One-step fabrication of isotropic poly(vinylidene fluoride) membranes for direct contact membrane distillation (DCMD)

Membrane distillation (MD) is a promising desalination process especially in small scale systems. However, the lack of commercial MD membranes severely impedes the industrialization. Although various approaches have been explored to develop high-performance membranes, the complicated processing procedures and high cost are two major obstacles to scale up the available membranes. In this study, a facile bottom-up method using water as coagulation bath was proposed to fabricate porous poly(vinylidene fluoride) (PVDF) membranes for direct contact membrane distillation (DCMD) in view of application in desalination. By covering a piece of non-woven substrate on the nascent film followed by immersion into a water bath, a skinless PVDF membrane with an isotropic structure was obtained. The SEM characterization confirmed the formation of a rough top surface and sponge-like granular membranes composed of spherulites. The water contact angles substantially increased from 71.7° for PVDF-N membrane to ca. 144° for bottom-up membranes. The DCMD flux of the bottom-up PVDF membrane was as high as 41.4 kg/(m2 h) with a polymer concentration of 15 wt%, when the feed and permeate temperatures were 70 °C and 20 °C, respectively. This facile, environmentally friendly approach provides the possibility of manufacturing large-scale high-performance MD membranes. © 2019 Elsevier B.V.