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. 2020 Jun 19;12(6):1378.
doi: 10.3390/polym12061378.

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

Teng Yuan  1   2   3 , Jian Yin  1 , Yingling Liu  1 , Weiping Tu  2 , Zhuohong Yang  1
Affiliations

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

Teng Yuan et al. Polymers (Basel). .

Abstract

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.

Keywords: coated mesh; micro-nanoscale binary rough structure; oil–water separation; superhydrophilic; underwater superoleophobic.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 1
Scheme 1
Preparation of nano SiO2 by ethyl silicate via hydrolytic condensation.
Scheme 2
Scheme 2
Preparation of the hydroxyl acrylic resin via radical polymerization.
Figure 1
Figure 1
Schematic of preparation of superhydrophilic and underwater superoleophobic composite membrane via a two-step coating method.
Figure 2
Figure 2
IR spectra (a) and particle size distribution (b) of the SiO2 nanoparticles.
Figure 2
Figure 2
IR spectra (a) and particle size distribution (b) of the SiO2 nanoparticles.
Figure 3
Figure 3
SEM images of different sizes of acrylic polymer nano-latex particles.
Figure 4
Figure 4
SEM images of hybrid-coated mesh films prepared from a stainless steel mesh with an average pore diameter of about 50 mm. The content of SiO2 is (a) 33%, (b) 40%, (c) 50%, (d) 60%, (e) 66%, (f) 75%, (g) 80%, (h) 90% and (i) 100%.
Figure 5
Figure 5
SEM images of hybrid-coated mesh films after secondary coating. The SiO2 content is (a) 33%, (b) 40%, (c) 50%, (d) 60%, (e) 66% and (f) 75%.
Figure 6
Figure 6
Contact angle of water on (a) the clean stainless steel mesh surface (91.3°), (b) the superhydrophilic membrane (0°), (c) contact angle of oil on the superhydrophilic membrane under water (158°).
Figure 7
Figure 7
The contact angle and rolling contact angle of various types of oils.
Figure 8
Figure 8
SEM images of the hybrid-coated mesh film prepared using stainless steel mesh with an average pore diameter of about 50 mm. (a) Large-area view of the stainless steel mesh, (b) large-area view of the hybrid -coated mesh film, and (c) enlarged view of the hybrid-coated mesh film.
Figure 9
Figure 9
Oil–water separation experiment performed using the hybrid-coated mesh.
Figure 10
Figure 10
Renderings of membrane separation of oil and water emulsion.
Figure 11
Figure 11
Effect of the number of membrane filtration on flux.
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