The discharge of industrial liquid waste continues to cause more and more environmental problems. The current research aims at developing a durable and highly efficient filter screen for oil-water separation. In this paper, hydrophobic nano-SiO 2 and phenolic resin were used as raw materials. Hydrophobic SiO 2 particles were fixed on the surface of the coated filter screen by heating and curing the anchored particles. The surface morphology, element composition, surface roughness and water contact angle of the prepared super hydrophobic SiO 2 /phenolic resin-coated filter screen were analyzed and discussed by using SEM, EDS, AFM, OCA and other instruments. The results showed that the prepared filter screen contained Si, O, C elements, which proved that the resin coating film had adhered to the filter screen surface. When the aperture of the phenolic resin-coated filter screen was 400 meshes, the drainage angle reached a maximum value of 153.8° ± 0.8°. When two layers of hydrophobic SiO 2 phenolic resin were coated on the screen, the surface of the filter screen had a sufficient nano-porous structure and high roughness. The tests showed that the minimum water contact angle of the filter screen exceeded 150°, which indicated excellent chemical resistance. Through the analysis of oil-water separation efficiency of isooctane, gasoline, n-hexane, dodecane, edible oil, dichloromethane and trichloromethane, it was concluded that the lowest separation efficiency for edible oil was 97.2%, and the highest separation efficiency for n-hexane was 99.4%. After 50 cycles of separation, the oil-water separation efficiency for n-hexane was still at 99%.
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Petroleum production, transportation and usage inevitably lead to oil leakage, which seriously threatens the ecological environment. How to treat oily sewage is the key to protecting the environment. Oil&#;water separation technology is based on the different physical and chemical properties of oil and water, such as gravity separation technology, filtration, centrifugation, and electrochemical methods [1]. However, the separation efficiency of these conventional oil-water separation technologies is extremely low, and it is difficult to recover oil. There is a high demand in finding simpler and more efficient oil-water separation technologies. Researchers have tried to adjust the inherent wettability of the interface to improve the flow behavior of the liquid phase on the solid surface. Another possible solution is to change the resistance of the filter medium to oil and water.
Recently, the application of superhydrophobic surface preparation has attracted more and more attention, especially in the research process. Liu [2] prepared a super hydrophilic underwater and super oil-repellent mesh membrane by a two-step hydrothermal method to coat pure inorganic ZnO-Co3O4 onto the surface of copper mesh. The contact angle of the oil under water could reach 159.2° ± 1.3° (with dichloroethane as the oil drop). Using a polyester non-woven fabric as the matrix and polyphenyloxazine (PBZ) and TiO2 as the raw materials, Xin [3] developed a simple dip coating and thermal curing method to construct the polyphenyloxazine/TiO2-modified fabric, which has super hydrophobic and super lipophilic properties. It can not only efficiently separate the oil-water mixture, but it can also decompose methylene blue under ultraviolet light to achieve self-cleaning of the membrane surface. In Gondal et al. [4], the stainless steel mesh surface was coated with a WO3 nano-structure via the spraying method to prepare the super hydrophilic underwater super oil-repellent composite mesh membrane. Under the self-gravity drive, the oil-water separation efficiency was significantly improved. Naoyuki Yokoi [5] prepared a super hydrophobic and super lipophilic mesh membrane material via the simple spraying method using alkali-treated polyester mesh as the matrix and SiO2 and perfluorooctyl triethoxysilane as the raw materials. The produced membrane had high wear resistance, acid and alkali resistance (pH = 2&#;14), and excellent oil-water separation performance.
SiO2 nanoparticles have attracted extensive research due to their low density, high porosity, low thermal conductivity, and other advantages. Yanbao Guo [6] prepared lipophilic and hydrophobic silica sol via a sol&#;gel method and dipped lipophilic and hydrophobic coating on a stainless steel net. Separation experiments of various oil-water mixtures were carried out. They found that the modified mesh had better lipophilic and hydrophobic properties. Consistent lipophilicity and hydrophobicity were obtained under ultrasonic cleaning conditions and in different pH (3&#;11) solutions. The modified filter screen had good separation and reusability for different types of oil-water mixtures. Song [7] proposed a new method to construct a three-dimensional hydrophobic nano-SiO2 porous TIM(thermal insulating material) through a micro-lotion treatment. The polymethyl-hydro-siloxane-modified TIM had a large water contact angle of 166° and had excellent durability under high temperatures up to 400 °C, 100% high humidity and chemical attack. Liu [8] prepared SiO2 nanospheres with surface mercaptan groups by using 3-mercaptopropyltriethoxysilane (KH590) and hydroxyl condensation reaction on the surface of silicon (SiO2) particles. This material effectively absorbed more than four times the oil solvent, and the separation efficiency was more than 99%. Under strong acid and alkali conditions or a seawater environment, SiO2 nanospheres also have more than 20 times the effective oil absorption capacity and high recoverability. To improve the thermal stability and waterproof performance of ordinary cotton, Xu [9] added hydrophobic SiO2 particles, WPUA (waterborne polyurethane acrylate) and silica aerogel (SA) powder onto the surface of the coating film. The experimental results showed that the thermal stability of coated fabrics is significantly improved by adding aeroneneneba gel and silane-modified SiO2. The water contact angle of the film increased significantly when the silane-modified SiO2 particles were mixed with SA/WPUA. Liu [10] combined a poly (methyl-3,3,3-trifluoropropyl siloxane) (PMTFPS)-modified silicon with low surface free energy fluorosilicone resin to design an ice-resistant surface with super hydrophobicity. The contact angle and rolling angle of the SiO2-PMTFPS coating reached 158.5° and 1°, respectively. After immersion in solutions of different pH and temperature, the coating had good chemical durability in an aqueous solution.
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Metal porous mesh membranes (such as stainless steel mesh, copper mesh, nickel mesh, etc.) have the advantages of good flexibility, strong pressure resistance, easy surface processing, etc., and are often used as the matrix of special wetting oil-water separation membrane materials. Extensive research has been carried out to construct micro-nano-rough structures, as well as the modification of hydrophilic substances on the surface of a metal mesh membrane. Lei [11] first developed a polytetrafluoroethylene coating on the surface of the stainless steel mesh, prepared a super hydrophobic and super lipophilic stainless steel mesh film material, and applied it to the study of oil-water separation. Tian [12] prepared a vertical array of micro/nano-hierarchical zinc oxide nanorods on the surface of stainless steel mesh by two solution deposition methods, obtained a super hydrophilic, underwater super hydrophobic film, and analyzed the oil-water separation mechanism in detail. Zhang [13] constructed a new type of super hydrophilic, underwater super oleophobic inorganic membrane material. The membrane was made of Cu(OH)2 nanowires grown on a copper mesh, which can effectively separate immiscible oil/water mixture and oil in water lotion by gravity. The membrane with high separation flux did not reduce the flux for the continuous separation of 10 L of oil/water mixture. It also had excellent antifouling performance, good oil-water separation effect, and low synthesis cost. Raturi [14] prepared zinc oxide nanowires (NWs), which were coated on a stainless steel (SS) grid by chemical vapor deposition. The synthesized ZnO nws coating mesh showed super underwater hydrophilic, super hydrophobic behavior. This mesh worked in &#;dehydration&#; mode, and its super hydrophilic and underwater super hydrophobic properties allowed water to penetrate through the mesh easily while preventing oil passing. The wettability of the Z-nws coating mesh can easily change from a super hydrophilic state to super hydrophobic state by alternating annealing at 300 °C, and vice versa in a hydrogen and oxygen environment.
In summary, people began to study the surface modification of the filter screen, build nanostructures on the surface of the filter screen, and combine them with micron-sized meshes to give the filter screen super hydrophobic/super lipophilic properties. Super hydrophobic/super lipophilic materials are characterized by hydrophobic and lipophilic properties, which can effectively achieve oil-water separation, and then recover the oil. At present, a lot of effort is put into developing various oil-water separation materials with special wettability and super hydrophobicity to achieve the purpose of greatly improving oil-water separation efficiency. New technologies have been explored that can successfully prepare materials for oil-water separation, but these technologies still have many limitations in the oil-water separation process, such as complex preparation process and harsh preparation conditions. Some technologies can only be applied to special substrates, and some still need to use strong acid or strong alkaline reagents, which pollute the environment. The prepared oil-water separation materials have the disadvantages of poor stability and cannot be used for a long time. It is of great significance to rapidly produce stable and repeatable super hydrophobic and super lipophilic mesh membranes from common cheap raw materials and simple preparation methods.
Because the separation efficiency of traditional oil-water separation materials is not high, the surface roughness of a traditional phenolic resin-coated filter screen is limited, resulting in insufficient hydrophobicity, which reduces the oil-water separation efficiency of the filter screen. In this paper, hydrophobic silicon dioxide particles are introduced into the phenolic resin system by curing method, and the SiO2 nanoparticles/phenolic resin coating film is prepared on the surface of the filter screen. Compared with the traditional phenolic resin coating film, due to the introduction of hydrophobic SiO2 nano-examples, the phenolic resin-coated filter screen increases the surface roughness of the filter screen, improves the surface hydrophobicity of the filter screen, improves the chemical resistance of the coating film, and improves the oil-water separation efficiency.
Hydrophobic SiO2 nanoparticles are widely used in many industrial fields due to their simple preparation, excellent performance, and easy access. Stainless steel filters have excellent mechanical, chemical and high-temperature resistance. In our current study, hydrophobic SiO2 nanoparticles were heated and solidified on a stainless steel filter screen through phenolic resin. Experimental and analyzing equipment such as SEM (scanning electron microscope), EDS (energy dispersion spectrum), OCA (overview contact angle), etc., were employed to investigate the surface morphology, element composition, water contact angle and other parameters of a SiO2 nano-phenolic resin filter screen. Six oil-water mixtures were used to test the oil-water separation performance of the filter screen. Obtained results were compared with those of relevant researchers. It was found that the developed filter screen has significant advantages in oil-water separation efficiency.
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