Interaction of inositol hexaphosphate on clays: Adsorption and charging phenomena

The interaction of myoinositol hexaphosphate (IHP) with goethite, and with phyllosilicates such as illite and kaolinite,was studied by assessing the adsorption mechanisms and the electrochemical modifications induced by adsorption of a molecule at such a high-charge density. In addition to quantitative studies, Fourier-Transform Infrared (FT-IR) spectroscopy was used to establish the mechanisms of interaction. Laser Doppler Velocimetry-Photon Correlation Spectroscopy (LDV-PCS) was employed to determine the electrophoretic mobility and the size of the particles. The experiments were also run with orthophosphate (Pi) for comparison. The quantity of adsorbed IHP reached 0.64 mu mol m(-2) on goethite, 0.38 mu mol m(-2) on illite, and 0.27 mu mol m(-2) on kaolinite. The mechanism of adsorption of MP involved the phosphate groups, whereas the organic moiety affected the process only in terms of conformational hindrance. Thus, on goethite surfaces, because IHP occupied an area equivalent to four sites for Pi, it was supposed to be bound to the oxide by four of its six phosphate groups, whereas the other two were free. On the illite and kaolinite surfaces, the area Occupied by MP was equivalent to about:two: sites for Pi, Suggesting that a lower number of phosphate groups-are bound to phyllosilicates. The phosphate groups that did. not react with the minerals caused a modification of the electrochemical properties. In particular, INP adsorption caused dispersion of the particles and a net increase bf the negative charge of the surface.