In this work, Magnesium manganite (MgMn2O4) tetragonal-spinel nanoparticles were successfully synthesized by tragacanth gel through the easy and inexpensive novel sol-gel method. This technique has many strong points such as facile, economical, non-toxic and quickness in comparison with other methods. The magnesium manganite nanoparticles characterized by energy dispersive x-ray analysis (EDX), powder x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transforms infrared spectroscopy (FTIR), UV-Visible Diffuse Reflectance spectroscopy (DRS), and percent of dye degradation which was followed by UV–Visible spectroscopy. The XRD pattern confirmed the formation of spinel tetragonal structure of MgMn2O4 nanoparticles with a crystallite size of 10 nm. The MgMn2O4 NPs expressed high photocatalytic activity for degradation of reactive blue 21 dye at room temperature in aqueous solution so that 95% of RB21 was degraded in 60 min. The spinel MgMn2O4 NPs reusability was examined by administering the degradation of RB21 dye with the spent catalyst, and it was considered that the photocatalyst exhibits a small decrease in its activity after the four recycles.
