Synthesis of α‐NiS Decorated Fe ₃ S ₄ Nanohybrid Composite and Its Heterogeneous Fenton Catalysis for Dye Degradation

Abstract Greigite (Fe 3 S 4 ) and millerite (NiS) are important transition metal sulfides that exhibit light‐driven Fenton catalytic activity. In absence of light, they show limited activity. To utilize these properties without relying on light, we synergized these sulfides to prepare a composite Fe 3 S 4 –NiS (FSNS). Under fixed reaction conditions, the composite demonstrated excellent Fenton activity, degrading 93% of fast green dye (FG) and 98.1% of eriochrome black T dye (EBT) within a short reaction time. The mechanism involves electron transfer from the reduced sulfur state (S 2− ) in both NiS and Fe 3 S 4 to the higher oxidation states of the metal ions viz. Fe 3+ and Ni 3+ to facilitate the redox cyclization in the Fenton process. The catalyst showed high stability for five cyclical tests by recovering it from solution with an external magnet.