Superwetting metal mesh membranes for oil/water separation: A comprehensive review

There is a strong demand for the effective treatment of oily wastewater discharged from industrial and manufacturing plants to reduce the threats and impacts on aquatic ecosystems, human health, and economic productivity. During the past decade, superwetting membranes have emerged as an advanced class of materials for efficiently separating stratified and emulsified oil/water mixtures. Superwetting membranes constructed from different metal meshes (e.g. stainless steel, Cu, Ti, Ni) have attracted a lot of research due to their flexibility, mechanical strength, chemical stability, controlled porosity, and feasible modification by diverse chemical and electrochemical approaches. This review provides a comprehensive overview of fabricating metal mesh membranes with different wettability including superhydrophobic/superoleophilic (SHB/SOL), superhydrophilic and underwater superoleophobic (SHL/UWSOB), superhydrophilic and superoleophobic (SHL/SOB) membranes. In each case, the discussion focuses on the employed chemical/ electrochemical strategies for controlling the surface roughness and the surface energy to attain a special wettability state. The separation of stratified oil/water mixtures, water-in-oil emulsions (w/o), and oil-in-water emulsions (w/o) is highlighted. Various types of advanced smart superwetting metal mesh membranes are presented including membranes with pre-wetting induced switchable wettability, stimuli-responsive metal mesh membranes (redox, light, pH), and Janus metal mesh membranes. The practical considerations for oil/water separation such as anti-oil-fouling and self-cleaning properties were discussed for SHL and SOB superwetting systems.