Ionothermal synthesis and characterization of two zinc phosphates from a protic ionic liquid

Protic ionic liquids (PILs) are a subset of ionic liquids, which are cost-effective and easily produced through the combination of a Brønsted acid and a Brønsted base. In this work, we have taken an organic amine, triethylenetetramine (TETA), as an example to form a PIL with acetic acid, and described the ionothermal synthesis of zinc phosphate in a PIL for the first time. Two crystalline zinc phosphate materials, ZnPO–TETA1 and ZnPO–TETA2, were successfully produced by using this PIL as the solvent and template. Powder X-ray diffraction, SEM, TGA and CHN analysis were used to characterize the two materials. The two crystalline solids are very similar to two known zinc phosphates. ZnPO–TETA1 has an open-framework and ZnPO–TETA2 has a ladder structure, and the TETA cation was incorporated into their final structure to balance the framework negative charge. It was found that the P/Zn ratio is crucial to the phase selectivity in a protic ionic liquid. Low P/Zn ratios favor the structure with higher dimensions and high P/Zn ratios tend to form the lower dimensional structures.