EXAFS, RAMAN AND P-31 NMR-STUDY OF AMORPHOUS TITANIUM PHOSPHATES

The reaction of phosphoric acid with titanium alkoxides for a PO4/Ti r atio ranging from 0.5 to 2 was investigated. For these compositions, a morphous precipitates are obtained. Their microstructure has been stud ied by means of Raman, nuclear magnetic resonance and X-ray absorption spectroscopies. The phosphatation of titanium alkoxide increases the Ti coordination number to 6 and the symmetry becomes purely octahedral for a P/Ti ratio of 2. For the composition range 0 < PO,/Ti less-than -or-equal-to 2, phosphate anions are homogeneously dispersed in the pr ecipitate and bound to titanium, the coordination of which is complete d by oxo-, hydroxo- and remaining alkoxy- groups. Short Ti-O distances are observed in the materials having the lowest P/Ti ratios.