GREEN SYNTHESIS OF PHASE-CONTROLLED Α- AND Β-MNO₂ NANOSTRUCTURES: STRUCTURAL, OPTICAL, AND ANTIMICROBIAL PROPERTIES FOR BIOMEDICAL APPLICATIONS

Abstract

In the work, preparation of α- and β-phase manganese dioxide (MnO₂) nanostructures was done in an eco-friendly route through a green synthesis method. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), fourier transform infrared spectroscopy (FTIR), and UV-visible spectroscopy were used in a systematic way to characterize the synthesized materials. XRD analysis revealed the successful formation of crystalline α-MnO₂ and - MnO₂ with different structural features. SEM micrographs showed that α-MnO2 had a nanowire-like morphology, but -MnO2 had nanosheet-like morphologies, implying morphology-dependent phase growth in the presence of green synthesis. The presence of manganese and oxygen without major impurities as confirmed by the EDS results confirmed the purity of the synthesized samples. The FTIR spectra showed typical MnO₂ vibrational modes which further confirmed the formation of Mn-O phases. The optical absorption behaviours evaluated by UV–visible tests revealed significant optical absorption characteristics of the nanostructured materials, which imply their applicability in photonic and biomedical applications. Both phases were tested against the chosen microbial strains regarding their antibacterial and antifungal effects, with β-MnO₂ showing much higher antimicrobial activity than that of α-MnO₂. The better bioactivity of  -MnO₂ is explained by the increased surface area and the nanosheet structure which enables the increased interaction with microbial cells. In sum, green synthesis route offers a viable approach to the synthesis of phase-controlled MnO₂ nanostructures that have potential biomedical applications.