A Mechanistic and Analytical Study of a Magnetically Separable Fe3O4/g-C3N4/SWCNT Photocatalyst: A Kinetic, GC-MS Degradation Pathways and AAS Leachate Analysis.

A novel magnetically separable ternary Fe3O4/g-C3N4/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 (R2 > 0.95) following the Langmuir-Hinshelwood mechanism. Scavenger studies identified photogenerated holes as the dominant reactive species (h+ > •O2 - > •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.