EXAFS, Raman and 31P NMR study of amorphous titanium phosphates

The reaction of phosphoric acid with titanium alkoxides for a PO4/Ti ratio ranging from 0.5 to 2 was investigated. For these compositions, amorphous precipitates are obtained. Their microstructure has been studied 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 < PO4/Ti ⩽ 2, phosphate anions are homogeneously dispersed in the precipitate and bound to titanium, the coordination of which is completed by oxo-, hydroxo- and remaining alkoxy- groups. Short TiO distances are observed in the materials having the lowest P/Ti ratios.