Effective separations of oil/water mixtures and emulsions present challenges worldwide due to the increasing production of industrial oily wastewater and frequent oil spills resulting from industrial accidents and sinking of oil tankers and other ships. In 2010, the explosion of BP's Deepwater Horizon oil rig released 210 million gallons of oil into the Gulf of Mexico. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essayTraditional techniques for oil/water separation such as air flotation, gravity separation combined with foaming, oil absorbent materials, coagulation and flocculation are limited and are not effective for separating emulsions, making further treatment necessary. Therefore, facile synthesis of superoleophobic or superhydrophobic materials is gaining much attention from industries. Consequently, there is a need to develop new materials that allow oil/water separations to be performed efficiently, at low cost, with high selectivities. Recently, materials possessing both superhydrophobic and superoleophilic properties have attracted widespread attention due to their ability to mediate the efficient separation of oils, organic pollutants, and other hydrophobic organic solvents from water. Although such previously developed materials can be effective agents for oil/water separation, they are easily fouled, or even blocked, by oils due to their inherent oleophilicity. Additionally, because water is generally denser than oil, it tends to settle beneath an oil phase, forming a barrier layer over the separation material and inhibiting oil permeation into it. Consequently, materials possessing superhydrophobicity and superoleophilicity are not suitable for the separation of water-rich oil/water mixtures or oil-in-water emulsions. Inspired by the wetting behavior of fish scales, it was possible to construct superoleophobic underwater surfaces in oil/water/solid three-phase systems. The development of underwater superhydrophilic and oleophobic materials with simple, inexpensive, environmentally friendly, and easily scalable manufacturing processes may lead to a more practical, alternative, and feasible approach for oil/water separations. OLEOPHOBICITYOleophobicity is a phenomenon in which a material does not allow oil to be spread on it, i.e. the contact angle of the oil on the material is >90°. However, oleophobic materials do not guarantee the complete non-wetting behavior of a material. To ensure complete non-wetting behavior, the contact angle between the material and the oil must be >150°. This is known as a superoleophobic material. RELATIONSHIP BETWEEN CONTACT AREA, SURFACE ROUGHNESS AND OLEOPHOBIC BEHAVIOR This is the Cassie-Baxter equation for the contact angle of oil in an oil/water/solid system with a rough surface where, the area fraction of the solid l the contact angle of the oil droplet on a smooth surface in water the contact angle of the oil droplet on a rough surface in water A smaller area fraction indicates a lower probability of the oil droplet entering in contact with the solid surface, the greater the contact angle of the oil in the water. Melamine sponges possess a very rough surface, which has a rather small area fraction of solid and a large oil contact angle. This is Young's equation for the contact angle of oil in water on a flat surface where?OA: the oil/air interface tension?OA: the contact angle of oil in air?WA: the tensionof the water/air interface?WA: the contact angle of water in the air?OW: the tension of the oil/water interface?OW: the contact angle of the oil in waterBecause the surface tension of the oil and organic liquids is much lower than that of water, we can see that hydrophilic surfaces in air can become oleophobic in water. Melamine sponge becomes superoleophobic when immersed in water. The underwater oil droplets were nearly spherical on the surface of the melamine sponge, and exhibited high contact angles (>150°). The rough surface structure and superhydrophilicity of the melamine sponge combine to cause a particular wettability that characterizes a three-phase oil/water/solid system.MELAMINE SPONGEThe melamine sponge is a commercially available three-dimensional porous material consisting of a formaldehyde bisulfite- melamine-sodium copolymer. These sponges exhibit superhydrophilicity and superoleophilicity. Melamine sponges pre-wet with water exhibit superhydrophilicity and superoleophobicity and could be used for effective oil/water separation. Wang et al. presented a simple and economical dipping method for fabricating an underwater superhydrophilic and super oleophobic polyvinylpyrrolidone (PVP)-modified melamine sponge. Melamine sponges are commercially available three-dimensional porous materials that exhibit underwater superhydrophilicity and superoleophobicity. When immersed in a PVP solution to improve Due to its oleophobicity, the thus prepared modified melamine sponge showed high separation capacity, allowing continuous separation of oil/water mixtures for up to 12 hours without any increase in oil content in the filtrate. The excellent performance of PVP-modified melamine sponge in oil/water separations and its preparation through an industrially feasible process suggest that it has potential applicability in both academic and industrial settings. Raw Sponge Behavior When a drop of water was placed on the surface of the raw melamine sponge, it spread and permeated there instantly, resulting in a contact angle of approximately 0°. The same situation occurred when using a drop of oil. Both processes were completed within 1 s, suggesting both hydrophilicity and oleophilicity of the melamine sponge in air. The melamine sponge became superoleophobic when immersed in water. When we immersed the melamine sponge in water, the water became trapped in its rough microstructure (a layer of water forms on the sponge's skeleton) which then formed an oil/water/solid composite interface in the presence of oil. The trapped water molecules significantly reduced the contact area between the oil and the sponge surface, resulting in a large oil contact angle. The pre-wetted sponge showed similar behavior for other organic solvents such as n-hexane, diesel and isooctane. Oil/ A water separation experiment, driven solely by gravity, was performed in which a sponge was clamped between two glass tubes and then an oil/water mixture (1:2 v/v) was poured into the tube superior. The water quickly passes through the pre-moistened melamine sponge and enters the glass below. Meanwhile, all the oil was retained on top of the sponge, due to the underwater superoleophobicity of the pre-wetted melamine sponge. The flow was quite high. GREECE SPONGE PROBLEM In continuous oil/water separation experiments of diesel/water mixtures, however, diesel permeated through the melamine sponge within 3 minutes. The raw sponge was unable to separate the emulsions. REQUIRED MODIFICATION TO THE RAW SPONGE the spongeof melamine was modified with polyvinylpyrrolidone (PVP) to improve its oleophobicity by the following process. Polyvinylpyrrolidone (PVP) (C6H9NO)n is a water-soluble polymer. It is soluble in water and other polar solvents. It has excellent wetting properties in solution and film form. Therefore, it can be used as a coating agent or as an additive to ensure good coating. A piece of raw sponge was immersed in 1.0 wt% aqueous PVP for 30 min. The treated sample was dried at 85°C. It was subsequently polymerized at 150°C for 5 minutes. The obtained sample was washed several times with hot water (50 °C). In the compression procedure, for the emulsion separation experiments, the PVP-modified sponge was compressed into a compact shape. CHARACTERIZATION OF THE MODIFIED SPONGE The modified melamine sponge maintained the microstructure of the pristine melamine sponge. FESEM images of the pristine sponge showed that the surface of the fibers in the pristine melamine sponge was quite smooth and smooth. After PVP treatment, FESEM images showed that some sort of deposition had occurred on these fibers. This deposition has made the fibers quite rough by nature, which significantly increases their oleorephobicity, considering the Cassie-Baxter equation and Young equation mentioned above. Since the aqueous PVP solution used was very dilute (1.0 wt% strength), so any effect of the deposition is only visible at the microstructure level. Despite deposition, the morphology was mostly maintained in the modified sponge compared to the original condition. For further inspection of the coating on the modified sponge fibers, Fourier transform infrared spectroscopy (FTIR) was performed on the raw and modified sponge for comparison. In the spectrum of the modified sponge, a peak appeared at 1654 cm-1 assigned to the C=O groups of PVP. This peak is not present in the spectrum of the raw sponge. So we can say that the rough coating on the modified sponge, as seen in the FESEM images, is PVP. It successfully adhered to the sponge fiber surface. PERFORMANCE IMPROVEMENT UPON MODIFICATION Using the PVP-modified melamine sponge, we could perform continuous separations of diesel/water and n-hexadecane/water mixtures for up to 12 hours, with no oil in the collected water mixture throughout the entire process, indicating the effectiveness of oil/water mixture separation using the modified sponge. Successful separation of several oil/water and organic solvent/water mixtures has been observed, including those containing n-hexadecane, isooctane, and diesel. We performed a continuous oil/water separation test by continuously adding water into the upper glass tube while maintaining the height of the oil/water mixture at 7 cm. The absence of oil content in the filtrate further demonstrated the robustness and antifouling properties of the melamine sponge. Oil/water mixtures, including those containing n-hexane, n-hexadecane, and isooctane, could separate in these continuous separation tests over a period of at least 1 hour while maintaining a high flow rate (L m-2 h- 1) This just shows further evidence that the PVP, which had been deposited on the sponge, has bonded very strongly to the cotton fiber and is serving its purpose by enhancing roughness to increase oleorephobicity. EMULSION SEPARATION Emulsified oil in wastewater is also a major environmental problem affecting a number of industries. Direct discharge of such wastewater harms both the environment and human health. Due to its large pores (>50 µm), raw melamine sponge could only separate loose mixtures.