By ionothermal synthesis method, a series of syntheses have been performed in an attempt to synthesize novel zirconium phosphate materials in an oxalic acid/tetrapropyl ammonium bromide ionic eutectic mixture. The two different zirconium phosphate materials, α-Zr(HPO₄)₂•H₂O and (NH₄)Zr₂(PO₄)₃ have been achieved by changing the synthetic conditions, tetrapropyl ammonium cation could not play its template role to form a new zirconium phosphate and the latter was synthesized at a high temperature (220 ℃) by templating the cation in situ generated from the ionothermal decomposition of the tetrapropyl ammonium (TPA) component. However, after adding a small amount of N-containing heterocyclic compound (piperazine), a known open-framework zirconium phosphate with 8-ring pore channels was obtained. The protonated piperazine not only plays a template role to form the zirconium phosphate framework but also acts as counter-ions to balance the anion framework. The used deep-eutectic solvent, therefore, can be used as an excellent ionic reaction medium to synthesize zirconium phosphate materials, the organic amine could be added to the initial reaction mixture to induce zirconium phosphate framework.

Key words: ionothermal synthesis, eutectic mixture, zirconium phosphate, crystal structure