cao nanoparticles with calcite signatures: antibacterial function and biosafety

Predominantly calcite-phase cao nanoparticles were prepared by alka-line precipitation followed by calcination and characterized by sem, xrd, ftir, uv–vis, and bioassays. xrd confirmed nanocrystallinity with crystallite sizes of approximately 37–45 nm and reflections indi-cating substantial conversion of cao to calcite during processing. ftir showed surface hydroxyls and carbonate groups consistent with hydrat-ed/carbonated cao, and uv–vis revealed strong absorption below 400 nm. antibacterial activity was dose-dependent, with the largest inhibi-tion zone (24 mm) against escherichia coli at 1,500 μg ml⁻¹. hemocom-patibility assays showed increasing hemolysis with dose (12.4% at 250 μg ml⁻¹ and 21.0% at 750 μg ml⁻¹) exceeding the conventional 10% safety threshold, while brine shrimp assays indicated low acute aquatic toxicity (lc₅₀ > 1,000 μg ml⁻¹; 33.3% mortality at that dose). overall, these calcite-rich cao nanoparticles exhibit notable antimicrobial ef-fects but pose hemolysis risks at higher concentrations; safer deploy-ment may benefit from immobilized or buffered formats and tighter co₂ control during synthesis to preserve phase stability.