Oil/water pollution caused by industrial activities and accidents (oil spill) has become a serious hazard to the environment and human health. The research in the field of oil/water separation has drawn increasing attention of scientists and engineers from all over the world. Conventional separation technologies like oil-skimmer, gravity-separation, centrifugation, air-flotation and so forth, are always limited due to their complex operating system, low separation efficiency, energy consumption and causing secondary-pollution. Therefore, novel separation technology and advanced separation material are highly desirable at the current moment.
Recently, fabrications of superwetting porous materials with special wettability (hydrophobicity & oleophilicity, hydrophilicity & oleophobicity) have become highly promising for separating oil/water mixtures because of their excellent selectivity towards water and oil. Superhydrophilic/underwater superoleophobic porous materials have engaged considerable attention in the application for the separation of oil/water mixtures. However, there still exist several challenges in the existing material designs for oil/water separation that need to be addressed, such as terrible stability, high production cost and complex fabrication procedure.
 Herein, a series of all-inorganic superhydrophilic and underwater superoleophobic filtration materials were designed and fabricated by coating TiO₂ via a facile and universal technique of self-assembly, as well as successfully applied for the separation of both stratified oil/water mixtures and emulsions. The as-prepared TiO₂ nanoparticle coating is extremely dense, ultrathin and widely applicable for various two-dimensional (2D) and three-dimensional (3D) substrates such as stainless-steel mesh (SSM), metal felt and glass fibrous (GF) membrane. The coating can even be coated on the ultrafine fibers with a diameter reaching hundreds of nanometers. The TiO₂ coated SSM with large pores (~35 μm diameter) could efficiently separate the stratified oil/water mixtures with the flux up to 54000 L/m²h. Moreover, the TiO₂ coated GF membrane with small pores (~5 μm diameter) can separate diverse surfactant-free and surfactant-stabilized emulsions with separation efficiency higher than 98%. More importantly, excellent filtration flux up to ~4000 L/m²h was realized under sole gravity, which is one to two orders of magnitude larger than the flux of traditional filtration membranes, as well as more superior than most of the reported superwettable membranes. Furthermore, the as-prepared GF membrane displays outstanding high-temperature resistance and reusability for long-term application of oil/water separation.
Further, this self-assembly nanocoating preparation technology can be expanded to other types of nanoparticles to tune the wettability of membranes. Follow this line of research, we developed a novel method to prepare the superhydrophobic-superoleophilic surface by using PTFE nanoparticles as building blocks. The as-prepared PTFE nanofibrous coating presented ultrathin morphology with high uniformity, excellent anti-corrosion and outstanding chemical stability. Overall, the self-assembling fabrication method presented in this report is simple, cost-efficient, productive, and very applicable for large-area treatment and industrialization
 

wettability,membrane,surface coating,superhydrophobic,superhydrophilic