Intrinsically superhydrophobic PVDF membrane by phase inversion for membrane distillation

Superhydrophobic surfaces have been considered as preferable property for desalination by membrane distillation (MD). Highly porous and intrinsically superhydrophobic PVDF membrane was prepared by phase inversion method using alcohols, namely methanol and ethanol, as nonsolvent on a nonwoven support. The water contact angle for the top and bottom surface of membrane and subsequent mechanical scratching demonstrated that not only surface of the membrane whole membrane film intrinsically possess the superhydrophobic behavior. The prepared membrane was characterized by using AFM, SEM, contact angle measurement, capillary flow porometer and water entry pressure test. The methanol phase induced PVDF membrane showed much superior results compared to conventional water phase induced PVDF membrane for the desalination of salt water by direct contact membrane distillation (DCMD) with water vapor flux up to 90 LMH at ΔT 60 °C and salt rejection of > 99.99%. The superhydrophobic membrane showed excellent salt rejection up to 200,000 ppm albeit with reduction in vapor flux. The long-term MD showed that the superhydrophobic membrane exhibited reasonably stable flux for a week time without compromising flux or NaCl salt rejection for 35,000–80,000 ppm range.