Application In Oil-water Separation Research Articles

Construct a stable super-hydrophobic surface through acetonitrile extracted lignin and nano-silica and its application in oil-water separation

It remains a great challenge for the simple, environmentally friendly and low-cost production of oil/water separation membrane. Under this backdrop, a highly efficient membrane based on filter paper, acetonitrile extracting lignin and silica is reported. Two impregnation steps are involved for the membrane preparation, firstly, a thin layer of lignin is coated on the surface of the filter paper and then, silica nanoparticles are adhered to the pre-coated filter paper, leading to the formation of a micro-nano binary structure, which turns the hydrophilicity nature of the filter paper into lipophilicity and strong hydrophobicity. The modified filter paper has a contact angle of 168°, which is 118° higher than that of a reference membrane prepared by technical lignin and silica nanoparticles. The modified filter paper exhibits an excellent separation efficiency as high as 98.6% in the process of oil/water separation. Notably, considering the applied low-cost substrates and the simple dipping operation, this modification route is expected to be easily extended to a versatile of other substrates that need to be hydrophobized.

Optimized microporous structure of ePTFE membranes by controlling the particle size of PTFE fine powders for achieving high oil-water separation performances

Advanced functional membranes consisting of low surface energy and tailored micropores are promising materials for oil-water separation applications. However, obtaining a high porosity yet controllable pore sizes to achieve high separation efficiency and flux remains challenging. Herein, four kinds of polytetrafluoroethylene (PTFE) powders with different particle sizes were simply sieved from a commercial resin and corresponding microporous membranes were fabricated through paste extrusion and thermal stretching processes. The microporous structure exhibited that choosing smaller powders caused the decrease of pore size but can still maintain a high porosity in stretched membranes, which was difficult to be realized by controlling processing conditions. The increased contact interfaces among small powders were regarded to promote the fibrillation during extrusion, thereby more entangled sites of fibrils were generated and only required a small amount of extension to get the target deformation during stretching. Consequently, more micropores with a smaller size were owned in the membrane by using smaller powders, which gave rise to superhydrophobicity with an ultrahigh water contact angle of 152° and superfast oil infiltration. As expected, the oil-water separation experiment obtained high separation efficiency closing 100% and the flux of 7500 L/m2·h, which were competitive in comparison to most of previously-reported PTFE microporous membranes. More significantly, such an outstanding separation capacity was suitable for many kinds of oils with different densities and almost stable even after 15 cycles. Meanwhile, the microporous structure of the membrane prepared by using smaller powders was also proven to be deformed more slowly when subjected to a large strain. Accordingly, this work provides a new and practical approach for fabricating PTFE microporous membranes suitable for applying in a wide variety of oil-water separation fields.

Efficient natural rubber latex foam coated by rGO modified high density polyethylene for oil-water separation and electromagnetic shielding performance

The current research work demonstrates preparation and characterization of Reduced Graphene Oxide (rGO)@ High-Density Polyethylene (HDPE) aerogel coated Natural Rubber Latex foam (NRLF) with superhydrophobic and superoleophilic character, good sorption capacity for oil-water separation, high electrical conductivity and electromagnetic interference shielding effectiveness (EMI SE) of the same were studied. The coated NRLF was prepared by using a solution of rGO and HDPE in xylene solvent with cooling process to result into thermally induced phase separation of the graphene and Polyethylene molecular network. The rGO modified HDPE aerogel coated NRLF showed superhydrophobicity with static water contact angle > 150°. The rGO@HDPE aerogel coated NRLF with 2 wt% rGO has reached EMI SE value of 24 dB, meeting commercial requirements. The electrical conductivity, EMI SE and the hydrophobicity of the composites significantly improved after mixing rGO into HDPE sol. This prepared superhydrophobic NRLF with high electric conductivity may find attractive application in oil-water separation and EMI Shielding, which would also be economically favored option in the current scenario.

One-step hydrothermal synthesis of the modified carbon cloth membrane: Towards visible light driven and self-cleaning for efficient oil-water separation

The CC@TiO2-Cu membranes with various Cu doping contents have been synthesized via a simple one-step hydrothermal method for oil-water separation application. It is found that a certain amount of Cu doping is beneficial for achieving visible light response and enhance the superhydrophilicity/underwater superoleophobic performance of CC@TiO2-Cu membranes. Importantly, the CC@TiO2-Cu2.5 membrane with cauliflower-like morphology shows excellent self-cleaning and antifouling performance under visible light driven. And its separation efficiency can still maintain up to 99.6% under gravity even after 80 cycles of oil-water separation experiments. The mechanisms of both oil-water separation and photocatalytic self-cleaning for the CC@TiO2-Cu membrane are discussed in detail. The study provides a new concept for designing self-cleaning membrane to apply in oil-water separation.

Fabrication of hydrophilic and underwater superoleophobic SiO2/silk fibroin coated mesh for oil/water separation

Anti-fouling silk fibroin (SF)-silicon dioxide (SiO2) nanocomposites membrane is fabricated by spraying composite on the stainless steel mesh. The optimal membrane with water contact angles (CAs) of 10° and oil CAs of 150° exhibited superior stability, underwater superoleophobicity, ultralow oil-adhesion and wear resistance, and hence it could separate the diesel/water mixture with high efficiency of 99.7%. The separation efficiency of other oils (kerosene, petrol, hexane) is also above 99.1%. In addition, after 50 cycles, the mesh still maintains high separation efficiency, which is larger than 98.6%. Meanwhile, the as-prepared meshes can not only separate oil-water mixtures in a mild environmental condition, but also can effectively function in harsh environments (including high salt concentration and extreme pH values). The prepared mesh has strong mechanical stability, and its underwater superoleophobicity is stable after long-term exposure to the air, rendering it promising for actual oil-water mixture separation applications.

Facile preparation of cotton fabric with superhydrophilicity–oleophobicity in air and superoleophobicity under water by using branched polyethyleneimine/perfluorooctanoic acid composites

Preparation of cotton fabric with superhydrophilicity-oleophobicity in the air and superoleophobicity under water by using branched polyethyleneimine/perfluorooctanoic acid composites and its application in gravity-controlled oil-water separation.

Preparation and Application in Crude Oil-Water Separation of Clay-Based Membranes

In this study, tubular ceramic membranes were prepared from a mixture of ball clay, talc and alumina. The mixture was characterized by the following techniques: particle size analysis, X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD) and thermal analysis. Tubular membranes were produced by extrusion process and thermal treated at temperatures between 1025 °C and 1175 °C. The membranes were characterized by XRD, linear shrinkage, apparent porosity, flexural strength, mercury porosimetry, scanning electron microscope (SEM) and contact angle. To evaluate the efficiency of the membranes, permeability tests with distilled water and oil-in-water emulsion were conducted in a tangential flow system. The results showed that the sintering of the specimens promoted the formation of α-cordierite phase and directly influenced the physical and mechanical properties such as linear shrinkage, porosity and flexural strength. Separation tests revealed that these membranes promoted high oil-water separation efficiency with values above 99.0%.

Underwater, Multifunctional Superhydrophobic Sensor for Human Motion Detection.

Superhydrophobic conductive materials have received a great amount of interest due to their wide applications in oil-water separation, electrically driven smart surface, electromagnetic shielding, and body motion detection. Herein, a highly conductive superhydrophobic cotton cloth is prepared by a facile method. A layer of polydopamine/reduced graphene oxide (PDA/rGO) was first coated on the cotton fabric, and then copper nanoparticles were in situ grown on the prepared surface. After further modification with stearic acid (STA), the wettability of the cotton surface changed from superhydrophilic to superhydrophobic (water contact angle (WCA) = 153°). The electrical conductivity of the PDA/rGO/Cu/STA cotton is as high as 6769 S·m-1, while the stearic acid effectively protects Cu NPs from oxidation. As a result, the superhydrophobic PDA/rGO/Cu/STA cotton has shown excellent electrical stability and can be used in detecting human motions in both ambient and underwater conditions. The sensor can recognize human motion from air into water and other underwater activities (e.g., underwater bending, stretching, and ultrasound). This multifunctional cotton device can be used as an ideal sensor for underwater intelligent devices and provides a basis for further research.

Mechanically strong polyimide aerogels cross-linked with dopamine-functionalized carbon nanotubes for oil absorption

We report a novel procedure to fabricate vacuum dried high-mechanical-strength polyimide (PI) aerogels cross-linked with dopamine-functionalized carbon nanotubes (mCNTs). Poly(amid acid) chains are in situ grafted onto the surface of mCNTs via “grafting from” method, thus providing the composite aerogels with superior mechanical properties due to covalently chemical cross-link networks and linear reinforcement. The addition of only 1.0 wt% of mCNT endows the composite aerogel with the specific modulus of 715.5 J/g, which is much higher than that of chemical agent cross-linked aerogels. The obtained composite aerogels also show high thermal stability and enhanced flame retardant performance, with only a slight increase in weight loss and shrinkage after firing test. Furthermore, mCNTs can serve as secondary reaction platform, thus superhydrophobic and oleophilic composite aerogels were fabricated by grafting octadecylamine onto the aerogel surface. The water contact angle is as high as 151°, and the maximum oil absorption capacity is 447%. Moreover, the composite aerogels exhibit stable hydrophobic and oleophilic properties after a long period of strong acid/base or high-temperature treatments, which is promising for practical oil-water separation applications under severe environments.

Design, fabrication, and characterization of a facile superhydrophobic and superoleophilic mesh-based membrane for selective oil-water separation

Superhydrophobic and superoleophilic (SHSO) membranes have found great attention in oil–water separation application. We fabricate a SHSO stainless steel mesh-based membrane, using a facile one-stage dip-coating technique, and investigate the effects of silane alkyl chain size, and ratio of micro-to-nanoparticles in the coating solid fraction. Silane compounds with short- and long-alkyl functional chains (Dynasylan® Sivo 408 and Dynasylan® F8261, respectively) are used as surface energy modifiers. To create hierarchical morphology, Aerosil® R812 and SIPERNAT® D13 are employed as the nano and microparticles, respectively. The long-silane features a higher water contact angle (WCA) at all solid compositions. Increasing the ratio of nano-to-microparticles increases the WCA with long-chain silane. Maximum WCAs = 165.8° and 164.2° are attained with the long and short silanes, respectively, when the coating solid is composed of 75 wt% nanoparticles and 25 wt% microparticles. Increasing the concentration of nanoparticles to 100% decreases hydrophobicity, which is more pronounced for the short-chain silane. The WCA decreases to 163.8° and 155.5° for the coating solutions containing the long and short silanes, respectively, with 100% nanoparticles to modify the surface roughness. Flower-like hierarchical roughness structures are observed using the coating solution of silanes with only nanoparticles. The average pore opening for the mesh decreases from 76 µm in the bare mesh to 48 µm for the coated mesh. Analytical surface characterization results (e.g., sliding angle, energy-dispersive X-ray spectroscopy (EDX), and Fourier transform infrared spectroscopy (FTIR)) confirm the SHSO features of the as-prepared mesh. Except for the exposure to 1.0 M NaOH solution, the membranes are stable (WCA > 145°) in H2SO4, NaOH, and NaCl concentrated solutions over four weeks. Using the fabricated mesh, the macroscopic separation efficiency of kerosene from water is >99%. The membrane fabrication strategy proposed in this study further highlights the importance of the SHSO wetting condition in the effective treatment of oily wastewater streams in a variety of food, chemical, and energy industries.

One-step fabrication of brass filter with reversible wettability by nanosecond fiber laser ablation for highly efficient oil/water separation

Recently with the development of industries and maritime oil transportation, water pollution due to frequent oil spilling has become a worldwide challenge. So, the fabrication of materials with special wettability and application in oil-water separation has attracted considerable attention. In the present study, a simple one-step method without any chemical modification is reported to fabricate the brass mesh using brass sheet drilling with a commercial nanosecond fiber laser system. Laser ablation creates hierarchical micro/nano structures by plasma created at the irradiated point. The morphology, elemental map and crystal structure of the pristine and drilled brass were analyzed by AFM, FE-SEM, EDS and XRD techniques. Wettability of fabricated brass mesh changes from superhydrophilic to highly hydrophobic (water contact angle 140°) after laser ablation and exposing to ambient conditions. Also, the obtained highly hydrophobic sample can switches to a superhydrophilic by thermal treatment. Then the superhydrophilic surface can switches again to the highly hydrophobic surface by exposuring to the air for several days. The reasons for wettability switching were discussed in details. The prepared brass mesh with uniform holes can be used as a filter for efficient separation of various organic solvents from water in many cycles without decreasing in its separation capability.

Asymmetric Sc-PLA Membrane with Multi-scale Microstructures: Wettability, Antifouling, and Oil-Water Separation.

In this work, an eco-friendly superhydrophobic stereo-complex polylactic acid (Sc-PLA) membrane was fabricated by a facile non-solvent-induced phase separation (NIPS) method, followed by peeling off its skin layer. By adjusting the thickness and roughness, membranes with various multi-scale microstructures could be obtained due to the formation of stereo-complex crystals during the process of phase separation. The Sc-PLA membranes display a hydrophobic wetting property. Interestingly, when the skin layer of the membrane with a 600 μm thickness was peeled off, the water contact angle on the surface of the membrane significantly improved from 142 to 152°, and the membrane displayed superhydrophobic wetting properties, which may be owing to the improvement of roughness for the surface by enlarging the exposure opportunity of finger holes and microstructures. In addition, the Sc-PLA membrane with superhydrophobicity shows excellent antifouling performance and large oil absorption capacity. Predictably, the Sc-PLA membranes may have potential applications in antifouling and oil-water separation.

Molecular simulations on the hydration and underwater oleophobicity of zwitterionic self‐assembled monolayers

AbstractZwitterionic materials have attracted increasing attentions in the underwater super‐oleophobic applications for its strong hydration via electrostatic interactions. Herein, molecular dynamics simulations were used to investigate the hydration and underwater oleophobicity of sulfobetaine‐terminated self‐assembled monolayers (SB‐SAMs) with different carbon spacer lengths (CSL) between oppositely charged groups of SB molecules. Simulation results show that the hydration of SB‐SAMs is positively dependent on CSL; the underwater oleophobicity is strengthened and then weakened with the increase of CSL, reaching optimal performance when CSL = 3; adhesion force of oil droplet on SB‐SAMs is inversely correlated with their contact angles, reaching the minimum value when CSL = 3. Moreover, the addition of NaCl can weaken the self‐association of SB molecules resulted from interactions between cationic and anionic groups, which promotes hydration and enhances underwater oleophobicity of SB‐SAMs. These results will benefit for the design of novel zwitterion‐based materials for anti‐fouling and oil–water separation applications.

Facile fabrication of acid-resistant and hydrophobic Fe3O4@SiO2@C magnetic particles for valid oil-water separation application

It is a big challenge to prevent the degradation of magnetic nanoparticles particularly under acid conditions. Here we demonstrated that the stability of magnetic Fe3O4 nanoparticles could be substantially improved after double coating with silica and carbon. The dense silica shell and hydrophobic porous carbon shell endowed the magnetic Fe3O4@SiO2@C nanoparticles remarkable anti-corrosion performance even under 10 M of HCl solution. More importantly, the demulsification of asphaltenes-stabilized water-in-toluene emulsion was realized with the aid of 2 wt% emulsion of our proposed double-coated magnetic particles due to their great interfacial activity. Besides, the magnetic Fe3O4@SiO2@C particles could be recycled up to six times while the magnetic Fe3O4@C particles would easily lose their interfacial activity. It is the first time to found that the inorganic shells showed a great interfacial activity. Thus, the high separation efficiency, excellent acid-anticorrosion, and easy recyclability of our proposed magnetic particles presented its great potential value in industrial application.

Perflurooctyltriethoxy silane and carbon nanotubes-modified PVDF superoleophilic nanofibre membrane for oil-in-water adsorption and recovery

Due to the increased rate of oil spills leading to environmental water pollution, the synthesis of nanofibre membranes with controlled superhydrophobic/superoleophilic properties has received remarkable attention for oil-water separation. In this research, superhydrophobic-superoleophilic nanofibre membranes were successfully prepared through a three-step deposition of perflurooctyltriethoxy silane (POTS) to carbon nanotubes (CNTs) followed by dispersing the mixture in polyvinylidene fluoride (PVDF) polymer solution prior to electrospinning. Upon the addition of POTS/CNTs on the nanofibre membranes, the hydrophobicity increased from 96.35° to 143.30°, thus, resulting in improved oil adsorption capacity from 60.20 to 111.4 g·g-1. The intraparticle diffusion model provided the information on external mass transfer and diffusion of the oil from the oleophilic sites of the adsorption active sites. The CNTs/POTS-modified PVDF nanofibre membranes demonstrated high adsorption efficiencies ∼ 99% towards avocado, sunflower, engine, and motor oils. Based on Chi-square test statistics, the adsorption of oils on CNTs/POTS-modified PVDF nanofibre membranes followed the first-order kinetics. The rate constants increased from 0.019 to 0.034 g·g-1 min-1 upon the incorporation of CNTs/POTS on PVDF nanofibre membranes; thus, indicating the improvement of adsorption of oils. Remarkably, PVDF-based nanofibre membranes were recycled and reused for more than 37 cycles, confirming their potential application for environmental oil-water separation.

A Novel Sepiolite-based Superhydrophilic/Superoleophobic Coating and Its Application in Oil-Water Separation

The separation of oil-water mixtures has attracted widespread attention for addressing increased oil spillage and oil-polluted water. In this study, a novel and low-cost oil-water separation coatin...

A durable, fluorine-free, and repairable superhydrophobic aluminum surface with hierarchical micro/nanostructures and its application for continuous oil-water separation

Artificial superhydrophobic surfaces have drawn a lot of attention owing to their multifunctional properties. However, the durability and environmental concerns of such surfaces are critical issues that have limited their widespread utilization in real-life applications. In this study, fluorine-free superhydrophobic aluminum surface was fabricated through a simple and cost-effective method. Its dual-scale micro-/nanostructures (MNS) was fabricated by combining chemical etching and hydrothermal processes. After modification with polydimethylsiloxane coating using a simple vapor deposition method, surface showed excellent superhydrophobicity, with a water contact angle of ~161° and sliding angle of 4°, and sustained its non-wetting properties against various food liquids. The effect of morphological change on the surface's wettability and the durability of the coating materials were investigated in sandpaper abrasion, tape-peeling, and blade-scratching tests. Compared with micro- or nanostructure surfaces, the MNS surface showed better robustness because of its dual-scale roughness. Furthermore, the abraded surface could effectively restore its superhydrophobicity after being recoated with PDMS. The surface also showed long-term superhydrophobic stability in an ambient environment for over 10 months. Finally, the method was applied to Al mesh with superhydrophobic/superoleophilic properties to separate various oil-water mixtures, yielding a high separation efficiency of up to 94% and outstanding reusability.

An unusual superhydrophilic/superoleophobic sponge for oil-water separation

Development of porous materials with anti-fouling and remote controllability is highly desired for oil-water separation application yet still challenging. Herein, to address this challenge, a sponge with unusual superhydrophilicity/superoleophobicity and magnetic property was fabricated through a dip-coating process. To exploit its superhydrophilic/superoleophobic property, the obtained sponge was used as a reusable water sorbent scaffold to collect water from bulk oils without absorbing any oil. Owing to its magnetic property, the sponge was manipulated remotely by a magnet without touching it directly during the whole water collection process, which could potentially lower the cost of the water collection process. Apart from acting as a water-absorbing material, the sponge can also be used as affiliation material to separate water from oil-water mixture and oil in water emulsion selectively, when fixed into a cone funnel. This research provides a key addition to the field of oil-water separation materials.

Endowing Metal Surfaces With Underwater Superoleophobicity by Femtosecond Laser Processing for Oil-Water Separation Application

In this paper, a widely applicable method that has promise in endowing various metals with oil-water separation ability by femtosecond laser processing is reported. We take an iron sheet as an example to show how to use a femtosecond laser to prepare underwater superoleophobic microstructure on metal substrates and then achieve oil-water separation. An array of through microholes was previously prepared on the iron sheet by a mechanical drilling process. Then, rough nanostructures were created on the surface of the porous sheet by femtosecond laser ablation, resulting in excellent superoleophobicity in water. When the mixture of water and oil was poured onto the porous underwater superoleophobic metal sheet, only the water in the mixture could pass through the sheet while the oil was intercepted, thus the oil/water mixture was successfully separated with high efficiency. Such a novel preparation process and separation manner can extend to different metal substrates. We believe that a wide range of metals like iron sheet can be potentially endowed with oil-water separation ability by femtosecond laser processing because femtosecond laser can process almost all of the metals.

One-step electrospinning cellulose nanofibers with superhydrophilicity and superoleophobicity underwater for high-efficiency oil-water separation

Cellulose nanofibers have been widely applied in many fields because of its unique advantages. However, it is a challenge to prepare cellulose nanofibers by electrospinning directly owing to the special molecular structure of cellulose. This limits the practical applications of cellulose nanofibers. In this work, cellulose nanofibers were successfully prepared directly by design of new electrospinning receiving device and optimization of process parameters. The as-prepared cellulose nanofibers exhibit good oil-water separation performances. Driven solely by gravity, the separation flux of the cellulose nanofibers for mixture of oil and water reaches 34,300.6 L m−2 h−1, and the separation flux and efficiency for surfactant-stabilized emulsion of oil and water reach 2503.7 L m−2 h−1 and over 98.3%, respectively. The as-prepared cellulose nanofibers also exhibit good mechanical properties and reusability. The breaking strength of the cellulose nanofibers can reach 148.2 cN. The separation fluxes of cellulose nanofibers for mixtures and emulsions of oil and water can be maintained 99.7% and 86.3% of the initial value after being used for 20 times. Furthermore, the as-prepared cellulose nanofibers have good degradability. These properties render as-prepared cellulose nanofibers as promising materials with potential applications in oil-water separation.