Interaction of Ag(I), Hg(II), and Cu(II) with 1,2-ethanedithiol immobilized on chitosan: Thermochemical data from isothermal calorimetry

The nature of interactions between metal ions Ag(I), Hg(II), Cu(II) and chitosan derivative of 1,2-ethanedithiol, QTDT, was investigated by isothermal calorimetry using the membrane breaking technique. Simultaneous determination of thermal effects, Qint, and amount of cation that interacts, nint, are described. The experimental data have been interpreted in terms of the Langmuir equation to determine the maximum adsorption capacity to form a monolayer, Nmon, and the energy of interaction for a saturated monolayer per gram of QTDT, Qmon. With Nmon and Qmon, the molar enthalpy of interaction for formation of a monolayer of anchored cations per gram of QTDT, ΔmonHm, was determined. The ΔmonHm values for Ag(I), Hg(II), and Cu(II) were −60.56, −58.05, and −84.36 kJ mol−1, respectively. Negative values of ΔG show the spontaneity of the interaction processes. The least entropically favourable processes, i.e., those which present more negative ΔS values, seem to be compensated by the more favourable enthalpic parameter.