Surface Engineering Materials of Superhydrophobic Sponges for Oil/Water Separation: A Review

Sponge-based materials have recently gained much attention in the field of oil/water separation due to their easy fabrication, recyclability, environmental friendliness, and low cost. Commercial sponges such as melamine sponge, polyurethane sponge, graphene-based sponge, and cellulose sponge have large surface area and high absorption capability, but they are hydrophilic/oleophilic (absorb both oil and water) in nature, which makes them not applicable in oil/water separation. To make them applicable in oil/water separation, the sponges have been modified with low surface energy materials and nano/micro hierarchical roughness, hence changing their wettability to superhydrophobicity/superoleophilicity (absorb oil and repel water). These materials include organosilicons, carbon-based materials, oxides, and metal–organic frameworks (MOFs) among others. We summarized the modifying materials for the fabrication of superhydrophobic/superoleophilic sponges used in oil/water separation even under harsh conditions such as pH-universal, high temperature, and so on. Furthermore, ideas for future application of the coating sponge materials in the field are discussed.