Engineering Carbon Nanotube Forest Superstructure for Robust Thermal Desalination Membranes

Abstract

Desalination by membrane distillation (MD) using low-grade or waste heat provides a potential route for sustainable water supply. Nonwetting, porous membranes that provide a selective pathway for water vapor over nonvolatile salt are at the core of MD desalination. Conventional water-repelling MD membranes (i.e., hydrophobic and superhydrophobic membranes) fail to ensure long-term desalination performance due to pore wetting and surface fouling. To address these challenges, a defect-free carbon nanotube forest (CNTF) is engineered in situ on a porous electrospun silica fiber substrate. The engineered CNTF forms an ultrarough and porous interface structure, allowing outstanding wetting resistance against water in air and oil underwater. As a result of this antiwetting property, the composite CNTF membrane displays a stable water vapor flux and a near complete salt rejection (>99.9%) in the desalination of highly saline water containing low surface tension contaminants. The antimicrobial property of the composite CNTF membrane imparted by the unique forest-like architecture and the oxidative effect of carbon nanotubes (CNTs) are further demonstrated. The results exemplify an effective strategy for engineering CNT architecture to elucidate the structure-property-performance relationship of the nanocomposite membranes and to guide the design of robust thermal desalination membranes.