A Mechanistic and Analytical Study of a Magnetically Separable Fe ₃ O ₄ /g‐C ₃ N ₄ /SWCNT Photocatalyst: A Kinetic, GC–MS Degradation Pathways and AAS Leachate Analysis

A novel magnetically separable ternary Fe 3 O 4 /g‐C 3 N 4 /SWCNT nanocomposite was prepared through high‐energy ball milling to achieve effective visible‐light‐mediated photocatalytic breakdown of methylene blue (MB). Under optimized conditions (pH 5, 30‐mg catalyst, 10 ppm MB, 2 mL oxalic acid), the nanocomposite achieved remarkable 94% degradation efficiency within 70 min. Kinetic analysis revealed pseudo‐first‐order behavior ( R 2 > 0.95) following the Langmuir–Hinshelwood mechanism. Scavenger studies identified photogenerated holes as the dominant reactive species (h + > • O 2 − > • OH), while GC–MS analysis revealed stepwise degradation through demethylation and ring‐opening pathways with identified intermediates (chlorogenic acid, phenylindane, and caffeine) leading toward complete mineralization. AAS analysis confirmed minimal iron leaching (~1.0%), with concentrations within EPA limits, ensuring environmental safety. The nanocomposite exhibited good reusability, retaining approximately 71% of its original activity after four cycles with facile magnetic recovery. This study highlights the strong potential of the developed system for efficient, scalable, and recyclable wastewater treatment applications.