Characterization and reactivity of chromia nanoparticles prepared by urea forced hydrolysis

Chromia (Cr₂O₃) nanoparticles were prepared by urea forced hydrolysis in the presence of chromium (III) nitrate using NaCl as a precipitating agent. The size, distribution, and purity of the particles were evaluated. The necessity of polyvinylpyrrolidone (PVP) as a surfactant to prevent aggregation was also investigated. In the presence of PVP, non-aggregated spherical-like nanoparticles (3 ± 1 nm) were formed, whereas in the absence of PVP, spherical-like weakly agglomerated nanoparticles (85 ± 16 nm) comprised of 10 nm nanoparticle subunits were produced, creating a large surface area. The as-formed hydrated Cr₂O₃ nanoparticles were amorphous, although they could be easily converted into crystalline form by heating to 400 °C for 1 h, with minimal particle aggregation and size reduction. Attenuated total reflectance Fourier transform infrared spectroscopy indicated that preparation methods (surfactant and precipitating agent) influence surface reactivity of the nanoparticles to catechol.