Oil-water Separation Research Articles

Advanced Low–Cost Natural Materials for High–Performance Oil–Water Filtration Membranes: Achievements, Challenges, and Future Directions

The development of affordable ceramic membranes is essential for reducing expenses and optimizing the treatment of oily wastewater. There is an urgent demand for membranes that are not only affordable and easy to operate but also stable and capable of managing high fluxes to address the increasing volumes of oily wastewater. The significant production demands associated with many commercially available ceramic membranes, primarily due to the use of specialised raw materials and intricate processing methods, limiting their suitability for many wastewater treatment applications. Consequently, there is a rising interest in creating innovative ceramic membranes using affordable materials and simpler production techniques. This study reviewed the oil–water ceramic membranes utilizing affordable natural ceramic materials aimed at improving membrane performance. It focused on reviewing the environmentally friendly and economically viable membranes derived from natural ceramic resources as an alternative to conventional synthetic membranes. These natural ceramic materials possess crucial properties like hydrophilicity and oleophobicity, which are vital for effective oil–water separation. The ceramic membranes were reviewed for their filtration performance and advantages. It was reported that these natural ceramic material-based membranes demonstrate superior separation efficiency, and strong mechanical stability, making them promising candidates for sustainable water treatment.

Development of a transverse-feeding vibration chiseling process for ultrafast and flexible texturing of metallic micropillars

Micropillar structures exhibit significant potential for various applications, including enhanced heat transfer to anti-icing, corrosion resistance, oil-water separation, and droplet manipulation. There is still a lack of high-efficiency and high-flexibility methods for the texturing of micropillars on metallic surfaces. Elliptical vibration chiseling has emerged as a novel process for fabricating high-aspect-ratio microstructures on metals. Nevertheless, the achievable structural shapes are primarily limited to microribs. This study proposes a transverse-feeding vibration chiseling (TFVC) process for the ultrafast and flexible fabrication of micropillars. In TFVC, an inclined 1D vibration trajectory is in the cutting plane, and a triangular-shaped tool moves perpendicularly to the cutting plane, which differs from conventional vibration cutting. As a result, a chip is generated but left on the surface in each vibration cycle, forming a micropillar structure. Due to the shear deformation in the chip, the grain of the micropillar structure material can be modified to present different contact properties from the substrate material. A finite element simulation is performed to explore the underlying mechanics and predict the surface generation of micropillar structures. Then, surface experiments are conducted on aluminum to verify the efficacy of the TFVC and explore its deterministic process parameters. The experimental results show a successful fabrication of micropillars by the TFVC. Finally, fish-scale-type microstructures and hierarchical grooves have been fabricated to demonstrate process flexibility. Furthermore, lotus leaf-inspired superhydrophobic surfaces and structurally colored surfaces with self-cleaning functions have been developed to illustrate the application potential of the TFVC.

Green Fabrication of Biobased and Degradable Poly(lactic acid)/Poly(butylene succinate) Open-Cell Foams for Highly Efficient Oil–Water Separation with Ultrafast Degradation

Green Fabrication of Biobased and Degradable Poly(lactic acid)/Poly(butylene succinate) Open-Cell Foams for Highly Efficient Oil–Water Separation with Ultrafast Degradation

Enhanced oil/water separation using superhydrophobic nano SiO2-modified porous melamine sponges

Recent advancements in functional sponge materials have garnered significant interest due to their efficacy and cost-effectiveness in oil spill remediation. This study introduces both silane coupling agent (methyltrichlorosilane and 3-aminopropyltriethoxysilane) and nano-SiO₂ particles into the melamine sponge framework via impregnation. Additionally, polydimethylsiloxane (PDMS) serves a crucial role in curing to fuse the substrate with the coating through robust covalent bonds. The modified sponges (SiMAPs) facilitate the formation of rough surfaces comprising hierarchical structures by the deposition of nano-SiO₂ particles, while the silane coupling agents and PDMS contribute to a reduced surface energy. These SiMAP sponges maintain high stability with a water contact angle of 162.6° and demonstrate an adsorption capacity ranging from 40 to 90 times their weight in oil or organic solvents. Furthermore, they achieve a separation efficiency exceeding 98% and an oil flux of 14.38 L/m2∙s in immiscible oil-water mixtures. Additionally, the sorption of trichloromethane reaches 88.1 g/g, and the separation efficiency for surfactant-stabilized emulsions containing diesel is 62.8%. Remarkably, the oil-water separation efficiency surpasses 99.8% in dynamic continuous oil-water separation cycles, as evidenced by 20 experimental trials. These results underscore the substantial potential of SiMAP-modified sponges for addressing oil pollution by enhancing oil-water separation.

Mesoporous MXene nanosheets/CNF composite aerogels for electromagnetic wave absorption and multifunctional response

To acquire excellent wave-absorbing materials with broadened applications, transition metal carbides (Ti3C2Tx, MXene) have been the research focus. However, the high conductivity of MXene limits its electromagnetic wave (EMW) absorption capability; meanwhile, the inferior mechanical properties of MXene-based aerogels severely restrict their applications. Here, porous MXene (PMXene) nanosheets were prepared by hydrogen peroxide etching, which was then physically and chemically crosslinked with cellulose nanofibres (CNF) to successfully prepare PMXene/CNF composite wave-absorbing aerogels with excellent mechanical properties. PMXene/CNF aerogel achieved a minimum reflection loss (RLmin) of − 72.27 dB and an effective absorption bandwidth (EAB) of 5 GHz at a thickness of 1.63 mm without any magnetic component. The aerogels exhibited excellent environmental stability at a density of 12.5 mg/cm3, including fatigue resistance (100 compression cycles, 0.075 energy loss efficiency) and low-temperature resistance. Refining the mechanical properties exploits the aerogel’s potential for motion monitoring and electronic skin applications. In addition, the aerogels integrate properties such as water–oil separation, photothermal conversion, and thermal insulation (thermal conductivity of 0.045 W/(m-K)). Therefore, multifunctional PMXene/CNF aerogels have a broad potential for future application in the defence industry, electronic devices, and smart wearable fields.

Eco-friendly poly (ε-caprolactone) based Microfiltration polymeric membranes - influence of dope composition on morphology and performance concerning oil-water separation

Eco-friendly poly (ε-caprolactone) based Microfiltration polymeric membranes - influence of dope composition on morphology and performance concerning oil-water separation

Preparation of superhydrophobic polyurethane sponge with photodegradation function and study on its oil-water separation performance

The surface of tetrapod-shaped zinc oxide whiskers (T-ZnOw) was hydrophobized by the sol-gel method, and then loaded onto the surface of polyurethane sponge by dip-curing method to prepare a superhydrophobic polyurethane sponge with photodegradation function. When the mass ratio of superhydrophobic tetrapod-shaped zinc oxide whiskers (ST-ZnOw) and polydimethylsiloxane (PDMS) was 0.5:1, the water contact angle of the sponge was 157.5°. After being soaked in acid and alkali corrosion solution, rubbed with sandpaper and heat treated, the sponge can still maintain excellent hydrophobic properties. The adsorption capacity for different oils and organic solvents is 12 to 35 times of its own mass. After repeated extrusion-oil absorption experiments, it can still maintain its good adsorption capacity and high hydrophobicity, showing excellent reusability. The continuous oil-water separation efficiency of the material for different oils and organic solvents is above 95%, and the separation efficiency for the emulsion prepared with span80 content of 0.1wt% is 99.84%. At the same time, the prepared material can degrade the organic dye methylene blue under ultraviolet light, with a degradation rate of 99.35%, showing excellent potential for degrading organic pollutants.

Unique dual superlyophobic covalent organic frameworks (COF-TpBD) intercalated MXene composite membrane for efficient oil-water separation

The development of composite membranes utilizing transition metal carbides and nitrides, exemplified by Ti3C2Tx (MXene), has proven efficacious in the treatment of oily wastewater. However, challenges arise from the prolonged and convoluted transport paths within MXene interlayer nanochannels, significantly impeding mass transfer and diminishing membrane permeability. This investigation incorporated porous covalent organic frameworks (COFs) as intercalating agents into two-dimensional (2D) MXene-based membranes to expand the interlayer nanochannels. The resulting MXene@COF-TpBD functional layer polyethersulfone (PES) composite membrane exhibited a distinctive dual superoleophobic surface, concurrently manifesting underwater superoleophobicity and underoil superhydrophobicity (underwater oil contact angle > 150°, underoil water contact angle > 150°). The membranes exhibited excellent water flux (up to 4092.7 L·m-2·h-1·bar-1), efficient oil-water emulsion separation (up to 1908.4 L·m-2·h-1·bar-1, rejection rates >99.78%), noteworthy fouling resistance and structural stability, outperforming most of existing similar membranes. Furthermore, supported by the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, the incorporation of COF-TpBD improved the antifouling characteristics of the composite membrane. This work presents innovative insights into the improvement of 2D MXene membranes and the use of COF-TpBD for the specific remediation of oily wastewater.

Advanced fabrication of ultra-high molecular weight polyethylene/ graphite nanoplates foam for enhanced oil–water separation and thermal insulation via a novel omnidirectional gas escape barrier mechanism

Advanced fabrication of ultra-high molecular weight polyethylene/ graphite nanoplates foam for enhanced oil–water separation and thermal insulation via a novel omnidirectional gas escape barrier mechanism

Foaming and emulsification synergies in skin mild and environmentally friendly detergents based on Gleditsia sinensis saponins

Gleditsia sinensis saponins (GS) is a biodegradable nonionic surfactant extracted from the plant pericarp. The objective of this study is to evaluate its potential for application in cleaning products in response to resource and environmental changes. Here, high-purity GS (93.92 %) was obtained through the macroporous resin adsorption technique and mixed with sodium lauroyl methylaminopropionate (LMA) to form a Gleditsia sinensis saponins- sodium lauroyl methylaminopropionate (GS-LMA) binary system. The synergistic effect was clarified by calculating the intermolecular interactions and thermodynamic parameters of the mixed micelles. The surface activity, foam stability, and emulsification characteristics were investigated to assess the detergent potential of the GS-LMA mixture. The results indicated that the formation of GS-LMA mixed micelles followed a non-ideal, spontaneous exothermic process. Furthermore, the addition of GS decreased the critical micelle concentration of the mixture while enhancing foam stability (98.34 %) and prolonging the oil–water separation time (103.11 min). The synergistic effects of foaming and emulsification enhanced the cleaning efficiency of the mixtures to 90.60 %. Further studies showed the mixture can reduce oil–water interfacial tension and form stable emulsions in various environments. This work can provide a theoretical basis for a better understanding the synergistic effects of binary surfactants and interfacial science.

Nature mimicking temperature induced self-healing soft subaquatic superoleophobic polymeric materials for oil-water separation

Nature mimicking temperature induced self-healing soft subaquatic superoleophobic polymeric materials for oil-water separation

Digital Light Processing (DLP) 3D Printing Fabrication of Hydrophobic Meshes Incorporating Fluorinated and Silicone-Based Acrylates Combined with Surface Engineering: Comparison of Their Oil–Water Separation Efficiency

Digital Light Processing (DLP) 3D Printing Fabrication of Hydrophobic Meshes Incorporating Fluorinated and Silicone-Based Acrylates Combined with Surface Engineering: Comparison of Their Oil–Water Separation Efficiency

Dynamic covalent bonds enabled robust and self-healing superhydrophobic coatings with multifunctions

Inspired by plants and animals in nature, durable superhydrophobic surfaces have been successfully developed in the past decades. However, the practical application of these superhydrophobic surfaces suffers from poor mechanical and chemical stability after damage or longtime usage. Thus, effective silicone-based polymers are developed to prepare the intelligent self-healing and durable superhydrophobic coatings with multifunctions. The superhydrophobic coatings are composed of dynamic silicone polymers and silica nanoparticles, which can be applicable in various substrates with enhanced water repellency. The abundant hydrogen bonds and reversible B-O covalent bonds in the dynamic silicone polymers enable a strong binding force with the substrate and self-healing nature. Thus, the superhydrophobic coatings exhibit a high contact angle up to 159.3°, and a low sliding angle of 6.9°. Meanwhile, it displays mechanical stability against washing and abrasion damage, and chemical stability in acid and alkaline environment. Especially, it is capable of repairing the superhydrophobicity after damage due to the reversible association/dissociation of dynamic B-O covalent bonds in silicone polymers. In addition, the superhydrophobic cotton fabric shows excellent anti-fouling, self-cleaning, antibacterial property, and can be applied in oil–water separation with high efficiency. This robust and versatile superhydrophobic coatings without containing perfluoro-compounds are promising in commercial textile fishing treatment with low cost.

Facile preparation of wood-based Janus membrane by hydrothermal ZnO with photoregulated wettability

This study developed a functional Janus wood (JW) membrane with designed wettability gradient through simple modification of balsa wood and evaluated its performance in liquid transport, fog collection, and oil–water separation. Zinc oxide (ZnO) nanoparticles were uniformly loaded into the wood membrane via vacuum impregnation and hydrothermal crystal growth, creating a stable hydrophobic layer. The single-side UV irradiation further induced the hydrophilic-hydrophobic gradually transitional structure. Uniform ZnO nanoparticle distribution was confirmed by SEM, XRD, XPS analyses, and so on. Increased surface area and targeted wettability differences were also detailly verified. UV treatment transformed ZnO to Zn(OH)2 altering the wettability transformation. The JW membrane demonstrated stable wettability under various pH, salinity, and abrasion conditions, with over 98.7% fog collection efficiency and reduced water evaporation. It also achieved over 99.6% separation efficiency for light and heavy oils with high flux and reusability. Due to its simple preparation process, cost effective, and excellent performance with durability, the JW membrane shows strong potential for applications in commercial environment. The study provided scenarios and solutions for multi-functional applications of sustainable wood and offered a new consideration for the design and preparation of Janus membranes.

A superwetting rough structured nanofibrous membrane with enhancing anti-fouling performance for oil–water separation

Oily wastewater generated from many industries has become a tremendous potential threat to ecological balance and human health. However, severely hindered by interfacial wettability, the present oil/water separation membranes are subjected to a serious oil fouling problem during long-term oily wastewater separation. Herein, we construct superwetting rough structured nanofibrous membrane (SRSNM) composed of superhydrophilic PVA/SA bead-on-string nanofibrous functional layer and PVA nanofibrous substrate by two step electrospinning together with chemical crosslinking. Benefitting from the inherent hydrophilic properties of SA and PVA combined with the rough structure endowed by the bead-on-string nanofibers, the SRSNMs exhibited fascinating superhydrophilicity and underwater superoleophobicity. Meanwhile, thanks to the submicron pores and high porosity, the SRSNM could separate submicron oil-in-water emulsions with robust permeation flux of 1319 L m-2h−1 and high separation efficiency of 99.9 % under the gravity driving (∼1 kPa). More importantly, this SRSNM showed excellent anti-oil-fouling performance with high flux recovery of 99 %, negligible irreversible oil fouling rate of 1 %, and intriguing reusability for the long-term separation. The design of such superwetting rough structured nanofibrous membrane may provide an efficacious strategy for synthesizing high-performance separation membranes.

Highly Efficient Oil-Water Separation in Different Scenarios through Synergistic Self-Assembly of ZIF-67@PPy Coatings with Unique Wetting Properties.

In recent years, oil pollution and industrial organic pollutants discharge has become a major problem affecting the ecological and human living environment, and the removal of oil in oily wastewater is increasingly urgent, especially for emulsion separation. Therefore, it is crucial to develop efficient oil-water separation membranes with low cost, green sustainability, and ease of operation. Herein, an ingenious spraying hybrid coatings containing ZIF-67 (Zeolitic Imidazolate Framework-67) and polypyrrole (PPy) onto stainless steel mesh (SSM) and polyvinylidene fluoride (PVDF) was proposed. Through solidification and cooperative self-assembly to build rough structures, oil-water separation membranes ZIF-67@PPy SSM and ZIF-67@PPy PVDF have been obtained, which are hydrophilic and oleophilic in air and superoleophobic underwater. Depending on the scenario, on-demand separation of light oil/water mixtures and oil-in-water emulsions can be easily realized. The resulting oil-water separation membranes performed well that the separation efficiency of ZIF-67@PPy SSM can exceed 99.3% for all kinds of light oil/water mixtures, with a water flux of up to 66250 L/(m2·h), and maintains a separation efficiency of 98.5% even after 50 cycles. ZIF-67@PPy PVDF has a separation efficiency of more than 99.4% for various oil-in-water emulsions, and sustains outstanding performance despite undergoing 10 cycles. In addition, ZIF-67@PPy SSM and ZIF-67@PPy PVDF are sustainable in harsh environments, with good mechanical durability and some antimicrobial properties. The coatings prepared in this work that can be used for the separation of light oil/water mixtures and oil-in-water emulsions, and the proposed combination of multiple separation strategies are expected to improve the selectivity, improve efficiency, enhance contamination resistance, and increase accessibility of oil-water separation technologies.

Superhydrophobic, Conductive and Magnetic Sponge for High Performance Oil-water Separation and Recycled Oil Absorption

Nowadays, the frequent occurrence of oil spills at sea has caused serious pollution to the ecosystem and has led to a gradual decrease in marine resources. Conventional adsorbent materials have difficulty absorbing high-viscosity oils and separating oil from water, and recycling still has great challenges. We developed a novel superhydrophobic, magnetic, and photo-thermal sponge (SMPS) with a simple preparation method, which is composed of polyurethane (PU) sponge, polydopamine (PDA), acidified carbon nanotubes (ACNTs), ferric tetroxide (Fe3O4), and polydimethylsilane (PDMS), modified by self-polymerization, ultrasonication, and soaking. The modification of ACNTs, Fe3O4, and PDMS further enhances the electrical conductivity, magnetism, photo-thermal effect, and superhydrophobicity of the PU sponge. The SMPS (PU/PDA/ACNTs-Fe3O4/PDMS) can reach a water contact angle of 168.32°, which can still be maintained at 150° in harsh environments, and it has a good oil adsorption capacity (up to 31.06g/g) and an oil-water separation efficiency of 96%. In addition, the SMPS has an excellent photo-thermal effect (surface temperature up to 204.9 ℃) for better adsorption of high-viscosity oils. It can also be used for oil adsorption and recycling in local areas through its own magnetism. This paper has studied PU sponges with superhydrophobic, magnetic, and photo-thermal performance, which provides a new research idea for large-scale, regional cleaning and recycling of marine high-viscosity oil pollution.

Doping Si/O to enhance interfacial occupancy of demulsifiers for low‐carbon breaking of water‐in‐heavy oil emulsions

AbstractSeparating water‐in‐heavy oil (W/HO) emulsions at low (room) temperature is challenging when exploiting heavy oil. We propose an adaptable strategy for constructing Si/O‐doped demulsifiers. A nonionic demulsifier (APBMP) has been synthesized based on polysiloxane modified by allyl polyether and butyl acrylate. APBMP achieves 95.97% dehydration within 5 min for W/HO emulsions at 288.15 K and complete dehydration in 15 min at 323.15 K. Mechanistic studies found that doping Si/O into the demulsifier molecules increases the number of hydrogen bond sites, which enables the demulsifiers to quickly disperse natural stabilizers (e.g., asphaltenes) and replace them at the oil–water interfacial film. The demulsifiers prefer to occupy the interfacial sites rather than dissolve into the bulk oil or water phases. Driven by hydrogen‐bond‐dominated noncovalent interactions, the oil–water interfacial film is softened, reconstructed, and broken. These findings provide insights into developing novel materials for oil–water separations in a low‐carbon way.

Numerical study of the dynamic aggregation behaviors of oil droplets in the porous filter media consisting of basalt particles

Porous granular media based on the gravity-driven principle have been proven to be efficient for the separation of oil-water emulsions. However, the complexity of the relevant parameters and the intricate structure of porous media pose great challenges to the design and optimization of the separation process. In this study, the dynamic behavior of oil droplets within the porous structure was numerically analyzed based on the Euler-Euler model and the coupling of the two-phase flow and level set method. The oil-water separation efficiency and droplet trajectory were analyzed under different conditions, considering the deformation of the droplets, kinetic viscosity, and interactions among the droplets. The simulation results show the real-time movement, aggregation, and detachment of oil droplets within the porous filter. The results are useful for understanding the demulsification in a microscopic perspective and provide theoretical guidance for designing more efficient oil-water separation systems.

Recyclable Amphiphilic Magnetic-responsive Mixed-Shell Nanoparticles With High Interfacial Activity Comparable to Janus Particles for Oily Water Purification.

Amphiphilic magnetic-responsive mixed-shell nanoparticles (Mag-MSNPs) with tailorable compositions are synthesized by electrostatic-mediated cross-linking of core-forming blocks of two diblock copolymers, followed by in situ growth of magnetite in the cross-linked core. The Mag-MSNPs have a magnetic-responsive core and hydrophilic/lipophilic mixed shells, firmly anchoring at the oil-water interface of emulsified oil droplets due to their high interfacial activity (13.1 mN m-1 at a rather low emulsifier concentration of 1.2 mg mL-1 in the n-hexane/water system), outperforming most of Janus particles. Driven by the magnetic field, the emulsified oil droplets with Mag-MSNPs at the interface are drawn to one side for collection. The oil-water separation efficiency reaches 99.5%, manifesting their excellent ability to remove emulsified oil droplets from oily water. After five separation and regeneration cycles, the separation efficiency remains at 98.8%, showcasing their potential for recyclable oily water purification.