C3N4/C3N5 homojunction induced peroxymonsulfate activation for efficient oxidation of sulfamethoxazole

As a widely used sulfonamide antibiotic, Sulfamethoxazole (SMX) poses considerable environmental risks for its persistence and antibio-degradability in aquatic ecosystems. Although Peroxymonosulfate (PMS)-based advanced oxidation processes show promise in antibiotic removal, metal-based activators often suffer from leaching and stability issues. Here, a novel metal-free C ₃ N ₄ /C ₃ N ₅ homojunction (rCN-AT) photocatalyst was synthesized via KBr-assisted thermal polymerization using cyanuric acid and 3-amino-1,2,4-triazole as precursors, for visible-light-driven PMS activation. The rCN-AT/PMS/Vis system achieved 99.98% SMX degradation within 45 min with the visible light irradiation, significantly outperforming C ₃ N ₄ /PMS/Vis (28.85%), C ₃ N ₅ /PMS/Vis s (33.92%), and CN-AT/PMS/Vis (83.64%). The enhanced activity is attributed to the homojunction structure and large specific surface area of rCN-AT, which facilitate efficient charge separation and promote PMS adsorption/activation. Electronic band structure determination indicates PMS acts as an efficient electron acceptor, improving photogenerated electron transfer efficiency. EPR analysis revealed the involvement of \(\:\text{S}{\text{O}}_{\text{4}}^{\text{∙-}}\), \(\:\text{∙OH}\), \(\:\bullet{\text{O}}_{\text{2}}^{\text{-}}\) , ¹ O ₂ and h ⁺ . Among these, h ⁺ , \(\:\bullet{\text{O}}_{\text{2}}^{\text{-}}\) and ¹ O ₂ were identified as the dominant species, indicating that both radical and non-radical pathways contribute to SMX degradation. This work provides an efficient metal-free homojunction photocatalyst and offers new insights into PMS activation mechanisms, which are valuable for the treatment of antibiotic-contaminated water.