Preparation of underwater superoleophobic membranes via TiO2 electrostatic self-assembly for separation of stratified oil/water mixtures and emulsions

Huge discharge of oily wastewater has seriously threatened the ecosystem and human's health. Superhydrophilic/underwater superoleophobic porous materials have engaged considerable attentions in the application for 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 diameter reaching to hundreds of nanometers. The TiO2 coated SSM with large pores (similar to 35 mu m diameter) could efficiently separate the stratified oil/water mixtures with the flux up to 54000 L.m(-2).h(-1). Moreover, the TiO2 coated GF membrane with small pores (similar to 5 mu m diameter) can separate diverse surfactant-free and surfactant-stabilized emulsions with separation efficiency higher than 98%. More importantly, excellent filtration flux up to similar to 4000 L.m(-2).h(-1) was realized under solely 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.