Thermodynamic parameters for Eu(III) binding to Datura innoxia root material.

Plants offer the potential for selective removal and sequestration of toxic heavy metals from contaminated soil. Phytoextraction of metal ions involve their transport through the plant's root system and into its shoots and leaves. This study investigates the thermodynamics of Eu(III) ion chemical interactions with Datura innoxia plant root materials under solution conditions of pH 4.0 and 5.0. Both changes in enthalpies (∆H) and entropies (∆S) of metal binding were elucidated from isotherms collected under varied temperature conditions using regularized regression data analysis and conditional affinity spectra. ∆H values for binding to root materials at pH 4.0 and 5.0 were each calculated to be +30 kJ/mol. Values of ΔS for these same materials were found to be +170 and +153 J/mol K for solution conditions of pH 4.0 and 5.0, respectively. These results suggest binding to the root material to be entropically driven (∆S° > 0 and ΔH > 0) through possible displacement of waters of solvation.