A review of 3D superhydrophilic porous materials for oil/water separation

The separation of oil/water mixtures has become a major problem worldwide as oil spills and the discharge of oily wastewater. Materials with special wettable surfaces have been developed over the past decades to separate oil and water efficiently. Compared to conventional superoleophilic "oil removal" materials, superhydrophilic "water removal" materials have been favored by researchers for their better performance. Among them, threedimensional (3D) porous materials have higher oil/water separation flux than two-dimensional (2D) materials, and their unique structure allows them to be applied to separate various oily wastewater. Therefore, 3D superhydrophilic porous materials have been widely manufactured and applied to oil/water separation. In this paper, we first introduced the theoretical model of oil/water separation and then described in detail the currently fabricated superhydrophilic sponges, foams, hydrogels, and aerogels from three types of substrate materials: organic, inorganic, and organic-inorganic co-hybrid. We mainly described the preparation methods, surface wettability, oil/water separation properties, and other properties each material possesses. We also identified and clarified the relationships and inconsistencies among the materials. Finally, we discussed and summarized the advantages and disadvantages of various types of 3D superhydrophilic porous materials, as well as some problems and challenges faced, and provided an outlook on their future development.