Conductive hydrogel/polyvinylidene fluoride Janus membrane capable of rejecting pollutants with varying charges during membrane distillation

Membrane fouling is a key issue restricting the development of membrane distillation (MD), especially when the types of contaminant are becoming diverse. In this study, a Janus membrane modified with wettable conductive hydrogel is prepared, which is synthesized via an interfacial free radical polymerization (FRP) of poly (ethylene glycol) diacrylate (PEGDA) monomers, utilizing the Joule heating effect of carbon nanotubes (CNTs). The resulted hydrogel exhibits a unique sandwich structure of dense hydrogel film-loose CNTs networks-dense hydrogel film. Firstly, positive roles of the ultra-thin PEGDA hydrogel and hydroxylated porous CNTs layer in increasing intermediate water ration and reducing water evaporation enthalpy are revealed. Then, their rejecting properties against contaminants with different charges are accessed, including cationic/anionic surfactants, cationic/anionic dyes and semi-volatile organic compound aniline. In the electric field-assisted MD system, switching the connected electrodes allows the membrane to resist these variously charged pollutants based on the enhanced electrostatic repulsion. Without an electric field, the transport of aniline molecules can be restricted based on size sieving effect and intermolecular hydrogen bond. These findings provide a strategy for constructing all-round anti-fouling MD system and reveal its application prospects in the recycling process of high-salinity organic wastewater.