A highly efficient, stable, durable, and recyclable filter fabricated by femtosecond laser drilling of a titanium foil for oil-water separation

It has been a long standing challenge to efficiently separate oil and water since prehistoric times, and now it has become even more desirable in oily wastewater purification and oil spill cleanup. Here we introduce a super oil-water separation filter with superhydrophilicity and underwater superoleophobicity, fabricated using femtosecond laser micro-hole drilling of a titanium foil. Such a simply-made filter, without any modification, can achieve a separation efficiency exceeding 99% in eight typical oil-water mixtures. It remains highly efficient after 40 cycles of recycling and after suffering erosion by corrosive media. Furthermore, the used filter, polluted with oil, could be recovered by ultraviolet illumination. The flux of filtered water is tunable by simply selecting the aperture of the microhole or the spacing between adjacent microholes. Such advanced functionality is due to roughness and the TiO2 layers on the ablated surface during fabrication. With superhydrophilic and superoleophobic surfaces, this oil-water filer is also suitable for applications in anti-fouling, anti-smudge, anti-fog, and self-cleaning.