Revisiting the Thermal Decomposition of Layered γ-Titanium Phosphate and Structural Elucidation of Its Intermediate Phases

The thermal transformations of γ-titanium phosphate, Ti(PO4)(H2PO4)·2H2O, have been studied by thermal analyses (thermogravimetry (TG) and differential thermal analysis (DTA)) and variable-temperature 31P magic-angle spinning (MAS)/CPMAS and 2D 31P−31P spin-exchange NMR. The structure of this material has been refined from synchrotron powder X-ray diffraction data (monoclinic, P21, a = 5.1811(2) Å, b = 6.3479(2) Å, c = 23.725(2) Å, β = 102.57(1)°). Vyazovkin’s model-free kinetic algorithms have been applied to determine the apparent activation energy to both dehydration and dehydroxylation of γ-titanium phosphate. In these processes, several overlapped steps have been detected. Structural models for Ti(PO4)(H2PO4)·H2O and Ti(PO4)(H2P2O7)0.5 intermediate layered phases have been proposed.