Facile fabrication of superhydrophilic/underwater superoleophobic polyvinyl acetate/sodium silicate composite coating for the effective water/oil separation and the study on the anti-fouling property, durability and separation mechanism

In this study, hydrophilic stainless steel meshes for water/oil separation were successfully prepared through the etching and subsequent modification of a polyvinyl alcohol (PVA)-sodium silicate (Na2SiO3) composite. The effects of the surface structure and component on the wetting behavior, separation efficiency, and separation flux were investigated. The long-term stability and anti-abrasion property were also studied. Furthermore, the separation mechanism of the hydrophilic mesh for water/oil separation was proposed based on investigations of the surface roughness, wetting behavior, separation efficiency, and separation flux. The results revealed that Na2SiO3 and PVA-Na2SiO3 coated meshes exhibit superhydrophilicity and underwater superoleophobicity (water contact angle (WCA): 10 degrees, underwater oil contact angle (UOCA): 150 degrees). Most of the prepared meshes could be used for the gravity-driven separation of the water/oil mixture and were characterized by a high separation efficiency (>97.0 %) and a high separation flux (over 1450 L/m(2) h). However, during the repetition separation, the superhydrophilic meshes exhibited more stable water films and higher separation fluxes than the other meshes, reflecting the superior anti-oil pollution property of the superhydrophilic meshes. Furthermore, the increase in the roughness of the hydrophobic surface would lead to oil accumulation and growing oil pollution, thereby yielding a considerable decrease in the separation flux after 10-cycle repetition separation. A stable UOCA was obtained for the prepared meshes after abrasion testing. However, compared with the other meshes, the meshes with poor hydrophilicity and a small pore size were more easily polluted by oil and were characterized by lower separation flux during the repetition separation. The results of the mechanism study revealed that the separation efficiency and the separation flux were mainly influenced by the surface roughness, wetting behavior, and water absorption ability of the surface. Hence, the water film strength was vital for the anti-oil pollution property of the water-removing separation mesh.

Automated summary

Hydrophilic stainless steel meshes were prepared for water/oil separation with superhydrophilicity and underwater superoleophobicity, exhibiting high separation efficiency and flux. Surface roughness, wetting behavior, and water absorption ability significantly influenced the separation efficiency and flux. Meshes with poor hydrophilicity and small pore size were more easily polluted by oil, leading to lower separation flux.