Highly efficient photocatalytic degradation of organic pollutants by Z-scheme Ni-C3N4/P-C3N4 heterojunction

Carbon nitride (g-C 3 N 4 ) photocatalysts face significant challenges in environmental water remediation, including limited visible light absorption, severe charge recombination, and slow charge transfer. To address these limitations, we developed a Z-scheme Ni-C 3 N 4 /P-C 3 N 4 heterojunction using an efficient and environmentally friendly ball milling method. Compared to g-C 3 N 4 , P-C 3 N 4 , and Ni-C 3 N 4 , the Ni-C 3 N 4 /P-C 3 N 4 heterojunction demonstrated significantly enhanced photocatalytic activity, achieving 99.1% and 86.8% degradation of tetracycline (TC) and rhodamine B (RhB) within 60   minutes, respectively. The total organic carbon (TOC) removal efficiencies were 78.2% for TC and 71.8% for RhB. This enhanced activity is attributed to the optimized heterojunction components and the tightly coupled heterojunction interface, which improve charge transfer and promote efficient separation of photogenerated carriers. Radical scavenging experiments and electron spin resonance (ESR) analysis revealed that holes (h⁺), hydroxyl radicals (·OH), and superoxide radicals (·O 2 − ) all synergistically contribute to the degradation process, with ·O 2 − being the dominant active species. Additionally, toxicity assessment of the degradation products confirmed the environmental safety of the photocatalytic process. This study provides a promising strategy for photocatalytic water purification and offers valuable insights into the design of heterojunction materials.