Massively Engineering the Wettability of Titanium by Tuning Nanostructures and Roughness via Laser Ablation

Efficient, environment-friendly, and low-cost oil-water separation is currently a global challenge, to which surface wettability engineering is a key. Here, we introduce an advanced titanium membrane with thousands of water-selective microchannel arrays in a Ti mesh, which is fabricated by femtosecond laser machining. The laser ablation accomplishes three tasks during one process: drilling microchannels, forming a TiO₂@Ti membrane, and engineering nanoscale surface roughness. Particles ejected during machining resolidify to produce rough surfaces with micro-/nanoscale hierarchical structures. This direct ablation gives a highly stable, self-cleaning, and pollutant-free oil-water filter with high separation efficiency. Furthermore, the critical values of the surface roughness and the pore size are analytically derived, providing a guidance for laser surface wettability engineering. Our results could be useful in surface engineering, laser machining, nanostructure engineering, and industrial-scale oil-water separation applications, including wastewater treatment, oil-spill cleaning, and petroleum mining.