Micro/Nanoscale Structured Superhydrophilic and Underwater Superoleophobic Hybrid-Coated Mesh for High-Efficiency Oil/Water Separation.

A novel micro/nanoscale rough structured superhydrophilic hybrid-coated mesh that shows underwater superoleophobic behavior is fabricated by spray casting or dipping nanoparticle-polymer suspensions on stainless steel mesh substrates. Water droplets can spread over the mesh completely; meanwhile, oil droplets can roll off the mesh at low tilt angles without any penetration. Besides overcoming the oil-fouling problem of many superhydrophilic coatings, this superhydrophilic and underwater superoleophobic mesh can be used to separate oil and water. The simple method used here to prepare the organic-inorganic hybrid coatings successfully produced controllable micro-nano binary roughness and also achieved a rough topography of micro-nano binary structure by controlling the content of inorganic particles. The mechanism of oil-water separation by the superhydrophilic and superoleophobic membrane is rationalized by considering capillary mechanics. Tetraethyl orathosilicate (TEOS) as a base was used to prepare the nano-SiO2 solution as a nano-dopant through a sol-gel process, while polyvinyl alcohol (PVA) was used as the film binder and glutaraldehyde as the cross-linking agent; the mixture was dip-coated on the surface of 300-mesh stainless steel mesh to form superhydrophilic and underwater superoleophobic film. Properties of nano-SiO2 represented by infrared spectroscopy and surface topography of the film observed under scanning electron microscope (SEM) indicated that the film surface had a coarse micro-nano binary structure; the effect of nano-SiO2 doping amount on the film's surface topography and the effect of such surface topography on hydrophilicity of the film were studied; contact angle of water on such surface was tested as 0° by the surface contact angle tester and spread quickly; the underwater contact angle to oil was 158°, showing superhydrophilic and underwater superoleophobic properties. The effect of the dosing amount of cross-linking agent to the waterproof swelling property and the permeate flux of the film were studied; the oil-water separation effect of the film to oil-water suspension and oil-water emulsion was studied too, and in both cases the separation efficiency reached 99%, which finally reduced the oil content to be lower than 50 mg/L. The effect of filtration times to permeate flux was studied, and it was found that the more hydrophilic the film was, the stronger the stain resistance would be, and the permeate flux would gradually decrease along with the increase of filtration times.