Effects of superhydrophobic SiO2 nanoparticles on the performance of PVDF flat sheet membranes for vacuum membrane distillation

Abstract

Polyvinylidene fluoride (PVDF)/SiO2 flat sheet composite membranes were prepared for vacuum membrane distillation (VMD) by the phase inversion immersion precipitation process. The effect of blending superhydrophobic SiO2 nanoparticles into the PVDF dope solution was studied. The concentration of the nanoparticles in the dope solution was varied at different wt.% (1, 2, 4, 6, 7, 8 and 10wt.%). The prepared membranes were characterized by scanning electron microscopy, water contact angle, porosity, liquid entry pressure of water, Fourier transformed infrared spectroscopy, and VMD at feed temperature of 27°C. The nanoparticles enhanced the membrane performance through a reduction in the sponge-like layer thickness and an increase in surface pore size, leading to increased vapour flux with a maximum at 7wt.%. The salt rejection was greater than 99.98% when a 35g/L NaCl solution was used as feed. At this concentration, the smallest thickness of the sponge-like layer and largest macro-voids were also achieved. Beyond 7wt.%, the sponge-like layer became predominant and the flux was reduced. With a vapour flux increase of up to 4 times (from 0.7 to 2.9kg/m2h) when compared to the neat membrane, this nanocomposite membrane could be of great potential in the desalination process through VMD.