In this work, a novel and facile method was used to coat a uniform and conformal TiO2 film on a stainless steel mesh via polyethylenimine-catalyzed biomineralization of titanium bis(ammonium lactato)dihydroxide at neutral pH, ambient temperature and pressure. The fabricated mesh showed excellent superhydrophilicity and underwater superoleophobicity. It separated immiscible oil/water mixtures by gravity at a high flux (similar to 3 x 10(4) L m(-2) h(-1)), high separation efficiency (similar to 99.999%), and exhibited excellent anti-oil-fouling ability. The mesh also demonstrated great durability: (1) it had outstanding stability in 1 M NaCl, 0.1 M HCl, 0.1 M NaOH solutions, and absolute ethanol; (2) it maintained underwater superoleophobicity in solutions of pH from 1 to 13 and saturated NaCl solutions; and (3) the separation efficiency was retained after high temperature treatment and mechanical wear tests (sonication, abrasion and crumpling). The biomineralization coating method was also applied on other substrates (nonwoven mesh, filter paper and PVDF membrane), which also showed good capability for oil/water separation. Therefore, this new environmentally benign approach of preparing superwetting surfaces provides a durable and sustainable solution to the treatment of oily wastewater.