Fabrication of Non-Fluorinated Hydrophilic-Oleophobic Stainless Steel Meshes for Oil-Water Separation

Oil-water separation is a worldwide concern due to the increasing emissions of oil-contaminated industrial water, frequent oil spill accidents and the shortage of drinking water. In this study, hydrophilic/oleophobic stainless steel (SS) meshes which can separate oil from water were fabricated by one step solution based coating method using methyltrimethoxysilane (MTMS). The coating materials were prepared by mixing MTMS with hydrochloric acid and sonicated in an ice bath for 5 min. Meshes were then immersed in the mixture for 2 min and dried in air. The dimensions of meshes were varied to study their effect on wettability and separation efficiency. Coated meshes were then used for gravity-driven oil/water separation with oil-water mixtures and oil-water emulsions. Contact angles, fluid flux, and separation efficiency were evaluated to determine the optimum mesh dimensions. The so called mesh 400 with an inter-fiber gap of 38 μm and fiber radius of 13 μm showed the best performance in separating oil-water mixtures. The coated mesh allows water flux as high as 7.16 × 10⁴ L·m^-2·h^-1, with water recovery rate up to 91.1 % and separation efficiency higher than 99.9 % solely driven by gravity. XPS and ATR-FTIR were performed on coated stainless steel surface to prove the presence of silanol groups that play a critical role in the unique wetting properties. Even with the presence of sand particles on the surface after sand impact testing, the treated meshes were still able to separate oil-water mixtures with high separation efficiency and water recovery. The coated mesh filters hold great promise for applications in fields such as oil spill cleanup, where sand and dust will inevitably contaminate the system. Additionally, the ability to separate oil droplets larger than its pore size from oil-water emulsions makes the meshes a cheap, attractive candidate for pretreatment in current large scale oil-water separation units.