CF4 plasma modified highly interconnective porous polysulfone membranes for direct contact membrane distillation (DCMD)

Abstract

Preparation of MD membranes with a low tortuosity and high DCMD flux is reported. Hydrophilic flat sheet polysulfone (PSf), blended with polyvinylpyrrolidone (PVP) membranes were prepared by dual-bath coagulation phase inversion, where N-methylpyrrolidone (NMP)/water mixtures were used as the first coagulant before immersion into a water bath. CF4 plasma modification was utilized to render the originally hydrophilic membranes hydrophobic. The membranes were characterized by scanning electron microscopy (SEM), water contact angle, X-ray photoelectron spectroscopy (XPS), liquid entry pressure (LEPw), and gas permeability. Results demonstrated that the first coagulation bath acted as a dense skin layer remover in comparison to a PSf membrane prepared in a single water bath. CF4 plasma modified porous PSf membranes using pure NMP as the first coagulant showed a contact angle of 144° and a DCMD flux of 53.33kg/m2·h (Tf=70.3°C), which was 80% higher than a commercial PVDF membrane with comparable performance stability. Heat and mass simulation modeling results demonstrated that the tortuosity of the PSf membranes is close to 1 in contrast to 2.5 for the commercial PVDF membranes. This result provides some theoretical understanding of the origin of the high performance of PSf MD membranes.