Superwetting Properties Research Articles

Bioinspired superhydrophobic polysulfone foams with micro/nano hierarchical structures for highly efficient solar-assisted cleanup of viscous crude oil

Three-dimensional (3D) superhydrophobic/superoleophilic foams are promising candidates for swiftly and continuously separating immiscible and emulsified oil–water mixtures, but still need further study to fully improve their comprehensive performance, especially for viscous oils. This work designed and prepared superhydrophobic core–shell polydopamine nanoparticles modified polysulfone foams (denoted as SPP foams) with hierarchical micro/nano-structures, which exhibited robust super-wetting property (θwater = 163.1°, θoil = 0°). Immiscible oil–water compounds and water-in-oil emulsions could be continuously separated by the SPP foams with separation efficiencies higher than 99 %. The SPP foams showed high absorption capacity towards different types of oils and organic solvents (between 20 and 30 times of self-weight). The SPP foams also exhibited excellent self-cleaning ability, resistance to strong acids and alkalis, and long-term reusability. Through the integration of polydopamine, the foams achieved prompt photothermal conversion (the surface temperature could be increased to 80.7 °C in 1 min under 1 sun), and the generated heat could noticeably decrease the viscosity of crude oil, realizing efficient recovery of vicious crude oil. This study made progress in superhydrophobic/superoleophilic absorbent fabrication and the obtained SPP foams had great potential in treating oil spills especially in the aspect of solar-assisted cleanup of viscous oils.

Nacre-inspired graphene oxide/polyethyleneimine-based ultra-thin heterogeneous superwetting membrane for highly stable separation of oil-in-water emulsions

Since the massive discharge of oily wastewater seriously affects both humans and natural development, the performance of conventional membrane materials in terms of interfacial stability and antifouling in the treatment of surfactant-containing emulsified oily wastewater is a major challenge. In this work, a novel nacre-inspired graphene oxide/polyethyleneimine-based ultra-thin chemically heterogeneous superwetting membrane was fabricated through vacuum-assisted self-assembly and post-modification methods for oil-in-water emulsion separation. The nacre-inspired heterogeneous membrane exhibited superhydrophilicity, underwater superoleophobicity (underwater oil contact angle was 157.7°), excellent crude oil adhesion resistance, high acid/alkaline stability, outstanding salt resistance, and good mechanical properties (Young’s modulus 1391.7 MPa). The heterogeneous membranes showed separation efficiencies of more than 99.9 % for a range of oil-in-water emulsions. The high-value membranes could achieve the permeances of 917–1256 L m−2h−1 bar−1 for pure water and 339.7–577 L m−2h−1 bar−1 for emulsion through a dead-end filter device, with the optimal long-term stable permeance only decreasing by 30.0 % compared to the initial value. After six test cycles, the membrane’s antifouling and self-cleaning properties were enhanced by constructing heterogeneous superwetting properties, and the flux recovery rate remained at 96.5 %. All of these results indicated that this method provides new ideas for the design and fabrication of highly stable and antifouling membrane materials.

Superhydrophilic and Underwater Superaerophobic Dual-Function Peony-Shaped Selenide Micro-nano Array Self-Supported Electrodes for High-Efficiency Overall Water Splitting Driven by Renewable Energy.

With the intensification of global environmental pollution and resource scarcity, hydrogen has garnered significant attention as an ideal alternative to fossil fuels due to its high energy density and nonpolluting nature. Consequently, the urgent development of electrocatalytic water-splitting electrodes for hydrogen production is imperative. In this study, a superwetting selenide catalytic electrode with a peony-flower-shaped micronano array (MoS2/Co0.8Fe0.2Se2/NixSey/nickel foam (NF)) was synthesized on NF via a two-step hydrothermal method. The optimal catalytic activity of cobalt-iron selenide was achieved by adjusting the Co/Fe ratio. The intrinsic catalytic activity of the electrodes was enhanced by incorporating transition metal selenides, which then served as a precursor for the subsequent loading of MoS2 nanoflowers on the surface to fully expose the active sites. Furthermore, the superwetting properties of the electrode accelerated electrolyte penetration and electron/mass transfer, while also facilitating bubble detachment from the electrode surface, thereby preventing "bubble shielding effect". This resulted in superior oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performance, as well as overall water splitting capabilities. In a 1.0 M KOH solution, the electrode required only 166 and 195 mV overpotential to achieve a current density of 10 mA cm-2 for OER and HER, respectively. When functioning as a bifunctional catalytic electrode, only 1.60 V of voltage was necessary to drive the electrolyzer to reach a current density of 10 mA cm-2. Moreover, laboratory simulations of wind and solar energy-driven water splitting validated the feasibility of establishing a sustainable energy-to-hydrogen production chain. This work provides new insights into the preparation of low-overpotential, high-catalytic-activity superhydrophilic and underwater superaerophobic catalytic electrodes by rationally adjusting elemental ratios and exploring changes in electrode surface wettability.

Robust photopolymerized superoleophobic/superhydrophilic mesh for oil-water separation

Selective superwetting surfaces preserve the opposite superwetting properties of oil and water and have attracted considerable attention for their application in oil-water separation owing to their efficient surface energy since 2000. Among these surfaces, superoleophobic/superhydrophilic surfaces are considered remarkable because of their anti-oil properties. The coexistence of superoleophobicity and superhydrophilicity poses a challenge based on the traditional surface/interface theory. However, the fabrication of superoleophobic surfaces requires extremely low surface energy, which is achieved by introducing compounds with long fluorocarbon chains. However, these compounds are harmful to the environment. Herein, a mesh with superoleophobic/superhydrophilic properties was developed by coating a chemically etched copper mesh substrate with photopolymerized short fluorocarbon chains and water-insoluble hydrophilic monomers. This mesh can separate different types of oil-water mixtures with a separation efficiency of >99 %. The mesh demonstrated excellent underwater stability as well as chemical and mechanical durability. The water resistance and chemical durability of the mesh are stronger than those of the control copper mesh using metal ions and long fluorocarbon chains. Moreover, oil-water separation was achieved even after immersion in deionized water and salt, acid, and alkali solutions. In addition, the mesh preserves the ability of oil-water separation after being cleaned and reused for 10 times. The proposed superoleophobic/superhydrophilic mesh offers a solution for continuous oil-water separation and has prospects for developing anti-fouling/sweat-absorbing fabrics and self-cleaning surfaces.

Enhancement of photothermal effect of Cu2S@CuS homojunction and applications of crude oil–water separation and ice removal

The recycle of crude oil with high viscosity from wastewater and anti-icing of outdoor power transmission lines are still challenges. High photothermal responses with excellent superwetting properties are critical issues for solving these problems. In the paper, the porous nanosheet arrays of Cu2S@CuS homojunction with narrow band have been prepared by anodizing Cu foam. After the surface modification of stearic acid (STA), the array surface is endowed with excellent wetting states of super-hydrophobicity and super-lipophilicity, and is suitable for the oil–water separation. The narrow band and homojunction structure induce the excellent light absorption, and further increase the photothermal conversion efficiency of the prepared Cu2S@CuS nanoarray to the value of 8.81 %. Under the irradiation of Xe lamp with 0.1 W/cm2, the surface temperature of Cu2S@CuS nanosheet array in air promptly increases to 96.5 ℃ from room temperature of 20.9 ℃ within 30 s, and increases to 69 ℃ from room temperature within 45 s in crude oil. Obviously, the prepared Cu2S@CuS nanoarrays with excellent photothermal responses are very suitable to be used as filter film for the crude oil–water separation. With the increase of light irradiation time, the local temperature of crude oil near the filter film continues to be increased to 69 ℃ within 45 s, and the gradually warmed crude oil was continuously pumped to the oil collecting beaker through rubber pipe, showing the high efficiency and excellent stability. Of course, it is also used to efficiently separate the oil with low viscosity from oil-water mixtures and emulsion.

Improving the hydrostability of zeolitic imidazolate framework coatings using a facile silk fibroin protein modification method

Zeolitic imidazolate frameworks (ZIFs) are an important subclass of metal-organic frameworks (MOFs) with zeolite-type topology, which can be fabricated under ambient synthesis conditions. However, the applications of ZIFs are commonly limited due to the weak hydrostability of their metal–ligand coordination bonds, particularly under humid and aqueous conditions. In this work, as an example, the hydrolysis behaviours of ZIF-L with a special focus on ZIF-L coatings were tested at aqueous conditions with a wide range of pHs to systematically study and fundamentally understand their structural stability and degradation mechanism. Pristine ZIF-L powder and ZIF-L coatings were severely damaged after only 24 h in aqueous media. Interestingly, the ZIF-L coatings showed two distinct hydrolyzation pathways regardless of pH conditions, exhibiting either a ring-shaped etching or unfolding behaviours. While the ZIF-L powders were hydrolyzed almost identically across all pH conditions. With this new understanding, a facile silk fibroin (SF) protein modification method was developed to enhance the hydrostability of ZIF-L coatings in aqueous media. The effect of protein concentration on surface coating was systemically studied. ZIF-L coating retained its surface morphology after soaking in water and demonstrated switchable super wetting properties and superior separation performance for oil/water mixture. As a result, the quick SF protein modification significantly enhanced the stability of ZIF-L coatings under various pHs, while retaining their switchable wetting property and excellent separation performance.

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.

Cellulose and cellulose derivatives in sustainable membrane development for oil/water separation

Cellulose is a natural polymer and most abundant organic substance on Earth. Inexhaustible hydroxyl groups on the cellulose surface allow derivatives of cellulose produced. This article discusses the recent progress of cellulose and cellulose derivatives in membrane development for oil/water separation. Functional groups that are available on the cellulose and its derivatives provide modification features to improve membrane wettability. Membranes with super wetting properties possess remarkable self-cleaning abilities which in turn can enhance permeation fluxes and extend membrane lifespan. However, the role of cellulose-based membranes in oily wastewater treatments is still in its early stages. This review article emphasizes on the development and modification of cellulose-based membranes for improvement of wettability, flux and separation efficiency, and the future directions of research.

In-situ ionized construction of PVDF/sodium polyacrylate-grafted-PVDF blend ultrafiltration membrane with stable anti-oil-fouling ability for efficient oil-in-water emulsion separation

Traditional polymeric membranes usually suffer from serious oil fouling and quick decline of water flux when separating oil-in-water emulsions. In this work, we report the fabrication of the sodium polyacrylate (PAAS) blended polyvinylidene fluoride (PVDF) ultrafiltration membrane which behaves hydrophilicity, underwater low-oil-adhesive superoleophobicity and outstanding anti-oil-fouling ability even for viscous crude oil. The blend membrane was fabricated via a two-step method, including the nonsolvent-induced phase inversion of PVDF/polyacrylic acid-grafted-PVDF (PVDF/PAA-g-PVDF) blend membrane and the subsequent in-situ ionization of PAA into PAAS. The two-step method improves the affinity between the strong hydrophilic additive PAAS and the hydrophobic polymer matrix PVDF, thus endowing the blend membrane with long-term stable superwetting property for 1,100 days. The PVDF/PAAS-g-PVDF blend membrane can efficiently separate multiple emulsifier-stabilized oil-in-water emulsions with ultrahigh separation efficiency of 99.97% (the residual oil content in the filtrate is lower than 3 ppm after one-step separation) and high water flux of 350 L m-2 h-1 bar-1. The blend membrane also shows good cycling performance, and can be easily cleaned by water washing during several separation cycles of the crude oil-in-water emulsion. This work inspires a feasible route of fabricating stable anti-oil-fouling membranes for separation of emulsified oily water.

Digital light processing technique aided 3D printing hierarchical super-wetting mesh coated with hydrophobic SiO2 for highly efficient oil-water separation

Gravity-driven filtration using super-wetting mesh surfaces holds significant promise in addressing oil pollution resulting from human activities. However, conventional techniques need help fabricating efficient separation mesh structures due to their limited stability in oily-water solutions. To overcome this, we employed a Digital Light Processing (DLP) 3D printing technique to fabricate a mesh with a micro-patterned surface using a UV light-curable polyurethane (PU). A post-UV curing step was implemented to transform the soft segments of PU into a solid state. To enhance the super-wetting properties, hydrophobic modified silica (m-SiO2)/UV curable polydimethylsiloxane (PDMS) solution was applied through dip coating, resulting in a hierarchical structure with high surface roughness and superhydrophobic characteristics. In oil–water separation tests, the hierarchical superhydrophobic mesh, featuring a pore size of 300 µm, demonstrated exceptional performance, achieving a remarkable flow flux of 37,410 L/m2 h with a separation efficiency of 97.46 %. Furthermore, the separation efficiency remained consistently above 97.0 % under varying pH conditions and oil mixtures, highlighting the excellent water-repellence capacity of the hierarchical mesh developed in this study.

Facile preparation and modification of robust BiOCl/Bi2O3 coated mesh with superwetting and anti-biofouling performance for oil/water separation and wastewater treatment

A superhydrophilic/underwater superoleophobic BiOCl/Bi2O3 coated mesh was successfully prepared through a facile one-step hydrothermal method, which exhibits outstanding mechanical stability against sandpaper friction and resistance to water erosion and corrosive liquids. Notably, it demonstrates excellent oil/water separation efficiency and photocatalytic performance under visible light irradiation while preventing the adhesion of microorganisms to the coating surface, endowing anti-biofouling properties to the mesh. To achieve simultaneous separation of oil from water as well as degradation of soluble dye and bacteria pollutants in a single device, a superhydrophobic/superoleophilic BiOCl/Bi2O3 coated mesh was also prepared using surface modification with octadecanethiol. Subsequently, a dual-layer mesh (DLM) was obtained by overlaying the superhydrophilic BiOCl/Bi2O3 coating onto the superhydrophobic BiOCl/Bi2O3 coating. The resulting dual-layer mesh with its superwetting properties enables concurrent oil–water separation, photodegradation of organic contaminants and photocatalytic bactericidal activity within trapped sewage. Furthermore, this versatile BiOCl/Bi2O3 coated mesh can serve as a template for fabricating other bismuth-containing micro/nanostructure coatings with remarkable wetting properties. It is anticipated that such a versatile BiOCl/Bi2O3 coated mesh possessing superior superwetting properties, robust mechanical durability, excellent anti-biofouling properties and outstanding photocatalytic activity will find promising applications in complex oily sewage purification systems.

Preparation of citric acid-modified cellulose materials with superwetting and antibacterial characteristics for highly-efficient separation of oil/water mixtures, emulsions, and dye-containing wastewater

Oil/water separation has become a pressing global challenge in the recent times due to the rapid increase in the development of industries, frequent oil spills, and chemical leakages. Therefore, it is in great demand to develop superwetting materials from bio-based and cheap substances for treating oil/water mixtures and emulsions. Herein, we prepared citric acid (CA)-modified cellulose materials (including cotton fabric and raw cotton) with superwetting properties through a green dip-coating approach. The as-prepared CA-modified cellulose materials showed superamphiphilicity in air and superoleophobicity underwater. The CA-modified cotton fabric (CMCF) can be utilized to treat oil/water mixtures and demonstrated remarkably high permeation fluxes (up to 107,900 L m−2h−1) along with excellent separation efficiency (>99.99 %). The CA-modified raw cotton (CMRC) was applied for separating both surfactant-stabilized oil-in-water and surfactant-stabilized water-in-oil emulsions (SSOIWEs and SSWIOEs) exhibiting ultra-high permeation fluxes (up to 8,960 and 25,080 L m−2h−1, respectively) under gravity. The separation efficiencies of SSOIWEs surpassed 99.18 % and the filtrates’ oil purity for SSWIOEs exceeded 99.98 %. In addition, the CMRC could be used to treat dye aqueous solutions and dye-containing emulsions. Moreover, CMRC also exhibited good antibacterial properties. Because of their excellent oil/water mixtures and emulsions separation abilities, green preparation process, and ease of mass production, our CA-modified cellulose materials have notable potential for practical applications.

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.

Design of photocatalytic self-cleaning poly (arylene ether nitrile)/nitrogen-doped Bi2O2CO3 composite membrane for emulsified oily wastewater purification

Membrane separation technique offers unique advantages for treating the emulsified oily wastewater with the oil droplet diameter less than 20 µm. However, the complicated membrane fouling originating from oils and soluble matters pose the huge challenges to membrane separation technique, which has stimulated the development of advanced membrane materials. Herein, we reported the photocatalytic and super-wetting poly (arylene ether nitrile) (PEN) fibrous composite membrane with high permeability and enhanced anti-fouling ability. The nitrogen-doped Bi2O2CO3 (N-Bi2O2CO3) was prepared by low-temperature chemical modification method and modified by dopamine (DA)-polyethyleneimine (PEI), which was further self-assembled on porous PEN support backbone. The hydrophilicity provided by the cross-linking reaction between PDA and PEI and micro-/nano- rough surface constructed by the flower-like N-Bi2O2CO3 contributed to the super wetting properties (WCA=0°, UOCA>150°), which imparted the membrane with ultra-low oil adhesion. In particular, the arrangement of flower-like N-Bi2O2CO3 effectively regulated the water channel of membrane, further increasing the permeate flux. Therefore, the fibrous composite membranes showed superior separation flux (632.79–762.81 L·m−2·h−1) and separation efficiency (>99.16%) for various oil-in-water emulsions, even under harsh conditions (90 ℃ and 2 M NaCl solution). More importantly, the N-Bi2O2CO3 rendered the membrane excellent degradation rates for various dyes (MO: 95.53%, MeB: 96.40%, CV: 96.45%, CR: 87.14%), achieving favorable photocatalytic self-cleaning ability. This work opens an alternative strategy to fabricate fibrous composite membrane with synergistically enhanced anti-fouling for the treating complicated emulsified oily wastewater in petrochemical industry.

Constructing superwetting membranes by sodium lignosulfonate-modified carbon nanotube for highly efficient crude oil-in-water emulsions separations

For the past few years, superwetting materials had been developed to enhance the treatment process of oily wastewater. Membranes are improved through the combination of surface topography and chemical modifications to achieve superwetting properties for treating oily wastewater effectively. In this work, we prepared an eco-friendly membrane by depositing sodium lignosulfonate (SLS)-modified carbon nanotube (CNT) on a cellulose acetate membrane via vacuum filtration without employing any organic solvents. The SLS@CNT membrane shows superhydrophilicity and underwater superoleophobicity with high stability. Furthermore, the SLS@CNT membrane exhibits outstanding antifouling and self-cleaning properties against crude oil of high viscosity. Most importantly, our SLS@CNT membrane exhibits outstanding oil-in-water emulsions separation performances including crude oil-in-water emulsions. For the surfactant-free and surfactant-stabilized emulsions, fluxes were revealed to reach up to 27,800 L m−2 h−1 bar−1 and 13,800 L m−2 h−1 bar−1, respectively, with very high separation efficiency (>99.97 % and 99.79 %, respectively). The distinguished performance of our SLS@CNT membrane, and its eco-friendly, low-energy consumption, and cost-effective preparation, demonstrate practical applicability.

Robust and self-healing under-liquid superlyophobic coating fabricated by a universal strategy for polar-nonpolar liquid separation

Surfaces showing desirable under-liquid superlyophobicity have attracted great interests due to their high potential applications, especially in the liquid separation. Nevertheless, it still remains a challenge to put forward a universal strategy to fabricate robust under-liquid superlyophobic surfaces with self-healing function. Herein, a highly durable and self-healing under-liquid superlyophobic coating is developed that can be applied onto various substrates (e.g., cotton, polyester, filter paper, wool, hemp, sponge, lyocell, etc.) via a two-step coating process, through depositing silica nanoparticles partially grafted by octadecylamine followed by crosslinking of polyurethane macromolecules containing polysorbate20. The obtained substrates show superamphiphilic in air, under-water superoleophobic and under-oil superhydrophobic properties. High-efficiency separations of polar-nonpolar liquids, e.g., water-heavy oil, water-light oil, immiscible organic liquid mixtures, can be achieved when the coated fabric was used as the separation membrane. Moreover, such under-liquid superlyophobic coating demonstrates excellent durability against repeated washing, long time UV irradiation, organic solvent attack, high temperature and plasma treatment. Even the coating surface is damaged chemically or physically, its original superwetting property can be recovered by a short time of heating treatment. This work could provide a guidance for developing durable under-liquid superlyophobic materials with self-healing ability for diversified applications, such as liquid separation, micro-fluid manipulation, anti-adhesive surfaces.

A Self-cleaning Fe(III)-doped Graphene Oxide Membrane for Emulsion Separation

High hydrophilicity, single-atom thickness and strong coordination properties of graphene oxide (GO) were utilized to create a multifunctional membrane for separation of oil-in-water emulsions. The new Fe(III)-doped GO membrane possessed the superwetting property of GO and Fe(III) catalytic sites for H2O2 activization promoted oxidative degradation of organic fouling agents. It was shown that the self-cleaning membrane can be utilized in a high-throughput flow through system for remediation of contaminated water. High hydrophilicity, single-atom thickness and strong coordination properties of graphene oxide (GO) are utilized to create a multifunctional membrane for emulsion separation. The new Fe(III)-doped GO membrane possesses Fe(III) catalytic sites for H2O2 activization promoted oxidative degradation of organic fouling agents and can be used for wastewater treatment in a continuous flow-through process.

Engineered Superhydrophilic/Superaerophobic Array Electrode Composed of NiMoO4@NiFeP for High-Performance Overall Water/Seawater Splitting

Exploring advanced electrocatalysts for overall water/seawater splitting is significant to massive green hydrogen production. Here, we report a novel self-sacrificing template strategy to fabricate a heterostructured NiMoO4@NiFeP electrode with superwetting properties as a bifunctional electrocatalyst for overall water/seawater splitting. Such an electrode exhibits superior intrinsic activity, more accessible active sites, effective charge transfer, and weak adhesion of gas bubbles. Its excellent corrosion resistance and superhydrophilic/superaerophobic nanoarrayed architecture ensure its catalytic performance under harsh seawater conditions. Accordingly, the electrode requires overpotentials of only 282 and 195 mV at 100 mA cm–2 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in 1 M KOH seawater together with its robust durability. Operando Raman spectroscopy together with ex situ characterization technologies reveal that NiMoO4@NiFeP was rapidly reconstructed to active Fe-doped β-Ni oxyhydroxides (β-Fe/NiOOH) during alkaline OER. Density functional theory calculations further disclose that Fe doping can optimize the energy barrier and modulate the d-band center of the catalyst, intrinsically boosting the OER performance. Consequently, the NiMoO4@NiFeP-assembled electrolyzer requires a voltage of 1.71 V at 100 mA cm–2 for seawater splitting and can stably maintain over 200 h without producing any hypochlorite. Our work holds great promise for constructing efficient non-noble-metal bifunctional electrodes toward water/seawater electrolysis applications.

Acid-resistant supramolecular nanofibrous hydrogel membrane with core-shell structure for highly efficient oil/water separation

Hydrogel is an ideal material for oily sewage treatment due to its strong hydration ability, low-adhesive and antifouling properties. Advanced hydrogel separation membranes with harsh-environment-tolerant (such as strong acidic environments) superoleophobicity are of significance but rarely reported. Herein, a supramolecular nanofibrous hydrogel membrane was designed via one-step coaxial electrospinning method with polyvinylidene fluoride (PVDF) as the reinforced core material. Dimethyl sulfoxide (DMSO) regulates hydrogen bond crosslinking between tannic acid (TA) and polyvinylpyrrolidone (PVP). With the evaporation of DMSO, the water-insoluble supramolecular shell was formed between PVP and TA, which was tightly wrapped around the PVDF core. The pore size and wettability of the resulting membrane could be tuned by the core/shell velocity ratio. The stable superwetting properties and interspatial connectivity endow the fibrous hydrogel membranes with high separation performance for various oil-in-water emulsions and even for strong acidic oil-water emulsion. The separation permeance can reach 22,293 L m−2 h−1 bar−1 for SDS stabilized acidic oil-water emulsion (pH = 1) and maintain at approximately 17,834 L m−2 h−1 bar−1 after 3 h continuous separation, exhibiting significant applicability for large-scale filtration.

Bioinspired under-liquid superlyophobic PVDF membrane via synchronous in-situ growth of sliver nanoparticles for oil/water emulsion separation

Effective oil/water separation is urgently demanded but still remains a global challenge. Membranes with super-wettability have been rapidly developed, but most of the membranes are suffered from the complicated fabrication procedures and inability of separating different types of emulsions. In this work, super-amphiphilic PVDF composite membranes were developed via synchronous in-situ growth and immobilization of Ag nanoparticles during phase inversion. This method allowed the membrane formation and nanoparticle immobilization at the same time. The impact of silver growth time on the surface morphology and wettability was comprehensively investigated. The introduction of Ag nanoparticles endowed the membranes with micro/nano-structures and super-wetting property, which made the membrane possess reversible under-liquid superamphiphobicity. The PVDF composite membranes exhibited high permeate flux and outstanding separation efficiency for different surfactant-stabilized oil/water emulsions. Moreover, the prepared membranes could be regenerated through a facile method of rinsing and drying and the high separation performance could be maintained after repeated cycles, indicating the outstanding anti-fouling performance of the membranes. Furthermore, the PVDF composite membranes exhibited superior antibacterial performance. This work made progress in fabricating super-wetting membranes with excellent emulsion separation performance and the membranes can be prospective candidate for oily-mixture separation in practical applications.