Transparent and Robust Amphiphobic Surfaces Exploiting Nanohierarchical Surface-grown Metal-Organic Frameworks.

Highly amphiphobic (repelling both water and low surface tension liquids) and optically transparent surface treatments have widespread demand. By combining a rational growth of metal-organic frameworks (MOFs) with functionalization by environmentally safe, flexible alkyl groups, here we present surfaces with nanohierarchical morphology, comprising two widely differing nanoscale features. These nanohierarchical MOF films show excellent amphiphobicity. We further present three key features. First, we demonstrate the need to use flexible alkyl chains to achieve low drop sliding angles and self-cleaning. Second, our thin (∼200 nm) MOF films display excellent optical transparency and robustness. Third, the nanohierarchical morphology enables a unique combination of additional desirable properties, e.g., resistance to high-speed liquid impact (up to ∼35 m/s, Weber number >4 × 104), thermal stability up to 200 °C, scratch resistance, low ice adhesion for >10 icing/deicing cycles, stability in harsh acidic and basic environments, and capability to remove carcinogenic pollutants from water.

A robust COF@MXene membrane for ultra-high flux of water-in-oil emulsion separation.

A facile covalent assembly strategy is proposed for the preparation of superhydrophobic COF-stabilized MXene separation membranes. Ultra-high separation fluxes of up to 54 280 L m-2 h-1 and 643 200 L m-2 h-1 bar-1 are obtained for emulsified water-in-oil mixtures by adopting gravity and external pressure, respectively. Moreover, the challenges of easy swelling and oxidation properties of MXene have been effectively overcome via the COF-stabilized mechanism.

Rational Design of Durable Anti-fouling Coatings with High Transparency, Hardness, and Flexibility.

Highly transparent, durable, flexible and smooth coatings with excellent anti-fouling properties have broad applications on cars, windows, and touch screens. However, the coexistence of these multi-functions is difficult to achieve in a single coating material. Here, a coating is developed with excellent performance of high transparency (98.8%), anti-fouling, high hardness (8H), and flexibility simultaneously (TAHF coating). In the material design, methyl etherified melamine formaldehyde resin, hexamethylene diisocyanate trimer, and mono-aminopropyl terminated polydimethylsiloxane (NH2-PDMS) were used as a polymer matrix to provide surface hardness, a cross-linker was used to provide toughness, and omniphobic groups from NH2-PDMS were used to provide anti-fouling performance. The TAHF coating has excellent liquid repellence even after six months of outdoor exposure, 260 h of UV light exposure, and 1500 wear and 2000 bending cycles, and its chemical shielding performance is superior to that of a commercial anti-corrosive coating. This strategy would provide a new route for the design of multifunctional anti-fouling coatings for practical applications.

Rapid control of switchable oil wettability and adhesion on the copper substrate.

We described a facile approach to rapidly achieve the reversible oil wettability and adhesion transition on the copper substrate. Plasma treatment and surface fluorination were used to tune the surface composition, and this tunability of the surface composition, along with the stable surface roughness, gave rise to the switchable wettability varying from superoleophobicity to superoleophilicity and reversible oil adhesion between sliding superoleophobicity and sticky superoleophobicity. It took only 1.25 min to realize the whole wettability transition and 5 min for the whole adhesion transition. Additionally, the application of a sticky superoleophobic surface was demonstrated. This study represents an important addition to the field of functional superoleophobic materials.

Counterion exchange to achieve reversibly switchable hydrophobicity and oleophobicity on fabrics.

We describe a simple layer-by-layer (LbL) technology and counterion exchange procedure to tune the liquid wettability of commercially available cotton fabrics. A polyelectrolyte multilayer is deposited on the fabric surface by the LbL technology, and counterion exchange is used to control the surface composition and thereby to modulate the solid surface energy. The tunability of the solid surface energy, along with the inherent re-entrant texture of the cotton fabric, results in simultaneously switchable wettability between a nonwetting state and a fully wetted state for water and hexadecane. This switchable hydrophobicity and oleophobicity can be explained within a robustness factor, which is a quantitative criterion for the transition between the two states. The counterion exchange can be confirmed by X-ray photoelectron spectroscopy analysis.

Reversible superhydrophobicity to superhydrophilicity switching of a carbon nanotube film via alternation of UV irradiation and dark storage.

We describe a simple method of fabricating a superhydrophobic carbon nanotube (CNT) film without any chemical modification. A remarkable surface wettability transition between superhydrophobicity and superhydrophilicity can be easily observed by the alternation of UV irradiation and dark storage. The adsorption and desorption of surface water molecules on the CNT surfaces account for their tunable surface wettability, which is disclosed by X-ray photoelectron spectroscopy analysis. We also perform a series of comparison experiments to confirm the explanation of its distinctive surface wettability. This switchable wettability on the CNT film could have potential applications in areas requiring multifunctional CNT-based films.

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.

Li-Ions Transport Promoting and Highly Stable Solid-Electrolyte Interface on Si in Multilayer Si/C through Thickness Control.

Lithium-ion batteries (LIBs) have been considered as promising electrochemical energy storage devices due to the high volumetric, gravimetric capacity and high power density. The charge/discharge rate and power output of LIBs largely depend on the transport property of lithium-ions (Li-ions). The Li-ions diffusion coefficient and diffusion length are the critical factors influencing the charge/discharge rate of LIBs. In this work, we present that silicon-carbon (Si-C) interfaces in an amorphous Si/C multilayer electrode promote the transport of Li-ions along the direction not only perpendicular to but also parallel to the Si-C interfaces after electrode cracking. The electrode, stacked with 5 nm amorphous carbon and 10 nm amorphous Si, has the most stable solid-electrolyte interface (SEI) formed at the cracks, even when the Si is in direct contact with the electrolyte. It exhibits highly stable cycle performance and a high retained specific capacity. Electron microscopy characterization shows that the structure contains uniform Si/C multilayer blocks of about 1 µm. A micro-size hierarchical multilayer-block design strategy with proper stacking thickness of amorphous Si and carbon is thus proposed for high-performance film LIB anodes. Furthermore, the results may be used as a reference for the design of high-performance core-shell LIB anodes.

Large-size and high performance visible-light photodetectors based on two-dimensional hybrid materials SnS/RGO.

We report a facile solvothermal method to synthesize two-dimensional hybrid materials consisting of layered SnS nanosheets and reduced graphene oxide (SnS/RGO). Large-size photodetectors with a channel length/width = 2 mm/7 mm are fabricated on Si/SiO2 substrates, showing an excellent photoresponsivity of 0.18 A W-1 under visible-light illumination with a detectivity of 4.18 × 1010 Jones, as well as fast rise and decay times (τ rise = τ decay = 0.4 s). SnS/RGO hybrids are therefore promising candidates for potential applications in optoelectronics and low cost, high performance, and reliable photodetectors.

[Study on preparation and spectroscopy of silica-alumina hydrogel and silica from kaolin].

In our research, silica-alumina hydrogel was prepared by activation with NaOH and reaction with HCl from kaolin, and silica was obtained from the hydrogel by drying and acidifying with HCl. IR, XRD and XRF were used for testing the results, and better result was obtained. The optimal conditions of processing for kaolin 40 g were 15-20 g of sodium hydroxide and 4-5 mol x L(-1) of hydrochloric acid. Finally, preparation processing to get silica, as well as the structure and purity of the resulting silica were characterized by means of IR, XRD and XRF.

Designing transparent superamphiphobic coatings directed by carbon nanotubes.

Creating surfaces with superamphiphobic property and optical transparency simultaneously would have fundamental and practical significance but has been proven extremely challenging. Herein, we develop a transparent superamphiphobic coating using carbon nanotubes (CNTs) as the template by a facile approach. CNTs enwrapped with SiO2 coating was produced by a sol-gel method and then sprayed onto the glass slides to form coatings. Subsequent thermal treatment and surface fluoration allowed the sprayed coating to exhibit enhanced transparency across a broad spectrum of ultraviolet and visible wavelengths and also display superrepellency toward water and a number of organic liquids, such as dodecane. The obtained transparent coating can sustain its superamphiphobicity even after thermal treatment at 400 °C. Separate experiment demonstrated that the CNTs-directed geometrical structure played a key role in establishing superamphiphobicity.

A versatile approach to produce superhydrophobic materials used for oil-water separation.

Designing functional materials that can be used for oil-water separation in an efficient and cost-effective process is highly desired yet still challenging. Herein, three functional materials used for oil-water separation are readily produced by a dip coating process. Three typical porous materials including copper mesh, fabric, and sponge were dipped into the solution of polyfluorowax-hydrophobic SiO2 to alter their surface texture and chemistry, allowing them to exhibit superhydrophobic property. It was found that the resulting superhydrophobic copper mesh and fabric can be used as a membrane to separate oil-water mixture efficiency; while the obtained superhydrophobic sponge was demonstrated as an oil sorbent scaffold to absorb oil from the oil-water mixture selectively. More importantly, these superhydrophobic materials can retain their oil-water separation efficiency even after 10 cycles of oil-water separation.

Robust and durable superhydrophobic cotton fabrics for oil/water separation.

By introducing the incorporation of polyaniline and fluorinated alkyl silane to the cotton fabric via a facile vapor phase deposition process, the fabric surface possessed superhydrophobicity with the water contact angle of 156° and superoleophilicity with the oil contact angle of 0°. The as-prepared fabric can be applied as effective materials for the separation of water and oil mixture with separation efficiency as high as 97.8%. Compared with other materials for oil/water separation, the reported process was simple, time-saving, and repeatable for at least 30 times. Moreover, the obtained fabric kept stable superhydrophobicity and high separation efficiency under extreme environment conditions of high temperature, high humidity, strong acidic or alkaline solutions, and mechanical forces. Therefore, this reported fabric has the advantages of scalable fabrication, high separation efficiency, stable recyclability, and excellent durability, exhibiting the strong potential for industrial production.

Facile fabrication of a superhydrophobic fabric with mechanical stability and easy-repairability.

The poor mechanical stability of superhydrophobic fabrics severely hindered their use in practical applications. Herein, to address this problem, we fabricated a superhydrophobic fabric with both mechanical stability and easy-repairability by a simple method. The mechanical durability of the obtained superhydrophobic fabric was evaluated by finger touching and abrasion with sandpaper. The results show that rough surface textures of the fabric were retained, and the fabric surface still exhibited superhydrophobicity after tests. More importantly, when the fabric lost its superhydrophobicity after a long-time abrasion, it can be easily rendered with superhydrophobicity once more by a regeneration process.

Rapid and reversible switching between superoleophobicity and superoleophilicity in response to counterion exchange.

We use a simple layer-by-layer (LbL) assembly and counterion exchange technology to rapidly and reversibly manipulate the oleophobicity of the textured aluminum surfaces. Such textured surfaces can be produced by the HCl etching and boiling water treatment of the flat aluminum plates. The LbL deposition of polyelectrolytes is performed on these surfaces to generate the polyelectrolyte multilayer films. The films are able to coordinate with perfluorooctanoate anions, leading to the surfaces with different oleophobicity. The resulting surface produced by 1.5 cycles of polyelectrolyte deposition exhibits superoleophobicity by displaying contact angles greater than 150° with low surface tension liquids. Counterion exchange in this polyelectrolyte multilayer emerged easily to control the surface composition, which leads to tunable wettability that can be rapidly and reversibly switched between superoleophobicity and superoleophilicity.

Facile fabrication of a superamphiphobic surface on the copper substrate.

A simple solution-immersion technique was developed for the fabrication of a superamphiphobic surface on the copper sheet. Hierarchical structure composed of nanorod arrays and microflowers was formed on the copper surface by an alkali assistant oxidation process; after fluorination, the surface became super-repellent toward water and several organic liquids possessing much lower surface tension than that of water, such as hexadecane. Such superamphiphobicity is attributed to the synergistic effect of their special surface chemicals and microscopic structures, which allows for the formation of a composite interface with all probing liquids tested. We also discuss the effects of surface chemical constituent and geometrical structure on hydrophobicity and oleophobicity; such information allows us to engineer surfaces with specific oleophobic behavior. Additionally, the stability of the composite interface on the created superamphiphobic surface is studied by the compression and immersion test.

Reversible conversion of water-droplet mobility from rollable to pinned on a superhydrophobic functionalized carbon nanotube film.

Poly(acrylic acid)-block-polystyrene (PAA-b-PS) functionalized multiwall carbon nanotubes (MWNTs) were prepared by nitroxide-mediated "living" free-radical polymerization. The product functionalized MWNTs (MWNT-PAA-b-PS) contained 20% by weight PAA-b-PS based on the infrared spectroscopy analysis and thermal gravimetric analysis. Such MWNT-PAA-b-PS nanoparticles can be used in spray coating method to fabricate superhydrophobic MWNT films, and water-droplet mobility on the superhydrophobic film can be reversibly converted from rollable to pinned through adjusting the appearance of PAA chains on the topmost surface of the film. Switching mechanism has been discussed in detail. We also directly observed the air-solid-liquid interface from the above of a water droplet by a microscope to confirm the superhydrophobic states, and proved that the transition between the wettability states appeared on the same surface with reversible conversion of water-droplet mobility.

Rapid formation of superhydrophobic surfaces with fast response wettability transition.

We have developed a facile and time-saving method to prepare superhydrophobic surfaces on copper sheets. Various surface textures composed of Cu(OH)2 nanorod arrays and CuO microflowers/Cu(OH)2 nanorod arrays hierarchical structure were prepared by a simple solution-immersion process. After chemical modification with stearic acid, the wettability of the as-prepared surfaces was changed from superhydrophilicity to superhydrophobicity. The shortest processing time for fabricating a superhydrophobic surface was 1.5 min. Interestingly, the rapid wettability transition between superhydrophobicity and superhydrophilicity can be realized on the prepared surfaces with ease by the alternation of air-plasma treatment and stearic acid coating. It took just 2 min to complete the whole wettability transition. Additionally, the regeneration of the superhydrophobic surface is also considered regarding its application.