Tetragonal MnO₂ Nanoparticles Synthesized via Lagerstroemia speciosa: Structural Characterization and Photocatalytic Potential

Manganese oxide nanoparticles (MnO₂-NPs) were biosynthesized using an aqueous extract of Lagerstroemia speciosa leaf powder. The plant is rich in phytochemicals such as phenolic compounds, alkaloids, α-amino acids, steroids, organic acids, terpenoids, reducing sugars, glycosides, carbohydrates, saponins, starch, flavonoids, and tannins. The phenolic compounds acted as both reducing and capping agents. The synthesized nanoparticles were characterized using UV–Vis–IR spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and Fourier-transform infrared spectroscopy (FTIR). The UV–Vis–IR spectrum revealed a distinct absorption peak at 365 nm, confirming the formation of MnO₂-NPs. FESEM images indicated rough, spherical, randomly oriented particles with sizes ranging from 83–400 nm. XRD analysis confirmed a pure tetragonal structure with preferential (110) plane orientation. The photocatalytic performance of the MnO₂-NPs was assessed via the sunlight-driven decolourization of methyl orange (MO) and bromocresol green (BCG) dyes.