Effects of thermal treatment of nanostructured trititanates on their crystallographic and textural properties

Nanostructured titanates (TTNT) with general formula NaxH2−xTi3O7·nH2O were synthesized by hydrothermally reacting different TiO2 anatase (distinct crystal sizes) with NaOH at 120 °C followed by washing with water or diluted acid and drying of the precipitate. The resulting powders with different sodium contents were submitted to various calcination temperatures up to 800 °C and each calcined product was characterized as for its phase structure, composition, crystallite size and textural properties, namely BET surface area, mesopore volume and pore size distribution. Thermal transformations of TTNT samples were investigated by monitoring the modifications on crystallographic (X-ray diffraction) and textural (N2 desorption isotherms) properties, revealing the influence of the type of starting anatase and sodium content over the stability of TTNT. Moreover, a detailed study on the reduction of the interlayer distance in TTNT samples upon thermal treatment allowed corroborating the formation of an intermediate nanostructured hexatitanate, just before phase transformation into the corresponding TiO2 polymorphs and/or titanate crystals, depending on the sodium content and calcination temperature.