Underwater Superoleophobic Properties Research Articles

Preparation and properties of bio-based PA56/SiO2–NH2 composite nanofiber membranes for high efficiency oil-water separation

With the continuous development of environmental protection and resource recycling demands, the development of bio-based separation membrane materials has increasingly attracted attention. Bio-based polyamide 56 (PA56), exhibiting excellent hydrophilicity, spinnability, and mechanical properties, is expected to complement and replace traditional separation membrane materials. In this study, the electrospinning preparation and structural control of PA56 nanofiber membranes were achieved through the optimization of PA56 content and mixed solvent ratios. The study found that when the PA56 content was 16 wt% and the formic acid to acetone ratio in the mixed solvent was 8:2, the nanofiber diameter distribution was the most uniform. Building on this, amino-functionalized modified silica (SiO2–NH2) nanoparticles were introduced to prepare PA56/SiO2–NH2 composite nanofiber membranes featuring a cobweb-like nanofiber network and micro-nodule structure. The effects of the addition of SiO2–NH2 nanoparticles on the morphology, structure, and properties of the fiber membranes were studied. The results indicate that the control of the mixed solvent ratio and the addition of SiO2–NH2 nanoparticles led to the formation of a cobweb-like nanofiber network and micro-nano nodular structure on the nanofiber surface, enhancing the hydrophilicity of PA56 nanofiber membranes. The M − 3 membrane with a nanoparticle addition amount of 0.8 wt% exhibited high hydrophilicity and underwater superoleophobic properties, achieving efficient separation of stable oil-in-water emulsions with a separation efficiency of 99.8 %. This work provides a new bio-based membrane material and its preparation method for treating oily wastewater using the membrane separation method.

Nickel-cobalt hydrogen phosphate membrane with outstanding anti-crude oil-fouling capability and its microscopic anti-fouling mechanism

Oil/water separation membranes with superior anti-fouling properties against highly viscous oils are crucial for the efficient treatment of oily wastewater. Herein, the effects of functional groups in an inorganic superhydrophilic membrane on the anti-fouling properties of the membrane are investigated. Using a facile one-step electrochemical deposition method, Ni1-xCoxHPO4·3H2O membranes were formed on a Cu(OH)2 microneedle-coated copper mesh (CCNC–P) with superhydrophilic and underwater superoleophobic properties. All CCNC–P membranes with different Co2+ contents showed outstanding anti-fouling capability for oily wastewater such as those containing crude oil. The CCNC–P(x = 0.5) membrane exhibited high separation efficiency reaching 99.7 % across five oil–water mixtures and oil-in-water emulsions, concurrently presenting an ultrahigh flux of 61695 L m−2 h−1 for crude oil–water mixture. Moreover, the membrane consistently maintained its separation performance during the long-term crude oil–water separation process. The flux decline ratio was below 1 %, and the flux recovery ratio approached 99.4 %. The CCNC–P membranes possessed superior chemical, thermal, and mechanical stability, suggesting significant potential for the industrial treatment of oily wastewater. Density functional theory calculation revealed that the HPO42− group in CCNC–P can strongly adsorb water molecules. The resultant stabilized hydration layer impeded the contact between the membrane surface and oil droplets, while the metal ions scarcely influenced the adsorption of water molecules on CCNC–P. These findings provide new insights into the development of novel oil–water separation membranes with higher anti-fouling capabilities against high-viscosity oils.

A novel asymmetric superwetting filter prepared by easily mass-produced strategy for high-efficient and switchable water/oil filtration

All-purpose materials with on-demand oil/water separation property have received broad attention recently. Herein, a filter paper (FP)-based filter with asymmetric wettability was designed and fabricated via simple combination of liquid phase reduction route with symmetry adhesion method. The fabricated filter exhibits underoil superhydrophobic (UOSHP) and underwater superoleophobic (UWSOP) property. Especially, the good underliquids lyophobicity is still maintained after tape peeling and corrosive, organic solvents treatments. By fixing the hydrophobic (HO) side of filter facing up, the water/light oil mixtures and oil-in-water (O-in-W) emulsions can be highly efficient separated, and the water/heavy oil mixtures and water-in-oil (W-in-O) emulsions are able to be separated with the HI side facing up. The separation efficiencies for water/oil mixtures and oil/water emulsions are higher than 98% and 99.1%, respectively. The study offers a new idea for the preparation of asymmetric superwetting materials with good stability and on-demand water/oil separation capability.

Facile one-step functionalised graphene oxide-phytic acid coating towards effective wax inhibition in waxy oil transportation

Wax deposition in pipelines is a global issue during the production and transportation of oil. Recently, superhydrophilic/underwater superoleophobic coatings have garnered much attention due to their wax inhibition potential based on water film theory. Herein, carbon steel (CS) substrates were made superhydrophilic by coating phytic acid (PA) functionalised graphene oxide (GO) materials prepared by very simple process. The superhydrophilic GO-PA coatings induced the formation of a hydration layer on the surface, thus inherently showing underwater superoleophobic properties in a water-contained waxy oil system. The optimised GO-PA/CS surface possessed a water contact angle of nearly 0° and an underwater oil contact angle of ∼ 160°. This coating demonstrated up to 89.5 % enhancement in oil passing speed during the oil transportation test. This enhancement is particularly significant for reducing wax deposition in laminar and transitional flow regimes. Moreover, in the cold-finger wax deposition tests, a wax inhibition efficiency of 95.8 % was achieved with the optimised GO-PA/CS surface in the laminar flow regime. Therefore, this research provides insights into a mechanically and chemically stable GO-based coating achieved via a facile one-step functionalisation, which has not been previously reported in the literature for applications in waxy oil transportation.

Buoyancy-Assisted Fabrication of Liquid Diode: Janus Nanofibrous Membrane for Efficient Wastewater Treatment.

The pressing need for effective methods to separate oil and water in oily wastewater has spurred the development of innovative solutions. This work presents the creation and evaluation of a Janus nanofibrous membrane, also known as the Liquid Diode, developed using electrospinning (e-spinning) and buoyancy-assisted hydrothermal techniques. The membrane features a unique structure: one side is composed of PVDF nanofibers embedded with a GO/TiO2 composite, exhibiting in-air superhydrophobic and superoleophilic properties, while the reverse side consists of PVDF nanofibers with a ZnO nanorod array, demonstrating in-air superhydrophilic and underwater (UW) superoleophobic properties. This distinct asymmetric wettability enables the membrane to effectively separate both water-in-oil (w-in-o) and oil-in-water (o-in-w) emulsions, achieving an impressive liquid flux and separation efficiency (SEff). The in-air superhydrophobic side of the Janus nanofibrous membrane achieves a maximum oil flux (Fo) of 3506 ± 250 L m-2 h-1, while the in-air superhydrophilic side achieves a maximum water flux (Fw) of 1837 ± 150 L m-2 h-1, with SEff exceeding 98% for both sides. Furthermore, the Janus nanofibrous membrane maintained reliable mechanical stability after 10 cycles of sandpaper abrasion test and demonstrated excellent chemical stability when subjected to acidic, alkaline, cold water and hot water conditions for 24 h. These properties, combined with its ability in breaking down of organic contaminants (98% ± 2% in 210 min) and pharmaceutical contaminants (97% ± 2% in 210 min) under visible light, highlight its photocatalytic potential. Additionally, the membrane's antifouling and antibacterial properties suggest long-term and sustainable use in wastewater treatment applications. The synergistic combination of these superior properties positions the Janus nanofibrous membrane as a promising solution for addressing complex challenges in wastewater treatment and environmental remediation.

Fabrication of mechanically stable fabric-based hydrogel membranes based on dual network toughening strategy for high efficient oil–water emulsion separation

Massive discharge of oily wastewater originating from oil-related industry, residential sewage and frequent oil spill accidents leads to serious environmental problems and health concerns. Amphoteric polyelectrolytes and hydrogel materials have been employed in the context of oil–water separation to resist oil pollution. However, the weak mechanical properties limit their practical application in complex environments. To address this, the design of a mechanically stable superhydrophilic/underwater superoleophobic composite membrane (PSBMA/PAM@CF) was been proposed by ingeniously in-situ growth of 3- [N, N-dimethyl −[2-(2-methylpropyl-2-enoxyloxy) ethyl] ammonium] propane-1-sulfonate (PSBMA)/polyacrylamide (PAM) dual network (DN) hydrogel on cotton fabric. The DN hydrogel strategy increased the stress of PSBMA hydrogel from 0.200 Mpa to 5.80 Mpa. The toughening effect of the DN hydrogel and its entanglement with cotton fibers endowed the membranes with excellent mechanical properties, and resulted in stable underwater superoleophobic and antifouling properties even after mechanical stability test. The PSBMA/PAM@CF membrane exhibited a separation efficiency exceeding 98.0 % for all types of oil-in-water emulsions stabilized by surfactants, and the membrane’s permeance remained at 1.75 × 103 L·m−2·h−1·bar−1 after 30 cycles. Additionally, the membrane exhibited a high permeance recovery rate of 98.2 %, surpassing general membranes. More significantly, we visualized the separation process through fluid dynamics simulations and revealed the separation mechanism of oil–water emulsions by membranes. It is expected that this work will provide new prospects for designing anti-oil-fouling membranes and applying in practical oil/water separation.

Efficient preparation of anisotropic cellulose sponge from cotton stalks: An excellent material for separation applications

Water pollution and solid waste resource reuse demand immediate attention and research. Here, we present a method to create anisotropic cellulose sponges from cotton stalk waste. Using the inherent structure of cotton stalks, we selectively remove lignin and hemicellulose via acid and alkali pretreatment. This process yields cellulose sponges with a natural pore structure. Our findings demonstrate that these sponges retain the original pore configuration of cotton stalks, providing excellent connectivity and compressibility due to their unique anisotropic three-dimensional structure. Moreover, these sponges exhibit exceptional super-hydrophilic and underwater super-oleophobic properties, with underwater oil contact angles exceeding 150° for all tested oils. External pressure can reduce the pore size of the cellulose sponge, facilitating the gravity-driven separation and removal of dyes and emulsions. Remarkably, removal efficiencies for Methylene Blue (MB), Congo Red (CR), water-in-oil (w/o) emulsions, and oil-in-water (o/w) emulsions exceed 99 %, 97 %, 99 %, and 99 %, respectively, highlighting superior removal and recyclability. Further investigation into the mechanisms of dye and emulsion removal employs X-ray photoelectron spectroscopy (XPS) characterization and molecular dynamics (MD) simulation. These insights lay the groundwork for the efficient recycling and resource utilization of waste cotton stalks, offering promising applications in water purification.

TiO2 deposited dual functional hydrogel coatings with superhydrophilic and photocatalytic properties for efficient oil/water separation and dye photodegradation

Hydrogel coatings have been applied in oil/water separation owing to the underwater superoleophobic and anti-oil fouling property. However, the intrinsic relatively poor mechanical performance of hydrogel coatings and inevitably polluted by organic pollutants induce the separation performance reduction in the long-term operation and even possibly cause the coatings to peel off. In this work, we developed a simple and robust TiO2 deposited polyacrylamide-sodium alginate (TiO2@PAS) composite hydrogel coating with underwater superoleophobic and dye photodegradation abilities. PDA/TiO2 nanoparticles were deposited on the substrate surface through the mussel inspired chemistry strategy. Moreover, Polyacrylamide and calcium alginate were crosslinked into the double network hydrogel to enhance mechanical performance. The prepared hydrogel coating was introduced onto different substrates to endow the coated substrates with robust superwetting and anti-oil fouling properties. Separation efficiency of TiO2@PAS hydrogel coated copper mesh for oil/water mixtures reached 99.1% after 50 cycle separation tests. The hydrogel coated PVDF membrane was prepared through the same method and separation efficiency for oil-in-water emulsion keeps above 99.3% during multiple cycles separation. Moreover, the photocatalysis active TiO2 nanoparticles allowed the TiO2@PAS composite hydrogel coating to degrade the organic dye methylene blue (MB) through the photo-Fenton-like photodegradation process with degradation efficiency as high as 98.7%. Notedly, the TiO2@PAS hydrogel coating shows robust superwetting performance even underwent abrasion test and acid-base immersing, which has the potential for adapting extreme operating condition. Overall, the study on the TiO2@PAS composite hydrogel coatings provides a general and simple design strategy for superwetting and photocatalytic hydrogel coatings for multi-demand water treatment application.

Simple surface modification of PVDF membrane via a quaternization of NM88B for efficient oil/water separation

Developing a stable MOF-modified membrane for efficient treatment of oily wastewater remains a challenge. In this study, NH2-MIL-88B(Fe) (NM88B) was deposited on the commercial polyvinylidene fluoride (PVDF) membranes, and grafted with perfluorohexane-1-sulfonic acid potassium salt (PFHx) to achieve quaternization modification. This reaction proceeds in an environmentally friendly manner due to the absence of any catalyst. The introduction of fluorine atoms through grafting PFHx resulted in the modified PVDF membrane (NPF) demonstrating remarkable underwater superoleophobic property with an underwater oil contact angle at ∼180°. In separation of various oil-water emulsions, the NPF membrane afforded a high permeation flux (up to 2043 L·m−2·h−1) and rejection rate (∼99 %). The oil rejection of NPF membrane was >99 % after 10 filtration cycles of n-hexadecane-water emulsion, and the pure water flux of the recovered membrane was kept at 82.65 % of the original flux, indicating a very good reusability and stability. Filtration of mixed dye/oil-water emulsions showed that the NPF membrane remove 99 % of both oil and dye from the mixture. This work provides a simple and stable modification of PVDF membrane, exhibiting remarkable underwater superoleophobicity and hydrophilicity, thereby harboring substantial prospects in the treatment of oily wastewater.

Analysis of wettability and oil-water separation mechanism of superhydrophilic/underwater superoleophobic mesh based on capillary force model

The Frequent oil spills at sea and large discharges of oily wastewater spills seriously jeopardize the ecological environment and lead to an increasing shortage of water resources, so the oil/water separation has become a hot spot of global research. As opposed to the conventional separation method, the membrane separation has received wide attention because of its advantages of green environmental protection, low energy consumption and easy operation. In this paper, Cu(OH)2 mesh with superhydrophilic and underwater superoleophobic properties were prepared by in-situ growth method using purple copper mesh as the substrate. Scanning electron microscopy, x-ray photoelectron spectroscopy and contact angle tests were used to evaluate the surface morphology, chemical composition and wetting behavior of the mesh. The results showed that the water contact angle was 0° in air and the contact angle was 155.4° for oil droplets underwater. The membrane exhibited high separation efficiencies (99%) and separation fluxes (3.67-6.54×104 L·m-2·h-1) for the five tested oils under gravity drive. The wettability of the mesh was unaffected after 20 separation experiments. The surface wettability and the oil/water separation mechanism were analyzed using the capillary force-based separation model combined with the Young and Cassie-Baxter equations.

Facile fabrication of polymeric-inorganic hybrid coated membrane with super-hydrophilic and underwater super-oleophobic properties for highly efficient crude oil-in-water emulsion separation

The oily wastewater is a huge wastewater stream that can potentially serve as an enormous source of clean water for water reuse applications such as groundwater recharge or irrigation. Given the huge potential of cleaning oily wastewater, we have developed an amino-functionalized nickel oxide nanoparticles coated inorganic-polymeric hybrid membrane with superhydrophilic and underwater superoleophobic properties for excellent crude oil-in-water (O/W) emulsion separation potential using a cross-flow filtration system. The use of ceramic alumina (Al2O3) support offers increased chemical, thermal, and mechanical stability while nickel oxide (NiO) decoration equips the membrane with special surface wettability to avoid membrane fouling. Moreover, the amino-functionalized NiO-coated polyamide network (F-NiO/PA) offers an active layer dense enough to separate the oil from water when the surfactant-stabilized crude oil-in-water emulsion was used as feed during separation experiments. Hence fabricated F-NiO/PA@Alumina membrane was studied by using different membrane characterization techniques to explore the features and understand the structure of F-NiO/PA@Alumina membrane. The F-NiO/PA@Alumina membrane possessed a superhydrophilic (water contact angle; θW, A = 0°) and underwater superoleophobic (oil contact angle; θO, W = 161°) surface wettability which is an ideal feature required for O/W emulsion separation. The F-NiO/PA@Alumina membrane demonstrated a high O/W emulsion separation efficiency of >99 % even with crude oil concentrations as high as 200 ppm using a cross-flow filtration system. The stability test of the separation performance of the F-NiO/PA@Alumina membrane also revealed a separation performance of >99 % for the duration of the test using a cross-flow filtration system.

Nano graphene oxide creates a fully biobased 3D-printed membrane with high-flux and anti-fouling oil/water separation performance

Facile fabrication of green and renewable bio-based membranes with good anti-fouling and oil/water separation performance is of great importance to solve the oil spills and industrial oily wastewater threatening the ecological environment. Here, a fully biobased oil/water separation membrane with an ordered porous structure was 3D printed ultraviolet-assisted direct ink writing. The components of the bio-ink were obtained by methacrylation of chitosan (CS) and gelatin (GEL) to synthesize methacrylated chitosan (CSMA) and methacrylated gelatin (GELMA), while the nanographene oxide (nGO) was derived from CS through a simple microwave-assisted hydrothermal carbonization followed by oxidation step. The addition of nGO boosted the printability of the bio-ink, and the anti-fouling property and water permeation flux of the printed membranes. As a result, the membrane M−CSMA/GELMA/nGO-0.7 with the optimal performance possessed a low water contact angle in air of 0°, and high underwater oil contact angle of 161.5°, demonstrating a combination of superhydrophilic and underwater superoleophobic properties. M−CSMA/GELMA/nGO-0.7 has good corrosion resistance and long service life as evidenced from the separation efficiency of n-heptane/water, which kept above 99.5 % and a high water permeation flux above 38,300 L m−2h−1 after 20 cyclic tests in the harsh aquatic conditions containing 1 M NaCl, 1 M HCl, or 1 M NaOH, respectively. This shows promising potential for real-life applications.

Simply Prepared, Wood‐Based Solar Evaporators for Highly Effective Oily Wastewater Purification

Oily wastewater has been causing serious water environment pollution and greatly affecting the safety of drinking water. Compared with superwettable oil‐water separation membrane technology, solar‐driven evaporators based on specific wettability can effectively remove not only oil but also ions, dyes, and other substances from wastewater. We report a longitudinally cut, porous, and wood‐based evaporator that exhibits superhydrophilic and underwater superoleophobic properties. By collaborating hydrophilic and oleophobic wettability, high porosity and the structural anisotropy of wood, the solar evaporators effectively remove different oils from oily emulsions. Separation efficiency of surfactant‐containing crude oil‐in‐water, peanut oil‐in‐water, silicone oil‐in‐water, diesel oil‐in‐water, and n‐dodecane‐in‐water emulsions can reach up to 99.57%, 99.1%, 99.86%, 99.75%, and 99.28%, respectively. The rate of evaporation increased by 1.83 times to 1.63 kg m−2 h−1 compared with the radially‐cut wood‐based evaporator. Meanwhile, it is also capable of purifying heavy metal ions, dyes, and acid‐base solution. This easily prepared and accessible solar evaporator provides a viable idea for obtaining pure water from oily wastewater treatment.

Preparation of superhydrophilic sodium alginate/chitosan-Ag composite membranes with antibacterial activity for effective oil–water emulsion separation

Oily wastewater as one of water pollutions has always been a hot issue in the field of chemical engineering and environment protection, and it is still challenge to separate oil water mixture effectively with low energy consumption. Polymer membranes with superhydrophilic and underwater superoleophobic properties are perfect substances for oil–water separation owning to their high separation efficiency, oil anti-adhesion and energy saving. However, these membranes are easily contaminated by microorganisms, leading to biofilms on the surfaces, and reducing their separation flux and efficiency. In order to solve the problems, sodium alginate/chitosan-Ag composite were successfully coated on commercial nylon membranes by self-assembly method, and the effects of the Ag on separation performance and biological activity of the membranes were investigated in detail. Under the optimized condition, the membrane can effectively separate oil-in-water emulsions containing anionic, cationic or non-ionic surfactants, with a maximum separation efficiency of 99.73%. More importantly, the inhibition ratios of the membrane could reach 95.42% and 98.05% against E. coli and S. aureus, respectively, and thus inhibits the formation of S. aureus biofilm, and maintain a high relative flux after being contaminated by S. aureus. The simple preparation process and incredible emulsion separation performance with antibacterial activity of composite membranes will provide great prospects for potential industrial applications.

Polyvinyl Alcohol/Graphene Oxide Nanocomposite Membrane for Highly Efficient Oil/Water Mixture Separation

The growing amount of oily wastewater caused by frequent oil spill accidents poses a severe threat to the ecological environment. Therefore, the development of highly efficient oil/water separation methods is highly necessary. This work reports the preparation of a nanocomposite membrane using graphene oxide (GO)/polyvinyl alcohol (PVA) coated on steel meshes for oil/water mixture separation. PVA firmly anchors GO nanosheets onto the mesh surface through strong hydrogen bonds using glutaraldehyde (GA) as a crosslinker. This nanocomposite membrane exhibited superhydrophilic and underwater superoleophobic properties, with the highest oil contact angle of 158º due to its highly rough structure. The synergistic effects of GO and PVA further improved the superhydrophilicity of the prepared membrane, due to the hydrophilic nature of both GO and PVA. The separation efficiencies and water flux for a variety of oil/water mixtures were above 97.8% and 6000.0 L m−2 h−1, respectively. The prepared membrane showed excellent chemical resistance under harsh conditions without evident change in its surface wettability. Moreover, its underwater superoleophobicity was maintained after 10 cycles of abrasion testing.

Superhydrophilic fluorinated heterogeneous membranes with boosting antifouling property and high stable permeance for efficient emulsion separation

It is yet a query that whether chemically heterogeneous superwetting surface is able to enhance the permeability and anti-fouling capability of membrane contemporaneously, heretofore which is lacking and well worth creating. Here, we propose a bio-adhesion coupled with self-assembly strategy, to construct superhydrophilic fluorinated heterogeneous membranes, through in-situ biomimetic adhesion of the hydrophilic polyphenol-silane coating (TAT) on the porous PVDF membrane, as a secondary reaction platform, and subsequently self-assembly of amphoteric fluorocarbon surfactant (FS-50). Unsurprisingly, we find that introducing FS-50 not only significantly strengthens the permeability, but also improves the anti-fouling self-cleaning, thanks to the formation of robust hydration layer and slippery micro-domains with low friction, to realize the dual anti-fouling effects of pollution resistance and release. The champion PVDF/TAT/FS-2.0 % composite membrane exhibits superhydrophilic and underwater superoleophobic (oil contact angle above 162.3°) property with very low oil-adhesion. This composite membrane possesses an ultrahigh water permeance of 29214.6 L m−2 h−1 bar−1, which is 2.8 times larger than that of pristine PVDF membrane. The PVDF/TAT/FS-2.0 % composite membrane presents the high separation efficiencies (above 99.5 %) for various surfactant-stabilized oil-in-water emulsions and high permeances of 3193.2–4212.3 L m−2 h−1 bar−1. Especially, the membrane at continuous operation for 1.0 h can reach a high stable permeance of 2505.1 L m−2 h−1 bar−1. Moreover, this composite membrane shows strong chemical stability and robustness. This research answers the initial question, and provides the insight for further design and production of chemically heterogeneous superwetting membranes with high permeability, selectivity and antifouling ability.

Fabrication of 1D/2D ATP/GO-COOH membrane with low-resistance transport pathways for highly efficient separation of oil-in-water emulsion

Attapulgite/carbonylated graphene oxide (ATP/GO-COOH) composite membranes have been successfully prepared by vacuum-assisted filtration of an aqueous ATP/GO-COOH dispersion on a microfiltration substrate. Due to the interaction between the OH groups of ATPs and COOH groups of GO-COOH, ATP rods showed excellent compatibility with GO-COOH nanosheets, and the ATP mass fraction was significantly improved. The large amount of ATP can establish a fast transport channel for the diffusion of water molecules in the composite membrane. As a result, the optimum membrane gave a permeation flux with 13582 L/(m2 h), which is significantly higher than that of the pure GO-COOH membrane (2281 L/(m2 h)). In addition, the underwater superoleophobic properties of the ATP/GO-COOH composite membrane enable it to have a low oil-adhesive water/membrane interfaces. The ATP/GO-COOH composite membrane showed good separation and separation stability for oil-in-water emulsion systems with different concentrations, pH, and oil types.

Rapid Construction of Caffeic Acid/p-Phenylenediamine Antifouling Hydrophilic Coating on a PVDF Membrane for Emulsion Separation.

The current methods of constructing modification strategies for hydrophilic membranes are time-consuming, complex in operation, and poor in universality, which limit their application on membranes. In this work, inspired by the adhesion properties and versatility of caffeic acid (CA) and p-phenylenediamine (PPDA), a simple, rapid, and universal method was designed for the separation of oil-in-water emulsion by preparing a stable hydrophilic coating separation membrane. The preparation time of the membrane was shortened to 40 min. The developed PVDF-PCA/PPDA membrane showed superhydrophilic and underwater superoleophobic properties. When applied to petroleum ether-in-water emulsion, isooctane-in-water emulsion, and dodecane-in-water emulsion separation, the oil rejection was more than 99.0%. In the circulating separation of 10 g/L soybean oil-in-water emulsion, the oil rejection was more than 99.3%, and the highest flux was 1036 L·m-2·h-1. The prepared PVDF-PCA/PPDA membrane performed well in the separation test of oily wastewater. The proposed strategy is simple and rapid; it may become a universal method for preparing membranes with super strong antifouling properties against viscous oil and accelerate the research progress of membrane separation of oil-in-water emulsions.

Nacre-like graphene oxide–calcium carbonate coated membrane with underwater superoleophobic property for highly efficient oil/water separation

Recently, oily wastewater is causing serious environmental pollution, and an effective disposal method is highly urgent. Membranes with superhydrophilic and underwater-superoleophobic (SUS) properties have shown prospective advantages. The development of a new nacre-like Li-Bentonite/graphene oxide-calcium carbonate coating membranes (Li-Bent/GO-CaCO3@PVDF CMs) was motivated by the unique mastoid structure of the lotus leaf and the robust layer of the nacre. This CMs were synthesized using a facile, cost-effective, and eco-friendly layer-by-layer (LBL) self-assembly approach. The commercially available polyvinylidene fluoride (PVDF) was utilized as a stable base for the fabrication of the CMs. Among these, GO nanosheets were introduced to imitate the “brick and mortar” structure of mother-of-pearl, and “hard bricks” with interspersed Li-Bent and GO were obtained by the LBL self-assembly method. The phenomenon of “biomineralization” confers an intricate surface structure to the membrane, thereby imparting it with a hydrophilic property of 8.3° and an exceptional non-adhesive behavior in submerged conditions. In addition, the membrane has SUS performance and superior permeability (WF ∼ 5476.3 ± 76 L·m−2·h−1), separation (OF∼3123.78 ± 56 L·m−2·h−1, OR ∼ 99.3 %) and anti-fouling properties (FRR decreased only 14.9 %). Significantly, the membrane has good stability, such as alkali, salt-resistance and aging-resistance. Moreover, this method is easy to operate, and is suitable for surface modification of diversified substrate membranes, with high research and application value.

Nanoflower-branched layered double hydroxide (LDH)-wrapped electrospun membrane synthesized with ZIF-67 templates for oil-containing emulsified wastewater separation

Designing hierarchical micro/nanostructures on the surface of a membrane to endow it with underwater superoleophobic properties and oil-fouling resistance, poses a considerable challenge. In this study, we propose an elaborate method for depositing layered double hydroxides (LDHs) on a ZIF-67 surface grown along nanofibers, resulting in a nanoflower-branched nanofibrous membrane (ZnCo-LDH@PAN) with an abundant cavity structure. The ZnCo-LDH@PAN membrane exhibited excellent mechanical and superdrophilic/underwater superoleophobic properties, reaching an outstanding separation efficiency (>99.0 %) for crude oil emulsion and various sodium dodecyl sulfate (SDS) stabilized oil/water emulsions, and a separation flux of up to 5434.8 L m−2 h−1 under a low-pressure drive. In the continuous separation of 1700 mL emulsion, the efficiency remained relatively stable, and the FRR (flux recovery rate) can be as high as 97.8 %. Further, the ZnCo-LDH@PAN membrane exhibited good mechanical and chemical stabilities. Overall, this study presents an advanced approach for designing separation membranes by combining LDHs with nanofiber-derived materials.