Green Synthesis, Characterization and Application of MnO₂ and Cr 2 O 3 Nanoparticles Using Calotropis gigantea Plant Extract

This study focuses on the green synthesis of manganese dioxide (MnO₂) and chromium oxide (Cr₂O₃) nanoparticles using Calotropis gigantea leaf extract as a natural reducing and stabilizing agent, providing an eco-friendly, cost-effective, and sustainable approach. The synthesized nanoparticles were characterized using UV–Visible, FT-IR, XRD, FE-SEM, EDAX, and thermal analysis, confirming successful formation with high purity, good crystallinity, and spherical to quasi-spherical morphology in the size range of 20–50 nm. The presence of metal–oxygen bonds and plant-derived functional groups was also verified, along with good thermal stability. Antibacterial studies showed moderate activity against both Gram-positive and Gram-negative bacteria, with MnO₂ being more effective against Gram-negative strains and Cr₂O₃ against Gram-positive strains. Corrosion studies indicated that nanoparticle coatings significantly improved the corrosion resistance of mild steel, with Cr₂O₃ exhibiting superior inhibition efficiency. Overall, Cr₂O₃ nanoparticles demonstrated better antibacterial and anticorrosion performance, highlighting their potential applications in protective coatings, environmental remediation, and biomedical fields.