Facile preparation of superhydrophobic PVDF microporous membranes with excellent anti-fouling ability for vacuum membrane distillation

Superhydrophobic polyvinylidene fluoride (PVDF) microporous membranes with micro-nano hierarchical structure were prepared by combining immersion precipitation with rolling embossing. This method was primarily consisted of semi-gelation process, rolling embossing process and water bath gelation process. The introduction of the semi-gelation process ensured the successful rolling embossing. The membranes were characterized by XRD, SEM, AFM, contact angle, pore size, porosity, N2 flux, and mechanical stability. The results indicated that the water contact angle and the sliding angle of the embossed membrane prepared under the optimal conditions were 151.2° and 5.4°, respectively. The N2 flux of the embossed membrane was higher than that of un-embossed membrane, and the micro-nano hierarchical structure had excellent mechanical stability. The synergy of mechanical properties, porosity, pore sizes and hydrophobicity made embossed membranes suitable for vacuum membrane distillation (VMD) applications. Compared with the un-embossed membrane, the embossed membrane showed better desalination performance and anti-fouling ability. The embossed membrane had a permeation flux of 24.81 kg/m2·h and a 99.9% rejection rate. Fouling was difficult to deposit on the membrane surface and was easy to clean, indicating great potential for applications in VMD. This novel method provides the possibility for the large-scale continuous preparation of superhydrophobic PVDF microporous membranes.