Plasma-Induced Metamorphosis of Polysulfone Ultrafiltration Membrane to Ameliorate Hydrophilic Functionalities

This study examines the effect of low-pressure Argon (Ar) plasma treatment on the surface modification and filtration performance of polysulfone (PSF) ultrafiltration membranes. Plasma treatment significantly enhances membrane hydrophilicity, as indicated by decreased water and hexadecane contact angles, and increased surface energy, as determined using the Owens-Wendt-Rabel-Kaelble (OWRK) method. Surface characterization via Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) reveals pore enlargement, macrovoid formation, and increased roughness. X-ray Photoelectron Spectroscopy (XPS) analysis confirms the incorporation of oxygen-containing functional groups, with a proposed mechanism for plasma-induced surface reactions further validated by Optical Emission Spectroscopy (OES). Fourier-transform infrared spectroscopy (FTIR) analysis reveals characteristic peaks corresponding to different surface functionalities on the membrane surface. The similarity between pristine and M12 spectra indicates that plasma treatment mainly affects the surface while leaving the bulk properties unchanged. Thermogravimetric Analysis (TGA) shows that the treated membranes maintain thermal stability up to 523 °C. Mechanical testing indicates a slight decrease in tensile strength but an increase in elongation at break, suggesting improved flexibility without compromising bulk integrity. Enhanced porosity, water flux, and rejection efficiency are observed in plasma-treated membranes, supported by Barrett-Joyner-Halenda (BJH) analysis. Long-term filtration studies demonstrate stability over repeated cycles with consistent rejection performance. Ageing studies show initial hydrophobic recovery within a week, stabilizing thereafter, which aligns with a diffusion-based ageing model. The cake filtration model explains the dominant fouling mechanisms. These findings underscore the potential of Ar plasma-treated PSF membranes for practical wastewater treatment applications, offering improved performance and long-term durability.