Superhydrophobic Mesh Research Articles

Preparation of pH-responsive reversible wettable surfaces and application for oil-water separation

With the continuous development of society, the discharge of oily wastewater in daily life and industry has gradually increased, causing considerable damage to the environment, and how to effectively treat oily wastewater is an urgent problem. In this paper, a simple method is proposed to prepare superhydrophobic stainless steel mesh with pH response. The relationship between the ratio of mixed thiols and the surface wettability was explored, as well as the morphology, chemical composition, and pH-responsive mechanism of the stainless steel mesh surface were analyzed, and the separation efficiency, recycling ability, and backwashing ability of the mesh were explored by oil–water separation experiments. It was found that when the molar fraction of 11-mercaptoundecanoic acid and 1-decanethiol in the mixed mercaptan was 2:3, the water contact angle of the surface at this point was 156.5 ± 1°, with pH response characteristics and good oil–water separation efficiency, backwashing and recycling capabilities.

Superhydrophobic Coatings Composed of Multifunctional Polymers Synthesized Using Successive Modification of Dihydropyrimidin-2(1H)-thione.

Polymer synthesis via multicomponent reactions (MCRs) has opened avenues in polymer chemistry and led to the development of various types of functional polymers. Herein, we developed a strategy to prepare multifunctional polymers via the successive modification of dihydropyrimidin-2(1H)-thione (DHPMT), which can be generated by the tricomponent Biginelli reaction. Four hydrophobic polymers were efficiently prepared by using DHPMT derivatives. These polymers can be dip-coated onto the oxidized copper mesh to obtain superhydrophobic meshes because of the strong attractive forces between the DHPMT derivatives and Cu(II). The optimized mesh has self-cleaning properties and outstanding stability in various liquid environments; it has also been successfully applied for oil/water separation with high separation efficiency and good durability. These results demonstrate that successive modification of DHPMT is a promising method for fabricating multifunctional polymers, which may have applications in polymer chemistry and materials science.

Facile electrodeposition of corrosion-resistant superhydrophobic Ni-plated stainless-steel mesh for oil–water separation

A simple constant-potential electrodeposition process was used to manufacture a superhydrophobic Ni-plated stainless-steel mesh (SNSSM) with high corrosion resistance and chemical stability for oil–water separation. This novel Ni plating had a mountain-like micro/nano structure. This resulted in a rough surface that was modified with stearic acid (SA) to provide a good superhydrophobicity as well as remarkable corrosion resistance, chemical stability, and oil–water separation. The effects of the electrodeposition potential and time on the microstructural evolution, wettability, and corrosion resistance were discussed. The SNSSM obtained by deposition at − 2.0 V for 60 min and modifying the surface with SA, had a water contact angle (WCA) of 156.5° and an oil contact angle (OCA) of 0°. The corrosion current density of the superhydrophobic coating in a 3.5 wt% NaCl solution was 1.737 × 10−8 A/cm2. The plating remained superhydrophobic after 96 h of immersion in the NaCl solution and maintained its superhydrophobicity in an environment with pH= 2–12. The SNSSM exhibited high separation efficiency and separation flux for mixtures of oil or organic solvents with water. In addition, it continued to exhibit a separation efficiency > 94.0% and stable reusability even after 30 cycles of separation.

Photoswitchable and reusable superhydrophobic/hydrophilic TiO2-coated stainless-steel mesh as oil–water separator

This study fabricated a superhydrophobic/hydrophilic stainless-steel mesh with a TiO2-coated surface for efficient oil–water separation. The mesh manifested both hydrophobic and hydrophilic properties upon incorporating fluorine- and amine-containing silanes, respectively. The photoswitching speed and recovery of surface properties were evaluated by adjusting the UV irradiation period. Additionally, the mesh was subjected to ultrasonic treatment to enhance the photoswitching speed. After alternating UV irradiation and ultrasonification treatments, the variations in contact angle confirmed the feasibility of reversible surface conversion: 158° → 15° → 149.4° → 9.1° → 146.8° → 8.4° → 147.3°. Furthermore, the oil–water separation efficiency of the fluorine-modified mesh was assessed using water and n-hexane solutions. Over eight cycles, the hydrophobic/hydrophilic mesh achieved an average separation efficiency of 95.3% and 96.7%, respectively. The separation process occurred within approximately 5 s. Thus, this study proposed a comprehensive approach for developing a single superhydrophobic mesh capable of facile and rapid photoswitching between hydrophilic and hydrophobic properties. The developed mesh offers precise filtration, durability, and reusability, contributing to sustainable oil–water separation processes.

Dynamic and Quasi-static Droplet Penetration through Meshes.

We investigate experimentally the effects of pore size, surface wettability, and penetration mode on the characteristics of liquid penetration through meshes. Utilizing the impact of droplets and the hydrostatic pressure, we study water penetration through superhydrophobic, hydrophobic, superhydrophilic, and hydrophilic meshes with different uniform radii and pitch values of the pores. In the case of dynamic penetration enabled by the droplet impact, our results show that surface wettability has a negligible effect on either the threshold speed of the droplet penetration or the penetrating liquid mass. The threshold droplet speed is found to be mainly determined by the synergistic effects of global and local dynamic pressures of the impacting droplet, and a modified expression for the threshold droplet speed is proposed. For the quasi-static penetration based on the applied hydrostatic pressure, we find that surface wettability and pore pitch do not affect the penetration threshold pressure but do affect the pressure at which the liquid penetration ceases. This is due to the fact that under quasi-static conditions, the droplet liquid spreads out and merges with that at the adjacent pores on the mesh underside, affecting the wetted area and, hence, the capillary pressure resisting penetration.

Production of small powder-stabilized droplets using superhydrophobic mesh

Massive production of tiny droplets is critical for industrial processes and biomedical applications. Such droplets are formed by splitting the bulk liquid (top-down) or condensation to grow the droplet (bottom-up). Various generation methods have been reported; however, the generated droplets stick to the contacting substrate and/or coalesce into a larger droplet, limiting handling flexibility and/or size uniformity. Herein, tiny powder-stabilized droplets were massively generated by applying pulse pressure to a “powdered” superhydrophobic mesh on a water pool. The generated droplets were stabilized by a fine hydrophobic powder, namely, liquid marble, which does not coalesce or stick to the contact materials. The effects of mesh size, wettability, powdering, and applied pressure on the droplet formation dynamics were investigated. The generated droplet size depended on the mesh size and droplets were not formed on the hydrophilic mesh. When the superhydrophobic mesh gradually sank into the water pool to apply quasi-static hydro-pressure, the penetrated water did not split, and a continuous large water droplet was formed. However, tapping the superhydrophobic mesh to apply pulsed hydro-pressure induced multiple droplets to split through the mesh penetration. Without powder, the formed droplets coalesced to form large droplets. However, when the superhydrophobic mesh was powdered, the formed droplets were coated with the hydrophobic powder to form a liquid marble, preventing their coalescence.

One-step fabrication of robust liquid-repellent mesh induced by femtosecond laser

Super liquid-repellent surfaces are deemed as an ideal candidate for self-cleaning and liquid separation. However, these surfaces still confront challenges in the aspect of inadequate mechanical durability, environmentally harmful reagents and complex fabrication procedures. Herein, a one-step femtosecond laser ablation process on various porous mesh with PDMS-assisted coverage was conducted. Then, the uniform and hierarchical micro-groove structures were formed on the cylindrical wires during the successive laser pyrolysis, accompanying by the hydrophobic silica deposited inside the micro-groove structures. The whole processing has no chemical solvents and complicated modification, which is of great significance for time-saving and eco-friendly preparation of mesh with super-hydrophobicity. Significantly, the super-hydrophobic mesh can bear 2000 abrasion cycle tests, 400 ℃ heat treatment and violent outdoor robustness tests, verifying its strong mechanical durability and thermal stability. The mechanisms involved in liquid-repellence and abrasion-resistance have been elucidated systematically. Furthermore, self-cleaning and on-demand oil water separation could be accomplished via tailoring the wettability of the mesh according to the oxygen plasma treatment and re-heating. The unique advantages of the as-prepared porous mesh provide feasibilities for wettability-oriented application such as protective surface with self-cleaning ability, multitasking immiscible liquid separation.

Fabrication of robust superhydrophobic–superoleophilic mesh for oil–water separation

Frequent oil spillage at sea and waste oily water draining cause severe harm to the environment and economy. Although various extremely wettable materials are designed to achieve oil–water separation, there are still limitations, such as expensive materials, fluorine-containing reagents and poor robustness of oil–water-separating materials. Here, the authors resolved the aforementioned problems by proposing a simple and low-cost sandblasting plating method with nickel (Ni), phosphorus (P) and 1-octadecanethiol modification to manufacture a robust superhydrophobic stainless steel mesh for separating oily water under harsh environments. The mesh can separate light and heavy oily water with outstanding separating efficiency and high purity. It can be also used to separate hydrochloric acid (HCl) solution–oil, sodium hydroxide (NaOH) solution–oil and sodium chloride (NaCl) solution–oil, with separating efficiency higher than 95%. Moreover, the mesh is still superhydrophobic and has outstanding oil–water-separating efficiency after sandpaper abrasion, tape stripping, simulated seawater corrosion and natural environment corrosion tests. Therefore, the robust superhydrophobic stainless steel mesh proposed in this work can very efficiently separate oily water in harsh environments.

Experimental Investigation on the Droplet Stability of Superhydrophobic Mesh

Superhydrophobic surfaces could repel water due to the capillary force associated with surface roughness, which has a large range of applications, such as underwater drag reduction, heat transfer enhancement, oil/water separation, and so on. However, the engineering applications of superhydrophobic surfaces rely on the stability of the superhydrophobic surfaces. In this study, a hydrophilic metal mesh was modified to be superhydrophobic. The resulting superhydrophobic mesh was designed as a bowl capable of holding water without leaking and as a boat floating on top of water without sinking. The stability of an impacting droplet on a superhydrophobic mesh was investigated using both experiments and theoretical analysis. It was demonstrated that the capillary force is able to prevent water from passing through the mesh and maintain the stability of the air–water interface under dynamic pressure. Furthermore, a theoretical model was developed to diagnose the stability of the air–water interface on the superhydrophobic mesh when in contact with water, and the results are consistent with the experimental findings. The results of this work can be utilized to design robust superhydrophobic meshes and advance the field of droplet manipulation.

Selective and Continuous Oil Removal from Oil-Water Mixtures Using a Superhydrophobic and Superoleophilic Stainless Steel Mesh Tube.

The development of continuous oil-water separation processes has applications in the treatment of industrial oily wastewater and effective management of oil spills. In this research, the performance of a superhydrophobic-superoleophilic (SHSO) membrane in oil-water separation is investigated through dynamic tests. We investigate the effects of the total flow rate and oil concentration on the separation efficiency using an as-fabricated SHSO mesh tube. To construct the SHSO membrane, a tubular stainless steel mesh is dip-coated into a solution, containing a long-chain alkyl silane (Dynasylan F8261) and functionalized silica nanoparticles (AEROSIL R812). The as-prepared SHSO mesh tube illustrates a water contact angle of 164° and an oil contact angle of zero for hexane. A maximum oil separation efficiency (SE) of 97% is obtained when the inlet oil-water mixture has the lowest flow rate (5 mL/min) with an oil concentration of 10 vol %, while the minimum oil SE (86%) is achieved for the scenario with the highest total flow rate (e.g., 15 mL/min) and the highest oil concentration (e.g., 50 vol %). The water SE of about 100% in the tests indicates that the water separation is not affected by the total flow rate and oil concentration, due to the superhydrophobic state of the fabricated mesh. The clear color of water and oil output streams also reveals the high SE of both phases in dynamic tests. The outlet oil flux increases from 314 to 790 (L/m2·h) by increasing the oil permeate flow rate from 0.5 to 7.5 (mL/min). The linear behavior of the cumulative amounts of collected oil and water with time demonstrates the high separation performance of a single SHSO mesh, implying no pore blocking during dynamic tests. The significant oil SE (97%) of the fabricated SHSO membrane with robust chemical stability shows its promising potential for industrial-scale oil-water separation applications.

Fabrication of super-hydrophobic copper mesh by liquid oxidation and vapor silylation

Super-hydrophobic copper mesh was fabricated by liquid oxidation using K2S2O8 as oxidant and followed by vapor silylation with hexamethyldisilazane (HMDS). The preparation process was optimized with respect to four factors. The samples were characterized by Water Contact Angle (CA), XRD, FTIR, respectively as well as evaluated by oil-water separation test. The obtained optimum preparation condition is a K2S2O8 concentration of 0.145 mol·L-1 , a oxidation time of 60 min, a calcaination temperature of 300 °C and a silylation temperature of 190 °C, under which the highest CA can achieve 154°. XRD and FTIR characterizations demonstrate the reaction result of the oxidation of CM to form OCM and of the silylation of OCM to form SOCM, respectively. CM, OCM and SOCM are shown to be low hydrophobicity, hydrophilicity and high hydrophobicity (CA = 154°), respectively. Three samples possess a oil-water (methylbenzene-water) separation ratio of 45.6%, 3.3% and 99.9%, respectively. The reusing experiments for methylbenzene, chloroform and kerosene indicate that SOCM can be utilized for 30 cycles and retains an oil-water separation efficiency of at least 98% for any one oil. It suggests that SOCM has an excellent hydrophobicity, which results from the vapor silylation as a vesatile method for modifying the copper mesh.

Simple anodic oxidation method for the preparation of superhydrophobic stainless-steel mesh for oil-water separation

Nowadays, all kinds of oil products have become an important pillar of human economic development. The generation and leakage of oily wastewater in the process of oil collection, processing and transportation will have a bad impact on human and nature. Oil-water separation has become a research hotspot. Materials with special wettability have attracted great attention. In this work, 316L stainless-steel mesh with micro-nano composite structure on the surface was obtained by a simple anodic oxidation method. After perfluorooctanoic acid modification, superhydrophobicity was obtained, which showed reverse affinity to oil and water, and could realize the separation and collection of oil in oil-water mixture. The separation efficiency of various oils was above 95 %. After 15 separation cycles for N-hexane and water mixture, the separation efficiency was still above 96 %. The simple anodic oxidation method can complete the construction of micro-nano composite structure of 316L stainless-steel mesh within 5 min, which has high preparation efficiency, and the superhydrophobic stainless-steel mesh can also be reused.

Application of Superhydrophobic Mesh Coated by PDMS/TiO2 Nanocomposites for Oil/Water Separation.

Superhydrophobic materials have recently attracted great interest from both academia and industry due to their promising applications in self-cleaning, oil-water separation, etc. Here, we developed a facile method to prepare hybrid PDMS/TiO2 fiber for superhydrophobic coatings. TiO2 could be uniformly distributed into PDMS, forming a hierarchical micro/nano structure on the surface of the substrate. The contact angle of the superhydrophobic coating could reach as high as 155°. The superhydrophobic coating possessed good self-cleaning performance, corrosion resistance, and durability. It was found that gravity-driven oil-water separation was achieved using stainless steel mesh coated with the PDMS/TiO2 coating. More importantly, the coated filter paper could not only separate oil and pure water but also corrosive solutions, including the salt, acid, and alkali solution.

Facile fabrication of superhydrophobic porous materials using the water-based aza-Michael reaction for high-efficiency oil-water separation

Superhydrophobic porous materials are widely used in oil-water separation due to their water-blocking and oil-passing properties. However, the preparation of most superhydrophobic porous materials is generally energy-intensive and must be performed using organic solvents. In this study, we describe a straightforward and cost-effective strategy for fabricating superhydrophobic coatings on nanosized soil particle-modified stainless steel mesh (SSM). The coating is prepared via the aza-Michael reaction of stearyl acrylate and melamine-urea–formaldehyde (MUF) resin catalysed by methyl cyclodextrin in water. Superhydrophobic meshes with water contact angles (WCAs) exceeding 150° are obtained, exhibiting extraordinary water repellency. The superhydrophobic mesh also effectively prevents surface contamination, creating a self-cleaning surface that is both waterproof and dustproof. Most importantly, the superhydrophobic mesh presents excellent oil separation performance for oil-water mixtures of various compositions, maintaining extremely high separation efficiency (>98%) even after 80 cycles. Additionally, we successfully apply this strategy to the preparation of superhydrophobic melamine sponges with excellent oil adsorption capacity (17.6–44.2 g/g). This innovative study provides an effective strategy for designing biomimetic superhydrophobic surfaces and is a promising development in the field of environmentally friendly oil-water separators.

Multifunctional superhydrophobic copper mesh for efficient oil/water separation and fog collection

Exploration of functional materials for use in water treatment is one global requirement for protecting life and the environment. However, the state-of-the-art the materials used in oil/water separation and water harvesting still face challenges such as complicated processing steps, poor microstructure controllability and small-scale preparation. Here, a novel wire electrical discharge machining (WEDM) strategy is introduced to fabricate a functional copper mesh by cross machining both sides of the substrate, followed by a one-step low surface energy modification. The WEDM process makes the three-dimensional micro-nano structures can be well protected, and the low energy modification renders the surfaces superhydrophobic. The surfaces with micro-nano structures exhibited excellent superhydrophobicity (WCA≈158.8° and RA≈2°) and high durability towards mechanical abrasion (>100 cycles) and ultraviolet irradiation (>152° for 24 h). For various light/heavy oil/water mixtures, the separation efficiency of the meshes reached 98.1%, and the oil flux could reach 128.5 kL /(mm2·h). The superhydrophobic mesh could realize a highly efficient fog collection [12.0 L/(m2·h)], which was 390% and 830% higher than those treated by WEDM and the untreated copper plates, respectively. Therefore, we expect that the multifunctional superhydrophobic meshes may serve as a promising candidate for alleviating the water pollution and shortage.

Facile approach to fabricate a high-performance superhydrophobic PS/OTS modified SS mesh for oil-water separation

Special wetting materials have been used for the oil and water separation due to their different interfacial attraction of oil and water. Herein, we successfully fabricated superhydrophobic coatings on stainless steel (SS) mesh by depositing successive layers of polystyrene (PS) and octadecyltrichlorosilane (OTS) through the dip-coating method. The as-prepared coating showed a water contact angle (WCA) of 157.5 ± 2°, a rolling angle of 6 ± 2° and an oil contact angle (OCA) of around 0°. The surface microstructure analysis of the coating revealed a regular pattern of microscale bumps with nanoscale folds on it, both of which improve the overall superhydrophobicity of the surface. The capacity of coatings to separate oil and water was examined by employing a variety of mixtures of oil and water, including petrol, diesel, kerosene, vegetable oil, and coconut oil. In case of low viscosity oil, the coated mesh demonstrated separation effectiveness of more than 97% and on the other hand, high viscosity oil demonstrated just 89% efficiency. Low viscosity oils showed a greater permeation flux through the mesh than extremely viscous oil. The mechanical strength of the coating was examined using bending, twisting, adhesive tape testing, sandpaper abrasion tests, and the findings indicated that coated mesh had exceptional mechanical resilience. In addition, the developed superhydrophobic mesh demonstrated excellent thermal stability and self-cleaning properties. Therefore, this superhydrophobic/superoleophilic mesh has a significant deal of application potential in practical.

Fabrication of epoxy/SiO2/ZnO superhydrophobic nanocomposite mesh membranes for oil-water separation: Correlating oil flux to fabrication parameters via Box-Behnken design

Superhydrophobic nanocomposite mesh membranes were constructed by facile scalable spray deposition method without using low surface energy modifiers for oil-water separation. The Box-Behnken design was applied to study the influence of the main fabrication parameters consisting of spray solution concentration (g.L−1), the mass ratio of SiO2:ZnO (wt%), and the mass ratio of epoxy resin to the total nanoparticles (wt%) on the permeation flux of mesh membranes. The results indicated that increasing the concentration of spray solution led to a decrease in the oil flux due to increasing the coating thickness. The permeation flux first decreased with an increase in the weight percentage of epoxy resin in the spray solution because of the formation of the high density of SiO2/ ZnO coating and then slowly increased due to decreasing coating thickness. The best performance of chloroform flux of 18.3E+03 L/m2.h and separation efficiency of >97% corresponded to the fabricated mesh membrane with 80 wt% of SiO2 to ZnO, 33.33 wt% of epoxy resin to total nanoparticles, and 30 g.L−1 of spray solution concentration. This mesh membrane exhibited superior superhydrophobic properties, outstanding chemical resistance, and excellent mechanical durability. The coated mesh displayed good icephobic characteristics with low ice adhesion.

Fabrication of Superhydrophobic Copper via Chemical Etching and Modification

Biological superhydrophobic surfaces are relatively common in nature. Inspired by the superhydrophobic feature, plentiful materials with hydrophobic surfaces have been fabricated for various purposes such as anti-corrosion, anti-icing, self-cleaning, friction reduction, and oil-water separation. In the present work, we report a scalable, simple, and rapid method to fabricate superhydrophobic film on copper substrates via a simple route including a chemical etching step in sodium persulfate and sodium hydroxide solution and followed by a modification step in stearic acid solution. The effect of the etchants concentration as well as etching time was investigated exhaustively. From the obtained results it was found that when a copper plate was etched in an etching solution with low etchant concentration, the contact angle of copper was greatly influenced by etching time. In contrast, the etching time hardly affected the contact angle of the copper plate at the high concentration of the etchants. The superhydrophobic feature of the copper surface (with a contact angle larger than 150o) was only achieved in certain fabrication conditions. The superhydrophobic copper substrates demonstrated good anti-corrosion properties. The corrosion current density of superhydrophobic copper substrates was 85 times smaller than that of pristine ones when manufactured under optimal conditions. In addition, the as-prepared superhydrophobic copper mesh was used to successfully separate toluene from its aqueous mixture. The superhydrophobic copper has great potential for applications in oil-water separation and anti-corrosion in aqueous environments.

Robust Superhydrophobic Brass Mesh with Electrodeposited Hydroxyapatite Coating for Versatile Applications.

A robust superhydrophobic brass mesh was fabricated based on a low-energy surface and a roughness on the nano/micro-meter scale. It was carried out by the forming of hydroxyapatite (HP) coatings on its surface through a constant current electro-deposition process, followed by immersion in fluoroalkylsilane solution. Surface morphology, composition and wetting behavior were investigated by field-emission scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high speed camera, and contact angle goniometer. Under optimal conditions, the resulting brass mesh exhibited superhydrophobicity, excellent anti-corrosion (η = 91.2%), and anti-scaling properties. While the surfactant liquid droplets of tetradecyl trimethyl ammonium bromide (TTAB) with different concentration were dropped on the superhydrophobic surface, maximum droplet rebounding heights and different contact angles (CAs) were observed and measured from side-view imaging. The plots of surfactant-concentration−maximum bounding height/CA were constructed to determine its critical-micelle-concentration (CMC) value. Close CMC results of 1.91 and 2.32 mM based on the determination of maximum rebounding height and CAs were obtained. Compared with its theoretical value of 2.1 mM, the relative errors are 9% and 10%, respectively. This indicated that the novel application based on the maximum rebounding height could be an alternative approach for the CMC determination of other surfactants.

Fabrication of Durable Superhydrophobic Stainless Steel Mesh with Nano/Micro Flower-Like Morphologies for Self-Cleaning and Efficient Oil/Water Separation

How to fabricate durable superhydrophobic materials for cyclic oil/water separation to solve oil-induced pollutions is still a problem. Herein, we fabricated a durable Superhydrophobic Stainless Steel Mesh (SH-SSM) with nano/micro flower-like sheets by self-assembly of zinc stearate for the cyclic separation of various oil/water mixtures. The SH-SSM exhibits durable superhydrophobicity against static or dynamic treatments. In virtue of durable superhydrophobicity of the SH-SSM, the dusts on surface of SH-SSM can be removed completely by running water immediately showing excellent self-cleaning performance. Moreover, the SH-SSM can be used to perform gravity-driven separation of heavy oil/water and light oil/water mixtures by utilizing its superhydrophobicity that oil phase penetrates the mesh and water phase is restricted. Separation efficiencies of the SH-SSM can reach 99.99%. After 20 cycles of separation, the separation efficiencies for are > 97.00% and > 98.25% for heavy oil/water and light oil/water mixtures, respectively. Flux values of dichloromethane, hexane and petroleum ether are 2.5 × 105 L m−2 h−1, 1.7 × 105 L m−2 h−1, and 1.8 × 105 L m−2 h−1, respectively. This study proposes a facial approach to prepare durable superhydrophobic and self-cleaning material for cyclic and fast separation of oil/water.