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Magnetically recoverable MgFe$_2$O$_4$ nanoparticles as efficient catalysts for rapid dye degradation in water

Monophasic MgFe$_2$O$_4$ nanoparticles synthesized by a simple autocombustion method were assessed as magnetically recoverable catalysts for the degradation of methylene blue (MB) in water. The NPs exhibit a crystallite size of $\sim$ 9 nm, a band gap of $\sim$ 2.11 eV, and soft ferrimagnetic behavior, enabling efficient photocatalytic and Fenton-like activity. The effects of irradiation, H$_2$O$_2$ concentration, agitation mode, catalyst loading, and exposure time were systematically evaluated. Rapid and complete MB discoloration was achieved within minutes in the presence of H$_2$O$_2$, even without illumination, indicating that the process is dominated by a surface-mediated heterogeneous Fenton-like mechanism rather than photocatalysis. Kinetic analysis reveals pseudo-first-order behavior, with rate constants governed by the combined effects of catalyst concentration, oxidant dosage, and dye concentration. Structural stability and excellent recyclability confirm the robustness of the catalyst. These findings position MgFe$_2$O$_4$ nanoparticles as a low-cost, efficient, and reusable material for sustainable wastewater under operationally simple conditions.