Scalable and Robust Bacterial Cellulose Carbon Aerogels as Reusable Absorbents for High-Efficiency Oil/Water Separation

Efficient selective separation of oils or organic pollutants from water is important for ecological, environmental conservation and sustainable development. Various absorption methods have emerged; the majority of them still suffer from defects including low removal efficiency, a complicated preparation process, and high cost. Herein, we present a highly porous and mechanical resilient bacterial cellulose (BC) carbon aerogel directly from BC hydrogel via facile directional freeze-drying and high-temperature carbonization. The resultant BC carbon aerogel showed excellent mechanical compressibility (maximal height compression ∼99.5%) and elastic recovery due to the porous structure. Taking advantages of the high thermal stability and superhydrophobicity, the BC carbon aerogel was directly used as a versatile adsorbent for oil/water separation. The result demonstrated that the BC carbon aerogel showed super oil/water separation selectivity with the oil absorption capacity as high as 132-274 g g^-1. More importantly, the BC carbon aerogel adsorbent can be reused by a simple absorption/combustion method and still keep high-efficiency oil absorption capacity and excellent superhydrophobicity after 20 absorption/combustion cycles, displaying recyclability and robust stability. In sum, the BC carbon aerogel introduced here is easy to fabricate, ecofriendly, highly scalable, low cost, mechanically robust, and reusable; all of these features make it highly attractive for oil/water separation application.

Mechanically Robust Janus Poly(lactic acid) Hybrid Fibrous Membranes toward Highly Efficient Switchable Separation of Surfactant-Stabilized Oil/Water Emulsions

An ideal oil/water separation membrane should possess the characteristics of high flux and separation efficiency, recyclability, as well as good mechanical stability. Herein, a facile method is applied to fabricate a Janus polylactic acid (PLA) fibrous membrane for efficiently separating surfactant-stabilized oil/water mixtures. The Janus PLA fibrous membrane architecture was prepared by electrospinning a PLA/carbon nanotubes (CNTs) fibrous membrane and the subsequent electrospinning of a PLA/SiO₂ nanofluids (nfs) membrane onto one side of the PLA/CNTs fibrous membrane. Due to the strong electrostatic interaction between SiO₂ nfs and CNTs, synchronous enhancement and plasticization of PLA fibrous membranes were achieved, which was far superior to that reported in the literature. The introduction of CNTs had caused an upshift of the hydrophobicity of the PLA/CNTs fibrous membrane (water contact angle (WCA) > 140°). In contrast, SiO₂ nfs bearing long-chain organic anions and cations located onto the surface of the fibers during electrospinning to achieve superhydrophilicity (WCA ≈ 0°). Benefiting from completely opposite wettability on both sides of the Janus membrane, the obtained asymmetric Janus membranes exhibited a high flux (1142-1485 L m^-2 L^-1) and excellent oil/water separation efficiency (>99%), which were superior to those reported for other Janus membranes. Furthermore, the Janus membranes showed desirable flux recovery without any treatment (>80% for water-in-oil emulsions and >90% for oil-in-water emulsions, respectively, after 11 cycles), showcasing promising applications for water treatment in the future.

Engineering and Characterization of Antibacterial Coaxial Nanofiber Membranes for Oil/Water Separation

In the present study, a coaxial nanofiber membrane was developed using the electrospinning technique. The developed membranes were fabricated from hydrophilic cellulose acetate (CA) polymer and hydrophobic polysulfone (PSf) polymer as a core and shell in an alternative way with addition of 0.1 wt.% of ZnO nanoparticles (NPs). The membranes were treated with a 2M NaOH solution to enhance hydrophilicity and thus increase water separation flux. Chemical and physical characterizations were performed, such as Fourier transform infrared (FTIR) spectroscopy, and surface wettability was measured by means of water contact angle (WCA), mechanical properties, surface morphology via field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and microscopy energy dispersive (EDS) mapping and point analysis. The results show higher mechanical properties for the coaxial nanofiber membranes which reached a tensile strength of 7.58 MPa, a Young's modulus of 0.2 MPa, and 23.4 M J.m-3 of toughness. However, treated mebranes show lower mechanical properties (tensile strength of 0.25 MPa, Young's modulus of 0.01 MPa, and 0.4 M J.m-3 of toughness). In addition, the core and shell nanofiber membranes showed a uniform distribution of coaxial nanofibers. Membranes with ZnO NPs showed a porous structure and elimination of nanofibers after treatment due to the formation of nanosheets. Interestingly, membranes changed from hydrophobic to hydrophilic (the WCA changed from 90 ± 8° to 14 ± 2°). Besides that, composite nanofiber membranes with ZnO NPs showed antibacterial activity against Escherichia coli. Furthermore, the water flux for the modified membranes was improved by 1.6 times compared to the untreated membranes.

Biomimetic Fabrication of Janus Fabric with Asymmetric Wettability for Water Purification and Hydrophobic/Hydrophilic Patterned Surfaces for Fog Harvesting

The long-term shortage of freshwater resources has drawn increasing research attention for water purification and collection. This work reports a facile method to prepare Janus fabrics with asymmetric wettability for on-demand oil/water separation and hydrophobic/hydrophilic patterned fabrics for efficient fog harvesting. Here, the superhydrophobic fabric was prepared by in situ polymerization of polydivinylbenzene (PDVB) on cotton fabric. By regulating the polymerization time, the PDVB polymer content was changed, thereby achieving the regulation of the surface structure and wettability of the prepared fabric. Meanwhile, the superhydrophobic fabric exhibited excellent self-cleaning and antifouling performance, mechanical abrasion and chemical resistance, and environmental durability. Moreover, the photocatalytic degradation properties of PDVB were utilized to prepare the Janus fabric with asymmetric wettability. Water droplets could spontaneously penetrate from the hydrophobic side to the hydrophilic side, while not vice versa, achieving unidirectional transport of water. In addition, the prepared Janus fabric could be used for on-demand oil/water separation, including the heavy oil/water mixture and light oil/water mixture. The separation efficiency and collected oil purity of each mixture were higher than 99.00 and 99.94%, respectively. Furthermore, the hydrophobic/hydrophilic patterned fabrics were prepared by using the lithographic masks with different apertures under UV light irradiation. Based on the fog-capturing ability of the hydrophilic areas and the water transport performance of the hydrophobic regions, efficient fog harvesting was achieved. For the patterned fabric with larger hydrophobic/hydrophilic areas, the water collection rate reached 224.7 mg cm^-2 h^-1. Therefore, this simple strategy to achieve controllable gradient wettability by adjusting the surface structure and chemical composition of the fabric shows great potential in the filtration of purification of oily sewage and the efficient condensed collection of water.

Robust Hydrogel Coating with Oil-Repellent Property in Air, Water, and Oil Surroundings

Development of a robust self-cleaning oil-repellent surface in a cost-efficient and green manner is highly desirable, yet still difficult to realize. Herein, we develop a poly(vinyl alcohol) (denoted as PVA) composite hydrogel on which the oily contaminations can be removed efficiently by water merely. Owing to its high affinity to water and resistance to oils, the water-wetted hydrogel establishes a slippery oil-repellent state in air, displays underwater superoleophobicity with ultralow adhesion to all probe oils, and blocks oil from permeating when immersed into an oil surrounding. Oily contaminations on the PVA hydrogel surface are removed just by titling or water immersion, with no oil residue left behind. This enhanced oil repellency was retained after hand-bending, water-jetting, and even 1000 cycles of sand abrasion, demonstrating mechanical robustness. Application of the PVA hydrogel-coated copper mesh is demonstrated to separate oil/water and oil/oil mixtures, with separation efficiency being greater than 98%.

Femtosecond Laser Microfabrication of Porous Superwetting Materials for Oil/Water Separation: A Mini-Review

Frequent oil-leakage accidents and large quantities of oil-bearing wastewater discharge cause severe environmental pollution and huge economic losses. Recently, superwetting porous materials are successfully utilized to separate oil/water mixture (OWM) based on the different interfacial behavior of water and oil. Here, we summarize the recent development of efficient oil/water separation (OWS) based on the femtosecond laser-induced superwetting materials. The typical wettability-based separation manners (including “oil-removing” and “water-removing”) and the characteristic of the femtosecond laser are introduced as background. Various laser-structured porous sheets with either superhydrophobicity or underwater superoleophobicity are successfully used to separate different OWMs. The laser processing methods, surface wettability, separation process, and separation mechanism of these laser-structured separation materials are reviewed. Finally, the current challenges and prospects in achieving OWS by femtosecond laser microfabrication are discussed.

Flexible and Superhydrophobic Composites with Dual Polymer Nanofiber and Carbon Nanofiber Network for High-Performance Chemical Vapor Sensing and Oil/Water Separation

Polymer nanofiber composites with superhydrophobicity are promising for the chemical vapor sensing or oil/water separation, but it remains challenging to develop superhydrophobic, anticorrosive, and durable nanofiber composites that can achieve both the organic solvent vapor detection and oil (organic solvent)/water separation with high separation flux and excellent recyclability. Here, a flexible, stretchable, and superhydrophobic/superoleophilic nanofiber composite membrane with excellent photothermal conversion performance is fabricated by decorating carbon nanofibers (CNFs) with a hollow structure onto the polyurethane nanofibers and subsequent polydimethylsiloxane (PDMS) modification. The combination of CNFs and PDMS greatly improves the membrane's tensile strength and Young's modulus without sacrificing its stretchability. The dual polymer nanofiber and CNF network are beneficial to the chemical vapor or liquid diffusion into the membrane and thus can be used for high-performance chemical vapor sensing and oil/water separation. The nanofiber composite is responsive to different organic vapors with a low detection limit and good selectivity. Also, the material can achieve fast oil/water separation with the oil (dichloromethane) permeate flux as high as 6577.3 L m^-2 h^-1. In addition, the separation flux and efficiency remain stable during the 30 separated oil/water separation tests, exhibiting excellent recyclability.

Superhydrophobic and Sustainable Nanostructured Powdered Iron for the Efficient Separation of Oil-in-Water Emulsions and the Capture of Microplastics

The pollution of oceans and seas by oils and microplastics is a significant global issue affecting the economy and environment. Therefore, it is necessary to search for different technologies that can remove these pollutants in a sustainable way. Herein, superhydrophobic powdered iron was used to efficiently separate stabilized oil-in-water emulsions and, remarkably, capture microplastic fibers. High-energy ball milling of iron particles was applied to decrease particle size, increase the specific surface area, and produce a nanostructured material. This was combined with the liquid phase deposition of lauric acid to modify the surface free energy. The nanostructured powder showed superhydrophobicity (WCA = 154°) and superoleophilicity (OCA = 0°), which were fundamental in separating stabilized oil-in-water emulsions of hexane with an efficiency close to 100%. Because of the superhydrophobic/superoleophilic properties of the powdered iron and its intrinsic properties of being able to freely move and adapt to the different morphologies of microplastics under continuous stirring, this material can capture microplastic fibers. Thus, we present a novel dual application of a superhydrophobic material, which includes the capture of microplastics. This has not been reported previously and provides a new scope for future environmental sustainability.

Fabrication of Magnetically Inorganic/Organic Superhydrophobic Fabrics and Their Applications

In order to solve the problem caused by oil spills and organic solvent contamination, novel magnetically inorganic/organic superhydrophobic fabrics are fabricated via a facile method. Cotton fabrics are immersed in a mixture of functionalized Co_0.2Mg_0.8Fe₂O₄ (FCMFO) nanoparticles, vinyl-terminated polydimethylsiloxane (VPDMS), trimethylolpropane triacrylate, and 2-hydroxy-2-methylpropiophenone before UV irradiation for 100 s to obtain the multifunctional superhydrophobic fabrics with magnetic property. The coated fabrics show excellent superhydrophobicity, and the water contact angle is 157.1° when the mass ratio of FCMFO nanoparticles to VPDMS is 0.3. These superhydrophobic fabrics have high oil/water separation efficiency (98.7% for dichloromethane/water) and high oil flux (71,506 L·m^-2·h^-1 for dichloromethane/water). Even after 20 separation cycles, oil/water separation efficiency and oil flux maintain 96.4% and 64,012 L·m^-2·h^-1, respectively. Furthermore, the magnetic property of these superhydrophobic fabrics could be used in the separation of oil from water. Moreover, the superhydrophobic fabrics possess exceptional self-cleaning performance, mechanical durability, chemical stability, and flame retardancy. These multifunctional superhydrophobic fabrics are potential for wide applications.

High-Capacity Reusable Chitosan Absorbent with a Hydrogel-Coated/Aerogel-Core Structure and Superhydrophilicity under Oil for Water Removal from Oil

In this work, inspired by the self-cleaning surfaces of fish scales, we prepared a porous chitosan aerogel (CSA) through a simple freeze-drying process. With the three-dimensional interconnected microstructure, the aerogel was highly porous (porosity > 98.16%) and ultralight with a density ranging from 10.19 to 36.05 mg/cm³. The core/shell structure of the CS-hydrogel-coated/CS-aerogel core (CSHA) was fabricated through a simple spray process. The aerogel with low-adhesion CS-hydrogel-coating exhibited superoleophobicity (θ_oil ∼ 162°) under water and superhydrophilicity (θ_water ∼ 0°) in oil. The hydrogel coating as a switch of the absorbent resists the oil phase and induces permeation of the water phase into the aerogel easily and quickly. The dry aerogel core with a porous structure has become a huge storage space. Taking advantage of this structure, an absorption capacity of 147 times could be obtained for water. The unique water absorption process along with switching between the aerogel and hydrogel gives the CSHA incredible potential for oil purification applications on site. Using the CSHA for oil purification, the purity of the obtained oil can be as high as 99.8%. Importantly, two facile approaches, including redissolving and drying, were applied to recycle the aerogels. The natural hydrophilic aerogels are made from dissolution and regeneration of chitosan powder, which is green, low-cost, simple and easy to scale-up. Using the as-obtained high-capacity recyclable CSA for oil/water separation, the mixture can be separated with high efficiency, making it a favorable candidate for applications in large-scale separation of oil-water mixtures in the future.

Biomimetic Durable Multifunctional Self-Cleaning Nanofibrous Membrane with Outstanding Oil/Water Separation, Photodegradation of Organic Contaminants, and Antibacterial Performances

Wastewater pollution has always been one of the most severe worldwide environmental problems. In addition, in light of the frequent oil spills that have occurred in recent years, the treatment of oily wastewater is particularly important. In this work, a novel zeolitic imidazolate framework-8@thiolated graphene (ZIF-8@GSH) composites-based polyimide (PI) nanofibrous membrane was developed via a facile electrospinning and in situ hydrothermal synthesis approaches for effective purification of oily wastewater. The membrane showed superhydrophobicity/superoleophilicity and high separation efficiency (>99.9%) for a wide range of oil/water mixtures and water-in-oil emulsions. Besides, the membrane demonstrated excellent photocatalytic dye degradation, antibacterial, self-cleaning, and mechanochemical durable abilities, showing high potential in oily wastewater treatment and water remediation.

Tuning the Wettability of Metal-Organic Frameworks via Defect Engineering for Efficient Oil/Water Separation

Zirconium-based metal-organic frameworks (MOFs) have attracted interest due to their chemical and thermal stabilities and structural tunability. In this work, we demonstrate the tuning of the wettability of a UiO-66 structure via defect-engineering for efficient oil/water separation. UiO-66 crystals with controlled levels of missing-linker defects were synthesized using a modulation approach. As a result, the hydrophilicity of the defect-engineered UiO-66 (d-UiO-66) can be varied. In addition, a thin layer of hydrophilic d-UiO-66 was successfully fabricated on a series of stainless steel meshes (d-UiO-66@mesh), which exhibited excellent superhydrophilic and underwater superoleophobic properties and displayed interesting separation performance for various oil/water mixtures.

Preparation and Characterization of Tris(trimethylsiloxy)silyl Modified Polyurethane Acrylates and Their Application in Textile Treatment

Three series of silicone modified polyurethane acrylate (SPUA) prepolymers were prepared from dicyclohexylmethane-4, 4'-diisocyanate (HMDI), PPG1000, triethylene glycol (TEG), 2-hydroxyethyl acrylate (HEA), and multi-hydroxyalkyl silicone (MI-III) with tris(trimethylsiloxy)silyl propyl side groups. Their structures were confirmed by 1H NMR, 13C NMR, and Fourier transformed infrared (FTIR) analysis, and SPUA films were obtained by UV curing. The properties of films were investigated by attenuated total reflection (ATR)-FTIR, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), water contact angle (WCA), thermogravimetric analysis (TGA), differential scanning calorimeter (DSC), water and hexane resistance, and tensile testing. The results showed that the structures and dosages of MI-III could influence the polymerization properties, surface properties, water and n-hexane resistance, and thermal and tensile properties of SPUA. For instance, the surface aggregation of tris(trimethylsiloxy)silyl propyl groups (even ~2.5 wt%) could endow SPUA films with less microphase separation, good hydrophobicity, lipophilicity, thermal stability, and mechanical properties. Interestingly, obvious regular winkles appeared on the surfaces of SPUAIII films, which are characterized by relatively high WCA values. However, relatively smooth were observed on the surfaces of SPUAIII films, which also exhibit lower water absorption ratio values. Furthermore, the ordinary cotton textiles would be transformed into hydrophobic and oleophilic textiles after treating with SPUA simply, and they were used in the oil/water separation study. Among them, consistent with water and hexane resistance analysis of SPUA films, SPUAII treated cotton textiles are characterized by relatively small liquid absorption capacity (LAC) values. Thus, phenyl groups and side-chain tris(trimethylsiloxy)silyl propyl groups are helpful to improve the hydrophobicity and lipophilicity of SPUA films. SPUAII-5 (even with 5 wt% MII) treated cotton textiles could efficiently separate the oil/water mixture, such as n-hexane, cyclohexane, or methylbenzene with water. Thus, this material has great potential in the application of hydrophobic treatment, oil/water separation, and industrial sewage emissions, among others.

Heat-Treated Micronized Polyethylene Powder for Efficient Oil/Water Separating Filters

The targeted separation of oil/water mixtures is a rapidly growing field of research, mainly due to contaminated water becoming an increasingly important environmental issue. Superhydrophobic materials are highly suited to this application; however, growing efforts are being devoted to developing applicable technologies within a range of research communities. The optimal technical solution is one that combines a high separation efficiency with a straightforward fabrication procedure at a low cost. In this report, micronized polyethylene powder has been utilized as a low-cost hydrophobic material to manufacture easy-to-fabricate filters. The effect of heating and solvent addition on the water repellence behaviour has been investigated, according to which the optimum fabrication conditions were determined. The filters show high water repellence (WCA = 154°) and efficient oil/water separation (~99%). The filters are designed to provide a readily achievable approach for the separation of oils (hydrophobic solvents) from water in a range of potential applications.

Simple and Low-Cost Oil/Water Separation Based on the Underwater Superoleophobicity of the Existing Materials in Our Life or Nature

The achievement of high-efficiency oil/water separation has huge implications for protecting environment and reducing economic losses, but there is still a great challenge. Currently, most artificial oil/water separating materials are fabricated through complex preparation process, resulting in the very high cost of separation. In this paper, we present a simple and low-cost method to achieve oil/water separation by using the underwater superoleophobic materials that already exist in our life or nature. Taking filter paper and zeolite layer as examples, we show the inherent porous microstructures of these materials. Such porous microstructures endow filter paper and zeolite layer with strong ability to absorb water and the underwater superoleophobicity. Based on the porous feature and underwater superoleophobicity, the pre-wetted filter paper and zeolite layer can be used to effectively separate the mixture of water and oil, with great separation capacity. The existing materials (e.g., filter paper and zeolite layer) with both porous microstructure and underwater superoleophobicity in our life or nature are green and low-cost, and can be easily obtained. Such advantages allow those materials to potentially solve the pollution problems caused by the discharge of industrial oily wastewater and the oil-spill accidents.

Hard-and-Soft Integration Strategy for Preparation of Exceptionally Stable Zr(Hf)-UiO-66 via Thiol-Ene Click Chemistry

UiO-66 metal-organic frameworks (MOFs) are unstable in some harsh aqueous environments, which limit their practical applications. We demonstrate a postsynthetic modification methodology to transform hydrophilic Zr(Hf)-UiO-66 into superhydrophobic Zr(Hf)-UiO-66-SH-y (SH = thiol, y = fluoroalkyl) by introducing long fluoroalkyl chains into organic linkers through a thiol-ene click reaction. Water contact angles of the four modified UiO-66 MOFs are all larger than 150°. The grafted low-surface-energy fluorine-containing groups become an effective protective shield for the MOFs, making them exhibit remarkable stability in extreme conditions such as alkaline (pH = 12), saturated HCl, and high concentration of NaCl solution (20 wt %). The Zr-UiO-66 MOFs grafted with 1H,1H,2H-perfluoro-1-hexene have high CO₂ adsorption contents of 1.54 and 2.88 mmol·g^-1 at 298 and 273 K, respectively. Moreover, the superhydrophobic MOFs also showed potential application in oil/water separation.

Three-Dimensional Chemically Stable Covalent Organic Frameworks through Hydrophobic Engineering

The development of three-dimensional (3D) covalent organic frameworks (COFs) with high chemical stability is of critical importance for their practical use. In this work, it is demonstrated that the stability of 3D COFs can be improved by periodic decoration of isopropyl groups on their backbones. Owing to the strong hydrophobicity of the alkyl groups, the resultant COFs show high crystallinity, permanent pores, and exceptional stability in harsh environments, such as strong acids (3 m HCl or 3 m H₂ SO₄ for one week), a strong base (20 m NaOH for one week), and boiling water (100 °C for one month). Furthermore, these highly stable and hydrophobic COFs display excellent oil/water separation performance with >99 % separation efficiency over a wide pH range. This work demonstrates the use of alkyl decoration in 3D COFs to tune their chemical stability and expand their potential applications.

Omni-Directional Protected Nanofiber Membranes by Surface Segregation of PDMS-Terminated Triblock Copolymer for High-Efficiency Oil/Water Emulsion Separation

An excellent antifouling membrane with high permeate flux is required for oil/water emulsion separation due to ever-increasing oily industrial wastewater. Thus, an intriguing integration of the Omni-directional protected porous membrane that combines a high porosity nanofiber membrane with a surface segregation mechanism is established for the first time. By applying polydimethylsiloxane(PDMS)-terminated triblock copolymer, the enrichment of the hydrophilic poly(ethylene oxide) (PEO) segment and the nonpolar PDMS segment on the surface of the nanofiber endowed the nanofiber membrane with underwater oleophobicity and low oil adhesion force, exhibiting oil resistance as well as oil release property. An ultrahigh permeate flux of ∼7115 L m^-2 h^-1 with a separation efficiency of ∼97.88% is achieved under the driving force of gravity (∼0.9 kPa), which is the highest permeate flux ever reported under similar conditions. Moreover, the surface segregation nanofiber membrane shows excellent reusability and ultrahigh permeate flux with the assistance of stirring in a long-term test, revealing the promising performances for the further particular application of oily wastewater.

Ultrafast Fabrication of Metal-Organic Framework-Functionalized Superwetting Membrane for Multichannel Oil/Water Separation and Floating Oil Collection

Traditional methods for oil/water separation suffer from many tricky problems such as low efficiency, high energy consumption, and difficulties in recycling and reusing. To address these hurdles, we developed a metal-organic framework-coated superwetting membrane for multichannel oil/water separation and collection of floating oils. The dip-coating method adopted in this paper is extremely flexible in manipulation and can be completed within 1 h under a low temperature without any assistance of high pressure. Interestingly, the strategy of fabricating superwetting membrane mainly includes introducing vital interlayers of Cu(OH)₂ nanowires, which not only construct the favorable hierarchical structures but also act as partly sacrificed templates for further growth of hydrophilic MOF nanowhiskers. In virtue of the high flexibility of the as-prepared mesh, this superwetting membrane can be applied for multichannel oil/water separation including gravity-driven oil/water separation, continuous oil/water separation, and floating oil collection. Moreover, the separation efficiency and flux of the superwetting membrane keep high and stable under multiple separation cycles. This study paves the way for a fast and facile preparation of a superwetting membrane with high applicability for multiple oil/water separation.

Superhydrophobic Nickel-Electroplated Carbon Fibers for Versatile Oil/Water Separation with Excellent Reusability and High Environmental Stability

Superhydrophobic filtrating materials have been widely developed for rapid removal or collection of oils from oil/water mixture due to the increasing water pollution caused by oil spills and oil-contaminated wastewater. However, poor reusability, superhydrophobic failure in harsh environments, and that only heavy oil or light oil was separated from water seriously restricted their practical application. Herein, superhydrophobic carbon fibers were first fabricated using a novel nickel electroplating for versatile oil/water separation with excellent reusability and high environmental stability. The interconnected nanometer-scale nickel grains formed on the micrometer-scale fibers and fluoroalkylsilane molecules enabled the fibers to be superhydrophobic with the water contact angle (CA) of ∼159.1° and superoleophilic with the oil CA of ∼0°. The nickel coating contributed to the improvement of the bonding strength, tensile strength, and oxidation resistance of the fibers. The as-prepared fibers could be applied for the separation of heavy or light oil/water mixtures with separation efficiencies above 99.1%, during which the oil content in the separated water all remained below 78 ppm. The fibers also realized the highly efficient separation of dichloromethane and various harsh environmental solutions such as hot water, acid, alkali, and salt. The superhydrophobicity of the fluorinated nickel-coated carbon fibers still remained even after 100 cycles of separation and 24 months of storage in air, demonstrating outstanding durability of the fibers. These novel superhydrophobic carbon fibers had promising potentials for versatile oil/water separation in practical applications.

Acoustic-Controlled Bubble Generation and Fabrication of 3D Polymer Porous Materials

Porous materials have a variety of applications such as catalysis, gas separation, sensing, tissue engineering, sewage treatment, and so on. However, there are still challenges in the synthesis of porous materials with light weight, high porosity, and superhydrophobicity. Herein, we demonstrate one acoustic-controlled microbubble generation method, which is used to synthesize 3D polymer porous materials. The acoustic-controlled microbubble generation based on focused surface acoustic wave (FSAW) is suitable for not only the generation of gas-in-oil microbubbles but also the gas-in-water microbubbles. The size of microbubbles can be real-time controlled by adjusting the frequency or the driving voltage of the FSAW. The as-prepared poly(vinyl alcohol) (PVA) foams composed of microbubbles can be used as a template to fabricate the PVA-based porous gel materials through freezing-thawing cyclic processing, and the various sized bubbles result in different porosity of the PVA-based porous gel materials. Moreover, excellent properties like oleophilicity and superhydrophobicity of the PVA-based porous gel materials can be obtained through a further hydrophobic modification treatment. The oil/water separation experiments have been done to demonstrate the good absorption and reliability of the modified porous gel materials, which are capable of multiple uses.

Functional Catechol-Metal Polymers via Interfacial Polymerization for Applications in Water Purification

Phenols and polyphenols have been used as a scaffold for generating multidimensional molecular architectures via complexation with metal ions. Here, we report the synthesis and characterization of metallopolymer films from three catechol derivatives having different alkyl/aryl substituents via complexation with iron and copper ions at the organic-water interface. Such interfacial polymerization is instantaneous, one step to generate functional materials, and gives good control over the organization of repeating units along the film. The films were transferred to different substrates such as filter paper, cotton, or polyester fabrics. The films are superhydrophobic with a contact angle >160° which can be tuned by regulating the orientation of nonpolar groups at the interface during polymerization. In addition, the fabricated cloth membrane showed excellent oil/water separation efficiency of more than 99% even after 50 cycles. The polymers also showed good dye extraction capacity from aqueous solutions with fast kinetics data. Such metallopolymer networks can serve as a versatile material for applications in catalysis, protective coatings, drug delivery, water filtration membranes, and liquid separations.

Progress in Sol-Gel Technology for the Coatings of Fabrics

The commercial availability of inorganic/organic precursors for sol-gel formulations is very high and increases day by day. In textile applications, the precursor-synthesized sol-gels along with functional chemicals can be deposited onto textile fabrics in one step by rolling, padding, dip-coating, spraying or spin coating. By using this technology, it is possible to provide fabrics with functional/multi-functional characteristics including flame retardant, anti-mosquito, water- repellent, oil-repellent, anti-bacterial, anti-wrinkle, ultraviolet (UV) protection and self-cleaning properties. These surface properties are discussed, describing the history, basic chemistry, factors affecting the sol-gel synthesis, progress in sol-gel technology along with various parameters controlling sol-gel technology. Additionally, this review deals with the recent progress of sol-gel technology in textiles in addressing fabric finishing, water repellent textiles, oil/water separation, flame retardant, UV protection and self-cleaning, self-sterilizing, wrinkle resistance, heat storage, photochromic and thermochromic color changes and the improvement of the durability and wear resistance properties.

One-Pot Preparation of Fluorine-Free Magnetic Superhydrophobic Particles for Controllable Liquid Marbles and Robust Multifunctional Coatings

In this paper, magnetic superhydrophobic particles were prepared by simultaneously coating silica microspheres and modifying 1,1,1,3,3,3-hexamethyl disilazane (HMDS) around the ferric oxide nanoparticles via a one-pot sol-gel process. The effect of the molar ratio of tetraethyl orthosilicate (TEOS) to HMDS on the wettability of superhydrophobic particles (Fe₃O₄@SiO₂/HMDS) was investigated. Various stable liquid marble encapsulated solvents with different surface tensions, pH values, volumes, and temperatures could be obtained by simply rolling them on superhydrophobic particles. The magnetic liquid marbles could be directional transported and fixed-point volatilized. Furthermore, superhydrophobic particles were sprayed onto different surfaces using polydimethylsiloxane (PDMS) as the binder to construct organic-inorganic composite multifunctional coatings by a one-step process. By optimizing the content of Fe₃O₄@SiO₂/HMDS and PDMS in the spraying solution, the prepared coatings showed superior superhydrophobicity with contact angles of larger than 150° and sliding angles of smaller than 10°. The coated fluorine-free fabric possessed excellent air permeability, tensile strength, and hydrostatic pressure resistance, thus fulfilling the practical wearable requirements. Besides, the prepared fabrics maintained stable water repellency even after withstanding mechanical damages or long-term exposure to severe environments. Moreover, the coated superhydrophobic materials could be applied for the on-demand separation of various oil/water mixtures. In addition, the superhydrophobic fabric presented excellent photothermal conversion performances, showing outstanding anti-icing and accelerated deicing properties. Thus, the prepared nonfluorinated and stable magnetic particles offer potential in the areas of controlled encapsulation and directional delivery and, as building blocks, are promising for the construction of robust, large-area, and multifunctional self-cleaning surfaces.

A Spiderweb-Like Metal-Organic Framework Multifunctional Foam

Processing metal-organic frameworks (MOFs) into hierarchical macroscopic materials can greatly extend their practical applications. However, current strategies suffer from severe aggregation of MOFs and limited tuning of the hierarchical porous network. Now, a strategy is presented that can simultaneously tune the MOF loading, composition, spatial distribution, and confinement within various bio-originated macroscopic supports, as well as control the accessibility, robustness, and formability of the support itself. This method enables the good dispersion of individual MOF nanoparticles on a spiderweb-like network within each macrovoid even at high loadings (up to 86 wt %), ensuring the foam pores are highly accessible for excellent adsorption and catalytic capacity. Additionally, this approach allows the direct pre-incorporation of other functional components into the framework. This strategy provides precise control over the properties of both the hierarchical support and MOF.