Thermodynamics of H+/Cs+ exchange on amorphous zirconium phosphate in mixed solvents

In aqueous, 30% isopropanol and acetone, and up to 90% methanol, the H+/Cs+ exchange on zirconium phosphate is entropy directed, while in 60% isopropanol and acetone it is enthalpy directed and a selectivity reversal occurs. ΔF0 decreases in all cases with increasing addition of the organic solvent. ΔH0 becomes appreciably negative (ΔH0 = 0 in aqueous medium) and ΔS0 decreases appreciably on addition of 30% organic solvent, but they increase with further addition. In presence of methanol, ion-solvent interaction effects are counteracted by effects of solid phase interactions but the former effects predominate and lead to decrease of ΔF0. On going from 30 to 90 % methanol, positive enthalpy and entropy changes occur due to solid phase interactions involving probably the dehydration of the ingoing Cs+. In presence of up to 60% acetone, ΔF0 (or selectively constant) changes mainly due to ion-solvent interactions and can be theoretically calculated from the value in the aqueous medium by use of transfer thermodynamics data. This is probably due to a limited imbibition of acetone. (author)