<p>Robust and scalable materials for oil-water separation are often limited by corrosion, fouling, and mechanical damage. Here, we demonstrate a simple, rapid, and low-temperature surface conversion that transforms commercial 316L stainless-steel meshes into superhydrophilic, underwater-oleophobic filters. A two-step reaction followed by Fe³⁺-tannic acid-phosphate complexation yields a thin nanogranular FeOOH/TA/PO₄ hybrid film that is chemically anchored to the steel surface. The coating imparts rapid wetting behaviour, with a static water contact angle of about 45° and dynamic superhydrophilicity that achieves complete wetting within 0.15 s, enabling high-performance gravity-driven separations. Single-pass treatment of diverse oil-water mixtures delivered oil rejections of 95–99% and water permeate fluxes in the range of 23,000–80,000&#xa0;L m^–2 h^–1, depending on mesh size. The meshes retained a robust performance over 50 separation cycles, 30 days of brine immersion, and exposures across pH 1–14 with negligible degradation. Abrasion resistance was further validated, and fouled meshes (e.g., with graphene oxide or edible oil) rapidly regained high flux and rejection after simple water rinsing, underscoring intrinsic self-cleaning behaviour. The process uses inexpensive reagents and is readily applicable to large-area mesh surface functionalization, providing a robust pathway to high-throughput, energy-free gravity separations for oily wastewater remediation.</p> Graphical abstract <p>A simple, scalable two-step conversion of 316L stainless-steel mesh into a superhydrophilic filter coated with a robust protective nanohybrid film, which enables ultrafast oil-water separation, strong abrasion and anti-fouling resistance, corrosion tolerance, and long-term durability. Background illustration was created using <i>Midjourney</i>, a text-to-image AI tool.</p>