Polymer-encapsulated crystalline zirconium phosphates as NH4+ and K+ ion exchangers for application in sorbent dialysis cartridges

The ion exchange properties of crystalline ⍺- and γ-zirconium phosphates in the sodium and hydrogen forms were investigated. The zirconium phosphates were synthesized by a mechanochemistry-assisted protocol. Amongst the compounds, ⍺-Na2-zirconium phosphate and γ-H2-zirconium phosphate were found to be excellent ion exchangers for NH4+ and K+ ions, two key cations in renal sorbent dialysis systems. The maximum NH4+ uptake by ⍺-Na2-zirconium phosphate was 5.5 mmol/g, close to the theoretical limit of exchangeable sites. In multi-ion solutions, γ-H2-zirconium phosphate was a selective exchanger for K+ with total uptake capacity of 2.9 mmol/g. The as-synthesized microcrystalline zirconium phosphates were encapsulated by polyacrylonitrile to form spherical porous beads of tailorable sizes. Owing to the porosity, access to the ion exchange sites of the embedded zirconium phosphates particles was unaffected, enabling fast kinetics in the uptake of NH4+ and K+. In this form, the PAN/ZrP beads can be easily handled in sorbent cartridges. The activity of the PAN/ZrP beads could be fully restored by simple regeneration with the appropriate electrolyte.