Under-liquid dual superlyophobic nanofibrous polymer membranes achieved by coating thin-film composites: a design principle

Hybrid-Electrolytes System Established by Dual Super-lyophobic Membrane Enabling High-Voltage Aqueous Lithium Metal Batteries

Aqueous electrolytes and related aqueous rechargeable batteries own unique advantage on safety and environmental friendliness, but coupling high energy density Li-metal batteries with aqueous electrolyte still represent challenging and not yet reported. Here, this work makes a breakthrough in "high-voltage aqueous Li-metal batteries" (HVALMBs) by adopting a brilliant hybrid-electrolytes strategy. Concentrated ternary-salts ether-based electrolyte (CTE) acts as the anolyte to ensure the stability and reversibility of Li-metal plating/stripping. Eco-friendly water-in-salt (WiS) electrolyte acts as catholyte to support the healthy operation of high-voltage cathodes. Most importantly, the aqueous catholyte and non-aqueous anolyte are isolated in each independent chamber without any crosstalk. Aqueous catholyte permeation toward Li anode can be completely prohibited without proton-induced corrosion, which is enabled by the introduction of under-liquid dual super-lyophobic membrane-based separator, which can realize the segregation of the most effective immiscible electrolytes with a surface tension difference as small as 6 mJ m-2. As a result, the aqueous electrolyte can be successfully coupled with Li-metal anode and achieve the fabrication of HVALMBs (hybrid-electrolytes system), which presents long-term cycle stability with a capacity retention of 81.0% after 300 cycles (LiNi0.8Mn0.1Co0.1O2 || Li (limited) cell) and high energy density (682 Wh kg-1).

Robust and flexible polyester fiber membrane with under-liquid dual superlyophobicity for efficient on-demand oil-water separation

Functional materials with under-liquid dual superlyophobicity have generated a great deal of concern from researchers due to their switchable separation ability oil-water mixtures and emulsions. Conceptually, under-liquid dual superlyophobicity is a Cassie state achievable under-liquid through the synergy of an under-liquid double lyophobic surface and the construction of a highly rough surface. However, obtaining an under-liquid dual superlyophobic surface remains difficult due to its thermodynamic contradiction and complex surface composition. Herein, we successfully prepared a functional coating by modifying the mixture of cellulose nanocrystals (CNCs) and nano-TiO2 with perfluorooctanoic acid (PFOA) via a simple method, then obtained a polyester fiber membrane with under-liquid dual superlyophobicity by roll coating method. The surface wettability of the polyester (PET) membrane was altered, transforming it from the original under-water oleophobic/under-oil superhydrophilic state to the under-water superoleophobic/under-oil superhydrophobic state after coated. The resulting membrane was applied to separate oil and water on-demand. The coated PET membrane exhibited high separation efficiency (>99 %) and high separation flux, effectively separating immiscible oil-water systems as well as oil-in-water and water-in-oil emulsions. The coated PET membrane also demonstrated the ability to perform alternate separation of oil-water mixtures through wetting, washing, and rewetting cycles, with repeated processes up to 10 times without significant reduction in separation efficiency. Furthermore, compared with the previous works, our approach offers a simpler and more convenient method for constructing under-liquid dual superlyophobic surface, making it more suitable for continuous corporate production. This study may provide inspiration for the production and application in large-scale of under-liquid dual superlyophobic membranes.

Covalent organic framework functionalized smart membranes with under-liquid dual superlyophobicity for efficient separation of oil/water emulsions

The smart membrane with under-liquid dual superlyophobicity, which can achieve on-demand separation of oil/water emulsions only by simple liquid pre-wetting, is of essential value for the treatment of complicated real oil/water systems. Here, we first fabricated a stable suspension of imine-linked covalent organic framework nanospheres (TPB-DMTP-COF), and subsequently fabricated COF functionalized smart membranes with under-liquid dual superlyophobicity by immersing polyacrylonitrile-based (PAN-based) membranes into TPB-DMTP-COF nanosphere suspension. Accordingly, effective switchable separation of both oil-in-water and water-in-oil emulsions by TPB-DMTP-COF/PAN membranes can be achieved by employing pre-wetting processes (both the oil contact angle under water and the water contact angle under oil are over 150°). Specifically, the separation flux and the separation efficiency are higher than 1200 L/m2‧h and 98.0 %, and 2100 L/m2‧h and 97.4 % for the surfactant-stabilized oil-in-water and water-in-oil emulsions, respectively. Furthermore, the ultralow adhesions in liquid contributed to the outstanding reusability and antifouling resistance of the prepared TPB-DMTP-COF/PAN membranes. This work provides a feasible approach for fabricating a smart membrane with under-liquid dual superlyophobicity for oily wastewater treatment.

Dual Superlyophobic Materials for Under-Liquid Microfluid Manipulation, Immiscible Solvent Separation, and CO2 Blockage

Oily water purification, immiscible solvent separation, sensitive microreaction, and CO₂ blockage are of great interest because of their importance for the environment and demands of controllable microreactions. However, one specific material that can meet all the requirements has yet to be reported. Herein, we developed a simple environment-benign method to prepare specific dual superlyophobic materials to solve the problems mentioned earlier. The dual superlyophobic materials can maintain their dual superoleophobicity in various oil/water systems, and no additional surface modifications were required when the oil/water system was changed. Moreover, the materials can be used to separate oil/water mixtures with separation efficiencies greater than 99.50% even after 40 separation cycles and separate immiscible organic solvents with efficiencies over than 99.25% after 20 cycles. Separations of meal waste oily water at 60 °C and crude oil/water were also successfully performed. The materials can be further applied to manipulate and block CO₂ bubbles under liquid. The materials can also act as a platform for microdrop manipulation/microreaction under liquid.

Bioinspired Under-Liquid Dual Superlyophobic Surface for On-Demand Oil/Water Separation

Porous membranes with under-liquid dual superlyophobic properties, which are difficult to achieve because of a thermodynamic contradiction, have attracted considerable interest in the field of switchable oil/water separation. Herein, a bioinspired mesh membrane with alternating hydrophilic and hydrophobic chemical patterns on its surface that endows it with superamphiphilic and under-liquid dual superlyophobic properties is fabricated by a simple liquidus modification process. The as-prepared membrane possesses a combination of under-oil superhydrophobic and under-water superoleophobic characteristics in the absence of external stimuli. Moreover, it can effectively perform the on-demand separation of various oil/water systems, including immiscible oil/water mixtures and oil/water emulsions owing to its under-liquid dual superlyophobic properties.

Controllable Fabrication of Durable, Underliquid Superlyophobic Surfaces Based on the Lyophilic-Lyophobic Balance

Surfaces possessing desirable underliquid special wettability, particularly underliquid dual superlyophobicity, have a high potential for extensive applications. However, there is still a lack of controllable preparation strategies to regulate the underliquid wettability via balancing the underliquid lyophilicity-lyophobicity. Herein, we develop a nanocomposite coating system comprising silica nanoparticles (NPs), glycerol propoxylate triglycidyl ether (GPTE), and fluorinated alkyl silane (FAS) to obtain controllable underliquid special wettability surfaces. FAS is the vital factor in guiding the preparation of the surface coating with expected underliquid superwettability. Increasing the FAS content results in a tendency toward underwater superoleophobicity/underoil hydrophilicity to underwater oleophilicity/underoil superhydrophobicity. Significantly, the underliquid dual superlyophobic surface can be achieved when an appropriate FAS content is located. After the coating treatment, the fabric exhibits superamphiphilicity in air and superlyophobicity in liquid (i.e., exhibiting both underwater superoleophobicity and underoil superhydrophobicity). The coating also exhibits an adaptable antioil fouling ability and high durability against harsh environments. Furthermore, oil/water separation based on the underliquid dual superlyophobicity of coated fabrics is successfully demonstrated. Our work proposes a new fabrication principle for the design of underliquid special wettability surfaces and offers broad applications, such as switchable oil/water separation, antibiofouling, liquid manipulation, and smart textiles.

Multifunctional Switchable Nanocoated Membranes for Efficient Integrated Purification of Oil/Water Emulsions

Surfaces with unusual under-liquid dual superlyophobicity are attractive on account of their widespread applications, but their development remains difficult due to thermodynamic contradiction. Additionally, these surfaces may suffer from limited antifouling ability, which has restricted their practical applications. Herein, we report a successful in situ growth of a hybrid zeolitic imidazolate framework-8 and zinc oxide nanorod on a porous poly(vinylidene fluoride) membrane (ZIF-8@ZnO-PPVDF) and its application as a self-cleaning switchable barrier material in rapid filtration for emulsified oily wastewater. The novel ZIF-8@ZnO-PPVDF exhibits superior mechanical strength, reversible under-liquid dual superlyophobicity, photocatalytic self-cleaning property, and an effective alternate separation capacity toward both oil-in-water (O/W) and water-in-oil (W/O) emulsions with ultrahigh fluxes and efficiencies (>99%). By simply using a "bait-hook-eliminate" method to separate the O/W emulsions containing soluble organic pollutants, we demonstrate that the ZIF-8@ZnO-PPVDF can achieve stable separation fluxes over 600 L m^-2 h^-1 with high efficiencies and be completely/nondestructively regenerated by visible-light irradiation after each cycle. This study would demonstrate a new approach to prepare an under-liquid dual superlyophobic revivable membrane for various applications.

Polarity-Dominated Stable N97 Respirators for Airborne Virus Capture Based on Nanofibrous Membranes

The longevity and reusability of N95-grade filtering facepiece respirators (N95 FFRs) are limited by consecutive donning and disinfection treatments. Herein, we developed stable N97 nanofibrous respirators based on chemically modified surface to enable remarkable filtration characteristics via polarity driven interaction. This was achieved by a thin-film coated polyacrylonitrile nanofibrous membrane (TFPNM), giving an overall long-lasting filtration performance with high quality factor at 0.42 Pa-1 (filtration efficiency: over 97 %; pressure drop: around 10 Pa), which is higher than that of the commercial N95 FFRs (0.10-0.41 Pa-1 ) tested with a flow rate of 5 L min-1 and the 0.26 μm NaCl aerosol. A coxsackie B4 virus filtration test demonstrated that TFPNM also had strong virus capture capacity of 97.67 %. As compared with N95 FFRs, the TFPNM was more resistant to a wider variety of disinfection protocols, and the overall filtration characteristics remained N97 standard.

Facile preparation of a superamphiphilic nitrocellulose membrane enabling on-demand and energy-efficient separation of oil/water mixtures and emulsions by prewetting

A membrane with superamphiphilicity presents many advantages in various oil/water separation applications due to its switchable wettability by prewetting. However, it is still a great challenge to switch between two types of superwettability on a single cellulose surface by switching between different liquid media. Herein, in order to obtain in-air superamphiphilic and under-liquid dual superlyophobic membranes, dopamine-modified nitrocellulose membranes (with a pore size of 0.22 μm) were prepared via a facile immersion modification approach. Under 0.08 MPa, the as-prepared NC membrane switches wettability by prewetting to achieve on-demand oil/water separation, and the separation efficiency is more than 99.9%. Futhermore, the membrane prepared in this work can also be applied to high-efficiency on-demand separation of surfactant-stabilized emulsions with a separation efficiency greater than 99.0%. Hence, the PDA-modified NC membrane is a promising controllable oil/water separation material in terms of repeatable cycles, separation efficiency, flux, prominent long-term durability and anti-oil fouling.

Modulation of solid surface with desirable under-liquid wettability based on molecular hydrophilic-lipophilic balance

There has been great interest in the fabrication of solid surfaces with desirable under-liquid wettability, and especially under-liquid dual-lyophobicity, because of their potential for widespread use. However, there remains the lack of a general principle to modulate the under-liquid wettability in terms of surface energy (SE). Herein, we found that the relative proportion between the polar and dispersive components in SE that reflects the competition between hydrophilicity and lipophilicity governs the under-liquid wettability of the solid surface. For the first time, we introduced hydrophilic–lipophilic balance (HLB) calculated solely based on the amount and type of hydrophilic and lipophilic fragments in surface molecules to rapidly predict the under-liquid wettability of a solid surface, thereby guiding the fabrication of solid surfaces with desirable under-liquid wettability. Accordingly, the under-liquid dual superlyophobic surfaces in a nonpolar oil–water-solid system were fabricated by grafting molecules with appropriate HLB values (e.g., 6.341–7.673 in a cyclohexane–water–solid system) onto porous nanofibrous membranes, which were able to achieve continuous separation of oil–water mixtures. This work provides reasonable guidance for the fabrication of solid surfaces with targeted under-liquid wettability, which may lead to advanced applications in oil–water–solid systems.

Hydrophilic–lipophilic balance calculated based on the component of surface molecules is introduced to predict the under-liquid wettability of solid surfaces, thereby guiding the fabrication of solid surface with desirable under-liquid wettabilities.

Molecular-Structure-Induced Under-Liquid Dual Superlyophobic Surfaces

Surfaces with under-water superoleophobicity or under-oil superhydrophobicity have attractive features due to their widespread applications. However, it is difficult to achieve under-liquid dual superlyophobic surfaces, that is, under-oil superhydrophobicity and under-water superoleophobicity coexistence, due to the thermodynamic contradiction. Herein, we report an approach to obtain the under-liquid dual superlyophobic surface through conformational transitions of surface self-assembled molecules. Preferential exposure of either hydrophobic or hydrophilic moieties of the hydroxythiol (HS(CH₂)_nOH, where n is the number of methylene groups) self-assembled monolayers to the surrounding solvent (water or oil) can be used to manipulate macroscopic wettability. In water, the surfaces modified with different hydroxythiols exhibit under-water superoleophobicity because of the exposure of hydroxyl groups. In contrast, surface wettability to water is affected by molecular orientation in oil, and the surface transits from under-oil superhydrophilicity to superhydrophobicity when n ≥ 4. This surface design can amplify the molecular-level conformational transition to the change of macroscopic surface wettability. Furthermore, on-demand oil/water separation relying on the under-liquid dual superlyophobicity is successfully demonstrated. This work may be useful in developing the materials with opposite superwettability.

PVDF-Modified TiO2 Nanowires Membrane with Underliquid Dual Superlyophobic Property for Switchable Separation of Oil-Water Emulsions

Separation membranes with underliquid dual superlyophobicity have recently caused widespread concern due to their switchable separation of oil-water mixtures and emulsions. However, the fabrication of the reported underliquid dual superlyophobic membranes is difficult, and the design of the underliquid dual superlyophobic surface of these membranes is challenging because of their complex surface composition. Theoretically, underliquid dual superlyophobicity is an underliquid Cassie state attainable by the synergy of the underliquid dual lyophobic surface and the construction of a high-roughness surface. Herein, we fabricated an underliquid dual superlyophobic membrane by combining underliquid dual lyophobic polyvinylidene fluoride (PVDF) and TiO₂ nanowires. PVDF-modified TiO₂ nanowire membranes with underliquid dual superlyophobicity were prepared via a simple adsorption and filtration approach. PVDF was coated onto TiO₂ nanowires to form a PVDF layer with a thickness of 6 nm. The PVDF modification provided flexibility to the fragile TiO₂ nanowires membrane and changed its wettability from underwater superoleophobicity/underoil superhydrophilicity to underliquid dual superlyophobicity. The PVDF-modified TiO₂ nanowires membrane efficiently separated both oil-in-water and water-in-oil emulsions. The binary cooperative effect between the TiO₂ nanowires and the coated PVDF layer was responsible for the underliquid dual superlyophobicity.

Preparation of a Phenolic-Resin-Based Polymer Sponge Composed of Intertwined Nanofibers with Tunable Wettability for High-Efficiency Separation of Oil-Water Emulsions

Nowadays, as the combination of water pollution and water shortage causes severe environmental and social issues, the special wettable materials, which can be selectively wetted by either water or oil, attract tremendous attention for high-efficiency separation of oil-water mixtures. Herein, we prepare a phenolic-resin-based sponge composed of intertwined nanofibers via a simple hydrothermal method. The wettability of the as-prepared polymer is tuned readily by controlling only the hydrothermal temperature. In the case of the hydrothermal temperature below 210 °C, the polymer sponge demonstrates superhydrophilic and underwater superoleophobic properties, affording the separation of oil-in-water emulsions. However, as the hydrothermal temperature increases above 220 °C, the resulting bulk phenolic-resin-based material becomes superhydrophobic and underoil superhydrophobic, realizing a high filtration flux of 6147 L m^-2 h^-1 for the separation of water-in-oil emulsions driven by an external pressure of 40 kPa. This provides a feasible platform for future practical applications. The wettability transition depending on the hydrothermal temperature is discussed in terms of the reaction mechanism. In addition, the stability and breakthrough pressure are also addressed from the viewpoints of thermodynamic and fluid mechanics, respectively.