A novel Z-scheme g-C₃N₄/g-C₃N₄/Pr₆O₁₁ heterojunction was fabricated by facile one-pot synthesis using melamine, urea, and praseodymium nitrate as co-precursors. The optimized 5wt%g-C₃N₄/g-C₃N₄/Pr₆O₁₁ heterojunction exhibited the highest degradation efficiency for sulfonamide under visible light irradiation. It was demonstrated by QSAR prediction and the growth test of wheat seeds that solutions degraded by photocatalysts showed good biocompatibility.

Photocatalytic technology, as an environmentally friendly technology, has a great application promise in the treatment of environmental pollutants caused by residual pharmaceuticals emissions. The Z-scheme heterojunction of g-C₃N₄/g-C₃N₄/Pr₆O₁₁ (Pr/CN) was successfully prepared by employing melamine, urea, and praseodymium nitrate as co-precursors. The structure composition and photoelectrochemical properties were characterized by XRD, XPS, EDS, SEM, FETEM, UV–Vis, EIS, photocurrent, and PL analyses. The optimized 5wt%Pr/CN heterojunction degrade 98% of SCP, 85% of SMM, and 87% of SDM, respectively. Taking SCP as an example, the degradation rate is 8 and 11.2 times higher than that of the g-C₃N₄/g-C₃N₄ homojunction and g-C₃N₄, respectively. The remarkable photocatalytic efficiency of Pr/CN heterojunction could be ascribed to enhanced visible light absorption and enhanced migration and separation of photogenerated charge carriers. Furthermore, the degradation products and degradation pathways of SCP and SMM were established by HPLC-MS/MS analysis. In addition, the toxicity of the intermediate was evaluated with quantitative structure–activity relationship (QSAR) prediction and the biocompatibility of sulfonamide-degrading solution over the Pr/CN photocatalyst was verified by the growth of wheat seeds.