Design, fabrication, and characterization of a facile superhydrophobic and superoleophilic mesh-based membrane for selective oil-water separation

Abstract

Superhydrophobic and superoleophilic (SHSO) membranes have found great attention in oil–water separation application. We fabricate a SHSO stainless steel mesh-based membrane, using a facile one-stage dip-coating technique, and investigate the effects of silane alkyl chain size, and ratio of micro-to-nanoparticles in the coating solid fraction. Silane compounds with short- and long-alkyl functional chains (Dynasylan® Sivo 408 and Dynasylan® F8261, respectively) are used as surface energy modifiers. To create hierarchical morphology, Aerosil® R812 and SIPERNAT® D13 are employed as the nano and microparticles, respectively. The long-silane features a higher water contact angle (WCA) at all solid compositions. Increasing the ratio of nano-to-microparticles increases the WCA with long-chain silane. Maximum WCAs = 165.8° and 164.2° are attained with the long and short silanes, respectively, when the coating solid is composed of 75 wt% nanoparticles and 25 wt% microparticles. Increasing the concentration of nanoparticles to 100% decreases hydrophobicity, which is more pronounced for the short-chain silane. The WCA decreases to 163.8° and 155.5° for the coating solutions containing the long and short silanes, respectively, with 100% nanoparticles to modify the surface roughness. Flower-like hierarchical roughness structures are observed using the coating solution of silanes with only nanoparticles. The average pore opening for the mesh decreases from 76 µm in the bare mesh to 48 µm for the coated mesh. Analytical surface characterization results (e.g., sliding angle, energy-dispersive X-ray spectroscopy (EDX), and Fourier transform infrared spectroscopy (FTIR)) confirm the SHSO features of the as-prepared mesh. Except for the exposure to 1.0 M NaOH solution, the membranes are stable (WCA > 145°) in H2SO4, NaOH, and NaCl concentrated solutions over four weeks. Using the fabricated mesh, the macroscopic separation efficiency of kerosene from water is >99%. The membrane fabrication strategy proposed in this study further highlights the importance of the SHSO wetting condition in the effective treatment of oily wastewater streams in a variety of food, chemical, and energy industries.