Underwater Oil Contact Angle Research Articles

Mussel-inspired fabrication of fouling-resistant PPSU-based nanocomposite membrane using polydopamine and tannic acid-functionalized CeO2 nanoparticles towards effective oil-water emulsions separation

Surface modification of membranes using hydrophilic nanoparticles has proved promising to improve the surface wettability and antifouling properties of the membranes that are otherwise prone to the attachment of oil droplets. Nonetheless, the strong adhesion of nanoparticles onto the membrane surface and their long-term performance pose problems for their widespread application. To address these issues, a novel organic-inorganic hybrid coating was constructed onto surfaces of polyphenylsulfone (PPSU) ultrafiltration membrane via simultaneous deposition of mussel-inspired polydopamine (PDA) followed by immobilization of tannic-acid functionalized cerium oxide (CeO2) nanoparticles. These prepared membranes were characterized by FTIR, XPS, FESEM, EDX, pore size, water contact angle (WCA), underwater oil contact angle (UOCA), and separation performance. The effects of functionalization and nanoparticle concentration on membrane properties were investigated. SEM and EDX results showed that functionalized nanoparticles (up to optimum concentration: 0.05 wt%) were uniformly distributed onto the membrane surface, which exhibited increase in permeate flux (∼375 %), UOCA (∼36 %), Fouling resistance ratio (FRR ∼ 300 %) with a decrease in irreversible fouling (∼94 %) and WCA (∼80 %) and high oil rejection of > 99 % compared to pristine PPSU membrane. Long-term operation (for six cycles) indicates that the optimum membrane possessed high efficiency and durability for oil-in-water emulsion separation due to superb antifouling properties and strong binding of the functionalized nanoparticles onto the membrane surface.

Robust and renewable hierarchical silica nanowires grown on a stainless steel mesh for oil/water separation

Porous filters with selective wetting properties offer a more effective route for separating oil and water than traditional industrial processes. However, developing durable structures for emulsion purification remains a challenge. Herein, we present a filter comprising a stainless steel mesh decorated with silica nanowires, which is highly resistant to fouling (almost 0° water contact angle and 166° underwater oil contact angle) and demonstrates excellent separation efficiency and reusability. The nanowire filter is particularly suited for separating n-hexane/water emulsions, where the oil phase could be completely separated by the filter. In addition, it demonstrates remarkable resistance to acid (pH 2 for 10 days), salt solution (37 days), butane flame, and abrasion, indicating its applicability in harsh environmental conditions. By combining the advantages of low-cost production, excellent separation, and enhanced durability, this nanowire filter holds significant potential for oil/water separation applications.

Dialdehyde cellulose (DAC) and polyethyleneimine (PEI) coated polyvinylidene fluoride (PVDF) membrane for simultaneously removing emulsified oils and anionic dyes

Developing high-efficiency membrane for oil and dye removal is very urgent, because wastewater containing them can cause great damage to human and environment. In this study, a coated membrane was fabricated by applying DAC and PEI onto the commercial PVDF microfiltration membrane for supplying the demand. The coated membrane presents superhydrophlic and superoleophobic properties with a water contact angle of 0o and underwater oil contact angle exceed 150°, as well as excellent low underwater oil adhesion performance. The coated membrane shows high separation efficiency exceeded 99.0% and flux 350.0 L·m−2·h−1 when used for separating for six kinds of oil including pump oil, sunflower oil, n-hexadecane, soybean oil, diesel and kerosene in water emulsions. Additionally, the coated membrane can effectively remove anionic dyes, achieving rejection rates of 94.7%, 93.4%, 92.3%, 90.7% for the CR, MB, RB5, AR66, respectively. More importantly, the membrane was able to simultaneously remove emulsified oil and soluble anionic dyes in wastewater containing both of them. Therefore, this novel coated membrane can be a promising candidate for treating complex wastewater.

PVDF-based nanofiber membrane decorated with Z-scheme TiO2/MIL-100(Fe) heterojunction for efficient oil/water emulsion separation and dye photocatalytic degradation

Membrane separation is one of the most widely used methods for water purification, but membrane fouling is a stumbling block that must be overcome for its further promotion and application. In this work, a self-cleaning PVDF-based hybrid nanofiber membrane with core-sheath structure were constructed via electrospinning and in-situ synthesis, using polyvinylidene fluoride/polyvinyl pyrrolidone (PVDF-PVP) electrospun nanofibers as skeleton cores and in-situ synthesis of Z-scheme TiO2/MIL-100(Fe) heterojunctions as photocatalytic sheaths. The hybrid membrane exhibited excellent superhydrophilicity (water contact angle of 0°) and underwater superoleophobicity (underwater oil contact angle of 161.4°) with high permeate fluxes and superior separation efficiencies (more than 99.5%) for various oil/water emulsions. Furthermore, the Z-scheme TiO2/MIL-100(Fe) heterojunctions anchored on the nanofibers possessed robust photocatalytic activity with the removal efficiency of dyes up to 99.9% under simulated sunlight. More importantly, the membrane has excellent recyclability due to its outstanding anti-fouling and self-cleaning properties. Therefore, the hybrid membrane has attractive potential application in wastewater purification.

PPS/TA-PEI/β-FeOOH membranes with powerful photo-Fenton self-cleaning capability for efficient oil–water emulsion separation

Polyphenylene sulfide (PPS) microporous membranes have garnered extensive research enthusiasm concerning their outstanding permeation performance and separation accuracy in treating oily wastewater. Nevertheless, the inherent hydrophobic chemical structure, along with the noticeable concentration polarization effect, predisposes them to severe membrane contamination during the separation process. Accordingly, it is desirable to design a PPS self-cleaning membrane with superior anti-fouling capability, fast transport, and remarkable flux recovery. This study marks the first combination of PPS membrane materials with the photo-Fenton process. In detail, the polyphenol (tannic acid, TA)-polycation (polyethyleneimine, PEI)-metal ion (Fe3+) double cross-linking coatings were first assembled on the PPS substrate surface. Subsequently, β-FeOOH photocatalysts were synthesized through in-situ mineralization to further strengthen the hydrophilicity of the membranes. The obtained PPS/TA-PEI/β-FeOOH composite membrane achieved exceptional separation of diverse oil-in-water (O/W) emulsions. The PPS/TA-PEI/β-FeOOH membranes exhibited in-air superhydrophilic and under-water superoleophobicity, exhibiting under-water oil contact angles greater than 151° for diverse oil agents. The fabricated composite membranes displayed high permeability (a flux of the petroleum ether-in-water (P/W) emulsion reached 3400.5 L m−2h−1 bar−1 driven by a pressure of 0.05 MPa) along with ideal oil rejection (98.6 %). Significantly, the PPS/TA-PEI/β-FeOOH membrane possessed powerful photo-Fenton self-cleaning capability, and its flux recoveries of the contaminated membrane exceeded 90.3 % for varied O/W emulsions after being cleaned by visible light for 10 min. We believe that our research presents a novel approach for the exploitation of PPS-based photo-Fenton self-cleaning membranes, which also exhibit great applicative potential in oily wastewater treatment.

Mussel-inspired superhydrophilic and antibacterial membranes for effective gravity-driven separation of oil-in-water emulsions

Substantial discharge of industrial oily wastewater calls for an efficient and sustainable treatment for resource recovery. Superwetting membranes offer a feasible approach to fractionate oil species and water from oily wastewater for addressing this technical challenge. In this study, we proposed a useful strategy for constructing a superhydrophilic membrane with superior antibacterial properties through rapid co-deposition of dopamine and 3-aminopropyltriethoxysilane (APTS) initiated by ammonium persulfate on the Cu nanoparticles-loaded porous PVDF substrate. The resultant superhydrophilic membrane yielded an underwater oil contact angle of 163.5°, enabling a fast and robust gravity-driven filtration for various oil-in-water emulsions with a separation efficiency of >99.9 %. Additionally, incorporating of Cu nanoparticles and polydopamine endowed the superhydrophilic membrane with superior antibacterial activity (100 % inhibition efficiency against Escherichia coli), and thereby remarkably enhancing the anti-biofouling performance. This study provides a viable approach to design high-performance membranes for separation of oil-in-water emulsions, with promising applications in the industrial and environmental sectors.

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.

Facile preparation of poly(melamine formaldehyde) sponge/bacterial nanocellulose composite for oil-water separation

The treatment of a large amount of oil-water mixture generated by oil leakage accidents is an environmental issue that cannot be ignored. Achieving fast and efficient oil-water separation is a goal pursued by both academia and industry. In this paper, poly(melamine formaldehyde) (PMF) sponges were modified by the hydrophilic bacterial nanocellulose (BNC) through mild and facile conditions. With increasing the concentration of BNC dispersion used, the pore size of the composite decreases. The water contact angle of the obtained PMF/BNC composite surface is 0° or so, and the underwater oil contact angle is greater than 150°. Based on its hierarchical pore structure, hydrophilicity and oil repellency, the PMF/BNC composite exhibits excellent oil-water separation efficiency and water treatment flux for layered oil-water mixture (>1.0×107L/(m2·h·bar)). In addition, the PMF/BNC composite also exhibits high water treatment flux and oil-water separation efficiency (> 95%) for oil-water emulsion with and without surfactant. Stacking several composite slices could achieve higher oil-water separation efficiency.

Ultra-high flux mesh membranes coated with tannic acid-ZIF-8@MXene composites for efficient oil-water separation

Oil/water separation has become a global concern due to the increasing discharge of multi-component harmful oily wastewater. Super wetting membranes have been shown to be an effective material for oil/water separation. Ultra-high flux stainless-steel meshes (SSM) with superhydrophilicity and underwater superoleophobicity were fabricated by tannic acid (TA) modified ZIF-8 nanoparticles (TZIF-8) and two-dimensional MXene materials for oil/water separation. The TZIF-8 increased the interlayer space of MXene, enhancing the flux permeation (69,093 L m−2h−1) and rejection of the composite membrane (TZIF-8@MXene/SSM). The TZIF-8@MXene/SSM membrane showed an underwater oil contact angle of 154.2°. The membrane maintained underwater superoleophobic after stability and durability tests, including various pH solutions, organic solvents, reusability, etc. In addition, the oil/water separation efficiency of TZIF-8@MXene/SSM membranes was higher than 99% after treatment in harsh conditions and recycling. The outstanding anti-fouling, stability, durability, and recyclability properties of TZIF-8@MXene/SSM membrane highlight the remarkable potential of membranes for complex oil/water separation process.

A polymeric-ceramic hybrid membrane with a self-cleaning and super-wettable surface decorated with polypyrrole-G-C3N4 photocatalyst for oily wastewater treatment

Treating oily wastewater is an enormous challenge as it leads to excessive membrane fouling due to the deposition of components of oily feed onto the membrane surface. Hence, the current work has been focused on developing a polymeric-ceramic hybrid membrane with photocatalytic self-cleaning antifouling properties. To yield the desired membrane, a polypyrrole-graphitic carbon nitride (PPy-G-C3N4) photocatalyst was decorated in the polyamide (PA) active layer of the membrane by interfacial polymerization (IP) onto the surface of alumina support. The chemistry of the active layer of the PPy-G-C3N4/PA@Alumina ceramic membrane led to the special wettability feature of being underwater superoleophobic which is reflected by underwater oil contact angle of θO, W = 159.9°. Even though the membrane surface features do not allow the oil to wet the membrane surface during filtration, the membrane surface fouling was inevitable during filtration experiments. With distilled water as feed, the permeate flux of PPy-G-C3N4/PA@Alumina ceramic membrane reached 650 L m−2 h−1 (LMH) at a pressure of 8 bar. A separation efficiency of >99 % was observed by using a feed of 100 ppm oil-in-water (O/W) emulsion. However, the permeate flux declined while using O/W emulsion as feed, where a 92 LMH to 50 LMH was observed after 60 min of continuous filtration. The performance of the membrane was recovered after exposure to solar-simulated light owing to the presence of PPy-G-C3N4 photocatalyst in the active layer where a recovery of ∼90 % of permeate flux was recorded. Hence, the current approach of fabricating a hybrid membrane proved to be useful for efficiently treating a challenging feed consisting of a complex oily matrix.

UV-activated superwetting ability of electrospun polysulfone/titanium dioxide membranes toward highly efficient methylene blue removal and oil/water separation

Enhancing the hydrophilicity/underwater superoleophobicity of fibrous membranes not only boosts their anti-contaminant property during oil/water separation, but also enhances their removal ability toward water-soluble pollutants. Here, a novel kind of electrospun polysulfone/titanium dioxide (PSF/TiO2) composite membranes with UV-activated superwetting ability were fabricated by depositing spherical TiO2 nanoparticles on the surface of PSF electrospun fibers through hydrothermal reaction. After activated by UV irradiation, the PSF/TiO2 composite membranes (FPT-A-UV) exhibited amphiphilic features with water contact angle (WCA) and oil contact angle (OCA) approaching 0° in air while under-water oil contact angle (UWOCA) and under-oil water contact angle (UOWCA) exceeding 150°, respectively. The composite membranes showed high removal ability toward methylene blue (MB). Under the complex condition in purifying the emulsion containing MB, the removal ratio of MB achieved 90.8 % with water flux of 780.3 (L m−2 h−1). The FPT-A-UV composite membranes also exhibited good demulsification effects on various emulsified solutions. It is reasonable to expect that the composite membrane has satisfactory application prospects in wastewater purification, especially in harsh environments.

Advanced polymer‐based surfactant for improved heat and salinity stability in enhanced oil recovery processes

AbstractEnhancing oil recovery through surfactants has proven to be a successful strategy in recent times. However, traditional surfactants have their limitations, particularly in terms of stability under high temperatures and salinity levels. This study delved into a groundbreaking macromolecular polymeric surfactant, S‐AV, which holds the unique ability to transform rock surface characteristics, effectively stripping away residual oil while maintaining resilience against elevated temperatures and salinity. S‐AV was synthesized through a free‐radical copolymerization process, incorporating benzyl, perfluoroalkyl, alkyl‐, benzyl‐, ethylene glycol, and amide‐alkyl‐sulfonate groups, ultimately yielding a comb‐like molecular structure. S‐AV demonstrated exceptional prowess, swiftly reducing the underwater oil contact angle to 53.4° in just 48 h. This synthesized surfactant also retained its phase stability up to salinity levels of 36,000 ppm, with temperature having no disruptive impact on its phase stability performance. Furthermore, S‐AV showcased remarkable viscosity reduction in conditions of high temperature and salinity. The core flooding experiments underscored the potential of S‐AV, as its injection led to a significant oil recovery rate of up to 83%. These findings position S‐AV as a promising candidate for practical enhanced oil recovery applications.

The optimized microbial-induced calcium carbonate precipitation process to fabricate underwater superoleophobic mesh for efficient oil-water separation

Microbial-induced calcium carbonate precipitation (MICP) is an environmentally-friendly and easy operation technique for separating oil-water mixtures. However, the effect of environmental factors on the wettability and oil-water separation performance of MICP remains unclear. In this study, three primary factors including mineralization solution (MS) concentration, bacterial suspension (BS) concentration, and temperature were carefully investigated. Under these varying conditions, stainless steel meshes (SSM) were chosen as the substrates for the growth of CaCO3 precipitations. Experimental results demonstrate a strong dependence of the morphology and wettability of CaCO3 precipitations on these factors. Higher MS concentration and temperature contribute to enhanced hydrophilicity of CaCO3 coatings due to the increased surface roughness. The water flux of MICP-coated SSMs decreases with the increase of BS concentration, MS concentration, and temperature. The MICP-coated SSM obtained with MS concentration of 0.15 M, BS concentration of 0.1 × 108 cells/mL, and mineralization reaction at 25 ℃ for 24 hours demonstrated the optimal comprehensive performance, exhibiting underwater superoleophobicity with an underwater oil contact angle (UWOCA) exceeding 151°, an ultra-high oil intrusion pressure (> 3.0 kPa), ultrahigh flux (28,644 L m−2 h−1), and a preferable oil rejection rate (> 99.9%). Additionally, the as-prepared mesh exhibited superior anti-oil-fouling property and reusability, while concurrently demonstrating excellent chemical and thermal stability. This work contributes to advancing our knowledge of the influence of various environmental factors on the wetting characteristics of MICP and provides a feasible solution for the highly efficient and low-cost preparation of oil-water separation membranes based on the MICP process.

Rational designed of PVDF membrane based on surface modification of εPL anchored by PC for crude oil emulsion separation

For high-viscosity wastewater containing crude oil, the membrane material is easily clogged with contaminations, resulting in decreased flux and potentially loss of separation ability. In this study, a superhydrophilic/underwater superoleophobic PVDF membrane (PVDF-PC-εPL) was designed by the self-polymerization of proanthocyanidins (PC) and the grafting reaction of ε-polylysine (εPL), which showed a rough micro-nano structure without adding the inorganic particles. The PVDF-PC-εPL membrane displayed outstanding self-cleaning ability for high-viscosity crude oil, and the separation efficiency of the crude oil-in-water emulsion could be greater than 99.4%. The underwater oil contact angle (UWOCA) of the PVDF-PC-εPL membrane was 165°, after the PVDF-PC-εPL membrane had been exposed to air or water for 6 weeks, or soaked in different pH or seawater for 24 h, the UWOCA remained above 154° and the water contact angle was always 0°. The modification method on the PVDF membrane proposed in this study offers a fresh perspective and choice for preparing the oil-water separation materials.

Amino-functionalization of tungsten oxide nanoparticles for stable decoration in the active layer of alumina-supported inorganic-organic hybrid membrane with super-wettable and photocatalytic self-cleaning surfaces for crude oil-in-water emulsion separation

The ceramic membrane was hybridized with an amino-functionalized inorganic metal oxide and organic polymer to achieve the optimal oil and water surface wettability and photo-catalytic self-cleaning capability. The resulting membrane was used for the treatment of crude oil-contaminated wastewater under cross-flow filtration mode. The fundamental functional material, tungsten oxide nanoparticles (NH2-WO3 NPs) modified by aminopropyl triethoxysilane (APTES) was created and coated on the alumina ceramic support surface via interfacial polymerization, in which the material covalently cross-links on the membrane's active layer in the presence of terephthaloyl chloride (TPC) as a cross-linker and piperazine (PIP) as an external amine. Achieving a unique combination of oil and water surface wettability- superhydrophilicity (0° water-in-air contact angle) and underwater super-oleophobicity (160.25° under-water oil contact angle) was the key to creating the water-permeating NH2-WO3/PA@alumina ceramic membrane. The second advantageous feature of the membrane is its capacity for self-cleaning, which results from WO3 NP's innate photocatalytic activity that has been further enhanced by amino functionalization. A water permeate flux of up to 250 L m−2 h−1 and an oil/water separation efficiency of nearly 100 % were attained for an oil concentration of 50 ppm of crude oil-in-water emulsion when NH2-WO3/PA@alumina ceramic membrane was employed as a separation medium in a cross-flow filtration system for the separation of crude oil-in-water emulsion. Furthermore, the permeate flux decreased to ∼25 % of its initial flux after using NH2-WO3/PA@alumina ceramic for approximately 210 min. This was caused by organic pollutants in the oily water clogging the membrane pores. The permeate flux was recovered by exposing the membrane to UV light for photo-catalytic self-cleaning. Due to its water-passing nature, this membrane has high efficiency. Additionally, because the self-cleaning add-on removes the need for chemical cleaning, it is environmentally friendly.

Oil/water separation copper membranes modified by laser induced ZnO nanowires growth with enhanced catalytic function

Oil/water separation is a significant area of scientific study, and also has significant practical applications in the treatment of industrial oily wastewater and oil spill pollution. In this study, the high-flux copper mesh is fabricated by laser in a Zn2+ precursor solution at room temperature. The copper mesh processed inside the solution has a higher flux than that processed in the air. The heat absorbed by the liquid promotes the growth of ZnO nanowires on the copper mesh surface. The copper mesh's underwater oil contact angle (OCA) is as high as 150°. Compared with conventional copper mesh, it has a higher stability and can maintain a contact angle of 150° in acid-base environments and high-temperature environments. It has hydrophilic and oleophobic properties and can be used for oil/water separation. After 50 oil/water separation cycles, the separation efficiency can keep higher than 97%. This new method exhibits excellent potentials for oil/water separation and oil purification attributed to its simple and ecologically friendly processing.

Preparation of carbon-based active nanofluids with temperature and salt resistance for enhanced oil recovery

The abundant hydrophilic surface groups endow carbon-based nanoparticles (CDs) with intrinsic great dispersibility, however, the strong hydrophilicity limits the oil–water interface activity, restraining the performance in enhanced oil recovery. Developing CDs with simultaneously ultra-small sizes, high temperature and salt tolerance, as well as superior interfacial activity is of great significance. In this work, CDs with the size of 3.3 nm and excellent temperature and salt resistance were prepared by hydrothermal reaction, using citric acid (CA) and ethylenediamine (EDA) as precursors. Carboxyl ether carboxylate-6Na (APEC-6Na) was selected as the compound agent to construct carbon-based active nanofluids (CANs) with excellent oil–water and oil-solid interfacial activities. CANs can reduce the oil–water interfacial tension to 8.9 × 10-4 mN m−1, withstand a temperature up to 90°C and a salinity up to 6.3 × 104 mg·L-1. Even at the highest tolerant salinity, the underwater oil contact angle of 155° can be achieved, demonstrating excellent wettability control capability, which could be attributed to the synergistic effect of the compound CANs system. The increase of the contact angle of underwater oil droplets facilitates the coalescence of oil film on the lipophilic surface to form oil droplets. The electrostatic repulsion generated by the adsorption of CDs and APEC-6Na at the oil–water interface and rock surface makes the coalesced oil droplets more easily detached from the rock surface, and the oil film reduction rate exceeds 97.7 % within 24 h. The excellent oil–water and oil-solid interface properties and the structural separation pressure endows CANs with remarkable performance in core displacement experiments. Compared with simulated formation water, CANs can improve the recovery rate by 26.3 %, exhibiting important application value for improving the recovery rate of ultra-low permeability reservoirs.

Antifouling multi-functional membrane for oil/dye wastewater treatment: Regeneration while treating mixed pollutants

Treatment of insoluble oils or soluble organic dyes in wastewater by membrane separation is considered to be one of the most effective strategies. However, simultaneously removing oils and dyes from wastewater is challenging. In this study, hydroxyl iron oxide was grown on PVDF membranes by in situ self-assembly and in situ self-growth strategies using proanthocyanidins as a bridge. The PVDF-PC-FeOOH membrane possesses excellent wettability and photo-Fenton catalytic properties (all types of underwater oil contact angles are larger than 150°, and the degradation efficiency of methylene blue within 20 min is greater than 70%). The emulsion separation flux and efficiency can reach 976.1 L·m-2h−1 and 99.7%, respectively. In addition, the photo-Fenton catalytic degradation process was discussed. The regeneration rate of the membrane is over 90%. The flux can be stabilized over a period of time in a continuous filtration process of 60 min (flux over 158.7 L·m-2h−1). Simultaneous removal of mixed pollutants and regeneration of the membrane is achieved in a single step. In multi-component oily wastewater, the membrane has selective adsorption capacity for cationic dyes, and the removal rate can achieve 98.6%. The strategy provided in the present study enhances the value of membranes for practical applications in the field concerning the filtration of oily wastewater and selective separation of dyes in the dyeing and printing industry.

A novel and facile preparation of superhydrophilic/superoleophobic Mg(OH)2/ZnO coated mesh for fast and efficient oil/water separation

This study presents a new method for the rapid preparation of a superhydrophilic/underwater superoleophobic Mg(OH)2/ZnO coated mesh. Through one-step electrodeposition, a high underwater oil contact angle of 168.54° was achieved on the coated mesh. The electrodeposition process involved the deposition of ZnO nanoparticles on the cathode due to the presence of Mg2+ in the electroplating solution, while Mg(OH)2 was simultaneously formed on the surface of the cathode copper mesh. The cathode surface, where hydrogen is generated, leads to the formation of micropores and nanosheets on the Mg(OH)2/ZnO coated mesh structure. This structural feature traps more water molecules, further enhancing the superhydrophilicity of the coated mesh. The oil/water separation efficiencies for p-xylene, kerosene, paraffin liquid, and mineral oil were 99.8 %, 99.3 %, 99.5 %, and 99.4 %, respectively. The separation efficiency remained higher than 99.2 % even after conducting 350 p-xylene/water separation experiments. Additionally, the coated mesh displayed a strong oil/water separation ability after being immersed in alkali and salt solutions (pH = 7, 9) for 10 h. The coated mesh exhibited an enhanced water flux of (2.99 ± 0.20) × 105 L·m−2·h−1, along with a heightened invasion pressure (>2.8 kPa) and excellent oil-resistance performance. Overall, the Mg(OH)2/ZnO coated mesh developed in this study shows promising potential as a membrane for fast and efficient oil/water separation, with outstanding durability.

Fully biobased hydrogel based on chitosan and tannic acid coated cotton fabric for underwater superoleophobicity and efficient oil/water separation

Underwater superoleophobic (UWSO) materials have garnered significant attention in separating oil/water mixtures. But, the majority of these materials are made from non-degradable and non-renewable raw materials, polluting the environment and wasting scarce resources while using them. Against this backdrop, this study aimed to fabricate an environmental-friendly UWSO textile using biobased materials. To achieve this, hydrogel consisting of chitosan (CS) and poly(tannic acid) (PTA) were formed and coated on cotton fabric (CTF) via dip-coating followed by oxidative polymerization. CS&PTA hydrogel endowed the CTF with a rough surface and high surface energy, leading to an UWSO CTF with an underwater oil contact angle as high as 166.84°. The CS&PTA/CTF had excellent separation capability toward various oil/water mixtures, showing separation efficiency above 99.84 % and water flux higher than 23, 999 L m−2 h−1. Moreover, CS&PTA/CTF possessed excellent mechanical and environmental stability with underwater superoleophobicity unchanged after sandpaper friction, ultrasonication, organic solvents, NaCl (m/v, 30 %) solution, and acid/base solution immersion, due to the strong interaction between the hydrogel and cotton fabric generated by the mussel-inspired adhesion owing to the presence of PTA. The fully biobased UWSO CTF exhibits great promising to be an alternative to traditional superwetting materials for separation of oil/water mixtures.