Impact of green-synthesized Mg-doped Mn ferrite nanoparticles on light-driven degradation of dyes and their optoelectronic applications

Using Ocimum sanctum extract as fuel, magnesium-doped manganese ferrite nanoparticles with the chemical formula Mg_xMn_1−xFe₂O₄, where x = 0.0, 0.2, 0.4, and 0.6, were synthesized using a green microwave-assisted combustion method and named MF, MMF-1, MMF-2, and MMF-3 NPs, respectively. The synthesized nanoparticles were characterized using XRD, FT-IR, SEM with EDS, TEM, CV, PL, and UV-visible spectroscopy. XRD patterns illustrated that lattice parameters increase as the magnesium dopant level increases, and the average crystallite sizes of NPs range from 4.51 to 6.98 nm. FT-IR spectra exhibited the stretching modes of the manganese-oxygen bond for octahedral sites at 426–456 cm⁻¹ and the iron–oxygen bond for tetrahedral sites at 566–589 cm⁻¹. SEM and HRTEM images showed that the structure resembles nanoflakes with porous structures, and EDS confirmed the presence of Mg, Mn, O and Fe elements in MDMF NPs. Bandgap was determined through UV-visible spectroscopy, and it displayed a decline with an increase in magnesium doping levels (3.76–3.41 eV). The synthesized NPs exhibited good electrochemical behaviour in CV studies; the peak intensity of the luminescence spectra decreased with an increase in the dose of magnesium dopants, with red emissions at 488 nm and blue emissions at 533 nm, corresponding to the recombination of photoexcited holes and electrons. The photocatalytic efficiency of the synthesized MMF-2 nanoparticles was assessed with methylene blue dye under visible light illumination (98.88%).