Membranes For Oil-water Separation Research Articles

A Critical Review on Superhydrophobic and Superhydrophilic Electrospun Nanofibrous Membranes for Oil-Water Separation

A Critical Review on Superhydrophobic and Superhydrophilic Electrospun Nanofibrous Membranes for Oil-Water Separation

Superhydrophilic polymer coatings based on PVDF membranes for oil-water separation

Recently, the excellent anti-pollution performance of superhydrophilic membrane has attracted much attention in the field of wastewater treatment and oil-water separationIn. At present, the widely used commercial membrane materials have good pore structure and mechanical properties, but most of the commercial membranes are hydrophobic, so a simple, environmentally friendly and universal method is urgently needed to change its hydrophobic membrane to superhydrophilic membrane. In this paper, tannic acid (TA, natural plant polyphenols) and polydopamine (PDA) were used to build an anti-stain coating. The synthesized hydrophilic polymer containing polyphenols crosslinks with the base layer through hydrogen bonding, π-π and Michael addition. After the modified PVDF membrane is moistened by water, the superhydrophilic polymer network on the surface binds the water to form a stable hydration layer, showing the superhydrophilic/underwater superhydrophobic properties. The wettability of the modified film in air and water was investigated. The contact Angle of the modified separation membrane prepared in this paper is more than 150°, and the separation efficiency exceeded 98%. The good flux and efficiency can be maintained after 5 cycles, and it is found that the membrane has a certain anti-protein adsorption capacity. The modified membrane has high separation flux and excellent reuse, and has great uses in other ways.

A photocatalytic degradation self-cleaning composite membrane for oil-water separation inspired by light-trapping effect of moth-eye

Membrane separation technology with superwetting surfaces is ideal for treating water pollution. However, the fouling problem of membranes limits their practical application in this field. Membranes with self-cleaning property during the separation are the key to solve this problem. In this study, inspired by the light-trapping effect of the moth-eye, a kind of composite membrane with efficient self-cleaning by photocatalytic degradation was proposed. The composite membrane is based on polyvinyl alcohol cross-linked tannic acid (PVA-TA) and its photocatalytic function is achieved by doping magnetic titanium dioxide nanoparticles (MTiO2) as well as MXene. Meanwhile, its surface was constructed by magnetically controlled self-assembly method using MTiO2 to mimic the moth-eye structure. The composite membrane has superhydrophilic/underwater superoleophobic, excellent oil-water separation efficiency (99.85%) and long service life (64 cycles). In addition, due to the light-trapping effect of the bionic moth-eye structure and the redox reaction at the interface of MTiO2-MXene composites under sunlight irradiation, the membrane can achieve efficient and convenient photocatalytic degradation self-cleaning by sunlight irradiation. This study will provide new insights into the self-cleaning method of oil-water separation materials.

Underwater superoleophobic copper mesh coated with block nano protrusion hierarchical structure for efficient oil/water separation

Compared with monolayer nanosheet membranes, multilayer nanosheet membranes have low energy consumption and can be mass-produced for industrial applications. Herein, a multi-layer nanostructured membrane, nickel-doped brochantite/Cu(OH)2 nano protrusion structure coated copper meshes (NBCPCMs), were successfully prepared. Firstly, the surface of the copper mesh was etched by chemical oxidation to form a disordered copper hydroxide nanosheet layer. Secondly, the etched copper mesh surface was coated with nickel-controlled brochantite block-like protrusions by hydrothermal synthesis method, and nickel-doped brochantite/Cu(OH)2 nanosheets were generated by high pressure. The results showed that NBCPCM-4 had excellent hydrophilic/underwater superoleophobicity, the oil–water separation efficiency of immiscible cyclohexane/water mixture was the highest, about 98.54%, and still had a very high flux (>60 (kL/(h·m2))) after multiple cycles of separation. In addition to ultra-high separation efficiency, NBCPCM-4 also had super durability. The copper mesh maintained good underwater superoleophobicity in different aqueous solutions. Therefore, NBCPCM-4 is a potential high-efficiency and sustainable oil–water separation membrane material. It is expected that the developed technology is useful for sea transportation and marine environment management, along with other industries.

Superhydrophilic quaternized calcium alginate based aerogel membrane for oil-water separation and removal of bacteria and dyes

In recent years, frequent oil spills and increasing industrial wastewater discharge have caused serious water pollution problems. In addition, there are often microbial and dye pollutants in oil-containing wastewater. The development of materials that can simultaneously treat these three pollutants is very important for the safe treatment and recovery of wastewater. In this work, a modified calcium alginate-based aerogel membrane (CTW) was prepared through sol spraying, Ca2+ crosslinking and freeze drying by using tetrabutylammonium hydroxide (TBA) quaternary ammonium salt modified sodium alginate (SA) as raw material and waterborne polyurethane (WPU) as adhesive. The results show that CTW membrane has super hydrophilic and underwater super-oleophobic properties, and can realize the separation oil-water emulsions under gravity, with the separation efficiency of >99 %. CTW membrane can also remove bacteria and dye such as Congo red from water by filtration, with removal rates of 100 % and 99 % respectively. The filtration results of mixed wastewater show that CTW membrane can realize one-step separation of oil, bacteria and dye in wastewater, and can also be recycled, having potential application prospect.

Application of in-situ microbubble method on SEP@MnO2/RGO composite membrane for efficient and long-acting treatment of oil field wastewater

The treatment of oilfield wastewater has been a problem for oil workers for a long time. Indeed, it is economical, efficient and environmental friendly to treat oilfield wastewater with membrane. However, the contamination and stability of membrane limit the application of membranes. This study focuses on improving the long-term integrated treatment of oilfield wastewater by commercial PVDF membranes in different environments. Sepiolite(Sep)@MnO 2 composites were synthesized by hydrothermal method. SEP@MnO 2 and graphene oxide(GO) were left on the commercial PVDF membrane after vacuum filtration. Then the membrane was subjected to 120 vacuum thermal reduction. The prepared Sep@MnO 2 /RGO composite membrane showed good separation result and flux for different proportion of oilfield wastewater. Moreover, it can remove some common salt (NaCl,MgSO 4 , CaCl 2 , MgCl 2 ) and heavy metal ions (Ni 2+ , Fe 3+ , Cr 6+ ) in oilfield wastewater. Even more valuable, a few addition of H 2 O 2 to oilfield wastewater caused an oxidation reaction and the produced in situ microbubbles greatly enhance the antifouling property of the membrane. After 15 cleaning tests and 12 h of cycling, the membrane still showed strong separation ability. Compared with other oil-water separation membranes reported, this membrane demonstrated a longer and better separation effectively. All the work promotes the application of membrane separation technology in oilfield wastewater treatment. Hopefully, the application of in-situ microbubble method on membrane will solve the problem of membrane pollution in oilfield wastewater treatment. • The membrane can effectively treat the oil field wastewater with heavy metals and salts. • The application of in-situ bubble method on the membrane enhances the anti-fouling property of the membrane. • The membrane is qualified in a table and long-active treatment of oilfield wastewater.

PDMS/PVDF Electrospinning Membranes for Water-in-Oil Emulsion Separation and UV Protection.

With industry development, the separation of oily wastewater is becoming more critical. Inspired by organisms such as lotus leaves, biomimetic superhydrophobic surfaces with micro-nano structures have shown great potential in this regard. In this work, PDMS/PVDF oil-water separation membranes with designed microstructures were prepared by electrospinning technology. The membrane-forming effect of electrospinning with different ratios of PDMS and PVDF was studied. The study found that membranes with high PDMS content were more likely to form microspheres, and PDMS tended to concentrate on the microspheres. The results also showed that the microspheres would bring better hydrophobicity to the membrane. When the ratio of PDMS to PVDF is 1:2, the membrane has a water contact angle of up to 150° and an oil contact angle of 0°. At this ratio, the separation efficiency of the membrane for the water-in-oil emulsion is 98.7%, and it can still maintain more than 98% after ten separation cycles, which is a good candidate for oil-water separation. Furthermore, microspheres enable the membrane to achieve macroscopic uniformity and microscopic phase separation so that the membranes have both good elongation and fracture strength. In addition, the PDMS/PVDF membranes also exhibit excellent UV resistance, and their UV protection factor is greater than 185, making them a potential UV protective material.

Antifouling graphene oxide membranes for oil-water separation via hydrophobic chain engineering

Engineering surface chemistry to precisely control interfacial interactions is crucial for fabricating superior antifouling coatings and separation membranes. Here, we present a hydrophobic chain engineering strategy to regulate membrane surface at a molecular scale. Hydrophilic phytic acid and hydrophobic perfluorocarboxylic acids are sequentially assembled on a graphene oxide membrane to form an amphiphilic surface. The surface energy is reduced by the introduction of the perfluoroalkyl chains while the surface hydration can be tuned by changing the hydrophobic chain length, thus synergistically optimizing both fouling-resistance and fouling-release properties. It is found that the surface hydration capacity changes nonlinearly as the perfluoroalkyl chain length increases from C4 to C10, reaching the highest at C6 as a result of the more uniform water orientation as demonstrated by molecular dynamics simulations. The as-prepared membrane exhibits superior antifouling efficacy (flux decline ratio <10%, flux recovery ratio ~100%) even at high permeance (~620 L m−2 h−1 bar−1) for oil-water separation.

Dual-functional superhydrophilic/underwater superoleophobic 2D Ti3C2TX MXene-PAN membrane for efficient oil-water separation and adsorption of organic dyes in wastewater

The incorporation of two-dimensional Ti3C2TX MXene nanoflakes into polymeric membranes has piqued researchers' enthusiasm as a way to improve the effectiveness of oil–water separation membranes. Herein, we developed a simple approach for fabricating two-dimensional Ti3C2TX MXene nanoflakes on a nanofibrous PAN membrane via vacuum filtration. The superhydrophilic/underwater superoleophobic MXene-PAN membrane showed remarkable separation performance for a diverse range of oil–water emulsions owing to its intrinsic hydrophilicity, low oil droplet adherence and regular stacking of 2D Ti3C2TX MXene nanosheets. The ultralow oil adhesion contributed to anti-oil fouling properties and outstanding recyclability, with a flux recovery ratio of about 80%. Moreover, the membrane possessed remarkable chemical stability when exposed to corrosive environmental conditions such as acid, alkali, salty and hot water medium and could also effectively separate emulsions in hostile environments. Furthermore, the MXene-PAN membrane could effectively adsorb the organic contaminants present in the oily effluent. The exceptional dual functionality of the MXene-PAN membrane, which combines outstanding separation performance and organic dye adsorption, opens up new prospects for treating oily wastewater.

Spray‐Coating of Superhydrophobic Coatings for Advanced Applications

Superhydrophobic coatings are widely applicable, e.g., as self‐cleaning surfaces or water–oil separation membranes, yet their wider usage is impeded due to costs of fabrication, size, or substrate limitation. Spray‐coating is a versatile coating procedures and might offer a good solution for the fabrication of these superhydrophobic coatings, due to the fact that coatings can be fabricated on various materials in a simple, fast, and inexpensive manner. Most procedures rely on hybrid coatings of hydrophobized nanoparticles and a polymeric matrix, which have several drawbacks including the easy loss of nanoparticles and difficult waste handling. Here, the fabrication of the superhydrophobic material, called Fluoropor, for the first time, by spray‐coating on various substrates including metals, tissues, concrete, and glass is presented. It is fabricated by spray‐coating a mixture of a highly fluorinated monomer blended with porogens followed by photopolymerization. The superhydrophobicity of the material relies on the porous structure on the micro‐/nanoscale across the bulk material and does not require any nanoparticles. Excellent self‐cleaning ability of these coatings, resistance against thermal and abrasive impact, and their application as oil–water separation membranes are shown. This versatile applicability is highly promising for real‐world application as self‐cleaning coatings or oil–water separating membranes.

Superhydrophobic and superoleophilic surfaces prepared by one-step plasma polymerization for oil-water separation and self-cleaning function

Efficient superhydrophobic and superoleophilic thin films for oil-water separation and self-cleaning were prepared using the atmospheric-pressure plasma polymerization of hexamethyldisiloxane (HMDSO). A dielectric barrier discharge (DBD) plasma jet with argon (Ar) was used for the deposition of the functional thin films onto several substrates. The oil-water separation membrane was synthesized by the plasma polymerization of HMDSO on fabric and offset printing paper. The superhydrophobic coatings were deposited on glass to demonstrate their self-cleaning ability. The hydrophobicity of the thin films was found to vary significantly, depending on the operating parameters such as the deposition time, applied voltage, and gas flow rate. The gaseous shield of the plasma jet also affected the hydrophobicity to a large extent. Nitrogen (N2) rather than inert gases such as Ar and He exhibited an excellent shielding effect against the interference of ambient air on the plasma jet. The wettability of the glass was completely switched from superhydrophilic to superhydrophobic with the water contact angle (WCA) reaching 165° and the sliding angle about 2°. In addition, superoleophilicity was obtained with the oil contact angle (OCA) reaching 0° under the optimal operating conditions.

Highly hydrophobic oil—water separation membrane: reutilization of waste reverse osmosis membrane

Highly hydrophobic oil—water separation membrane: reutilization of waste reverse osmosis membrane

Fabrication of sugarcane bagasse ester-based porous nanofiber membrane by electrospinning for efficient oil-water separation

With the increasing demand for oily sewage treatment, the lignocellulosic biomass-based membrane has aroused great attention due to its renewability and efficient performance for oil-water separation. However, the application of lignocellulosic biomass generally needs complex fractionation to use one of the components for materials preparation, causing extra energy cost and potential environmental pollution. In this study, sugarcane bagasse (SCB) was directly esterified with different functional groups to improve its solubility and hydrophobicity to enable electrospun into nanofiber membrane for oil-water separation. The obtained nanofiber exhibited high porosity, leading to an excellent oil adsorption capacity of 1455 wt% for pump oil. Notably, the SCB benzyl ester-based membrane shows outstanding oil/water mixture separation performance (separation efficiency of 99.54% and purity of 99.9% for n-hexane/water mixture) and oil/water emulsion separation performance (rejection of 99.6% with the separation flux of 419.8 L·m−2 h−1 with the force of gravity). Furthermore, the decent structural stability of SCB based membrane allowed recycling for multiple time, therefore endow the SCB ester-based nanofiber with great potential on the commercial oil-water separation.

A new antifouling metal-organic framework based UF membrane for oil-water separation: A comparative study on the effect of MOF (UiO-66-NH2) ligand modification

A new antifouling metal-organic framework based UF membrane for oil-water separation: A comparative study on the effect of MOF (UiO-66-NH2) ligand modification

Highly durable and sustainable heterogeneous fabric using in-and-out fluorinated urethane coating for elimination of bacteria and oil–water separation

To address the poor oil–water separation efficiency and bactericidal properties of existing oil–water separation membranes for the treatment of industrial oily wastewater discharge, this study designed an in-and-out coating material for modifying the inner site and outer surface of porous activated carbon fabric (ACF) using urethane reactions. To this end, fluorinated polyurethane (F-PU) coating materials were synthesized using perfluoroalkyl alcohol, ethylene glycol (EG), and isophorone diisocyanate (IPDI). Subsequently, the inner and outer surface of the ACF were coated with F-PU via the urethane reaction of the hydroxyl groups (–OH) of the surface of ACF and the isocyanates of F-PU. The successfully fabricated in-and-out F-PU-coated heterogeneous fabric exhibited excellent hydrophobic properties, anti-scratch performance, oil–water separation performance, and bacterial penetration blocking efficiency (>99% for gram negative and gram positive bacteria). Furthermore, the in-and-out-coated ACF exhibited high durability, and retained its bacterial penetration blocking performance after scratch tests.

Flux vs. permeability: How to effectively evaluate mass transfer performance of membranes in oil-water separation

Membrane filtration has attracted surging attention for various water treatment applications, such as oil-water separation, because of its low energy consumption, high separation efficiency, and wide applicability for various feed solutions. The advances of fabricated membranes are often emphasized by high permeation flux and separation efficiency. However, as “membrane-independent factors” (e.g. filtration areas and pressures) also contribute to the variation of mass transfer during the separation, the comparison based on the flux from batch experiments leads to a pitfall in evaluating the membrane performance. Our water permeation experiments using different set-ups demonstrate that the permeability result are more reliable and comparable than the flux value for evaluating membrane permeation performance since it considers the driving force from either hydraulic pressure or external pressure. However, flux and permeability may vary significantly among different studies, depending on the selection of the measurement period during the filtration experiment. To effectively evaluate the mass transfer performance, we recommend using the permeability profile with a constant driving force. The permeability profile under a constant driving force is a desirable way to evaluate the membrane performance, as it can describe both the mass transfer performance and the antifouling performance of a membrane. These key conclusions are drawn from oil-water separation membranes but also applicable for other pressure-driven separation membranes. This study provides a guideline for effective membrane performance evaluation by demonstrating improved experimental and data analysis methods.

Fabrication of fibrous MXene nanoribbons (MNRs) membrane with efficient performance for oil-water separation

Oily wastewater discharge due to industrial activities and oil spills has taken great tolls on human health and global environment. Fabrication of high-efficiency membrane is of critical importance since membrane separation has emerged as one of the best solutions to oily wastewater problem. In this work, fibrous MXene nanoribbons (MNRs) were firstly prepared and then combined with mixed cellulose (MCE) membrane to obtain a novel two-dimensional MCE-MNRs membrane. The MCE-MNRs membrane displayed superhydrophilicity and underwater superoleophobicity, corresponding to outstanding resistance to oil droplets. The filtration experiments illustrated that the MCE-MNRs membrane possessed an extremely high pure water permeance (PWP) of 15860 L m−2 h−1·bar−1, and simultaneously over 99% rejection rates for filtration of four typical oil-water mixtures (diesel, gasoline, edible oil and n-hexane). The performance outperforms those of the state-of-the-art membranes for oil-water separation to our knowledge. The excellent performance can be put down to a water layer formed on the membrane surface during filtration, which allow water to pass through freely but block oil droplets. In addition, the MCE-MNRs membrane possessed the photocatalytic self-cleaning ability which can efficiently raise the flux recovery rate (FRR) by ultraviolet light irradiation. The facile preparation method and excellent separation performance of the MCE-MNRs membrane cater to the current industrial production needs and show a promising application prospect in oil-water separation.

Tannic acid (TA)-based coating modified membrane enhanced by successive inkjet printing of Fe3+ and sodium periodate (SP) for efficient oil-water separation

Wettability of membrane is of vital importance for treatment of oily wastewater. In recent years, hydrophilic modifications based on plant polyphenol have been widely investigated to enhance the anti-fouling property of membranes due to their mild conditions, versatility and low cost. However, there are still some problems in improving raw material utilization and hydrophilicity. Herein, a facile method was proposed to optimize tannic acid (TA)-based membrane modification process by synergistically inducing TA deposition by Fe3+ and SP with the assistance of inkjet printing. The hydrophobicity of polyvinylidene fluoride (PVDF) membrane was converted to hydrophilicity (WCA = 34.6°) and underwater oleophobicity (UOCA = 144.4°) in very short time (10 min). The optimum PVDF/Fe-TA-SP422 membrane possessed high flux (4968.4–7340.4 L m−2 h−1·bar−1) for a number of oil/water emulsions with high separation efficiency (>98%), outperforming most state-of-the-art membranes for oil-water separation. Furthermore, the optimized membrane displayed not only high antifouling property and reusability with flux recovery ratio of 89.1%–98.0% after eight-cycle filtration, but also desired stability under near neutral pH conditions during long-term running. The combination of inkjet printing method with these materials proposed in this study is convenient, efficient and low cost, and the prepared membranes are versatility, providing novel insights into preparation of high efficiency membranes for oily wastewater treatment.

Performance evaluation of emerging block copolymer membranes for oil-water separation

Membrane processes such as microfiltration (MF) and ultrafiltration (UF) are known to be the best advanced technologies for water reuse application. Numerous research efforts have been conducted in areas of modifying commercial MF/UF products or synthesizing novel materials promising enhanced oil-water separation performances. Block copolymer (BCP)-based membranes have recently gained increased popularity due to their improved water permeabilities. This study applies a comprehensive testing protocol for performance evaluation of two emerging poly (styrene-block-methyl methacrylate) BCP membranes developed by the project team. Tests mimicking industrial conditions were conducted by using a representative synthetic produced water and operating repeat tests. Both BCP membranes (referred to as A & B) were found to possess high permeabilities of 5538 and 12,424 LMH/bar, respectively. Membrane B showed higher organic rejection at 79% against 74% rejection obtained for membrane A. The novel membranes were then compared to a relevant commercial product. Lower permeability at 3831 LMH/bar and slightly higher rejection performance (within ~ 10%) were obtained for the commercial membrane as compared to the BCP membranes. Test results obtained for those novel membranes being still in the development stage will be utilized in future studies investigating further optimization of the membrane structure and oil-water separation performance.Graphical

Molecular and structural design of polyacrylonitrile-based membrane for oil-water separation

Herein, a durable superhydrophobic/superoleophilic membrane with micro-/nano-hierarchical structure was achieved through molecular and structural design of fluorinated polyacrylonitrile-based membrane. In which, the introduction of perfluorooctanol acrylate into copolymer chain and usage of electrospinning/electrospraying technology followed by heat post-treatment provided low surface energy and durable hierarchical structure, respectively. The resultant membrane demonstrated superhydrophobicity and superoleophilicity with water contact angle of 160° and oil contact angle of 0° in air, which endowed the membrane with excellent separation ability for oil/water mixture with separation efficiency above 99% and ultrahigh flux beyond 8000 L/m 2 /h. Furthermore, the obtained membrane maintained its superhydrophobicity after exposure to broad pH, organic solvents, high temperature and ultrasonic treatment, ascribed to the chemical reaction of cyano groups on the surface of fibers and particles during the heat post-treatment. This work provides a promising strategy to fabricate superwetting membrane to remove trace amount of water in oil. A durable and robust membrane with micro-/nano-hierarchical structure was achieved through molecular and structural design of polyacrylonitrile-based membrane for efficient separation of various oil/water mixtures. • A novel fluorinated polyacrylonitrile copolymer was synthesized. • Membrane with micro-/nano-scale structures was constructed by using the copolymer. • The fibers and particles in membrane were integrated by chemical interactions. • Durable superhydrophobicity of membrane was achieved. • The membrane showed excellent separation efficiency for oily wastewater.