Oil spills and industrial organic pollutants have induced severe water pollution and threatened every species in the ecological system. To deal with oily water, special wettability stimulated materials have been developed over the past decade to separate oil-and-water mixtures. Basically, synergy between the surface chemical composition and surface topography are commonly known as the key factors to realize the opposite wettability to oils and water and dominate the selective wetting or absorption of oils/water. In this review, we mainly focus on the development of materials with either super-lyophobicity or super-lyophilicity properties in oil/water separation applications where they can be classified into four kinds as follows (in terms of the surface wettability of water and oils): (i) superhydrophobic and superoleophilic materials, (ii) superhydrophilic and under water superoleophobic materials, (iii) superhydrophilic and superoleophobic materials, and (iv) smart oil/water separation materials with switchable wettability. These materials have already been applied to the separation of oil-and-water mixtures: from simple oil/water layered mixtures to oil/water emulsions (including oil-in-water emulsions and water-in-oil emulsions), and from non-intelligent materials to intelligent materials. Moreover, they also exhibit high absorption capacity or separation efficiency and selectivity, simple and fast separation/absorption ability, excellent recyclability, economical efficiency and outstanding durability under harsh conditions. Then, related theories are proposed to understand the physical mechanisms that occur during the oil/water separation process. Finally, some challenges and promising breakthroughs in this field are also discussed. It is expected that special wettability stimulated oil/water separation materials can achieve industrial scale production and be put into use for oil spills and industrial oily wastewater treatment in the near future.

Solid surfaces possessing both superhydrophobic and superoleophilic properties have attracted significant interest in fundamental investigations and potential applications in the fields of self-cleaning surfaces, oil/water separation, and microfluidic channels. In this paper, a general methodology for robust superhydrophobic fabrics and sponges was proposed via the in situ growth of both transition-metal oxides and metallic nanocrystals, including the simple neutralization reaction and oxidation-reduction reaction. The porous surfaces coated with Group VIII and IB nanocrystals (such as Fe, Co, Ni, Cu, and Ag) can not only present multiscale surface roughness, but also readily coordinate with thiols, leading to special wettability. In our previous work, it has been confirmed that the interaction between the nanocrystals and thiols plays a significant role in the introduction of hydrophobic ingredients. In this work, it has been demonstrated that the efficient control of the nucleation and growth of Group VIII and IB nanocrystals on the porous surfaces becomes the key factor in the formation of multiscale surface roughness, resulting in the achievement of controllable special wettability. In addition, these as-prepared superhydrophobic and superoleophilic fabrics and sponges were successfully used for application in oil/water separation.