Dual-modified g-C3N4 for the solar-driven degradation of structurally diverse emerging micropollutants in stormwater

This study presents a dual-modified graphitic carbon nitride (g-C 3 N 4 ) photocatalyst, synthesized via thermal polymerization of a urea/K 2 HPO 4 mixture to achieve simultaneous potassium doping and phosphate surface functionalization (PKCN), for photo-assisted advanced oxidation of stormwater contaminants using simulated solar irradiation. The photocatalyst was evaluated for the degradation of four structurally diverse emerging micropollutants frequently detected in urban runoff: 1,3-diphenylguanidine (DPG), 2-hydroxybenzothiazole (HBT), 2-(4-morpholinyl)benzothiazole (MoBT), and 5-tolyltriazole (TTZ). The optimal photocatalyst (PKCN5, 5 wt% K 2 HPO 4 ) exhibited ~ 60-fold faster degradation of DPG compared to unmodified g-C 3 N 4 , using only 0.05 g/L under simulated solar light. Material characterization revealed that the enhanced performance was driven by improved charge separation, cyano group formation, and elevated production of HO • and O 2 •– radicals. The observed degradation trend (DPG > MoBT > TTZ > HBT) was attributed to differences in solubility, surface affinity, and reactivity with reactive oxygen species. In a synthetic stormwater matrix containing all four contaminants, PKCN5 maintained >90 % removal within 3 h despite ionic complexity. Degradation pathways of MoBT and TTZ were elucidated via UPLC-QTOF-MS, identifying several intermediate byproducts. Toxicity assays showed a slight reduction in microbial inhibition following treatment, and ECOSAR predictions indicated that key transformation products were less toxic than their parent compounds. These findings highlight the promise of PKCN as a sustainable photocatalyst for stormwater remediation. • K 2 HPO 4 -modified g-C 3 N 4 introduced potassium doping and phosphate functionalization • PKCN5 showed ~60× higher DPG degradation than unmodified g-C 3 N 4 under solar light • Enhanced • OH and O 2 •– and reduced charge recombination increases performance • Nearly complete removal of DPG, HBT, MoBT, and TTZ in synthetic stormwater matrix • MoBT and TTZ follow different degradation pathways; byproducts show lower toxicity