Advanced materials with desired wettability are extremely important for environmental sustainability, such as oily industrial wastewater treatment and oil spill cleanup. To meet this demand, a scalable nanoengineering approach was developed to fabricate superhydrophilic and underwater superoleophobic inorganic meshes for cross-flow filtration and oil/water separation. The resulting nanostructured copper meshes exhibit superhydrophilicity and underwater superoleophobicity (oil contact angle approaching to 159°). With these meshes, very high values of filtration flux (≥900,000 Lh-1m-2) have been achieved, with ultra-low oil residue in the filtrate (<40 ppm) and long water retention time (more than 1 h). The proposed nanoengineering method paves the way for effective gravity-driven separation of immiscible oil/water mixtures, especially for low-density oil purification.