Design and fabrication of superwetting fiber-based membranes for oil/water separation applications

The separation of oily wastewater, including immiscible oil/water mixtures and emulsified oil/water mixtures, is a worldwide challenge because of the large amount of oily wastewater produced in many industrial processes and daily life. For the treatment of oily wastewater, membrane technology is considered the most efficient method because of its high separation efficiency and relatively simple operational process. Due to highly specific surface areas, interconnected nanoscale pore structures, controllable pore size, the potential of surface texture, and ease of chemical modification, fiber-based membranes with superwetting have become promising versatile platforms for the separation of oil/water mixtures and emulsions. Such fiber-based membranes can be categorized based on type of fiber membrane substrate and the surface wettability. Here, the theory and design of various superwetting states for selective oil/water separation including superhydrophobicity/superoleophilicity, superhydrophilicity/underwater superoleophobicity, Janus wettability, and smart wettability are discussed. Two types of fiber-based membrane substrate including inorganic fibers (e.g. metal mesh, carbon nanotube, and inorganic oxide fibers) and organic fibers (e.g. fabrics fiber and nonwoven fibers) are summarized. The unique advantages of each type fibers have been highlighted, with emphasis on the membrane wetting properties, membrane fouling and representative works. Moreover, the detail progress of fiber-based membrane for separation of both immiscible oil/water mixtures and emulsified ones were introduced. Finally, the challenges and future research directions of fiber-based membrane were briefly discussed.