In situ Fourier-transform infrared spectroscopy studies of inorganic ions adsorption on metal oxides and hydroxides

In this work, the studies describing the use of attenuated total reflection-infrared spectroscopy to obtain information on the sorption mechanism of inorganic ions on metal oxy-hydroxides are reviewed. ATR-IR is amongst the rare techniques which allow to analyze the sorption phenomena in situ and led to several results about the speciation of sorbed anions (sulfate, carbonate, phosphate, perchlorate, ...) or ternary inorganic complexes since it is able to distinguish outer-sphere and inner-sphere complexes. The principles of this method are summarized, and the experimental protocols, the results and the limitations are elaborated. The sample deposition method, initially based on a paste or a concentrated suspension, has evolved towards the coating of the ATR crystal by a colloid layer, increasing the sensibility and the reproducibility of the measurements. Observed absorption frequencies of ions sorbed on metal oxy-hydroxides (goethite, hematite, alumina, silica, TiO2, ...) are reported to help the identification of peaks in new experimental works. This method, characterized by an in situ analysis performed with a special cell used in a widespread instrumentation (IR spectrometer), is very recent but its advantages suitable for the current problems in the sorption field should help its rapid development for the next years.