A Possible Mechanism behind the Discovery of Prussian Blue

In this work, we synthesized Prussian Blue (PB) by pyrolysis of nitrogen-rich organic compounds and ferric/ferrous salts in the presence of alkali metal salt in inert atmosphere at high temperature, which was completely different form popular method based on the reaction of ferric ions and ferrocyanide ions. By exploring the history of Prussian Blue and some research results, we proposed a possible mechanism to explain the formation of Prussian Blue. The mechanism is as follows: Firstly, carbon, nitrogen and oxygen element in the mixture were transformed to cyanate by the catalysis of alkali metal species. With the increasing of temperature, organic compounds decomposed to release reducing gases such as H₂ and CO and eventually formed carbon materials. The reducing gases reduced part of Fe³⁺ to Fe²⁺ and the carbon reduced the cyanate to cyanide. So Prussian Blue was formed by cyanide, Fe³⁺ and Fe²⁺. The most import substance in the process is the alkali salts and a key intermediate product namely cyanate is proposed. Detailed experiments can be found in PDF file.