Behavior of Prussian blue-based materials in presence of ammonia

Prussian blue and related materials, usually considered that behave as a zeolite for ammonia adsorption, when hydrated are unstable in the presence of this gaseous species. They remain stable only in the anhydrous form. In the decomposition products ammonium hexacyanometallates and an XRD amorphous iron(III) oxyhydroxide are detected. The crystallization and adsorbed water present in these solid materials participates in a decomposition reaction to give NH₄⁺ and OH^-. The very basic OH^- anion removes the iron(III) cations from the complex to form Fe(OH)₃ and finally FeOOH, while the formed NH₄⁺ appears as the salt of the complex anion. As reference reactions, the interaction of ammonia with ferrocyanic acid and ferric chloride, both in solid state, were studied where crystalline ammonium ferrocyanide and ammonium chloride, respectively, are formed.