Effect of calcination on titanium phosphate produced by H3PO4 treatment of anatase

Abstract

The effect of calcination at different temperatures on anatase treated with H₃PO₄ has been studied by several techniques, in order to understand the mechanism of the formation of stable titanium phosphates. Calcination at 573 K of the hydrated phosphate, α-Ti(HPO₄)₂·H₂O, obtained by reaction of anatase with H₃PO₄, leads to the formation of TiP₂O₇, although its crystallinity is perturbed by the presence of an excess of phosphoric acid in the starting material. Calcination at 873 K eliminates the excess of H₃PO₄, probably by formation of volatile P₂O₅, and a better crystallized TiP₂O₇ is obtained. A ³¹P magic-angle spinning nuclear magnetic resonance study of the pyrophosphate indicates that the nine lines observed in the spectrum are due to the presence of a 3 × 3 × 3 cubic superlattice.