Asymmetric Wettability Research Articles

Janus Antipyretic Pastes for Efficient, Durable and Comfortable Personal Physical Cooling.

Prompt and prolonged cooling is extremely important when the body is in a fever state. Here, we proposed a concept of Janus antipyretic paste (JAP) with unique asymmetric wetting for effective and durable personal physical cooling. The prepared JAP possesses greater one-way transport capacity, and faster average water evaporation rate (∼2 times) than the original fabric. Compared to the wet cotton fabric (a reduction of ∼2.9 °C) and medical antipyretic paste (MAP) (no cooling after 5 h), the JAP achieved the best cooling effect and long cooling duration (cooling by 3.8 °C, at least 5-7 h) in practical application tests. In addition, the wearability of JAP is well validated, including its excellent breathability and good flexibility, which can maximum improve the comfort of our body. We believe the new JAP with superior cooling and comfort properties will provide promising design guidelines for the next generation of family or hospital physical cooling products.

Industrial production of asymmetric wettability patterned fabric for efficient atmospheric water harvesting

While harvesting water from the atmosphere is considered as a promising technology to address the increasing issue of water scarcity, its wide applications are still limited by the difficulty in mass production of water harvesting materials. Here, an industrial-producible asymmetric wettability patterned fabric (AWPF) with high water harvesting capacity is developed using a continuous and low-cost weaving technology. Four textile patterns are developed for high-efficiency atmospheric water harvesting. The alternating patterned surface in AWPF is constructed with hydrophilic bumps and hydrophobic grooves using one set of green fluorine-free superhydrophobic polyester warp yarns and two sets of superhydrophobic polyester/hydrophilic viscose weft yarns. We optimized the water collection performance of the single-sided AWPF by spraying co-MBAA-DVB superhydrophobic material on the back of the AWPF to construct a wetting gradient, that is, double-sided AWPF. The double-sided AWPF shows a strong water harvesting capacity of 2840.2 mg·6h−1·cm−2, which increased the water harvesting efficiency by 43.2 % compared with the unoptimized single-sided AWPF. To reduce the pressure drop, 6 mm wide the double-sided AWPF was designed, resulting in a water harvesting capacity that is 1.23 times higher than that of without cutting. This advanced industrialized weaving technology with an asymmetric fabric structure design holds great potential for substantial water harvesting.

Electrically switched asymmetric interfaces for liquid manipulation.

External field driven fluid manipulation, in particular electric field, offers the advantages of real-time control and exceptional flexibility, rendering it highly promising for applications in microfluidic devices, liquid separation and energy catalysis. However, it is still challenging for controlled liquid transport and fine control of droplet splitting. Herein, we demonstrate a strategy to achieve direction-controlled liquid transport and fine droplet splitting on an anisotropic groove-microstructured electrode surface via an electrically switched asymmetric interface. The balance of asymmetric capillary force generated by microstructures and electro-capillary force is critical in determining directional liquid transport and fine droplet splitting. Asymmetric bubbles generated by liquid electrolysis form an asymmetric liquid-gas-solid interface and result in gradient liquid wetting behavior on the two neighboring electrode surfaces. The electric field further enhances the asymmetric wetting of a liquid droplet on the electrode surface, exhibiting electric field direction-dependent motion. Moreover, the groove-microstructured electrode surface can strengthen the liquid droplet anisotropic wetting and correspondingly refine the volume range of the splitting sub-droplet. Even unidirectional/bidirectional liquid droplet transport can be controlled in collaboration with the asymmetric groove-microstructure and electric field. Thus, this work provides a new route for liquid transport and droplet splitting, showing great potential in controllable separation, microreaction and microfluidic devices.

Sustainable Water Management with Photocatalytic Janus Mesh: Efficient Fog Harvesting, Water Purification, and Microbial Disinfection.

Water scarcity is a critical global challenge, especially in arid and semiarid regions. Fog harvesting has emerged as a promising solution; however, concerns about air pollution and bacterial growth in humid environments have raised doubts about the safety and sustainability of such systems. This study introduces a Janus mesh with asymmetric wettability on its two faces, fabricated through a simple and scalable method. The unique design of the Janus mesh enables the transport of water droplets from the superhydrophobic side to the hydrophilic side in a unidirectional manner, enhancing its fog harvesting efficiency. The mesh's photocatalytic properties not only elevate the fog harvesting rate to 4.7 kg·m-2h-1 but also effectively purify the harvested water by removing organic contaminants (94%) and microbial impurities (99.98%). Additionally, its inherent bactericidal activity prevents biofouling, ensuring sustained efficiency in water collection. The mesh's self-cleaning abilities through photocatalysis maintain its surface integrity, promising long-term stability for fog harvesting applications. This technological advancement in fog harvesting offers a sustainable and economical solution to water scarcity concerns, addressing safety and sustainability issues associated with existing systems. By potentially transforming the livelihoods of communities struggling with water scarcity, this innovation paves the way for a more sustainable future.

Diatoms Inspired Green Janus Fabric for Efficient Fog Harvesting

AbstractFog harvesting is a promising path against the global freshwater scarcity. Asymmetric wettability fabric‐based fog collection materials inspired by the Namib desert beetle have been reported widely due to their easy access and adjustable structures. Nevertheless, the single drive force for water transportation produced by the asymmetric wettability is insufficient, causing a non‐ideal fog harvesting efficiency. Moreover, sustainability challenges persist for fog collection materials, primarily due to their heavy dependence on chemical treatments. Herein, a diatom‐inspired Janus fabric (Ly/Csp‐3) based on asymmetric wettability and aperture gradient is developed without additional physical or chemical treatment. The wettability gradient and aperture gradient generate dual directional drive forces that regulate the water transport direction more accurately and enhance the transportation rate more effectively. Ly/Csp‐3 reaches a one‐way transport index of 390.7% and a water collecting rate (WCR) of 1170.5 mg cm−2 h−1, while exhibiting the capability of anti‐acid rain and the resistance to sunlight. This work provides an efficient and programmable biomimetic design proposal for fibrous fog harvesting devices.

Multi-Bioinspired Fog Harvesting Structure with Asymmetric Surface for Hydrogen Revolution.

The urgent need for sustainable energy storage drives the fast development of diverse hydrogen production based on clean water resources. Herein, a unique type of multi-bioinspired functional device (MFD) is reported with asymmetric wettability that combines the curvature gradient of cactus spines, the wetting gradient of lotus, and the slippery surface of Nepenthes alata for efficient fog harvesting. The precisely printed MFDs with microscale features, spanning dimensions, and a thin wall are endowed with asymmetric wettability to enable the Janus effects on their surfaces. Fog condenses on the superhydrophobic surface of the MFDs in the form of microdroplets and unidirectionally penetrates its interior due to the Janus effects, and drops onto the designated area with a better fog harvesting rate of 10.64gcm-2 h-1. Most significantly, the collected clean water can be used for hydrogen production with excellent stability and durability. The findings demonstrate that safe, large-scale, high-performance water splitting and gas separation and collection with fog collection based on MFDs are possible.

Multi-inspired bump-liked medical protective clothing for effectively profuse perspiration management

Janus medical protective clothing (MPC) with asymmetric wetting properties can enhance the comfort of healthcare workers by transporting sweat from the skin to exterior surfaces. However, these textiles fail to promptly remove heavy sweat (e.g., several liters), resulting in soaked fabrics and reduced comfort. Herein, inspired by superabsorbent polymers (SAPs) and lotus leaves, we propose a bump-liked MPC (BPC) for profuse perspiration management. The fabrics can enable unidirectional sweat transport through the inner Janus fabric layer and sustained absorption of large amounts of sweat by the median layer of SAPs. The bump-liked structure can store SAPs and adapt them to swelling. An external polydimethylsiloxane (PDMS)-coated layer can effectively block water, blood, and ethanol from penetrating the skin (synthetic blood contact angle, 118°; anti-blood penetration resistance, 4.8 kPa), thereby ensuring excellent protective properties. More importantly, BPC possesses an unrivalled sweat removal rate of 5.9 ml cm−2 min−1, which is three orders of magnitude higher than the human sweat rate during high-intensity exercise. This work addresses the dual challenge of profuse perspiration management and resistance to liquid penetration, which represents a promising direction for improving the thermal-moisture comfort of medical protective clothing.

Yarn-Based Degradable Janus PPDO Fabric for Multifunctional Applications.

The growing high standard of people's wear has put forward requirements for fabrics, and multifunctional fabrics have been developed precisely in response to the requirements of the times. However, the incineration of waste fabrics produces a large amount of pollutants, resulting in a massive waste of resources and environmental pollution. Herein, the degradable nanofiber yarns (NYs) with self-cleaning properties were fabricated by in situ growth of SiO2 nanoparticles on the surface of the electrospun poly(p-dioxanone) (PPDO) NYs using the Stöber method. Then, the PPDO NYs were blended with carbon fibers and the PPDO/SiO2 NYs with themselves to form the Janus PPDO fabrics, respectively. The Janus PPDO fabric offered asymmetric wettability and dual personal thermal management properties. The PPDO/C side of the Janus PPDO fabric provided 65.8 °C at 1.5 V or 58.5 °C under one sunlight intensity for radiative heating. The PPDO/SiO2 side exhibited high solar reflectivity (81.8%) and mid-infrared (MIR) emissivity (99.1%), which reduced the skin temperature by 4.6 °C, resulting in radiative cooling. Moreover, the Janus PPDO fabrics display an excellent electromagnetic interference (EMI) shielding performance (53.3 dB). Therefore, yarn-based degradable Janus fabric has a promising future in multifunctional wearable products.

Asymmetric Wettability Hydrogel Surfaces for Enduring Electromyographic Monitoring.

Hydrogel electrode interfaces have shown tremendous promise in the acquisition of surface electromyography (EMG) signals. However, the perspiration or moisture environments will trigger the deadhesion between hydrogel electrodes and human skin. Despite the hydrophobic/hydrophilic surfaces can perform the anti-moisture or adhesion respectively, it remains a challenge to integrally form a Janus hydrogel with homogeneous mechanical elasticity and electronic performance. Herein, a surface induction strategy is proposed to approach the hydrophobic/hydrophilic hydrogel surfaces. The hydrophobic interaction between surfactants and molds regulates the distribution of hydrophobic/hydrophilic monomers on the surface. The hydrophobic molds induce a hydrophilic hydrogel surface, while the hydrophilic molds induce a hydrophobic surface. It presents a new phenomenon of reversal wettability inducing and optional hydrogel surfaces. The integral Janus hydrogel can be easily obtained by the hydrophilic molds. Balance of adhesion, elasticity, and conductivity endows the hydrogel electrode patch with durable conformal adhesion and high-fidelity EMG signals even in the sweaty epidermis due to the asymmetric wettability surfaces. This hydrogel performs the quantitative description of muscle strength and accurate fatigue assessment. It offers a reliable candidate for future practical applications in continuous digital healthcare and intelligent human-machine interaction, even the Metaverse.

Smart temperature-adaptive thermal regulation textiles integrating passive radiative cooling and reversible heat storage

Passive radiative cooling (PRC) textiles have garnered significant interest in next-generation wearable technology. However, current PRC textiles often fail to regulate temperature effectively throughout the day due to unnecessary cooling at nighttime. Herein, a smart temperature-adaptive thermal regulation (STATR) textile seamlessly integrating PRC technology and phase-change heat storing/releasing strategy is developed on a bilayered configuration. Highly temperature-sensitive heat-storing microparticles constructed by phase change microcapsule (PCM) core and tightly incorporated BN nanoparticle shell are designed, which is homogeneously encapsulated in ultra-stretchable nonwoven microfibers for thermal energy storage in hot daytime and heat release in cold nighttime. Moreover, TiO2 microparticle-embedded PRC fibers with high emissivity (maximum emissivity>97 %) and reflective porosity (sunlight reflectivity>90 %) are assembled on the heat-storing layer, obtaining the bilayered STATR textile with a remarkable passive cooling effect during the day (10.6°C and 4.2°C compared to pristine textile and PRC textile) and a long-term heating performance at nighttime (2.1°C above pristine textile). Concurrently, the collaboration of asymmetric porosity and wettability in the bilayered STATR textile simultaneously facilitates efficient perspiration, thereby also ensuring lengthy wet comfort on human skin. Therefore, this STATR textile opens a promising avenue for zero-energy and all-weather thermal regulation technology.

A novel asymmetric superwetting filter prepared by easily mass-produced strategy for high-efficient and switchable water/oil filtration

All-purpose materials with on-demand oil/water separation property have received broad attention recently. Herein, a filter paper (FP)-based filter with asymmetric wettability was designed and fabricated via simple combination of liquid phase reduction route with symmetry adhesion method. The fabricated filter exhibits underoil superhydrophobic (UOSHP) and underwater superoleophobic (UWSOP) property. Especially, the good underliquids lyophobicity is still maintained after tape peeling and corrosive, organic solvents treatments. By fixing the hydrophobic (HO) side of filter facing up, the water/light oil mixtures and oil-in-water (O-in-W) emulsions can be highly efficient separated, and the water/heavy oil mixtures and water-in-oil (W-in-O) emulsions are able to be separated with the HI side facing up. The separation efficiencies for water/oil mixtures and oil/water emulsions are higher than 98% and 99.1%, respectively. The study offers a new idea for the preparation of asymmetric superwetting materials with good stability and on-demand water/oil separation capability.

Enhancing demulsification efficiency and sustaining constant separation flux in oil/water emulsions via Janus membrane inspired by spider silk

Conventional special wettable membranes for the separation of the surfactant-stabilized oil/water emulsions primarily rely on the “size-sieving” mechanism, which enhances efficiency by reducing the pore size, leading to a trade-off between separation flux and efficiency. Inspired by spider silk, we developed a novel Janus membrane (JPSPP) capable of high demulsification capacity and constant separation flux. This membrane combines a superhydrophobic PS@PDMS membrane (PPM) with spindle-knotted structures on a negatively charged superhydrophilic PAN@SAS membrane (PSM) through electrospinning. The synergy of electrostatic force generated by charged surfaces, the Laplace pressure created by spindle-knotted geometry, and the wettability gradient resulting from asymmetric wettability enhance the demulsification capacity. The high and constant separation flux was achieved as Laplace pressure drives rapid coalescence of demulsified oil droplets towards the top of the spindle-knotted structures, facilitating oil detachment and efficient water permeation downward. As a result, the JPSPP membrane achieved a separation efficiency exceeding 99.9 %, with a constant separation flux of up to 1952.27 L m−2 h−1, representing a 3–4 folds improvement compared to the pure PAN membranes (PM). The separation performance of the JPSPP still maintains excellent separation performance with efficiency above 98.3 % and a slight attenuation in flux after twenty filtration cycles. The research proposes groundbreaking solutions that significantly enhance the demulsification efficiency and maintain a constant separation flux for oil/water emulsions, with the potential to profoundly impact multiple industries including food processing, energy production, and the petroleum industry, etc.

Assembled Wood-Polyester Fabric-Hydrogel Janus Evaporator for Sustainable Seawater Desalination.

Solar-driven interfacial evaporation technology is a novel and efficient desalination process that helps alleviate the global shortage of freshwater resources. We developed a Janus evaporator assembled from cotton hydrogel, hydrophilic polyester fabric (PF), and Hydrophobic Wood (PW). By doping graphene oxide and TiO2 as light-absorbing materials within the hydrogel, we achieved a high absorptivity of over 90% across the entire solar spectrum. The hydrophilically modified PF, combined with the PW substrate, provided robust water transport and reduced thermal losses. Subsequent optical path simulations using TracePro74 software verified that the sawtooth light-trapping design of the wood substrate increased multiple light reflections and absorption (compared to a flat structure), enhancing light absorption capabilities. The sawtooth interface also enlarged the evaporation area, further boosting evaporation performance. The cleverly designed evaporator exhibited an evaporation rate of 1.722 kg m-2 h-1 and an efficiency of 83.1% under 1 sun irradiation. Additionally, after applying polydimethylsiloxane to the single surface of the photothermal hydrogel for low surface energy treatment, the resulting Janus structure demonstrated asymmetric wettability that prevented salt ions from accumulating on the irradiated interface. After 8 h of continuous evaporation in saline water (10 wt %), only slight salt crystallization occurred at the edges. The evaporator maintained long-term stability during a 15 day cyclic test, and the produced freshwater fully met the relevant drinking water standards. The components of the evaporator are characterized by simple fabrication, low cost, and eco-friendliness, offering significant application potential in the global context of energy conservation and emission reduction initiatives.

Achieving superior Laplace pressure in electrospun PVDF/PAN Janus membranes: A morphological approach

Janus membranes have asymmetric wettability on each side. This contrasting structure gives them an internal driving force for spontaneous fluid transport (caused by Laplace pressure). The objective of this research is to attain the maximum Laplace pressure for electrospun PVDF/PAN Janus membranes by adjusting the fiber diameter and, consequently, the pore size and contact angle in each layer of the membrane. To achieve this goal, the Taguchi method was employed, and the parameters of the electrospinning process were modified to determine the optimal conditions for obtaining the smallest and largest fiber diameters for PAN and PVDF polymers. Accordingly, four distinct types of Janus membranes with different morphologies in each layer were synthesized. SEM analysis was employed to characterize the structural and morphological properties of the fibers in each layer. Additionally, the contact angle (CA) was measured to assess the hydrophilicity of each layer and determine the droplet penetration rate across the membrane. According to the results, the maximum Laplace pressure (205.60 kPa calculated by the analysis of SEM images and 197.4 kPa calculated by the bubble point test) and highest droplet penetration rate (0.83 µL/s) were attributed to the Janus membrane with the lowest pore size in the hydrophilic layer (0.65 µm) and the highest pore size in the hydrophobic layer (3.44 µm). The performance of the optimized membrane was evaluated with respect to unidirectional water transport and water–oil mixture separation. The results showed a rectification ratio of3.92, a permeate flux of7.9 × 104 L·m−2·h−1·bar−1, and a separation efficiency of96.8 %. Finally, it was demonstrated that the Laplace pressure of the optimal Janus membrane in this study is 2.66 times superior to that of the best similar one in previous studies. The appropriate and allowable range for pore size and contact angle, necessary to attain a satisfactory Laplace pressure (exceeding 100 kPa), has been explored, determined, and recommended for future researchers to foster inspiration in the field of Janus membranes.

Buoyancy-Assisted Fabrication of Liquid Diode: Janus Nanofibrous Membrane for Efficient Wastewater Treatment.

The pressing need for effective methods to separate oil and water in oily wastewater has spurred the development of innovative solutions. This work presents the creation and evaluation of a Janus nanofibrous membrane, also known as the Liquid Diode, developed using electrospinning (e-spinning) and buoyancy-assisted hydrothermal techniques. The membrane features a unique structure: one side is composed of PVDF nanofibers embedded with a GO/TiO2 composite, exhibiting in-air superhydrophobic and superoleophilic properties, while the reverse side consists of PVDF nanofibers with a ZnO nanorod array, demonstrating in-air superhydrophilic and underwater (UW) superoleophobic properties. This distinct asymmetric wettability enables the membrane to effectively separate both water-in-oil (w-in-o) and oil-in-water (o-in-w) emulsions, achieving an impressive liquid flux and separation efficiency (SEff). The in-air superhydrophobic side of the Janus nanofibrous membrane achieves a maximum oil flux (Fo) of 3506 ± 250 L m-2 h-1, while the in-air superhydrophilic side achieves a maximum water flux (Fw) of 1837 ± 150 L m-2 h-1, with SEff exceeding 98% for both sides. Furthermore, the Janus nanofibrous membrane maintained reliable mechanical stability after 10 cycles of sandpaper abrasion test and demonstrated excellent chemical stability when subjected to acidic, alkaline, cold water and hot water conditions for 24 h. These properties, combined with its ability in breaking down of organic contaminants (98% ± 2% in 210 min) and pharmaceutical contaminants (97% ± 2% in 210 min) under visible light, highlight its photocatalytic potential. Additionally, the membrane's antifouling and antibacterial properties suggest long-term and sustainable use in wastewater treatment applications. The synergistic combination of these superior properties positions the Janus nanofibrous membrane as a promising solution for addressing complex challenges in wastewater treatment and environmental remediation.

Surface-energy ratchet motor with geometrical symmetry driven by biased random walk

A geometrically symmetric gear with asymmetric surface wettability exhibits one-way spin on a vibrating water bed. On the side face of the gear, a parafilm was coated to create asymmetry in the surface energy. The gear shows fluctuations in both directions within a shorter timescale; however, for a longer timescale, the gear exhibits a one-way spin. This unique motion is generated by a stochastic process with a biased driving force produced by the interaction between the vibrating water surface and the side face of the gear. This new model resembles an active Brownian ratchet. Until now, most ratchet motors, which obtain regular motion from nonthermal fluctuations, utilize a geometrical ratchet structure. However, in this study, the surface energy forms a ratchet that rectifies the noisy motion.

Tailoring asymmetric wettability of Janus nanofiber membranes for directional oil transport and oil capture from oil/water mixtures and oil-in-water emulsions

The separation of oil from oil-in-water emulsions is crucial for the recycling of valuable resources. Janus membranes, characterized by their asymmetric configuration, have shown promise in capturing oil from these emulsions due to their ability to efficiently catch micro-size oil droplets with competitive flux rates, minimal energy costs, and fouling-free operations. This study explored the impact of asymmetric wettability on the oil capture capabilities of Janus nanofiber membranes (JNMs). The wettability of the JNMs’ skin layer was modified from oleophilic, with an oil contact angle (OCA) of ∼0°, to oleophobic, with an OCA of ∼142.7°. This adjustment significantly influenced the oil capture process. The oleophobic skin layer acted as a barrier, reducing oil permeation flux from the feed side. However, this same repellent effect facilitated the directional transport of oil once it breached the skin layer. Interestingly, this led to divergent outcomes in the JNMs’ ability to capture oil from oil/water mixture versus oil-in-water emulsion, a distinction not reported in previous studies. These findings are expected to contribute to the enhancement of Janus membranes, optimizing them for more efficient oil recovery from both oil/water mixture and oil-in-water emulsion.

Water vapor assisted fabrication of Janus fabric with asymmetric wettability for salt-free and efficient solar desalination

Interfacial solar water evaporation technology (ISWE), capable of extracting clean water from the abundantly available seawater, represents a promising avenue for alleviating structural water scarcity. However, the aggregation of salts on the evaporator surface is difficult to suppress in true seawater desalination, rendering efficient seawater desalination unsustainable. In this work, we propose a universal, environmentally friendly, and easy-to-operate water vapor assisted unidirectional coating strategy to fabricate Janus photothermal fabrics with asymmetric wettability on both sides. A unique porous structured hydroxylated carbon nanotubes (HCNTs)@Polydimethylsiloxane (PDMS) photothermal coating was formed on cotton fabric by harnessing the spontaneous water vapor diffusion within the fully wetted fabric. This coating not only robustly adhered to the fabric substrate but also endowed the Janus fabric with excellent photothermal performance and outstanding salt aggregation suppression capabilities. The introduction of Janus fabrics into a double-side evaporation mode demonstrated a stable evaporation rate of 1.36 kg m−2h−1 and an energy efficiency of >90 % during the continuous evaporation of true seawater, overcoming the contradiction between salt aggregation suppression and evaporation performance. The facile and sustainable production process of the salt-repellent solar evaporator demonstrated in this work paves the way for the large-scale application of ISWE in seawater desalination.

Amphiphilic Janus cotton gauze with enhanced moisture management and blood coagulation for rapid hemostasis and wound healing

Cotton gauze is commonly used in initial emergency care. However, its high hydrophilicity and limited clotting capacity can lead to the excessive absorption of blood, resulting in unnecessary blood loss. Herein, an amphiphilic Janus cotton gauze with excellent moisture management and enhanced blood coagulation has been developed via in situ generating bioactive glass (BG) onto the cotton gauze (CG), and then attaching cardanol (CA) onto one side of the BG-loaded CG (CG@BG) via click reaction. The Janus gauze (CA-CG@BG) has asymmetric wetting properties with a hydrophilic side (CA-CG@BGHL) and a hydrophobic side (HBCA-CG@BG). When applied to hemostatic, the porous and active BG on CA-CG@BGHL can rapidly initiate coagulation cascade to form a robust thrombus. CA on HBCA-CG@BG can entangled with each other, creating a hydrophobic barrier that prevents blood from flowing out. The hemostatic performance of CA-CG@BG is superior to that of CG in both rats and pigs. Interestingly, CA-CG@BG possesses unidirectional exudate removal. When applied to wound healing, the exudate can penetrate the hydrophobic HBCA-CG@BG to the hydrophilic CA-CG@BGHL, resulting in faster wound healing than CG. CA-CG@BG exhibits excellent cytocompatibility and hemocompatibility. This unique Janus dressing shows promise as a potential material for clinical applications in the future.

Novel conductive Janus membranes with water diode effect assisted by an electrostatic field for efficient mass transfer and oil-water separation

Membrane separation technology is effective for treating oily wastewater but is limited by the lack of membranes that are both highly permeable and fouling-resistant. Janus membranes, with asymmetric wettability and electrostatic repulsion of charged oil droplets, offer a potential strategy for oil-water separation. This study developed novel electrically enhanced conductive Janus membranes using metal-modified organic membranes to achieve high-efficiency treatment. Conductive metal Janus membranes were fabricated using a straightforward two-step method involving simple electroless nickel plating and surface peeling. The resulting nickel-coated surface of the membrane demonstrated extreme hydrophilicity, underwater oleophobicity, and excellent conductivity (approximately 4.7 Ω). Fascinatingly, the developed membranes exhibited a “water diode” effect, facilitating unidirectional liquid transport without external pressure. Gravity-driven oil-water separation achieved a flux rate of 4874 L m−2 h−1 and over 99 % oil removal efficiency, surpassing most existing studies. During electro-filtration of oil-water emulsions, the conductive Janus membrane as a cathode generated electrostatic repulsion, preventing emulsified oil droplet adhesion. Applying an external voltage increased the flux by approximately 13 times and oil removal efficiency to 99.6 %. The membrane's separation capability remained consistent across six cycle tests, demonstrating robust stability. As all, this work first synthesized conductive “water diode” Janus membranes with high oil-water separation efficiency, offering fresh perspectives on the design and fabrication of Janus membranes as well as on the processes for treating oily wastewater.