Patterned superhydrophobic polyvinylidene fluoride (PVDF) membranes for membrane distillation: Enhanced flux with improved fouling and wetting resistance

Abstract

The industrial implementation of membrane distillation (MD) is still limited due to major barriers such as membrane wetting and low permeate flux. In this study, we fabricated a two-layer patterned superhydrophobic polyvinylidene fluoride (PVDF) membrane by combining non-solvent induced, and vapor induced phase separation processes (NIPS and VIPS), and a subsequent surface fluorination to lower the membrane's surface energy. A simple spacer imprinting method induced changes in the formation mechanism and formed a uniform pattern at the membrane surface increasing the effective surface area and achieving 18% higher flux, compared to a commercial membrane. Moreover, the patterns introduced surface turbulence and favorable flow hydrodynamics that highly improved fouling mitigation when tested in MD with real sweater feed, where the flux was reduced by only 15.2% after 97 h of operation, compared to complete fouling and 100% flux reduction for the commercial membrane. The superhydrophobicity of the developed membrane, characterized by its high water contact angle of 154.5°, also achieved improved wetting resistance when low surface tension surfactant sodium dodecyl sulfate (SDS) was introduced to lower the surface tension of the feed seawater. Our findings indicate the ability of a patterned superhydrophobic membrane surfaces to produce high flux while at the same time enhance fouling and wetting durability, demonstrating their advantage for MD treatment of challenging feeds comprising both fouling and wetting contaminants.