Efficient degradation of Orange II and tetracycline via synergistic nitrogen–Sulphur dual vacancies and an S-scheme heterojunction

The presence of residual azo dyes, such as Orange II, and organic antibiotic pollutants, such as tetracycline hydrochloride, in water and soil environments is a growing global concern. Conventional water treatment technologies often show limited effectiveness in removing these contaminants. To overcome these challenges, this study proposes a method to modify triazole using ammonium chloride and presents the successful construction of a carbon nitride/indium sulphide (C 3 N 5 /In 2 S 3 ) photocatalyst with nitrogen–sulphur dual vacancies using an in situ growth approach. Systematic characterisation and evaluations of the structure and performance of the material revealed that the modified C 3 N 5 exhibited significantly enhanced crystallinity and formed an intimate 2D/2D interfacial structure with In 2 S 3 . Coupled with an S-scheme heterojunction, the nitrogen–sulphur dual vacancies jointly enhanced the capacity for light absorption, improved the separation efficiency of charge carriers, and optimised the redox potential. When exposed to a 300 W xenon lamp, the degradation rate constants of the C 3 N 5 /In 2 S 3 catalyst for Orange II and tetracycline hydrochloride were 11.51 and 16.62 times that of the singly modified C 3 N 5 and 3.91 and 1.92 times that of pure In 2 S 3 , respectively, demonstrating significant photocatalytic synergy. The C 3 N 5 /In 2 S 3 catalyst maintained good stability, with its degradation efficiency decreasing by only 7.6 % after four consecutive cycles. Moreover, it adapted to a wide pH range, ionic environments, and sunlight exposure, indicating its potential for applications in real water bodies. Provides innovative design principles and experimental evidence for developing highly efficient S-type heterojunction photocatalysts with dual vacancy regulation mechanisms, paving the way for expanded environmental remediation applications.