Enhanced photocatalytic degradation of sulfadiazine under LED light using Pd-decorated g-C3N4: Structure–activity relationship, mechanism, and toxicity assessment

Graphitic carbon nitride (g-C 3 N 4 ) is a sustainable photocatalyst, however, its practical application is severely limited by rapid charge recombination and insufficient redox capability. In this work, a Pd x OCN-y photocatalyst was synthesized via photoreduction and evaluated under LED irradiation. The Pd 8 OCN-3 sample exhibited superior performance toward sulfadiazine (SDZ) degradation, achieving 90% removal within 180 min, with a reaction rate 6.53 times higher than that of pristine g-C 3 N 4 . The enhanced activity was attributed to increased surface area, narrowed bandgap, improved charge separation, and suppressed electron–hole recombination. Radical scavenging tests indicated •O 2 − and •OH as the dominant reactive species. Pd 8 OCN-3 also demonstrated high stability and recyclability across multiple cycles. Additionally, phytotoxicity assays using mung bean germination confirmed the reduced toxicity of degradation products, in agreement with QSAR-based predictions. This study not only elucidates the structure–activity relationship of Pd x OCN-y but also provides a viable strategy for designing highly efficient and eco-safe photocatalysts for antibiotic-contaminated wastewater treatment.