Green synthesis of Cr2O3 nanoparticles using aerial part extract of Russian knapweed (Acroptilon repens L.): experimental and atomic-scale approach
摘要
This paper presents an experimental and computational analysis of green-synthesized chromium oxide (Cr2O3) nanoparticles, combining the use of Acroptilon repens L. (Russian knapweed) extract. The biosynthesized nanoparticles were characterized by x-ray powder diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared (FTIR) spectroscopy, energy-dispersive system (EDS) spectroscopy, dynamic light scattering (DLS), and Ultraviolet-visible (UV–Vis) spectroscopy techniques, and they revealed the existence of a pure rhombohedral phase, an average size of 70 nm, and well-characterized absorption peak at 370 nm (Cr 3d→3d* transition). Experimentally measured and simulated UV-Vis spectra showed an optical bandgap of 3.31 and 3.35 eV, respectively. In contrast, DFT + U calculations yielded a direct bandgap of 2.74 eV, with the difference attributed to excitonic effects and quantum confinement. Molecular dynamics simulation reconstructed the experimental UV-Vis spectrum with very good accuracy, showing characteristic peaks at 370 nm corresponding to Cr³+ d-d transitions. Projected density of states (PDOS) analysis revealed strong hybridization between Cr 3d and O 2p orbitals in the − 5 to 5 eV energy range, validating the ionic-covalent mixed character of the material’s bonding. Mulliken population analysis validated the charge transfer from Cr (+ 0.92|e|) to O (-0.61|e|), consistent with the material’s electronic structure. The excellent agreement between experiment and simulation validates the green synthesis technique for the formation of Cr2O3 nanoparticles with designed optoelectronic properties and demonstrates the power of multiscale modeling for nanomaterial behavior prediction. These findings are a foundation for the advancement of Cr2O3-based materials toward spintronic and photocatalytic applications.