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 a dsorption mechanisms and the electrochemical modifications induced by adsor ption of a molecule at such a high-charge density. In addition to quantitat ive studies, Fourier-Transform Infrared (FT-IR) spectroscopy was used to es tablish the mechanisms of interaction. Laser Doppler Velocimetry-Photon Cor relation Spectroscopy (LDV-PCS) was employed to determine the electrophoret ic mobility and the size of the particles. The experiments were also run wi th 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 mo l m(-2) on kaolinite. The mechanism of adsorption of MP involved the phosph ate groups, whereas the organic moiety affected the process only in terms o f conformational hindrance. Thus, on goethite surfaces, because IHP occupie d an area equivalent to four sites for Pi, it was supposed to be bound to t he oxide by four of its six phosphate groups, whereas the other two were fr ee. On the illite and kaolinite surfaces, the area Occupied by MP was equiv alent to about:two: sites for Pi, Suggesting that a lower number of phospha te groups-are bound to phyllosilicates. The phosphate groups that did. not react with the minerals caused a modification of the electrochemical proper ties. In particular, INP adsorption caused dispersion of the particles and a net increase bf the negative charge of the surface.