Chapter 2. Contribution of isothermal titration calorimetry to elucidate the mechanism of adsorption from dilute aqueous solutions on solid surfaces: data processing, analysis, and interpretation

This chapter describes the use of isothermal titration calorimetry (ITC) to monitor the enthalpy changes accompanying the adsorption of ionic species from dilute aqueous solutions on charged solid surfaces. From the application point of view, it thus covers a broad range of interfacial phenomena of great interest in environmental remediation and catalysis but also in medicinal and pharmaceutical research. The incremental titration procedure is thoroughly detailed together with the subsequent data processing on the basis of appropriate thermodynamic analysis so as to evaluate the cumulative enthalpy of displacement and its changes along the adsorption isotherm in single-solute and two-solute systems. Some illustrative examples of data analysis and processing in selected adsorption systems are presented to highlight the main challenges in correlating the enthalpy balance recorded upon dilution and adsorption calorimetry runs with the measurements of individual adsorption isotherms. It is explained how to exploit the comparison between the measurements carried out in single-solute and two-solute systems in order to get insight into competitive or cooperative effects in ion adsorption at a charged solid-liquid interface. The most important parameters to be controlled or, at least, monitored carefully during the measurements are identified, and their impact on the adsorption mechanisms is discussed.