Electrospun PTFE/PI bi-component membranes with robust 3D superhydrophobicity and high water permeability for membrane distillation.

Membrane distillation (MD) is an attractive membrane process for seawater and brine water desalination. One of the main obstacles for MD application is the absence of an effective MD membrane with high water permeability and an excellent salt rejection. This work proposes a novel design strategy of hydrophobic/hydrophilic bi-component membranes for MD by electrospinning and calcination. Unlike the conventional dual-layer hydrophobic/hydrophilic membranes, the bi-component membrane developed in this work is composed of multiple layers of hydrophilic polyimide (PI) nanofibers and hydrophobic polytetrafluoroethylene (PTFE) microclusters, which interweave with each other in the entire membrane. The optimal hydrophobic/hydrophilic bi-component membrane #PTFE/PI-2 shows robust three-dimensional (3D) superhydrophobic and self-cleaning properties. It exhibits a highly competitive permeation flux of 42 ± 3 L m−2 h−1 and an excellent salt rejection above 99.9% in a 400-h continuous DCMD operation when the feed solution was synthetic seawater with a NaCl concentration of 3.5 wt% at 60 °C. Moreover, it is able to achieve an outstanding water flux of 40 ± 2 L m−2 h−1 and a salt rejection over 99.9% when the feed solution was brine water with a NaCl concentration of 25 wt%. The high vapor permeability of #PTFE/PI-2 should be attributed to the high membrane porosity, negligible mass transfer resistance of PI nanofibers and more effective water evaporation area on its superhydrophobic surface. Meanwhile, the excellent anti-wetting property should be due to a unique 3D superhydrophobicity constructed by multiple layers of PTFE microclusters. Image 1 • Hydrophobic/hydrophilic bi-component membrane is proposed. • It composes of PTFE microclusters and PI nanofibers. • The resultant membrane exhibits robust 3D superhydrophobicity. • #PTFE/PI-2 shows a water flux of 40 ± 2 L/m2·h and a salt rejection above 99.9% in MD. [ABSTRACT FROM AUTHOR]