Multitechnique characterization and antibacterial evaluation of Cr2O3 nanoparticles calcined at variable temperatures

Chromium(III) oxide nanoparticles (Cr2O3 NPs) were synthesized via a sol–gel method and calcined at 300, 400, and 500 °C to examine the influence of thermal treatment on structural, magnetic, and antibacterial properties. XRD confirmed the formation of phase-pure α- Cr2O3 at all temperatures, with enhanced crystallinity and reduced microstrain observed at 400 °C. Williamson–Hall analysis showed crystallite sizes of ~15.7 nm (300 °C), ~19.2 nm (400 °C), and ~14.9 nm (500 °C). FTIR spectra indicated progressive removal of residual hydroxyl and nitrate groups with increasing temperature, while TEM revealed improved particle uniformity at 400 °C. VSM analysis of Cr2O3 NPs calcined at 500 °C exhibited weak ferromagnetic behavior with a maximum magnetization of ~0.09 emu g⁻¹, remanent magnetization of ~0.025 emu g⁻¹, and low coercivity (~120), attributed to surface spin canting in the nanoparticles. Antibacterial studies against Streptococcus pneumoniae showed maximum inhibition at 400 °C, highlighting its optimal physicochemical and biological performance for biomedical applications.