Underwater Superoleophobicity Research Articles

In situ deposition of double Fe-based Fenton catalysts on the porous membrane for the development of multi-defense against various foulants toward highly efficient water purification

Membrane separation technology has been widely employed in wastewater separation, although, it is restricted by terrible membrane fouling. The acceptable “single defense” is insufficient to generate a desirable antifouling surface against various organic foulants in complex wastewater. Therefore, this work designs and constructs a porous surface with “multi-defense” by integrating hydrophilic, underwater superoleophobic, and anti-bacterial nano Fe-based Fenton catalysts of β-FeOOH nanorods and CuFeO2 nanoparticles on the polyvinylidene difluoride membrane via metal-ion-induced deposition process. The obtained composite membrane (MFeOOH/CF) has ultra-stable underwater superoleophobicity and ultra-low oil adhesion, which prevent oils from adhering to the membrane and benefit to separate various surfactant-stabilized oil-in-water emulsions with high water flux and separation efficiency of 99%. MFeOOH/CF also exhibits nearly 100% bactericidal activity against Escherichia coli. Moreover, the various foulants (such as bovine serum albumin, methylene blue, and crude oil) adhered to the membrane after filtration can be successfully degraded by MFeOOH/CF under the solar-driven Fenton process, leading to ultrahigh flux recovery ratio (FRRV) of 98.2 ± 0.3% and a low irreversible fouling ratio (RirV) of 2.0 ± 0.1%. The apparent degradation rate constant (k) of MFeOOH/CF is 2.5 times the β-FeOOH coated membrane (MFeOOH) because the introduction of CuFeO2 nanoparticles provides more reactive sites and lowers the Fe3+/Fe2+ redox potential. This study is working to bring about a highly efficient “multi-defense” on the porous membrane, which will realize membrane regeneration and boost wastewater purification.

Anionic ammonium polyphosphate coated underwater superoleophobic cotton fabric for effective oil/water separation

Considering the great threat of oil spilling to human safety and ecological balance, treatment of oily wastewater became a worldwide challenge. Inspired by the underwater superoleophobic property of fish scale surface, we fabricated the superhydrophilic and underwater superoleophobic cotton fabric (CF) through grafting modification of ammonium polyphosphate (APP) followed by surface deposition of Fe3O4 nanoparticles via micro-dissolution method. The incorporation of APP, which contained numerous anionic groups, was found to be advantageous in enhancing the water holding capacity of fabric. More significantly, the micro-nanoscale rough structure resulting from Fe3O4 nanoparticles was pivotal in achieving superwetting ability towards water. The synergistic effect of hydrophilic chemical and rough structure significantly improved the superhydrophilicity and underwater superoleophobicity of the CF. The as-prepared fabric not only exhibited applicability for separating oil/water mixture, but also demonstrated exceptional performance in the separation of emulsions with relatively high water flux. The presence of numerous anionic groups was crucial in facilitating water flux during emulsions separation by screening electrostatic repulsion. Furthermore, benefiting from the self-glue effect of micro-dissolved CF, the as-prepared fabric exhibited remarkable stability against harsh conditions such as mechanical abrasion, immersion in acid or alkali solution, high temperature and frequent laundering. In general, this study would contribute to the development of fabric-based materials for oily wastewater separation with excellent separation performance and high stability.

Photocatalytic self-cleaning membrane with polyaniline/NH2-MIL-125 heterojunction for highly oil-water/seawater separation and bacterial inactivation

Emulsified oils and microbial contaminations in water environments have posed huge risks to human health and ecological balance. In this work, we fabricated a polyaniline/NH2-MIL-125 (PANI/MIL) heterojunction decorated hydrolyzed polyacrylonitrile (HPAN) membrane with photocatalytic self-cleaning property for oil–water separation and bacterial inactivation. In which, PAN membrane was prepared by electrospinning and then HPAN membrane was obtained by alkaline hydrolysis. The photo-responsive PANI/MIL heterojunction was immobilized on HPAN membrane by vacuum-assisted assembly using protocatechuic acid (PCA) as the binder. The resultant PANI/MIL@HPAN composite membrane has a wettability of in-air superamphilicity and underwater superoleophobicity as well as surface nano-micro heterostructure. The composite membrane showed good separation efficiency (above 99.4%) and high flux (1446–3744 L m−2h−1) in a series of oil-in-water/seawater emulsions separation. In particular, the membrane can effectively deal with viscous oil fouling under visible light to achieve a desired flux recovery ratio (FRR) after separating crude oil from water, which was ascribed to the self-cleaning capacity originating from the surface coating photocatalyst. Meanwhile, the multifunctional composite membrane showed 100% photocatalytic inactivation efficiency against pathogenic Gram-negative bacteria E. coli and Gram-positive bacteria S. aureus (6 log units) in water under visible light with low power intensity. The oil–water separation performance as well as photocatalytic inactivation efficiency of PANI/MIL@HPAN are superior to MIL@HPAN. The studies on the wettability, photothermal properties and photoelectric properties suggested that the coupling of conductive polymer PANI can simultaneously enhance the underwater superoleophobicity of the composite membrane, as well as improve the photocatalytic activity by creating a type II heterojunction to promote the separation of charge carriers and amplifying the photothermal effect, making the PANI/MIL@HPAN multifunctional membrane achieve the improved oil/water separation performance and antibacterial activity synergistically. This work provides a new strategy for developing effective self-cleaning membranes both toward oil/water separation and bacterial inactivation applications based on MIL metal–organic framework coupling with conductive polymers.

Constructing superwetting membranes by sodium lignosulfonate-modified carbon nanotube for highly efficient crude oil-in-water emulsions separations

For the past few years, superwetting materials had been developed to enhance the treatment process of oily wastewater. Membranes are improved through the combination of surface topography and chemical modifications to achieve superwetting properties for treating oily wastewater effectively. In this work, we prepared an eco-friendly membrane by depositing sodium lignosulfonate (SLS)-modified carbon nanotube (CNT) on a cellulose acetate membrane via vacuum filtration without employing any organic solvents. The SLS@CNT membrane shows superhydrophilicity and underwater superoleophobicity with high stability. Furthermore, the SLS@CNT membrane exhibits outstanding antifouling and self-cleaning properties against crude oil of high viscosity. Most importantly, our SLS@CNT membrane exhibits outstanding oil-in-water emulsions separation performances including crude oil-in-water emulsions. For the surfactant-free and surfactant-stabilized emulsions, fluxes were revealed to reach up to 27,800 L m−2 h−1 bar−1 and 13,800 L m−2 h−1 bar−1, respectively, with very high separation efficiency (>99.97 % and 99.79 %, respectively). The distinguished performance of our SLS@CNT membrane, and its eco-friendly, low-energy consumption, and cost-effective preparation, demonstrate practical applicability.

Clay-Coated Meshes with Superhydrophilicity and Underwater Superoleophobicity for Highly Efficient Oil/Water Separation.

A novel clay-coated mesh was fabricated via a simple brush-coating method without the use of special equipment, chemical reagents, and complex chemical reactions and operation processes. Possessing superhydrophilicity and underwater superoleophobicity, the clay-coated mesh can be used for efficiently separating various light oil/water mixtures. The clay-coated mesh also exhibits excellent reusability, maintaining a high separation efficiency of 99.4% after 30 repeated separations of the kerosene/water mixture.

Robust Zwitterionic Poly(imidazolium)-Coated PVDF Membrane for Oily Water Treatment with Antibacterial and Anti-Biofouling Performances

Membrane fouling remains a major challenge during oily wastewater purification, resulting in reduced water flux and separation efficiency. Zwitterionic polymers have been introduced to the PVDF membrane and shown their fouling resistance ability. However, most current zwitterions lack bactericidal effects and tend to be fouled by the attachment of bacteria and biofilm formation in long-term service. Herein, a synthetic zwitterionic poly(imidazolium), poly(ZIM-co-VTS), was introduced onto the PVDF membrane by co-assembly with polydopamine (PDA) and tetraethyl orthosilicate (TEOS) as a silica source. The in situ covalent bond can be formed between the catechol from PDA and silanol groups from both TEOS and imidazole-based polymers. Further, Fe3+ cross-linking contributes to the robust chemical stability of modified PVDF. The as-prepared coating exhibits superhydrophilicity and underwater superoleophobicity under harsh conditions (pH = 1 and 13), remaining high separation efficiency (>99%) toward various surfactant-stabilized oil-in-water emulsions without an apparent water flux (>1013 L m–2 h–1 bar–1) decline. More importantly, the cationic imidazolium in poly(ZIM-co-VTS) endues the excellent bacterial killing efficiency toward Staphylococcus aureus (4.5 log10 reduction) and Escherichia coli (4.7 log10 reduction). The zwitterionic poly(imidazolium)-modified PVDF exhibited long-term durability with anti-biofouling properties and was a promising candidate for practical oily wastewater remediation.

Converting pomelo peel biowaste into multifunctional sponges integrated underwater superoleophobicity and catalytic ability for sewage treatment

Fabricating practical multitasking materials integrating efficient oil-water separation ability and excellent catalytic performance is significant for water remediation but challenging for substrates and subsequent surface modification causing high cost, high power consumption, and poor reusability. Herein, a multitasking sponge was designed for water purification by successively modifying the biomass pomelo peel (PP) with polypyrrole (PPy), Au nanoparticles (NPs), and polydopamine (PDA). The cost-effective and renewable PP substrates, facile surface decoration of PP with PPy coating, in-situ spontaneous growth of Au NPs, and the protection of the outermost PDA coating endowed the as-obtained PP/PPy-Au/PDA sponges high sewage treatment efficiency and the potential for large-scale preparation. The PP/PPy-Au/PDA sponges exhibited high catalytic reduction activity for 4-nitrophenol (4-NP) and excellent reusability without remarkable decline in catalytic activity even after 10 recycles due to the synergistic effect among PPy, Au NPs and PDA. In addition, this sponge also displayed superior separation efficiency and high filtration flux towards both immiscible oil-water mixtures and O/W emulsions due to its underwater superoleophobicity. Integrating above properties, the PP/PPy-Au/PDA sponge could perform catalytic degradation of organic molecules and meanwhile separation of oil-water mixtures.

Deployment of Superhydrophilic and Super-antifouling Cr-soc-MOF-1-Based Membrane for Ultrafast Separation of Stabilized Oil-in-Water Emulsions.

In spite of massive progress in oil-water separation, attributable to the use of advanced materials, the separation process faces challenges such as low permeance and fouling problems. Therefore, superwettable materials used in several fields are considered potential candidates for oily wastewater treatment. Metal-organic frameworks (MOFs) are receiving more and more interest in various separation applications due to their wide potential applications. Nevertheless, MOFs have been rarely explored for separating stabilized oil-in-water emulsions due to the difficulty in finding highly hydrolytic stable MOF candidates for this application. Furthermore, oil can clog water-stable materials owing to its high density, causing the degradation of MOF particles. As a result, there is a need to develop better MOF materials that can fulfill these requirements. Herein, we have explored Cr-soc-MOF-1 as a candidate for this application and deployed it as a membrane, which exhibited superhydrophilicity and underwater superoleophobicity for separating stabilized oil-in-water emulsions. The Cr-soc-MOF-1 membranes were synthesized by assembling the as-prepared MOF particles on a mixed cellulose ester substrate using a vacuum-assisted self-assembly technique. The Cr-soc-MOF-1 membrane exhibited ultrahigh water permeance (7465.9 L·m-2·h-1·bar-1), very high oil rejection (99.9%), and excellent anti-oil-fouling properties. The Cr-soc-MOF-1 membranes also exhibited excellent recyclability over 10 continuous separation cycles. Further, they exhibited an outstanding performance in separating various surfactant-stabilized oil-in-water emulsions. Thus, the Cr-soc-MOF-1 membranes exhibit a high potential in treating oily wastewater.

Anti-oil fouling poly(vinylidene fluoride) membrane with excellent underwater superoleophobicity and high-efficient photo-Fenton oxidation for oily water purification

Oil fouling makes serious trouble to the membranes for oil-in-water emulsion separation and purification. Here, an anti-oil fouling membrane was designed and constructed by loading β-FeOOH nanorods and carbon quantum dots (CQDs) on the poly(vinylidene fluoride)/poly(2-hydroxyethyl methacrylate) blend membrane. The fabricated BM@(β-FeOOH/CQDs) membrane can efficiently separate various oil-in-water emulsions. Furthermore, BM@(β-FeOOH/CQDs) exhibits stable underwater superoleophobicity with an underwater oil contact angle (UWOCA) of 152.5 ± 1.1° and a sliding angle (SA) of 2.2 ± 0.2°, which is beneficial to prevent oil droplets from contacting and adhering to the separation porous surface. Moreover, BM@(β-FeOOH/CQDs) has excellent photo-Fenton oxidation efficiency, which can photo-activate H2O2 to degrade oil droplets on the separation membrane. The flux recovery ratio of the membrane increases by 1.8 times when the photo-Fenton reaction was activated. This work provides an effective strategy for the engineering of anti-oil fouling membranes to purify oily wastewater.

Superoleophobic Polyketone Nanofiber Membranes for Efficient Separation of Oil/water Emulsions

AbstractElectrospun nanofiber membranes derived from polyketone (PK) are precisely fabricated to exhibit an excellent separation efficiency for oil/water emulsions. The fiber diameter and pore size of the membrane are controlled by introducing NaOH to the precursor solution prior to electrospinning. The surface properties of the nanofibers are then controlled by the removal of NaOH with water and reduction of functional groups with sodium borohydride (NaBH4) to exhibit an air‐water superhydrophilicity and underwater superoleophobicity. This surface conversion process is easily monitored by the water contact angle and the underwater oil contact angle. Oil/water emulsions, including toluene, soybean oil, and hexadecane are filtered through the membranes to examine their separation efficiency and flux using total organic carbon and UV‐Vis measurements. The optimized membrane exhibits the minimum 97 % separation efficiency for all three oil/water emulsions and recyclability without notably losing its flux under gravity‐driven filtration conditions.

Mussel inspired stable underwater superoleophobic cotton fabric combined with carbon nanotubes for efficient oil/water separation and dye adsorption

Currently reported biobased superwetting cotton fabrics (CF) for wastewater purification were limited because they can only separate oil/water mixtures but cannot remove other pollutants such as dyes from wastewater. In this study, we reported a superhydrophilic and underwater superoleophobic cotton fabric (SUSCF) which was fabricated via a facile two-step method, i.e., dip-coating in poly(sodium 4-styrenesulfonate) (PSS) wrapped carbon nanotube (CNT) dispersion and subsequent in-situ deposition of polydopamine (PDA). The deposited PDA particles and coated CNT endowed CF with superhydrophilicity and underwater superoleophobicity by improving surface roughness and hydrophilicity. The obtained SUSCF showed an underwater oil contact angle of 160°, which made it an attractive water-removing material for oil/water separation with separation efficiency and water flux of higher than 99.8% and 10,834 L m-2h−1, respectively. The combination of CNT, PSS, and PDA endowed the SUSCF with outstanding cationic dye adsorption capacity, especially leading to a maximum removal ratio of 97% toward methylene blue. In addition, the SUSCF exhibited excellent stability to survive after exposure to sandpaper abrasion, boiling water, organic solvents, salt solution, and acidic/alkali erosion, due to the strong hydrogen bonds and mussel-inspired adhesion between coated components and fabric surface. The stable biobased underwater superoleophobic cotton fabric with integrated excellent oil/water separation performance and dye adsorption capacity shows great potential in wastewater purification even under some harsh conditions.

Simple and eco-friendly fabrication of highly tolerant chitosan/alginate@sepiolite hybrid films on nylon textile for oil/water separation in harsh conditions

Because of the need of achieving efficient separation to oil/water mixture, the construction of separation coating with good mechanical strength and chemical resistance are highly desired. Although many polysaccharide-based coating for oil/water separation have been prepared, the poor durability and the environmentally unfriendly preparation process greatly restrict their applications. Herein, sepiolite (SP) was introduced into chitosan/alginate (CS/AG) matrix to produce nacre-like composite films with superb robustness and stability via a simple and green layer-by-layer (LbL) self-assembly technique. After the composite films are fabricated on nylon textile (NT), the hydrophilicity and underwater superoleophobicity of the NT surface are significantly improved. The composite coating also reveals excellent oleophobic stability after being subjected to corrosive liquids immersion, high-temperature treatment, strong abrasion, and organic solvents immersion. Furthermore, the modified NT is able to separate oil/pure water, oil/cold corrosive water, and oil/hot corrosive water mixtures with high filtration efficiency (>98.3 %). Especially, the separation to oil/hot corrosive solution mixtures can be repeated at least 40 times without obvious decrease of separation efficiencies. This investigation offers a new and eco-friendly strategy to prepare SP coating-based membrane materials with good superhydrophilicity, mechanical property, and recyclability for oily wastewater purification.

Carbonaceous nanofibrous membranes with enhanced superhydrophilicity and underwater superoleophobicity for effective purification of emulsified oily wastewater

High performance oil–water separation membranes with stable physical–chemical properties are highly desirable for the treatment of emulsified oily wastewater in various conditions. Carbonaceous nanofibrous membranes are promising due to several merits, including good thermal resistance, chemical inertness, non-toxicity, and harmlessness. However, the hydrophobicity and oleophilicity of carbon, as well as the poor mechanical property of carbon nanofibers, make it challenging to use the corresponding membrane for the separation of oil-in-water emulsions. Herein, we demonstrate a facile and effective strategy to fabricate a superhydrophilic and underwater superoleophobic carbonaceous nanofibrous membrane. The mechanical property and surface wettability of the membrane could be well regulated through heteroatom doping and thermal induced oxidation. As a result, the obtained carbonaceous nanofibrous membrane exhibited intriguingly durable mechanical flexibility and oil–water selective wettability, which were comparable to that of polymeric membranes. In the meanwhile, a plausible mechanism for the underwater superoleophobicity of the membrane was proposed based on a series of structural analyses and molecular dynamic simulations. With the synergy of developed pores and high oil–water selective wettability, the obtained carbonaceous nanofibrous membrane was effective for separating various oil-in-water emulsions. Moreover, the membrane, thanks to its gratifying underwater anti-oil adhesion property, could be efficiently reused after a simple process of hydraulic washing, demonstrating great potential for the purification of emulsified oily wastewater.

One-Step Hydrothermal Strategy for Preparation of a Self-Cleaning TiO2/SiO2 Fiber Membrane toward Oil-Water Separation in a Complex Environment

Oil pollution caused by a large number of industrial activities and oil spill accidents has posed serious harm to the environment and human health. However, some challenges remain with the existing separation materials, such as poor stability and fouling resistance. Herein, a TiO2/SiO2 fiber membrane (TSFM) was prepared by a one-step hydrothermal method for oil-water separation in acid, alkali, and salt environments. The TiO2 nanoparticles were successfully grown on the fiber surface, endowing the membrane with superhydrophilicity/underwater superoleophobicity. The as-prepared TSFM exhibits high separation efficiency (above 98%) and separation fluxes (3016.38-3263.45 L·m-2·h-1) for various oil-water mixtures. Importantly, the membrane shows good corrosion resistance in acid, alkaline, and salt solutions and still maintains underwater superoleophobicity and high separation performance. The TSFM displays good performance after repeated separation, demonstrating its excellent antifouling ability. Importantly, the pollutants on the membrane surface can be effectively degraded under light radiation to restore its underwater superoleophobicity, showing the unique self-cleaning ability of the membrane. In view of its good self-cleaning ability and environmental stability, the membrane can be used for wastewater treatment and oil spill recovery and has a broad application prospect in water treatment in complex environments.

Spray-assisted LBL assembly of chitosan/nanocellulose as coatings of commercial membranes for oil-in-water emulsion separation

Owing to the limitation of their wettability and pore size, lab filter membranes could not separate oil/water emulsions. Herein, we present surface modification of commercial membranes with chitosan/nanocellulose coatings via a spray-assisted layer-by-layer (LBL) assembly technology. By alternate spraying chitosan (CS) solution and TEMPO-oxidized tunicate cellulose nanofiber (TCNF) suspension, (CS/TCNF)n multilayers were obtained, where n denotes the number of bilayers. The (CS/TCNF)6 coated membrane possessed superhydrophilicity, underwater superoleophobicity, and outperforming anti-oil-fouling properties, which could effectively separate various oil-in-water emulsions. Importantly, the (CS/TCNF)6 coated membrane not only had stable permeate flux with nearly 100 % recovery ratio for the separation of pump oil-in-water emulsion, but also exhibited good harsh-environment-tolerant property. This work provided a novel strategy for designing and preparing stable anti-oil-fouling membranes for oily wastewater treatment.

Bioinspired copper-graphene oxide hybrid membrane prepared via electrochemical-driven strategy: design, mechanism, and oil-water separation

Constrained by intricate manufacturing processes, poor flux, and unsatisfied durability, a handy strategy to produce hybrid membranes with superior properties in oil–water separation was highly desired. Herein, a novel electrochemical-driven method was developed to realize graphene oxide (GO) production and simultaneously self-growth of Cu-GO hybrids on stainless-steel mesh to obtain the desired lanceolate Cu-GO microstructure. After optimization, the microstructure endowed the resultant Cu-GO hybrid membrane (Cu-GO HM) with underwater superoleophobicity (165.8° for kerosene), superior anti-oil-fouling performance, and excellent stability under harsh conditions (e.g., saturated NaCl, acidic, alkaline solutions, and various organic solvents). Noteworthily, Cu-GO HM can achieve around 99.5% separation efficiency and a superior flux of 182160 L m-2h−1 for oil/water mixtures solely driven by gravity. Additionally, the membrane can effectively separate oil-in-water emulsions. Even after suffering from multi-cycle sandpaper sanding and high-frequency ultrasonic damage, lanceolate Cu-GO microstructure still showed strong cohesion, guaranteeing the mechanical stability and durability of Cu-GO HM. The membrane also showed brilliant reusability through 50 cycles and long-term separation tests. Furthermore, the mechanism of the preparation and separation process was discussed in detail. The distinctive advantages of Cu-GO HM synthesized by electrochemical driven can ensure an available strategy for efficient oil–water separation.

Superwetting membrane by co-deposition technique using a novel N‑oxide zwitterionic polymer assisted by bioinspired dopamine for efficient oil–water separation

Superwetting membranes have good prospective for treatment of oil-containing wastewaters. However, development of simple and environment-friendly membranes with efficient oil–water separation performance remains a great challenge that needs to be addressed urgently. In this study, inspired by the secretion of trimethylamine-N-oxide (TMAO) by saltwater fish, we report a novel N‑oxide zwitterionic polymer (PTMAO) with ultralow fouling property possessing directly linked opposite charges in their molecules and superior hydrophilicity, as compared to conventional zwitterionic ones. Using biomimetic co-deposition technique of dopamine (DA) and PTMAO, a zwitterionic polymer network was formed via self-polymerization of DA and followed by hydrogen bonding and cation-π effects between the oxidatively generated polydopamine (PD) and PTMAO. As expected, the fabricated membrane exhibited excellent superhydrophilicity and underwater superoleophobicity. The M–PD/PT/2:2 membrane achieved high efficiency of oil–water separation performance under ultra-low-pressure conditions, with an oil–water emulsion flux of 1121.1 L/m2 h, a recovery rate of 93.1%, and oil rejection as high as 99.2% in the cyclic oil–water emulsion separation process. Meanwhile, the M–PD/PT/2:2 membrane showed excellent stability. Therefore, this work provides a new idea for the preparation of superwetting membranes using dual-biomimetic techniques for effective separation of oil–water emulsion.

Chemically Customizing Mechanical Properties and Optical Transparency in Underwater Superoleophobic Coating

AbstractThe inherent ability of bio‐inspired underwater superoleophobicity to prevent oil/oily fouling underwater makes it appropriate for a wide range of applications related to environmental remediation, bio‐adhesion, microfluidics, chemical sensing, etc.; however, the co‐association of mechanical durability and optical transparency is essential for realistic performance. While the design of mechanically durable and absolutely optically transparent underwater superoleophobic coating remains challenging, here, a covalently cross‐linked and chemically reactive sol‐gel conversion process is introduced through 1,4‐conjugate addition reaction to achieve a substrate‐independent and tolerant coating for orthogonally modulating the underwater oil wettability, optical transparency, and even mechanical properties of highly deformable porous and fibrous substrates. The post‐modification of residual chemical reactivity in the prepared coating allows to embed underwater superoleophobicity, and the β‐amino‐ester‐cross‐links improve the mechanical property of selected deformable substrates. Moreover, it displayed unperturbed performance even after prolonged (30 days) exposures in practically relevant chemically harsh aquatic conditions—including extremes of pH, artificial seawater, surfactant contaminated water, etc. The approach is successfully applied to coat various substrates—including porous, fibrous, and planar objects, and it would be useful in protecting various relevant marine infrastructures from oil/oily fouling, and various other potential applications.

Superhydrophilic and underwater superoleophobic ceramic membranes grafted by layered polydopamine and polydopamine encapsulated silica particles for efficient separation of oil-in-water emulsions

Owing to frequent oil spills and the increasing discharge of oily wastewater, oil pollution has threatened the sustainability of the ecosystem. Ceramic membranes (CM) have been employed for oily wastewater treatment because of their mechanical and chemical stability, but a suitable separating layer is required to treat surfactant-stabilized oil-in-water emulsions effectively. Herein, a separating layer was rationally designed on the CM surface by combining cross-linked layered polydopamine (CL-LPDA) and polydopamine-encapsulated silica particles (SiO2@PDA) with appropriate permeation flux and antifouling characteristics. The resulting CL-LPDA-SiO2@PDA-CM demonstrated superhydrophilicity with a water contact angle of 0° and underwater superoleophobicity with an underwater oil contact angle of 157°, making it an ideal membrane for separating oil-in-water emulsions. The designed membrane could treat a surfactant-stabilized oil-in-water emulsion with a maximum separation efficiency of 97 % and a permeation flux of 109.76 L m−2h−1. The CL-LPDA-SiO2@PDA-CM has also shown significant resistance to fouling under 20 cycles of observation, and the flux recovery ratio (FRR) was higher than 90 %, indicating that pore-clogging could be effectively prevented in the separating layer.

Photo-responsive Mn-doped TiO2-based superhydrophobic/ underwater superoleophobicity membrane for efficient oil-water separation and photothermal decontamination

In recent years, oily wastewater has become an important factor in environmental pollution. As a transition metal element, manganese is able to introduce new impurity band gaps using d-orbital hybridization to extend the photoresponse range of TiO2, thus enabling TiO2 to be self-cleaned under UV irradiation more easily. Therefore, we synthesized superhydrophobic/submerged superoleophobic Mn@TiO2-modified membranes which possess a self-cleaning property under UV light using manganese element-doped titanium dioxide and cotton fabric as the substrate by hydrothermal method and then investigated the relevance between the doping concentration of Mn and super-hydrophobicity. The results showed that water contact angles of prepared membranes with the Mn ions doping concentrations of 0.5 mol/L, 1.0 mol/L, and 1.5 mol/L were 147.89°, 150.43°, and 153.37°, respectively. The membrane with 1.5 mol/L was effective for the separation of the dichloromethane-water mixture. Under Xenon lamp irradiation, three membranes with different concentrations showed a significant temperature increase with the maximum rising to 53.1 ℃ within 2 min, reflecting an excellent photothermal conversion capability. In addition, the decontamination ability of the Mn@TiO2 membrane was tested under UV light. The Mn@TiO2 membrane was able to degrade the oil-red solution dripping on the surface, showing that the membrane had a good self-cleaning performance, which was significant for industrial applications.