New process of preparation, structure, and physicochemical investigations of the new titanyl phosphate Ti2O(H2O)(PO4)2
Résumé
New titanyl phosphate Ti2O(H2O)(PO4)2 has been prepared and characterized by X-ray and neutron diffraction, nuclear magnetic resonance, infrared and Raman spectroscopies and thermogravimetric analysis. The crystal structure has been solved from neutron powder diffraction data at 300 K by Rietveld method in P21 space group. The refinement led to satisfactory profile factors (Rp=2.7%, Rwp=3.2%) and crystal structure model indicators (RB=5.8%, RF=3.2%). The cell is monoclinic with a=7.3735 Å, b=7.0405 Å, c=7.6609 Å and β=121.48°, Z=4. The structure can be described as a three-dimensional framework built up by chains of [TiO5(OH2)] octahedra with alternative short bonds [Ti(1)-O(12); Ti(2)-O(12), 1.88-1.84 Å] and long ones [Ti(1)-OW; Ti(2)-OW, 2.25-2.23 Å] along c-axis and connected via [PO4] tetrahedra. Oxygen atom denoted O(12) is only linked to two titanium atoms and Oxygen atom denoted OW is linked to two titanium atoms and two hydrogen atoms. O(12) and OW are not linked to P atoms and justify the titanyl phosphate formulation Ti2O(H2O)(PO4)2. The infrared and Raman spectra presents peaks due to vibrations of Ti-O, P-O and O-H bonds. The 31P MAS NMR spectrum reveals two 31P resonance lines, in agreement with the structure which showed two crystallographic sites for phosphorus. The thermogravimetric analysis show that Ti2O(H2O)(PO4)2 is thermally stable until 400 °C. Above this temperature, it losses water and decomposes to Ti5O4(PO4)4 and TiP2O7. © 2007 Elsevier Inc. All rights reserved.