Probing the separation efficiency of sulfur-doped graphitic carbon nitride (g-C₃N₄)/polysulfone low-pressure ultrafiltration mixed matrix membranes

Pre-synthesized sulfur-doped graphitic carbon nitride (S–g-C₃N₄) nanoparticles were blended with polysulfone (PSf) casting solution to form low-pressure ultrafiltration mixed matrix membranes (MMM) using a nonsolvent-induced phase inversion method. The prepared materials were characterized using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectrometer, scanning electron microscopy (SEM), atomic force microscopy (AFM), water contact angle and water sorption to ascertain their morphological, chemical, wettability, surface and porosity measurements. The membrane performance was evaluated using water flux and bovine serum albumin (BSA) rejection. ATR-FTIR results confirmed that both the membranes and the nanoparticles are carbon-based and this would promote intercalation. The addition of nanoparticles increased the surface roughness of the membranes and enhanced membrane surface wettability with the reduction of the contact angle from 74.7° for pristine membranes to 59.9° for 0.5 wt% S–g-C₃N₄ loaded membranes. Also water absorption increased upon nanoparticle loading with maximum uptake at 0.3 wt% nanoparticle loading. In addition, at 0.3 wt% nanoparticle loading, the membranes showed the highest porosity (46%) and BSA rejection of up to 99% compared to 84.8% for the pristine membranes. The improved BSA rejection could be linked to the reduction in pore density upon S–g-C₃N₄ incorporation. Overall the enhancement in hydrophilic properties and reduction in fouling propensity of the fabricated MMMs confirms that the modified membranes have a potential to be used for water separation and purification.