Precursor Particle Size as the Key Parameter for Isothermal Tuning of Morphology from Nanofibers to Nanotubes in the Na2−xHxTinO2n+1 System through Hydrothermal Alkali Treatment of Rutile Mineral Sand

Morphology control in the (Na,H)2TinO2n+1 system has been achieved by introducing particle size as the key parameter during hydrothermal synthesis. The process is applied for the synthesis of TiO2-based nanofibers and nanotubes from natural rutile sand. The method is favorable for large-scale production due to the simple synthetic approach and the low-cost precursor used. The morphology of the final product is controlled through variation of the precursor particle size by mechanical milling prior to hydrothermal treatment. Hydrothermal alkali treatment of natural rutile sand without milling at 140 °C for 70 h resulted in the formation of nanofibers. Some portion of unreacted rutile coexisted in the reaction product. However, when the adequately milled precursor was used under the same condition, the unreacted material disappeared in the product, while the morphology of the product was changed from nanofibers to nanotubes. To the best of our knowledge tubular nanostructures of titanates have not been synth...