Microwave-Assisted Synthesis of Pd/g-C3N4 for Enhanced Photocatalytic Degradation of Sulfamethoxazole

Sulfamethoxazole (SMX) is a widely used antibiotic for bacterial infections and is frequently found in surface waters and wastewater treatment plant effluents, where it is commonly co-administered with trimethoprim. Because of its emerging ecological and health risks, the development of effective elimination strategies is urgently required. In this study, a rapid microwave-assisted technique was employed to synthesize a Pd/g-C3N4 photocatalyst for the elimination of SMX in aqueous solution. The structure and optical properties of all samples were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL), and UV–visible diffuse reflectance spectroscopy. The photocatalytic performance of Pd/g-C3N4 was systematically evaluated under visible-light irradiation. The results demonstrated that Pd/g-C3N4 achieved a 97% removal efficiency, significantly outperforming pure g-C3N4, which reached only 57% removal. The degradation rate constant for Pd/g-C3N4 was calculated to be 0.0139 min−1, approximately 6.6 times higher than that of bare g-C3N4. This enhanced performance is attributed to the incorporation of Pd nanoparticles, which effectively suppressed the recombination of photogenerated electron–hole pairs and promoted charge separation. The influence of key operational parameters, including pH, SMX concentration, and catalyst dose, were systematically examined. Furthermore, the photocatalytic mechanism of the Pd/g-C3N4 photocatalyst was explored to elucidate its degradation pathways.