Innovative nonfluorinated-omniphobic membranes using palmitic acid surface grafting for efficient low-pressure desalination via membrane distillation

Abstract

Membrane distillation (MD) as thermal-driven membrane separation commonly uses hydrophobic membrane, but this membrane has limitation due to wetting issues from low surface tension liquids, such as oils and surfactants. The strategic improvement to overcome the wetting issue is via omniphobic surface modification as it has the ability to repel low surface tension liquids. This research aims to fabricate and evaluate the anti-wetting properties of omniphobic polyvinylidene fluoride (PVDF) membrane modified with ZnO nanoparticles (ZnO Nps) as the re-entrant structure and palmitic acid (PA) as “green material” of the hydrophobic agent. The deposition of ZnO Nps was carried out using dip coating approach with variations of ZnO Nps loadings (1, 2, and 3 wt%) and then followed by palmitic acid surface grafting with various immersion times of 3, 6, 12, and 24 h. The developed omniphobic membrane was characterized using contact angle goniometer, scanning electron microscope (SEM), atomic force microscope (AFM), liquid entry pressure test, and leaching test. The results showed that the modification with ZnO Nps and palmitic acid obtained contact angle above 90° when tested with water, ethylene glycol, and 0.4 mM sodium dodecyl sulfate (SDS), which meets the omniphobic criteria. The presence of ZnO Nps was confirmed by surface morphology from SEM and surface topography of AFM. The PZ3-PA membrane exhibited remarkable water flux of 7.64 L/m²h for 3 days of operation time under the presence of humic acid, crude oil, and SDS as fouling agent, and high salt rejection which is almost 100%. Therefore, omniphobic surface modification with the combination of ZnO Nps and palmitic acid is very promising, as it imparts excellent anti-wetting properties and desalination performance.