Green synthesis for production of chromium(III) oxide nanoparticles in fine powder

In this paper, a green synthesis method for chromium(III) oxide nanoparticles (Cr 2 O 3 NPs) is presented. The proposed route utilizes weed biomass as a reducing agent to produce a solid solution that readily precipitates as a fine powder of Cr₂O₃ nanoparticles. The synthesized Cr 2 O 3 NPs were characterized using UV-vis, TEM, EDS, and XRD. UV–vis spectra exhibited intense d–d transitions, characteristic of Cr3+. TEM analysis revealed quasi-monodisperse nanoparticles with a size of 38 ± 2 nm (SD), spherical morphology, and a log-normal size distribution. EDS measurements confirmed the presence of Cr and O as the main elements in the samples' composition, and XRD identified the corundum-type Cr₂O₃ phase, characterized by sharper peaks, which indicates higher crystallinity. In the comparative evaluation against a reference method, the statistical analysis demonstrated a highly significant difference between the two synthesis methods ( t -test, p < 0.05; ANOVA, F (1555) = 6712.5, p < 0.001). The proposed method showed superior reproducibility, enhanced stability under sunlight exposure, and improved control over particle growth and agglomeration. Additionally, the formation of fine powder grains is analyzed from the perspective of nanoparticle agglomeration, using a predictive ANN model and confirmed experimentally by TEM. These results demonstrate that the proposed synthesis route is a robust and effective approach for producing solid-state Cr₂O₃ nanoparticle powders with controlled size, phase purity, and enhanced stability, making them suitable for various applications, including catalysis, optics, and coatings.