Optimization and reusability of photocatalytic g-C₃N₄/W-TiO₂/PVDF membranes for degradation of sulfamethazine

Pharmaceuticals and personal care products (PPCPs) are prevalent emerging pollutants in the aquatic environment. The photocatalysis process has proven high efficiency in degrading PPCPs; however, the fate and repercussions of photocatalyst residuals are a major concern. To avoid that, we developed a composite from graphitic carbon nitride/tungsten doped with titanium dioxide (g-C₃N₄/W-TiO₂) and loaded it on polyvinylidene fluoride (PVDF) membranes by the phase-inversion method. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and other different analyses implied the successful synthesis of g-C₃N₄/W-TiO₂ composite and coating on PVDF membranes. A Box–Behnken design (BBD) was used to optimize the operational parameters, including pH, g-C₃N₄ ratio in the composite, and initial SMZ concentration by the response surface methodology (RSM). The highest SMZ degradation percentage was 98.60% after 240 min of irradiation. Liquid chromatography with tandem mass spectrometry (LC–MS/MS) along with suspect screening was used to identify the intermediate transformation products and propose the SMZ degradation pathway. The loss in membrane activity after five cycles of photocatalytic degradation was about 18%. According to the current study, the photocatalytic membrane g-C₃N₄/W-TiO₂/PVDF is promising for removing sulfonamide antibiotics from wastewater.