Simple surface modification of steel mesh for efficient oil/water separation via gravity filtration

Improving surface chemistry of a material is important for oil/water separation. In this work, we demonstrated a simple approach that could be employed to flexibly modify the properties of steel mesh to be either hydrophi-licity or hydrophobicity for oil/water separation via gravity filtration. Dip-coating method was used to form a coating layer atop the mesh. Polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) were used to prepare hydrophilic coating, while poly(4-vinylpyridine) (P4VP) and triethoxy(octadecyl)silane (TEOS) were used to promote the mesh's hydrophobicity. Our findings showed that the mesh coated with PVP and PEG displayed improved surface hydrophilicity (i.e. lower water contact angle (WCA)) which led to increased water flux. Oppositely, the WCA of mesh increased from 126.4o to 135.3o and 142.5o , respectively when P4VP and TEOS were used as coating material. The PEG-coated mesh is the best filter in producing water as permeate (up to 578 L/m2.h) while the TEOS-coated mesh is excellent in transporting organic solvents (e.g., toluene, n-hexane and chloroform), achieving 999-1205 L/m2.h. The results also indicated that the modified meshes were able to attain >98 % oil/water separation efficiency with either oil or water as the permeate. The flux of modified-mesh was also stable over 20 filtration cycles and did not experience major changes after being immersed in toluene for 30 days. Our work demonstrated an alternative efficient way of treating oil/water mixture via gravity filtration in which either water or oil could be the permeate product depending on the surface properties of the mesh chosen.