Superwetting Properties Research Articles

A facile strategy for fabricating robust superhydrophobic and superoleophilic metal mesh via diazonium chemistry

A facile and friendly one-step in situ polymerization technique is proposed for preparing robust superhydrophobic and superoleophilic metal mesh with hierarchical-layered micro/nano structures via diazonium chemistry at room temperature. The superhydrophobic and superoleophilic metal mesh possesses good resistant to harsh environmental conditions, such as salt, alkali, acid, mechanical abrasion and tape-peeling. The water contact angles of the superhydrophobic surface still maintained above 155° and the sliding angles are below 8° after 10 cycles of abrasion test or 50 cycles of tape-pelling test, and the oil contact angles are 0° all the time. Due to the superwetting properties, the fabricated metal mesh could be used for self-cleaning, oil-in-water emulsion separation and high efficiency oil/water separation, and the gravity-driven separation efficiency and infiltrate flux are up to 98.2% and 25.3 k L m −2 h −1 , which can be repeated for at least 10 cycles, respectively. Therefore, the metal mesh modified with hydrophobic radicals by in situ polymerization exhibited excellent self-cleaning, high-flux oil/water separation, outstanding recyclability, chemical resistant, and mechanical durability. This facile technique via diazonium chemistry to graft the substrate possesses promising practical applications on various metal-based substrates. • A robust superhydrophobic and superoleophilic metal mesh was prepared by one-step in situ polymerization technique. • This system is suitable for multiple electron-rich substrates via diazonium chemistry. • The modified metal mesh exhibits outstanding recyclability and mechanical durability. • The modified metal mesh shows excellent self-cleaning and high-flux oil/water separation.

Molecular grafting and zwitterionization based antifouling and underwater superoleophobic PVDF membranes for oil/water separation

Effective surface modification strategies are at the core of developing efficient and antifouling membranes for a range of separation, purification, and wastewater treatment applications. The inherently hydrophobic nature of most polymeric membranes is one of the primary factors for their high fouling susceptibility. In this work, we have designed a simple and straightforward membrane modification methodology utilizing the reactive nature of polydopamine to molecularly graft short chain amino alkanes followed by zwitterionization using 1,3-propanesultone. The prepared membranes demonstrated superhydrophilicity accompanied with underwater superoleophobicity originating from the hydrophilic nature of polydopamine, aminoalkanes, and strong hydration due to zwitterionic functionality. The surface chemistry, nanostructuring, and surface roughness play an essential role in delivering required properties in the membranes. The prepared membranes showed ultrahigh BSA protein resistance and low oil droplets adhesion. The functionalized membranes showed a manifold boost in permeability for pure water and BSA solution, and separation of oil-water emulsion at high permeation rates. The antifouling nature of the membranes helped in maintaining the permeation behavior for multiple cycles with >96% flux recovery after ten consecutive cycles and excellent rejection in oil-water emulsion separation (>98%). The superwetting properties, along with high permeation, rejection, and antifouling properties, make these membranes a potential candidate for oily water separation and demonstrate the effectiveness of simple molecular level grafting and functionalization as a straightforward method for membrane modifications.

Nanostructural Manipulation of Polyphenol Coatings for Superwetting Membrane Surfaces

Functional coatings have gained significant attention in multiple environmental and energy-related research fields. One of the coatings with superwetting surfaces has received significant interest, owing to the favorable properties like self-cleaning and antifouling as well as the roles it plays in processes of water harvesting and oil–water separation. Hydrophilic polyphenol molecules show good adhesion to different substrates and provide multiple interactive sites, which serve as building blocks for the preparation of superwetting coatings. In this study, to realize the controlled formation of a polyphenol-based coating and to demonstrate the nanostructural dependence of its superwetting performance, tannic acid (TA) complexed with cations was employed to construct coating networks with either nanorough or nanosmooth surface morphology through a layer-by-layer (LbL) self-assembly method. Both nanostructures could be precisely controlled by adjusting the TA concentration and number of LbL cycles to observe the evolution of the wetting state of the coating. More importantly, while the nanosmooth and nanorough coatings exhibited similar surface chemistry, pore sizes, and superwetting properties, the separation efficiency for oil-in-water emulsions using the membrane with the nanorough coating is 2–5 and 2–10 times that of the one with a nanosmooth coating and the pristine one without a coating, respectively. The experimental results confirmed that the nanorough coating structure contributed to the superwetting state of the membrane surface and, therefore, possessed a stronger ability to repel oil than the nanosmooth coating during the separation process. This work demonstrates a novel strategy for the molecular self-assembly of polyphenols and may provide guidance for designing superwetting coatings.

MoS2/CuS nanosheets coated on brass mesh with switchable superwettability for efficient immiscible organic solvent/water separation

MoS2/CuS nanosheets coated on brass mesh with switchable superwettability have been prepared through a facile hydrothermal method. The MoS2/CuS coated mesh shows excellent underwater superlyophobicity and underliquid superhydrophobicity for gravity-driven immiscible organic solvent/water mixtures separation. Switchable permeation function of water-removing or organic solvent-removing can be achieved by water or organic solvent pre-wetted mesh. After 20 cycles of organic solvent/water separation, the MoS2/CuS coated mesh demonstrates high separation efficiency above 99.5% for both of cyclohexane/water mixture and tetrachloroethylene/water mixture. The MoS2/CuS coated mesh presents satisfactory chemical stability under acidic or alkaline conditions in the pH range of 1–13. The switchable superwetting property and chemical stability make it possible to be a potential candidate in separation of immiscible organic solvent/water mixture.

Flexible and robust polyimide membranes with adjustable surface structure and hierarchical pore distribution for oil/water emulsion and heavy oil separation

Highly porous membranes with super-wetting property have been widely researched for oil/water separation. However, most membranes can only be used for a single type of oil-water mixture or emulsion due to their fixed microstructure. Experimental fabrication of multifunctional membranes for efficient separation of various oily wastewater and heavy oil is still a challenge. Herein, flexible and super-hydrophobic polyimide membranes modified by MCNTs and fluorosilane (MCNTs/FPIMs) are innovatively fabricated with adjustable surface structure and hierarchical pore distribution by a versatile and simple phase inversion strategy. Surface corrosion is adapted to adjust the surface pore size by using triethylamine to dissolve the surface dense layer, which aims to construct rough surfaces and effectively increases the oil/water separation performance. The results demonstrate that the hierarchical pore distribution can achieve both high oil/water selectivity and high separation efficiency. The as-prepared FPIMs can realize the rapid gravity-driven separation of light oil (~ 69510 L h-1·m-2), oil/water emulsion (~ 895 L h-1·m-2), and heavy oil (~ 195 L h-1·m-2) by adjusting the surface structure and pore size distribution. The flexible and robust FPIMs with adjustable surface structure exhibit highly efficient oil/water separation performance and reusability, which makes them promising application in practical oil spills and wastewater purification.

Design of Aligned Porous Carbon Films with Single-Atom Co-N-C Sites for High-Current-Density Hydrogen Generation.

Metal- and nitrogen-doped carbon (M-N-C) materials as a unique class of single-atom catalysts (SACs) have increasingly attracted attention as the replacement of platinum for the hydrogen evolution reaction (HER); however, their employment as HER electrodes at high current densities of industrial level remains a grand challenge. Herein, an aligned porous carbon film embedded with single-atom Co-N-C sites of exceptional activity and stability at high current densities is designed. Within the film, the atomic CoNx moieties exhibit high intrinsic activity, while the multiscale porosity of the carbon frameworks with vertically aligned microchannels afford facilitated mass transfer under the conditions of high production rate and ultrathick electrodes. Moreover, the superwetting properties of the film promote electrolyte wetting and ensure the timely removal of the evolving H2 gas bubbles. The as-designed film can work as an efficient HER electrode to deliver 500 and 1000mA cm-2 in acid at overpotentials of 272 and 343mV, respectively, and can operate uninterruptedly and stably at 1000mA cm-2 for at least 32 h under static conditions. These findings pave the road toward the rational design of SACs with improved activity and stability at high current densities in gas-evolving electrocatalytic processes.

Fabrication of durable super-hydrophilic/underwater super-oleophobic poly(arylene ether nitrile) composite membrane via biomimetic co-deposition for multi-component oily wastewater separation in harsh environments

The polymer membranes with super-wetting surface have shown promising application for oily wastewater treatment. However, the synergistic separation of multi-component oily wastewater in harsh environments is still a big challenge. In this work, we demonstrated a facile strategy to construct the durable super-hydrophilic/underwater super-oleophobic PEN composite membrane for the synergistic treatment of oil-in-water emulsions and dye. First of all, based on the thermally stable carboxyl poly (aryl ether nitrile), the hydrophilic polymer membrane with rough trench surface was prepared by non-solvent phase conversion, using non-woven fabric (NWF) as template. Secondly, the TiO2 nanoparticles were firmly immobilized onto the membrane surface via biomimetic co-deposition of dopamine (DA), aminopropyltriethoxysilane (APTES), and TiO2 nanoparticles. Especially, the physical confinement effect of rough trench surface, strong adhesion of polydopamine, and chemical crosslinking between APTES and DA contributed to the stable super-wetting performance of composite membrane (CA: 0° and UOC: 151°). Meanwhile, the obtained super-wetting composite membrane exhibited promising synergistic separation performance of multi-component oily wastewater (oil-in-water emulsions and dye). For the separation of oil-in-water emulsions containing 50 ppm methylene blue, the flux and rejection ratio reached 552.25 ± 25 L/(m2 h) and 99.38 ± 1.3%, respectively. More importantly, the prepared composite membrane could keep stable super-wetting property and separation efficiency under high-temperature and corrosive environments (80 °C/4 M HCl and 80 °C/1 M NaOH). In addition, the low oil adhesion and high tensile strength endowed the composite membrane with high antifouling resistance and excellent recyclability for the separation of multi-component oily wastewater. This work provides an alternative platform for constructing durable super-wetting composite membrane, which shows the potential application for treating complicated oily wastewater of petro-chemistry industry in harsh environments.

Super-wetting properties of functionalized fluorinated graphene and its application in oil–water and emulsion separation

Superhydrophobic–superoleophilic dithiocarbamate-functionalized fluorinated graphene injected PDMS sponges displaying selective oil/organics sorption from oil–water mixtures and emulsion separation.

Sustained graphene oxide coated superhydrophilicity and superwetting using humidity control

The use of superhydrophilic surfaces for superwetting applications can be hampered by their wetting degradation over time. In this work, superhydrophilic surfaces were fabricated by graphene oxide (GO) deposition on roughened polyvinyl chloride (PVC) substrates. These surfaces were found to exhibit zero contact angle when enhanced green fluorescent protein (EGFP) was deposited on the surface immediately after GO was applied. However, when the GO-coated substrate was stored for 3 h, the surface displayed a contact angle of 54°. The main contact line spreading of the EGFP drop was more easily discernible using normal (500 lx, low glare and shadow free) lighting than with blue LED lighting in the dark. The average radius of the spreading main contact line was found to follow a power-law relationship that increased at a faster rate with higher relative humidity. Confocal imaging revealed rings of EGFP deposition following superwetting that is attributable to pinning around the islands of GO accumulation. Substrate superhydrophilic and superwetting properties can be preserved by adequate control of relative humidity. Relative humidity of 80 % was easily maintained for 150 min by incorporating a 20 μL water drop in a sealed 240-mL container.

Functionalized porous filtration media for gravity-driven filtration: Reviewing a new emerging approach for oil and water emulsions separation

Oil and water separation technology has been continuously progressing throughout the years. Recently, gravity-assisted filtration has gained considerable attention, although most of the studies have focused on oil and water synthetic mixtures which can be easily separated under gravity. It is deemed challenging for mechanically and chemically stabilized emulsions to be separated without the addition of an external pressure other than static gravity head. For this to be realized, filtration media should have high porosity to attain high flux but controlled pore size to achieve high selectivity. Moreover, in order to break down the emulsion, the surfaces of the filtration media should be endowed with superwetting properties. In this paper, different porous filtration media (metallic meshes, organic membranes, inorganic membranes, filter paper, and 3D materials) and the corresponding modification techniques and/or functionalization strategies utilized to improve their properties for efficient gravity-driven filtration applications are comprehensively reviewed.

Superwetting TiO2-decorated single-walled carbon nanotube composite membrane for highly efficient oil-in-water emulsion separation

With the advantages of one-dimensional hollow structure, high porosity and prominent mechanical strength, single-walled carbon nanotubes (SWCNTs) have been extensively utilized to improve conventional filtration membranes for oil/water separation. Their intrinsic hydrophobicity, however, adversely affects the anti-fouling performance of the SWCNT membrane. Herein, a super-hydrophilic and underwater super-oleophobic hierarchical modified membrane with enhanced permeability and anti-fouling property was fabricated using the vacuum-assisted filtration technique by synergistically assembling SWCNTs and titanium dioxide (TiO2) nanoparticles on a cellulose acetate membrane. Highly dispersed SWCNTs were obtained by carboxylating treatment of agglomerate SWCNTs. The controlled stacking of SWCNTs fibers and a controllable amount of TiO2 rendered a modified membrane with high porosity and hierarchical structure, leading to an ultrahigh water flux up to 4,777.07 L·m−2·h−1, and excellent separation performance with efficiency greater than 99.47%. Most importantly, the membrane exhibited excellent anti-fouling ability during ten cycles with the aid of the super-wetting property of TiO2 nanoparticles. The results indicated that coating TiO2 nanoparticles on SWCNTs modified the surface topography of the obtained SWCNT/TiO2 membrane, which improved hydrophilicity, permeability and anti-fouling property, manifesting attractive potential applications in oil/water separation.

Robust Bifunctional Compressed Carbon Foam for Highly Effective Oil/Water Emulsion Separation.

In this study, we report the pure compressed carbon foam (CCF) that offers a brand-new solution for separating emulsified oil/water mixtures. The CCF was fabricated by low-temperature carbonization of three-dimensional commercial melamine foam, which was then compressed without any further chemical modification. The CCF has amphiphilicity in air, underwater superoleophobicity, and underoil superhydrophobicity; therefore, it has been proved to be successfully utilized in highly emulsified oil-in-water and water-in-oil emulsions with excellent separation efficiencies, and it merely relies on gravity in the absence of external force. The CCF can also maintain its superwetting property under different harsh conditions, including strong acid, alkali, and salt solution conditions; this property offers great opportunities for widespread applications. Importantly, the CCF exhibits excellent permeability, separation efficiency, antifouling, and reusability performance. This novel CCF material has great potential application in handling oily wastewater owing to its low-cost raw materials, easily scaled-up preparation process, excellent antifouling property, and high separation capacity of materials.

A CVD-Assisted Modification Approach for Preparing a Dual Superlyophobic Fabric with In-Air Superhydrophobicity and Underwater Superoleophobicity.

Superhydrophobicity and underwater superoleophobicity demonstrate mutual advantages in various water-related interfacial applications. However, achieving such two opposite superwetting states on a single one-fabric surface without introducing any continuous external stimulus remains a great challenge. In this work, a chemical vapor deposition (CVD) modification methodology for achieving superhydrophobicity and underwater superoleophobicity on a single one-fabric surface is presented. The CVD methodology plays a crucial role in realizing such unusual superwetting properties that can be achieved through a moderate synergetic effect from hydrophobic and hydrophilic components in surface chemistry. Driven only by gravity, the as-prepared fabric with reasonable resistance to repeatable laundering cycles and long-time corrosive liquid submersion can be further applied in high-efficiency on-demand oil-water separation.

Organosilicate compound filler to increase the mechanical strength of superhydrophilic layer-by-layer assembled film

Technologies that can overcome the poor mechanical properties of the coatings with bacterial anti-adhesion effect based on super-wetting properties are still challenging. In this study, we developed a durable superhydrophilic nanocomposite coatings composed of polysaccharide matrix and organosilicate (OS) compound filler. In brief, carboxymethylcellulose (CMC) and chitosan (CS)-based multilayer films were fabricated via Layer-by-layer (LbL) assembly then crosslinking for the films was performed to improve inner stability and induce superhydrophilicity. As second step, we synthesized a biocompatible and robust organosilicate compound via sol-gel reaction and incorporate it as reinforcing filler into the superhydrophilic films. Consequently, durable hybrid superhydrophilic nanocomposites were coated on the substrate, and various chemical analysis and performance evaluations of the coatings were performed. The mechanical properties of the composite coatings were significantly improved due to the OS acting as a reinforcing filler in the multilayer films. Furthermore, the coatings exhibited excellent biocompatibility and transparency and exerted antibacterial effect based on superhydrophilic property. This study presents a practical strategy to solve the poor durability, the limitation of super-wetting coatings widely applied in various fields.

Ag@TiO2NPs/PU composite fabric with special wettability for separating various water-oil emulsions.

In the present study, Ag@TiO2 nanoparticles (NPs) were successfully synthesized by a hydrothermal method. Then the fabric (treated by dielectric barrier discharge (DBD) plasma and alkali desizing) was sprayed by solutions of polyurethane (PU) adhesive and as-prepared Ag@TiO2NPs in sequence for constructing a robust multi-level structure. Afterwards, the durable superhydrophilic and underwater superoleophobic coatings were obtained on the fabric surface. With further octadecyl trichlorosilane (OTS) modification, the wetting behaviour of the coating was transferred to superhydrophobicity and superoleophilicity. Observations showed that both cotton fabrics exhibited excellent superwetting properties and antimicrobial activities even after experiencing repeated rinsing by water or oil, abrasion with the original cotton fabric or sand paper, and in chemical stability tests in a base and acid, etc. Moreover, the two types of Ag@TiO2NPs/PU composite fabrics could successfully serve as filtering membranes for the fine reclamation of water or oil from their emulsion mixtures, which demonstrated high selectivity and efficiency, offering the theoretical foundation to extend the range of practical applications for textiles.

One-Step Transformation of Metal Meshes to Robust Superhydrophobic and Superoleophilic Meshes for Highly Efficient Oil Spill Cleanup and Oil/Water Separation.

Phytic acid (PA), which is a natural and innoxious plant constituent, can strongly adsorb on the metal surface because of its six phosphate groups. In this work, based on the chelating properties of PA and the reaction between PA and hydrolyzable vinyltriethoxysilane (VTES), we developed a novel and facial strategy to generate hierarchical-layer nanospheres on the metal mesh surface and fabricated robust superhydrophobic and superoleophilic miniature metal mesh ships. Because of their superwetting properties, the modified meshes could easily remove and recycle the oil spills from the water surface (>90% collection efficiency), and have high oil/water separation capacity (>96%). The excellent stability, corrosion resistance, and robust mechanical durability endow the modified mesh ships with more advantages in a marine environment. We envision that these superhydrophobic meshes modified with PA and VTES are sustainable, environmentally friendly, and easy to scale up and hence display great potential in practical application.

Facile and eco-friendly preparation of super-amphiphilic porous polycaprolactone

Super-amphiphilic (highly oleophilic and hydrophilic) materials have attracted tremendous interest for fundamental research and potential applications, owing to their unique affinity for both oil and water. In this work, a novel super-amphiphilic porous polycaprolactone (PCL) was fabricated via an efficient and eco-friendly method, in which stearic acid (SA) was used as both a porogen and a dopant precursor. The porous PCL had an interconnected hierarchical pore structure and was capable of absorbing oil and water rapidly. The complementary cooperation of the oleophilic and hydrophilic domains on the pore surface induced the amphiphilicity, while the capillary forces caused a wicking action. The synergy of the two effects gave rise to the super-wetting property. The special amphiphilic feature of the porous PCL had a positive effect on its biocompatibility and the material can be considered as a promising candidate for tissue engineering applications.

Robust Graphene/Poly(vinyl alcohol) Janus Aerogels with a Hierarchical Architecture for Highly Efficient Switchable Separation of Oil/Water Emulsions.

Given the complexity and diversity of actual oily sewages, developing multifunctional separation materials with features of high separation efficiency and low energy consumption for separating diverse oil/water emulsions is urgently needed, yet it remains a formidable challenge till now. Herein, a superior graphene/poly(vinyl alcohol) Janus aerogel (J-CGPA), showing an intriguing three-dimensional (3D) hierarchical architecture (a dense skin-layer and a larger internal cell network) and desirable asymmetric wettability, was exploited via a simple direct freeze-shaping technique and subsequent mussel-inspired hydrophilic modification. Benefiting from the controlled unilateral decoration of dopamine, the resultant aerogels displayed completely opposite superwettability on two antithetic sides, i.e., one side is highly hydrophobic (water contact angle (WCA), 143°), whereas the other side is superhydrophilic. On the basis of the favorable 3D hierarchical structure and binary cooperative superwetting properties, the Janus aerogels achieved a remarkable switchable separation performance for both highly emulsified oil-in-water and water-in-oil emulsions as well as stratified oil/water mixtures accompanied with outstanding separation efficiencies. Particularly, an ultrahigh permeation flux of 1306 L m-2 h-1 along with a high rejection efficiency of 99.7% was acquired solely under the driving of gravity (<1 kPa), which is 1-2 order of magnitude higher than that of pioneering two-dimensional Janus polymeric/inorganic membranes recently reported. Moreover, together with robust reusability, this novel 3D Janus aerogel indicates a promising practical application for high-performance oily wastewater remediation.

A fully bio-based composite coating with mechanical robustness and dual superlyophobicity for efficient two-way oil/water separation

Recently, two-way oil/water separation materials bearing both “water-removing” and “oil-removing” functions are of great interest for treating environmental water pollution. Despite having switchable surface wettability, these materials are generally designed to possess superhydrophilicity in air, which, standing on the viewpoint of thermodynamics, is unstable and easy to lose the superwetting property. Concerning the full exploitation of sustainable biomass resources, herein, we use soy protein and ramie fiber to fabricate a cross-linked biocomposite whose amphiphilicity can be tuned by introducing a low surface-energy agent, octadecylamine. The resultant composite can be used as a coating for stainless steel meshes, preparing stably hydrophobic surface in air as well as achieving dual superlyophobicity under liquid that is required for efficiently separating light and heavy oils from water. Furthermore, a high separation efficiency is acquired for both light oil/water and heavy oil/water mixtures during cyclicusage. Notably, the fully bio-based coating displays high resistance against mechanical abrasion and harsh chemical corrosions (acid, alkaline, and salt) without losing high separation efficiency, indicating the potential application of such material in oily wastewater treatment.

Thermally and chemically stable poly(arylene ether nitrile)/halloysite nanotubes intercalated graphene oxide nanofibrous composite membranes for highly efficient oil/water emulsion separation in harsh environment

Oil/water emulsion sewage separation in strong corrosive and high-temperature harsh environment is a big challenge for polymer-based filtration membrane system due to the intrinsic defect of polymers. In this work, we demonstrated novel thermally and chemically stable composite membranes consisting of halloysite nanotubes (HNTs) intercalated graphene oxide (GO) coating on porous poly(arylene ether nitrile) (PEN) nanofibrous mat, which were prepared by controlled assembly of HNTs intercalated GO (skin layer) onto the surface of electrospun PEN nanofibrous mats (supporting layer) and further mussel-inspired polydopamine coating. Typically, the micro-/nano-rough structure and hydrophilic property of polydopamine contributed to super-hydrophilic and underwater super-oleophobic nature of composite membranes. Therefore, the resulting composite membranes exhibited high preferable rejection ratio (more than 99.0%) and remarkable antifouling performance for various oil/water emulsions. Furthermore, flexible channel control of skin layer by intercalation of HNTs, porous PEN supporting layer, and super-wetting property endowed the composite membranes with high permeate flux (1130.56 L/m2 h). More importantly, the resulting composite membranes could separate various high-temperature (90 °C), strong corrosive acidic (pH = 1), and basic (pH = 14) oily emulsions with high separation efficiency and excellent reusability, showing promising application for water cleaning and resource recovery.