Oil/water separation accounts for an important step of water treatment due to expanding production of industrial oily wastewater and is also necessary to manage frequent oil spills. Membrane technology is attractive for oil/water separation because it works without chemicals addition, with low energy requirement and undemanding operations and it can achieve high separation efficiency and speed if the wettability of the membranes is well designed. Engineering surface wettability constitutes an essential strategy of developing membranes for oil/water separation and practical applications emphasize the need for economic and robust candidate membranes. In this work, uniform, smooth, and thin TiO2 layers were conformally coated on stainless steel mesh via an environmentally benign approach that is facile, inexpensive, and scalable. The TiO2 coating turned the mesh from hydrophobic to superhydrophilic and rendered the mesh with underwater superoleophobicity for various types of oil. The TiO2-coated mesh can separate immiscible oil/water mixtures solely driven by gravity with high flux (~3×104 Lm-2h-1), high separation efficiency (~ 99.999%), and excellent stability of the separation performance (no performance decline after 36 cycles separation of petroleum/water mixtures). The underwater superoleophobicity was not diminished after the coated mesh was immersed in saline solution, strong acidic and alkaline solutions, as well as organic solvent for 24 h. In addition, the TSSM held great repellence to oil droplets under water of pH ranging from 1 to 13 and of NaCl concentration up to 357 g/L. More importantly, separation functionality of the TSSM was retained after mechanical wear tests, including calcination, sonication, abrasion and crumpling. The versatility of the coating method was also investigated on other substrates, including nonwoven stainless steel mesh, filter paper and PVDF membrane, and these coated substrates show good capability for oil/water separation. Mechanistic study revealed that the engineered wettability was ascribed to the surface energy modification by TiO2-coating. Therefore, the TiO2-coated stainless steel mesh is an economic, robust and sustainable solution to the treatment of oily wastewaters and this coating approach opens a new avenue to preparing superwetting surface materials for environmental applications.

Facile, inexpensive, and scalable approach enabled robust TiO2-coating on stainless steel mesh for oil/water separation

2019 Spring National Meeting

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