Preparation of monodisperse Prussian blue nanoparticles via reduction process with citric acid

A new procedure to prepare monodisperse Prussian blue nanoparticles was investigated. Using gelatin as a protective colloid, citric acid solution was added to the starting solution containing Fe(NO3)3, K3Fe(CN)6, and HNO3, where the acid was added to avoid cross-linking among gelatin molecules to coagulate by Fe(CN)63− ions. Monodisperse Prussian blue nanoparticles having 70 nm of mean size were obtained via reduction reaction of Fe3+ by citric acid at 35 °C. The XRD pattern was in good agreement with the face-centered cubic structure with 10.15 Å of lattice parameter. The crystallite size estimated from the XRD peak with Scherrer equation was 32 nm, suggesting polycrystalline structure of the particles. Effect of citric acid concentration was also evaluated. The linear time increase of particle size and 94 kJ mol−1 of the activation energy for the growth process suggest that the growth of Prussian blue nanoparticles was controlled by surface reaction process in the present system.