Strontium chloride

Zeolite granules CaA and NaX (granule size 1.6–2.5 mm, Luoyang Jalong Micro-nano New Materials Co., Ltd., Henan, China), calcium chloride (anhydrous, 93% purity, Alfa Aesar) and strontium chloride (anhydrous, 99% purity, Alfa Aesar) were purchased and used as pristine materials. To reduce the formation of unexpected salts, e.g., NaCl, during the impregnation process, CaA and NaX granules were first treated by ion exchange to replace the Ca²⁺ and Na⁺ cations with Sr²⁺. The impact of time on the ion-exchange process and the concentration of the SrCl₂ solution during the ion-exchange process were investigated (Section S1, ESI†). All the ion-exchanged granules were dried at 150 °C for 1 h. As-received CaA granules were directly impregnated with CaCl₂ solution since the formation of byproduct salts was not expected. The impregnation process was done by dripping the AEMHs solution to the granules as shown in Fig. 1(f). The loading of the AEMHs solution was from 12 wt% to 45 wt% (Section S2, ESI†). After the impregnation, the granules were dried at 150 °C for 1 h. The processing conditions of the obtained impregnated granules are listed in Table 1.

Strontium chloride (hexahydrate, 99+%) and lithium hydroxide (monohydrate, 98%) were purchased from Alfa Aesar (Haverhill, MA, USA). Polyethylene glycol 600 (PEG) and titanium (IV) chloride (99.9%) were obtained from Sigma-Aldrich (St. Louis, MO, USA).