Superoleophobic Properties Research Articles

Fabrication of Janus cellulose nanocomposite membrane for various water/oil separation and selective one-way transmission

For satisfying various demands of water-oil emulsions separation, a Janus cellulose nanocomposite membrane has been fabricated in this study. Specifically, the cellulose paper with the superhydrophilic and underwater superoleophobic properties served as the substrate, meanwhile the PVDF/hydrophobic-SiO2 nanocomposite were successfully assembled to the top of substrate with the adhesion of PU by the technologies of high pressure spraying and electrostatic spinning for obtaining the superhydrophobic and superoleophilic layer. Under the action of gravity, Janus cellulose nanocomposite membrane effectively separated the water-in-oil emulsions when PVDF/hydrophobic-SiO2 nanocomposite layer (obverse) was on the top, and removed the small oil droplets from its oil-in-water emulsions when the cellulose layer (reverse) was on the top. Notably, the Janus cellulose nanocomposite membrane could complete the selective one-way transmission when the gravity effect was excluded. Moreover, the results of resistance against acid and base, abrasion resistance, filtration efficiency, repeatability, flux, etc. confirmed the remarkable superwetting durability and high selectivity of Janus cellulose nanocomposite membrane towards various emulsions, suggesting its enormous potential in practical water-oil separation.

A method for preparing the pH-responsive superhydrophobic paper with high stability

In this paper, a simple method for preparing high stability superhydrophobic paper with pH-induced wettability transition was proposed. Firstly, the pH-responsive monomer 2- (dimethylamino) ethyl methacrylate (DMAEMA), the silicon-containing crosslinking monomer 3-trimethoxysilyl propyl methacrylate (TSPM) and the fluorine-containing monomer hexafluorobutyl methacrylate (HFMA) were polymerized to prepare the pH-responsive polymer PHFMA-PTSPM-PDMAEMA. Afterwards, the amino-modified SiO2 was grafted onto the polymer to provide roughness and then coated on the paper to prepare the superhydrophobic paper with pH-responsive properties. Further research found that the modified paper prepared by this method not only has strong stability and transparency, but also can realize the reversible regulation of superhydrophobic & lipophilic and super-oleophobic & hydrophilic properties under different pH-induction, and it has important application value in the field of oil-water separation in industrial applications.

3D antifouling hierarchical micro/nanostructures with underwater superoleophobicity via one-step electrodeposition on anode and cathode

Superhydrophilic and underwater superoleophobic materials have demonstrated good application prospects in the oil/water separation. However, their fabrication process may be inefficient and high energy consumption. For this reason, this paper proposes a method for simultaneously deposited hierarchical structures with superhydrophilic and underwater superoleophobic properties on the anode and cathode via one-step electrodeposition. The materials fabricated on both anode and cathode exhibit superior antifouling performance and excellent oil/water separation efficiency (above 96.2% for all five experimental oils) with a considerable permeation flux (4125 ± 67 L m−2 h−1). Moreover, the as-prepared materials maintain excellent oil/water separation efficiency after 20 separation cycles, which are higher than 98.1% and 98.8%, respectively. Besides, the materials can be stored in different concentrations of salt water for 50 days, demonstrating their outstanding corrosion resistance. Our study provides a strategy for the fabrication of superwetting materials, which is expected to promote the development of oil/water separation technology.

Synthesis of Si-Based High-Efficiency and High-Durability Superhydrophilic-Underwater Superoleophobic Membrane of Oil-Water Separation.

Oil pollution is caused by the frequent discharge of contaminated industrial wastewater and accidental oil spills and is a severe environmental and health concern. Therefore, efficient materials and processes for effective oil–water separation are being developed. Herein, SiO2-Na2SiO3-coated stainless steel fibers (SSF) with underwater superoleophobic and low-adhesion properties were successfully prepared via a one-step hydrothermal process. The modified surfaces were characterized with scanning electron microscopy (SEM), and contact angle measurements to observe the surface morphology, confirm the successful incorporation of SiO2, and evaluate the wettability, as well as with X-ray diffraction (XRD). The results revealed that SiO2 nanoparticles were successfully grown on the stainless-steel fiber surface through the facile hydrothermal synthesis, and the formation of sodium silicate was detected with XRD. The SiO2-Na2SiO3-coated SSF surface exhibited superior underwater superoleophobic properties (153–162°), super-hydrophilicity and high separation efficiency for dichloromethane–water, n-hexane–water, tetrachloromethane–water, paroline–water, and hexadecane–water mixtures. In addition, the as-prepared SiO2-Na2SiO3-coated SSF demonstrated superior wear resistance, long-term stability, and re-usability. We suggest that the improved durability may be due to the presence of sodium silicate that enhanced the membrane strength. The SiO2-Na2SiO3-coated SSF also exhibited desirable corrosion resistance in salty and acidic environments; however, further optimization is needed for their use in basic media. The current study presents a novel approach to fabricate high-performance oil–water separation membranes.

Fabrication of superhydrophilic and underwater superoleophobic CuxO/TiO2 mesh for oil–water separation

Superhydrophilic and underwater superoleophobic meshes were fabricated for oil–water separation applications. High purity copper (Cu) meshes were anodized to produce a mixed-phase copper oxide (CuxO) layer. Titanium dioxide (TiO2) films were grown on the CuxO meshes via reactive sputter deposition in an admixture of argon and oxygen plasma followed by heat treatment. The CuxO/TiO2 meshes exhibited superhydrophilicity through the complete wetting of water in air. When the meshes were submerged underwater, the superoleophobic property was revealed using a mineral oil droplet with a contact angle of up to 151°. Separation of mineral oil from water (1:1 v/v) using the CuxO/TiO2 meshes was demonstrated using a custom-built separator. Chemical oxygen demand (COD) concentration measurement of the filtrates showed a decrease from 350 mg O2/L using a Cu mesh only to 84 mg O2/L using the CuxO/TiO2 mesh. Visible-light sensitivity was realized with the coupling of CuxO with TiO2. When the meshes were exposed to simulated solar light, self-cleaning property of the composite was activated. The visible-light irradiation of the used mesh exposed for at least 30 min degraded the residual oil thereby restoring the superhydrophilic property of the surface. The restoration would allow reusability of the CuxO/TiO2 meshes. After visible-light-induced cleaning of the mesh and reusing the mesh with a fresh oil–water sample, the COD of the filtrate was 86 mg O2/L.

Superhydrophobic and superoleophobic property enhancement on guard ring micro-patterned PDMS with simple flame treatment

Effects of new micro-structure design, a flame treatment process, and the addition of semifluorinated silane (SFS) on an improvement of superhydrophobicity and superoleophobicity of PDMS surfaces were investigated in this study. PDMS and PDMS-SFS surfaces with the special design of circular rings and eight stripe supporters (C-RESS) with a hexagonal guard ring (HGR) structure were found to be the most durable which maintained their superhydrophobicity after scratch tests. The flame treatment at 700 °C/15 s formed a unique nanoscale flower-like on the PDMS-SFS surface. A formation of re-entrant micro-structure on the C-RESS with the HGR structure exhibited superhydrophobicity and superoleophobicity with water and ethylene glycol contact angles of 160.5° ± 2.0° and 160.2° ± 6.6°, respectively. The addition of the SFS was found to increase surface roughness and decrease surface energy. In conclusion, the flame-treated C-RESS with the HGR structure on the PDMS-SFS surface is considered one of the promising antifouling approaches in several applications.

One-step in-situ fabrication of carbon nanotube/stainless steel mesh membrane with excellent anti-fouling properties for effective gravity-driven filtration of oil-in-water emulsions

The occurrence of membrane fouling has resulted in limited wastewater treatment applications. The development of superhydrophilic-underwater superoleophobic materials has received significant attention owing to their good anti-fouling properties. However, to fabricate such materials need costly regents and tedious steps. Thus, developing a one-step process to prepare a low-cost material for oil/water separation is still desired. In this study, bio-inspired from an arachnid, inorganic carbon nanotube stainless steel meshes (CNT@SSMs) having superhydrophilic-underwater superoleophobic and excellent anti-fouling properties and a unique fiber structure were fabricated via a one-step thermal chemical vapor deposition method. The CNT@SSMs had a small pore size enabling a high water flux of 10,639 L m−2h−1 and the separation of oily wastewater, including various emulsions, at a high rejection ratio of >98.89%. As a result of its excellent chemical stability under high temperatures, a broad pH range, and saline environments, the CNT@SSM has the potential to be used in extreme conditions. In summary, these CNT@SSMs are easy to fabricate and are low-cost as a result of inexpensive reagents involved. Moreover, these novel superwetting membranes are promising candidates for treatment of hazardous oily wastewater.

Facile fabrication of ultra-robust underwater superoleophobic coating with remarkable self-cleaning performance in harsh environments

Preparation of robust oil-repellant surfaces in aqueous environment with mechanical stability is imperative, yet challenging for the extensive range of real applications where high durability is required. We report the robust underwater superoleophobic properties of mineral surfaces coated with a nanofluid based on synthesized TiO2/Al2O3 nanocomposites functionalized by poly(vinyl alcohol) (PVA). The produced nanofluid demonstrated predominant stability in harsh environments including acid/base solutions, saline solutions with strong ionic strength and high temperature–high pressure conditions. The sandpaper abrasion test (grit numbers 400, 240 and 180; 57 kPa) exhibited that the obtained coating retains its functions significantly after suffering the abrasion distance of 16000 cm. Meanwhile, the multifunctional coating nanofluid impart properties of self-cleaning. A crude oil droplet released at height of 9 mm from the coated surface undergoes first a lateral movement from its trajectory and misshaping, touching the surface after 300 ms, bouncing and rolling off easily with no tilt of solid substrate. This durable underwater superoleophobic nanofluid has thermal stability up to 150 °C; novel industrial applications include within Chemical Enhanced Oil Recovery (CEOR) methods applied to produce trapped oil from naturally oil-wet reservoirs.

One-step fabrication of robust and durable superamphiphobic, self-cleaning surface for outdoor and in situ application on building substrates

HypothesisWater and oil inhibition treatment is essential for protecting natural and artificial stone surfaces. Bioinspired super-antiwetting surfaces with “lotus effect”, together with superoleophobic properties, can be achieved combining very low-surface-energy materials and suitable surface roughness. Exploiting the natural roughness of stone surfaces, the simple and inexpensive fabrication of superamphiphobic surfaces through the coating dispersion deposition is expected. It seems the ideal method for the safeguard of contemporary and historical constructions, since the physical, chemical and aesthetic properties can be maintained. ExperimentsThe new coating agent (3-perfluroether-amidopropylsilane) was synthesized via one-step amidation. Hydrophobicity, robustness and environmental durability were systematically studied on stone surfaces through several tests: contact angle (CA), contact angle hysteresis (CAH), water inhibition efficiency, vapor diffusivity, chemical and mechanical resistance, artificial and field-exposure ageing. FindingsThe as-prepared coating demonstrated superamphiphobicity (oil and water CA > 150° with CAH < 10°) on stones with low and high porosity. Moreover, it manifested very high water inhibition efficacy while maintaining high vapor diffusivity and aesthetic properties of substrates. The superhydrophobic coating showed good robustness towards corrosive chemical agents, peeling, mechanical abrasion, water immersion and environmental weathering, thereby permitting various outdoor applications, including stone protection in rainy regions where acid rain is also present.

One-pot Synthesis of Multifunctional KGM/PDA/PVDF Composite Membrane for Efficient Treatment of Oil–water Emulsion and Dye

A new multifunctional KGM/PDA/PVDF composite membrane was successfully prepared via facile nonsolvent induced phase inversion method. Here, the KGM component consisted of numerous covalent bonds, which could improve the corrosion resistance of membrane materials. The dopamine, as a natural “glue” between PVDF substantial and KGM, is capable of integrating different materials together suitably. The as-prepared membrane possessed superior superhydrophilic/underwater superoleophobic property, great corrosion resistance and antifouling property. The separation efficiency was as high as 99.01%, and could stay relatively stable even in the acid, alkali or high salty environment. Additionally, the membrane had great regeneration performance and could keep stable after 15 cyclic separation, which was appropriate for efficient various oil–water separation process. Moreover, the composite membrane could also effectively separate dyes in different environments and the efficiencies were all more than 91%. All in all, the multifunctional composite membrane with facile preparation method might provide a promising strategy and significant theoretical basis for the efficient separation of oil–water emulsions and dyes.

Energy Efficient Ultrahigh Flux Separation of Oily Pollutants from Water with Superhydrophilic Nanoscale Metal–Organic Framework Architectures

AbstractThe rising demand for clean water for a growing and increasingly urban global population is one of the most urgent issues of our time. Here, we introduce the synthesis of a unique nanoscale architecture of pillar‐like Co‐CAT‐1 metal–organic framework (MOF) crystallites on gold‐coated woven stainless steel meshes with large, 50 μm apertures. These nanostructured mesh surfaces feature superhydrophilic and underwater superoleophobic wetting properties, allowing for gravity‐driven, highly efficient oil–water separation featuring water fluxes of up to nearly one million L m−2 h−1. Water physisorption experiments reveal the hydrophilic nature of Co‐CAT‐1 with a total water vapor uptake at room temperature of 470 cm3 g−1. Semiempirical molecular orbital calculations shed light on water affinity of the inner and outer pore surfaces. The MOF‐based membranes enable high separation efficiencies for a number of liquids tested, including the notorious water pollutant, crude oil, affording chemical oxygen demand (COD) concentrations below 25 mg L−1 of the effluent. Our results demonstrate the great impact of suitable nanoscale surface architectures as a means of encoding on‐surface extreme wetting properties, yielding energy‐efficient water‐selective large‐aperture membranes.

Energy Efficient Ultrahigh Flux Separation of Oily Pollutants from Water with Superhydrophilic Nanoscale Metal-Organic Framework Architectures.

The rising demand for clean water for a growing and increasingly urban global population is one of the most urgent issues of our time. Here, we introduce the synthesis of a unique nanoscale architecture of pillar‐like Co‐CAT‐1 metal–organic framework (MOF) crystallites on gold‐coated woven stainless steel meshes with large, 50 μm apertures. These nanostructured mesh surfaces feature superhydrophilic and underwater superoleophobic wetting properties, allowing for gravity‐driven, highly efficient oil–water separation featuring water fluxes of up to nearly one million L m−2 h−1. Water physisorption experiments reveal the hydrophilic nature of Co‐CAT‐1 with a total water vapor uptake at room temperature of 470 cm3 g−1. Semiempirical molecular orbital calculations shed light on water affinity of the inner and outer pore surfaces. The MOF‐based membranes enable high separation efficiencies for a number of liquids tested, including the notorious water pollutant, crude oil, affording chemical oxygen demand (COD) concentrations below 25 mg L−1 of the effluent. Our results demonstrate the great impact of suitable nanoscale surface architectures as a means of encoding on‐surface extreme wetting properties, yielding energy‐efficient water‐selective large‐aperture membranes.

PH-RESPONSIVE WOOD SLICES FOR THE CONTINUOUS SEPARATION OF LIGHT OIL/WATER/HEAVY OIL TRIPHASE MIXTURES

Light oil/water/heavy oil triphase mixtures are common in industrial wastewater, while nearly all separation materials with superwettability can only separate biphase mixtures of light oil/water or/and heavy oil/water. Here, a balsa wood slice with superhydrophilic/superoleophilic property in air was fabricated by a blade-cutting and ethanol-treating process. Therefore, the slice could be dually prewetted with both water and oil and thus showed underwater superoleophobic and underoil superhydrophobic properties without any further chemical modification. Such a slice showed underoil superhydrophobicity in nonbasic environment while transition into underoil superhydrophilicity under basic condition. Combining with the porous structure possessed by wood designed to transport liquids, this superwettability of the treated wood slice could be leveraged in the continuous separation of light oil/water/heavy oil triphase mixtures only driven by gravity with a high permeation flux and separation efficiency. After each separation, the slice was easily recovered by washing with acidic solution, and it could be recycled up to 15 times without any loss of pH responsibility. During repeated cycling separation, the slice exhibited excellent separation stability.

Dual-functional superwettable nano-structured membrane: From ultra-effective separation of oil-water emulsion to seawater desalination

Freshwater contamination and scarcity have progressively exacerbated the worldwide water crisis. Developing a feasible method to remediate polluted water as well as converting the abundant seawater to freshwater has become a matter of urgency. Here we demonstrate a nanofibrous poly(vinyl alcohol) based membrane (NPM) with dual functions: oil/water separation and solar water desalination. Interconnected polypyrrole (PPY) nanoparticles were decorated on the NPM as solar light absorber as well as enabling the membrane with superwettability. The underwater superoleophobic property endows the NPM with excellent anti-fouling performance and capacity to treat surfactant-stabilized industrial wastewater containing oil or various non-polar organic solvents with a separation efficiency of more than 99%. Mechanical robustness of the membrane is enhanced by mixing graphene oxide (GO) into NPM. Meanwhile, the efficient solar thermal conversion enables NPM to further desalinize the seawater under one sun solar radiation with excellent efficiency and durability with an evaporation rate of 2.87 kg m−2h−1. In the on-site desalination test, the solar vapor system demonstrated a daily solar water purification yield of 14.3 L m−2 under natural sunlight irradiation, suggesting a promising “green” application as mass manufacture seawater purification system without extra energy source. The outstanding performances of NPM for oil-in-water emulsion separation and the high-rate seawater desalination suggest its great potential for industrial applications in the future.

Molecular Understanding and Design of Porous Polyurethane Hydrogels with Ultralow-Oil-Adhesion for Oil-Water Separation.

Materials with opposite affinities toward oil and water have been extensively used to coat porous substrates for oil-water separation, but the applications of these materials have been limited by the need for complex coating processes as well as the short-term adherence of these materials onto different substrates under extreme conditions. As reported herein, the robust porous polyurethane hydrogel has been theoretically and structurally designed with ultralow-oil-adhesion properties which is free stand without depending on additional substrates. The combination of superhydrophilic properties along with the underwater superoleophobic behavior of this porous hydrogel allows gravity driven separations of oil-water mixtures, and its antiadhesion performance toward oil prevents undesirable oily fouling. The underwater superoleophobic properties were also illustrated by molecular dynamics simulation to understand the resisting effect of hydrated layers. The as-prepared porous hydrogel shows ultrahigh oil-water separation efficiencies of 99.9% for various oil-water mixtures, ranging from those containing viscous oils (pump oil and peanut oil) to organic solvents (n-hexane, n-hexadecane, and toluene). In addition, this hydrogel is durable even with exposure to various harsh conditions including acidic and basic media (pH 0-14) as well as exposure to mechanical abrasion. We believe that the combination of facile preparation, substrate independence, gravity driven separation, antifouling properties, high durability, as well as the outstanding separation flux and efficiency of this robust porous hydrogel will help to advance the design and application of materials in oil-water separation fields.

Biomimicking properties of cellulose nanofiber under ethanol/water mixture

The two types of cellulose nanofiber (CNF) surface characteristics were evaluated by oil contact angle under ethanol–water solution at several concentrations as well as in air. Wood pulp-based 2,2,6,6-tetramethylpiperidine-1-oxylradical (TEMPO)-oxidized cellulose nanofiber (TOCNF) sheets and bamboo-derived mechanical counter collision cellulose nanofiber (ACC-CNF) sheets were fabricated by casting followed by drying. The CNF shows underwater superoleophobic mimicking fish skin properties and slippery surface mimicking Nepenthes pitcher. The underwater superoleophobic properties of CNF was evaluated theoretically and experimentally. The theoretical calculation and experimental results of contact angle showed a large deviation. The roughness, zeta potential, and water absorption at different concentrations were key factors that determine the deviation. Antifouling investigation revealed that CNF was a good candidate for antifouling material.

Oil-immersion stable superamphiphobic coatings for long-term super liquid-repellency

• The coatings consist of pre-modified SiO 2 nanoparticles with high-degree densification. • The coatings exhibit stable superamphiphobicity under prolonged immersion of mixed oils. • The performance is over 20 times more immersion-durable against pre-existing surfaces. • Coated impellers achieve up to 65% contamination-resistance under accelerated testing. Superamphiphobic coatings have attracted tremendous interest from both academia and industry owing to their potential for self-cleaning and anti-fouling. However, many state-of-the-art superamphiphobic coatings are unable to preserve their super-repellent properties after prolonged liquid immersion. Thus, practical applications have so far been drastically limited. Herein, we highlight the immersion-stable performance of a nanostructurally-densified superamphiphobic coating possessing super liquid repellency to water and various low-surface-tension liquids. They exhibit excellent superoleophobic properties and functional stability even after prolonged immersion in mixed synthetic and vegetable oils. This immersion-stable superamphiphobic coating was also tested on household kitchen appliances under real-world conditions. Particularly inaccessible components such as the impeller and grease traps of range hoods were coated. Impellers demonstrate an improvement of up to 65% contamination-resistance while grease traps remained largely dry after collected oils were disposed. These findings highlight the potential of using nanostructurally-densified superampiphobic coatings as anti-fouling surfaces in the kitchen environment, with potential applications in petroleum extraction and oil transportation.

Porous Membranes with Special Wettabilities: Designed Fabrication and Emerging Application

Porous materials have become a burgeoning research interest in materials science because of their intrinsic porous characteristics, versatile chemical compositions, and abundant functionalities. Re...

Fabrication of superhydrophilic PVDF membranes by one-step modification with eco-friendly phytic acid and polyethyleneimine complex for oil-in-water emulsions separation

Superhydrophilic membranes with simultaneous underwater superoleophobicity are highly desirable and worth exploring for separation of emulsified oil from water. In this work, combining the strong negative charges of phytic acid (PA) and the high cationic charge density of polyethyleneimine (PEI), an eco-friendly PA@PEI polyelectrolyte complex was synthetized in aqueous solution. And then the polyelectrolyte complex was deposited onto hydrophobic PVDF membranes through a one-step assembly approach with high convenience, endowing the membranes with superhydrophilic and underwater superoleophobic property. The as-prepared PA@PEI/PVDF membrane shows outstanding static and dynamic water stability, and was successfully used to separate multiple oil-in-water emulsions, with an average rejection rate exceeding 98.5% and a water flux up to 12203.6 L m−2∙h−1∙bar−1. Furthermore, the water flux can be recovered to a high level after four separation-washing cycles, showing excellent antifouling performance and recovery capability. Together with its natural raw materials and environmentally friendly preparation strategy, the PA@PEI/PVDF membrane shows great potential in practical treatment of emulsified oily wastewater.

Multifunctional PDMS polyHIPE filters for oil-water separation and antibacterial activity

Herein, we present the fabrication of multifunctional polydimethylsiloxane (PDMS) foams with antibacterial, hydrophilic, and underwater superoleophobic properties for the separation of oil-water mixtures and simultaneous water disinfection. The PDMS foams, prepared following the high internal phase emulsion templating method, exhibit a porous interconnected structure and were further functionalized with a polydopamine (PDA) layer and in-situ grown silver nanoparticles (Ag NPs) upon successive dipping processes in dopamine and silver nitrate solutions. We demonstrate the successful use of the developed foams as 3D filters for the gravity-driven separation of oil-water mixtures and the subsequent disinfection of the filtered water. The flow rate of oil-water mixtures is strongly correlated to the in-situ grown Ag NPs density present on the foams, in contrary to the oil rejection efficiency, which is above 99.99% in all the studied cases. In fact, the flow rate values increase with the increasing density of the in-situ formed Ag NPs starting from 1937.7 ± 580.4 L m−2 h−1 for the foam without Ag NPs and reaching 4043.0 ± 710.7 L m−2 h−1 for the foam with the highest amount of NPs. Taking the latter as an example, we prove that the foams can be used for several filtration cycles without any modification of their oil rejection efficiency. In addition to efficient oil-water separation, the foams have antibacterial properties and are able to disinfect the permeate. The simple preparation method, effective gravity-driven filtration, robust nature, and antibacterial capability make the herein engineered multifunctional foams promising for highly efficient filtration processes.