Engineering Janus PTFE composite membranes with high anti-fouling and anti-scaling performance for membrane desalination

Development of membranes with robust anti-scaling and anti-fouling properties are highly required for vacuum membrane distillation (VMD) of saline solution. Therefore, we proposed a facile and benign strategy to construct a polytetrafluoroethylene (PTFE)-based membrane with an asymmetric surface wetting Janus structure consisting of a hydrophobic PTFE substrate and a thin hydrophilic hydrogel-like coating layer. The coated layer was made of the ionic cross-linked alginate and chitosan networks through electrostatic interaction and hydrogen bonding. Owing to the favorable swelling behavior and reduced water evaporation enthalpy of hydrogel top layer, the Janus composite membranes (noted as PTFE@CS/SAH) maintained the stable vapor flux of 32 L m⁻² h⁻¹ at 50 °C. Notably, the PTFE@CS/SAH sustained stable desalination efficiency for the treatment of challenging saline solution containing mineral oil or surfactant. Moreover, the long-term VMD operation test demonstrated that PTFE@CS/SAH exhibited strong scaling- and organic fouling- resistance facing simulated seawater. The simultaneous anti-scaling and anti-fouling mechanism of PTFE@CS/SAH have been systematically investigated and summarized as the synergistic effect of dense hydration layer, favorable electrostatic interaction as well as the robust capillary pressure imparted by coating layer. This work brings fresh insights for the controllable design and construction of Janus structured membranes for VMD application.