Bacterial-Responsive and Dye-Selective Janus Membranes via Laser-Directed Fluorinated Graphene Interfaces

Abstract

Antibacterial properties are as critical as filtration efficiency in water treatment membranes, as they determine longevity and biofouling resistance. This study reports the fabrication of flexible antibacterial films featuring an in situ fluorine-doped laser-induced graphene (F-LIG) surface, generated via direct CO2 laser writing on fluorinated polyimide (F-PI) substrates. By adjusting laser parameters, the surface wettability of F-LIG is tuned from hydrophilic to highly hydrophobic (contact angle: 131.5°). The hydrophobic F-LIG exhibited synergistic antibacterial activity through (1) chemical inhibition, where fluorination-induced low surface energy suppressed bacterial adhesion, and (2) physical disruption, where nanoscale roughness mechanically damaged bacterial cells. Antibacterial tests against Escherichia coli and Staphylococcus aureus demonstrated up to 80.7% bacterial removal, surpassing the hydrophilic variant. Furthermore, a bacterial-responsive Janus membrane is fabricated by combining an F-LIG top layer with a porous fluorinated polyimide (F-PPI) substrate, prepared via non-solvent-induced phase separation (NIPS). Permeability and dye removal experiments using pigment blue 15:3 and methylene blue revealed that the porous F-LIG membranes achieved removal efficiencies of up to 96.3% and 83.9%, respectively, despite slightly lower permeability than commercial PVDF filter paper. These results highlight the promise of F-LIG-based membranes that integrate antibacterial and filtration functions within a single platform.