α-zirconium phosphate (α-ZrP) is a known ion exchanger in both its amorphous and crystalline forms. The relationship between crystallinity and ion exchange has been investigated for α-ZrP prepared by reflux and direct precipitation. Hydrothermal synthesis of α-ZrP yields unique micron-sized particles with low aspect ratios, but the exchange behavior has not been thoroughly investigated. In this study, we prepare α-ZrP of varying crystallinity by hydrothermal synthesis and systematically evaluate the sodium ion exchange behavior using two distinct titration methods, incremental addition and continuous addition, at three temperatures. At room temperature, hydrothermal α-ZrP (HT ZrP) does not achieve full exchange by either titration method, but the ion uptake is improved as the exchange of the second proton is made more favorable, either by decreasing crystallinity or increasing the reaction temperature. Temperature plays a more significant role with crystalline HT ZrP and titrations by continuous addition, where exchange capacities above 95% were achieved at elevated temperatures. These insights provide a foundation for the rational design of materials with distinct ion exchange behavior and the optimization of exchange-based processes. We demonstrate the latter by the intercalation of Rhodamine 6G within zirconium phosphate at 50 °C, where the intercalation product is obtained in minutes rather than days, corresponding to an approximately 480-fold reduction in reaction time.
Hernández et al. (Thu,) studied this question.