Construction of S-scheme N,S-NiFe-LDH/N-Bi₂MoO₆ heterojunction for efficient visible-light photocatalytic degradation of tetracycline

A novel S-scheme heterojunction N,S-NiFe-LDH/N-Bi₂MoO₆ was successfully constructed. • 5 wt% N,S-NiFe-LDH/N-Bi₂MoO₆ showed the highest activity, degrading 86.3% of TC in 100 min under visible light. • Element doping and interface engineering synergistically enhanced visible-light absorption and charge separation. • ·OH and ·O₂ − were the dominant active species responsible for TC degradation. A step-scheme (S-scheme) heterojunction photocatalyst was constructed via a hydrothermal method, consisting of N,S co-doped NiFe layered double hydroxide (N,S-NiFe-LDH) and nitrogen-doped bismuth molybdate (N-Bi₂MoO₆). The morphology, crystal structure, optical properties, elemental valence states, and charge separation/transport performance of the composite catalyst were systematically investigated using various characterization techniques, including SEM, TEM, HRTEM, XRD, UV–Vis DRS, XPS, and EIS. Its photocatalytic activity was evaluated through tetracycline (TC) degradation experiments under visible light irradiation, and the catalytic mechanism was elucidated by EPR radical detection. The results showed that the incorporation of N,S-NiFe-LDH enhanced the photocatalytic performance of the composite catalyst. Among the tested samples, the 5 wt% N,S-NiFe-LDH/N-Bi₂MoO₆ composite exhibited the highest degradation efficiency, achieving 86.3% TC removal within 100 min. The synergistic interaction between N,S-NiFe-LDH and N-Bi₂MoO₆ promoted the separation efficiency of electrons and holes, thereby significantly enhancing the photocatalytic activity.