Membranes For Oil-water Separation Research Articles

Fabrication of Photo-Responsive Mesh Membrane with Surface-Engineered Wettability for Oil-Water Separation and Photocatalytic Degradation of Organic Pollutants.

A photo-responsive TiO2-coated stainless-steel mesh membrane (TiO2@SSM), possessing unique surface wettability, was fabricated. This TiO2@SSM membrane is found to be capable of separating oil and water from oily water and has the potential to carry out photocatalytic self-cleaning and/or the degradation of organic pollutants present in water. The fabrication of TiO2@SSM is quite simple: titanium dioxide (TiO2) nanoparticles were spray-coated onto stainless steel microporous mesh (SSM) substrates and annealed at the temperature of 500 °C. The fabricated TiO2@SSM membrane was structurally and morphologically characterized by XRD, FE-SEM, EDX, and elemental mapping. The contact angle measurements using a goniometer showed that the fabricated TiO2@SSM membrane surface is superhydrophilic and superoleophilic in air and superoleophobic under water. This is a favorable wetting condition for the water passing oil-water separation membrane, and this water passing property of the membrane eased the common problem of the fast clogging of the membrane by oil. An oil-water separation efficiency of about 99% was achieved, when the TiO2@SSM membrane was used as the separating medium in the gravity-driven oil-water separation system, unlike the uncoated stainless steel mesh membrane, which allowed both oil and water to pass together. This confirmed that the oil-water separating functionality of the membrane is attributed to TiO2 coating on the stainless steel mesh. The photocatalytic degradation property of the TiO2@SSM membrane is an added advantage, where the membrane can be potentially used for self-cleaning of the membrane's surface and/or for water purification.

Facile fabrication of SWCNT film-based superhydrophobic cotton fabrics for oil/water separation and self-cleaning

With the increase of oily waste, oil-water separation has become an urgent and difficult task. However, the current challenge is to fabricate such efficient membrane materials for oil-water separation. Herein, superhydrophobic single-walled carbon nanotubes (SWCNTs)/cotton fabric (CF) was prepared via a dry process. In which the ultrathin SWCNT films with a low content of hydrophilic groups were prepared by a facile floating catalyst chemical vapor deposition method and directly deposited on CF without solvent dispersion. The obtained SWCNT@CF was further treated by 1 H,1 H,2 H,2 H-perfluorooctyltriethoxysilane (POTS). Due to the synergistic effect of SWCNTs and POTS, the POTS-modified SWCNT@CF displayed excellent superhydrophobicity with a water contact angle（WCA）of ∼163.3°, and consequently can be further used as a membrane for oil-water separation. These superhydrophobic fabrics have high oil/water separation efficiency (99.2% for dichloromethane/water) and high oil flux (28.71 ×103 L·m−2·h−1 for dichloromethane/water). Even after 25 separation cycles, oil/water separation efficiency and oil flux maintain 98.8% and 25.15 × 103 L·m−2·h−1, respectively. In addition, it exhibits high separation efficiency (∼99%) for water-in-oil emulsion. Moreover, under extreme environmental conditions, the contact angle of the obtained POTS-modified SWCNT/CF was maintained at ∼155°, keeping stable superhydrophobicity. This reported preparation strategy of superhydrophobic fabrics is environmentally friendly, low cost, sustainable, and easy to scale up, thereby exhibiting great potential in practical applications.

Transfer-Printed Environmental-Friendly Anisotropic Filter with Laser-Controlled Micropores for Efficient Oil/Water Separation

Water is indispensable for sustaining life on Earth. Oil–water mixtures/or emulsions from industrial waste and other sources are a serious environmental concern for both human beings and aquatic life. Specially treated meshes and textiles with opposing wettability for oil–water separation have been widely reported as a solution to this challenge. Nonetheless, such membranes are hindered by certain drawbacks, including high manufacturing costs, usage of harmful chemicals, and lack of diverse applicability. Here, we report a facile method to fabricate Janus oil–water separation membrane with a controllable pore structure that has a unique directional flux rate. The superhydrophobic (SHB) layer of the membrane is formed by transfer-printing (TP) carbon soot particles onto a polydimethylsiloxane (PDMS)-coated paper surface. Meanwhile, a spin-coated thin layer of chitosan on the other side of the film served as a hydrophilic (SHL) and underwater oleophobic face. A pulsed laser beam is used to produce micropores with conical structures. The separation ability of the membrane for both light oil–water and heavy oil–water mixtures is thoroughly investigated. Moreover, the significance of the pore shape and the size is also elucidated. The flexible Janus membrane showed high thermal stability and ideal (i.e., 99.8%) separation efficiency. The membrane can be produced over a 151 cm2 size range. Besides having flexibility and superior performance, the fabricated membrane is environmentally friendly and economically viable. This work establishes a scalable basis for efficient and low-cost oil/water membranes from non-porous substrates.

Binary nanofibrous membranes with independent oil/water transport channels for durable emulsion separation

Oil fouling threatens the stability of water permeability for oil-water separation membrane. Homogeneous hydrophilic surface modification provided an opportunity to prevent oil pollution, but failed to maintain stable water traverse due to oil accumulation. Here we report a binary nanofibrous membrane (BNM) through co-electrospinning technique and Michael addition reaction, where hydrophilic polyacrylonitile (mPAN) and hydrophobic poly (vinylidene fluoride) (mPVDF) nanofibers with certain ratio constructed independent water/oil transport channels respectively. The fabricated binary nanofibrous membrane provides stable permeance and high separation efficiency (>99.5%) for viscous oily emulsions in continuous cross-flow filtration. The oil droplets transport experienced deposition, migration, coalescence and removal to significantly alleviate fouling. The binary nanofibrous membrane with heterogenous wetting property provides durable permeation and separation efficiency for durable emulsion separation, which sheds light on a new approach for the development of ideal oil/water separation membranes.

Membrane wettability manipulation via mixed-dimensional heterostructured surface towards highly efficient oil-in-water emulsion separation

Membranes with super-wetting surface work well at separating oil-water mixtures, but efficient and continuous separation of surfactant-stabilized oil-in-water emulsion is difficult to achieve due to widely spread oil droplet size and stable droplet nature. This work reported a mixed-dimensional heterostructured oil-water separation membrane with electrospun hydrophobic polydimethylsiloxane/polyvinylidene fluoride (PDMS/PVDF) nanofibers on top of a hydrophilic polyaniline (PANI) coated microfiltration membrane support. It is discovered that small oil droplets are captured and coalesced by the hydrophobic-oleophilic PDMS/PVDF nanofibers, while water passes through the membrane from uncovered hydrophilic PANI micro-regions. Precise regulation on the proportion of hydrophilic and hydrophobic regions is achieved by controlling the electrospinning conditions, and highly efficient oil-in-water emulsion separation is thus accomplished with membrane pore size much larger than emulsified oil droplets. Multi-cycled and long-term crossflow separation experiments result in relatively stable membrane flux and oil-water separation efficiency higher than 99%, as coalesced larger oil droplets are continuously removed from the membrane surface by shear flow. Such heterostructured membranes with highly tunable wettability could therefore combine the merit of good separation efficiency and operation stability for practical surfactant-stabilized oil-in-water emulsion separation.

Preparation of a Janus-polyvinylidene fluoride micro/nano fiber membrane by centrifugal spinning and investigation into its unidirectional water transfer and oil–water separation functions

Traditional oil–water separation membranes have a high energy consumption and complicated operation. To solve this problem, an asymmetric wetting polyvinylidene fluoride (PVDF) fiber membrane with a hydrophobic side and a hydrophilic side was prepared. Octamethylcyclotetrasiloxane was grafted onto one side of a centrifugal spun PVDF fiber membrane by plasma initiation, and dopamine was sprayed on the other side of the fiber membrane. The Janus-PVDF fiber membrane prepared can separate a mixture of water and dibromoethane, a toluene–water emulsion and a mixture of n-hexane and water. The initial interception rates were 98.53% ± 1.31%, 98.52% ± 1.12% and 98.61% ± 1.23%, respectively. After five cycles of separation, the separation rates remained at 96.15% ± 1.25%, 95.02% ± 1.21% and 96.91% ± 1.42%, respectively. The Janus-PVDF fiber membrane has excellent unidirectional water transfer capability and possesses well-repeated separability. The preparation of its unique Janus structure also provides a new direction for the field of 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 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

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