CRYSTALLINE ALPHA-TITANIUM(IV) HYDROGENPHOSPHATE AND ITS SODIUM-INTERCALATED AND N-BUTYLAMMONIUM-INTERCALATED FORMS - ION-EXCHANGE AND THERMOCHEMISTRY

Crystalline alpha-titanium(IV) hydrogenphosphate and its sodium- and n -butylammonium-intercalated forms were used as exchangers with MX2 (M = Zn or Cu; X = Cl, NO, or MeCO2) in aqueous medium at 298.2 +/- 0.2 K . An enhancement of the exchange capacity was observed for alpha-Ti(HP O4)(2) and its sodium form when acetate was used as the counter ion fo r both zinc and copper cation solutions. Thermodynamic determinations for all ion-exchange processes were performed by titrating calorimetri cally a suspension of a given exchanger in water (2.0 cm(3)) with an a queous cation solution in a heat-flow microcalorimeter at 298.15 +/- 0 .01 K. In all cases the net thermal effects were calculated after subt racting the corresponding dilution thermal effects. With the exception of exothermic ion-exchange processes involving CuCl2 with the alpha-T i(HPO4)(2) and sodium forms, and Zn(NO3)(3) with alpha-Ti(HPO4)(2), wh ich gave -2.40 +/- 0.12, -1.01 +/- 0.01 and -12.26 +/- 0.15 kJ mol(-1) , respectively, all other exchange processes were endothermic in natur e with low enthalpy values, varying from 0.010 +/- 0.001 to 8.59 +/- 0 .14 kJ mol(-1) for the Zn(NO3)(2) and Zn(O2CMe)(2) systems, with the s odium form. The number of moles exchanged did not correlate with the c orresponding enthalpies. However, the thermodynamic data are in agreem ent with the occurrence of a spontaneous and entropically favourable i on-exchange process for all systems considered.