and nickel foam electrode interfaces have been applied for solar light-driven self-cleaning of methyl orange (MO) dye and electrocatalytic oxygen evolution reaction (OER), respectively. Compared to bulk, 2D-g-C₃N₄ coated interfaces show higher surface roughness (1.094 > 0.803) and enhanced hydrophilicity (θ ∼ 32° < 62° for cotton fabric and θ ∼ 25° < 54° for Ni foam substrate) due to oxygen defect induction as confirmed from morphological (HR-TEM and AFM) and interfacial (XPS) characterizations. The self-remediation efficiencies for blank and bulk/2D-g-C₃N₄ coated cotton fabrics are estimated through colorimetric absorbance and average intensity changes. The self-cleaning efficiency for 2D-g-C₃N₄ NS coated cotton fabric is 87%, whereas the blank and bulk-coated fabric show 31% and 52% efficiency. Liquid Chromatography-Mass Spectrometry (LC-MS) analysis determines the reaction intermediates for MO cleaning. 2D-g-C₃N₄ shows lower overpotential (108 mV) and onset potential (1.30 V) vs. RHE for 10 mA cm^-2 OER current density in 0.1 M KOH. Also, the decreased charge transfer resistance (R_CT = 12 Ω) and lower Tafel's slope (24 mV dec^-1) of 2D-g-C₃N₄ make it the most efficient OER catalyst over bulk-g-C₃N₄ and state-of-the-art material RuO₂. The pseudocapacitance behavior of OER governs the kinetics of electrode-electrolyte interaction through the electrical double layer (EDL) mechanism. The 2D electrocatalyst demonstrates long-term stability (retention ∼94%) and efficacy compared to commercial electrocatalysts.

Spray-assisted LBL assembly of chitosan/nanocellulose as coatings of commercial membranes for oil-in-water emulsion separation

Owing to the limitation of their wettability and pore size, lab filter membrane could not separate oil/water emulsions. Herein, we present surface modification of commercial membranes with chitosan/nanocellulose coatings via a spray-assisted layer-by-layer (LBL) assembly technology. By alternate spraying chitosan (CS) solution and TEMPO-oxidized tunicate cellulose nanofiber (TCNF) suspension, (CS/TCNF)_n multilayers were obtained, where n denotes the number of bilayers. The (CS/TCNF)₆ coated membrane possessed superhydrophilicity, underwater superoleophobicity, and outperforming anti-oil-fouling properties, which could effectively separate various oil-in-water emulsions. Importantly, the (CS/TCNF)₆ coated membrane not only had stable permeate flux with nearly 100 % recovery ratio for the separation of pump oil-in-water emulsion, but also exhibited good harsh-environment-tolerant property. This work provided a novel strategy for designing and preparing stable anti-oil-fouling membranes for oily wastewater treatment.

Preparation and Characterization of a Janus Membrane with an "Integrated" Structure and Adjustable Hydrophilic Layer Thickness

Oil-water emulsions are types of wastewater that are difficult to treat. A polyvinylidene fluoride hydrophobic matrix membrane was modified using a hydrophilic polymer, poly(vinylpyrrolidone-vinyltriethoxysilane), to form a representative Janus membrane with asymmetric wettability. The performance parameters of the modified membrane, such as the morphological structure, the chemical composition, the wettability, the hydrophilic layer thickness, and the porosity, were characterized. The results showed that the hydrolysis, migration, and thermal crosslinking of the hydrophilic polymer in the hydrophobic matrix membrane contributed to an effective hydrophilic layer on the surface. Thus, a Janus membrane with unchanged membrane porosity, a hydrophilic layer with controllable thickness, and hydrophilic/hydrophobic layer "structural integration" was successfully prepared. The Janus membrane was used for the switchable separation of oil-water emulsions. The separation flux of the oil-in-water emulsions on the hydrophilic surface was 22.88 L·m^-2·h^-1 with a separation efficiency of up to 93.35%. The hydrophobic surface exhibited a separation flux of 17.45 L·m^-2·h^-1 with a separation efficiency of 91.47% for the water-in-oil emulsions. Compared to the lower flux and separation efficiency of purely hydrophobic and hydrophilic membranes, the Janus membrane exhibited better separation and purification effects for both oil-water emulsions.

Overflow Control for Sustainable Development by Superwetting Surface with Biomimetic Structure

Liquid flowing around a solid edge, i.e., overflow, is a commonly observed flow behavior. Recent research into surface wetting properties and microstructure-controlled overflow behavior has attracted much attention. Achieving controllable macroscale liquid dynamics by manipulating the micro-nanoscale liquid overflow has stimulated diverse scientific interest and fostered widespread use in practical applications. In this review, we outline the evolution of overflow and present a critical survey of the mechanism of surface wetting properties and microstructure-controlled liquid overflow in multilength scales ranging from centimeter to micro and even nanoscale. We summarize the latest progress in utilizing the mechanisms to manipulate liquid overflow and achieve macroscale liquid dynamics and in emerging applications to manipulate overflow for sustainable development in various fields, along with challenges and perspectives.

Anisotropic cellulose nanocrystalline sponge sheets with ultrahigh water fluxes and oil/water selectivity

Oily sewage caused by oil spill accidents has become a severe problem in the last decades. Hence, two-dimensional sheet-like filter materials for oil/water separation have received widespread attention. Porous sponge materials were developed using cellulose nanocrystals (CNCs) as raw materials. They are environmentally friendly and easy to prepare, with high flux and separation efficiency. The 1,2,3,4-butane tetracarboxylic acid cross-linked anisotropic cellulose nanocrystalline sponge sheet (B-CNC) exhibited ultrahigh water fluxes driven by gravity alone, depending on the aligned structure of channels and the rigidity of CNCs. Meanwhile, the sponge gained superhydrophilic/underwater superhydrophobic wettability with an underwater oil contact angle of up to 165.7° due to its ordered micro/nanoscale structure. B-CNC sheets displayed high oil/water selectivity without additional material doping or chemical modification. For oil/water mixtures, high separation fluxes of approximately 100,000 L·m^-2·h^-1 and separation efficiencies of up to 99.99 % were obtained. For a Tween 80-stabilized toluene-in-water emulsion, the flux reached >50,000 L·m^-2·h^-1, and the separation efficiency was above 99.7 %. B-CNC sponge sheets showed significantly higher fluxes and separation efficiencies than other bio-based two-dimensional materials. This research provides a facile and straightforward fabrication method of environmental-friendly B-CNC sponges for rapid, selective oil/water separation.

Lignin microparticles-reinforced cellulose filter paper for simultaneous removal of emulsified oils and dyes

The presence of multiple pollutants in wastewater, often with complex interactions, poses a significant challenge for conventional membranes to effectively remove multiple pollutants simultaneously. Herein, a lignin microparticles-reinforced cellulose filter paper (FP@AL-LS-DA) was fabricated via an aldol condensation between lignin and cellulose filter paper and cross-linking with dopamine hydrochloride (DA), which showed desired rejection of oil-in-water emulsions and dyes. Characterizations revealed that the addition of lignin and DA effectively narrowed the pore size (from 4.45 μm to 2.01 μm) and enhanced the rigidity and stability of the cellulose filter paper, thus making it not easily damaged in the water environment and showing excellent tolerance to strong acid and high-salt environments. The oil-in-water emulsions removal efficiency was higher than 99 % even after ten times usage, and the oil flux was kept stable at 52.54 L·m^-2·h^-1, indicating that FP@AL-LS-DA had outstanding reusability and stability. Remarkably, FP@AL-LS-DA showed excellent removal efficiency (>99 %) for complex pollutants containing dyes and oil-in-water emulsions. In this work, we demonstrate a lignin microparticles-reinforced cellulose filter paper that is simple to prepare and can efficiently separate oil-in-water emulsions and remove dyes.

Demulsifier-Inspired Superhydrophilic/Underwater Superoleophobic Membrane Modified with Polyoxypropylene Polyoxyethylene Block Polymer for Enhanced Oil/Water Separation Properties

Demulsifiers are considered the key materials for oil/water separation. Various works in recent years have shown that demulsifiers with polyoxypropylen epolyoxyethylene branched structures possess better demulsification effects. In this work, inspired by the chemical structure of demulsifiers, a novel superhydrophilic/underwater superoleophobic membrane modified with a polyoxypropylene polyoxyethylene block polymer was fabricated for enhanced separation of O/W emulsion. First, a typical polyoxypropylene polyoxyethylene triblock polymer (Pluronic F127) was grafted onto the poly styrene-maleic anhydride (SMA). Then, the Pluronic F127-grafted SMA (abbreviated as F127@SMA) was blended with polyvinylidene fluoride (PVDF) for the preparation of the F127@SMA/PVDF ultrafiltration membrane. The obtained F127@SMA/PVDF ultrafiltration membrane displayed superhydrophilic/underwater superoleophobic properties, with a water contact angle of 0° and an underwater oil contact angle (UOCA) higher than 150° for various oils. Moreover, it had excellent separation efficiency for SDS-stabilized emulsions, even when the oil being emulsified was crude oil. The oil removal efficiency was greater than 99.1%, and the flux was up to 272.4 L·m^-2·h^-1. Most importantly, the proposed F127@SMA/PVDF membrane also exhibited outstanding reusability and long-term stability. Its UOCA remained higher than 150° in harsh acidic, alkaline, and high-salt circumstances. Overall, the present work proposed an environmentally friendly and convenient approach for the development of practical oil/water separation membranes.

Thermal and magnetic dual-responsive switchable device with superhydrophilicity/underwater superoleophobicity and excellent targeted oil–water separation performance

In view of the increasingly serious problem of oil–water separation, it is a convenient and practical method to introduce a hydrogel coating on the surface of materials to make super-wetting materials. Nowadays, researchers of super-wetting materials pay more attention to the research and development of responsive materials. Here, a thermal and magnetic dual-responsive superhydrophilicity/underwater superoleophobicity switchable device (Fe3O4@PNIPAM-Cu) was simply fabricated using the Fe3O4 nanoparticles, poly-N-isopropylacrylamide (PNIPAM) hydrogel as the functional coating and copper foam as the skeleton through a one-step solution immersion method. The separation efficiency of the benzene-water mixture of this dual-responsive device can reach up to 99.98%. Even after 10 separation cycles, it maintained an efficiency of more than 99.90%. At temperatures above ~34°C, the device can stop oil–water separation. The experiments presented here demonstrate this dual-responsive device possesses excellent superhydrophilicity/underwater superoleophobicity, thermal-responsive property and magnetic navigation function.

Recent advances in eco-friendly fabrics with special wettability for oil/water separation

Considering the serious damage to aquatic ecosystems and marine life caused by oil spills and oily wastewater discharge, efficient, environment-friendly and sustainable oil/water separation technology has become an inevitable trend for current development. Herein, fabrics are recognized as eco-friendly materials for water treatment due to their good degradability and low cost. Particularly, fabrics with rough structures and natural hydrophilicity/oleophilicity enable the construction of superwetting surfaces for the selective separation of oil/water mixtures and even complex emulsions. Therefore, superwetting fabrics for efficiently solving oil spills and purifying oily wastewater have received extensive attention. Especially, Janus and smart fabrics are highly anticipated to enable the on-demand and sustainable treatment of oil spills and oily wastewater due to their changeable wettability. Moreover, the fabrication of superwetting fabrics with multifunctional performances for oily wastewater purification can further promote their practical industrial applications, such as photocatalytic, self-cleaning, and self-healing characteristics. However, some potential challenges still exist, which urgently need to be systematically summarized to guide the future development of this research field. In this review, firstly, the fundamental theories of wettability and the separation mechanisms based on special wettability are discussed. Then, superwetting fabrics for efficient oil/water separation are systematically reviewed, such as superhydrophobic/superoleophilic (SHB/SOL), superhydrophilic/superoleophobic (SHL/SOB), SHL/underwater superoleophobic (SHL/UWSOB), and UWSOB/underoil superoleophobic (UWSOB/UOSHB) fabrics. Most importantly, we highlight Janus, smart, and multifunctional fabrics based on their superwetting property. Correspondingly, the advantages and disadvantages of each superwetting fabric are comprehensively analyzed. Besides, super-antiwetting fabrics with superhydrophobic/superoleophobic (SHB/SOB) property are also introduced. Finally, the challenges and future research directions are explained.

Atmospheric Pressure Plasma-Treated Polyurethane Foam as Reusable Absorbent for Removal of Oils and Organic Solvents from Water

This paper reports the optimization of a two-step atmospheric pressure plasma process to modify the surface properties of a polyurethane (PU) foam and, specifically, to prepare a superhydrophobic/superoleophilic absorbent for the removal of oils and nonpolar organic solvents from water. In particular, in the first step, an oxygen-containing dielectric barrier discharge (DBD) is used to induce the etching/nanotexturing of the foam surfaces; in the second step, an ethylene-containing DBD enables uniform overcoating with a low-surface-energy hydrocarbon polymer film. The combination of surface nanostructuring and low surface energy ultimately leads to simultaneous superhydrophobic and superoleophilic wetting properties. X-ray photoelectron spectroscopy, scanning electron microscopy and water contact angle measurements are used for the characterization of the samples. The plasma-treated PU foam selectively absorbs various kinds of hydrocarbon-based liquids (i.e., hydrocarbon solvents, mineral oils, motor oil, diesel and gasoline) up to 23 times its own weight, while it completely repels water. These absorption performances are maintained even after 50 absorption/desorption cycles and after immersion in hot water as well as acidic, basic and salt aqueous solutions. The plasma-treated foam can remove mineral oil while floating on the surface of mineral oil/water mixtures with a separation efficiency greater than 99%, which remains unaltered after 20 separation cycles.

Advances in Asymmetric Wettable Janus Materials for Oil-Water Separation

The frequent occurrence of crude oil spills and the indiscriminate discharge of oily wastewater have caused serious environmental pollution. The existing separation methods have some defects and are not suitable for complex oil-water emulsions. Therefore, the efficient separation of complex oil-water emulsions has been of great interest to researchers. Asymmetric wettable Janus materials, which can efficiently separate complex oil-water emulsions, have attracted widespread attention. This comprehensive review systematically summarizes the research progress of asymmetric wettable Janus materials for oil-water separation in the last decade, and introduces, in detail, the preparation methods of them. Specifically, the latest research results of two-dimensional Janus materials, three-dimensional Janus materials, smart responsive Janus materials, and environmentally friendly Janus materials for oil-water separation are elaborated. Finally, ongoing challenges and outlook for the future research of asymmetric wettable Janus materials are presented.