Benzenecarboxylate surface complexation at the goethite (alpha-FeOOH)/water interface: I. A mechanistic description of pyromellitate surface complexes from the combined evidence of infrared spectroscopy, potentiometry, adsorption data, and surface complexation modeling
Jf. Boily et al., Benzenecarboxylate surface complexation at the goethite (alpha-FeOOH)/water interface: I. A mechanistic description of pyromellitate surface complexes from the combined evidence of infrared spectroscopy, potentiometry, adsorption data, and surface complexation modeling, LANGMUIR, 16(13), 2000, pp. 5719-5729
An investigation combining IR spectroscopy, potentiometric titrations, and
adsorption experiments was carried out to study pyromellitate (1,2,4,5-benz
enetetracarboxylate) sorption at the goethite (alpha-FeOOH)/ water interfac
e. The IR spectra show evidence of outer-sphere complexation throughout the
pH range from 3 to 9. Below pH 6 additional IR spectroscopic features appe
ar, which are tentatively assigned to inner-sphere complexes. A normalized
IR peak area plot for each peak indicative of inner- and of outer-sphere co
mplexes as a function of pH provided a semiquantitative surface speciation
scheme. This scheme was successfully reproduced using surface complexation
theory with a multisite complexation model calibrated on potentiometric tit
ration and on adsorption data. The surface speciation was described with a
binuclear outer-sphere complex on the {110} plane of goethite and a mononuc
lear inner-sphere complex on the {001} plane. Furthermore, as the IR spectr
a also indicated partial protonation of pyromellitate complexes at low pH,
a partially protonated outer-sphere species on the {110} plane was included
in the model.