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Oil remains an important and irreplaceable energy source. About one-third of the world's oil production is carried out in the ocean. Offshore oil production is prone to oil spills. For example, in April 2010, an oil spill occurred on the Deepwater Horizon drilling platform in the Gulf of Mexico, USA. The accident caused about 560,000 tons of crude oil to leak into the sea, forming a severely polluted area of more than 3,200 square kilometers. The oil spill has been described as "an unprecedented environmental disaster in the United States." Some accidents may also occur during transportation. For example, in January 2018, the Panamanian tanker "Sanchi" collided with the Hong Kong-registered cargo ship "CF CRYSTAL" in the East China Sea, causing the hull to catch fire and seriously leak oil, with an oil spill area of 1,616 square kilometers. Oil exploration on land requires the use of a large amount of water. This leads to the formation of a large amount of oil-water mixture. Oil/water mixtures are not limited to the oil production process; they also exist in people's daily lives and various industrial sectors, including metallurgy, textiles, printing, dyeing, etc., which produce a large amount of oily wastewater.
In order to treat oily wastewater more efficiently, economically and environmentally friendly, many mature oil-water separation technologies have emerged. Examples of these technologies include mechanical devices, membrane separation, chemical treatment methods, biomimetic surfaces and electric field-assisted technologies. Mechanical oil-water separators and electric field-assisted methods consume a lot of electricity, waste energy and are complex to operate. Chemical treatment methods are not environmentally friendly because various chemicals are added, which may cause secondary pollution. These methods have been proven to be effective in treating oily wastewater under certain conditions. Membrane treatment has the advantages of low energy consumption, good repeatability and no secondary pollution during the treatment process. In addition, it can be applied to various environments and can be designed to have other advantages. For example, Cheng prepared polylactic acid (PLA) membranes by electrospinning. Electrospun PLA membranes can be prepared with few processing steps and produce degradable membranes that are easy to handle, reducing plastic pollution.
The main point of this paper
Definition of smart oil/water separation membrane:
Smart oil/water separation membrane refers to a membrane that can change its wettability according to different external stimuli (such as temperature, pH, light, etc.). These membranes can be amphiphilic or amphiphobic, and have the characteristics of a double-sided membrane, that is, the wettability on both sides is different, and flipping the membrane will change the type of material passing through it.
Preparation method:
The methods for preparing smart oil/water separation membranes include electrospinning, vapor deposition, template method, sol-gel method and layer-by-layer assembly. Among them, electrospinning technology has attracted widespread attention due to its simplicity and high efficiency.
Application field:
The application of smart membranes in the field of oil-water separation has been increasingly valued, especially in the treatment of oily wastewater. The change in membrane wettability can be achieved by the design of stimulus-responsive materials, thereby improving the efficiency of oil-water separation.
Research progress:
Recent studies have shown that smart membranes have great potential for application in oil-water separation. For example, Zhang et al. prepared a thermally driven emulsion separation membrane that can exhibit different wettability at different temperatures, thereby achieving oil-water separation
In addition, Wang et al. prepared a TiO2-doped PVDF nanofiber membrane by electrospinning, which can selectively allow water or oil to pass through alone under ultraviolet irradiation, achieving reversible separation of oil-water mixtures
Definition and Importance of Smart Oil-Water Separation Membranes:
Smart oil-water separation membranes are membranes that can change their wettability in response to different external stimuli, such as pH, light, heat, electric or magnetic fields. Such membranes can be amphiphilic or amphiphobic under certain conditions, and oil-water separation is achieved by changing the wettability of the membrane
Preparation Methods:
The preparation methods of smart oil-water separation membranes include electrospinning, vapor deposition, template method, sol-gel method, and layer-by-layer assembly. These methods can obtain microfiltration membranes, nanofiltration membranes, and bioactive membranes
Properties of Stimuli-Responsive Membranes:
Stimuli-responsive membranes change their physical properties when the pH changes, when exposed to light or heat, or when an electric or magnetic field is applied. Special attention is paid to changes in wettability rather than changes in other properties
Applications of Electrospinning Technology:
Electrospinning technology is a simple and efficient method for preparing smart oil-water separation membranes. Membranes prepared by electrospinning can be modified to contain different chemical and biological components, and the diameter of the filaments can range from micrometers to nanometers, and this size can be adjusted to control certain properties, such as superhydrophobicity
Types and applications of smart membranes:
Smart membranes include Janus membranes, pre-wetted membranes, and responsive membranes. These membranes can reversibly switch the interfacial wettability between superhydrophobic and superhydrophilic according to external stimuli, achieving on-demand oil/water separation
Research on electrospinning smart oil-water separation membranes has been progressing rapidly. These membranes have attracted widespread attention because electrospinning is a simple method to quickly generate porous polymer membranes. These membranes combine the advantages of electrospinning technology and smart materials to provide an efficient and controllable solution for oil-water separation. Among them, the change in membrane wettability is mainly achieved through Janus structure, pre-wetting, pH, heat, gas and light.
Janus structure is one of the important ways to achieve smart oil-water separation membranes. This structure makes the membrane surface asymmetric in terms of wettability of oil and water. This asymmetry makes one side of the membrane hydrophilic/oleophobic and the other side hydrophilic/oleophilic. Janus membranes have been shown to quickly separate oil and water from mixtures and emulsions. The selectivity and efficiency of oil-water separation can be further improved by carefully designing and regulating the Janus structure, and in the future, the performance of the membrane can be improved by mimicking biological structures and surface chemistry.
