Improved desalination properties of hydrophobic GO-incorporated PVDF electrospun nanofibrous composites for vacuum membrane distillation

Abstract

Hydrophobic nanofibers have attracted great attention in the membrane distillation (MD) process because of their extremely high specific surface area. In this study, hydrophobic nanofibrous composites for vacuum membrane distillation (VMD) consisting of a hydrophobic polyvinylidene fluoride (PVDF) nanofibrous layer and a hydrophobic polypropylene (PP) nonwoven fabric (NWF) substrate were presented. PVDF nanofibrous layer was directly fabricated on the surface of PP NWF substrate by electrospinning technique. 1H, 1H, 2H, 2H -perfluorooctyltriethoxysilane (FTES) functionalized GO nanosheets were incorporated in the PVDF nanofiber layer during the electrospinning process to enhance the hydrophobicity and permeation water flux for VMD. Membrane surface morphology and composition were characterized through SEM and FTIR. The effects of FTES-GO nanosheets content on the VMD desalination properties were investigated. And the transfer mechanism of water vapors through the FTES-GO incorporated nanofibrous layers was also proposed. Compared with the original PVDF nanofibrous layer, the surface hydrophobicity, liquid entry pressure (LEP) and water permeability of the FTES-GO incorporated nanofibrous layers had all been improved. When FTES-GO content was 4 wt%, the WCA increased from 104.0° for the neat PVDF nanofibrous layer to 140.5° for the modified nanofibrous layer. The permeation water flux reached a maximum value of 36.4 kg m−2 h−1. It was two times the water flux of the original membrane and meanwhile the salt rejection remained above 99.9% (50 °C, 3.5 wt% NaCl aqueous solution and permeation pressure of 31.3 kPa). No obvious wetting phenomenon was observed for FTES-GO incorporated membrane during the continuous VMD experiment for 60 h.