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.