Minimal liquid-assisted method for synthesis of ammonium, sodium, and potassium intercalated zirconium hydrogen phosphate: the effect of the cation used on the formation of an α- or γ-structure

Abstract

Zirconium hydrogen phosphates intercalated with ammonium, sodium, and potassium cations were successfully synthesized via a minimal liquid-assisted approach, involving the grinding of a zirconium precursor with the corresponding metal dihydrogen phosphate, followed by thermal treatment. The resulting crystalline phase—either α- or γ-type zirconium phosphate—was found to depend on both the intercalating cation and the zirconium source. Potassium dihydrogen phosphate consistently yielded compounds with α-structure, whereas ammonium and sodium dihydrogen phosphates led to either α- or γ-phases, depending on the dihydrogen phosphate and phosphoric acid molar ratio in the starting reaction mixture, and also the zirconium source employed. An increase in the P/Zr molar ratio and reaction temperature enhanced product crystallinity without altering phase composition. The presence of α- or γ-type intercalates was confirmed through hydrochloric acid treatment, which selectively yielded α- or γ-zirconium phosphate, and further validated through solid-state ³¹P NMR spectroscopy.