Pure sponge-like membranes bearing both high water permeability and high retention capacity

Porous poly(vinylidene fluoride) (PVDF) membranes were prepared using phase inversion method. It was found that three pure sponge-like membranes could be generated using composite additive such as ferrous chloride/nano-silica, calcium chloride/nano-silica, and ferrous chloride/hydroxylamine hydrochloride. The generated sponge-like membranes all bear obviously higher water permeability and higher or little lower retention capacity compared with their counterpart macrovoid membranes, which were prepared using ferrous chloride or calcium chloride as additive. High magnification SEM (scanning electron microscopy) photos revealed the great differences between the two kinds of macroscopically similar sponge structures. The specific area (BET surface area), pore volume, and pore size distribution, measured using the nitrogen adsorption–desorption method, indicated that the sponge-like membranes (X1, Y1, and Z1) are more porous and hold narrower (X1 and Z1) pore size distributions than their counterpart membranes. The trends revealed by the BET data agreed relatively well with the flux and retention data, thus implied that the N2 adsorption–desorption method might be an effective means to investigate the structure–property relationship of polymeric membranes. The comparison study indicates that the sponge-like membranes in this work have comparable and even better performance than some of the commercial PVDF membranes in terms of flux and retention.

Research highlights
► Generating pure sponge-like membranes with composite additive.
► Pure sponge-like membranes bearing both high permeability and high retention capacity.
► The BET method was tested to reveal the pore structure of polymeric membranes.