Superhydrophilic and underwater superoleophobic Ti foam with fluorinated hierarchical flower-like TiO2 nanostructures for effective oil-in-water emulsion separation

In this work, a superhydrophilic Ti foam was designed and fabricated by applying a novel one-step hydrothermal approach to achieve highly efficient oil in water emulsion separation. Attributed to the synergistic effect of the surface roughness constructed by hierarchical flower-like TiO2 nanostructures and the surface hydrophilicity induced by titanium oxy-fluoride groups, the as-prepared Ti foam exhibited superhydrophilicity and underwater superoleophobicity. The formation of flower-like TiO2 nanostructures was studied and a possible "partial replacement" fluorinated process was proposed. Oil in water emulsion separation test showed that the superhydrophilic Ti foam could handle with various emulsions only under gravity with high separation efficiency over 99%. The separation efficiency remained high even after 20 times of reusing, demonstrating good reusability. More importantly, the superhydrophilic Ti foam could still maintain its wettability after immersed corrosive solutions for 48 h or stored under ambient atmosphere for three months, indicating excellent anti-corrosion property and long-term storage stability. We envision the methodology for the construction of a superhydrophilic surface by a simple and low-cost hydrothermal process will shed light on the Ti-based material design and also pave the way for applications in other fields such as liquid manipulation, fluidic devices and bioadhesion control.