Special Wettable Membranes for Oil/Water Separations: A Brief Overview of Properties, Types, and Recent Progress

Periodical oil spills and massive production of industrial oil wastewater have impacted the aquatic environment and has put the sustainability of the ecosystem at risk. Oil–water separation has emerged as one of the hot areas of research due to its high environmental and societal significance. Special wettable membranes have received significant attention due to their outstanding selectivity, excellent separation efficiency, and high permeation flux. This review briefly discusses the fouling behavior of membranes and various basic wettability models. According to the special wettability, two major classes of membranes are discussed. One is superhydrophobic and superoleophilic; these membranes are selective for oil and reject water and are highly suitable for separating the water-in-oil emulsions. The second class of membranes is superhydrophilic and underwater superoleophobic; these membranes are highly selective for water, reject the oil, and are suitable for separating the oil-in-water emulsions. The properties and recent progress of the special wettable membranes are concisely discussed in each section. Finally, the review is closed with conclusive remarks and future directions.