Development of a novel multi-scale structured superhydrophobic nanofiber membrane with enhanced thermal efficiency and high flux for membrane distillation.

Permeability and selectivity are the two most important parameters in membrane distillation process. The membrane with high porosity and superhydrophobicity could increase the mass transfer coefficient, decrease the heat losses and improve the resistance to wettability. To satisfy this purpose, a novel superhydrophobic polyvinylidene fluoride (PVDF)/tetrabutylammonium hexafluorophosphate (TBAHP)/polystyrene (PS) multi-scale nanofiber membrane (MNM) with high porosity and low thermal conductivity was successfully designed and developed via one-step electrospinning. The formation of multi-scale structures was caused by the addition of TBAHP. PS owns low thermal conductivity and low surface energy which can enhance the thermal efficiency and improve the hydrophobicity of MNMs. Besides, the addition of PS can amplify the classifying effect, construct the nano-micron structure and endow the membrane with superhydrophobicity. The results showed that the thermal conductivity of membranes decreased from 0.03361 W/mK to 0.02777 W/mK and the water contact angle increased from 138.2° to 151.7°. The PVDF/TBAHP/35%PS MNMs exhibited a stable MD performance with an average permeation flux of 50 ± 3 L/m2 h and a satisfactory salt rejection higher than 99.9% during 72-h continuous DCMD operation (3.5 wt% NaCl solution, the feed/permeate temperatures were 60/20 °C, respectively). Unlabelled Image • A multi-scale nanofiber membrane (MNM) was developed by electrospinning. • The MNMs exhibited high porosity and narrow pore size distribution. • The MNMs possessed low thermal conductivity and superhydrophobicity. • The MNMs showed high permeate flux (51.96 L/m2 h) and salt rejection (99.99%). [ABSTRACT FROM AUTHOR]