Ag modified Janus membranes with dual hydrophilic/hydrophobic layers for antibacterial ultrafiltration

Membrane technology has emerged as a highly efficient strategy for wastewater treatment. Nevertheless, conventional membranes continue to have drawbacks, including low permeate flux, low efficiency, and a high fouling tendency. Janus membranes in ultrafiltration (UF) have been widely explored for their multifunctionality; however, their application to the treatment of real industrial wastewater remains limited. In this study, an antibacterial Janus membrane was prepared via asymmetric surface modification, including hydrophobic stearic acid coating, in situ oxidative polymerization of polyaniline (PANI), and immobilization of Ag nanoparticles through a silver mirror reaction on the polyvinylidene difluoride (PVDF) sublayer for industrial dairy wastewater treatment. After depositing a PANI layer onto the hydrophobized PVDF membrane, the asymmetric wettability of the Janus structure was obtained. The physical and chemical properties of the membranes were comprehensively characterized using Field Emission Scanning Electron Microscopy (FE-SEM), energy-dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), X-ray diffraction (XRD), water contact angle (WCA) measurements, and AFM. The final membrane simultaneously exhibited a twofold increase in permeate flux compared with the conventional UF membrane, a high rate of Chemical Oxygen Demand (COD) removal, which reached 92 ± 1%, and excellent antifouling performance. In addition, the membrane indicated strong antibacterial activity against both bacterial strains, namely the Gram-positive Staphylococcus aureus (S. aureus) and the Gram-negative Escherichia coli (E. coli).