pH-Controllable On-Demand Oil/Water Separation on the Switchable Superhydrophobic/Superhydrophilic and Underwater Low-Adhesive Superoleophobic Copper Mesh Film

Abstract

Recently, materials with controlled oil/water separation ability became a new research focus. Herein, we report a novel copper mesh film, which is superhydrophobic and superhydrophilic for nonalkaline water and alkaline water, respectively. Meanwhile, the film shows superoleophobicity in alkaline water. Using the film as a separating membrane, the oil/water separating process can be triggered on-demand by changing the water pH, which shows a good controllability. Moreover, it is found that the nanostructure and the appropriate pore size of the substrate are important for realization of a good separation effect. This paper offers a new insight into the application of surfaces with switchable wettability, and the film reported here has such a special ability that allows it to be used in other applications, such as sewage purification, filtration, and microfluidic device.

Oil‐Water Separation: A Gift from the Desert

“…Following this strategy, many mesh and porous materials that are underwater superoleophobic have been fabricated, and these materials have been successfully applied in oil-water separation. [18][19][20][21][22][23][24][25] For example, Jiang and co-workers coated microscale porous stainless steel mesh with a nanostructured hydrogel to give a novel underwater superoleophobic rough mesh. [ 18 ] This hydrogelcoated mesh effi ciently removed water from water-oil mixtures and did not become fouled with oil.…”

“…Problems that have not been adequately addressed are the cost of the materials, the equipment required, and the preparation processes required -all of which prevent large-scale applications. Another issue is that the most widely used materials are metal meshes and porous polymers that have rough microscale-nanoscale hierarchical structures, which are generally formed using chemical corrosion or other chemical methods, [20][21][22][23][24][25] meaning that solving one environmental problem (oil pollution) could cause another (disposing of the waste produced to create the superoleophobic material). It is therefore very important that we develop or fi nd stable materials that are underwater superoleophobic and can be used to simply, cheaply, and effi ciently separate large amounts of oil-water mixtures.…”

“…"Water-removing" superhydrophilic and superoleophobic materials have been developed to address the problems described above, and they have proved extremely effective in practical applications. [15][16][17][18][19][20][21][22][23][24][25] However, it is harder to produce a superoleophobic material (with an oil contact angle (OCA) greater than 150°) than to produce a superhydrophobic material because the surface tensions of oils are lower than the surface tension of water. [26][27][28][29][30] A surface that is superoleophobic several metal elements, as shown in Figure S1 of the Supporting Information.…”

Superwetting Materials of Oil–Water Emulsion Separation

“…The specific wettability of the SWCNT film endows its ability for oilwater separation including surfactant-free and surfactant-stabilized emulsions with droplet sizes in the micrometer and nanometer scale. Wang et al 52 prepared a pH-responsive copper mesh film which can be used as a separating membrane with good controllability through assembling the responsive thiol molecules on the Cu(OH) 2 nanorod-structured copper mesh substrate. Due to its superhydrophobic and superhydrophilic properties for non-alkaline water and alkaline water, respectively, and superoleophobicity property in alkaline water, the oilwater separating process can be triggered on-demand.…”

Purification of oily seawater/wastewater using superhydrophobic nano-silica coated mesh and sponge

“…Despite the fact that many oil-water separation methods such as adhesion, membrane filtration, and absorbance have been developed and are widely used [2], achieving an energy-and cost-effective oil-water separator with high efficiency remains a great challenge. Since oil-water separation is governed by the interfacial features of the substrate, fabrication of preferential wettability materials toward oil or water is desirable and effective [3,4].…”