Enthalpy of interfacial reactions at TiO2 aqueous interface

Thermodynamic functions related to reactions associated with formation of charged surface sites at TiO2/electrolyte interfaces have been measured by calorimetry and potentiometry. The calorimetry experiments were interpreted as “symmetrycal calorimetry experiments” yielding the difference in standard enthalpy of deprotonation and protonation of amphoteric surface sites as ΔdpH°=(55±5) kJ mol−1. The potentiometry experiments were measurements of the temperature dependency of pH of concentrated suspensions containing different portions of strong acid or strong base. Theoretical analysis on the basis of the surface complexation model enabled determination of the difference in standard enthalpy and entropy of deprotonation and protonation as ΔdpH°=50 kJ mol−1 and ΔdpS°=−85 J K−1 mol−1. The data obtained with samples containing acid or base enabled estimation of the electrostatic contribution to enthalpy, entropy and Gibbs energy.