Calorimetry of heterogeneous systems: H+ binding to TiO2 in NaCl

A simultaneous calorimetric and potentiometric technique has been developed for measuring the thermodynamics of proton binding to mineral oxides in the presence of a supporting electrolyte. Modifications made to a commercial titration calorimeter to add a combination pH electrode and maintain an inert atmosphere in the calorimeter reaction vessel are described. A procedure to calibrate potentiometric measurements in heterogeneous systems to correct for the suspension effect on pH is given.

The enthalpy change for proton dissociation from TiO₂ in aqueous suspension as a function of pH is reported for 0.01, 0.1, and 0.5 M NaCl. The enthalpy change for proton dissociation is endothermic, ranging from 10.5 ± 3.8 to 45.0 ± 3.8 kJ mol⁻¹ over the pH range from 4 to 10.