Hierarchical Janus membrane via a sequential electrospray coating method with wetting and fouling resistance for membrane distillation

Abstract Membrane wetting and fouling issues are two major obstacles which hinder the practical application of membrane distillation (MD). In this study, a sequential electrospray method was introduced to impart a dual-layered superhydrophilic/superhydrophobic Janus skin onto a commercial polyvinylidene fluoride (PVDF) substrate. The bottom superhydrophobic layer was obtained by incorporating octaphenylsilsesquioxane (POSS) nanoparticles into PVDF carriers to construct a POSS@PVDF multiscale rough surface via electrospraying. At the same time, the top hierarchical-structured hydrophilic coating was composed of PAN beaded nanofilaments, rendering an intriguing in-air hydrophilicity and underwater superoleophobicity which benefited from the loose packing state of the interconnected beads and nanofibers. Further, this Janus skin exhibited good integrity and strong adhesion with the substrate, and due to its underlying superhydrophobicity and slightly decreased pore size, the hierarchical Janus membrane possessed a greatly enhanced liquid entry pressure of water (LEPw). Once applied in the MD process, with soybean-oil-in-saline-water emulsions as feed, this Janus membrane exhibited stable and excellent desalination performance with a high flux and nearly perfect salt rejection, whereas both the commercial and superhydrophobic membranes failed from oil contaminating. This suggests the remarkable simultaneous anti-wetting and anti-fouling property of Janus membranes, which possess great potential in water reclamation for challenging hypersaline oily wastewaters.