Thermochemistry and adsorption equilibria at hematite — water interface

Abstract

Enthalpy of charging of hematite surface was determined by calorimetry and also by measuring the dependence of the point of zero charge (p.z.c.) on temperature. The calorimetric experiment was designed in such a way that the point of zero charge was in the middle between the initial and final pH. In that case, the reaction heat corresponds to the difference in standard reaction enthalpies of surface deprotonation andprotonation reactions, without electrostatic contribution. The following obtained calorimetric value: Δ_b H ⁰ — Δ_α H ⁰=33.3 kJ mol⁻¹ agrees well with the result of p.z.c. measurements; Δ_b H ⁰ — Δ_α H ⁰=33.2 kJ mol⁻¹. In addition to the thermochemistry results, the adsorption of dodecylsulfate and salicylate ions on the hematite was examined.