A facile approach for oil-water separation using superhydrophobic polystyrene-silica coated stainless steel mesh bucket.

Inspired by traditional shaduf technology in the irrigation field, we fabricated a superhydrophobic stainless steel mesh bucket by layering polystyrene and SiO2 nanoparticles through a facile dip coating technique for effective oil-water separation. The superhydrophobic steel mesh bucket could effectively lift oil as well as microplastic pollutants from the water surface. The water contact angle of a two-layered polystyrene-silica coating was 158.5° ± 2°, while the oil contact angle was nearly 0°. The oil-water separation performance of superhydrophobic mesh was tested using several kinds of oil. The separation efficiency achieved for low viscous oil was 99.33 %, while 86.66 % efficiency was recorded for high viscous oil. The superhydrophobic mesh showed high durability against mechanical tests including bending, folding, twisting, adhesive tape tearing (25 cycles), and sandpaper abrasion (20 cycles). The mesh presented admirable thermal and chemical durability. The present superhydrophobic steel mesh bucket is a suitable candidate for large-scale application.

Spatial Compartmentalization of Cobalt Phosphide in P-Doped Dual Carbon Shells for Efficient Alkaline Overall Water Splitting.

Highly durable and earth-abundant bifunctional catalysts with low cell voltage are desirable for alkaline overall water splitting in the industrial fields. Herein, a novel carbon-based CoP hybrid with spatial compartmentalization of CoP nanoparticles (NPs) in P-doped dual carbon shells is achieved via a cheap Co-glycerate-template strategy. Benefitted from the uniform atomic blending of Co2+ ions in the Co-glycerate precursors, CoP NPs in situ formed in the confined space with NaH2PO2 as phosphorus source during the annealing process; meanwhile, glycerate suffered carbonization and transformed into P-doped dual carbon shells during the annealing process, including interior thin carbon coating, closely encircled CoP NP, and peripheral hollow carbon sphere loading a lot of CoP NPs. Not only does spatial compartmentalization of CoP NPs avoid the aggregation and expose more active sites but also P-doped dual carbon shells improve the conductivity and durability of the catalyst. As expected, the optimized hybrid exhibits outstanding electrocatalytic activities in alkaline media, such as hydrogen evolution reaction (HER) overpotential of 101 mV, oxygen evolution reaction (OER) overpotential of 280 mV, and a low cell voltage of 1.66 V to deliver a current density of 10 mA cm-2. Moreover, durability and stability are greatly improved under harsh electrochemical conditions. The current strategy shades new insight into the development of carbon-based transition metal phosphides (TMP) catalysts for electrocatalysis applications.

Charge Separation in TiO2/BDD Heterojunction Thin Film for Enhanced Photoelectrochemical Performance.

Semiconductor photocatalysis driven by electron/hole has begun a new era in the field of solar energy conversion and storage. Here we report the fabrication and optimization of TiO2/BDD p-n heterojunction photoelectrode using p-type boron doped diamond (BDD) and n-type TiO2 which shows enhanced photoelectrochemical activity. A p-type BDD was first deposited on Si substrate by microwave plasma chemical vapor deposition (MPCVD) method and then n-type TiO2 was sputter coated on top of BDD grains for different durations. The microstructural studies reveal a uniform disposition of anatase TiO2 and its thickness can be tuned by varying the sputtering time. The formation of p-n heterojunction was confirmed through I-V measurement. A remarkable rectification property of 63773 at 5 V with very small leakage current indicates achieving a superior, uniform and precise p-n junction at TiO2 sputtering time of 90 min. This suitably formed p-n heterojunction electrode is found to show 1.6 fold higher photoelectrochemical activity than bare n-type TiO2 electrode at an applied potential of +1.5 V vs SHE. The enhanced photoelectrochemical performance of this TiO2/BDD electrode is ascribed to the injection of hole from p-type BDD to n-type TiO2, which increases carrier separation and thereby enhances the photoelectrochemical performance.

Gravity-driven hybrid membrane for oleophobic-superhydrophilic oil-water separation and water purification by graphene.

We prepared a simple, low-cost membrane suitable for gravity-driven oil-water separation and water purification. Composite membranes with selective wettability were fabricated from a mixture of aqueous poly(diallyldimethylammonium chloride) solution, sodium perfluorooctanoate, and silica nanoparticles. Simply dip-coating a stainless steel mesh using this mixture produced the oil-water separator. The contact angles (CAs) of hexadecane and water on the prepared composite membranes were 95 ± 2° and 0°, respectively, showing the oleophobicity and superhydrophilicity of the membrane. In addition, a graphene plug was stacked below the membrane to remove water-soluble organics by adsorption. As a result, this multifunctional device not only separates hexadecane from water, but also purifies water by the permeation of the separated water through the graphene plug. Here, methylene blue (MB) was removed as a demonstration. Membranes were characterized by high-resolution scanning electron microscopy (HRSEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FT-IR) spectroscopy to elucidate the origin of their selective wettability.

Superhydrophobic surfaces developed by mimicking hierarchical surface morphology of lotus leaf.

The lotus plant is recognized as a 'King plant' among all the natural water repellent plants due to its excellent non-wettability. The superhydrophobic surfaces exhibiting the famous 'Lotus Effect', along with extremely high water contact angle (>150°) and low sliding angle (<10°), have been broadly investigated and extensively applied on variety of substrates for potential self-cleaning and anti-corrosive applications. Since 1997, especially after the exploration of the surface micro/nanostructure and chemical composition of the lotus leaves by the two German botanists Barthlott and Neinhuis, many kinds of superhydrophobic surfaces mimicking the lotus leaf-like structure have been widely reported in the literature. This review article briefly describes the different wetting properties of the natural superhydrophobic lotus leaves and also provides a comprehensive state-of-the-art discussion on the extensive research carried out in the field of artificial superhydrophobic surfaces which are developed by mimicking the lotus leaf-like dual scale micro/nanostructure. This review article could be beneficial for both novice researchers in this area as well as the scientists who are currently working on non-wettable, superhydrophobic surfaces.

Electrospun polystyrene nanofiber membrane with superhydrophobicity and superoleophilicity for selective separation of water and low viscous oil.

The ability to prepare solid surfaces with well-controlled superhydrophobic and superoleophilic properties is of paramount importance to water-oil separation technology. Herein, we successfully prepared superhydrophobic-superoleophilic membranes by single-step deposition of polystyrene (PS) nanofibers onto a stainless steel mesh via electrospinning. The contact angles of diesel and water on the prepared PS nanofiber membrane were 0° and 155° ± 3°, respectively. Applications of the PS nanofiber membrane toward separating liquids with low surface tension, such as oil, from water were investigated in detail. Gasoline, diesel, and mineral oil were tested as representative low-viscosity oils. The PS nanofiber membranes efficiently separated several liters of oil from water in a single step, of only a few minutes' duration. The superhydrophobic PS nanofiber membrane selectively absorbs oil, and is highly efficient at oil-water separation, making it a very promising material for oil spill remediation.

Thermally induced superhydrophilicity in TiO2 films prepared by supersonic aerosol deposition.

Superhydrophilic and superhydrophobic surfaces enable self-cleaning phenomena, either forming a continuous water film or forming droplets that roll off the surface, respectively. TiO2 films are well-known for their extreme hydrophilicity and photocatalytic characteristics. Here, we describe nanostructured TiO2 thin films prepared by supersonic aerosol deposition, including a thorough study of the effects of the annealing temperature on the crystal structure, surface morphology, surface roughness, and wetting properties. Powder X-ray diffraction showed that supersonic deposition resulted in fragmentation and amorphization of the micrometer-size anatase (60%)-rutile (40%) precursor powder and that, upon annealing, a substantial fraction of the film (~30%) crystallized in the highly hydrophilic but metastable brookite phase. The film morphology was also somewhat modified after annealing. Scanning electron microscopy and atomic force microscopy revealed rough granular films with high surface roughness. The as-deposited TiO2 films were moderately hydrophilic with a water contact angle (θ) of ~45°, whereas TiO2 films annealed at 500 °C became superhydrophilic (θ ~ 0°) without UV illumination. This thermally induced superhydrophilicity of the TiO2 films can be explained on the basis of the combined effects of the change in the crystal structure, surface microstructure, and surface roughness. Supersonic aerosol deposition followed by annealing is uniquely able to produce these nanostructured films containing a mixture of all three TiO2 phases (anatase, rutile, and brookite) and exhibiting superhydrophilicity without UV illumination.

Dynamic electrowetting-on-dielectric (DEWOD) on unstretched and stretched teflon.

Dynamic electrowetting-on-dielectric (DEWOD) of the unstretched and stretched Teflon is reported in the experiments with water drop impact and rebound. We explore experimentally and theoretically the situation with the capacitance different from the standard static electrowetting. Deionized water drops impact onto either an unstretched hydrophobic Teflon surface or Teflon stretched up to 250% strain normally to the impact direction. The surface roughness of the unstretched Teflon increased after stretching from 209.9 to 245.6 nm resulting in the increase in the equilibrium water contact angle from 96 ± 4° to 147 ± 5°, respectively. The electric arrangement used in the drop impact experiments on DEWOD results in a dramatically reduced capacitance and requires a much higher voltage to observe EW in comparison with the standard static case of a drop deposited on a dielectric layer and attached to an electrode. In the dynamic situation we found that as the EW sets in it can greatly reduce the superhydrophobicity of the unstretched and stretched Teflon. At 0 kV, the water drop rebound height (hmax) is higher for the stretched Teflon (hmax ≈ 5.13 mm) and lower for the unstretched Teflon (hmax ≈ 4.16 mm). The EW response of unstretched Teflon is weaker than that of the stretched one. At the voltage of 3 kV, the water drop sticks to the stretched Teflon without rebound, whereas water drops still partially rebound (hmax ≈ 2.8 mm) after a comparable impact onto the unstretched Teflon. We found a sharp dynamic EW response for the stretched Teflon. The contact angle of deionized water ranged from 147 ± 5° (superhydrophobic) to 67 ± 5° (partially hydrophilic) by applying external voltage of 0 and 3 kV, respectively. Dynamic electrowetting introduced in this work for the first time can be used to control spray cooling, painting, and coating and for drop transport in microfluidics.

Highly efficient wettability control via three-dimensional (3D) suspension of titania nanoparticles in polystyrene nanofibers.

Electrospinning is a simple and highly versatile method for the large-scale fabrication of polymeric nanofibers. Additives or fillers can also be used to functionalize the nanofibers for use in specific applications. Herein, we demonstrate a novel and efficient way to fabricate superhydrophobic to hydrophilic tunable mats with the combined use of electrospinning and electrospraying that may be suitable for mass production on the merits of rapid deposition. The tunable nanocomposite mats were comprised of hydrophobic polystyrene nanofibers and hydrophilic titania nanoparticles. When the electrical conductivity of the electrospinning solution was increased, the surface morphology of the mats changed noticeably from a bead-on-string structure to an almost bead-free structure. Polystyrene (PS)-titania nanocomposite mats initially yielded a static water contact angle as high as 140° ± 3°. Subsequently exposing these mats with relatively weak ultraviolet irradiation (λ = 365 nm, I = 0.6 mW/cm²) for 2 h, the unique 3D suspension of the photoactive titania nanoparticles maximized the hydrophilic performance of the mats, reducing the static water contact angle to as low as 26° ± 2°. The tunable mats were characterized by scanning electron microscopy (SEM), static water contact angle (WCA) measurements, and energy-dispersive X-ray spectroscopy (EDX). Our findings confirmed that the tunable mats fabricated by the simultaneous implementation of electrospraying and electrospinning had the most efficient ultraviolet (UV)-driven wettability control in terms of cost-effectiveness. Well-controlled tunable hydrophobic and hydrophilic mats find potential applications in functional textiles, environmental membranes, biological sensors, scaffolds, and transport media.

Water repellent porous silica films by sol-gel dip coating method.

The wetting of solid surfaces by water droplets is ubiquitous in our daily lives as well as in industrial processes. In the present research work, water repellent porous silica films are prepared on glass substrate at room temperature by sol-gel process. The coating sol was prepared by keeping the molar ratio of methyltriethoxysilane (MTES), methanol (MeOH), water (H(2)O) constant at 1:12.90:4.74, respectively, with 2M NH(4)OH throughout the experiments and the molar ratio (M) of MTES/Ph-TMS was varied from 0 to 0.22. A simple dip coating technique is adopted to coat silica films on the glass substrates. The static water contact angle as high as 164° and water sliding angle as low as 4° was obtained for silica film prepared from M=0.22. The surface morphological studies of the prepared silica film showed the porous structure with pore sizes typically ranging from 200nm to 1.3µm. The superhydrophobic silica films prepared from M=0.22 retained their superhydrophobicity up to a temperature of 285°C and above this temperature the films became superhydrophilic. The porous and water repellent silica films are prepared by proper alteration of the Ph-TMS in the coating solution. The prepared silica films were characterized by surface profilometer, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier Transform Infrared (FT-IR) spectroscopy, humidity tests, chemical aging tests, static and dynamic water contact angle measurements.

Preparation of MTMS based transparent superhydrophobic silica films by sol-gel method.

Superhydrophobic surfaces with water contact angle higher than 150 degrees generated a lot of interest both in academia and in industry because of the self-cleaning properties. Optically transparent superhydrophobic silica films were synthesized at room temperature (27 degrees C) using sol-gel process by a simple dip coating technique. The molar ratio of MTMS:MeOH:H(2)O (5 M NH(4)OH) was kept constant at 1:10.56:4.16, respectively. Emphasis is given to the effect of the surface modifying agents on the hydrophobic behavior of the films. Methyl groups were introduced in the silica film by post-synthesis grafting from two solutions using trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDZ) silylating agents in hexane solvent, individually. The percentage of silylating agents and silylation period was varied from 2.5 to 7.5% and 1 to 3 h, respectively. The TMCS modified films exhibited a very high water contact angle (166+/-2 degrees) in comparison to the HMDZ (138+/-2 degrees) modified films, indicating the water repellent behavior of the surface. When the TMCS and HMDZ modified films were heated at temperatures higher than 350 degrees C and 335 degrees C, respectively, the films became superhydrophilic; the contact angle for water on the films was smaller than 5 degrees. Further, the humidity study was carried out at a relative humidity of 85% at 30 degrees C temperature over 30 days. The films have been characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), % optical transmission, humidity tests and contact angle (CA) measurements.