Preparation and Characterization of PVA/PCTFE Janus Membrane Coated by PDMS and FAS-17 for MD Process

Membrane distillation (MD) is a promising desalination technology, but it suffers from fouling and pore wetting especially in large-scale application. Janus membranes with hierarchical architectures have been proposed to enhance the performance of direct contact MD (DCMD). In this study, a hydrophilic polyvinyl alcohol (PVA)/catechol film was coated on the surface of hydrophobic polychlorotrifluoroethylene (PCTFE) substrate whose inner pore surfaces were modified with hydrophobic polydimethylsiloxane (PDMS) and fluorinated silane (FAS-17) agents. Comprehensive characterization using SEM, AFM, ATR-FTIR(6), Raman spectroscopy, tensile testing, EDS, and surface wettability analyses confirmed the successful formation of Janus structures with dual functionality. The Janus samples exhibited a pure water flux (PWF) higher than both the PCTFE support (37.25 kg m^-2 h^-1) and commercial (34.48 kg m^-2 h^-1) membranes. By incorporating PDMS and FAS-17, fluxes of 46.7 and 44.4 kg m^-2 h^-1 were achieved, respectively, while maintaining a salt rejection of ≥ 99.7% for 35,000 ppm NaCl. Both PDMS and FAS-17 modified membranes displayed improved resistance to wetting and scaling, even under complex saline conditions containing CaCl₂, NaCl, and surfactants (CTAB, SDS). Among them, the sample coated with FAS-17 exhibited the best anti-fouling and stability due to its fluorinated sublayer and superior interfacial hydrophobicity. The results demonstrated that the engineered Janus membranes, integrating hydrophilic and hydrophobic functionalities, achieved high permeate flux, excellent salt rejection, and strong fouling resistance, thereby contributing to the development of membrane materials for MD desalination.