Ultra-high capacity micron-sized truncated octahedral calcium hexacyanoferrate for selective removal of Cs+

Prussian blue analogs materials have been widely studied in radioactive waste treatment due to its excellent Cs + selectivity, but their low mechanical strength and fine particle size significantly limit their further development. Herein, an ultra-large Prussian blue analogs material, calcium hexacyanoferrate (KCaFC-H), with a 4–8 μm truncated octahedral structure is reported, which can be easily separated from aqueous solutions and exhibits a strong affinity for Cs + . KCaFC-H possesses an extremely high ion-exchange capacity ( q max = 758.42 mg/g), higher than all previously reported materials, reaching 94.21 % of the theoretical capacity. KCaFC-H removes >99 % of Cs + at pH 4–12 ( K d ˃1.3 × 10 5 mL/g) and up to 94.66 % even at pH = 2. Furthermore, KCaFC-H maintains a high distribution coefficient in the presence of excess Na + , K + , Ca 2+ , and Mg 2+ , and this performance is also retained in actual wastewater ( K d > 10 4 mL/g). The high selectivity for Cs + is explained from the perspective of binding energy through DFT calculations. The study elucidates the capture mechanism of Cs + in the open backbone framework of KCaFC-H, in which complete ion exchange of K + dominates the adsorption process, while the synergistic participation of Ca 2+ further enhanced the adsorption capacity. With advantages of convenient synthesis, easy separation, high capacity, and environmental friendliness, KCaFC-H shows great promise as an efficient material for the removal of radioactive nuclides. • Ultra-large size truncated octahedral shaped calcium hexacyanoferrate were synthesized. • The maximum adsorption capacity of KCaFC-H for Cs + is 758.42 mg/g. • KCaFC-H has extremely high Cs + selectivity in extreme environments. • KCaFC-H is more environmentally friendly than other Prussian Blue analogue.