More recently, underwater superoleophobic graphene-based materials have been prepared and applied in the separation of oil/water mixtures 17. They also used a sol-gel method to prepare superhydrophilic single-walled carbon nanotube/TiO 2 nanocomposite films, which were applicable for the separation of both a surfactant-free emulsion and a surfactant-stabilized oil-in-water emulsion 16. Jin and coworkers developed nanowire-haired inorganic membranes possessing superhydrophilicity and underwater ultralow adhesive superoleophobicity that could effectively separate both immiscible oil/water mixtures and oil-in-water emulsions with high separation efficiencies 15.
described a superhydrophilic and underwater superoleophobic hydrogel-coated mesh for the efficient separation of oil/water mixture 14. Following this strategy, several materials possessing both superhydrophilicity and underwater superoleophobicity have been prepared, using various methods, with the aim of using them for efficient oil/water separations 14, 15, 16, 17, 18, 19, 20, 21, 22, 23. Inspired by the wetting behavior of fish scales and taking advantage of high-energy materials having water-favoring properties, it has been possible to construct underwater superoleophobic surfaces in oil/water/solid three-phase systems 13. Accordingly, materials possessing superhydrophobicity and superoleophilicity are not suitable for the separation of water-rich oil/water mixtures or oil-in-water emulsions. Furthermore, because water is generally denser than oil, it tends to settle below an oil phase, forming a barrier layer above the separation material and inhibiting oil permeation into it. Although such previously developed materials can be effective agents for oil/water separation, they are readily fouled, or even blocked up, by oils because of their intrinsic oleophilicity.
Recently, materials possessing both superhydrophobic and superoleophilic properties have attracted broad attention because of their capacity to mediate the efficient separation of oils, organic pollutants and other hydrophobic organic solvents from water 6, 7, 8, 9, 10, 11, 12. As a result, there is a need to develop new materials that would allow oil/water separations to be performed efficiently, at low cost, with high selectivity 3, 4, 5. Traditional techniques for oil-water separation (e.g., gravity separation combined with skimming, flotation, oil-adsorbing materials, flocculation and coagulation) 1, 2 have low separation efficiencies and high energy costs and require complex separation steps. In 2010, the explosion of BP’s Deepwater Horizon oilrig resulted in 210 million gallons of oil being released into the Gulf of Mexico. Effective oil/water separation is a challenge worldwide because of the expanding production of industrial oily wastewater and the frequent oil spills arising from industrial accidents and the sinking of oil tankers and other ships.
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